Comparison of Shear Strength after Bonding of Orthodontic Brackets with Immediate and Late Light Curing

Objective: This study aimed to compare the shear bond strength of brackets bonded to tooth enamel with immediate and late light curing of different orthodontic resins.

Materials and Methods: 108 bovine teeth were used, divided into three groups of 36, according to the type of resin used for bonding (G1 Transbond XT, G2 Orthocem, G3 Natural Ortho) and each group was subdivided into three subgroups of 12, with immediate light curing (T0), delay of 5 minutes (T5), and delay of 10 minutes (T10). The mandibular incisor brackets were bonded to the teeth and, after 24 hours, subjected to the shear test in a universal testing machine with a 500N load cell and a constant speed of 1mm/min. Intergroup comparisons were performed using the ANOVA and Tukey tests.

Results: There was a significant difference between the types of resin and time for light curing. The Transbond XT resin showed significantly higher shear strength at times T5 and T10. Regarding the comparison between the light-curing times, there was a significant difference for the Transbond XT resin and all resins together, with the adhesion strength at T10 being significantly higher than at T0.

Conclusion: The delay in photopolymerization tends to increase the adhesion strength of orthodontic resins, as there was a significant difference between immediate and 10-minute delayed photopolymerization when all resins were compared together.