DOI: 10.1111/j.1365-263X.2011.01213.x

the occlusal surface of primary

Bond strength and morphology of resin materials applied to

molars

LETICIA VARGAS FREIRE MARTINS LEMOS1, KLISSIA ROMERO FELIZARDO1, SILVIO ISSAOMYAKI2, MURILO BAENA LOPES1 & SANDRA KISS MOURA1

1School of Dentistry, UNOPAR, Londrina, PR, Brazil, and 2School of Dentistry, UNESP, Sao Jose dos Campos, Sao Paulo,

Brazil

International Journal of Paediatric Dentistry 2012; 22: 435–

441

Background. Hydrophilic adhesives may be used

as pit and fissure sealants (sealants), but there is

concern about the ability of self-etching adhesives

to bond sealants to enamel.

Aim. To study the bond strength (BS) and mor-

phology of adhesive systems used as sealants.

Design. OptiBond FL, OptiBond All-in-One, com-

bined OptiBond All-in-One + OptiBond FL adhe-

sive, and Fluroshield were applied to the occlusal

surfaces of 16 primary molars (n = 4). Teeth were

stored in distilled water (24 h at 37�C) and sectioned

through the interface to obtain sticks (0.8 mm2)

Correspondence to:

S. K. Moura, Universidade Norte do Parana (UNOPAR),

Curso de Odontologia, Rua Marselha, no 183, Jardim Piza,

CEP 86041-140, Londrina, PR, Brazil.

E-mail: kissmoura@gmail.com

� 2012 The Authors

International Journal of Paediatric Dentistry � 2012 BSPD, IAPD and Bla

tested under a tensile load (0.5 mm ⁄ min). Failure

modes were observed. Data were analysed by

ANOVA and Tukey’s tests (a = 5%). The morpho-

logy of 12 primary molars was examined in terms

of the etching pattern and resin reproduction.

Results. Differences in the BS were found

(P = 0.001), with OptiBond FL showing the highest

(36.84 ± 5.7 MPa), Fluroshield (24.26 ± 2.13 MPa)

and OptiBond All-in-One (17.12 ± 4.97 MPa) simi-

lar, and OptiBond All-in-One + OptiBond FL adhe-

sive the lowest (9.8 ± 2.94 MPA). OptiBond FL

showed the best results in terms of morphology.

Conclusion. Under the conditions of this study,

OptiBond FL was the best material to be used for

sealing.

Introduction

Primary and permanent tooth enamel have

some important differences. For example, pri-

mary enamel has a thicker aprismatic layer

and lower degree of mineralization; therefore,

it is more susceptible to decay1,2. In 81.5% of

cases in children aged 6–36 months who have

caries, injury occurs in the posterior teeth3.

With the discovery of acid etching4, which

demineralizes enamel and creates irregulari-

ties that can be filled by resins, it has become

possible for resin materials to be adhered to

enamel, resulting in micromechanical reten-

tion5.

Use of occlusal sealants is an effective method

for preventing decay6,7, because sealants act as

a mechanical barrier to biofilm accumulation.

Studies evaluating the use of sealants in pri-

mary teeth8,9 indicate that contamination by

saliva or gingival fluid during the adhesive pro-

cedure is a main reason for sealant failure10.

Because conventional sealants are hydropho-

bic, studies have evaluated the use of hydro-

philic adhesive systems as intermediary agents

between the etched enamel and occlusal seal-

ant11,12. Other authors have clinically evalu-

ated the use of hydrophilic adhesive systems as

a substitute for proper occlusal sealants10,13.

Favourable bond strength (BS) results were

obtained for adhesive systems applied as a sin-

gle material to intact primary molars, regardless

of contamination by saliva14,15.

Self-etching adhesives reduce the clinical

time needed for restorations by eliminating

the separate etching step. This technique

could have particular application for paediat-

ric dentistry, where the use of resin materials

is constantly challenged by the potential risk

of saliva contamination. Hydrophilic adhe-

sives may be used as sealants, but there is

concern about the ability of self-etching

ckwell Publishing Ltd 435

436 L. V. F. M. Lemos et al.

adhesives to bond sealants to enamel. There-

fore, the objective of this study was to evalu-

ate the BS and morphology of resin materials

applied to the occlusal surface of primary

molars. The null hypothesis was that adhesive

systems provide similar BS to enamel and

morphological findings as sealants.

Material and methods

The research protocol was approved by the

Ethical Committee of the Dental Scholl (Pro-

tocol PP0108 ⁄09). A total of 28 primary

molars obtained within 6 months of exfolia-

tion15 were disinfected in 0.5% chloramine

solution at 4�C 16 and cleaned with a slurry

of pumice and water. Teeth were randomly

divided into two groups: 16 teeth were used

for BS measurement, and 12 teeth were used

for micromorphological experiments.

Bond strength measurement

Because a very thin layer of dentin remains

within the crown after physiologic tooth

resorption, the purpose of restoring the pulp

chamber is to prevent enamel cracking during

preparation of the specimen for the BS test15.

Pulp chambers of 16 primary molars were

acid-etched with 35% phosphoric acid for

15 s, washed for 15 s, dried, and restored

with the Adper Single Bond 2 adhesive sys-

tem and Filtek Z250 composite (3M ESPE

Dental Products; St Paul, MN, USA), accord-

ing to the manufacturer’s directions. Occlusal

surfaces were cleaned with pumice and water

and randomly divided into four groups

(n = 4).

Surfaces were restored by a sealant (Fluro-

shield, Dentsply, Petropolis, RJ, Brazil),

conventional adhesive system (OptiBond

FL; Kerr Co, Orange, CA, USA), self-etching

system (OptiBond All-in-One; Kerr Co,

Orange, CA, USA), or combination system

(OptiBond All-in-One + OptiBond FL). After

the materials were applied (Table 1) and light

curing was preformed (60 mW ⁄cm2, VIP, Bi-

sco; Schaumburg, IL, USA), resin blocks (Fil-

tek Z250, 3M ESPE Dental Products, St Paul,

MN, USA) were built up in three increments

of 2 mm each.

International Journal of Pa

Restored teeth were kept in distilled water

for 24 h at 37�C. They were serially sec-

tioned14,15 with a diamond disc (Extec 12205

High Concentration, Enfield, CT, USA) in a

cutting machine (Isomet 1000; Buehler Ltd,

Lake Bluff, IL, USA). Sectioning was per-

formed perpendicularly to the bonding inter-

face in the mesio-distal direction, yielding

0.9-mm-thick slices. The flattest area of the

occlusal interface of each slice was delimited

for the second section of 0.9 mm thick,

producing stick samples of 0.8 mm2.

Specimens were tested in a universal testing

machine (EMIC DL2000; Sao Jose Dos Pinhais,

PR, Brazil) under tension at 0.5 mm ⁄min14,15.

Fragments were mounted on an aluminium

support, covered with gold ⁄palladium, and

observed in a scanning electron microscope

(SEM; JEOL 5600; Tokyo, Japan). Fractures

were classified as cohesive (enamel or compos-

ite), adhesive (interface), or mixed (presence

of composite and ⁄or enamel in the same frag-

ment). The percentages of fracture modes and

of specimens fractured before testing were

recorded for all groups15.

For statistical analysis, the tooth was con-

sidered to be the experimental unit. Average

values of BS (MPa) of each group were trea-

ted by one-way analysis of variance (ANOVA)

and Tukey’s test (a = 5%). Power analysis

was performed with the G Power program,

considering a critical effect size of 1.03 after

one-way ANOVA.

Micromorphology analysis

The micromorphology of resin materials

adhered to enamel was observed in 12 pri-

mary molars. Four molars were used to eval-

uate the etching pattern. Phosphoric acid

(37%) or self-etching adhesive was applied as

described in Table 1. For molars treated with

phosphoric acid, the acid was washed with an

air–water spray, and the occlusal surface was

dried with compressed air. For molars treated

with self-etching adhesive, after application,

the molars were immersed in baths of

acetone and ethanol (3 · 20 s each) to

remove the monomers, and the surfaces were

dried with compressed air17. All teeth were

placed in aluminium holders, coated with

� 2012 The Authors

ediatric Dentistry � 2012 BSPD, IAPD and Blackwell Publishing Ltd

Table 1. Materials used, composition, and application modes.

Material (Batch number) Composition Application Mode

OptiBond FL(Primer 3124126;Adhesive 3101101)

37.5% phosphoric acid; Primer: ethyl alcohol (20–25%),alkyl dimetacrylate resins, water; Adhesive: uncuredmethacrylate ester (50–60%), TEGDMA (5–10%),ytterbium trifluoride (12–17%), inert mineral fillers,photoinitiators, stabilizers

Acid etching (15 s);Wash (15 s)Dry (5 s)

Apply one coat of primer (15 s)Dry (5 s at 1 cm)Apply one coat of adhesive (15 s)Light cure (20 s at 600 mW ⁄ cm2)Apply one coat of adhesive (15 s)Light cure (20 s at 600 mW ⁄ cm2)

Fluroshield(047065A)

Gel etchant: phosphoric acid, water, colloidal silica,inorganic colour;

Fluroshield (50% inorganic fillers): Bis-GMA modifiedurethane, TEGDMA, aluminium and bariumborosilicate, phosphoric acid tetracyclic ester, sodiumfluoride, N-methyl dietamolamine, canforoquinone

Acid etching(15 s)Wash (15 s)Dry (5 s at 1 cm)Apply one coat of sealantLight cure (20 s at 600 mW ⁄ cm2)

OptiBond All-In-One(3075076)*

Uncured methacrylate ester (33–43%), ethyl alcohol(4–9%), water, Acetone (35–45%), monomers, inertmineral fillers, ytterbium fluoride, photoinitiators,accelerators and stabilizers

Apply a first coat of adhesive vigorously (20 s)Apply a second coat of adhesive vigorously (20 s)Dry with air stream (5 s at 1 cm)Light cure (20 s at 600 mW ⁄ cm2)

OptiBond All-In-One(AIO) (3075076) +OptiBond FL adhesive(3101101)

AIO: Uncured methacrylate ester (33–43%), ethyl alcohol(4–9%), water, Acetone (35–45%), monomers, inertmineral fillers, ytterbium fluoride, photoinitiators,accelerators and stabilizers; FL adhesive: uncuredmethacrylate Ester (50–60%), TEGDMA (5–10%),Ytterbium trifluoride (12–17%), inert mineral fillers,photoinitiators, stabilizers

Apply a first coat of AIO vigorously (20 s)Apply a second coat of AIO (20 s)Dry with air stream (5 s at 1 cm)Apply FL adhesive (15 s)Light cure (20 s at 600 mW ⁄ cm2)

Bis-GMA, bisphenolglycidyl methacrylate; TEGDMA, triethylene glycol dometacrilate; HEMA, 2-hydroxyethyl methacrylate;*Material Safety Data Sheet, acc. to OSHA Hazard Communication Standard¢s requirement (29 CFR 1910.1200) reviewed on11 ⁄ 19 ⁄ 2008; Kerr.

Pit and fissure sealing with adhesive systems 437

gold–palladium, and observed by SEM (Jeol

5600; Tokyo, Japan) at 12Kv.

Resin reproduction (tags) was observed in

eight molars, in which the occlusal surfaces

were restored as described for the BS measure-

ment. Restored teeth were immersed for 12 h

in 6N hydrochloric acid for tooth demineraliza-

tion. Demineralized teeth were washed in tap

water and immersed in 1% sodium hypochlo-

rite for 10 min for deproteinization17. Samples

were mounted on an aluminium support,

coated with gold–palladium, and observed by

SEM (Jeol 5600; Tokyo, Japan) at 12Kv.

Table 2. Number of specimens (representative percentages) distrexperimental condition.

Material

Fracture pattern

Mixed (%) Cohesive enamel

OptiBond FL 38 (76) 8 (16)Fluroshield 20 (41.67) 14 (29.17)OptiBond All-In-One 26 (66.67) 3 (7.69)OptiBond All-In-One +OptiBond FL adhesive

12 (52.17) 1 (4.35)

� 2012 The Authors

International Journal of Paediatric Dentistry � 2012 BSPD, IAPD and Bla

Results

Bond strength measurement

Uniformity of the stick cross-sectional area

(mm2) was analysed by one-way ANOVA. The

areas ranged 0.87–1.02 mm2. No differences

were observed among the experimental

groups (P > 0.05), suggesting that this aspect

did not affect BS to the occlusal surface.

Table 2 shows the percentages of premature

failures and fracture modes for each experi-

mental condition. Mixed fractures were

ibuted according to the fracture pattern for each

(%) Cohesive resin (%) Premature failures (%)

0 (0) 4 (8)7 (14.58) 7 (14.58)1 (2.56) 9 (23.08)0 (0) 10 (43.48)

ckwell Publishing Ltd

Table 3. Mean values and standard deviation (MPa) ofbond strength for the experimental groups*.

MaterialMeans(Standard deviations)

OptiBond FL 36.84 (5.7)aFluroshield 24.26 (2.13)bOptiBond All-In-One 17.12 (4.97)bOptiBond All-In-One +OptiBond FL adhesive

9.8 (2.94)c

*Similar letters shows similar means (P > 0.05).

438 L. V. F. M. Lemos et al.

prevalent in all groups, indicating that the

enamel ⁄ adhesive interfaces were tested at

tensile.

Table 3 shows the mean BS values (MPa)

and standard deviations. Power analysis per-

formed after one-way ANOVA revealed a power

of 1.0. Significant differences in BS were

(a) (

(c) (

(e) (

Fig. 1. Etching pattern of 37.5% phosphoric acid gel (a) and Opt

Fluroshield (d), OptiBond All-In-One (e), OptiBond All-In-One + O

International Journal of Pa

found among the materials (P = 0.001). Opti-

Bond FL showed the highest, OptiBond

All-in-One + OptiBond FL adhesive showed

the lowest, and Fluroshield and OptiBond

All-in-One showed similar and intermediate

values of BS.

Micromorphology

Figure 1 shows the results of the micromor-

phological analysis. Dissolution of the prism

periphery after etching in 37.5% phosphoric

acid (i.e., type II etching pattern18) is shown

on Fig. 1a. OptiBond All-in-One resulted in

smooth and undefined etched surfaces

(Fig. 1b). Well-defined resin tags were

observed for OptiBond FL (Fig. 1c). Fluro-

shield (Fig. 1d) and OptiBond All-in-One

(Fig. 1e) showed similar resin tags, which

b)

d)

f)

iBond All-In-One (b); resin tags of OptiBond FL (c),

ptiBond FL adhesive (f). Bar = 10 micrometres.

� 2012 The Authors

ediatric Dentistry � 2012 BSPD, IAPD and Blackwell Publishing Ltd

Pit and fissure sealing with adhesive systems 439

were less defined than those for OptiBond FL.

The combination of OptiBond All-in-One +

OpfiBond FL adhesive did not produce well-

defined resin tags (Fig. 1f).

Discussion

Among the factors that favour caries develop-

ment on the occlusal surface is the eruption

stage, or functional use of the tooth and its

specific anatomy19. Obliteration of pits and

fissures of the tooth by sealants was first

described by Cueto and Buonocore (1967).

Previous studies have shown the effectiveness

of sealing with hydrophilic adhesive systems

in caries prevention7,13. In the case of pri-

mary dentition, the seal should remain at

least until the tooth comes into occlusion,

implying post-eruptive maturation and instal-

lation of self-cleaning20.

Few studies of adhesion to enamel by self-

etching systems on the occlusal surface of pri-

mary teeth have been carried out14,15. Some

studies have shown less enamel conditioning

by self-etching, compared to phosphoric acid

etching, in permanent21 and primary

teeth22,23. The etch-and-rinse approach uses

phosphoric acid to demineralize the enamel.

A washing step is included to remove the acid

gel and create irregularities4 that are filled

with resin5. In the self-etch approach, the

etching and priming steps are combined into

a single procedure, without the need for

washing. Self-etching systems differ from

etch-and-rinse adhesives in several aspects:

for example, they generally have a higher

pH24, because bonding relies on the ability of

self-etching materials to infiltrate and par-

tially dissolve hydroxyapatite for filling by

resin. The effectiveness of this process varies

with the acidity of the self-etch25, although

the performance of self-etching systems can-

not solely be attributed to their acidity26.

Therefore, this study analysed the adhesion of

resin materials with different etching

approaches to the occlusal surface of primary

molars.

OptiBond FL had the highest BS to the

occlusal surface of primary molars, consistent

with the results of previous studies14,15. The

high BS of conventional 3-step adhesives to

� 2012 The Authors

International Journal of Paediatric Dentistry � 2012 BSPD, IAPD and Bla

enamel has been observed consistently in the

literature27 and clinical research10,13. We

observed a relationship between the BS of

this adhesive and the enamel micromorpho-

logy, which displayed a well-defined etching

pattern and resin tags. Daronch et al. (2003)

studied the etching patterns of conventional

and self-etching adhesive systems on primary

molars. They observed that the thicker layer

of aprismatic enamel in the primary tooth

influenced the conditioning etching pattern,

which was discrete in the case of self-etching

and formed resin tags. Similar findings were

observed by Fava et al. (2003). These previous

observations help explain why the BS of

OptiBond All-in-One (which also showed a

relationship between BS and micromorpho-

logy) was lower than that of OptiBond FL.

The BS of Fluroshield was similar to that of

OptiBond All-in-One, but no relationship was

observed between the etching pattern and

BS. The etching pattern of Fluroshield was

similar to that of OptiBond FL, but the resin

tags were similar to those of OptiBond All-in-

One. This result may be explained by the vis-

cosity of the sealant, which contains 50%

inorganic filler, compared with the viscous

OptiBond All-in-One that contains ytterbium

fluoride in some extensions. Hydrophilic

adhesives that are less viscous than the seal-

ant can improve the marginal sealing of

sealants on the enamel surface by filling the

microporosity produced by the acid28.

In general, all-in-one adhesives are associ-

ated with low bonding effectiveness24. The

application of an additional hydrophobic resin

layer of OptiBond FL after the OptiBond

All-in-One adhesive was based on a previous

study that found an improvement in the

immediate BS of some all-in-one adhesives to

enamel29. In the present study, however, the

lowest BS to enamel was achieved with the

combination of OptiBond All-in-One + Opti-

Bond FL adhesive. This low BS may be

explained by a possible mismatch interaction

between the acidic primer, which contains a

high amount of solvents (45% acetone and

9% ethanol), and the OptiBond FL resin.

Adhesives containing solvents have lower

cohesive strengths than hydrophobic adhe-

sives without solvents30 (e.g., OptiBond FL

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440 L. V. F. M. Lemos et al.

adhesive), in part because of the inability to

remove all of the water and solvent mixtures

during clinical application. The BS results for

this group were related to the micromorpho-

logical analysis of enamel and resin tag

formation.

Among the groups, the combination of

OptiBond All-in-One + OptiBond FL resulted

in the most premature debonding specimens

(around 43.48%; Table 2). Premature deb-

onding occurred at the sectioning step of the

method. The micromorphological findings

and high percentage of premature debonding

emphasize the fragility of the enamel bonding

in this association. Unfortunately, most previ-

ous studies have neglected to analyse the

amounts of premature debonding and other

types of fracture modes recorded with micro-

tensile BS31. Such analyses are needed to

improve the understanding of the drawbacks

of the method and to analyse the BS results.

Under the conditions of this study, it may

be concluded that BS to enamel and morpho-

logical findings varied among the studied

materials. For this reason, the null hypothesis

must be rejected. Future studies should ana-

lyse the bonding durability of resin materials

used for occlusal sealing.

Why this study is important to paediatric dentists

d Owing to the risk of saliva contamination in paediatric

dentistry, the use of hydrophilic adhesive systems

should be encouraged.d The conventional 3-step etch-and-rinse adhesive is a

possible sealant choice for paediatric dentistry.

Acknowledgements

The authors thank Dr. Karen Barros Parron

Fernandes for the Power Analysis evaluation.

Conflict of Interest

The authors declare no conflict of interest.

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