Effect of tooth surface morphology and bracket base configuration on the shear bond strength of the orthodontic brackets

Abstract

Debonding of brackets is one of the most frustrating aspects during orthodontic treatment because it results in increased treatment time and additional costs. Several studies, involving different factors have been carried out, however, the effect of bracket base configuration and tooth surface morphology are not yet fully investigated in literature. The purpose of this study was to evaluate the effect of bracket base configuration and tooth surface morphology on shear bond strength of orthodontic brackets, using finite element method. Methods and materials: In vitro shear bond test on two groups of 25 human teeth (upper central and canine) and stress analysis using finite element method on five human teeth (upper central, premolar, canine and lower central and premolar) were performed. Considering non-normality of the experimental test data, Mann Witney U test was used to compare two groups. Results obtained from both tests were then comprehensively investigated. Three different bracket base shapes (ellips, tetragonal, pentagonal) were modeled and compared, using FEM. Results: Stress distribution in teeth with plane enamel surface topography was limited to a narrow margin in the border with lower stress. However, stress was higher in teeth with curvature and spread from borders to center. Experimental result also showed that upper canine had lower shear strength than upper central (p=0.001). Ellipse bracket base shape had more appropriate stress distribution than the others. Conclusion: The present study revealed that shear bond strength was significantly influenced by tooth shape and bracket base configuration, whereby a curvature configuration tended to have lower bond strength.