Methodology: strength of conventional composites (n=40×2=80) under the

Methodology:

80 sound human premolar teeth indicated for extraction were collected. Inclusion criteria included the teeth selected should not have any cracks, free of caries, not be attrited, or have any kind of restorations. Later teeth were stored in 0.5% aqueous thymol solution after extraction to control the bacterial growth. After selection, the teeth were rinsed thoroughly with distilled water. Each tooth was embedded in self-curing acrylic resin, the exposed buccal crown surface of each premolar was rinsed and dried after a 15-second polish with fluoride free pumice in a rubber cup and rinsed in distilled water. The enamel was dried with moisture-free compressed air.

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? 80 teeth were divided into 2 groups with 40 teeth in each group (n=40).In one group conventional adhesive system with primer was gently rubbed onto the buccal surface of teeth according to the manufacturer’s instructions and dried with moisture-free air. Using light cure adhesive, the brackets were bonded to the prepared enamel and excess adhesive was removed and light cured according to the manufacturer’s instructions.

? In another group, the same procedure is followed but without the use of a primer.

The samples collected were used to test the shear bond strength of conventional composites (n=40×2=80) under the influence of orthodontic forces. After etching and priming, the resin composite adhesive was applied to the stainless steel metal premolar brackets with a micro-etched base (3M) and seated on the enamel with an MBT gauge. Premolar stainless steel brackets ( ortho organizers) were used in this study.Excess of resin was removed with an explorer. The mesial and distal sides of the bracket were light cured (Ivoclar Vivadent) for 30 seconds each.

The groups were coded as follows:

{GROUP I – WITH PRIMER}  – Thin coat of primer was applied, the adhesive resin was applied to the base of the bracket and pressed hard onto the tooth, left over adhesive was removed from the base of the bracket, and then light-cured.

{GROUP II – WITHOUT PRIMER}  –  Adhesive without the primer was applied to the base of the bracket and pressed firmly onto the tooth. Excess adhesive was removed from the base of the bracket before setting and light cured.

Shear Bond Strength (SBS) testing was carried out for two groups with a universal testing machine (UTM) as shown in figure 4.

 

MECHANICAL TESTING:

The bond strength of these specimens was tested with the help of a universal testing machine (UTM). A crosshead speed of 1mm/min was used to test the shear bond strength of the orthodontic adhesive. (Fig 4) .The specimens were assured in a special jig attached to the base plate of a universal testing machine and positioned so that the leading edge was aimed at the enamel-composite interface before being brought into contact. The load was applied under the incisal wings of each bonded bracket and parallel to long axis of each mounted tooth. The load was applied till the bond failure occurred and the force required to debond the bracket were measured. The shear bond strength of each adhesive was recorded in kilogram-force which was then converted into MPa, as it is a common SI unit generally referred for bond strength. Once the debonding occurred the brackets were examined under the stereomicroscope and the adhesive remnant index was used to assess the adhesive remaining on the bracket base at 10 x multiplication. (Fig 5)

DETERMINATION OF REMAINING RESIDUAL ADHESIVE ON BRACKET BASE AFTER DEBONDING:

The bracket base was examined under a stereomicroscope ( Fig­­­5) to assess the site of bond failure and assess the amount of adhesive left on the bracket base after debonding. (Fig 7)

Any adhesive remnants were graded as per adhesive remnant index by Artun and Bergland47:

0: All adhesive on bracket base

1: more than 50% of adhesive on bracket base

2: less than 50% of adhesive on bracket base

3: Entire adhesive left on the tooth with a distinct impression of the bracket base.

 

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