The comparison of the effect of different types of curing of orthodontic metal brackets on bond strength and degree of polymerization

Abstract

Objective: The aim of this study was to investigate the effect of the direction of light-curing on bond strength and adhesive polymerization of orthodontic metal brackets. Materials and Methods: This in vitro study contained 75 extracted human upper premolars randomly divided into three groups according to curing direction: group A (20 second curing from occlusal side of the bracket), group B (10 seconds from occlusal and 10 seconds from gingival), group C (5 seconds from four corners of the bracket). After bonding, the brackets were subjected to shear bond strength (SBS) test performed with universal testing machine. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) analysis was used to find the polymerization ratio of the adhesives in each groups. Kruskal-Wallis and Mann-Whitney U test were used to statistical analysis of SBS and FTIR data at a 0.05 level of significance. Results: The difference in SBS of metal brackets was not statistically significant between the groups (p > 0.05). However the difference in polymerization ratio was significant between all groups where the highest and lowest ratio was belonged to group A and B respectively (p < 0.05). Conclusion: Curing of metal brackets from four corners does not increase its bond strength and/or polymerization.