A Comparison of the effect of resin removal methods on enamel surface and shear bond strength of rebounded brackets

Considering the high failure rate of bracket bonding in orthodontics treatment, in the event of either the patient accidentally applying inappropriate forces to the bracket or poor bonding techniques, the objective of this study was to determine the effect of resin removal methods on enamel surface and shear bond strength of rebonded brackets. A total of 76 fresh human premolars were used in this experimental (in vitro) study, seventy of which were divided into three experimental groups(N:20) and one control group (N:10).(Simple random sampling). After the bonding procedure in the experimental groups using No-mix composite and mesh base brackets, debonding was performed with use of plier. Buccal surface of each sample was examined by an optical microscope (×10) to determine the location of the bond failure interface, using an Adhesive Remnant Index (ARI). The remnant adhesives were cleaned up with three 1- High speed-Tungsten Carbide Bur (TCB), 2- Low speed-TCB, 3- Sandblast with Microetcher. For rebounding procedure each experimental group divided into two subgroups of 10. A- With use of new bracket, B- Sandblasted bracket. Rebounding was performed on 70 samples in experimental and control groups and the second set of SBS and ARI were calculated and statistically evaluated. In six samples, the buccal surface of each tooth divided into four groups for bonding composite to observe the effect of the above interventions on the enamel structure by SEM (×1000). The data was analyzed with (One-way & Two-way) ANOVA, Dunnett t and Kruskul-Wallis. No significant difference was found between control and experimental groups reading Shear Bond Strength (SBS) and ARI detachment levels with respect to resin cleanup methods and bracket type.(P>0.6) But SEM studies showed complete destruction of enemal surface as a result of sandblasting with micro etcher. enamel surface preservation was found to be closest to it normal morphology in TCB group. Enamel damage after rebounding seems to be inevitable but with TCB it can be reduced and also reasonable SBS should be achieved.