The Effect of Different Light Curing Units and Composite Thicknesses on the Shear Bond Strengthof Composite to Dentin

Abstract Background and Aim: Development of new composite resins is one of the most important technological advances in the field of cosmetic dentistry. The aim of this study was to investigate the effect of different light curing units and composite thick-nesses on the shear bond strength of composite to dentin. Materials and Methods: In this experimental in-vitro study, the test groups were composed of 80 dentinal samples, prepared on occlusal surfaces of 80 maxillary pre-molar teeth and routinely divided into 8 groups of 10. Two cylindrical molds (2.5×2mm (in groups 1, 4, 5, and 6) and 2.5×5 mm(in groups 2, 3, 7, and 8)) were filled in bulk using P60 (groups 1, 3, 4, and 8) and Ceram X (groups 2, 5, 6, and 7) composites and light cured with LED ( in groups (4, 6, 7, and 8) and QTH (in groups 1, 2, 3, and 5) light curing units .After curing and 3 months aging in 37°c water, shear bond strength of all samples were evaluated using a universal testing machine with 1mm/min crosshead speed. One- and three-way ANOVA were used for statistical analysis using SPSS software. Results: The maximum (31.75 MPa) and minimum (15.34 MPa) mean of shear bond strength was in groups 1 and 7, respectively. Type and thickness of composites had significant effects on shear bond strength and no significant differences were found between two light curing units. Conclusion: The shear bond strengths of P60 and CeramX composites tested were much lower when cured in a 5-mm than in a 2-mm increment. The two types of light curing units tested did not show any significant differences in the amount of shear bond strength. Key Words: Shear bond strength, composite resin, light curing unit