Comparative evaluation of orthodontic bracket base shapes on shear bond strength and adhesive remnant index: An in vitro study

Abstract

Background: The objective of this study was to evaluate the effect of orthodontic bracket base shape on shear bond strength and adhesive remnant index. Material and Methods: In this in vitro study using 140 bovine incisors, shear bond strength (SBS) of brackets with different base shapes (rectangle, flower, round, heart, diamond, star and football) were measured with an Instron universal testing machine and tested until bond failure. Adhesive Remnant Index (ARI) scoring was evaluated after debonding to evaluate the location of bond failure. Descriptive, one-way ANOVA and post-hoc Tukey statistical analyses were performed with statistical significance set at p < 0.05. Results: Statistically significant difference in mean SBS in Newtons was observed for multiple base shapes (p < 0.05). The highest mean SBS (N ± SD) was observed in football and flower base shapes (73.83 N ± 53.46; 65.82 N ± 37.89 respectively); the lowest mean was observed with diamond and heart shapes (30.51 N ± 11.73; 33.28 N ± 16.89 respectively). When reported in Megaspascals, statistically significant difference was observed for rectangle base shape (3.54 MPa ± 2.69) when compared to all other base shapes. Conclusions: Bracket base shape has an effect on SBS. Higher SBS (N) for rectangle, flower, and football base shape indicates even stress distribution throughout the bracket base. Base shape with a pronounced converging tip over the axial plane may contribute to the reduction in SBS due to increased peak stress concentration resulting in bond failure.