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Download date: 12 Sep 2020

Dave Lie Sam Foek

BONDED ORTHODONTIC RETAINERS:CLINICAL SURVIVAL, ADHESION

AND MATERIAL ASPECTS

Bonded orthodontic retainers:

Clinical survival, adhesion and material aspects

Dave Lie Sam Foek

ISBN: 978-90-9030900-2 Bookdesign: Sgaar Groningen, Saar de VriesCover: Dave Lie Sam FoekPrinted by: Drukkerij van der Eems Heerenveen © D.J. Lie Sam Foek, 2018

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanically, by photocopy, by recording or otherwise, without permission of the author.

Bonded orthodontic retainers:

Clinical survival, adhesion and material aspects

ACADEMISCH PROEFSCHRIFT

ter verkrijging van de graad van doctoraan de Universiteit van Amsterdamop gezag van de Rector Magnificus

prof. dr. ir. K.I.J. Maexten overstaan van een door het College voor Promoties ingestelde commissie,

in het openbaar te verdedigen in de Agnietenkapelop vrijdag 8 juni 2018, te 10:00 uur

doorDave Johan Lie-Sam-Foek

geboren te Paramaribo, Suriname

Paranimfen:

Drs. M.P.E. Tacken

Drs. C.G. Sabajo

Promotiecommissie:

Promotoren: Prof. dr. M. Özcan Rijksuniversiteit Groningen Prof. dr. A.J. Feilzer Universiteit van Amsterdam

Overige leden: Prof. dr. M.S. Cune Rijksuniversiteit Groningen Prof. dr. F.J.M. Roeters Universiteit van AmsterdamProf. dr. C.J. Kleverlaan Universiteit van Amsterdam Dr. I. Nedeljkovic Universiteit van AmsterdamDr. T.J. Algera Universiteit van Amsterdam

Faculteit der Tandheelkunde

CONTENTS

Chapter 1 Introduction 9

Chapter 2 Survival of flexible, braided, bonded stainless steel lingual retainers: A historic cohort study

19

Chapter 3 Adhesive properties of bonded orthodontic retainers to enamel: Stainless steel wire versus fiber-reinforced composites

33

Chapter 4 Fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers in vitro

55

Chapter 5 Clinical survival of multi-stranded stainless steel bonded lingual retainers as a function of composite type: Up to 3.5 years follow-up

69

Chapter 6 Displacement of teeth without and with bonded fixed orthodontic retainers: 3D analysis using triangular target frames and optoelectronic motion tracking device

85

Chapter 7 General discussion and clinical implications 103

Chapter 8 Summary 111

Chapter 9 Samenvatting 117

Acknowledgement 125

Curriculum Vitae 133

The studies of this thesis were conducted at:- The Kolff / BMSA institute (Institute for Biomedical engineering, Material Sciences

and Application, University Medical Center Groningen, University of Groningen,

The Netherlands.

- The Department of Prosthodontics and Dental Materials, University of Bologna,

Italy.

- The Division of Dental Materials, University of Zurich, Switzerland.

- Academic Center for Dentistry Amsterdam (ACTA), Department of Dental Material

Science, Amsterdam, The Netherlands.

This thesis was supported by ACTA Research Institute of the Academic Center

for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, the

Netherlands.

Chapter 1

Introduction

10 11

along the fiber orientation.24-27 Commonly used FRC materials are carbon, kevlar,

polyethylene and glass fibers with unidirectional or woven fiber orientations.28

Some of such fibers are readily silanized and pre-impregnated with resin matrix,

whereas others need to be silanized and impregnated by the operator.29 Today,

FRCs are widely used in the fabrication of crowns, fixed dental prosthesis (FDP)

made directly at chairside or indirectly in a dental laboratory,24 root-canal posts,25

periodontal splints26 and orthodontic splints.27 In prosthodontic applications, the

two most important mechanical properties of FRCs are strength and stiffness.30,31

Stiffness or rigidity of the material is referred to as the modulus of elasticity. A

high modulus is necessary for FRC FDP, as it is expected to support the more

brittle overlying restorative resin composite. Typical preimpregnated unidirectional

dental FRCs incorporate approximately 45% glass fibers, having flexure modulus

in the range of 28 to 34 GPa and flexure strengths of about 600 to 1000 MPa.29

These values are almost 10 times higher than those for dental resins alone.33

From the available biocompatible fibers, glass fibers have drawn the most

attention due to their aesthetic qualities and easy manipulation in orthodontics

(Fig. 1b).32 Important factors influencing the mechanical properties of FRCs

include inherent material properties of fibers and polymer matrices, fiber surface

treatment (sizing) and impregnation of fibers with resin adhesion of fibers to the

polymer matrix, quantity of fibers, direction, position, orientation of fibers and

water sorption of the FRC matrix.3

A B

Figures. 1a-b: Lingual orthodontic retainer made of a) multi-stranded stainless steel wire and b) fiber reinforced composite bonded using resin composite.

Clinical challenges associated with the adhesion of orthodontic retainersOrthodontic retainers made of either stainless steel or FRCs in general

require conditioning of the enamel on the lingual or palatal tooth surfaces with

phosphoric acid (35-37%) which yields to dissolution of hydroxyapatite through

which micromechanical retention of the resin material is achieved for bonding

Bonded orthodontic retainersOrthodontic retainers are used at the end of an orthodontic treatment to retain the

achieved tooth position. Without a phase of retention, there is a tendency for the

teeth to relapse towards their initial position after completion of the treatment.1-3

The aetiology of relapse is not fully understood but relates to a number of factors

that involves periodontal and occlusal aspects.4-6 Soft tissue pressures through lip

and tongue or physiological growth have also been reported as factors that affect

the tooth position and the incidence of relapse.7-9

Retention, which refers to the fixation of the achieved orthodontic result, can

be accomplished using removable or fixed retainers.3,10 Due to the advances

in adhesive technologies, the use of fixed retainers bonded to lingual or palatal

surfaces of incisor teeth has been widely used for more than three decades and

replaced removable retainers to a great extent.11,12

Materials used for orthodontic retainersStainless steel wiresThe most frequently used bonded orthodontic retainer material is stainless steel

wire, with varying stiffness and configuration (Fig. 1a).1,2,13 Lingual retainers are

either fabricated from relatively thick flat or round wires (0.030 - 0.032 inch) or from

thinner multistranded wires (0.0195 - 0.0215 inch).1,2,14 Typically, such wires are

bonded to each six anterior teeth in the maxilla and/or mandible. In some cases,

these wires are solely bonded to mandibular canines without bonding the retainer

onto the incisors.15,16 Clinical reports to date are more in favour of multistranded

(5-stranded 0.0215-inch wire) wires compared to single or multistranded wires

containing 3 or less strands that should be bonded to all anterior teeth in a

segment.1,2 Moreover, the use of multistranded wires decreases wire breakage

due to fatigue as a consequence of increased wire flexibility.2 Additionally, the

use of multistranded wires, reduces the individual mobility of the bonded teeth

while maintaining physiologic mobility.2,17 Yet, based on the previous clinical

reports, several shortcomings of the use of stainless steel wires remains to be

debonding, wire breakage, torque differences in the bonded teeth yielding to

positional changes of the teeth, metal allergy and aesthetic concerns.18-23 Due to

such limitations of these stainless steel wires, almost two decades ago, resin-

based bonded retainers were introduced.

Fiber Reinforced Composites Fiber reinforced composites (FRCs) are typically composed of fibers and a resin

matrix. In FRC structures, fibers are the main reinforcement elements while the

matrix bonds the fibers together in a given shape and transfers stresses between

the reinforcing fibers. The primary function of the fibers is to carry the loads

12 13

forces may be considered as factors for failures, which did not receive much

attention in the orthodontic literature.

Objectives of this thesisThe following research questions were addressed in this thesis:

1 What is the survival of flexible, braided, bonded stainless steel lingual retain-

ers as a function of gender, age, location and operator experience?

2 Do the fiber-reinforced composite retainers adhere better than stainless

steel retainers on enamel?

3- Are fiber-reinforced composite retainers more fatigue resistant compared to

braided stainless steel wires?

4 Is the survival of flexible, braided, stainless steel lingual retainers affected by

the type of resin composite used for their adhesion to tooth surfaces?

5 Does incremental loading increase the level of tooth displacement and what

are the margins of displacement in non-bonded and bonded conditions?

the retainers.1,34 Durable adhesion between the retainer and the tooth surface is

crucial in order to maintain the achieved orthodontic result.30 Debonding of the

retainer yield to unwanted tooth movement towards the original tooth position

prior to the orthodontic treatment.35 This could be referred as dental relapse often

requiring re-treatment which is both costly and time consuming for the patient,

orthodontist and the health care systems.31

Previous studies showed that the use of multi-stranded stainless steel wires may

show a higher success rate due to the reduced stress on the wire compared to

single-strand stainless steel wires.2,35,36-39 Detachment from the tooth surface and

breakage of such conventional retainers however do occur in clinical practice.22,35

In fact, failure rates varying from 5.9 to 53% have been reported over an average

period of 3 years.1,19,21,23,35,40-43 The failures reported were frequently associated

with loss of adhesion and/or micro-cracks at or around the composite-stainless

steel wire interface that resulted in detachment of the wires from the composite

mass.2 Due to the fact that multi-stranded wires present retentive morphologies,

the adhesion of the resin composite to the wire is mainly mechanical and not

chemical. The failures related to metal wires could be also multifactorial where,

location, operator experience and age is of significance.2,3,10,19,21 Therefore, the

chemical adhesion of FRC retainers to both the resin composite and the teeth

was anticipated to solve the adhesion problem experienced with stainless steel

wire retainers. Since a fiber bundle has a larger surface area and could be bonded

to each tooth due to its resinous matrix, more adhesion could be expected from

an FRC retainer after photo-polymerization. Certainly, the tooth-coloured FRC

presents more aesthetic outcome as opposed to metal ones, which could also be

considered as a solution to metal allergy experienced with metal retainers that is

reported to be 17% in female population.44

To date, there are no clear guidelines for the application mode of the polyethylene

or glass FRC retainers in orthodontics. While some manufacturers recommend

direct application of the FRC bundle on the tooth surface that is then covered

by the low-viscosity resin composite, others advice embedding the FRC bundle

in the bed of the low-viscosity resin, followed by coverage of the bundle again

with low-viscosity resin. Not only the application mode and adhesion forces

but also the fatigue conditions and the physico-chemical properties of the resin

composite could have direct impact on the durability of adhesion and thereby

clinical longevity of the retainers. An FRC retainer is flexible at the initial stage

before photo-polymerization that needs to be contoured to the tooth surface.

Direct application and pliability of FRC retainers allows for single appointment

application and eliminates laboratory procedures that can be the case with metal

retainers. Moreover, in contrast to the stainless steel wire retainers, in case of

chipping or fracture, FRC materials could be repaired easier.45 Furthermore, the

physiologic adaptation to the new position of the teeth resisting the adhesive

14 15

18. Will LA. Stability and Retention. Front Oral Biol 2016;18:56-63.

19. Segner D, Heinrici B. Bonded retainers-clinical reliability. J Orofac Orthop 2000;61:352-358.

20. Menezes LM, Campos LC, Quinta CC. Bolognese AM. Hypersensitivity to metals in orthodontics Am J Orthod Dentofacial Orthop 2004;126:58-64.

21. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008:30:199-204.

22. Renkema AM, Renkema A, Bronkhorst E, Katsaros C. Long-term effectiveness of canine-to-canine bonded flexible spiral wire lingual retainers. Am J Orthod Dentofac Orthop 2011;139:614-612.

23. Pandis N, Fleming PS, Kloukos D, Polychronopoulou A, Katsaros C, Eliades T. Survival of bonded lingual retainers with chemical or photo polymerization over a 2-year period: a single-center, randomized controlled clinical trial. Am J Orthod Dentofacial Orthop 2013;144:169-175.

24. De Boer J, Vermilyea SG, Brady RE. The effect of carbon fiber orientation on the fatigue resistance and bending properties of two denture resins. J Prosthet Dent 1984;51:119-121.

25. Karna JC. A fiber composite laminate endodontic post and core. Am J Dent 1996;9:230-232.

26. Strassler HE. Tooth stabilization improves periodontal prognosis: a case report. Dent Today 2009;28:88-92.

27. Rose E, Frucht S, Jonas IE. Clinical comparison of a multistranded wire and a direct-bonded polyethylene ribbon reinforced resin composite used for lingual retention. Quintessence Int 2002;33:579-83.

28. Freilich MA, Karmaker AC, Burstone CJ, Goldberg AJ. Development and clinical appli-cations of a light-polymerized fiber-reinforced composite. J Prosthet Dent 1998;80:311-318.

29. Freilich MA, Meiers JC, Duncan JP, Goldberg AJ. Clinical evaluation of fiber-reinforced fixed bridges. J Am Dent Assoc 2002;133:1524-1534

30. Freudenthaler JW, Tischler GK, Burstone CJ. Bond strength of fiber-reinforced composite bars for orthodontic attachment. Am J Orthod Dentofacial Orthop 2001;120:648-653.

31. Lie Sam Foek DJ, Özcan M, Krebs E, Sandham E. Adhesive properties of bonded orthodontic retainers to enamel: stainless steel wire versus fiber-reinforced-composites. J Adhes Dent 2009;11:381-390.

32. Karacaer O, Dogan A, Dogan OM, Usanmaz A. Dynamic mechanical properties of dental base material reinforced with glass fiber. J Appl Polym Sci 2002;85:1683-1697.

REFERENCES

1. Zachrisson BU, Büyükyilmaz T. Bonded retainers. In: Graber LW, Vanarsdall RL, Vig KW, editors. Orthodontics: Current principles and techniques. 5th ed. Philadelphia: Elsevier Mosby; 2012. p. 756-784.

2. Zachrisson BU. Multistranded wire bonded retainers: From start to success. Am J Orthod Dentofacial Orthop 2015;148:724-727.

3. Littlewood SJ, Millet DT, Doubleday B, Bearn DR, Worhington HV.Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database of Systematic Reviews. 2016;29: CD002283.

4. Southard T, Southard K, Tolley E. Periodontal force: a potential cause of relapse. Am J Orthod Dentofacial Orthop 1992;101:221-227.

5. Thilander B. Orthodontic relapse versus natural development. Am J Orthod Dentofacial Orthop 2000;117:562-563.

6. Thilander B. Biological basis for Orthodontic relapse. Semin Orthod 6 Part 3 2000:190-205.

7. Boese LR. Fiberotomy and reproximation without lower retention 9 years in retrospect: part II. Angle Orthod 1980;50:169-178.

8. Proffit WR, McGlone RE, Barrett MJ. Lip and tongue pressures related to dental arch and oral cavity size in Australian Aborigines. J Dent Res 1975;54:1161–1172

9. Gkantidis N, Christou P, Topouz N. The orthodontic-periodontic interrelationship in inte-grated treatment challenges: a systematic review. J Oral Rehabil 2010;37:377-390.

10. Zachrisson BU. Differential retention with bonded retainers. World J Orthod 2007;8:190-196.

11. Zachrisson BU. The bonded lingual retainer and multiple spacing of anterior teeth. Swed Dent J 1982;15:247-255.

12. Zachrisson BU. Third-generation mandibular bonded lingual 3-3 retainer. J Clin Orthod 1995;29:39-48.

13. Renkema AM, Sips E, Bronkhorst E, Kuijpers-Jagtman AM. A survey on orthodontic retention procedures in the Netherlands. Eur J Orthod 2009;31:432-437.

14. Årtun J, Zachrisson BU. Improving the handling properties of a composite resin for direct bonding. Am J Orthod Dentofacial Orthop 1982;81:269-276.

15. Knierim R. Invisible lower cuspid-to- cuspid retainer. Angle Orthod 1973:43:218-220.

16. Wolfsen J, Servoss JM. Bandless but fixed retention. Am J Orthod Dentofacial Orthop 1974; 66:431-434.

17. Watted N, Wieder M, Teuscher T, Schmitz N. Comparison of incisor mobility after insertion of canine-to-canine lingual retainers bonded to two or to six teeth. A clinical study. J Orofac Orthop 2000;62:387-396.

16 17

33. Lassila LVJ, Nohrstrom T, Vallittu PK. The influence of short-term water storage on the flexural properties of unidirectional glass fiber-reinforced composites. Biomaterials 2002;23:2221-2229.

34. Burstone CJ, Kuhlberg AJ. Fiber-reinforced composites in orthodontics. J Clin rthodont 2000;34:271-279.

35. Dahl E H, Zachrisson BU. Long term experience with direct bonded lingual retainers. J Clin Orthodont 1991;25:619-630.

36. Zachrisson BU. Clinical experience with direct-bonded orthodontic retainers Am J Orthod 1977;71:440-448.

37. Zachrisson BU. Improving orthodontic results in cases with maxillary incisors missing Am J Orthod 1978;73:274-289.

38. Zachrisson BU. The bonded lingual retainer and multiple spacing of anterior teeth. Swed Dent J 1982;15:247-255.

39. Radlanski RJ, Zain ND. Stability of the bonded lingual wire retainer-a study of the initial bond strength. J Orofac Orthop 2004;65:321-335.

40. Andrén A, Asplund J, Azarmidohkt E, Svensson R, Varde P, Mohlin B. A clinical evaluation of long term retention with bonded retainers made from multi-strand wires. Swed Dent J 1998;22:123-131.

41. Årtun J, Spadafora A T, Shapiro PA. A 3-year follow-up study of various types of orthodontic canine-to-canine retainers. Eur J Orthodont 1997;19:501-509.

42. Lumsden K W, Saidler G, McColl JH. Breakage incidence with direct bonded lingual retainers. Br J Orthod 1999;26:191-194.

43. Störmann I, Ehmer UA. Prospective randomized study of different retainer types. J Orofac Orthoped 2002;63:42-50.

44. Milheiro A, Kleverlaan C, Muris J, Feilzer AJ, Pallav P. Nickel release from orthodontic retention wires-the action of mechanical loading and pH. Dent Mater 2012;28:548-553.

Chapter 2

Survival of flexible, braided, bonded stainless steel lingual retainers: A historic cohort study

Lie Sam Foek D.J.

Özcan M

Verkerke G.J.

Sandham A

Dijkstra P.U.

Eur J Orthod. 2008 Apr;30(2):199-204.

20 21

INTRODuCTION

Bonded retainers are extensively used after orthodontic treatment with fixed

appliances in order to maintain the achieved result by preventing secondary

crowding of incisors after tooth alignment (Keim et al., 2002; Zachrisson and

Büyükyilmaz, 2005). Despite the various forms of retainers, the most commonly

used are the thick mandibular canine-to-canine (3-3) bonded retainer bar (0.030

or 0.032 inch) and the thin 0.0215 inch, flexible, spiral wire retainers (Littlewood

et al., 2004, 2006; Zachrisson and Büyükyilmaz, 2005). These types of bonded

retainers have been reported to have fairly high long-term (up to 15 years)

success rates (Zachrisson, 1978, 1982, 1986, 1995, 1996; Dahl and Zachrisson,

1991; Bearn, 1995; Årtun et al., 1997). Failure types reported in these studies

were loosening (debonding) and wire breakage. For a thin flexible spiral wire

in the mandible, failure rates of less than 10% have been reported, particularly

with the five-stranded Penta-One wire up to 2 - 3 years (Årtun and Urbye, 1988;

Dahl and Zachrisson, 1991; Bearn, 1995; Årtun et al., 1997). However, given the

importance of this phenomenon, relatively limited clinical research has been

performed, with reported mandibular failure rates ranging from 5.9% to 53%

(Dahl and Zachrisson, 1991; Årtun et al., 1997; Andrén et al., 1998; Lumsden et

al., 1999; Störmann and Ehmer, 2002). Although this wire type is the one most

often recommended, the range of failures shows high variation, indicating that

successful treatment maintenance with such wires cannot be achieved in the

long-term.

When these flexible spiral wire retainers are placed meticulously, they have the

advantage of allowing for safe retention of the treatment results. On the other

hand, when correct retention is difficult or impossible to achieve with traditional

removable appliances, flexible spiral wire retainers are considered appropriate,

and they are independent of patient cooperation. They also allow slight movement

of all bonded teeth and segments of teeth; they are highly efficient and, almost,

invisible (Segner and Heinrici, 2000; Zachrisson and Büyükyilmaz, 2005). The

disadvantages of flexible spiral wire retainers are that they may be subject

to mechanical stress and, if too thin, or not placed passively onto the enamel

surface, they may result in undesirable tooth movement (Årtun and Thylstrup,

1986; Dahl and Zachrisson, 1991; Årtun et al., 1997).

Due to the limited number of clinical studies that have been conducted to date

(Årtun et al., 1997; Lumsden et al., 1999; Zachrisson and Büyükyilmaz, 2005) and

the large range in failure rates with twisted wires, an alternative flexible, braided

wire retainer (Quad Cat stainless steel, twisted wire, 0.022 × 0.016 inch, GAC

International, Bohemia, New York, USA) is available for orthodontic treatment

purposes. Unfortunately, limited clinical information is available concerning such

braided wires (Southard and Southard, 1990; Zachrisson and Büyükyilmaz, 2005).

SuMMARy

The objectives of this study were to retrospectively evaluate the clinical survival

rate of flexible, braided, rectangular bonded stainless steel lingual retainers, and

to investigate the influence of gender, age of the patient, and operator experience

on survival after orthodontic treatment at the Department of Orthodontics,

University of Groningen, between the years 2002 and 2006.

The study group comprised of 277 patients [162 females: median age 14.8 years,

interquartile range (IQR) 13.6 - 16.5 years and 115 males: median age 15.3 years,

IQR 14.2 - 16.7 years]. After acid etching the lingual surfaces of each tooth, an

adhesive resin was applied and retainers were bonded using a flowable resin

composite. Data concerning, failures, gender, age of the patient, and operator

experience were retrieved from the patient files that were updated by chart

entries every 6 months or when failure was reported by the patient. The maximum

follow-up period was 41.7 months. All 277 patients received flexible, braided,

bonded mandibular canine-to-canine retainers. Eighteen failures were observed

in the maxilla. A failure was recorded when there was debonding, fracture, or

both, occurring in one arch. Only first failures were used for statistical analysis.

When failures occurred in both jaws, these were considered as two separate

incidences.

Ninety-nine debonding (35.7%), two fractures (0.7%), and four debonding and

fracture (1.4%) events were observed. No significant effect (P > 0.05) of gender

(females: 41%, males: 32%) or patient age (<16 years: 37%, ≥ 16 years 38.7%)

was observed. The failure rate did not differ due to operator experience (n = 15;

less experienced: 38.0%; moderately experienced: 28.9%, professional: 46.7%;

P > 0.05; chi-square test). Kaplan- Meier survival curves showed a 63% success

rate for the bonded lingual retainers over a 41.7 month period.

22 23

assumption was made that there must have been a bonded retainer in the maxilla

as well as in the mandible.

Follow-upThe patient data included the information derived from chart entries of clinical

examinations carried out every 6 months, or when the patient reported a failure.

The inclusion period for this retrospective cohort study was from December 2002

to May 2006, therefore the maximum follow-up period possible was 42 months.

Failure of a retainer occurs as a result of debonding, fracture, debonding and

fracture, or retainer loss. Information was unavailable on the site of failure e.g.

single tooth bond failure, enamel/adhesive failure, or adhesive wire failure. In

all cases where debonding was recorded, rebonding was undertaken. When

fracture and/or retainer loss occurred, a new retainer was made (Bond-A-Braid,

dead soft wire, Hilgers, Reliance Orthodontic Products Inc., Itasca, Illinois, USA)

at the chairside and bonded to the enamel surfaces after cleaning the enamel of

remnants of the adhesive and/or resin (Birnie, 2007).

In total, 87 failures occurred in the mandible (1 fracture, 82 debonding, and 4

debonding plus fractures). In the maxilla, 18 failures were observed (1 fracture

and 17 debonding). Due to the delegation strategy at the department (system

of work), different operators working under the supervision of one experienced

orthodontist were allowed to place the retainers. The experience of the operators

placing the retainers was categorized as 0 - 5 years (least experienced), 6 - 10

years (moderately experienced), 11 - 15 years (experienced), 16 - 20 years (most

experienced), and 21 years or more (very experienced).

Statistical analysisStatistical analysis was performed using the Statistical Package for Social

Sciences (version 12.0, SPSS Inc., Chicago, Illinois, USA). Descriptive statistics

and Kaplan-Meier curves were calculated. In the Kaplan-Meier curves, the cu-

mu lative survival rate of the retainers was compared against the time interval

between placement of the retainers and occurrence of the first failure. Only first

failures were counted and no distinctions were made in failure location in case of

debonding. A reported failure in the maxilla or in the mandible was counted as a

separate incidence. In addition, multiple failure sites in one retainer were counted

as one failure. Furthermore, failure was considered when there was debonding,

fracture, debonding and fracture, or retainer loss. A chi-square test was used in

order to analyse the influence of gender, age of the groups, and experience of

the operators on the survival rate. P values less than 0.05 were considered to be

statistically significant.

Therefore, the aims of this study were to analyse the survival rate of flexible,

braided, rectangular, bonded, lingual stainless steel wire retainers by means of a

historic cohort study, and to investigate the influence of gender, patient age, and

operator experience on survival.

SuBJECTS AND METHODS

Sample Initially, patient files, without pre-selection were retrieved from the Department

of Orthodontics, Groningen, The Netherlands by undertaking a search of the

computer program (OrtWin 2.0, Netpoint, Kaatsheuvel, The Netherlands). All

selected patients (n = 277) satisfied the inclusion criteria of having finished

their orthodontic treatment with fixed appliances and having received a bonded

retainer between December 2002 and May 2006.

One hundred and sixteen patients were treated with removable functional and

fixed appliances (combined treatment) and 161 only with fixed appliances. All 277

patients [162 females: median age 14.8 years, interquartile range (IQR) 13.6 - 16.5

years and 115 males: median age 15.3 years, IQR 14.2 - 16.7 years] received a

mandibular flexible bonded retainer from canine to canine (3-3). It is not known

which proportion of the total sample also received a bonded retainer in the maxilla

at baseline. A modified maxillary removable Hawley retainer was usually worn for

a period of 1 year by some patients after completion of orthodontic treatment.

Application of retainers The flexible, braided, rectangular, stainless steel wire retainers (Quad Cat, 0.022 ×

0.016 inch, GAC International) were initially prepared for the maxilla and mandible

on plaster cast models by dental technicians (Ortholab Dental Technicians, Doorn,

The Netherlands). Since such flexible retainers need to be bonded to each tooth

(Zachrisson and Büyükyilmaz, 2005), the enamel was acid etched for 10 seconds

per tooth with 38% H3PO4 and rinsed thoroughly, before the bonding adhesive

(Heliobond, Ivoclar Vivadent, Schaan, Liechtenstein) was applied and air thinned.

All retainers were bonded using a flowable resin composite (Tetric Flow, Cavifill

210 A3, Ivoclar Vivadent) and light polymerized for 20 seconds per tooth using

a light-emitting diode polymerization device (Ortholux™, 3M Unitek, St Paul,

Minnesota, USA) and placed by orthodontists (n = 1), postgraduate students

(n = 4), dental hygienists (n = 8), or dental assistants (n = 2). Moisture control for

the retainers was accomplished using cotton rolls and saliva ejectors. All subjects

(n = 277) received a mandibular bonded retainer. Due to the retrospective

nature of this study, the exact number of bonded retainers placed in the maxilla

was unknown. If failure of a bonded retainer in the maxilla was reported, the

24 25

RESuLTS

The maximum follow-up period was 41.7 months (median 19.9 months, IQR 15.2

- 23.7, mean 19.1 months, SD 7.2). Table 1 shows a summary of the demographic

characteristics of the patient population and the effect of confounding factors on

the survival rate.

Of the total number of treated patients, 66.1% were younger than 16 years and

33.9% were older than 16 years; 58.5% were female and 41.5% were male.

In total, 99 debonding (35.7%), two fracture (0.7%), and four debonding plus

fracture (1.4%) failures were observed. No significant effect of gender [females:

41% (confidence interval, CI: 16.3 - 83.9), males: 32% (CI: 24.8 - 41.8)], patient

age [<16 years: 37% (CI: 30.3 - 44.0), ≥16 years: 38.7% (CI: 29.4 - 48.9)], and

operator experience (least experienced: 38.5%, moderately experienced: 28.9%,

very experienced: 46.7%) on failure rate was found (chi-square test; P > 0.05;

Figure 1).

Kaplan-Meier survival curves showed a gradual decrease in failure rate, being

highest at 6 months at 78%. According to the plot, if the retainers survived the

first 2 years, they usually continued to function well. Figure 2 shows that the

cumulative survival rate for the bonded lingual retainers was 63%. Exact data for

the mandibular definition indicated a survival rate of 68.4%.

Table 1: Summary of the demographic characteristics of the patient population and the effect of confounding factors on the failure rate of lingual bonded retainers.

Number of retainers placed

Failure (%) 95% Confidence Interval

Gender

Females 162 41.4 34.1, 49.1

Males 115 33.3 25.3, 42.4

Age*

<16 years 181 37.0 30.3, 44.3

≥16 years 93 38.7 29.4, 48.9

Operator experience**

0-5 years 200 38.5 32.0, 45.4

6-10 years - - -

11-15 years - - -

16-20 years 45 28.9 17.7, 43.4

≥21 years 30 46.7 30.3, 63.9 *Data of three patients missing. †Number of patients treated by operators (n = 15). Note that data of two patients were missing.

Cu

mu

lati

ve S

urv

ival

Time (months)

Female

Male

0,00 10,00 20,00 30,00 40,00 50,00

0,0

0,2

0,4

0,6

0,8

1,0

Figure 2: Kaplan-Meier survival curve showing a 63% success rate for the bonded lingual retainers over a 41.7 month period.

Cu

mu

lati

ve S

urv

ival

Time (months)

0

0,0

0,2

0,4

0,6

0,8

1,0

6 12 18 24 30 36 42

Figure 1: Cumulative survival rates of bonded lingual retainers for females (n = 162) and males (n = 115).

26 27

ments of the retainer wire during the setting process of the adhesive could impair

ideal adhesion. In vitro and in vivo studies (Ibe and Segner, 1995; Hajrassie and

Khier, 2007) have also concluded that a certain percentage of bonding sites may

be unsatisfactory, although the mean bond strength may be initially sufficient.

The in vitro findings could be expected to apply even more strongly for in vivo

placements due to a less favourable working environment. Such sites with

insufficient bond strength will manifest themselves in the first week or months

after bonding.

Other explanations for the early failures could be based on biological reasons.

Tuverson (1980) suggested that rotational relapse may be due to small contact

points at the axial part of the bonded teeth which seem to be unstable. Surbeck

et al. (1998) commented that the presence of more crowded and irregular

dentitions prior to treatment may not necessarily be a sole indicator of greater risk

for relapse after treatment. In addition, factors such as orthodontic expansion,

incomplete tooth alignment, and interdental spacing might be responsible for

post-treatment relapse leading to failure of bonded retainers. Unfortunately, in

retrospective studies, such aspects cannot always be identified.

Huang and Årtun (2001) found an association between a narrow intercanine width

and relapse of the maxillary and mandibular incisors. Fudalej and Årtun (2007)

concluded that neither forward nor backward rotational growth patterns, at the

time of appliance removal, are associated with increased risk of post-retention

relapse. Particularly, in adolescent orthodontic patients, the type of post-

treatment growth is difficult to predict. The sample in the present study consisted

mostly of adolescent patients which could perhaps explain the high rate of failure.

On the other hand, Yoshida et al. (1999) suggested that rapid remodelling of the

periodontal ligament and the surrounding alveolar bones could be the main cause

of tooth relapse. While different factors play a role in post-treatment relapse, it is

most likely that the forces exceed the adhesive strength of the bonded retainers

causing them to fail.

Successful clinical outcomes are often reported by experienced orthodontists

(Dahl and Zachrisson, 1991; Årtun et al., 1997) especially in private practice

settings. The experience of the operator is expected to be the most likely key

factor influencing the failure rates. Higher failure rates could be expected when

less experienced operators are involved. Interestingly, however, in the present

study, neither different operators nor experience played a significant role in

failure rate. Due to the considerable design differences of the retainers placed

by different operators, a high failure rate ranging from 28.9% to 46.7% between

practitioners was observed. However, in clinical trials, particularly in dentistry,

experience may not be always quantified in years of practice. Also in this study,

the number of retainers bonded by the experienced operators decreased with

the increase in delegation. It is also difficult to distinguish the transition between

DISCuSSION

Total survival rate for the flexible, lingual, braided bonded retainers was 63%

over an observation period of 41.7 months. The survival rate decreased during

this time, with the highest number of failures being observed within the first 6

months after placement. This finding is in accordance with the results of Årtun

et al. (1997) and Segner and Heinrici (2000). Although the retrospective design

of the study contributed to the lack of data for the precise number of retainers

placed in the maxilla, exact data concerning the failure rate for the mandible was

found to be 31.6%. These results are slightly lower than the findings of Andrén et

al. (1998) who reported a failure rate of 35% for the mandible. On the other hand,

they were higher than the 18%failure rate for the 0.0195 inch and lower than the

53% failure rate for the 0.0215 inch retainer reported by Störmann and Ehmer

(2002). However, the failure rate found in this study was higher than the 27.2 per

cent for the thin, flexible spiral wires reported by Årtun et al. (1997). Similarly,

Dahl and Zachrisson (1991) reported a failure rate of 10.3% with the use of three-

stranded spiral wire (Triflex or Wildcat) and 5.9% with the five-stranded spiral

wire (Penta-One). In their investigation, as in most previous studies (Zachrisson,

1982; Dahl and Zachrisson, 1991; Årtun et al., 1997), the retainer wires were

bonded with a chemically polymerized resin composite (Concise).

The failure rates recorded in the present investigation are less favourable than

those published previously by Dahl and Zachrisson (1991) and Årtun et al. (1997).

In both of those studies, all the retainers were bonded in private practice by one

or two experienced operators, while in the present study the retainers were

bonded by 15 different operators, with a great difference in experience. Similar

to the study of Segner and Heinrici (2000) where the retainers were bonded by

28 different operators, in the present study bonding was undertaken by multiple

operators. This may account for the difference in failure rates.

The position in the present study of the wire on the lingual surfaces of the teeth,

being either more cervical or more incisal, is unknown. According to Andrén et al.

(2001), a more incisal positioning of the retainer results in less flexibility.

Some studies (Dahl and Zachrisson, 1991; Bearn, 1995; Andrén et al., 1998;

Segner and Heinrici, 2000) reported higher failure rates for the maxilla compared

with the mandible but this could not be verified in this investigation due to missing

data for the maxilla. The fracture rate in the present study was found to be 0.2%,

but the true fracture rate might be slightly higher than the figures calculated due

to the incomplete data.

A noticeable finding of the present investigation was that the failures occurred

mostly in the first 6 months after the retainers were bonded. One explanation

for this could be insufficient composite bond strength to enamel that is often

technique sensitive. Factors such as a lack of moisture control or minute move-

28 29

REFERENCES

1. Andrén A, Asplund J, Azarmidohkt E, Svensson R, Varde P, Mohlin B 1998 A clinical evaluation of long term retention with bonded retainers made from multi-strand wires. Swedish Dental Journal 22 : 123-131

2. Årtun J, Thylstrup A 1986 Clinical and scanning electron microscopic study of surface changes of incipient caries lesions after debonding. Scandinavian Journal of Dental Research 94 : 193-201

3. Årtun J, Urbye K S 1988 The effect of orthodontic treatment on periodontal bone support in patients with advanced loss of marginal periodontium. American Journal of Orthodontics and Dentofacial Orthopedics 93 : 143-148

4. Årtun J, Spadafora A T, Shapiro P A 1997 A 3-year follow-up study of various types of orthodontic canine-to-canine retainers. European Journal of Orthodontics 19 : 501-509

5. Audenino G, Giannella G, Morello G M, Ceccarelli M, Carossa S, Bassi F 2006 Resin-bonded fixed partial dentures: ten-year follow-up. International Journal of Prosthodontics 19 : 22-23

6. Bearn D R 1995 Bonded orthodontic retainers: a review. American Journal of Ortho-dontics and Dentofacial Orthopedics 108 : 207-213

7. Birnie D 2007 Stability and retention. Excellence in Orthodontics, London, pp. 411-432.

8. Dahl E H, Zachrisson B U 1991 Long term experience with direct bonded lingual re-tainers. Journal of Clinical Orthodontics 25 : 619-630

9. Davidson C L, de Gee A J 2000 Light-curing units, polymerization, and clinical implica-tions. Journal of Adhesive Dentistry 2 : 167-173

10. Fudalej P, Årtun J 2007 Mandibular growth rotation effects on postretention stability of mandibular incisor alignment. Angle Orthodontist 77 : 199-205

11. Hajrassie M, Khier S 2007 In-vivo and in-vitro comparison of bond strengths of orthodontic brackets bonded to enamel and debonded at various times. American Journal of Orthodontics and Dentofacial Orthopedics 131 : 384-390

12. Huang L, Årtun J 2001 Is the postretention relapse of maxillary and mandibular incisor alignment related? American Journal of Orthodontics and Dentofacial Orthopedics 120 : 9-19

13. Ibe D, Segner D 1995 Improvement in the adhesive strength of orthodontic brackets on unit-cast and Fired dental alloys by microsandblasting. Journal of Orofacial Orthopedics 56 : 110-117

14. Keim R G, Gottlieb E I, Nelson A H, Vogels 3rd D S 2002 JCO study of orthodontic diagnosis and treatment procedures. 1. Results and trends. Journal of Clinical Orthodontics 36 : 553-568

15. Littlewood S J, Millett D T, Doubleday B, Bearn D R, Worthington H V 2004 Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database of Systematic Reviews 1: CD002283

the least experienced and the experienced. Nevertheless, the findings of this

research represent a more real-life clinical situation.

The results did not show significant differences in failure rates between genders

and age, in agreement with the findings of Lumsden et al. (1999) where the mean

age of the subjects was 15.5 years. The results related to age were, however,

lower than those reported by Dahl and Zachrisson (1991) where the mean age

of the patient population was 31.2 years. It should, however, be noted that their

sample size was only 17 for the mandible, whereas for the present study the total

sample was 277. A direct comparison is therefore not possible since the reason

for failures could be related to the relapse response in the adults or simply to the

low power of the study.

Although previous investigations (Dahl and Zachrisson, 1991; Årtun et al., 1997;

Störmann and Ehmer, 2002) have shown a difference in failure rate when different

types of retainers are used, no randomized controlled clinical trials have been

performed to date. Future investigations should concentrate on this aspect. In the

current study, moisture control was achieved using only saliva ejectors and cotton

rolls. However, the survival rate of resin-bonded restorations has been reported

to be higher when bonding procedures are performed under rubber dam isolation

(Audenino et al., 2006). Prospective studies should also perhaps concentrate on

other confounding factors such as effective moisture control, light intensity of

the polymerization device (Davidson and de Gee, 2000), and the composite and

adhesive resin used.

Conclusions

The following conclusions can be drawn from this study:

1. The success rate of the flexible, braided, bonded lingual retainers was 63%

over 41.7 months.

2. The survival rate for the mandible was 68.4%.

3. Most failures occurred during the first 6 months.

4. Gender and age of the patient and operator experience did not affect the

failure rate.

AcknowledgementThe authors would like to extend their gratitude to Dr. M.W.J. Bierman for helpful

discussions.

3130

16. Littlewood S J, Millett D T, Doubleday B, Bearn D R, Worthington H V 2006 Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database of Systematic Reviews 1: CD002283

17. Lumsden K W, Saidler G, McColl J H 1999 Breakage incidence with direct bonded lingual retainers. British Journal of Orthodontics 26: 191-194

18. Segner D, Heinrici B 2000 Bonded retainers-clinical reliability. Journal of Orofacial Orthopedics 61 : 352-358

19. Southard K A, Southard T E 1990 Conservative management of anterior spacing and deep bite: a case report. Quintessence International 21: 801-811

20. Störmann I, Ehmer U 2002 A prospective randomized study of different retainer types. Journal of Orofacial Orthopedics 63: 42-50

21. Surbeck B T, Årtun J, Hawkins N R, Leroux B 1998 Associations between initial, posttreatment, and postretention alignment of maxillary anterior teeth. American Journal of Orthodontics and Dentofacial Orthopedics 113: 186-195

22. Tuverson D L 1980 Anterior interocclusal relations. Part II. American Journal of Orthodontics 78: 361-393

23. Yoshida Y, Sasaki T, Yokova K, Hiraide T, Shibasaki Y 1999 Cellular roles in relapse processes of experimentally - moved rat molars. Journal of Electron Microscopy 48: 147-157

24. Zachrisson B U 1978 Improving orthodontic results in cases with maxillary incisors missing. American Journal of Orthodontics 73: 274-289

25. Zachrisson B U 1982 The bonded lingual retainer and multiple spacing of anterior teeth. Swedish Dental Journal 15: 247-255

26. Zachrisson B U 1986 Bonding in orthodontics. In: Graber L W (ed). Orthodontics: current principles and techniques. Mosby, St Louis, pp. 526-561

27. Zachrisson B U 1995 Third-generation mandibular bonded lingual 3-3 retainer. Journal of Clinical Orthodontics 29: 39-48

28. Zachrisson B U 1996 Clinical implications of recent orthodonticperiodontic research findings. Seminars in Orthodontics 2: 4-12

29. Zachrisson B U, Büyükyilmaz T 2005 Bonding in orthodontics. In: Graber L W (ed). Orthodontics: current principles and techniques, 4th edn. Mosby, St Louis, pp. 621- 659.

Chapter 3

Adhesive properties of bonded orthodontic retainers to enamel: stainless steel wire versus fiber-reinforced composites

Lie Sam Foek D.J.

Özcan M

Krebs E

Sandham A

J Adhes Dent. 2009 Oct;11(5):381-90.

34 35

INTRODuCTION

During orthodontic treatment, the position of teeth is adjusted in order to correct

malocclusion. There is an inherent tendency for teeth to relapse to their original,

pretreatment position after the removal of orthodontic appliances.1,11 With the

possibility of acid etching and bonding, it has become common practice to

apply bonded fixed retainers for long-term retention of the achieved orthodontic

results.2,7 Currently, such retainers are often made of either stainless steel wires

or fiber-reinforced composites (FRC) of diverse types. Limited clinical studies

have shown that there is a relatively high failure rate ranging between 2.9% to

47% in a comparatively short follow-up period.1-3,7,15 The failure type is usually

either detachment of the wire retainer from the tooth surface or at the wire and/

or resin composite interface. Although the reasons for these failures have not

been extensively studied, several factors are described in the dental literature,

such as insufficient composite material and/or abrasion of the composite,3,4 less

abrasion resistance and wear as a consequence of chewing or tooth brushing,3,4

thickness of the wire,15 and intermittent forces of mastication.3,4 Another reason

for debonding rates was attributed to the forces resulting from tension in the

wire or between the wire and the teeth when the wire has not been adapted

properly to the surface of the teeth.3 Nevertheless, detachment of the bonded

retainers has negative consequences for the treatment result, since the teeth

may change position or relapse to their original position after the completion of

the orthodontic treatment. This is costly for both the medical system and the

patient, as it renders the lengthy and costly previous treatment ineffective, possi-

bly making retreatment necessary.

Recently, FRC materials have been introduced for the fabrication of fixed dental

prostheses (FDP), root posts, periodontal splints, and also as possible alternatives

to stainless steel wire retainers for both active and passive applications in

orthodontics. Resin pre-impregnated FRCs have a suitable flexural modulus

and flexural strength for functioning successfully in the mouth as restorative

materials.16,31 It is thought that elimination of the metal wire in the retainer by

using FRC systems may lead to more stable bonding, since adhesion of such

retainers would solely rely on adhesion of the flowable composite or the resin

matrix of the FRC to the etched and bonded enamel. Theoretically, FRC materials

are attractive because of their elastic modulus, esthetics, pliability, and the

possibility of chemical adhesion both to the composite materials and the tooth,

as opposed to the metal wires. Considering the clinical failures with stainless

steel retainers related to debonding, especially the adhesion aspect warrants the

comparison of FRC materials to their metallic counterparts.

FRC materials are available in different forms and volumes, either preimpregnated

with different resin monomer matrices or requiring impregnation prior to application

ABSTRACT

Purpose: The objectives of this study were to compare the bond strength of a

stainless steel orthodontic wire versus various fibre-reinforced-composites (FRC)

used as orthodontic retainers on enamel, analyze the failure types after debonding

and to investigate the influence of different application procedures of stainless

steel wires on bond strength.

Materials and Methods: Caries-free, intact human mandibular incisors (N=80, n=10

per group) were selected and randomly distributed into 8 groups. After etching with

37% H3PO4 for 30 seconds, rinsing and drying, bonding agent (Stick Resin) was

applied, light polymerized and one of the following FRC materials were applied on

the flowable composite (Stick Flow) using standard molds: Group 1: Angelus Fibrex

Ribbon; Group 2: DentaPreg Splint; Group 3: everStick Ortho and Group 4: Ribbond.

In Group 5, Quad Cat Wire was applied in the same manner as in FRC groups.

In Group 6, after bonding agent (Stick Resin), Quad Cat Wire was placed directly

on the tooth surface and covered with Stick Flow composite. In Group 7, after

bonding agent (Heliobond) was applied, Quad Cat Wire was placed directly on the

tooth surface and covered with Tetric Flow composite. In Group 8, after applying

bonding agent (Heliobond), Tetric Flow composite was applied, not polymerized

and Quad Cat Wire was placed and covered with Tetric Flow again. Specimens

were thermocycled for 6000 cycles between 5-55°C and loaded in a universal

testing machine under shear stress (crosshead speed: 1 mm/min) until debonding

occurred. The failure sites were examined under an optical light microscope. Data

were analyzed using 1-way ANOVA and Tukey-Kramer adjustment test (α = 0.05).

Results: Significant differences were found between the groups (p = 0.0011)

(ANOVA). Bond strength results did not significantly differ neither between the

FRC groups (Groups 1-4) (6.1±2.5 to 8.4±3.7 MPa) (p > 0.05) or the wire groups

(Groups 5-8) (10.6±3.8 to 14±6.7 MPa) (p > 0.05). Failure types varied within the

FRC groups, but mainly composite was found left adhered on the enamel surface at

varying degrees. In the stainless steel wire groups, when the retainer was applied

onto the bonding agent and then covered with flowable resin, partially attached

composite on the enamel was often found after debonding. When the wires were

embedded in the flowable composite, the Heliobond group (Group 8) showed more

adhesive failures between the enamel and the composite compared to Group 5,

where bonding agent was Stick Resin.

Conclusion: Regardless of their application mode, stainless steel orthodontic

bonded retainers delivered higher bond strengths than those of fiber retainers.

The differences were statistically significant compared to those of Angelus Fibrex

Ribbon and DentaPreg Splint.

Keywords: bond strength, fiber-reinforced composite, lingual retainer, orthodontics,

relapse, stainless steel wire.

36 37

MATERIALS AND METHODS

Specimen PreparationEighty caries-free human mandibular central incisors of similar size, stored in

distilled water with 0.1% (wt/vol) thymol at room temperature, were selected

from a pool of recently extracted teeth. To determine that the enamel was free

of crack lines, all teeth were evaluated under blue light transillumination. The

roots were then sectioned with a diamond bur under water cooling. The crowns

were mounted in polyethylene rings (diameter: 15 mm, thickness: 10 mm), with

the buccal surface exposed, using autopolymerized polymethyl methacrylate

(Candulor; Wangen,Switzerland) (Fig 1). Before embedding, the teeth were

cleaned of any remaining soft tissue and calculus and stored in distilled water with

0.1% (wt/vol) thymol up to 2 months until the experiments. The enamel surfaces

were cleaned and polished using water and fluoride-free pumice (Zircate Prophy

Paste, Dentsply Caulk; Milford, DE, USA, batch #077809) with a prophylaxis

brush (Hawe Prophy- Cup Latch-Type, KerrHawe; Bioggio, Switzerland, batch

#960/30), rinsed with water, and dried using an air syringe.

Bonding ProceduresIn all groups, labial enamel surfaces were etched with a 37% orthophosphoric

acid (TopDent, DAB Dental; Upplands Väsby, Sweden) for 30 s and then rinsed

thoroughly using an oil-free air-water spray for 20 s. The enamel surfaces

were air dried until they appeared frosty. Description of brands, compositions,

manufacturers, and batch numbers of FRC and wire retainers are listed in Table 1.

Representative SEM (JSM-5500, JEOL Instruments; Tokyo, Japan) micrographs

of the FRC materials and stainless steel wire are presented in Figure 2.

by the clinician. The adhesive performance of the FRCs may vary depending on

the variations in their inherent properties and impregnation. Although individual

studies exist on adhesion of resin based materials to enamel, to the authors’

knowledge, no research has been conducted to date comparing the adhesive

properties of FRC splint materials with conventionally bonded stainless steel

wires in the same study design. Both FRC and stainless steel wires are bonded

to enamel in orthodontic wire applications using resin based materials, but their

flexural behavior may vary due to the variations in the adhesion of resin materials

to resins and metals. Furthermore, different application modes of stainless

steel wires have been noted in the orthodontic literature, i.e., placing the wire

directly on the etched and bonded enamel 3,4 or embedding the wire in flowable

resin composite or bonding agents with various properties/compositions3,4,35

that may affect the bond strength and the failure types. Because resin-based

materials adhere better to enamel than do metals,21 it was hypothesized that FRC

materials would demonstrate higher bond strength than the metal ones, and that

the bond strength of the stainless steel wires would increase when the wires

were embedded in flowable composite, instead of being applied directly onto the

bonding agent on the enamel.

Preimpregnated systems usually involve monomers like urethane dimethacrylate

(UDMA), urethane tetramethacrylate (UTMA), bisphenol glycidylmethacrylate

(bis-GMA), or polymethyl methacrylate (PMMA).9,19 Evidence is still lacking on

whether ultrahigh molecular weight polyethylene (UHMWPE) fibers can be used

to fabricate durable FRC restorations.10,27,31 Criticism has been focused on the

inadequate interfacial adhesion between polyethylene fibers and dental polymers30

compared to glass and silica fibers, which can be silanized.13,30 Therefore, it was

also hypothesized that silanized and pre-impregnated glass-fiber FRCs would

possess better adhesive properties than plasma-coated, custom impregnated

polyethylene FRC materials.

Therefore, the objectives of this study were twofold: 1. to compare the bond

strength and failure types of a commonly used stainless steel orthodontic wire

with differently impregnated FRC materials with various textures, and 2. to

investigate the influence of different application procedures of stainless steel

wires.

Figure 1: Mandibular incisor embedded in auto-polymerized polymethylmethacrylate with the labial surface exposed for bonding purposes.

38 39

Table 1: The brand names, group numbers, compositions, manufacturers and batch numbers of the materials used in this study.

Brand name Groups Composition Manufacturer Batch number

Angelus Interlig 1 E-glass/Bis-GMA Angelus, Londrina, Brazil

2199

DentaPreg Splint 2 S2-glass, mixture of dimethacrylates, initiators and stabilizers

ADM a.s., Brno, Czech Republic

4742

everStick Ortho 3 E-glass/PMMA/Bis-GMA StickTech Ltd, Turku, Finland

88

Ribbond 4 Ultra High Molecular Weight Polyethylene

Ribbond Inc., Seattle, USA

9543

Quad Cat Wire 5-8 Stainless steel, three-strand twisted wire 0.022” x 0.016”

Quad Cat, GAC International, New York, USA

197

Stick Resin Silanated silica 30% - 70% 2,2- bis[4-(2-hydroxy-3-methacryloxyropoxyl)]-phenonylpropane 30% - 70% Triethyleneglycol dimethacrylate

StickTech Ltd, Turku, Finland

5504765

Heliobond Monomer matrix: dimethacrylate < 60% Bis-GMA < 40% Triethyleneglycol

Ivoclar Vivadent, Schaan, Lichtenstein

H29583 154518

Stick Flow Mixture of resin based on Bis-GMA, Methacrylates, catalysts, stabilizers, pigments

StickTech Ltd, Turku, Finland

D3-DA3-3

Tetric Flow < 14% Bis-GMA < 8% Triethylene glycoldimethacrylate < 15% Urethanedimethacrylate

Ivoclar Vivadent, Schaan, Lichtenstein

J01476 154518

FRC Retainers (Groups 1 to 5) All FRC retainers were bonded following the same procedures with the same

adhesive resin and the flowable resin material. The FRCs were cut by means of

a pair of special scissors (Ribbond fiber cutter, Ribbond; Seattle, WA, USA) to

the same length (3 mm). A filler- and solvent-free lightcuring bonding agent (Stick

Resin, StickTech; Turku, Finland) was applied with a microbrush on the acid-

etched enamel surface and blown into a thin layer. It was then light polymerized

for 40 s with a conventional halogen light curing unit (Demetron LC, SDS Kerr;

Danbury, CT, USA) (light output: 400 mW/cm2). The irradiation distance between

the exit window and the resin surface was maintained at 2 mm to obtain adequate

Figures 2a-e: Representative SEM pictures ofa) Angelus Fibrex Ribbon (original magnification x80),b) DentaPreg Splint (original magnification x80),c) everStick Ortho (original magnification x 80). Note the resin impregnation of the fibers on as-received samples,d) Ribbond (original magnification x40), ande) Quad Cat stainless steel-wire (original magnification x40).

A

C

E

B

D

40 41

flowable composite was applied and the wire was placed in the bed of this

flowable resin. The wire was then covered again with flowable composite, and

light polymerization was performed. The specimens were stored in distilled water

with 0.1% (wt/vol) thymol solution at 37°C for one week and thermocycled 6000

times between 5ºC and 55°C (dwell time: 30 s, transfer time from one bath to the

other: 2 s) (Willytec; Gräfelfing, Germany).

Shear Bond TestingThe specimens were mounted in the jig of the universal testing machine (Zwick

ROELL Z2.5 MA 18-1-3/7; Ulm, Germany) where the force was applied at the

composite/ retainer-enamel interface from the occluso-cervical direction.

The shearing blade had a taper of 45 degrees at the tip. The specimens were

loaded at a crosshead speed of 1.0 mm/min until failure occurred, and the

stress-strain curve was analyzed with the proprietary software program

(Zwick ROELL). The force required to shear-peel the retainer was recorded

and converted into MPa using the known surface area of the mold (7.04 mm2)

representing the bonded area. Schematic drawings of the FRC and wires in

relation to their application modes and the shear blade are depicted in Fig 4.

Subsequently, digital photographs (Nikon D1, Micro Nikon 60 lens; Tokyo,

Japan) were taken of the substrate surfaces and the debonded retainers.

polymerization. Flowable resin composite (Stick Flow, StickTech) was applied to

the enamel surface and the respective FRC material was placed on the bed of

the flowable composite, arranged horizontally on the largest area of the incisor in

a rectangular polyethylene mold (3.2 x 2.2 x 1.5 mm) (Fig 3). The FRC materials

were rewetted with the bonding agent (Stick Resin) and then covered with the

flowable resin (StickFlow, StickTech). This was also light polymerized for 40 s

from a distance of 2 mm.

Stainless Steel Wires (Groups 5 to 8)The orthodontic retainer wire used in this study was a flexible, braided, rectangular,

stainless-steel wire (Quad Cat,0.022 in x 0.016 in, GAC International; Bohemia,

NY, USA).

Specimens in group 5 were prepared in the same manner with the procedure

used for the FRC materials. In groups 6 to 8, the attempt was made to simulate

different aspects of commonly used clinical methods. In groups 7 and 8, a

different bonding agent and a flowable composite was used.

Group 6: A filler and solvent-free light-curing bonding agent (Stick Resin, StickTech)

was applied with a microbrush on the acid-etched enamel surface and blown into

a thin layer. It was then light polymerized for 40 s with a conventional halogen

light curing unit (Demetron LC, SDS

Kerr) (light output: 400 mw/cm2). The irradiation distance between the exit

window and the resin surface was maintained at 2 mm to obtain adequate

polymerization. A piece of wire (3 mm) which was previously bent to adapt to

the individual surface of each specimen, was placed on the tooth surface, and

flowable composite (Stick Flow) was applied on top of the wire. This was then

light polymerized for 40 s.

Group 7: The same protocol was followed as described for group 6 but a different

bonding agent (Heliobond, Ivoclar Vivadent; Schaan, Liechtenstein) and flowable

resin (Tetric Flow, Cavifill 210 A3, Ivoclar Vivadent) were used. Group 8: The same

materials were used as in group 7, but this time after bonding agent application,

Figure 4a: Schematic drawings of the cross-section of a specimen showing FRC or wire in relation to their application modes and the position of the shearing blade of the universal testing machine.

Figure 4b: Schematic drawings of the cross-section of a specimen in Group 6 showing wire in relation to their application modes and the position of the shearing blade of the universal testing machine.

Ena

mel

Fiber or Wire

Flowable composite

Shearing blade

Figure 3: Rectangular polyethylene mold (3.2x2.2x1.5 mm) used for positioning the retainer and the flowable resin in a controlled manner.

Ena

mel

Fiber or Wire

Flowable composite

Shearing blade

A B

42 43

Table 2: The mean (±standard deviations-SD) shear bond strength (MPa) values for the experimental groups. *The same letters indicate no significant differences (Tukey’s test, α=0.05).

Groups Mean (+SD) Homogeneous groups

1 6.9±2.2 B C

2 6.1±2.5 C

3 7.6±2.6 A B C

4 8.4±3.7 A B C

5 11.7±2.5 A B C

6 10.6±3.8 A B C

7 13±6.6 A B

8 14±6.7 A

Figure 5: Mean shear bond strength results per experimental group.

Failure TypesTable 3 presents the modes of failures for the FRC and stainless steel retainers

after debonding. Enamel fractures were slightly more frequent (5 out of 40) in

the FRC retainer groups than in the wire groups (2 out of 40). In none of the FRC

retainer groups were adhesive failures between the enamel and the composite

observed. Failure types varied within the FRC retainer groups. The most frequently

observed failure types were 1a (5/40) and 1b (17/40), where flowable composite

remained adhered to the enamel surface at varying degrees after debonding. This

failure type was followed by the cohesive failures within the FRCs, regardless

of their preimpregnation and texture (16/40). In the stainless steel wire groups,

when the retainer was applied on the bonding agent and then covered by

flowable resin (groups 6 and 7), partially attached composite was often found on

Failure AnalysisAfter debonding, the failure sites were examined by two calibrated operators (E.K.,

M.Ö.) both visually and using an optical microscope at different magnifications

(up to 40X). A scoring system was created for failure type evaluation considering

adhesive or cohesive failures at two interfaces, namely, enamel base/flowable

resin, base or covering flowable resin/FRC/wire retainer, as well as cohesive

failures within FRC or wire retainer.

Statistical AnalysisStatistical analysis was performed using Statistix 8.0 for Windows (Analytical

Software, Version 8.0, 2003; Tallahase,FL, USA). The means of each group were

analyzed with one-way ANOVA. Because of the significant group factor (p =

0.0011), multiple comparisons were made with the Tukey-Kramer adjustment test

to determine the significant differences between groups, where the dependant

variable was shear bond strength and the independent variable was various

combinations of application procedures and materials. P values less than 0.05

were considered to be statistically significant in all tests.

RESuLTS

Shear Bond StrengthThe results of the shear bond strength test for the FRC and stainless steel wire are

presented in Table 2 and Fig 5. One-way ANOVA showed a significant difference

between the groups (p = 0.0011).

Bond strength results did not significantly differ either between the FRC groups

(groups 1 to 4) (6.1 ± 2.5 to 8.4 ± 3.7 MPa) (p > 0.05) or the stainless steel wire

groups (groups 5 to 8) (10.6 ± 3.8 to 14 ± 6.7 MPa) (p > 0.05) (Tukey’s test).

Of the stainless steel wire groups, group 8 (14 ± 6.7 MPa) showed significantly

higher results than those of two FRC materials, namely group 1 (Angelus Fibrex

Ribbon) (6.9 ± 2.2 MPa) and group 2 (DentaPreg Splint) (6.1 ± 2.5 MPa) (p < 0.05).

Both E-glass or S2-glass FRC retainers (groups 1 to 3) did not show significant

differences compared to UHMWP FRC (group 4) (p > 0.05).

0

5

10

15

20

25

1 2 3 4 5 6 7 8

Shear Bond Strength (MPa)

44 45

compared to that of a commonly used stainless steel orthodontic wire.

Mean bond strength results did not significantly differ between the FRC groups,

although their compositions and textures were different. Except Ribbond,

the other FRC materials used were silanized, pre-impregnated glass FRCs.

Interestingly, between pre-impregnated glass FRCs and Ribbond, there were

no significant differences. In fact, preimpregnation of fibers not only improves

handling characteristics and enables a higher fiber volume, but also results in

improved adhesion because of the semi-IPN (interpenetrating polymer network)

structure of the polymer matrix.13 Based on this information, one could expect

more adhesive failures between the FRC and the flowable composite (failure

types 3 or 5, see Table 2); however these failure types were not observed with

the Ribbond fiber. The manufacturer of Ribbond suggests the use of any adhesive

monomer for its pre-impregnation. In this study, Stick Resin was used for pre-

impregnation. Apparently, this resin with a mixture of mono- and di-functional

methacrylates was sufficient to achieve good adhesion of the flowable resin to

the fibers.

The incidence of attached flowable composite on the enamel (failure types 1a

and 1b) after debonding was more frequent in group 3 (everStick Ortho) than

those of other groups, which indicates good adhesion compared to failure type

0. Although there were differences in terms of failure types, considering that

the mean bond strength values between the FRC retainer groups did not differ

significantly, the hypotheses could be partially rejected. The failure behavior of

FRC materials is very complex because of their anisotropic character.11,27,28,31

Laminated composites are known to have a relatively poor ability to absorb energy

due to local impact damage.33 For this reason, application of more fibers in a given

composite volume may change the load bearing capacity of the whole structure.

Clinically, however, this approach is not desirable and almost impossible; the

splint should be kept at minimum thickness in order to avoid bulky constructions

that may cause plaque accumulation and sometimes irritations for the tongue.

Static compression tests demonstrated that with the increasing fiber content, the

flexural strength increases linearly. 5,18 This information is often derived from bar-

shaped specimens prepared according to the ISO norms, where usually 2 mm of

veneering composite was placed on the FRC material. Considering the geometry

of the specimens prepared in this study, made to represent the clinical situation

as closely as possible, and the insignificant differences between the four FRC

materials, it can be stated that the adhesion of the flowable base composite is

also one of the predominant factors that play a role in the bond strength results.

On the other hand, considering the higher bond strength results obtained from

the stainless steel wire groups vs those of some FRCs tested, it appears that

the FRC actually weakens instead of strengthens the fiber/ composite complex.

It was expected that the FRC materials would show higher bond strengths

the enamel after debonding. When the retainers were embedded in the flowable

composite, the Heliobond + Tetric Flow group (group 8) showed more adhesive

failures between the enamel and the composite compared to group 5, where the

bonding agent was Stick Resin and the flowable composite was Stick Flow.

Table 3: Failure types and their distribution per experimental group for FRC or stainless steel wire retainers.

Groups Dislodged* Score of type of failures Cohesive enamel fracture

0 1a 1b 2 3 4 5

1 0 0 1 3 0 0 6 0 0

2 0 0 1 2 0 0 5 2 2

3 0 0 2 7 0 0 1 0 1

4 0 0 1 6 0 0 4 0 2

5 0 1 1 6 0 0 0 2 1

6 0 0 9 0 0 0 1 0 0

7 0 2 8 0 0 0 0 0 0

8 0 6 4 0 0 0 0 0 1

Score 0= no composite left on the enamel surfaceScore 1a= less than half of the composite left;Score 1b= more than half of the composite left;Score 2= cohesive failure within the base flowable resin; Score 3= all composite left on the enamel surface, with a distinct impression of theFRC/wire; Score 4= cohesive failure within the FRC separation/fracture of the wire; Score 5= adhesive failure between the FRC/wire and the covering flowable resin.*During thermocycling or testing.

DISCuSSION

Although much research is currently being conducted in diverse fields of FRC

applications in dentistry, very few studies have focused on the use of FRCs as

orthodontic retainers.6,11,25 High failure rates of bonded orthodontic post-treatment

stabilization splints have been reported,1-4 and therefore FRCs were considered

as possible alternative materials for such applications. Since debonding remains a

clinical problem, one aspect needing research was FRC bond strength to enamel

compared to conventional retainer material, which is generally stainless steel.

Therefore, in this study, adhesive aspects of several FRC retainer materials were

46 47

In the shear-peel tests, the cutting blade was placed between the tooth surface

and the flowable composite in such a manner that the cutting edge was as

close to the enamel surface as possible. One could assume that what is being

inadvertently measured is the adhesion of the composite rather than the effect

of the wire or fiber. In this study, however, there were no significant differences

between wire groups either when they were applied in the bed of flowable

composite (groups 5 and 8) or directly on the bonding agent (groups 6 and 7).

Furthermore, there were significant differences between some FRC groups

(groups 1 and 2) and all the wire groups (groups 5 to 8). This clearly indicates that

the debonding forces are diverted differently, regardless of whether there was

flowable composite on the bonded surface or not. The height of the specimens

was kept at 1.5 mm in order to achieve grasp of the blade in the universal testing

machine. This was determined during the preliminary experiments. In clinical

practice, this thickness may still be considered high. The dilemma remains of how

to control the thickness of the flowable composite in bonded retainers clinically.

It should also be emphasized that in shear bond strength tests, the adherend is

bonded to enamel surfaces that are not completely flat. Although an attempt

was made to control this by using lower central incisors which have relatively

more flat surfaces, the true shear stresses cannot be measured. Similarly lingual

retainers are placed on the lingual sufaces of the anterior teeth that present even

promounced concavity.

The mean bond strength values of the FRC retainers in this study (6.1 to 8.4

MPa) were lower than those reported in other studies (14 to 23 MPa).16,28,29

Several factors might have contributed to this result, such as application methods

and materials,26,29 the direction of the load on the fiber,12,13,29 and storage

conditions.16,28,29 Reynolds and von Fraunhofer24 reported that a minimum bond

strength of 6 to 8 MPa could give a satisfying clinical performance and successful

clinical bonding of brackets in orthodontics. The results obtained from the wire

retainers (10 to 14 MPa) exceed these recommended values. However, in this

study, specimens were thermocycled for 6000 cycles. It can be anticipated that

the temperature elevations and water uptake of the adhesive resin might result

in lower bond strength. Although the results obtained in all groups were within or

exceeded this range, the recommended bond strength values should be evaluated

with caution, because thermal or other types of aging procedures were not taken

into consideration.20-22,24 It should also be noted that the retainers are expected

to remain intact as long as possible after orthodontic treatment, whereas a

semi-permanent kind of adhesion is expected from the brackets. In this context,

perhaps recommended adhesion values to etched enamel should serve as the

golden standard, which is known to be on the order of 15 to 30 MPa.14,33 In that

respect, the bond strengths obtained in this study are not sufficient to function

as well as restorative composites. The occurrence of enamel fractures indicates,

than the wire, because the adhesive properties between the fiber and the

composite are chemical, contrary to those of the wire, which rely on mechanical

retention. Reports on the causes of failure of bonded orthodontic wire retainers

often indicate that the composite covering the wire is insufficient, resulting in

detachment of the wire.4 It was advised that by increasing the surface area

(diameter) of the wire3 or using less abrasive composite materials, debondings

could be avoided.4 However, Bearn et al4 found no significant difference in the

retention of differently shaped 3- and 6-stranded wires in a composite material.

In another study, insufficient composite thickness was reported to play a major

role in clinical failures.10 Due to this contradiction, in this study, the retainers were

completely covered with the flowable resin.

Comparative studies regarding the shear strength of FRCs incorporated into

particulate resin composites on enamel generally showed no difference when

compared to the control groups where no FRC was used.16,17 A significant increase

in shear strength was reported for some fibers,16 but other studies showed no

significant increase in shear bond strength.16,28,29 Meiers et al17 reported that

a nonimpregnated fiber, Connect (Kerr, Orange, CA, USA), showed higher

shear bond strengths than Ribbond (Seattle, WA, USA) and preimpregnated

unidirectional woven Splint-it (Jeneric/Pentron; Wallingford, CT, USA). In that

study, the specimens were thermocycled 1000 times. In an other study, Meiers

et al16 compared the same fiber materials and also found a significant increase

in the shear bond strengths to enamel with the use of Connect, while the other

fibers showed no significant difference compared to each other and the control

flowable composite (Tetric Flow) without a fiber. In contrast, another study28

found no significant differences between any groups when bond strengths of

EverStick and StickTech’s preimpregnated FRCs that were applied either directly

on a bed of flowable composite (Tetric Flow) or in combination with particulate

filler composite (Filtek Z250) on human enamel were compared. The addition of

flowable composite did not improve bond strength values. It was also found that

the addition of bidirectional or random continuous fibers (StickNet, everStickNet,

and an experimental random FRC) did not yield any significant improvement

in bond strength to enamel and dentin compared to the control of particulate

filler composite (Filtek Z250).29 In these studies, composites covering the fibers

were 4 to 5 mm thick. Therefore, a different effect of reinforcement and crack

propagation could be expected than in this study.

It should also be emphasized that in shear bond strength tests, the adherend is

bonded to enamel surfaces that are not completely flat. Although an attempt was

made to control this by using mandibular central incisors which have relatively

more flat surfaces, the true shear stresses cannot be measured. Similarly, lingual

retainers are placed on the lingual surfaces on the anterior teeth that present even

more pronounced concavity.

48 49

Conclusions

1. Bond strength results did not significantly differ either between the FRC

groups or the stainless steel wire groups. Only group 8, in which Heliobond

and Tetric Flow were used and the wire was placed in the bed of the flowable

resin, showed significantly higher mean bond strengths than those of

DentaPreg Splint and Angelus Fibrex Ribbon.

2. Preimpregnated and custom impregnated FRC materials performed the

same in terms of bond strength.

3. Changing the application mode of wire retainers did not result in significant

changes in bond strength, but the failure modes showed variations between

the experimental groups.

Clinical relevanceRegardless of their application mode, stainless steel orthodontic bonded retainers

delivered higher bond strengths than those of fiber retainers but the failure types

varied between the tested materials.

Acknowledgements We express our appreciation to the ADM a.s., Brno, Czech Republic, Ribbond

Inc., Seattle, USA, and Angelus® Dental Solutions, Brazil for donation of some of

the fiber materials used in this study.

however, that the adhesion exceeded the cohesive strength of the enamel itself

in some cases in the FRC groups (5 enamel fractures out of 40 specimens).

Enamel fractures may present a clinical problem during bracket debonding. Yet

for lingual retainers, from which retention is desired to maintain the achieved

orthodontic result for a long time, this aspect would not be considered a problem.

Nonetheless, one could speculate that the failure is not only a result of adhesion

or bond strength. After orthodontic treatment, when the teeth tend to revert to

their original position, the interfacial forces might exceed the adhesive strength

of the flowable composite to the tooth surface. In this case, variations between

the flowable composites may affect the results. However, in this study, wire

retainers bonded with either StickFlow or Tetric Flow composites presented no

significant differences (groups 5 to 8). Although the results were higher (but not

significantly), the group in which Heliobond was used as a bonding agent showed

more adhesive failures (failure type 0) when compared to StickResin. This may

be due to 2,2-bis[4-(2- hydroxy-3-methacryloxyropoxyl)]-phenonylpropane in the

composition of the latter that might have better surface wettability properties.

In one clinical study by Rose et al,25,20 patients were randomly assigned to receive

Ribbond fiber or multistranded wire retainers from canine to canine following

the completion of orthodontic treatment. The retainers remained in place for

an average of 11.5 and 23.6 months, respectively, with a statistically significant

difference. This limited clinical evidence indicates that the multistranded

wire is superior to the plasma-treated woven polyethylene ribbon, which is a

nonpreimpregnated fiber. Nevertheless, both retainers presented unacceptable

survival rates. Therefore, it can be concluded that orthodontists are still confronted

with debonding of bonded retainers.

Fixed lingual retainers connect at least two teeth and are therefore certainly longer

than 3 mm. One limitation of this study could be short length of the retainer

compared to the clinical situation. Adhesion tests require some standardization

before complex situations can be tested. Hence, this study solely dealt with the

adhesive properties of various fibers placed at different locations and in different

manners. Other factors, such as length and curvature of the teeth, had to be

excluded in order to isolate the effect of the retainer type and location on the

bond results. Because no significant difference has been found between bonding

results to buccal and lingual surfaces,8,35 the attempt was made to eliminate

the convexity factor by using only the labial surfaces of the teeth for adhesion

purposes.

Under the influence of compressive cyclic stresses, the damage associated with

delamination may reduce the overall stiffness as well as the residual strength,

leading to structural failure. The behavior of FRC and metal wires under fatigue

conditions is being investigated in our laboratories.

5150

17. Meiers JM, Kazemi RB, Freilich MA. Direct intra-oral applications of fiber-reinforced composites. The influence of FRC on particulate resin composite to enamel shear bond strengths. In: Vallitu PK, editor. The Second International Symposium on Fiber-Reinforced Plastics in Dentistry, 10-13 October, Nijmegen, The Netherlands. University of Turku Publishing Office, 2001.

18. Narva KK, Lassila LV, Vallittu PK. The static strength and modulus of fiber reinforced denture base polymer. Dent Mater 2005;21:421-428.

19. Nohrström TJ, Vallittu PK, Yli-Urpo A. The effect of placement and quantity of glass fibers on the fracture resistance of interim fixed partial dentures. Int J Prosthodont 2000;13:72-78.

20. Øilo G. Bond strength testing, what does it mean? Int Dent J 1993;43:492-498.

21. Özcan M, Pfeiffer P, Nergiz. A brief history and current status of metal/ceramic surface conditioning concepts for resin bonding in dentistry. Quintessence Int 1998;29:713-724.

22. Pickett KL. In vivo orthodontic bond strength: comparison with in vitro results. Angle Orthodont 2001;71:141-148.

23. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-178.

24. Reynolds IR, Von Fraunhofer JA. Direct bonding in orthodontic attachments to teeth: the relation of adhesive bond strength to gauze mesh size. Brit J Orthodont 1975;3:91-95.

25. Rose E, Frucht S, Jonas IE. Clinical comparison of a multistranded wire and a direct-bonded polyethylene ribbon reinforced resin composite used for lingual retention. Quintessence Int 2002;33:579-583.

26. Scribante A, Cacciafesta V, Sfondrini MF. Effect of various adhesive systems on the shear ond strength of fiber-reinforced composite. Am J Orthod Dentofacial Orthop 2006;130:224-227.

27. Takagi K, Fujimatsu H, Usami H, Ogasawara S. Adhesion between high strength and high modulus polyethylene fibers by use of polyethylene gel as an adhesive. J Adhesion Sci Technol 1996;9:869-882.

28. Tezvergil A, Lassila LVJ, Vallitu PK. Strength of adhesive-bonded fiber-reinforced composites to enamel and dentin substrates. J Adhesive Dent 2003;5:301-311.

29. Tezvergil A, Lassila LVJ, Vallitu PK. The shear bond strength of bidirectional and random-oriented fiber-reinforced composite to tooth structure. J Dent 2005;33:509-516.

30. Vallittu PK. Glass fiber reinforcement in repaired acrylic resin removable dentures: preliminary results of a clinical study. Quintessence Int 1997;28:39-44.

31. Vallitu PK. The effect of glass fiber reinforcement on the fracture resistance of a pro-visional fixed partial denture. J Prosthet Dent 1998;79:125-130.

32. Vallitu PK. Strength and interfacial adhesion of FRC-tooth system. In: Vallitu PK, editor. The Second International Symposium on Fiber-Reinforced Plastics in Dentistry, 10-13 October, Nijmegen, The Netherlands. University of Turku Publishing Office, 2001. p.2-28.

REFERENCES

1. Andrén A, Asplund J, Azarmidohkt E, Svensson R, Varde P, Mohlin B. A clinical evaluation of long term retention with bonded retainers made from multi-strand wires. Swed Dent J 1998;22:123-131.

2. Årtun J, Spadafora A, Shapiro P. A 3-year follow-up study of various types of orthodontic canine-to-canine retainers. Eur J Orthod 1997;19:501-509.

3. Bearn DR. Bonded orthodontic retainers: a review. Am J Orthod Dentofacial Orthop 1995;108:207-213.

4. Bearn DR, McCabe JF, Gordon PH, Aird JC. Bonded orthodontic retainers: The wire-composite interface. Am J Orthod Dentofacial Orthop 1997;111:67-77.

5. Behr M, Rosentritt M, Lang R, Handel G. Flexural properties of fiber reinforced composite using a vacuum/pressure or a manual adaptation manufacturing process. J Dent 2000; 28: 509-514.

6. Cacciafesta V, Sfondrini MF, Lena A, Scribante A, Vallittu PK, Lassila LV. Flexural strengths of fiber-reinforced composites polymerized with conventional light-curing and additional postcuring. Am J Orthod Dentofacial Orthop 2007;132:524-527.

7. Dahl E, Zachrisson BU. Long term experience with direct bonded lingual retainers. J Clin Orthod 1991;25:619-630.

8. Tüfekçi E, Almy DM, Carter JM, Moon PC, Lindauer SJ. Bonding properties of newly erupted and mature premolars. Am J Orthod Dentofacial Orthop 2007;131:753-758.

9. Freilich MA, Meiers JC, Duncan JP, Goldberg AJ. Fiber-reinforced composites in clinical dentistry. Chicago: Quintessence Pub; 1999. p.9-21.

10. Gutteridge DL. Reinforcement of poly(methyl methacrylate) with ultrahigh-modulus polyethylene fiber. J Dent 1992;20:50-54.

11. Karaman A., Kir N, Belli S. Four applications of reinforced polyethylene fiber material in orthodontic practice. Am J Orthod Dentofacial Orthop 2002;121:650-654.

12. Lassila LV, Tezvergil A, Dyer SR, Vallitu PK. The bond strength of particulate filler composite to differently oriented fiber-reinforced composite substrate. J Prosthodont 2007;16:10-17.

13. Lastumaki TM, Kallio TT, Vallitu PK. The bond strength of light-curing composite resin to finally polymerized and aged glass fiber-reinforced composite substrate. Biomat 2002;23:4533-4639.

14. Latta MA, Barkmeier WW. Dental adhesives in contemporary restorative dentistry. Dent Clin North Am 1998;42:567-577.

15. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of bonded stainless steel lingual retainers: A historic cohort study. Eur J Orthod 2008;30:199-204.

16. Meiers JC, Kazemi RB, Donadio M. The influence of fiber reinforcement of composites on shear bond strengths to enamel. J Prosthet Dent 2003;89:388-393.

52 53

33. Van Meerbeek B, Perdigao J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent 1998;26:1-20.

34. Wang J, Crouch SL, Mogilevskaya SG. Numerical modelling of the elastic behaviour of fiber-reinforced composites with inhomogeneous interphases. Compos Sci Technol 2006;66:1-18.

35. Wang WN, Tarng TH, Chen YY. Comparison of bond strength between lingual and buccal surfaces on young premolars. Am J Orthod Dentofacial Orthop 1993;104:251-253.

36. Zachrisson BU, Büyükyilmaz T 2005 Bonding in Orthodontics. In Graber L W (ed): Orthodontics: Current principles and techniques. Mosby, St. Louis, 4th p. 621-659.

Chapter 4

Fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers in vitro

Lie Sam Foek D.J.

Yetkiner E

Özcan M

Korean J Orthod. 2013 Aug;43(4):186-92.

56 57

INTRODuCTION

Lingual retainers are generally used for long-term retention.1 They are preferred

particularly when the post treatment intercanine width should be maintained and

periodontal tissue support is lacking.1,2 However, breakage of the retainer material

and debonding of the resin pad that attaches the retainer onto the tooth surface

are commonly experienced in clinical practice.2-5 The main factors determining

the longevity and success of lingual retainers are the type of retainer material,

type of composite resin used for bonding, number of units included for bonding,

and location of the retainer (i.e., maxillary or mandibular arch).2-5

The most frequently used retainer material is stainless steel wire, with varying

stiffness and integral properties.2,5 Initially, lingual retainers were fabricated from

relatively thick round wires (0.030 - 0.032 inch) bonded only to the ends of the

retention area.3,4 With this type of retainer, the intercanine width could be well

preserved and the retention area was easily accessible to oral hygiene instruments,

but rotation of the interlying teeth was evident because they were not bonded

to the retainer. Thinner multistranded wire (0.0195 - 0.0215 inch) bonded to each

interlying tooth was introduced to overcome this problem.3,4 However, this retainer

type increased the susceptibility to plaque accumulation and presented higher

failure rates due to wire breakage and resin pad detachment.2,5 Subsequently,

fiber-reinforced composite (FRC) was introduced to replace stainless steel wire,

thus allowing chemical adhesion of the retainer to the bonding agent.6 FRC

was expected to reinforce the resistance of the bonding agent by transferring

the loads acting on the retainer complex to the glass fibers. Furthermore, the

bonding interface of two materials with different physical properties (i.e., wire

and composite resin) would be eliminated.6,7 Nevertheless, retainer failures still

occurred and clinical survival studies did not reveal significant results. Therefore,

multistranded stainless steel wire is still the most frequently used material for

lingual retainers.1,2,5

The causes of lingual retainer failures are still not clear. The most frequent problems

of metal retainers are failure of the wire-composite interface, breakage of the

wire, and detachment of the resin pads at the composite-enamel interface.1-4,7

Wire-composite interface failure is attributable to two main factors. First, the

composite covering the retainer, usually a small resin pad, becomes thinner and

weaker because of abrasion caused by brushing and food consumption. This, in

turn, results in detachment of the retainer from the resin pad, which stays stable

on the tooth surface.1-4,7 Second, propagation of internal cracks due to constant

movement of the retainer between the overlying and the underlying resin pads

during physiological tooth movement is linked to wire-composite interface

failure.1,2,7 This is also a possible reason for breakage of the retainer due to the

stress accumulation at bending points.3,4 On the other hand, composite-enamel

ABSTRACT

Objective: To analyze the fatigue resistance, debonding force, and failure type of

fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless

steel wire lingual retainers in vitro.

Methods: Roots of human mandibular central incisors were covered with silicone,

mimicking the periodontal ligament, and embedded in polymethylmethacrylate.

The specimens (N = 50), with two teeth each, were randomly divided into five

groups (n = 10/ group) according to the retainer materials: (1) Interlig (E-glass),

(2) everStick Ortho (E-glass), (3) DentaPreg Splint (S2-glass), (4) Ribbond

(polyethylene), and (5) Quad Cat wire (stainless steel). After the recommended

adhesive procedures, the retainers were bonded to the teeth by using flowable

composite resin (Tetric Flow). The teeth were subjected to 10,00,000 cyclic loads

(8 Hz, 3 - 100 N, 45o angle, under 37 ± 3°C water) at their incisoproximal contact,

and debonding forces were measured with a universal testing machine (1 mm/

min crosshead speed). Failure sites were examined under a stereomicroscope

(×40 magnification). Data were analyzed by one-way analysis of variance.

Results: All the specimens survived the cyclic loading. Their mean debonding

forces were not significantly different (p > 0.05). The DentaPreg Splint group (80%)

showed the highest incidence of complete adhesive debonding, followed by the

Interlig group (60%). The everStick Ortho group (80%) presented predominantly

partial adhesive debonding. The Quad Cat wire group (50%) presented overlying

composite detachment.

Conclusions: Cyclic loading did not cause debonding. The retainers presented

similar debonding forces but different failure types. Braided stainless steel wire

retainers presented the most repairable failure type.

Key words: Lingual, Bonding, Relapse, Retention

58 59

MATERIALS AND METHODS

Specimen preparation One hundred caries-free human mandibular central incisors stored in 0.1% thymol

solution at 40C up to 6 months were selected under blue-light transillumination to

ensure that the enamel was free of cracks. The roots of pairs (i.e., right and left)

of the selected teeth were dipped in hot liquid wax (Modern Materials utility wax;

Heraeus Kulzer GmbH, Hanau, Germany) and embedded in silicone impression

material (Adisil® blau 9:1; Böhme & Schöps GmbH, Goslar, Germany) in a plastic

mold with axial contact. After the impression material had set, the same process

was repeated with polymethylmethacrylate (Vertex 2 SMS, 24 × 24 × 33 mm;

Vertex-Dental B.V., Zeist, The Netherlands). The wax layer was removed with hot

water (100oC) and the created space was filled with light-body silicone (Pro Fill;

Heraeus Kulzer GmbH) to mimic the periodontal ligament, supposedly allowing

some physiological movement during cyclic loading.19,20 The roots of the teeth

were then inserted into the silicone (Figure 1). Fifty specimens, each containing a

pair of incisors, were used for the experiments.

Figure 1: Representative photographs of human mandibular central incisor pairs embedded in polymethylmethacrylate up to the cementoenamel junction to receive bonded lingual retainers: a, lingual and b, proximal views.

Before the bonding procedures, the lingual surfaces of the embedded teeth were

polished with fluoridefree pumice (Zircate Prophy Paste; Dentsply Caulk, Milford,

DE, USA) by using a prophylaxis brush (Hawe Prophy Cup and Brush, latch-type;

Kerrhawe Sa, Bioggio Svizzera, Switzerland) for 20 seconds, rinsed with water,

and air-dried. The mesiodistal dimensions of the two teeth in each specimen

were measured and the midpoint 3 mm below the incisal edges was marked as

the area for bonding by using a permanent marker.

interface failure is attributable to adhesion failure of the resin pad. Debonding of

the resin pad from the tooth surface is mostly associated with deficient bonding

procedures, such as inadequate moisture control or mishandling of the resin

material.1,3,7 Furthermore, increased tooth mobility due to a widened periodontal

ligament space or lack of bone support could cause deterioration of the adhesion

at the composite-enamel interface.1

The in vivo failure and survival rates of lingual retainers, in vitro testing of different

retainer material complexes, and interpretation of the results are highly con

troversial.5,8,16 In a recent clinical report of metal and FRC retainers, the conventional

multistranded wire retainers were suggested to remain the gold standard for

orthodontic retention and the use of FRC retainers was discouraged because

of their high failure rate (12% vs 51%, respectively).14 Similarly, multistranded

wire retainers were reported to be significantly superior to polyethylene ribbon-

reinforced retainers.13 On the other hand, a recent 6-year clinical follow-up

study showed no significant differences between FRC and multi stranded wire

retainers; the results indicated that FRC retainers could be a viable alternative to

multistranded wire retainers.15 Two recent clinical studies showed a 37.9% failure

rate in a 6-month period with multi stranded wire retainers11 and a 94.8% survival

rate in a 4.5-year period with FRC retainers.16 From the adhesion perspective, the

debonding force of FRC retainers was not found to be dependent on the type of

bonding agent used.17 Contrarily, superior adhesion has been reported with the

use of a specific lingual retainer adhesive instead of a flowable composite resin.18

The disagreement among such studies is highlighted in a review by Littlewood et

al.,5 implying that further research for retainer comparisons is necessary.17

The objective of this in vitro study was to analyze the fatigue resistance,

debonding force, and failure type of FRC, polyethylene ribbon-reinforced, and

braided stainless steel wire lingual retainers. The null hypotheses were that the

fatigue resistance of the FRC and polyethylene ribbon-reinforced retainers would

not be greater and their debonding forces would not be higher than those of the

braided stainless steel wire retainer.

A B

60 61

debonding occurred. Only the maximum force causing debonding of the retainers

was recorded.

Table 1: Details of the retainer materials tested in this study (GMA, Glycidyl methacrylate; PMMA, polymethyl methacrylate).

Codes Composition Manufacturer Batch No.

Interlig ANG E-glass, bis-GMA Angelus, Londrina, Brazil 2199

everStickOrtho

EST E-glass, PMMA, bis-GMA

StickTech Ltd, Turku, Finland

000088

DentaPregSplint

DTP S2-glass, mixture of dimethacrylate initiators and stabilizers

ADM a.s., Brno, Czech Republic

4742

Ribbond RIB Ultra High Molecular Weight Polyethylene

Ribbond Inc., Seattle, USA

9543

Quad Cat Wire

QC Stainless steel, three-strand twisted wire 0.022” x 0.016

Quad Cat, GAC International, New York, USA

0197

Failure analysisFailure sites were examined under a stereomicroscope at varying magnifications

(up to ×40). After the initial evaluation of the specimens, four types of failure were

categorized, as follows: type 1, complete adhesive debonding of the retainer from

the tooth surface; type 2, partial adhesive detachment of the retainer from one

of the teeth; type 3, retainer did not debond from the tooth surface but fractured;

and type 4, retainer did not debond from the tooth surface but the overlying

composite detached.

Retainer materialsThe specimens were randomly divided into five groups (n = 10 per group)

according to the main retainer materials: (1) E-glass (Interlig; Angelus Ltd.,

Londrina, Brazil), (2) E-glass (everStick Ortho; Stick Tech Ltd., Turku, Finland), (3)

S2-glass (DentaPreg Splint; ADM a.s., Brno, Czech Republic), (4) polyethylene

(Ribbond; Ribbond Inc., Seattle, WA, USA), and (5) stainless steel (Quad Cat wire;

GAC International Inc., Islandia, NY, USA).

Retainer placementBraided stainless steel wires (0.022 × 0.016 inch) were adapted to the lingual

surfaces of the teeth in each specimen and ultrasonically cleaned in ethyl alcohol

(Vitasonic; Vita Zanhfabrik H. Rauter GmbH & Co. KG, Bad Säckingen, Germany)

for 20 seconds. The marked bonding area was then etched with 38% H3PO4

(Top Dent; DAB Dental, Tillverkare, Sweden) for 20 seconds, rinsed with water

for 20 seconds, and air-dried. An adhesive resin (Heliobond; Ivoclar Vivadent,

Schaan, Liechtenstein) was applied by using a microbrush (ApplyTip; Hager &

Werken, Oisterwijk, The Netherlands), gently air-blown, and photo-polymerized

for 20 seconds on each tooth surface with an LED polymerization lamp (Ortholux

LED curing light, light output = 400 mW/ cm2; 3M Unitek, Landsberg am Lech,

Germany). A thin layer of flowable composite resin (Tetric Flow, Cavifill 210, shade

A3; Ivoclar Vivadent) was applied and the retainer was placed in the composite

resin. After initial polymerization, the composite resin was applied to cover the

retainer surface and photo-polymerized for 40 seconds on each tooth surface.

The irradiation distance between the light-source tip and the resin surface was

maintained at 2 mm.

Retainers fabricated from standard lengths of the FRCs and polyethylene ribbon

were bonded in exactly the same manner as described for the stainless steel wire

retainers.

The brand names, abbreviations, compositions, manufacturer details, and batch

numbers of the tested materials are listed in Table 1.

Cyclic loading and debonding force testing The specimens were subjected to 10,00,000 cyclic loading. The load was applied

at the incisoproximal contact of the tooth pair from the lingual side to the labial side

by using a jig (Figure 2). The force vector formed an approximately 450 angle with

the long axis of the tooth pair. The load frequency was 8 Hz and alternated from 3

N to 100 N. The specimens were kept in 37 ± 30C water during the procedure.21

Following fatigue formation, the specimens were tested for the debonding force

by using a universal testing machine (Z2.5MA, 18-1-3/7; Zwick GmbH & Co. KG,

Ulm, Germany) at a crosshead speed of 1 mm/min. The debonding force was

applied with the same settings and jig as in the cyclic loading experiment until

Figure 2: The loading jig used for measuring the debonding force of the bonded lingual retainers.

62 63

Table 2: Frequencies (%) of failure of the bonded lingual retainers subjected to cyclic loading.

Retainer Type 1 Type 2 Type 3 Type 4 Dislodged*

ANG 60 - 30 0 10

EST 20 80 0 0 -

DTP 80 20 0 0 -

RIB 50 - 40 0 10

QC 20 10 0 50 20

Type 1: complete adhesive debonding of the retainer from the tooth surface; Type 2: partial adhesive detachment of the retainer from one of the teeth; Type 3: retainer did not debond from the tooth surface but fractured; Type 4: retainer did not debond from the tooth surface but the overlying composite detached.

See Table 1 for detailed description of the groups. *Each specimen consisted of a pair of teeth

DISCuSSION

In this study, none of the retainers failed during cyclic loading and all the tested

materials showed similar debonding forces. However, their failure types varied.

The null hypotheses that the fatigue resistance of the FRC and polyethylene

ribbon-reinforced retainers would not be superior to that of the stainless steel

wire retainer and they would not have higher debonding forces were accepted.

Under clinical conditions, lingual retainers are subjected to cyclic stresses

because of mastication, occlusion, and intraoral habits.22-24 This repeated sub-

critical loading induces fatigue and may cause partial or total failure of one or

more components of the retainer complex. These forces are usually below the

maximum debonding forces in in vitro studies, but they may have the destructive

effect of high-magnitude sudden impacts that seldom occur in real life.22-24

Therefore, fatigue tests are expected to clarify the clinical durability better than

static tests.22-24 However, the degree of fatigue necessary to induce failure in

initially intact specimens cannot be easily predicted.

The two main factors determining the effect of fatigue on composite materials

are (1) the factors associated with the cyclic load (i.e., quantity, magnitude, and

direction of load application) and (2) the factors associated with the test material

(e.g., type of rein forcement, filler-matrix ratio, and interfacial strength). The

cyclic load quantity in previous fatigue studies ranged from 20,000 to 2,000,000,

showing great variation.7,24 Supposedly, 2,000,000 cycles correspond to approxi-

mately 4 years of normal occlusal and masticatory activities.24 Although merely

an estimation, 1,000,000 cycles, as applied in this study, would correspond to

approximately 2 years of clinical service. This quantity was used on the basis of

Statistical analysis Statistical analysis was performed by using Statistix 8.0 for Windows (Analytical

Software Inc., Tallahassee, FL, USA). Means were analyzed by one-way analysis

of variance (ANOVA). p -values less than 0.05 were considered significant.

RESuLTS

All the specimens survived the cyclic loading. The mean debonding forces were

706 ± 312 N, 772 ± 348 N, 830 ± 258 N, 731 ± 329 N, and 670 ± 323 N in the

Interlig, everStick Ortho, DentaPreg Splint, Ribbond, and Quad Cat wire groups,

respectively, without significant differences ( p > 0.05) (Figure 3).

According to the failure analysis, the highest incidence of type 1 failure occurred

in the DentaPreg Splint group (eight specimens) followed by the Interlig group (six

specimens). The everStick Ortho group presented predominantly type 2 failure

(eight specimens) and the Quad Cat wire group showed type 4 failure in five

specimens (Table 2)

.

Figure 3: Mean and standard deviation of the debonding force of the bonded lingual retainers. See Table 1 for a detailed description of the groups.

64 65

that the same bonding agent was used in all the groups, this failure type indicates

that the interfacial strength between the tested material and the bonding resin

exceeded the adhesion between the bonding resin and enamel. In contrast,

the everStick Ortho retainers (80%) presented partial adhesive debonding

from one of the teeth. The Ribbond retainers presented adhesive failure and

material breakage in 50% and 40% of the specimens, respectively. Resin

adhesion to polyethylene FRCs was less favorable in previous in vitro studies

mainly because of the difficulty in plasma coating, silanization, and impregnation

of the polyethylene fibers.7 Such combinations of failure types may not cause

direct enamel damage but will necessitate removal of the attached retainers by

using rotary instruments and renewal of the bonding procedure. The potential

detrimental effects of debonding a retainer from enamel during either bracket

debonding or retainer removal present an iatrogenic problem. Therefore, all these

material options cannot be considered durable and favorable.

The Quad Cat wire group presented type 4 failure in 50% of the specimens.

This result implies that either the adhesion at the composite-enamel interface

was superior to the adhesion at the composite-wire interface or the cyclic

load weakened the latter. This type of failure could surely allow repair of the

detached composite part without removal of the remnants. Therefore, it could

be considered a reversible situation and perhaps more favorable than the other

failure types. Reinforcement of the composite in the other materials might have

been accomplished, but the lack of flexibility eventually led to different failure

types in the Quad Cat wire group.

Conclusions

1. Fatigue created by cycling loading did not cause failure of the lingual retainer

materials tested.

2. All the tested materials performed similarly in terms of the debonding force

following fatigue formation.

3. The failure types varied among the materials. The braided stainless steel wire

retainer presented the most repairable failure type.

AcknowledgementWe would like to acknowledge mr. Anne Wietsma for preparing the specimen

molds, Mrs. Graciela Galhano for her assistance with the cyclic loading

experiments and K.G. Bijlstra Stichting for their financial support to purchase the

materials used in the study.

the outcomes of clinical studies in which retainer failures due to debonding were

reported within this period.2-4,9 Another factor affecting fatigue formation is the

magnitude of the load acting on the test material. In previous studies, constant

or varying forces between 40 and 600 N were applied.21-25 In the present study, a

load ranging from 3 N to 100 N was applied at a frequency of 8 Hz. In reality, the

applied force is considered zero in the absence of occlusal contact or function;

however, to maintain the contact of the load cell on the specimen, 3 N was

applied as the minimum load. Nevertheless, a standard method for fatigue tests

has not been established, because chewing cycles vary in every individual as well

as experimental settings. Therefore, these tests still present limitations and their

outcomes should be interpreted with caution.

The adverse effect of fatigue on materials with similar physical properties is more

predictable, because cyclic loading will have an equal impact on them.21-25 Therefore,

elimination of wires in the retainer complex by using FRC might improve stability

and reduce fatigue formation, because adhesion would rely only on bonding of

the flowable composite resin or resin matrix of the FRC to the etched enamel.

However, in the present study, none of the retainers failed during fatigue formation

and no significant differences were observed in terms of the debonding force.

These results are attributable to the specimen properties, where only two units

were included, forming a very short retainer complex compared with that used

clinically. However, the cyclic load could not be applied on 4- or 6-unit retainer

specimens because of the experimental settings and design.

From the chemical perspective, hydrolysis, which can break the covalent bonds

in the resin,25 and plasticization, which can diminish the mechanical resistance

of the polymer,26 were possibly not effective enough to cause failure during

fatigue formation. This lack of an effect might be attributable to the relatively

stable water temperature (37 ± 30C) in which the specimens were kept during

fatigue formation; clinically, higher temperatures are encountered. Future studies

should incorporate temperature alterations in the fatigue formation procedures

for testing lingual retainers.

The lack of debonding during cyclic loading and the insignificant difference in

the debonding forces of the retainers may initially suggest that all the tested

materials behaved similarly. Interestingly, even the stainless steel wire retainer,

with its smaller bonding area than that of the FRC retainers, demonstrated a

similar debonding force. The extent of fatigue created in this design cannot be

determined, and the failure types deserve more attention than the performance

of the tested materials. The failure types should be evaluated with regard to not

only the adhesion quality but also the clinical reversibility, with the least damage

to enamel during removal or repair of the failed retainer. The FRC retainers

themselves showed various failure types. Those composed of Interlig (60%) and

DentaPreg Splint (80%) mainly presented complete adhesive debonding. Given

66 67

16. Kumbuloglu O, Saracoglu A, Özcan M. Pilot study of unidirectional E-glass fibre-reinforced composite resin splints: up to 4.5-year clinical follow-up. J Dent 2011;39:871-7.

17. Meiers JC, Kazemi RB, Donadio M. The influence of fiber reinforcement of composites on shear bond strengths to enamel. J Prosthet Dent 2003;89:388- 93.

18. Scribante A, Cacciafesta V, Sfondrini MF. Effect of various adhesive systems on the shear bond strength of fiber-reinforced composite. Am J Orthod Dentofacial Orthop 2006;130:224-7.

19. Fokkinga WA, Le Bell AM, Kreulen CM, Lassila LV, Vallittu PK, Creugers NH. Ex vivo fracture resistance of direct resin composite complete crowns with and without posts on maxillary premolars. Int Endod J 2005;38:230-7.

20. Özcan M, Valandro LF. Fracture strength of endodontically- treated teeth restored with post and cores and composite cores only. Oper Dent 2009;34:429- 36.

21. Baldissara P, Özcan M, Melilli D, Valandro LF. Effect of cyclic loading on fracture strength and microleakage of a quartz fiber dowel with different adhesive, cement and resin core material combinations. Minerva Stomatol 2010;59:407-14.

22. McCabe JF, Carrick TE, Chadwick RG, Walls AW. Alternative approaches to evaluating the fatigue characteristics of materials. Dent Mater 1990;6:24- 8.

23. Ruse ND, Shew R, Feduik D. In vitro fatigue testing of a dental bonding system on enamel. J Biomed Mater Res 1995;29:411-5.

24. Grandini S, Chieffi N, Cagidiaco MC, Goracci C, Ferrari M. Fatigue resistance and structural integrity of different types of fiber posts. Dent Mater J 2008; 27:687-94.

25. Sahafi A, Peutzfeldt A, Ravnholt G, Asmussen E, Gotfredsen K. Resistance to cyclic loading of teeth restored with posts. Clin Oral Investig 2005;9:84-90.

26. De Munck J, Van Landuyt K, Peumans M, Poitevin A, Lambrechts P, Braem M, et al. A critical review of the durability of adhesion to tooth tissue: methods and results. J Dent Res 2005;84:118-32.

REFERENCES

1. Renkema AM, Renkema A, Bronkhorst E, Katsaros C. Long-term effectiveness of canine-to-canine bonded flexible spiral wire lingual retainers. Am J Orthod Dentofacial Orthop 2011;139:614-21.

2. Bearn DR. Bonded orthodontic retainers: a review. Am J Orthod Dentofacial Orthop 1995;108:207-13.

3. Dahl EH, Zachrisson BU. Long-term experience with direct-bonded lingual retainers. J Clin Orthod 1991; 25:619-30.

4. Artun J, Spadafora AT, Shapiro PA. A 3-year followup study of various types of orthodontic canine-tocanine retainers. Eur J Orthod 1997;19:501-9.

5. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Orthodontic retention: a systematic review. J Orthod 2006;33:205-12.

6. Burstone CJ, Kuhlberg AJ. Fiber-reinforced composites in orthodontics. J Clin Orthod 2000;34:271-9.

7. Foek DL, Özcan M, Krebs E, Sandham A. Adhesive properties of bonded orthodontic retainers to enamel: stainless steel wire vs fiber-reinforced composites. J Adhes Dent 2009;11:381-90.

8. Lumsden KW, Saidler G, McColl JH. Breakage incidence with direct-bonded lingual retainers. Br J Orthod 1999;26:191-4.

9. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008;30:199-204.

10. Lee KD, Mills CM. Bond failure rates for V-loop vs straight wire lingual retainers. Am J Orthod Dentofacial Orthop 2009;135:502-6.

11. Taner T, Aksu M. A prospective clinical evaluation of mandibular lingual retainer survival. Eur J Orthod 2012;34:470-4.

12. Cooke ME, Sherriff M. Debonding force and deformation of two multi-stranded lingual retainer wires bonded to incisor enamel: an in vitro study. Eur J Orthod 2010;32:741-6.

13. Rose E, Frucht S, Jonas IE. Clinical comparison of a multistranded wire and a direct-bonded polyethylene ribbon-reinforced resin composite used for lingual retention. Quintessence Int 2002;33:579-83.

14. Tacken MP, Cosyn J, De Wilde P, Aerts J, Govaerts E, Vannet BV. Glass fibre reinforced versus multistranded bonded orthodontic retainers: a 2 year prospective multi-centre study. Eur J Orthod 2010; 32:117-23.

15. Bolla E, Cozzani M, Doldo T, Fontana M. Failure evaluation after a 6-year retention period: a comparison between glass fiber-reinforced (GFR) and multistranded bonded retainers. Int Orthod 2012; 10:16-28.

Chapter 5

Clinical survival of multi-stranded stainless steel bonded lingual retainers as a functionof resin composite type: Up to 3.5 years follow-up

Lie Sam Foek D.J.

Feilzer A.J.

Özcan M

Submitted to: American Journal of Orthodontics and Dentofacial Orthopedics, 2017.

70 71

INTRODuCTION

After an orthodontic treatment, it is essential to maintain and stabilize the

achieved result as long as possible.1,2 In the absence of retention, after 10 to 20

years 40 to 90% relapse could be expected.1,3,4 Since the cause for the relapse is

multifactorial,3-11 the orthodontist is obliged to choose the best way of retention

that require long-term stability.

Orthodontic retainers could be either categorized as removable or bonded

retainers.12 Due to the fact that removable retainers require patient’s cooperation

by large13 and bonded lingual retainers are considered more patient friendly, the

latter is classified as golden standard in orthodontics.14 Bonded retainers made of

wires present various configurations where the most commonly used ones are

individually adjusted multi-stranded stainless steel wires.15 Failure of such bonded

retainers is however a frequently observed clinical problem, which inevitably

results in full or partial loss of the retainer in function and when unobserved, may

lead to relapse.16

From the configuration type of view, Zachrisson et al. has reported that the

optimal wire retainer, when bonded to all the lingual or palatal surfaces of the

teeth in a segment, would be a 5-stranded 0.0215-in wire.17 Based on clinical

reports, among all wire types, multi-stranded wires consisting of five or even more

number of wires are preferred over single or 3-stranded wires.15,18-20 Moreover,

multi-stranded wires with 3 or less strands show considerably more wire-fatigue

fractures, debonding of the wire at the enamel-composite interface.15,18,19 Arnold

et al. showed that rectangular braided wires had better resistance to torsional

forces in comparison to round braided ones.21 In terms of bond strength, round

and rectangular braided wires revealed higher bond strength in comparison to

plain rectangular smooth wires.22 Yet, one of the most frequent failure type of

orthodontic retainers remains to be debonding ranging from 23 to 58% in the

maxilla and 5 to 37% in the mandible up to 10 years, regardless of the retainer

type used.23,24 In addition to possible relapse which is a clinical problem, revisits

to the orthodontist for rebonding are both timely and costly procedures both

for the patient and the clinician. The recent Cochrane review listed a number

of possible factors for the cause of relapse such as the recoil of fibers that hold

the teeth in the jaw bone, pressures form the lip, cheeks and tongue and further

growth which consequently could also yield to failure of the retainer.23 However,

material aspects received no attention in the reviewed material that could also

have potential effect on debonding of the retainers.

It has to be noted that the clinical adhesion of bonded retainers start with etching

the enamel, application of resin adhesive, placement of the wire and then coverage

of the wire with resin-based composite either using flowable or highly filled resin

composite materials. Since highly filled resin composites typically present higher

ABSTRACT

Objectives: This prospective clinical trial evaluated the survival of multi-stranded

stainless steel lingual retainers (SSR) bonded using different resin composite

types.

Methods: Between April 2011 and March 2013, a total of 75 patients (40 women,

35 men; mean age: 16.3 years old) received full arch orthodontic treatment after

which SSRs (Multi-strand 1 x 3 high performance wire, 0.022” x 0.016”, PG

Supply Inc.) (N=150) were bonded in the maxilla and/or mandible on all 6 anterior

teeth. After etching enamel surfaces with 35% H3PO4, adhesive resin was

applied (Clearfil SE Bond) and photo-polymerized for 20 s. SSRs were bonded

using one of the following resin composites: a) Hybrid (Clearfil AP-X, Kuraray

Noritake) (H1), b) Hybrid (Light Cure Retainer, Reliance Orthodontic Products Inc.)

(H2), c) Flowable (Clearfil Majesty Flow, Kuraray) (FL). At baseline and thereafter

at 1, 2, 3, 6, 12 and 24 months, SSRs were checked upon macroscopically for

partial or complete debonding or fracture. SSRs were scored as failed if any

operative intervention was indicated for repair, partial or total replacement. Data

were analyzed using Kaplan-Meier and Log Rank (Mantel-Cox) (α=0.05).

Results: SSRs were observed for a minimum of 6, and maximum 43 months

(mean: 19.5 months). At the final control (24 months), 10 patients could not be

followed up (H1: 12, H2: 4, FL: 4) due to drop out. In total, in 150 SSRs, 28

failures were observed (n=19 in the maxilla, n=9 in the mandible). The majority

of the failures were observed with FL (n=12), followed by H1 (n=8) and H2 (n=8)

being not statistically significant (maxilla: p=0.133; mandible: p=0.551). Overall,

3 fractures of the SSR were observed all of which were in the maxilla. Overall,

cumulative survival rate was 81.3% up to 43 months (Kaplan-Meier). Location of

the SSRs did not show significant difference (maxilla: 74.7%, CI: 29.4-37.7 and

mandible: 88% (CI: 35.7-41.7) (p>0.05). No significant difference was observed

between gender type (female: 78.8%; male: 81.3%) (p=0.059).

Conclusion: Although microhybrid flowable resulted in slightly more frequent

incidence of failures, the type of composite, the location and the gender did not

significantly affect the clinical survival of multi-stranded stainless steel bonded

lingual retainers in the studied sample.

Keywords: Adhesion; Adhesive dentistry, Clinical study, Orthodontic retainers,

Resin composite

72 73

suction and cotton rolls. Lingual enamel surfaces of all frontal teeth were etched

with 35% H3PO4 (Temrex Gel Etch, Temrex Corporation 112 Albany Avenue,

Freeport, NY, USA) for 20 seconds, rinsed with copious water and air-sprayed

and dried for about 5 seconds until the frosted enamel was visible. When this

was not the case, the particular tooth was etched again in the same manner.

Table 1: The brand, type, manufacturer, and chemical composition of the main materials used in this study.

Brand Type Manufacturer Chemical composition

1 x 3 high performance wire

Multi-stranded wire, 0.022” x 0.016”

PG Supply Inc., Avon, CT, USA

Stainless steel

ClearfilAP-X

Resincomposite

KurarayNoritake, Okayama, Japan

Bis-phenol A diglycidylmethacrylate <12 w%triethylene glycol dimethacrylate <5 w%Silanated barium glass filler Silanated silica fillerSilanated colloidal silica (80 w%, 70 v%)dl-Camphorquinone catalysts Accelerators, pigments

Light Cure Retainer

Resincomposite

Reliance Orthodontic Products Inc., Itasca, IL, USA

Glass filler 75 v%bis-phenol A diglycidylmethacrylate 10-30 w%Triethylene glycol 5 w% Dimethacrylate 5-10w%Amorphous silica 1-5 w%

Clearfill MajestyFlow

Resincomposite

KurarayNoritake

Triethylene glycol dimethacrylate <7 w%Hydrophobic aromatic dimethacrylate Silanated barium glass filler Silanated colloidal silica (80 w%, 62 v%)dl-CamphorquinoneAccelerators, pigments

TemrexEtch

Etchingagent

Temrex Corporation, NY, USA

35% H3PO4

ClearfilSE Bond

Adhesiveresin

KurarayNoritake

Bis-phenol A diglycidylmethacrylate 25-45%2-hydroxyethyl methacrylate 20-40%10-Methacryloyloxydecyl dihydrogen phosphateHydrophobic aliphatic methacrylate Colloidal silicadl-Camphorquinone initiators Accelerators

tensile strength and elasticity modulus,24 it could be anticipated that the use of

hybrid resin material could increase the survival rate of bonded retainers.

The objective of this study therefore was to evaluate the survival of multi-stranded

stainless steel lingual retainers (SSR) bonded using different resin composite

types. The hypothesis tested was that hybrid resin composite used for bonding

SSRs would result in higher rate of clinical survival compared to low viscosity

composite.

MATERIALS AND METHODS

Study designThe brands, types, chemical compositions and manufacturers of the materials

used in this study are listed in Table 1.

Inclusion and exclusion criteriaBetween April 2011 and March 2013, a total of 75 patients (40 women, 35 men;

mean age: 16.3 years old) received full arch orthodontic treatment after which

SSRs (Multi-strand 1 x 3 high performance wire, 0.022” x 0.016”, PG Supply Inc.,

Avon, CT, USA) (N=150) were bonded in the maxilla and mandible on all 6 anterior

teeth in private practice settings where specialized orthodontists deliver dental

services solely in orthodontics. As the bonded retainers in this study were made

as a part of standard dental care employed after orthodontic treatment, no ethical

committee approval was requested.

Information was given to each patient regarding the function of the retainers, and

informed consent was signed. The inclusion criteria were as follows: having no

active periodontal or pulpal diseases, having no primary caries, not allergic to resin-

based materials, not pregnant or nursing, having antagonist teeth opposing the

SSR, willing to return for follow-up examinations as outlined by the investigators.

Clinical proceduresAll bonded retainers were placed 1 month prior to the debonding of the

orthodontic appliances and thus with the fixed appliances in situ. At least one

week prior to retainer placement, the lingual and interproximal tooth surfaces

were cleaned from calculus and stain with a scaler or cavitron (H6-H7 Hu-Friedy

Mfg. Co., Chicago, IL USA and/or W&H Dentalwerk Bürmoos GmbH, Bürmoos,

Austria) On the appointment of retainer placement, all surfaces were cleaned

with non-fluoride containing pumice (Polo Dent Polish, American Dental Trading.

BV, Oisterwijk, The Netherlands) using silicone rubbers and cups (Hawe Kerr,

Kerr Corp. CA, USA). A cheek retractor (Reliance Orthodontic Products., IL, USA)

was used for better visibility of the working area. Dry field was created only with

74 75

RESuLTS

Distribution of SSRs in the maxilla and mandible is presented in Table 2. SSRs

were observed for a minimum of 6, and maximum 43 months (mean: 19.5

months). At the final control (24 months), 10 patients could not be followed up

(H1: 12, H2: 4, FL: 4) due to drop out. In total, in 150 SSRs, 28 failures were

observed (n=19 in the maxilla, n=9 in the mandible) (Table 3).

Table 2: Distribution of stainless steel bonded lingual retainers in the maxilla and mandible using two hybrid (H1 and H2) and one flowable (FL) resin composite material (H1: Clearfil AP-X; H2: Light Cure Retainer; FL: Clearfil Majesty Flow).

Maxilla Mandible Total (N)

H1 H2 FL H1 H2 FL

Females 13 12 15 13 12 15 75

Males 12 13 10 12 13 10 75

25 25 25 25 25 25

Total (N) 75 75 150

Table 3: Distribution of failure types of stainless steel bonded lingual retainers in the maxilla and mandible using two hybrid (H1 and H2) and one flowable (FL) resin composite material. See Table 2 for group abbreviations.

Maxilla Mandible Total (N)

H1 H2 FL H1 H2 FL

Partial debonding 4 3 8 3 2 4 24

Complete debonding 1 0 0 0 0 0 1

Wire fracture 3 3

Total (N)5 6 8 3 2 4

19 9 28

The majority of the failures were observed with FL (n=12), followed by H1 (n=8)

and H2 (n=8) being not statistically significant (maxilla: p=0.133; mandible:

p=0.551). Overall, 3 fractures of the SSR were observed all of which were in the

maxilla in H2 group. Regardless of the composite type, six partial debondings in

25 SSRs involved the canines. Except for 4 failures that occurred at 12 months

follow up, all other were observed within the first 6 months.

Overall, cumulative survival rate was 81.3% up to 43 months (Kaplan-Meier) (Fig.

1). Location of the SSRs did not show significant difference (maxilla: 74.7%, CI:

After etching enamel surfaces, adhesive resin was applied (Clearfil SE Bond,

Kuraray Noritake, Okayama, Japan) a thin coat using microbrush, air-thinned and

photo-polymerized for 20 s using an LED device (3M ESPE Elipar S10, St. Paul,

Minn, USA) with an output of ~ 1000 mW/cm2. SSRs were bonded using one of

the following resin composites: a) Hybrid (Clearfil APX, Kuraray) (H1), b) Hybrid

(Light Cure Retainer, Reliance, Itasca, IL, USA) (H2), c) Flowable microhybrid

(Clearfil Majesty Flow, Kuraray) (FL). Two operators who had experience in

orthodontics (>1-3 years since specialization) and 6 orthodontic assistants under

their supervision (>1-5 years) have bonded the SSRs with one of the resin

materials depending on their preference of materials.

Dental floss was placed between the central incisors and distal parts of the lateral

incisors in order to hold the SSRs in place that was individually bent in place. Each

layer of resin composite, covering the SSR in small buds (2 to 4 mm) was photo-

polymerized using an LED polymerization device (ESPE Elipar) for 20 s on each

tooth. The output of the polymerization device was controlled every 4 weeks.

After occlusion control using occlusion papers (Dr. Jean Bausch GmbH & Co. KG,

Köln, Germany), premature contact points were removed with carborundum burs

(Hager & Meisinger GmbH, Neuss, Germany) at 30.000 rpm under water. Excess

adhesive resin remnants were removed with a scaler (H6-H7 Hu-Friedy Mfg. Co.,

Chicago, IL USA). Resin composite surfaces were finished with carborundum

burs (Hager & Meisinger GmbH, Neuss, Germany) and polished with rubbers.

Patients received individual instructions to maintain their plaque control.

EvaluationAt baseline and thereafter at 1, 2, 3, 6, 12 and 24 months, SSRs were checked

upon macroscopically for partial or complete debonding or fracture. SSRs were

scored as failed if any operative intervention was indicated for repair, due to partial

or complete rebonding or total replacement due to fracture. Patients were asked

to contact the practice if they would perceive any problem or change in the SSRs.

Only the first experienced failures were considered as absolute failures over the

observation time.

Statistical analysisSurvival analyses were performed with statistical software program (SPSS 14.0;

SPSS Inc, Chicago, IL, USA) using Kaplan-Meier and Log Rank (Mantel-Cox)

tests to obtain the cumulative survival rates in relation to observation time. P

values less than 0.05 were considered to be statistically significant in all tests.

76 77

DISCuSSION

This study was undertaken in an attempt to evaluate the survival of SSRs bonded

using different resin composite types at private practice settings. Based on

the results, the incidence of failures were more frequent with FL which was a

microhybrid low viscosity resin composite compared to other hybrid composites,

but the survival statistics did not show significant difference between the resin

composites used for bonding the SSRs. Thus, the tested hypothesis was rejected.

Various types of resin composite have been described for the bonding of SSRs

in the literature25 but to our knowledge no study has looked at the differences

between resin composite type having different thixotropies. The amount of filler

content in resin composites is associated with higher mechanical properties.26

Hybrid composites, usually used for Class II, III and IV restorations are typically

highly filled, show higher elasticity moduli, fracture resistance, wear resistance

and therefore are less pliable in comparison to flowable composites.26 This is

one reason why the latter is often preferred in bonding SSRs in orthodontics.27

The insignificant difference between the FL and other hybrid composites could

be attributed to the filler content of 62 v% which could still be considered a high

amount for a low viscosity composite. Yet, the hybrid composites tested presented

70 v% for H1 and 75 v% for LCR being higher than that of FL. The failures related

to low viscosity resin materials may also be ascribed as a consequence of water

sorption over time. Hybrid composites used in this study, were meant to be less

prone to water sorption and showed higher depth of polymerization in comparison

to a similar composites used for the bonding of SSRs.28 However, the incidences

of the majority of the SSR failures in this study were experienced within the first

6 months. Therefore, the possible water sorption effect on the failures of resin

composites could not be disclosed in this study.

The majority of the failures were partial adhesive debonding of the SSRs from the

tooth surface. One reason for this type of failure could be lack of ideal conditioning

of the enamel surface which typically starts with etching with 35-37% H3PO4.

Adhesive types of failures are an indication of less adhesive forces between

the adhesive resin and the enamel surface. In this study, enamel surfaces

were etched only and no attempt was made to remove the most upper layer

of the enamel by roughening which is not a common practice in orthodontics

considering the age of the patient. Although enamel tissue removal is usually

not needed in orthodontics, due to the prerequisite of temporary adhesion,

SSRs serve a different purpose and lifespan and therefore require a different

application procedure. A commonly used application in reconstructive dentistry

is the removal of the possible aprismatic enamel at different levels using either

burs, disks or air-borne particle abrasion. The aim of these methods is to increase

the surface area and therefore enhance adhesion of the resin based material onto

29.4-37.7 and mandible: 88% (CI: 35.7-41.7) (p>0.05) (Figs. 2a-b). Annual failure

rate was 6.4%. No significant difference was observed between gender type

(female: 78.8%; male: 81.3%) (p=0.059).

The debonded SSRs were rebonded using the same resin composite and the

corresponding protocol.

Figures 2a-b: Event-free survival rates of stainless steel bonded lingual retainers ina) maxilla (n=75; 19 failures), b) mandible (n=75; 9 failures)(1: Clearfil AP-X; 2: Light Cure Retainer; 3: Clearfil Majesty Flow)

Cu

mu

lati

ve S

urv

ival

(%

)

Months

Survival Functions Maxilla

ResinComposite

Type

0

0,0

0,2

0,4

0,6

1,0

1231-censored2-censored3-censored

10 20 30 40 50

0,8

A

Cu

mu

lati

ve S

urv

ival

(%

)

Months

ResinComposite

Type

0

0,0

0,2

0,4

0,6

1,0

10 20 30 40 50

0,8

1231-censored2-censored3-censored

Survival Functions Mandible

B

78 79

adhesive dentistry, the high of failures indicates that other factors may play a

more dominant role in the debonding of SSRs. A number of factors have been

assigned for the failures of SSRs in orthodontics. Since the location, gender,

composite type, humidity control, operator factor could not be disclosed in this

study the cause of failures needs further investigations focusing on the effect

of orthodontic forces that disturb the microenvironment of the periodontal

ligament that in turn cause relapse and thereby increase forces between the SSR

and the tooth surface.41-43

One limitation of this study was that out of 150 SSRs, 20 of them could not be

followed up at 24 months follow up (H1: 12, H2: 4, FL: 4). Bearing in mind that the

oral environment is complex and that resin composites are susceptible to aging,

the survival of SSRs may decrease over time which needs long-term evaluations.

Conclusions

1. Resin composite type and the location did not significantly affect the clinical

survival of multi-stranded stainless steel lingual retainers.

2. Failures were in general due to partial or complete adhesive debonding of the

retainer from the tooth surface.

AcknowledgementsThe authors would like to extend their gratitude to Dr. M.P.E. Tacken for the helpful

discussions and cooperation during treatment of the patients and the whole

team of orthodontic assistants for their support and labour at the Apeldoorn

Orthodontie Welgelegen practice.

Conflict of interestThe authors did not have any commercial interest in any of the materials used in

this study.

enamel by means of micromechanical retention. Enamel, is the hardest structure

in the human body and is made of arranged hydroxyapatite prisms, consisting of

96 wt% inorganic matter.29,30 Hydroxyapatite crystals of enamel show a unique

structure with small rods. Each rod is usually built out of about 100 crystals. 29,30

Dental restorations and orthodontic appliances, largely depend on the surface

preparation of the enamel for their adhesion.31 Moreover, untreated enamel usually

smooth and non-retentive, impairs adhesion due to the existence of a pellicle

layer and the possible presence of the top aprismatic enamel layer that is usually

between 20 and 80 mm thick.29,31 Enhancement of adhesion, may be achieved by

enamel preparation by means of rotating instruments, which in turn leave a smear

layer behind which also compromises adhesion. Therefore, subsequent enamel

conditioning either chemically or mechanically is needed to expose fresh enamel

surface and increase the surface area for micromechanical retention.

Micro retention is achieved after acid etching with H3PO4 that can easily be

wetted by hydrophobic resin-based adhesives. Penetration of the applied

adhesive resin on the etched enamel surface through capillary action and

subsequent photo polymerization of the applied resin facilitates micromechanical

adhesion. Although the most commercially available enamel-etching agents have

a concentration ranging between 30-40%, a concentration of 37% has been

shown to be superior. Lower concentrations may lead to dicalcium phosphate

dihydrate precipitation in the micro retention cracks of the enamel surface which

are very difficult to remove by rinsing.32-34 In this study, in case of no frosted

appearance after etching, a second attempt was made to etch the enamel.

Adhesive procedures should be at best performed in dry environment. In this

study, this was achieved by not using rubberdam but cotton rolls and suction.

Saliva control could be anticipated to be less compared to maxilla leading to

higher survival in the maxilla. Yet, in this study, the failures were more common

in the maxilla than that of mandible, again disclosing the possible humidity control

effect in the mandible. In other words, since the location did not affect the results

significantly, it could be stated that cotton rolls and suction could be sufficient

when used ideally. The high incidence of failures in the maxilla however is in line

with previous studies where different materials were used that could be also due

to the continuous contact with anterior incisors as a result of bite depth during

mastication.35-37 Similarly, the lack of gender effect on the survival of SSRs is n

agreement with previous studies.38-40

The incidence of wire breakage was observed only in 3 SSRs. Likewise, previous

studies reported less incidence of failures in terms of wire fracture as opposed to

debonding.18-20 Although the exact reason is unknown, heat treatment seems to

decrease wire stiffness unpredictably yielding to early wire breakage which was

also practiced in this study.21

Nevertheless, even though adhesion to enamel is known to be the best in

80 81

18. Zachrisson BU. Clinical experience with direct-bonded orthodontic retainers. American Journal of Orthodontics and Dentofacial Orthophedics 1977;71:440-448.

19. Zachrisson BU. Improving orthodontic results in cases with maxillary incisors missing. Amer-ican Journal of Orthodontics and Dentofacial Orthophedics 1978;73:274-289.

20. Zachrisson, B.U. The bonded lingual retainer and multiple spacing of anterior teeth. Journal of Clinical Orthodontics 1983;17:838-844.

21. Arnold DT, Dalstra M, Verna C. Torque resistance of different stainless steel wires commonly used for fixed retainers in orthodontics. Journal of Orthodontics 2016;43:121-129.

22. Paolone MG, Kaitsas R, Obach P, Kaitsas V, Benedicenti S, Sorrenti E, Barberi F. Tensile test and interface retention forces between wires and composites in lingual fixed retainers. International Orthodontics 2015;13:210-220.

23. Artun J, Spadafora AT, Shapiro PA. A 3-year follow-up study of various types of orthodontic canine-to-canine retainers. Eur J Orthod. 1997;19:501-509.

24. Milheiro A, de Jager N, Feilzer A J, Kleverlaan CJ. In vitro debonding of orthodontic retain-ers analyzed with finite element analysis. European Journal of Orthodontics 2015;37:491-496.

25. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database of Systematic Reviews 2016;29:CD002283.

26. Lohbauer U, Frankenberger R, Krämer N, Petschelt A. Strength and fatigue performance versus filler fraction of different types of direct dental restoratives. Journal of Biomedical Materials Research B Applied Biomaterials 2006;76:114-120.

27. Talic NF. Failure rates of orthodontic fixed lingual retainers bonded with two flowable light-cured adhesives: a comparative prospective clinical trial. Journal of Contemporary Dental Practice 2016;17:630-644.

28. Catalbas B, Uysal T, Nur M, Demir A, Gunduz B. Effects of thermocycling on the degree of cure of two lingual retainer composites Dental Materials Journal 2010;29:41-46.

29. Özcan M, Sadiku M. Analysis of structural, morfological alterations, wettability characteristics and adhesion to enamel after various surface conditioning methods. Journal of Adhesion Science and Technology 2016;22:2453-2465

30. Hellwig E, Klimek J, Attin T. Einführung in die Zahnerhaltung: Prüfungswissen Kariologie, Endodontologie und Parodontologie; mit 60 Tabellen, ed. 6. Köln: Dt. Ärzte-Verl.; 2013.

31. Shahabi M, Ahrari F, Mohamadipour H, Moosavi H. Microleakage and shear bond strength of orthodontic brackets bonded to hypomineralized enamel following different surface preparations. Journal of Clinical Experimental Dentistry 2014;6:e110-e115.

32. Lasers in Restorative Dentistry: A Practical Guide. Rome: Springer; 2015. p.3-6.

REFERENCES

1. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. American Journal of Orthodontics and Dentofacial Orthophedics 1988;93:423-428.

2. Shah AA. Postretention changes in mandibular crowding: a review of the literature. Ameri-can Journal of Orthodontics and Dentofacial Orthophedics 2003;124:298-308.

3. Riedel RA. A review of the retention problem. Angle Orthodontics 1960;30:179-199.

4. Boese LR. Fiberotomy and reproximation without lower retention 9 years in retrospect: part II. Angle Orthodontist 1980;50:169–178.

5. Southard T, Southard K, Tolley E. Periodontal force: a potential cause of relapse. American Journal of Orthodontics and Dentofacial Orthophedics 1992;101:221-227.

6. Al Yami EA, Kuijpers-Jagtman AM, van ‘t Hof MA. Stability of orthodontic treatment outcome: follow-up until 10 years postretention. American Journal of Orthodontics and Dentofacial Orthophedics 1999;115:300-304.

7. Kim TW, Little RM. Postretention assessment of deep overbite correction in Class II Division 2 malocclusion. Angle Orthodontist 1999;69:175-186.

8. Thilander B. Biological basis for Orthodontic relapse. Seminars in Orthodontics 2000;6:195-205.

9. Thilander B. Orthodontic relapse versus natural development. American Journal of Ortho-dontics and Dentofacial Orthophedics 2000;117:563-565.

10. Proffit WR, Fields HM, Sarver DM. Contemporary orthodontics. 4th edn. St. Louis: CV Mos-by, 2007.

11. Gkantidis N, Christou P, Topouz N. The orthodontic–periodontic interrelationship in integrat-ed treatment challenges: a systematic review. Journal of Oral Rehabilation 2010;37:377-390.

12. Daskalogiannakis J. Glossary of Orthodontic terms. 1st edition Berlin: Quintessence Publishing Co. 2000;230.

13. Ackerman MB, Thornton B. Posttreatment compliance with removable retention in a teenage population: a short-term randomized clinical trial. Orthodontics (Chic.) 2011; 12:22.

14. Bearn DR. Bonded orthodontic retainers: a review. American Journal of Orthodontics and Dentofacial Orthophedics 1995;108: 207-213.

15. Zachrisson BU. Multistranded wire bonded retainers: from start to success. American Jour-nal of Orthodontics and Dentofacial Orthophedics 2015;148:724-727.

16. Radlanski RJ., Zain ND. Stability of the bonded lingual wire retainer – a study of the initial bond strength. Journal of Orofacial Orthophedics 2004;65:321-335.

17. Dahl EH, Zachrisson BU. Long-term experience with direct-bonded lingual retainers. Journal of Clinical Orthodontics 1991;25:619-630.

82 83

33. Schwartz RS. Fundamentals of operative dentistry: A contemporary approach. Quintessence books. Chicago: Quintessence Publ; 1996. p. 209.

34. Kugel G, Ferrari M. The science of bonding: from first to sixth generation. Journal of American Dental Association 2000;131 Suppl:20S-25S.

35. Schneider E, Ruf S. Upper bonded retainers. Angle Orthodontist 2011;81:1050-1056.

36. Renkema AM, Sips ET, Bronkhorst E, Kuijpers-Jagtman AM. A survey on orthodontic retention procedures in The Netherlands. European Journal of Orthodontics 2009;31:432-437.

37. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. European Journal of Orthodontics 2008;30:199-204.

38. Lumsden KW, Saidler G, McColl JH Breakage incidence with direct bonded lingual retainers British Journal of Orthodontics 1999;26:191-194.

39. Yoshida Y, Sasaki T, Yokoya K, Hiraide T, Shibasaki Y. Cellular roles in relapse processes of experimentally-moved rat molars. Journal of Electron Microscopy (Tokyo). 1999;48:147-57.

40. Jónsdóttir SH1, Giesen EB, Maltha JC. The biomechanical behaviour of the hyalinized periodontal ligament in dogs during experimental orthodontic tooth movement. European Journal of Orthodontics. 2012;34:542-546.

41. Feng L, Yang R, Liu D, Wang X, Song Y, Cao H, He D, Gan Y, Kou X, Zhou Y. PDL progenitor-mediated PDL recovery contributes to orthodontic relapse. Journal of Dental Research 2016;95:1049-1056.

Chapter 6

Displacement of teeth without and with bonded fixed orthodontic retainers:3D analysis using triangular target frames and optoelectronic motion tracking device

Chakroun F

Colombo V

Lie Sam Foek D.J.

Gallo L

Feilzer A.J.

Özcan M

Submitted to: Journal of the Mechanical Behavior of Biomedical Materials, 2017.

86 87

Keywords: Adhesion; bonded retainers; dynamic stereometry; periodontal

ligament; three- dimensional; tooth movement

INTRODuCTION

After an orthodontic treatment, the aligned teeth in their achieved positions need

to be stabilized using bonded retainers (Little et al., 1998; Shah, 2003). In the

absence of retention, 40 to 90% of relapse has been reported up to 10 to 20 years

(Little et al., 1998; Al Yami et al., 1999; Kim et al. 1999). Failure of such bonded

retainers is however a frequently observed clinical problem after the active

treatment and when unnoticed they may lead to unwanted tooth movement

(Radlanski et al., 2004). This is due to the fact that teeth have a tendency to

return to their former position which is typically described as orthodontic relapse

(Joondeph, 2011). Possible causes for such unwanted post-treatment tooth

movements are multifactorial and have been attributed to the reorganization

of the supporting tissues surrounding the teeth, neuromuscular imbalances,

continued facial growth, aging and continuous unwanted oral habits (Reitan et

al., 1960, 1967; Vaden et al., 1997; Blake et al., 1998; Rossouw, 1999; Joondeph,

2011; Heyman et al., 2012). Prevention of these unwanted tooth movements is a

necessity in order to maintain the achieved orthodontic result (Dahl et al., 1991)

Bonded retainers usually made of single or multi-stranded stainless steel wires are

considered as golden standard in orthodontics with the advantage of allowance

for physiologic tooth movement compared to more stiff materials such as fiber

reinforced composites (Bearn, 1995; Zachrison, 2015) Yet, a high incidence

of failures, varying from 5.9 to 53% has been reported in previous studies,

regardless of the variations in material types, configurations and application

modes of bonded retainers (Segner and Heinici, 2000; Lie Sam Foek et al., 2008;

Pandis et al., 2013) Nevertheless, former studies have shown that failure rates

were often independent of gender, age and operator experience which leads to

the assumption that the biological and physiological factors are more responsible

causes for unwanted tooth movement and thereby debonding of the retainers (Lie

Sam Foek et al., 2008; Maltha et al., 2017) In this context, periodontal ligaments

(PDL) and gingival fibers composing the periodontium are stretched during tooth

movement of any kind, which may cause strain between the bonded retainer and

the tooth surface (Gerami et al., 2012; Franzen et al., 2013; Maltha et al., 2017).

The role of PDL on relapse has been studied in animal experiments mainly on

two teeth without considering the arch formation (Maltha et al., 2017). In fact, the

force distribution could be anticipated to decraese when they are disseminated

on multiple teeth in an arch where the retainers are bonded. To the best of our

knowledge, no study has looked at the tooth displacement in a configuration

ABSTRACT

Purpose: The objective of this study was to evaluate the anterior tooth movement

without and with bonded fixed orthodontic retainers under incremental loading

conditions.

Materials and Methods: Six extracted mandibular anterior human teeth were

embedded in acrylic resin in True Form I Arch type and 3D reconstruction of Digital

Volume Tomography (DVT) images (0.4 mm3 voxels) were obtained. The anatomy

of each tooth was segmented and digitally reconstructed using 3D visualization

software for medical images (AMIRA, FEI SVG). The digital models of the teeth

were repositioned to form an arch with constant curvature using a CAD software

(Rhinoceros) and a base holder was designed fitting the shape of the roots. The

clearance between the roots and their slot in the holder was kept constant at

0.3 mm to replicate the periodontal ligament thickness. The holder and the teeth

were then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a

resin material for dental applications (E=2-3 GPa). The 3D printed teeth models

were then positioned in the holder and the root compartments were filled with

silicone. The procedure was repeated to obtain three identical arch models. Each

model was tested for tooth mobility by applying force increasing from 5 to 30

N with 5 N increments applied perpendicular on the lingual tooth surface on

the incisal one third (crosshead speed: 0.1 mm/s). The teeth on each model

were first tested without retainer (control) and subsequently with the bonded

retainers (braided bonded retainer wire; Multi-strand 1x3 high performance wire,

0.022” x 0.016”). Tooth displacement was measured in terms of complicance

(F/Δ movement) (N/mm) using custombuilt optoelectronic motion tracking

device (OPTIS) (accuracy: 5 mm; sampling rate: 200 Hz). The position of the

object was detected through three LEDs positioned in a fixed triangular shape on

a metal support (Triangular Target Frame). The measurements were repeated for

three times for each tooth. Data were analysed using mixed model with nesting

(alpha=0.05).

Results: The use of retainer showed a significant effect on tooth mobility

(0.008±0.004) compared to non-bonded teeth (control) (0.014±0.009)

(p<0.0001). The amount of displacement on the tooth basis was also significantly

different (p=0.0381) being the most for tooth no. 42 (without: 0.024±0.01; with:

0.012±0.002) (p=0.0018). No significant difference was observed between

repeated measurements (p=0.097) and the incremental magnitude of loading

(5-30 N: 0.07±0.01- 0.09±0.02) (p>0.05).

Conclusion: Mandibular anterior teeth showed less tooth mobility when bonded

with stainless steel wire as opposed to non-bonded teeth but the tooth mobility

varied depending on the tooth type. Intermittent increase in loading from 5 to 30

N did not increase tooth displacement.

88 89

Experimental proceduresTooth mobility was tested by applying force increasing from 5 to 30 N with 5

N increments applied perpendicular on the lingual tooth surface on the incisal

one-third at a crosshead speed of 0.1 mm/s. Each model was mounted on a

custom-made loading device (RPETS, University of Zurich) allowing precise and

repeatable positioning of the arch. The device was composed of two main parts:

a metal support where the arch could be aligned with the teeth to be tested and

motor controlled loading mechanism, pressing a conic shaped tip (single point

force application) on the selected tooth with a prescribed force, measured by

means of a force sensor (ME Messsysteme GmbH, Henningsdorf, Germany).

The teeth on each model were first tested without retainer that acted as the control

group and subsequently with the bonded retainers (braided bonded retainer wire;

Multi-strand 1x3 high performance wire, 0.022” x 0.016”, PG Supply Inc., Avon,

Connecticut, USA). On the lingual surfaces of each tooth an adhesive resin was

applied (Heliobond, Ivoclar Vivadent, Ivoclar Vivadent, Schaan, Lichtenstein) and

photo-polymerized for 20 s (Bluephase, Ivoclar Vivadent). The lingual retainer was

individually bent on all teeth and made sure to have a passive fit. The retainers

were bonded on all teeth using resin composite (Tetric Evo Ceram, Ivoclar

Vivadent) and photo polymerized for 20 s on each tooth (Figs. 1a-d).

Figs. 1a-d Workflow of the model preparation. a) The anatomy of six anterior teeth (canine to canine) was acquired with DVT and digitally reconstructed; b) digital models of the teeth were repositioned to form a standard arch form, c) base holder was designed fitting the shape of the roots; d) holder and the teeth were manufactured using 3D printing and positioned in the holder where the root compartments were filled with silicone.

of the frontal mandibular arch. Yet, it is an easy task to study the amount of

tooth displacement in a complete arch segment under administered magnitudes

of forces. Establishment of a model for measurement of tooth mobility under

different bonded materials would also allow making measurements for different

adhesives and retainer materials.

The objectives of this study therefore were to investigate the anterior tooth

movement without and with bonded fixed orthodontic retainers under incremental

loading conditions. The hypotheses tested were that:

a) the use of bonded retainer would show less tooth mobility as opposed to

non-bonded ones,

b) the tooth mobility would increase with the increased magnitude of force,

c) displacement amount would be similar regardless of the tooth type.

MATERIAL AND METHODS

Model preparationSix extracted mandibular anterior human teeth were embedded in acrylic resin

(Technovit, Kulzer GmbH, Wehrheim, Germany), in True Form I Arch type (G&H

Wires, Franklin, Indiana, USA) and 3D reconstruction of Digital Volume Tomography

(DVT) images (Kavo 3D Exam1, Kavo GmbH, Leutkirsch, Germany) (0.4 mm3

voxels) were obtained. All teeth used in the present study were extracted for

reasons unrelated to this project. Written informed consent for research purpose

of the extracted teeth was obtained by the donor prior to extraction according

to the directives set by the National Federal Council. Ethical guidelines were

strictly followed and irreversible anonymization was performed in accordance

with State and Federal Law (World Medical Association, Declaration of Helsinki,

2013; Human Research Act, 2015). The anatomy of each tooth was segmented

and digitally reconstructed using 3D visualization software for medical images

(AMIRA, FEI SVG, Thermo Fisher Scientific, Hillsboro, Oregon, USA). The digital

models of the teeth were repositioned to form an arch with constant curvature

using CAD software (Rhinoceros, Mc Neel Euope, Barcelona, Spain) and a base

holder was designed fitting the shape of the roots. The clearance between the

roots and their slot in the holder was kept constant at 0.3 mm to replicate the

periodontal ligament thickness (Provatidis, 2000). The holder and the teeth were

then manufactured by 3D printing (Obect Eden 260VS, Stratasys, Commerce

Way Eden Prairie, Minesota, USA) using a resin material for dental applications

(Clear Biocompatible, MED 610, Stratasys, Commerce Way Eden Prairie) (E=

2-3 GPa). The 3Dprinted teeth models were then positioned in the holder and

the root compartments were filled with silicone (President, Coltene, Altstätten,

Switzerland). The procedure was repeated to obtain three identical arch models.

A

C

B

D

89

Experimental proceduresTooth mobility was tested by applying force increasing from 5 to 30 N with 5

N increments applied perpendicular on the lingual tooth surface on the incisal

one-third at a crosshead speed of 0.1 mm/s. Each model was mounted on a

custom-made loading device (RPETS, University of Zurich) allowing precise and

repeatable positioning of the arch. The device was composed of two main parts:

a metal support where the arch could be aligned with the teeth to be tested and

motor controlled loading mechanism, pressing a conic shaped tip (single point

force application) on the selected tooth with a prescribed force, measured by

means of a force sensor (ME Messsysteme GmbH, Henningsdorf, Germany).

The teeth on each model were fi rst tested without retainer that acted as the control

group and subsequently with the bonded retainers (braided bonded retainer wire;

Multi-strand 1x3 high performance wire, 0.022” x 0.016”, PG Supply Inc., Avon,

Connecticut, USA). On the lingual surfaces of each tooth an adhesive resin was

applied (Heliobond, Ivoclar Vivadent, Ivoclar Vivadent, Schaan, Lichtenstein) and

photo-polymerized for 20 s (Bluephase, Ivoclar Vivadent). The lingual retainer was

individually bent on all teeth and made sure to have a passive fi t. The retainers

were bonded on all teeth using resin composite (Tetric Evo Ceram, Ivoclar

Vivadent) and photo polymerized for 20 s on each tooth (Figs. 1a-d).

Figs. 1a-d Workfl ow of the model preparation. a) The anatomy of six anterior teeth (canine to canine) was acquired with DVT and digitally reconstructed; b) digital models of the teeth were repositioned to form a standard arch form, c) base holder was designed fi tting the shape of the roots; d) holder and the teeth were manufactured using 3D printing and positioned in the holder where the root compartments were fi lled with silicone.

90 91

parameter “compliance” was observed as a measure of the response of the arch

to the pressure in terms of elasticity, being the inverse of the elastic modulus (K)

according to the following formulas:

K= F/ΔM (1)

where K was the elasticity modulus (GPa), F, the applied force (N), ΔM, change

in movement (mm)

C=1/K (2)

where C was the Compliance and K the elasticity modulus.

The measurements were repeated for three times for each tooth on each model

yielding to 54 measurements.

Statistical analysisData were analyzed using a statistical software package (IBM SPSS Software V.23,

Chicago, IL, USA). Kolmogorov-Smirnov and Shapiro-Wilk tests were used to test

normal distribution of the data. Values of mean, standard deviation, maximum and

minimum were calculated for all teeth in an arch in the two observed conditions

(without and with the retainer) and for each tooth. In order to determine the

dependency of tooth mobility as a function of 1) the use of a retainer, 2) the tooth

position and 3) the repetition, a mixed effects statistical model with nesting was

employed. “Arch” and “individual tooth” were considered as random factors and

“individual tooth” was nested in “arch”. In contrast, “retainer”, “tooth position”

and “repetition” were reflected as fixed factors. Furthermore, the logarithm of

the slopes was taken in the mixed effects model in order not to violate modelling

assumptions. P values less than 0.01 were considered to be statistically significant

in all tests.

RESuLTS

Descriptive statistics results of the compliance derived from the control condition

and with the retainer are presented in Table 1. Overall, the mean value of the

compliance was smaller with the retainer than in the control condition.

The use of retainer showed a significant effect on tooth displacement

(0.008±0.004) compared to non-bonded teeth (control) (0.014±0.009)(p<0.0001).

Tooth displacement was measured using custombuilt optoelectronic motion

tracking device (OPTIS, University of Zurich, Switzerland) based on 3 non-collinear

Charge-coupled device (CCD) cameras (Spectral Instruments, Tuscan, AZ, USA)

recording the movements of Light Emitting Diodes (LEDs) with an accuracy of 5

mm and a sampling rate of 200 Hz. In order to define the position of the object

to be detected, three LEDs are positioned in a fixed triangular shape on a metal

support called Triangular Target Frame (TTF). One TTF was glued to each tooth

and the other to the arch holder through which the relative movement of the

tested tooth was determined. Digital models of the teeth were animated with

the tracked movements by means of a custom-made software application (Figs.

2a-c).

Figs. 2a-c. a) Custom-made device for force application on the lingual surfaces of the teeth on the mandibular arch composed of a metal support in which the arch is aligned with the tooth to be tested and electronically controlled loading mechanism, b) the arch model in its base holding the Triangular Target Frame (TTF) with light emitting diode (LED)s used during the kinematic recording and the conic shaped tip applying force on the selected tooth with the administered force, c) 3 non-collinear charge-coupled device (CCD) cameras used recording the movements of LEDs with an accuracy of 5 μm and a sampling rate of 200 Hz.

The mid-incisal point (IP) of each tooth was marked and its trajectory was

determined. The vector between two subsequent recorded positions of IP was

computed. The relationship between the force and displacement for each tooth

was determined by calculating the linear regression line between the values of

the displacement vector obtained for each tooth at each adminstered force. The

A

C

B

92 93

Table 1: Descriptive statistics of the compliance results regardless of the tooth type and force in all tested mandibular arch models.

Without Bonded Retainer (Control)

With Bonded Retainer

Mean 0.014 0.008

Median 0.013 0.008

Std. Deviation 0.009 0.004

Minimum -0.001 -0.015

Maximum 0.038 0.016

CI Lower Bound 0.011 0.007

CI upper Bound 0.016 0.009

Std. Error 0.001 0.001

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Figures. 3a-b. Displacement (mm) of teeth a) regardless of the tooth type in all mandibular arches tested, b) on the basis of tooth type as a function of incremental force application from 5 to 30 N.

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94 95

30 N is considerably less compared to normal masticatory forces. However, the

linear increase exceeding 30 N was not significant in this study and therefore

the threshold value of 30 N was considered as the highest magnitude of force.

Nevertheless, in this study in none of the cases, debonding or other types of

retainer failures were experienced. In both model scenarios without and with

bonded retainers, the maximum complianc did not exceed 0.038 witout and 0.016

with retainer ndicating that this amount of mobility does not yield to debonding,

providing that some degree of tooth movement could also be dictated by the

flexibility of the wire tested.

Typically, teeth are surrounded by the PDL which is a thin membrane consisting

of collagen fibers. This ligament provides the attachment of the tooth to the

surrounding alveolar bone, and under normal circumstances there is no direct

contact between the root and the bone. Forces applied to the crown of the tooth

are transmitted to the alveolar bone through this layer, stretching, and compressing

the ligament (Van Schepdael et al., 2012). Different cell types, like fibroblasts,

osteocytes and osteoblasts, respond to the changes in mechanical environment.

This biological environment has been tried to be simulated using different

materials in the dental literature. Some authors preferred to simulate the PDL with

polyether (Behr et al., 1999; Rosentritt et al., 2006; Xie et al., 2007; Kolbeck et al.,

2008; Minami et al., 2009), others gum resin (Kern et al., 1994; Chitmongkolsuk

et al., 2002; Attia et al., 2006; Att et al., 2007), latex (Kohorst et al., 2007), wax

(Pfeiffer and Grube, 2003), polysulfide (Grajower et al., 1981) or silicone (Wolfart

et al., 2007). Provatidis (2000) followed the work of Haack and Haft (1972) in

representing the root of a maxillary central incisor as a paraboloid, surrounded by

the ligament. In the analyzed in vitro studies, dipping the roots in these materials

simulated the presence of PDL. This simplistic approach considered neither the

elastic modulus nor the thickness of the used PDL materials. Furthermore, since

lateral displacement forces are dominated with the thickness of the PDL material,

it can be expected that the forces would be unfavourable when PDL is thicker.

In this study, although the tooth morphology varied in the studied sample, in an

attempt to standardize the PDL thickness the clearance between the root surfaces

and the model was maintained at 0.25 mm. A thickness of 0.229 mm was found

to be common on maxillary incisors (Provatidis, 2000). Also, the measurements

were made consecutively in order to avoid the stiffness of the silicone material

over time. Yet, due to the lack of neuromuscular forces silicone PDL could still be

considered as a simplistic approach and therefore can only provide prediction of

tooth displacement in relation to the used retainer or adhesive materials and the

administered force applied.

Although initially no significant difference was expected on the tooth type basis,

interestingly, tooth number 42 showed the highest mean values for compliance.

One possible explanation could be the root morphology of this very tooth

The amount of displacement on the tooth basis was also significantly different

(p=0.0381) being the most for tooth no. 42 (without: 0.024±0.01; with:

0.012±0.002) (p=0.0018) (Table 2)

No significant difference was observed between repeated measurements

(p=0.097) and the inceremental magnitude of loading (5-30 N: 0.07±0.01- 0.09

±0.02) (p>0.05) (Figs. 3a-b).

DISCuSSION

This study was undertaken in order to investigate the anterior tooth movement

without and with bonded fixed stainless steel orthodontic retainers under loading

conditions. Based on the results of this study, since the presence of retainer

significantly decreased the tooth mobility, the first hypothesis could be accepted.

However, the increased magnitude of force did not significantly effect the tooth

displacement. Thus, the second hypothesis could be rejected. Displacement

amount was similar in all teeth except for one, namely tooth number 42) and

therefore, the third hypothesis could only be partially accepted.

A number of factors alone or simultaneously cause the failures of bonded

retainers in orthodontics. Since the location, gender, composite type, humidity

control, operator factor could not be disclosed in previously studies (Lie Sam

Foek et al., 2008; Segner and Heinrici, 2000), tooth mobility was of focus in this

study. In an attempt to make a close approximation to the clinical situation, an

ideal mandibular arch model was chosen and the extracted human teeth from

the same patient were positioned accordingly. The association between the

debonding of retainers and tooth mobility was assessed previously on simplified

models where the retainers were adhered to only two teeth set up (Lie Sam Foek

et al., 2009; Paolone et al., 2015). However, the contradictory clinical findings

and the ones obtained from such simplified models, encouraged us to use of a

full segment when studying tooth displacement under loading and stability of

bonded retainers. Furthermore, in an arch model, ‘free wire’ which should be

ideally 2.5 mm in between the buds of resin composite adhered on the tooth

surface allows for more flexibility of the wire compared to simplified models

(Milheiro et al., 2015).

The methodology used in this study proved to be reproducible. Since the models

with the teeth were replicas of the extracted human anterior teeth, the employed

method could be used to study tooth displacement using other bonded retainer

types. In this study, tooth displacement was measured under compression

where the forces were increased by 5 N up to 30 N. Three dimensional tooth

displacement was linearly correlated with the applied force. One can argue that

96 97

AcknowledgementsThe authors acknowledge Mr. A. Trottmann, University of Zurich, Center for

Dental and Oral Medicine, Zürich, Switzerland, for his assistance with the speci-

men preparation, Mr. C. Lüscher for his support with the development of the

custom made device, Mr. S. Erni from the Clinic of Masticatory Disorders, for

his assistance with the analysis, Dr. E. Yetkiner for his assistance during model

preparations, and Dr. D. Widemeier, University of Zurich, Switzerland for his

support with the statistical analysis.

Conflict of interestThe authors did not have any commercial interest in any of the materials used in

this study.

which possibly differed from those of others. Since the clearance values was

standard, the lack of significant difference in terms of compliance could be not be

considered surprising. However, the significantly higher variation of compliance

observed with tooth number 42 raises the question whether root morphology

plays a role in the torsional component of the applied compressive load.

Measurement of tooth movement is a complex procedure and includes translational

and rotational components of motion. In this study, only translations were

quantified and they were linearly related to the force applied with compression

steps of 5 N. It could be estimated that not only the compression but also torsional

forces could be responsible for debonding of retainers. Furthermore, force in this

study was applied at a constant speed and in clinical situations variable speeds

of force may occur during function which may cause debonding of the retainers.

Nevertheless, the analysis of tooth displacement could be instrumental for finite

elements analysis of the stresses at the roots of the teeth with different types of

lingual retainers or adhesives used. The tooth mobility obtained using stainless

steel wires should be compared with those of fiber reinforced retainers where

contradictory clinical results are presented some of which attributes the failures

to the lack of mobility due to the stiffness of the material. The utilized method with

its favourable reproducibility in this study could be instrumental for measurement

of tooth displacement with fiber reinforced composite retainer types.

Conclusions

From this study, the following could be concluded:

1. Mandibular anterior teeth showed less tooth displacement when bonded

with stainless steel wire compared to the non-bonded control group.

2. Tooth displacement varied on the mandibular arch depending on the tooth

type being the highest for tooth number 42 in both bonded and non-bonded

models.

3. Increase in the magnitude of force on the inciso-lingual direction on the teeth,

intermittent from 5 to 30 N did not result in increased tooth displacement and

the simulated model showed reliable reproducibility.

Clinical RelevanceBonded stainless steel lingual retainers in the studied arch model resulted in less

tooth movement compared to non-bonded ones not exceeding the mean value of

0.008. Intermitttent increase of loading from 5 to 30 N did not cause debonding

of the retainer with the tested materials.

98 99

17. Kim TW, Little RM. Postretention assessment of deep overbite correction in Class II Division 2 malocclusion. Angle Orthod 1999;69:175-186.

18. Kohorst P, Herzog T, Borchers L, Stiesch-Scholz M. Load-bearing capacity of all-ceramic posterior four-unit fixed partial dentures with different zirconia frameworks. Eur J Oral Sci 2007;115:161-166.

19. Kolbeck C, Behr M, Rosentritt M, Handel G. Fracture force of tooth-tooth- and implant-tooth-supported all-ceramic fixed partial dentures using titanium vs. customised zirconia implant abutments. Clin Oral Implants Res 2008;19:1049-1053.

20. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008;30:199-204.

21. Lie Sam Foek DJ, Özcan M, Krebs E, Sandham A. Adhesive properties of bonded orthodontic retainers to enamel: stainless steel wire vs fiber-reinforced composites. J Adhes Dent 2009;11:381-390.

22. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. Am J Orthod Dentofacial Orthop 1988;93:423-428.

23. Maltha JC, Kuijpers-Jagtman AM, Von den Hoff JW, Ongkosuwito EM. Relapse revisited-Animal studies and its translational application to the orthodontic office. Semin Orthod 2017 (EPub).

24. Milheiro A, de Jager N, Feilzer AJ, Kleverlaan CJ. In vitro debonding of orthodontic retainers analyzed with finite element analysis. Eur J Orthod 2015;37:491-496.

25. Pandis N, Fleming PS, Kloukos D, Polychronopoulou A, Katsaros C, Eliades T. Survival of bonded lingual retainers with chemical or photo polymerization over a 2-year period: a single-center, randomized controlled clinical trial. Am J Orthod Dentofacial Orthop 2013;144:169-175.

26. Pfeiffer P, Grube L. In vitro resistance of reinforced interim fixed partial dentures. J Prosthet Dent 2003;89: 170-174.

27. Paolone MG, Kaitsas R, Obach P, Kaitsas V, Benedicenti S, Sorrenti E, Barberi F. Tensile test and interface retention forces between wires and composites in lingual fixed retainers. Int Orthod 2015;13:210-220.

28. Provatidis CG. A comparative FEM-study of tooth mobility using isotropic and anisotropic models of the periodontal ligament. Finite element method. Med Eng Phys 2000;22:359-370.

29. Radlanski RJ., Zain ND. Stability of the bonded lingual wire retainer - A study of the initial bond strength. J Orofac Orthop 2004;65:321-335.

30. Rosentritt M, Behr M, Gebhard R, Handel G. Influence of stress simulation parameters on the fracture strength of all-ceramic fixed-partial dentures. Dent Mater 2006;22:176-182.

REFERENCES

1. Al Yami EA, Kuijpers-Jagtman AM, van ‘t Hof MA. Stability of orthodontic treatment outcome: follow-up until 10 years postretention. Am J Orthod Dentofacial Orthop 1999;115:300-304.

2. Attia A. Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns. J. Appl Oral Sci 2010;18:194-200.

3. Attia A, Abdelaziz K, Freitag S, Kern M. Fracture load of composite resin and feldspathic all-ceramic CAD/CAM crowns. J Prosthet Dent 2006;95:117-123.

4. Bearn DR. Bonded orthodontic retainers: a review. Am J Orthod Dentofacial Or-thop 1995;108:207-213.

5. Behr M, Rosentritt, M, Leibrock A, Schneider-Feyrer S, Handel G. In-vitro study of fracture strength and marginal adaptation of fibre-reinforced adhesive fixed partial inlay dentures. J Dent 1999;27:163-168.

6. Blake M, Bibby K. Retention and stability: a review of the literature. Am J Orthod Dentofacial Orthop 1998;114:299-306.

7. Chitmongkolsuk S, Heydecke G, Stappert C, Strub J. Fracture strength of all-ceramic lithium disilicate and porcelain-fused-to-metal bridges for molar replacement after dynamic loading. Eur J Prosthodont Restor Dent 2002;10:15-22.

8. Dahl EH, Zachrisson BU. Long-term experience with direct-bonded lingual retainers. J Clin Orthod 1991;25:619-630.

9. Franzen TJ, Brudvik P, Vandevska-Radunovic V. Periodontal tissue reaction during orthodontic relapse in rat molars. Eur J Orthod. 2013;35:152-159.

10. Geramy A, Retrouvey JM, Sobuti F, Salehi H. anterior teeth splinting after orthodontic treatment: 3D analysis using finite element method. J Dent (Tehran). 2012;9:90-98.

11. Grajower R, Stern N, Zamir S, Kohavi D. Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro. J Prosthet Dent 1981;45:49-51.

12. Haack DC, Haft EE. Ananalysis of stresses in a model of the periodontal ligament. Int J Eng Sci 1972;10: 1093-1106.

13. Heymann GC, Grauer D, Swift EJ Jr. Contemporary approaches to orthodontic retention. J Esthet Restor Dent 2012;24:83-87.

14. Human Research Act (810.30), Art. 2 and 32, Human Research Ordinance (810.301), Art. 30. 2015.

15. Joondeph DR. Retention and relapse. In Graber TM, Vanarsdall R, Vig KWI., eds. Orthodontics, current principles and techniques. 5th ed. Philadelphia: Elsevier Mosby; 2011:991-1019.

16. Kern M, Fechtig T, Strub J. Influence of water storage and thermal cycling on the fracture strength of all-porcelain, resin-bonded fixed partial dentures. J Prosthet Dent 1994;71:251-256.

31. Rossouw PE. Terminology: semantics of postorthodontic treatment changes in the dentition. Semin Orthod 1999;5:138-141.

32. Segner D, Heinrici B. Bonded retainers-clinical reliability. J Orofac Orthop 2000;61:352-358.

33. Shah AA. Postretention changes in mandibular crowding: a review of the literature. Am J Orthod Dentofacial Orthop 2003;124:298-308.

34. Vaden JL, Harris EF, Gardner RL. Relapse revisited. Am J Orthod Dentofacial Orthop 1997;111:543-553.

35. Van Schepdael A, Geris L, Van der Sloten J. Analytical determination of stress patterns in the periodontal ligament during orthodontic tooth movement. Med Eng Phys 2013;35:403-410.

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37. Xie Q, Lassila L, Vallittu P. Comparison of load-bearing capacity of direct resin-bonded fiber-reinforced composite FPDs with four framework designs. J Dent 2007;35:578-582.

38. Zachrisson BU. Multistranded wire bonded retainers: from start to success. Am J Orthod Dentofacial Orthop 2015;148:724-727.

101 100

Chapter 7

General discussion and clinical implications

104 105

the literature.6 However, before undertaking any clinical trials, more information

was targetted to be collected for adhesion and fatigue properties of such retainer

materials and compare their performance with the golden standard, stainless steel

wires.7 Interestingly however, adhesion results did not differ significantly between

any of the FRCs tested and the stainless steel wire when the wire was applied in

the bed of flowable resin and covered with flowable resin again.8 This indicated

that the amount of resin composite on the stainless steel wire was sufficient to

provide adequate adhesion. Nevertheless, failure types showed different trends

among the tested retainer materials, namely the stainless steel resulted in partial

debondings with less than half of the composite left on the enamel surface. On

the other hand, FRCs showed failures where more composite was left adhered

or more cohesive failures within the retainer material. This indicated in part the

limited flexibility of the FRC compared to the metal wires.

Such results highlighted the importance of interpretation of failure types rather

than evaluating the bond strength only. It was however still not clear whether

hydrothermal aging would be sufficient to simulate aging between wire-resin-

tooth interfaces. Therefore, the adhesion behaviour of the tested retainers

was further investigated under fatigue conditions where they were exposed to

100.000 cycles of fatigue at 37 °C in water.9 Fatigue cycling however, did not

show debonding of retainers. Hence, they were subsequently loaded until failure.

The results showed no significant difference in debonding force regardless of the

retainer type. Though, again failure types varied in that the stainless steel wire

showed higher incidence of cohesive failures in the overlying resin composite

followed by complete adhesive failure. On the contrary, E-glass (Angelus) and

S2 glass (Dentapreg) resulted in mainly complete adhesive detachment meaning

that adhesion was not favourable with these fibers. Polyethylene FRC on the

other hand, showed rather adhesive failures or FRC fractures both of which could

be considered unfavourable in clinical situations. In addition, PMMA impregnated

E-glass (Everstick) presented also complete adhesive or partial detachment of

resin composite, which was a low viscous one (Tetric Flow). Basically, none of

the retainer materials showed complete durability and most likely the flexibility

of the wire resulted in less complete debondings. However, the model employed

in this study consisted of only two teeth and in fact, in an arch segment different

force distribution could be expected. Since only flowable composite was used

in this study, it was also thought that the resin composite type could affect the

debonding rate of stainless steel retainers.

In order to answer this question, 150 retainers bonded using 2 hybrid and one

flowable resin composite were observed in a private practice setting.10 Similar to

the above-mentioned study at the university setting, also in this study multiple

operators were involved and no significant difference between the factors of age,

gender, location, and operators were noted. Although the use of flowable resin

GENERAL DISCuSSION AND FuTuRE PERSPECTIVES

This thesis evaluated several aspects of the clinical problem related to debonding

of bonded retainers used in orthodontics with a particular emphasis on retainer

material properties, adhesive resins and application modes of retainers.

Clinical problem – Retainer DebondingWithout a phase of retention, the teeth tend to relapse towards their initial

position after completion of the orthodontic treatment.1,2 Thus, durable retention

of the retainers are crucial in maintaining the achieved results. The objectives

of this thesis was initiated as a consequence of recognition of high incidence

of retainer debondings both based on the reports in the literature and our own

observations at the University of Groningen, Department of Orthodontics. Since

the stainless steel retainers were bonded with multiple operators and dental

hygienists at the university settings, it was anticipated that the operator factor

could be one factor affecting the incidence of such failures. Using the historic

cohort available, 277 patient recordings were retrospectively investigated with

the outcome measure of retainer debonding in an attempt to gain an overview

on possible factors affecting retainer debondings under the conditions when the

same retainer material (multi-stranded stainless steel wire) and adhesives were

used.3 Similar to previous findings, our results also indicated that most failures

occurred within the first 6 months and the gender and age did not affect the

failure incidence. Opposite to the expectations, operator factor was also disclosed

in failure incidence. However, 37% of failures already in a mean observation time

of 41 months were discouraging and created the need for the analysis of other

possible factors in these types of failures.

Adhesion and material perspectivesThe clinical problem of retainer debonding with stainless steel wires was expected

to be solved after the introduction of fiber reinforced composites (FRC) as retainer

materials in orthodontics.4 FRCs allow for larger bonding surface and that there

is more chemical adhesion of the resin composite to the FRC as opposed to the

stainless steel wires where mainly mechanical retention is present. At the early

phase of this thesis and soon after the introduction of FRC retainers in our clinic,

some cases were treated using FRC retainers of various kinds. It was however,

soon recognized that the application modes differed significantly between the

FRC products and that there were no guidelines available for practitioners.

Furthermore, while some FRC materials were readily preimpregnated with a

monomer resin, others had to be silanized and impregnated by the operator at

chairside which could affect their mechanical properties.5 Mechanical properties

due to fiber orientation and volume were mentioned in favour of glass FRCs in

106 107

stranded stainless steel wires should still be preferred over the use of FRC ones.

Starting with humidity control, slight enamel preparation in order to remove

the aprismatic enamel, calibration of the operators for adhesion protocols to be

employed, weekly controls of the output of the photo-polymerization devices, the

use of highly filled hybrid resin composites would most likely maximize the survival

of bonded orthodontic retainers. Since of the retainer debondings mostly occur

within the first 6 months after completion of the orthodontic treatment, strict

follow up of the patients is essential and therefore patients should be reimbursed

by the health care systems. Furthermore, clinical follow up studies should report

on more detailed information on failure location and types on the tooth and arch-

basis. Likewise, accurate methods should be developed for the measurement of

tooth displacement and possible associated simultaneous forces in vivo.

composite showed slightly higher incidence of retainer debondings, no significant

difference was found between resin composite materials during the follow up

period. The flowable resin used in this study was highly filled (62 v%) which

might have affected the results being more in favour of the one (Tetric Flow) used

in university settings presented in this thesis.10

Nevertheless, in a mean observation time of 43 months, 19.7% failures with

the vast majority occurring within the first 6 months indicated that retainer

debonding problem is not a consequence of material choice and perhaps more

related to post-treatment tooth displacement resulting in more tension between

the retainer-resin-tooth complex.

Tooth displacement- a reason for debonding?The use of multistranded wires was postulated to reduce the individual mobility

of the bonded teeth while maintaining physiologic mobility.11 On the contrary, with

the FRC materials, less mobility of teeth and thereby less incidence of retainer

debondings were expected. In the meantime, clinical studies reporting on the

survival of FRC retainers demonstrated survival of 49% in 2 years4, 79% in 1

year12,13 and 79.6% in 6 years.14 These figures clearly show that the debonding

problem is not completely resolved even with the use of FRC materials. Thus,

the most likely governing factor for retainer debonding was estimated to be the

tooth displacement after immediate orthodontic treatment. The amount of tooth

displacement was measured using 3D analysis where triangular target frames

and optoelectronic motion tracking device was employed. Based on the results,

mandibular anterior teeth showed less tooth mobility when bonded with stainless

steel wire compared to the non-bonded control group. The experimental model

showed very good reproducibility which could be used15 for further investigations

on tooth displacement in conjunction with FRC materials.

Concluding remarks and clinical implicationsThe results of a series of investigations and the clinical studies presented in this

thesis, clearly indicates that the retainer debonding in orthodontics is an unsolved

problem which occurs in a considerably short follow up time. Early observations

of debondings could not be related to fatigue related phenomena. In spite of

the fact that multiple factors have been attributed to the cause of this clinical

problem, in this thesis, at least several aspects such as age, gender, operator,

resin composite type could be disclosed.

Biological simulation of tooth displacement is a difficult task in laboratory

settings but future studies would focus on the parameter of tooth displacement

accompanied with rotational and torsional forces also involving differences in root

morphologies.

Based on the results obtained in this thesis and the available literature, multi-

108 109

REFERENCES

1. Al Yami EA, Kuijpers-Jagtman AM, van ‘t Hof MA. Stability of orthodontic treatment outcome: follow-up until 10 years postretention. Am J Orthod Dentofacial Orthop 1999;115:300-304.

2. Joondeph DR. Retention and relapse. In Graber TM, Vanarsdall R, Vig KWI., eds. Orthodontics, current principles and techniques. 5th ed. Philadelphia: Elsevier Mosby; 2011:991-1019.

3. Lie Sam Foek DJ, Özcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008:30:199-204.

4. Rose E, Frucht S, Jonas IE. Clinical comparison of a multistranded wire and a direct-bonded polyethylene ribbon reinforced resin composite used for lingual retention. Quintessence Int 2002;33:579-83.

5. Freilich MA, Karmaker AC, Burstone CJ, Goldberg AJ. Development and clinical applications of a light-polymerized fiber-reinforced composite. J Prosthet Dent 1998;80:311-318.

6. De Boer J, Vermilyea SG, Brady RE. The effect of carbon fiber orientation on the fatigue resistance and bending properties of two denture resins. J Prosthet Dent 1984;51:119-121.

7. Bearn DR. Bonded orthodontic retainers: a review. Am J Orthod Dentofacial Or-thop 1995;108:207-213.

8. Lie Sam Foek DJ, Özcan M, Krebs E, Sandham A. Adhesive properties of bonded orthodon-tic retainers to enamel: stainless steel wire vs fiber-reinforced composites. J Adhes Dent 2009;11:381-390.

9. Lie Sam Foek DJ, Yetkiner E, Özcan M. Fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers in vitro. Korean J Orthod. 2013;43:186-192.

10. Lie Sam Foek DJ, Feilzer AJ, Özcan M. Clinical survival of multi-stranded stainless steel bonded lingual retainers as a function of resin composite type: Up to 3.5 years follow-up. (Unpublished data)

11. Zachrisson BU. Multistranded wire bonded retainers: From start to success. Am J Orthod Dentofacial Orthop 2015;148:724-727.

12. Sobouti F, Rakhshan V, Saravi MG, Zamanian A, Shariati M. Two-year survival analysis of twisted wire fixed retainer versus spiral wire and fiber-reinforced composite retainers: a preliminary explorative single-blind randomized clinical trial. Korean J Orthod 2016;46:104-110.

13. Scribante A, Sfondrini MF, Broggini S, D’Allocco M, Gandini P. Efficacy of esthetic retainers: clinical comparison between multistranded wires and direct-bond glass fiber-reinforced composite splints. Int J Dent 2011;548356.

14. Bolla E, Cozzani M, Doldo T, Fontana M. Failure evaluation after a 6-year retention period: a comparison between glass fiber-reinforced (GFR) and multistranded bonded retainers. Int Orthod 2012;10:16-28.

15. Chakroun F, Colombo V, Lie Sam Foek DJ, Gallo L, Feilzer AJ, Özcan M. Displacement of teeth without and with bonded fixed orthodontic retainers: 3D analysis using triangular tar-get frames and optoelectronic motion tracking device. (Unpublished data).

Chapter 8

Summary

112 113

Specimens were thermocycled for 6000 cycles between 5-55°C and loaded in

a universal testing machine under shear stress (crosshead speed: 1 mm/min)

until debonding occurred. The failure sites were examined under an optical light

microscope. Significant differences were found between the groups (p = 0.0011).

Bond strength results did not significantly differ neither between the FRC groups

(Groups 1-4) (6.1±2.5 to 8.4±3.7 MPa) (p > 0.05) or the wire groups (Groups

5-8) (10.6±3.8 to 14±6.7 MPa) (p > 0.05). Failure types varied within the FRC

groups, but mainly composite was found left adhered on the enamel surface

at varying degrees. In the stainless steel wire groups, when the retainer was

applied onto the bonding agent and then covered with flowable resin, partially

attached composite on the enamel was often found after debonding. When the

wires were embedded in the flowable composite, the Heliobond group (Group

8) showed more adhesive failures between the enamel and the composite

compared to Group 5, where bonding agent was Stick Resin. Regardless of their

application mode, stainless steel orthodontic bonded retainers delivered higher

bond strengths than those of fiber retainers. The differences were statistically

significant compared to those of Angelus Fibrex Ribbon and DentaPreg Splint.

The aim of Chapter 4 was to analyze the fatigue resistance, debonding force, and

failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and

braided stainless steel wire lingual retainers in vitro. Roots of human mandibular

central incisors were covered with silicone, mimicking the periodontal ligament,

and embedded in polymethylmethacrylate. The specimens (N = 50), with two

teeth each, were randomly divided into five groups (n = 10/ group) according

to the retainer materials: (1) Interlig (E-glass), (2) everStick Ortho (E-glass), (3)

DentaPreg Splint (S2-glass), (4) Ribbond (polyethylene), and (5) Quad Cat wire

(stainless steel). After the recommended adhesive procedures, the retainers

were bonded to the teeth by using flowable composite resin (Tetric Flow). The

teeth were subjected to 10,00,000 cyclic loads (8 Hz, 3 - 100 N, 45o angle,

under 37 ± 3°C water) at their incisoproximal contact, and debonding forces

were measured with a universal testing machine (1 mm/min crosshead speed).

Failure sites were examined under a stereomicroscope (×40 magnification). All

the specimens survived the cyclic loading. Their mean debonding forces were

not significantly different (p > 0.05). The DentaPreg Splint group (80%) showed

the highest incidence of complete adhesive debonding, followed by the Interlig

group (60%). The everStick Ortho group (80%) presented predominantly partial

adhesive debonding. The Quad Cat wire group (50%) presented partial overlying

composite detachment. Cyclic loading did not cause debonding. The retainers

presented similar debonding forces but different failure types. Braided stainless

steel wire retainers presented the most repairable failure type.

In Chapter 5, in a prospective clinical trial the survival of multi-stranded stainless

steel lingual retainers (SSR) bonded using different resin composite types was

The debonding of bonded orthodontic retainers is one of the most frequently

reported failure type in orthodontics as a consequence of multiple reasons. This

thesis was conducted in an attempt to identify some of the possible factors

causing the failure of bonded orthodontic retainers.

The objectives of the retrospective clinical study in Chapter 2 were to evaluate the

clinical survival rate of flexible, braided, rectangular bonded stainless steel lingual

retainers, and to investigate the influence of gender, age of the patient, and

operator experience on survival after orthodontic treatment at the Department

of Orthodontics, University of Groningen, between the years 2002 and 2006.

The study group comprised of 277 patients (162 females: median age 14.8 years

and 115 males: median age 15.3 years). Data concerning, failures, gender, age

of the patient, and operator experience were retrieved from the patient files that

were updated by chart entries every 6 months or when failure was reported by

the patient. The maximum follow-up period was 41.7 months. All 277 patients

received flexible, braided, bonded mandibular canine-to-canine retainers. A failure

was recorded when there was debonding, fracture, or both, occurring in one arch.

Eighteen failures were observed in the maxilla. Only first failures were used for

statistical analysis. Ninety-nine debonding (35.7%), two fractures (0.7%), and four

debonding and fracture (1.4%) events were observed. No significant effect (P

> 0.05) of gender (females: 41%, males: 32%) or patient age (<16 years: 37%,

≥ 16 years 38.7%) was observed. The failure rate did not differ due to operator

experience (n = 15; less experienced: 38.0%; moderately experienced: 28.9%,

professional: 46.7%; P > 0.05). Kaplan- Meier survival curves showed a 63%

success rate for the bonded lingual retainers over a 41.7 month period.

In Chapter 3 the bond strength of a stainless steel orthodontic wire was

compared versus various fibre-reinforced-composites (FRC) used as orthodontic

retainers on enamel, analyze the failure types after debonding and to investigate

the influence of different application procedures of stainless steel wires on

bond strength. Caries-free, intact human mandibular incisors (N=80, n=10 per

group) were selected and randomly distributed into 8 groups. After etching with

37% H3PO4 for 30 seconds, rinsing and drying, bonding agent (Stick Resin) was

applied, light polymerized and one of the following FRC materials were applied

on the flowable composite (Stick Flow) using standard molds: Group 1: Angelus

Fibrex Ribbon; Group 2: DentaPreg Splint; Group 3: everStick Ortho and Group

4: Ribbond. In Group 5, Quad Cat Wire was applied in the same manner as in

FRC groups. In Group 6, after bonding agent (Stick Resin), Quad Cat Wire was

placed directly on the tooth surface and covered with Stick Flow composite. In

Group 7, after bonding agent (Heliobond) was applied, Quad Cat Wire was placed

directly on the tooth surface and covered with Tetric Flow composite. In Group 8,

after applying bonding agent (Heliobond), Tetric Flow composite was applied, not

polymerized and Quad Cat Wire was placed and covered with Tetric Flow again.

114 115

was tested for tooth mobility by applying force increasing from 5 to 30 N with 5 N

increments applied perpendicular on the lingual tooth surface on the incisal one

third (crosshead speed: 0.1 mm/s). The teeth on each model were first tested

without retainer (control) and subsequently with the bonded retainers (braided

bonded retainer wire; Multi-strand 1x3 high performance wire, 0.022” x 0.016”).

Tooth displacement was measured in terms of complicance (F/Δ movement) (N/

mm) using custombuilt optoelectronic motion tracking device (OPTIS) (accuracy:

5 mm; sampling rate: 200 Hz). The position of the object was detected through

three LEDs positioned in a fixed triangular shape on a metal support (Triangular

Target Frame). The measurements were repeated for three times for each tooth.

The use of retainer showed a significant effect on tooth mobility compared to

non-bonded teeth (control) (p<0.0001). The amount of displacement on the tooth

basis was also significantly different (p=0.0381) being the most for tooth no. 42

(without: 0.024±0.01; with: 0.012±0.002) (p=0.0018).

evaluated. Between April 2011 and March 2013, a total of 75 patients (40 women,

35 men; mean age: 16.3 years old) received full arch orthodontic treatment after

which SSRs (Multi-strand 1 x 3 high performance wire, 0.022” x 0.016”, PG

Supply Inc.) (N=150) were bonded in the maxilla and/or mandible on all 6 anterior

teeth. After etching enamel surfaces with 35% H3PO4, adhesive resin was

applied (Clearfil SE Bond) and photo-polymerized for 20 s. SSRs were bonded

using one of the following resin composites: a) Hybrid (Clearfil AP-X, Kuraray

Noritake) (H1), b) Hybrid (Light Cure Retainer, Reliance Orthodontic Products Inc.)

(H2), c) Flowable (Clearfil Majesty Flow, Kuraray) (FL). At baseline and thereafter

at 1, 2, 3, 6, 12 and 24 months, SSRs were checked upon macroscopically for

partial or complete debonding or fracture. SSRs were scored as failed if any

operative intervention was indicated for repair, partial or total replacement.

SSRs were observed for a minimum of 6, and maximum 43 months (mean: 19.5

months). At the final control (24 months), 10 patients could not be followed up

(H1: 12, H2: 4, FL: 4) due to drop out. In total, in 150 SSRs, 28 failures were

observed (n=19 in the maxilla, n=9 in the mandible). The majority of the failures

were observed with FL (n=12), followed by H1 (n=8) and H2 (n=8) being not

statistically significant (maxilla: p=0.133; mandible: p=0.551). Overall, 3 fractures

of the SSR were observed all of which were in the maxilla. In total, cumulative

survival rate was 81.3% up to 43 months (Kaplan-Meier). Location of the SSRs

did not show significant difference (maxilla: 74.7%, and mandible: 88%) (p>0.05).

No significant difference was observed between gender type (female: 78.8%;

male: 81.3%) (p=0.059). Although microhybrid flowable resulted in slightly more

frequent incidence of failures, the type of composite, the location and the gender

did not significantly affect the clinical survival of multi-stranded stainless steel

bonded lingual retainers in the studied sample.

In Chapter 6 the objective was to evaluate the anterior tooth movement without

and with bonded fixed orthodontic retainers under incremental loading conditions.

Six extracted mandibular anterior human teeth were embedded in acrylic resin

in True Form I Arch type and 3D reconstruction of Digital Volume Tomography

(DVT) images (0.4 mm3 voxels) were obtained. The anatomy of each tooth was

segmented and digitally reconstructed using 3D visualization software for medical

images (AMIRA, FEI SVG). The digital models of the teeth were repositioned

to form an arch with constant curvature using a CAD software (Rhinoceros)

and a base holder was designed fitting the shape of the roots. The clearance

between the roots and their slot in the holder was kept constant at 0.3 mm

to replicate the periodontal ligament thickness. The holder and the teeth were

then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a resin

material for dental applications (E=2-3 GPa). The 3Dprinted teeth models were

then positioned in the holder and the root compartments were filled with silicone.

The procedure was repeated to obtain three identical arch models. Each model

Chapter 9

Samenvatting

118 119

Flow) waarbij gebruik gemaakt werd van gestandaardiseerde mallen: Groep 1:

Angelus Fibrex Ribbon; Groep 2: DentaPreg Splint; Groep 3: everStick Ortho and

Groep 4: Ribbond. In Groep 5, werd Quad Cat draad op dezelfde manier als in de

FRC-groepen vastgeplakt. In Groep 6 werd, na het appliceren van een bonding

agent (Stick Resin), Quad Cat draad direct op het tandoppervlak geplaats, waarna

deze werd bedekt en vastgezet met Stick Flow composiet. In Groep 7 werd, na

het appliceren van een bonding agent (Heliobond), Quad Cat draad direct op het

tandoppervlak geplaatst, waarna deze werd bedekt en vastgezet met Tetric Flow

composiet. In Groep 8 werd, na het appliceren van een bonding agent (Heliobond),

het tandoppervlak eerst bedekt met een laag van Tetric Flow composiet doch nog

niet uitgehard. Vervolgens werd het Quad Cat draad geplaats, waarna er opnieuw

een laag Tetric Flow overheen werd geplaatst en uitgehard. De proefmonsters

ondergingen vervolgens een thermische veroudering van 6000 cycli tussen

5-55°C, waarna zij werden belast door een universal testing machine onder schuif

krachten (1 mm/min) tot dat debonderig optrad. Alle mislukkingen werden onder

een optische licht microscoop bekeken en geanalyseerd. Significante verschillen

werden gevonden tussen de verschillende groepen (p = 0.0011). Resultaten

met betrekking tot de hechtsterkte verschilden niet significant tussen de FRC-

groepen (Groepen 1-4) (6.1±2.5 to 8.4±3.7 MPa) (p > 0.05) en de draad groepen

(Groepen 5-8) (10.6±3.8 to 14±6.7 MPa) (p > 0.05). De mislukkingen varieerden

in de FRC-groepen, waar voornamelijk alleen composiet in verschillende mate

gefixeerd aan het glazuur gevonden is. In de roestvrijstalen draad groepen,

waarbij de draad spalk direct op de bonding agent geplaatst werd en waarna

deze afgeplakt werd met een flowable composiet werd veelal gedeeltelijke

composiet breuk waargenomen. Wanneer de draad spalken na het appliceren

van een bonding agent in een bedje van flowable composiet werden geplaatst

en vervolgens weer afgedicht werden met dezelfde composiet, de Heliobond

groep (Group 8) werden meer adhesieve mislukkingen tussen het glazuur en de

composiet waargenomen dan in vergelijking met Groep 5, waar de bonding agent

Stick Resin was. Ongeacht de applicatie methode vertoonden de roestvrijstalen

draad spalken de grootste hechtsterkte waarden in vergelijking met de FRC’s.

De verschillen bleken statistisch significant in vergelijking met de groepen van

Angelus Fibrex Ribbon and DentaPreg Splint.

In Hoofdstuk 4 werd de verouderingsresistentie, debondeer kracht en type

mislukkingen van glasvezel versterkte composieten en gevlochten roestvrijstalen

retentie spalken in vitro onderzocht. De radices van humane, mandibulaire

centrale incisieven werden bedekt met een flinterdun siliconen laag, teneinde

het parodontaal ligament na te bootsen en waarna deze ingebed werden in

polymethylmethacrylate. De test monsters (N = 50), elk met 2 incisieven,

werden gerandomiseerd verdeeld in vijf groepen (n = 10/ groep) aan de hand

van het retainer materiaal: (1) Interlig (E-glass), (2) everStick Ortho (E-glass), (3)

Het debonderen van orthodontische retentie spalken is een veel voorkomend

en ruim beschreven probleem, waarbij gedacht wordt dat de mogelijke oorzaak

multifactorieel van aard is. Het doel van het onderzoek dat onderwerp is van

dit proefschrift, is om mogelijke factoren met name vanuit materiaalkundig

perspectief, die voor het debonderen van deze retentie spalken zorgen te

identificeren.

In Hoofdstuk 2 wordt retrospectief gekeken naar het klinische succespercentage

van flexibele, gevlochten, rechthoekige, roestvrijstalen retentie spalken en

de invloed van geslacht, leeftijd van de patiënt en ervaring van de operateur

in relatie tot het succespercentage aan Afdeling Orthodontie, Universiteit van

Groningen, van patiënten behandeld tussen 2002 en 2006. De onderzoeksgroep

bestond uit 277 patiënten (162 meisjes: met een gemiddelde leeftijd van 14.8

jaar en 115 jongens: met een gemiddelde leeftijd van 15.3 jaar). Alle benodigde

gegevens inzake het debonderen, geslacht, leeftijd van de patiënt en ervaring

van de operateur is verkregen uit de patiëntenkaarten welke om de zes maanden

bijgewerkt werden of wanneer er een debond plaatsvond. De maximale follow-

up periode bedroeg 41.7 maanden. Alle 277 patiënten kregen een retentie spalk

in de onderkaak, welke van de hoektand tot de hoektand liep en welke op alle

elementen van het onderfront bevestigd was. Een faalmoment of mislukking

werd gescoord wanneer er een debonding, draadbreuk of een combinatie

van één van deze optrad. Achttien faalmomenten werden geobserveerd in de

maxilla. Alleen het eerste moment van mislukking werd gescoord en gebruikt

voor de statistische analyse. Negenennegentig debonderingen (35.7%), twee

draadbreuken (0.7%), en vier mislukkingen met een combinatie van beide (1.4%)

werden geobserveerd. Geen significant effect (P > 0.05) voor leeftijd (meisjes:

41%, jongens: 32%), patiënten leeftijd (<16 jaar: 37%, ≥ 16 jaar 38.7%) werd

geobserveerd. Het percentage voor falen van een retentie spalk bleek ook voor de

ervaring van de operateur niet significant te zijn (n = 15; weinig ervaring: 38.0%;

gemiddelde ervaring: 28.9%, professional: 46.7%; P > 0.05). Kaplan- Meier

overleving curves weergaven een succespercentage van 63% voor gefixeerde

linguale retentie spalken weer over een periode van 41.7 maanden.

In Hoofdstuk 3 is de hechtsterkte van roestvrijstalen retentie spalken vergeleken

met verschillende glasvezel versterkte composieten (FRC), welke als retentie

spalk op glazuur zijn geplakt en vervolgens geanalyseerd op het faal type.

Tevens is er ook gekeken naar de invloed van verschillende applicatie methoden

van roestvrijstalen retentie spalken en hun hechtsterkte. Intacte, cariës-vrije,

humane mandibulaire incisieven (N=80, n=10 per groep) werden geselecteerd

en gerandomiseerd verdeeld in acht groepen. Na etsen met 37% H3PO4 voor

30 seconden, spoelen en drogen, werd er een bonding agent (Stick Resin)

geappliceerd, met behulp van licht uitgehard en vervolgens werd één van de

volgende FRC materialen geplakt op een bedje van flowable composiet (Stick

120 121

DentaPreg Splint (S2-glass), (4) Ribbond (polyethylene), en (5) Quad Cat wire

(roestvrij staal). Na de geadviseerde adhesieve procedure, werden de retainers

geplakt op de tanden met een flowable composiet (Tetric Flow). De monsters

ondergingen vervolgens cyclische belasting van 10,00,000 (8 Hz, 3 - 100 N, 45o

hoek, onder 37 ± 3°C water). Aan hun incisoproximale contactpunt, werden de

debonding krachten gemeten met een universal testing machine (1 mm/min

crosshead speed). De exacte locaties en type mislukkingen werden beoordeeld

met behulp van een stereomicroscoop (×40 vergroting). Alle monsters

overleefden de cyclische belasting. De gemiddelde debondeer krachten bleken

niet significant te verschillen (p > 0.05). De DentaPreg Splint groep (80%)

vertoonde het meeste aantal complete adhesieve debonderingen, gevolgd door

de Interlig groep (60%). De everStick Ortho groep (80%) vertoonde voornamelijk

partiële adhesieve debonderingen. De Quad Cat draad groep (50%) vertoonde

voornamelijk het gedeeltelijk losraken van het overliggende composiet. Cyclische

belasting resulteerde niet in debonderingen. De retainers presenteerden allemaal

vergelijkbare debondeer krachten, maar verschillende typen mislukkingen. De

roestvrijstalen retentie spalken vertoonden de meest eenvoudig te repareren

mislukkingen.

In Hoofdstuk 5, is prospectief de levensduur van de roestvrijstalen, gevlochten,

draad retentie spalken (SSR) klinisch onderzocht aan de hand van verschillende

typen composiet. Van april 2011 tot en met maart 2013 kregen in totaal 75

patiënten, (40 meisjes, 35 jongens; gemiddelde leeftijd: 16.3 jaar oud) na

behandeld te zijn met volledige, vaste orthodontische apparatuur, een linguale

retentie spalk in zowel de boven- als de onderkaak. Zowel in de bovenkaak als de

onderkaak werd de retentie spalk SSRs (Multi-strand 1 x 3 high performance wire,

0.022” x 0.016”, PG Supply Inc.) (N=150) op alle 6 anterieure tanden geplakt. Na

het etsen van de glazuur oppervlakken met 35% H3PO4, werd bonding geplaatst

(Clearfil SE Bond) en met behulp van licht uitgehard voor 20 s. Alle SSRs werden

hierna vastgeplakt met één van de volgende composieten: a) Hybrid (Clearfil AP-

X, Kuraray Noritake) (H1), b) Hybrid (Light Cure Retainer, Reliance Orthodontic

Products Inc.) (H2), c) Flowable (Clearfil Majesty Flow, Kuraray) (FL). Vanaf T=0 en

hierna, 1, 2, 3, 6, 12 en 24 maanden, werden de SSRs klinisch beoordeeld op partiële

of complete debonderingen of op draadfractuur. Een SSRs werd als mislukking

gescoord wanneer er (reparatieve) interventie nodig was, bij het zij partiële of

totale vervanging en reparatie. Alleen eerste mislukkingen werden gescoord. Alle

SSRs werden ten minste zes maanden en maximaal 43 maanden na plaatsing

gevolgd en beoordeeld (gemiddelde observatie tijd: 19.5 maanden). Bij de finale

controlegroep (24 maanden), konden 10 patiënten niet vervolgd worden (drop-

outs) (H1: 12, H2: 4, FL: 4). In totaal, werden bij de 150 SSRs, 28 mislukkingen

waargenomen (n=19 in de bovenkaak, n=9 in de onderkaak), waarbij de meeste

mislukkingen geobserveerd werden in de FL groep (n=12), gevolgd door de H1

groep (n=8) en tot slot de H2 groep (n=8). Al deze mislukkingen bleken statistisch

niet significant (bovenkaak: p=0.133; onderkaak: p=0.551). Over het geheel

werden drie draadbreuken van de SSR’s waargenomen, welke allemaal in de

bovenkaak voorkwamen. Het totale, cumulatieve overlevingspercentage bedroeg

81.3% voor een totale periode van 43 maanden (Kaplan-Meier). De locatie van de

SSRs bleek niet significant te verschillen (bovenkaak: 74.7%, en onderkaak: 88%)

(p>0.05). Zo werd ook geen statistische significantie waargenomen voor het

geslachtstype en leeftijd (meisjes: 78.8%; jongens: 81.3%) (p=0.059). Hoewel

de microhybride flowable composiet net iets meer mislukkingen vertoonde,

bleek ook het verschil in gebruikte composiet types de klinische levensduur van

gevlochten roestvrijstalen retentie spalken niet significant te beïnvloeden.

Het doel van Hoofdstuk 6 was om de mate van anterieure tand verplaatsing

in of zonder de aanwezigheid van een retentie spalk onder dezelfde condities

te onderzoeken. Zes geëxtraheerde, humane mandibulaire snijtanden en

hoektanden werden in een acrylhars ingebed. Vervolgens werden deze modellen

3D gereconstrueerd met behulp van Digital Volume Tomography (DVT), waarna

hier foto’s (0.4 mm3 voxels) van zijn vervaardigd. De anatomie van elk element

werd gesegmenteerd en digitaal gereconstrueerd middels 3D visualisatie

software voor medische foto’s (AMIRA, FEI SVG). De hieruit verkregen digitale

informatie van deze zes elementen werd volgens een in de orthodontie veel

voorkomende boogvorm, de True Form I Arch type, gepositioneerd en met

behulp van CAD software (Rhinoceros) werd er een zogenaamde basishouder

vervaardigd. De exacte en hierbij horende inclinatie en angulatie van de radices

werd hierin geprogrammeerd. Er werd een vaste vrije ruimte rondom elke radix

en de basishouder (0.3 mm) gecreëerd. Zowel de houder als de elementen

werden vervaardigd met behulp van 3D printing (Object Eden 260VS, Stratasys),

waarbij gebruik gemaakt is van materiaal voor tandheelkundige doeleinden.

(Clear Biocompatible, MED 610, Stratasys, Commerce Way Eden Prairie) (E=2-

3 GPa). Vervolgens werden de 3D geprinte elementen geplaatst in de houder

en werd de vrije ruimte tussen de houder en de elementen met siliconen

opgevuld met als doel het parodontaal ligament na te bootsen. De procedure

werd in totaal drie keer herhaald onder exact dezelfde condities. Elk model

werd getest op tandverplaatsing waarbij elke tand onderworpen werd aan

krachten variërend tussen de 5 tot 30 N en waarbij er elke keer stappen van

5 N werden aangebracht perpendiculair aan de linguale tandoppervlakken van

het incisaal 1/3 deel van de tand (crosshead speed: 0.1 mm/s). De elementen in

het model werden eerst getest zonder de aanwezigheid van een retentie spalk

(controlegroep) en vervolgens met een retentie spalk (braided bonded retainer

wire; Multi-strand 1x3 high performance wire, 0.022” x 0.016”, PG Supply Inc. Avon, Connecticut, U.S.A). Tandverplaatsing werd gemeten met behulp van een

specifiek hiervoor vervaardigde optoelectronische, bewegingvolgend apparaat

122 123

(OPTIS) (nauwkeurigheidsgraad: 5 mm; sampling rate: 200 Hz). Hierbij werd de

positie van het element met behulp van drie LEDs, welke triangulair gefixeerd

waren aan een metalen standaard, gemeten. Alle metingen werden voor elk

model en voor elk element in drievoud herhaald. Het gebruik van een retentie

spalk vertoonde een significant effect op tandverplaatsing (0.008±0.004),

in vergelijking met de modellen zonder een retentie spalk (controlegroep)

(0.014±0.009) (p<0.0001). Het verschil in tandverplaatsing bij de basis van de

elementen bleek ook statistisch significant te zijn (p=0.0381), waarbij dit het meest

gold voor tand nummer 42 (zonder retentie spalk: 0.024±0.01; met retentie spalk:

0.012±0.002) (p=0.0018). Er werd statistisch geen verschil gevonden tussen

de herhaalde metingen(p=0.097) en het stapsgewijs verhogen van de kracht

(5-30 N: 0.07±0.01- 0.09±0.02) (p>0.05). Het mandibulair onderfront segment,

bestaande uit snijtanden en hoektanden vertoonde een verminderde mate van

tandverplaatsing wanneer er een retentie spalk van roestvrijstaal werd gebruikt

in vergelijking met de elementen waarbij er geen retentie spalk werd gebruikt.

Echter varieerde de mate van tandverplaatsing per element type en bleek een

verhoging van de kracht tussen de 5 en 30 N de mate van tandverplaatsing niet

te vergroten.

Acknowledgement

126 127

tandheelkunde heb ik de verschillende practica Materiaalkunde, onder jouw lei-

ding mogen volgen. Zelf had ik nooit gedacht dat wij elkaar, nu onder deze om-

standigheden, weer zouden tegenkomen. Dank voor jouw bereidwilligheid om te

opponeren.

Dr. I. Nedeljkovic, member of the reading committee, Dear Ivana thank you for

your willingness to participate as a member of the reading committee. Thank you

for getting in touch via Linkedin.

Dr. T. J. Algera, lid van de leescommissie, Beste Tjalling, hartelijk dank voor jouw

enthousiaste reactie tijdens het BSSO-congres in Haarlem en jouw bereidwillig-

heid om te opponeren en derhalve zitting te nemen in de leescommissie.

Prof. dr. A. Sandham, Dear Andrew, I started the post graduate specialty training

under your supervision which I really enjoyed. Although the time we have worked

together was limited due to your departure to Australia, I admired your way of

finding solutions for problems, within and through your internationally orientated

circle of colleagues. I hope all is well and wish you all the best. Thank you for all

your help.

Prof. dr. y. Ren, beste Yijin, de opleiding tot orthodontist heb ik na prof. dr. A.

Sandham onder uw leiding mogen afronden. Wetenschappelijk gezien was dit

voor mij een roerige periode daar ook prof. dr. M. Özcan naar Zürich vertrok. Hier-

door hebben wij ondanks ieders beste intenties nooit de lopende projecten zoda-

nig samen kunnen integreren dat deze vruchtbaar waren. Dit vind ik oprecht heel

spijtig, daar ik Groningen en de faculteit nog altijd een zeer warm hart toe draag.

Desalniettemin, wil ik u oprecht dankzeggen voor alle hulp en inspanningen.

Drs. M. Bierman, beste Michiel, ik heb mijn klinische opleiding onder jouw su-

pervisie genoten. Een goed, waar ik jou elke dag zeer dankbaar voor ben. Het is

niet altijd even gemakkelijk geweest, maar nu ik zelf full-time in de praktijk werk,

begrijp ik jou eindelijk een heel stuk beter. Ik ben jouw opmerking tijdens de Oud

Assistentendag in ‘t Feithhuis, onder het genot van een goed glas wijn; je moet

het afmaken!, nooit vergeten. Ik wil jou oprecht bedanken dat jij, ondanks enige

moeite in het begin, mij toch hebt gesteund dit onderzoek te continueren en af te

maken. Alle goeds wens ik jou en jouw familie toe.

Dhr. A. Wietsma, Beste Anne, ik wil jou bedanken voor jouw praktische hulp,

jouw bescheidenheid, doch zeer rijke klinische ervaring en jouw hulp met het

ontwikkelen van alle siliconen mallen en samen proefondervindelijk een opstelling

bedenken welke uiteindelijk geresulteerd heeft in een gepubliceerd artikel. Nu de

3D technologie verder ontwikkeld is, hebben wij onze ideeën van toen uitgebreid

en kunnen optimaliseren waardoor wij hopelijk weer een stapje dichterbij zijn bij het

antwoord op de vraag ‘wat gebeurt er nou eigenlijk’. Dank voor alle hulp.

DANKWOORD (ACKNOWLEDGEMENTS)

Naar alle waarschijnlijk is dit het meest toegankelijke deel van het proefschrift dat

bovendien door veel mensen vaak als eerste wordt gelezen. Wat mij betreft is

dat volkomen terecht, want vanzelfsprekend is mijn proefschrift geen ‘one man

show’. Het is tot stand gekomen dankzij de hulp van velen. Mijn dank gaat dan

ook uit naar alle personen die mij gesteund hebben bij het verwezenlijken hiervan.

Graag wil ik bij deze gelegenheid stil staan en een aantal mensen persoonlijk

bedanken.

Prof. dr. M. Özcan, hooggeleerde eerste promotor, Dear Mutlu, this journey

started a long time ago in the basement of the faculty of Dentistry in Gronin-

gen. Young and not knowing at all where this journey would end, we joined

forces. Although it took some time to get this Phd done, we finally finished it.

I would sincerely like to thank you for all your effortless help, drive, dedication,

love of honest and sound dentistry which always gets me enthusiastic, your hon-

est and upfront feedback, but most of all I would like to thank you for becoming

and being a dear friend. Without you, I would not be standing here today. It has

really been a privilege being able to work with you. Not knowing what the future

holds for us, I wish you well and thank you for everything!

Prof. dr. A.J. Feilzer, hooggeleerde tweede promotor, beste Albert. De cirkel is

rond. Ik heb mijn studie Tandheelkunde in Amsterdam genoten en nu sta ik hier

weer, dit keer echter ter verdediging van mijn proefschrift. In de korte tijd dat ik

jou als promotor heb mogen leren kennen, heb ik jouw manier van wetenschap-

pelijk denken in relatie tot de klinische toepasbaarheid leren waarderen. Dit is een

manier van werken en denken die mij heel erg aanspreekt. Dank voor jouw snelle

en kritische, doch praktische kijk op zaken. Dank voor alle hulp.

Prof. dr. M.S. Cune, lid van de leescommissie, beste Marco, erg fijn dat jij in

de beoordelingscommissie van mijn promotie wilt participeren. Bedankt hiervoor.

Hoewel ik jou nog niet in ‘real life’ de hand heb mogen schudden, werken wij al

geruime tijd samen in de praktijk. Ik waardeer de prettige en hoogwaardige sa-

menwerking tussen ons bij al die ingewikkelde, multidisciplinaire casussen, wel-

ke wij samen mogen behandelen. Ik zou het oprecht fijn vinden (ondanks onze erg

drukke agenda’s) een keer rustig samen te kunnen zitten, teneinde van gedachten

te wisselen hoe wij deze moeilijke behandelingen kunnen verbeteren. Dank voor

de zeer fijne samenwerking.

Prof. dr. F.J. M. Roeters, lid van de leescommissie, beste Joost, hartelijk dank dat

u tijdens mijn promotie wil opponeren.

Prof. Dr. C.J. Kleverlaan, lid van de leescommissie, Beste Cees, als student

128 129

Sandra Tolhuizen, lieve Sandra, ik wil jou ook hartelijk bedanken voor je lange en

rijke ervaring in dit vak, jouw bereidwilligheid om samen de protocollen te bedenken

en de daar uit voortvloeiende klinische handelingen te plannen, welke de basis zijn

geweest voor dit onderzoek. Je bent altijd positief en flexibel. Dank voor al jouw hulp

bij het samen plaatsen van alle (glasvezel) spalken, het leerrijk weekend in het mega

koude Turku, Finland, na een gecancelde vlucht en een busrit waarbij je het gevoel

kreeg alsof wij op weg waren naar de Noordpool. Maar vooral dank voor de leuke tijd

samen tijdens de opleiding. Alle goeds voor jou en de boys.

Dr. T.J.M. Van Steenbergen, beste Martijn dank dat jij mij tijdens deze ‘high

stress period’ op een zeer plezierige en goede manier hebt weten te leiden en dat

jij mij hebt bijgestaan. Excuses voor al mijn foutjes, maar fijn dat wij naderhand

hierom konden lachen.

Dr. N. Al-Haj Husain, dear Nadin, it is finally finished. I would sincerely like to thank

you for always being there to help us. All the long weekends at the University, late

on saturday night or very early on the sunday mornings. Thank you for helping me

with all the figures and always making sure, we never had an empty stomach. Thank

you for everyting! I wish you all the best in Bern.

Dr. B. van Eggermont – Oosterkamp, beste Barbara, dank voor jouw hulp en advies

op cruciale momenten tijdens deze reis. Zonder jouw advies, was ik Mutlu wellicht

nooit tegengekomen en al helemaal niet op het juiste moment. Zo ook op het mo-

ment toen ik het even niet meer zag zitten om dit traject überhaupt af te ronden.

Dank voor jouw positieve en praktische kijk op zaken. Ik wens jou, Bas en de kids

alle goeds toe en bovenal goede gezondheid.

Jaargenoten: Dima, Heleen, Manon en Huib, bedankt voor de leuke tijd samen

tijdens de opleiding! De tosti’s kan ik inmiddels weer ‘verdragen’, maar wat een

tijd was dat vergeleken met nu. We zien elkaar helaas niet zo vaak meer, daar een-

ieder druk aan het werk is in de praktijk. Toch denk ik nog altijd met veel plezier en

waardering voor jullie allemaal terug aan de tijd die wij samen hebben doorgebracht.

Oprecht wens ik jullie allen zowel in het vak, maar zeer zeker ook privé alle goeds

toe. Speciaal voor jullie een dikke kus van Baba Ganoush en ik hoop jullie eens een

keer weer te zien aan de Pfeillgasse (mit Auspuff!) Dank voor alles.

Drs. Mr. A.M. Essed, beste oom Thoon, dank voor uw positieve, doch kriti-

sche noot(en)! Ik waardeer u en tante Thecla zeer en zal de herhaaldelijke vraag

‘WANNEER is het proefschrift nu eindelijk af’ ECHT nooit meer vergeten. Zonder

uw aanmoediging, oprechte gesprekken en hulp, vanaf het begin (1997-1998)

stond ik hier vandaag niet. Tot de dag van vandaag, waardeer ik het ritje naar het

Alto Visto kapel te Aruba! Many thanks voor alles en nu samen een goed glas

wijn heffen!

Dr. F.L. Gulje, Beste Felix, zonder jouw hulp hadden Michel en ik ons nooit kun-

nen vestigen in Apeldoorn. Hier ben ik jou zeer erkentelijk voor. De bereidheid

om jouw vakkundigheid en berg aan klinische ervaring te delen, waardeer ik zeer.

Maar het is vooral de laagdrempeligheid en gelijkwaardigheid waarin wij elkaar

kunnen aanspreken over moeilijke multidisciplinaire behandelingen wat ik erg

prettig vind. Ik hoop dat wij nog lang samen mogen werken. Dank voor alles.

Team Mondhoek, Beste Jessica, Azzie en dames. Dank dat jullie ons destijds

onderdak hebben geboden en oprecht dank voor de zeer prettige samenwerking.

Alle collegae (verwijzers) Apeldoorn en omstreken, Geachte collegae, zonder

jullie kunnen wij er niet zijn. Ik zou graag van de gelegenheid gebruik willen ma-

ken en jullie oprecht dankzeggen voor het in mij (ons) gestelde vertrouwen. Als

broekies een praktijk opzetten lijkt eenvoudig, maar is het helemaal niet. Dit is ons

dan ook niet geleerd tijdens de opleiding. Vallen en weer opstaan in de breedste

zin van het woord, heeft ervoor gezorgd dat wij nu zijn waar wij nu zijn. Elke dag

is weer een nieuwe dag en elke dag leren wij weer van elkaar, met elkaar en van

onze patiënten. Ik hoop nog lang samen met u allen op dezelfde plezierige manier

te mogen samenwerken.

Kaakchirurgie Gelre Ziekenhuizen, Apeldoorn, Beste Peter en Steven, Rob en

Bert- Jan, ook jullie wil ik bedanken voor de plezierige en hoogwaardige samen-

werking. We begonnen met niets en mede door jullie enthousiasme en wil om

te verbeteren zijn de OSU spreekuren nu wat ze zijn. Door alle technologische

veranderingen binnen de 3D planning kunnen wij nu de gezamenlijke patiënten

beter van dienst zijn hetgeen tot een kwaliteitsverbetering leidt. Het is erg prettig

om op deze manier van elkaar en met elkaar te leren. Thanks heren!

Kaakchirurgie St. Antonius, Nieuwegein, Beste Joost, Kelly en Leander, ook

jullie waardeer ik zeer. Jullie kennis, kunde en de bereidwilligheid deze met ons,

mij te delen zijn allemaal aspecten die ervoor zorgen dat wij samen een zeer fijne

en hoogwaardige samenwerking hebben. Dank hiervoor.

Alle collegae (verwijzers) Nieuwegein en omstreken, Geachte collegae, dank

voor het vertrouwen en de aangename samenwerking. Werken in de randstad,

vraagt toch een andere manier van werken dan werken in Gelderland. In het begin

ging dit niet vanzelf, maar mede dankzij jullie support en vertrouwen hebben wij

ons dit een beetje eigen gemaakt.

Patiënten van de verschillende klinische onderzoeken, bedankt voor het vertrou-

wen en jullie participatie in de verschillende klinische onderzoeken.

Medewerkers van Ortholab, Beste Emanuel, Carlos, Yoni, Berisha en Stefan,

dank voor jullie hulp met alle (verschillende) retentie draden en advies over de

130 131

pad gekozen, soms naar een ver land en soms iets dichterbij. Hoewel wij elkaar

vanwege de afstand en het tijdsverschil niet zo vaak zien of spreken, wil ik dat

jullie weten dat ik jullie liefheb. Jullie zijn mijn matties en I aint got nothing but

love for you guys!

Alle familieleden en vrienden, In het bijzonder tante Joan en oom George, dank

dat jullie mij destijds hebben opgevangen. Zo ook dank aan u, oom Robby en tante

Alice, na de grote orkaan Luis in 1995. Jane, Jim en tante Mem, dank voor jullie

hulp en dank aan eenieder die belangstelling en steun heeft getoond tijdens deze

reis.

Lieve Monique, Rob, Jamie en Darren, vanwege het feit dat ik zo vroeg het ou-

derlijk huis uit ben gegaan hebben jullie niet altijd alles meegekregen van wat mij

bezighield en waar ik mee bezig was. Andersom is dit natuurlijk ook zo geweest.

Dit was dan ook niet altijd even goed bij te houden na minimaal 25 keer te zijn

verhuisd naar en binnen 5 verschillende (ei)landen. Heel veel hebben wij destijds

via de telefoon en met brieven moeten delen, maar ondanks dat er toen nog geen

skype, whatsapp of andere social media bestond, is de band tussen ons altijd heel

hecht gebleven. Dank dat jullie er altijd voor mij, ons zijn! Ik wil jullie bedanken

voor jullie steun en liefde en wil dat jullie weten dat jullie te allen tijde op mij kun-

nen rekenen. Ik denk aan jullie en mis jullie elke dag! Love Always.

Lieve pa en ma, zonder jullie aanmoediging, onvoorwaardelijke steun en liefde

stond ik vandaag hier niet. Het is me dan ook een eer jullie dit proefschrift te mo-

gen overhandigen. Jullie hebben mij nooit iets in de weg gelegd om mij verder

te kunnen ontwikkelen. Jullie hebben mij altijd gestimuleerd om verder te kijken

en open te staan voor (andere) mogelijkheden of uitdagingen. Op kruispunten in

mijn leven kon ik altijd op jullie onvoorwaardelijke steun, liefde en advies rekenen.

Jullie hebben mij geleerd altijd nederig en bescheiden te blijven en dankbaar te

zijn. Maar ook het fundament te leggen in het besef dat wat de wetenschap ook

aan kennis moge brengen, de werkelijke wijsheid in het kennen van de Here ligt.

Woorden schieten te kort om jullie te bedanken voor alles wat jullie voor mij heb-

ben gedaan en hebben geleerd!

Pa en ma, jullie beiden zijn altijd mijn rolmodellen geweest, dank voor alles! Ik

draag dit proefschrift dan ook op aan jullie beiden en vind het erg fijn de vreugde

van dit moment met jullie te mogen delen.

Mijn laatste dank gaat uit naar mijn lieve vrouw, Kim. Jij bent de grote motor thuis

en jij bent mijn steun en toeverlaat. Jij brengt de rust en zorgt voor het evenwicht.

Jij bent de onvoorwaardelijke supporter achter dit proefschrift. Ik realiseer mij dan

ook heel goed dat ik (te) vaak tekort geschoten ben door veel te laat thuis zijn of

het ‘even’ doch ‘alweer’ naar Zürich vliegen teneinde dit onderzoek af te maken

spalken. Het ziet er allemaal zo eenvoudig uit, tot je het zelf moet doen! Dank

voor jullie geduld. Sorry, dat ik altijd weer aan de telefoon hang, foto’s stuur over

wat wij anders kunnen doen teneinde te verbeteren of te bespreken wat fout

ging. Ik waardeer jullie oprecht en waardeer ook de prettige samenwerking.

Medewerkers van Apeldoorn Orthodontie Welgelegen en Orthodontieprak-tijk Nieuwegein, Lieve dames, zonder jullie kunnen wij niet werken en kunnen

wij niet bestaan. Ik realiseer mij dan ook dat ik mijn waardering wellicht te wei-

nig laat blijken, hiervoor mijn oprechte excuses. Ik waardeer jullie ZEER. Jullie

zijn allemaal toppers en zeer belangrijk. Eenieder van jullie vormt elk een unieke

schakel in de ketting die het wiel uiteindelijk moet draaien en draaiende moeten

houden. Dank voor al jullie hulp en inzet.Saskia, hoewel jij een ander avontuur

bent aangegaan, wil ik jou in het bijzonder bedanken voor al jouw inspanningen

om al die patiënten te traceren en herhaaldelijk op te bellen zodat wij aan alle data

konden komen.

Mw. S. de Vries, lieve Saar sorry dat ik zo slecht bereikbaar ben en op de meest

onchristelijke tijden app of mail. Dit komt echt door de dagelijkse drukte en andere

verplichtingen, maar zoals je inmiddels weet, reageer ik altijd. Hartelijk dank voor

jouw hulp. Mede door jouw inzet ziet dit proefschrift er nu zo mooi uit.

Drs. L.B.H.G. Tacken, Beste vader Tacken dank voor al uw kritische adviezen op

de juiste momenten. Ik waardeer dit oprecht.

Drs. M.P.E Tacken, Bro wat kan het leven raar lopen. Wie had ooit kunnen beden-

ken dat wij elkaar, zonder van elkaar af te weten, elkaar tijdens het najaarscongres

2005 van de Nederlandse Vereniging van Orthodontisten, de hand zouden schud-

den naar aanleiding van mail contact over soortgelijk onderzoek om vervolgens in

2009 samen een praktijk op te zetten. Ik wil jou dankzeggen voor de fijne samen-

werking en waardeer je oprecht. Dank dat jij mijn paranimf wil zijn. God Bless!

Drs. C.G. Sabajo, Lieve Claire, zoveel jaren kennen wij elkaar al. Alles begon in

het inmiddels gesloopte Wentgebouw toen wij samen Farmacie studeerden. Wij

hebben door de jaren heen heel veel mooie momenten, maar ook minder plezie-

rige momenten gekend en gedeeld. Dit heeft ons heel close gemaakt en zijn wij,

ondanks dat wij elkaar niet elke dag zien of spreken, haast broer en zus gewor-

den. Ik wil je dankzeggen voor jouw vertrouwen, liefde en begrip, maar bovenal

dat wij altijd onszelf kunnen zijn in bijzijn van elkaar. Sinds kort heb je een man

in je leven, iemand die ik zeer waardeer en respecteer. Ik wil jullie dan ook alle

goeds toewensen en vanzelfsprekend kom ik jullie ook helpen verhuizen naar jul-

lie nieuw stekkie. Dank voor de vriendschap en dank dat je mijn paranimf wil zijn.

Martin, Maurice en Jimmy, waar gaat de tijd. Rimini, Bangkok, New King, Rio

de Janeiro, wat een tijd. Eenieder van ons is ouder geworden en heeft zijn eigen

132 133

en altijd maar weer achter die computer te zitten. Ik wil jou oprecht bedanken

voor alle begrip, onvermoeibare en oprechte steun maar bovenal voor jouw on-

voorwaardelijke liefde. Ik ben blij dat ik altijd bij jou terecht kan en hoop dat ik dit

ook voor jou mag doen, op weg naar de afronding van jouw eigen proefschrift. Wij

hebben het afgelopen jaar samen een heel moeilijk jaar doorstaan, maar saam-

pjes staan we sterk en gaan we door. Stap voor stap. Dank dat je de beste moe-

der bent voor onze lieve, zoon Luca. Hij is werkelijk een geschenk van God en

altijd het zonnetje in huis. Vervult met blijdschap kijk ik uit naar eind juli, en kan me

alleen maar voorstellen hoe fijn het straks zal zijn met ons vieren. Ik hou van jullie!

Curriculum Vitae

Dave Lie Sam Foek was born on July 6th, 1977 in Paramaribo, Suriname (South

America). He received his primary and part of secondary education at the

Bernadetteschool and Christus Koningschool both in Paramaribo, Suriname. After

having finished secondary school in 1997 at Milton Peters College (HAVO) on Sint

Maarten (Dutch West Indies), he continued to finish his pre-university education in

1998 at the Collegio Arubanu (VWO) on Aruba (Dutch Antilles). In 1998 he started

a study on Pharmacy at the University of Utrecht, Netherlands and in 1999 he

was accepted at the University of Amsterdam to study dentistry. During his study

the author was active in several (student) committees and worked in a private

practice as a dental assistant. During the last year of his dentistry education, he

joined an international collaboration with the University of São Jóse dos Campos,

Brazil, on which he wrote his master thesis. He graduated in 2004 and took on

a partial position as a staff member on the pre-clinic (Department of Cariology

and Endodontics) as well as working in several private practices as a dentist.

In 2005 he started his speciality training at the Department of Orthodontics,

University Medical Center, University of Groningen, Groningen, The Netherlands.

He currently works in two private practices restricted to orthodontics.

Dr. Dave J. Lie Sam Foek, DDS Apeldoorn Orthodontie Welgelegen

Burgemeester Jonkheer Quarles van Uffordlaan 103

7321 ZN Apeldoorn

The Netherlands

T +31(0) 555766480

M +31(0) 642129950

E d.j.liesamfoek@gmail.com