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Endodontology, Vol. 15, 2003

Bond strength of wire-composite resin interface

of dental splints using different wire surface

treatments - An in vitro study*Jacob J **Nandlal B

ABSTRACT

The study was undertaken to evaluate the optimal method of enhancing

the wire-composite bond strength of dental splints using different wire

surface treatments. Further, a comparison of bond strength of the wire-

composite resin interface with commonly used composite materials for

dental splints was also attempted. The study sample consisted of 360

bovine mandibular incisors embedded in acrylic resin which were utilized

as bonding surfaces for evaluation of the bond strength of the wire-composite interface when using light activated composite resin (Gluma)

and chemically activated composite resin (Rely-a-bond) with both

flexible (0.016" round, 0.017" X

0.025" rectangular) and rigid (0.036" round) stainless steelwires.

The results of the study indicated that sandblasting the portions of the

stainless steel wires embedded in composite resin enhanced the strength

of the wire-composite bond for both the types of composite materials. The

use of metal primer on stainless steel wires either separately or in

combination with sandblasting had lower wire-composite interface bond

strength than sandblasting alone, while no surface treatment on the wire

had the least, for both the light activated and chemically activated

composite resins.

Key words : Bond strength, dental splint, luxation injuries, surface treatment of

dental wires.

Introduction

Of the traumatic injuries occurring inchildren, avulsion and displacement of teethare some of the common problems

encountered in the primary as well as mixeddentition period. Dental splinting after

traumatic tooth injury is needed to stabilizesubluxated, luxated, avulsed and root

fractured teeth1. Rigid

* Post Graduate Student

** Professor & Head

Dept. of Pedodontics & Preventive Dentistry

J.S.S. Dental College & Hospital

Mysore - 570 015

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dental splinting has been the treatment ofchoice until the 1970s which were based onthe principles of bone fracture immobilizationin which total immobility improves healing

without cal lus formation 1.However, experimental and clinical studieshave shown that early restoration of

masticatory function improves pulpal and

periodontal healing2.

The bond strength of the wire to the

composite resin is an important factor in a

successful wire-composite splint. Most of the

failures of this wire-composite splint occurs

at the wire-composite resin interface.

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Jacob and Nandlal Wire-composite interface...

Methods of increasing the bond strengthbetween metals and composites werethrough mechanical retention methods likeundercuts and roughening of the metalsurface , microretention methods likesandblasting, electrolytic etching and tin-plating and chemical adhesion through the

use of metal bonding agents (MetalPrimers)3,4,5. Thin flexible wires have beenrecommended for the wire- composite

splint6. Two types of composite materialshave been advocated for the wire- compositesplint; namely the chemically curedcomposite and the light cured composite

resin6,7. This study was to evaluate theoptimal method of enhancing the wire-composite bond strengths of dental splints

using different wire surface treatments.

Materials and Methods

The study sample consisted of 360

bovine mandibular incisors embedded in

acrylic blocks in test groups of 15 samples

each. The test group were different wire

surface treatments like Sandblasting (Sb),

Sandblasting + Metal Primer (Sb+Mp), Metal

Primer alone (Mp) and No surface treatment

(Nst). Two different types of composite

materials namely light activated composite

resin (Gluma) and chemically activated

composite material (Rely-a-bond) were

tested on 0.036" round S.S. wire, 0.016"

round S .S . wire and 0.017" X 0 .025"

rectangular S.S. wire for the different wire

surface treatments. Bovine mandibular

incisors were cleaned of soft tissue and

stored in a refrigerated Chloramine-T

solution. Before bonding, the facial surfacewas cleaned with distilled water to remove

debris and dried with tissue paper. The apical

1/3rd of the roots were sliced with a diamond

disc. The mounting of the bovine tooth was

done using a split rectangular aluminum

box and the tooth was stabilized with self

cure acrylic resin. The bovine tooth

surface was covered with adhesive tape

except for bonding site of radius

4.4mm. This was done to have a uniform

etching and bonding area for all the test

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samples8. To consistently place the wire

within the composite resin, a standard splint

acrylic template was devised. The template

had a round well of 4.4mm diameter and

1.75mm depth with a uniform 15.2mm of

composite bonding surface area. A slot for

the wire extended from the end of the well to

the end of the template. The length of the slot

was 10cms and the width of the slot was1mm more than the diameter of each of the

test wire. The well ensured approximately

1mm of composite over the wire, placing the

wire as close to the bovine tooth surface as

possible while still surrounding it with the

composite resin. The test sample was placed

on a flat surface along with the aligning jig

which aligned as well as stabilized the

bonding template over the bovine tooth

surface. Acid etching and bonding procedurefor both the test composite resins were done

following manufacturers' instructions.

The wires were sandblasted with a 50

microns aluminium oxide at a pressure of 75

psi for approximately 15 seconds, resulting in

approximately the last 6-7 mm of the wire

etched to a dull finish. The metal bonding

agent (Alloy Primer) was applied directly to

the wire surface with a brush for 15 seconds

and then air dried for 5 seconds. The wires

were then immediately bonded to the

composite resin. The cured samples were

placed in distilled water and stored in an

incubator at 37C for

48 hours and then thermocycled between

4C and 60C for 100 cycles with a dwelltime in each therma l bath of 1 minute9. Afte r thermocycling, the samples werefurther returned to the incubator for storage

before testing 24 hours later. Testing of thesamples was done using a Universal Testing

Machine (Llyods) at a crosshead speed of1mm per minute. The test samples were

placed in the lower jaw of the testingmachine and the wire was pulled along its

long axis by the testing machine until the wirewas fully dislodged from the composite

resin. The maximum force needed todislodge the wire was recorded. The force

was converted to MPa by using the

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surface area of the wires. In analyzing the

results of the variables under various

methods considered in this s tudy, the

statistical techniques like Arithmetic Mean,

Standard Deviation, Student's 't' test,

Analysis of Variance (ANOVA) and the

Duncan's Multiple Range Test (DMRT) were

used appropriately.

Results

Results are shown numerically in Table1,

2, 3. Different surface treatments of wires in

both light activated and chemically cured

composite resin were significantly different

from each other (ANOVA, P

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Endodontology, Vol. 15, 2003

and adhesion promoters on the wire-

composite interface bond strength of dental

splints are few.

With both, the light activated composite

resin (Gluma) and chemically activated(Rely- a-bond), sandblasting of the 0.036"

stainless steel wires provided thestrongest wire- composite interface. The

bond strength of the wire-compositeinter face obta ined wi th sandblasted

wires (268.45MPa) was significantly higherthan no surface treatment (13.59MPa)

(p

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treatmentsDMRT

activatedMean F value

activatedMean F value 't' value

S.D. (MPa) S.D. (Mpa)

Sb (d) 235.102.92 79467.70 191.191.26 126574.78 053.52***

Sb+Mp (c) 227.890.98 184.101.37 100.83***

Mp (b) 31.821.20 24.650.94 018.19***

Nst (a) 11.890.44 10.310.52 009.00***

Jacob and Nandlal Wire-composite interface...

TABLE 1: Mean Bond strength of the 0.036" wire-composite interface

Surfacetreatments

Lightactivated

Chemicallyactivated

Mean S.D. (MPa)

F value Mean S.D. (Mpa)

F value 't' value

Sb (d) 268.454.84 31354.93 206.072.06 69601.23 45.94***Sb+Mp (c) 246.102.83 194.621.80 59.47***

Mp (b) 43.791.46 36.667.39 31.02***

Nst (a) 13.590.49 11.870.90 6.55***

ANOVA : Mean bond strength were significantly different from each other (p

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bond strengths when compared with

sandblasting (p