Influence of C-factor and light-curing mode on gap formation in resin composite restorations

To investigate the influence of the C-factor (Cf) and light-curing mode (LCM) on gap formation in resin composite (RC) restorations. Cylindrical Class I cavities with a 5.0 mm diameter andthree different depths (1.0, 2.0 and 3.0 mm) were prepared in the occlusal surfaces of 60 human molars and restored with P60 (P) and Supreme (Su). RCs were light-cured in accordance with two modes: Standard (S)--850mW/cm2/20 seconds and Ramp (R)-100 up to 1000mW/cm2/10 seconds +1000mW/cm2/10 seconds. After storage in distilled water, the restorations were cut into three slices and the gap widths were analyzed in a 3D-scanning system. The data were analyzed by ANOVA and Student-Newman-Keul's test (alpha = 0.05). ANOVA detected significant influence for the RC, Cf and LCM independent factors and for the double interactions RC vs Cf and LCM vs Cf. Smaller gap formation was found for cavities restored with Su. R was responsible for the smaller gap formation. The highest gap formation was found for cavities with Cf = 3.4, followed by Cf = 2.6 and 1.8 without statistical differences between them. These findings suggest that Cf played an essential role in gap formation. R LCM may allow RC relaxation during polymerization reaction. Finally, nanocomposites (Su) may lead to less gap formation at the resin-dentin interface.