Light polymerization during cavity filling: Effect of ‘exposure reciprocity law' and the resulted shrinkage forces on restoration margins

Abstract

Objective. To evaluate shrinkage development and marginal integrity of a micro hybrid restorative composite as a function of irradiance. Materials and methods. Linear displacement and shrinkage were measured with custom-made devices for irradiances of 100, 200, 400, 800 and 1600 mW/cm² at a constant radiant exposure of 16 J/cm². Marginal adaptation (MA) of composite restorations performed with a self-etch adhesive (Syntac Classic, Ivoclar Vivadent) and a micro hybrid composite (Tetric, Ivoclar Vivadent) was evaluated before and after mechanical loading with 300,000 cycles at 70 N. Results. The highest percentage of MA was attained by the group light cured with an irradiance of 100 mW/cm² for 160 s. No significant differences were observed between the rest of the groups. Shrinkage development was similar in all groups. Conclusions. For the material tested in this study, the reciprocal relationship between irradiance and time of exposure had no significant effect on restoration margins and shrinkage stress development within the range of 200–1600 mW/cm² with a constant radiant exposure of 16 J/cm²