The Effect of Light-Curing Time to Adhesive Layer on Shear Bond Strength of Composite to Dentin

Statement of problem: For reducing light exposure time of tooth-colored restorations, and chair time reduction, different experiments have been conducted. The purpose of this study was to determine the effect of different light exposure times to adhesive layers (Excite and Prompt L-pop) on the shear bond strength of dentin- composite interface. In this in-vitro study, 72 human intact premolar teeth were mounted in acrylic casts and enamel buccal surfaces were removed. The bonding surfaces were equalized using a surface index. Teeth were divided into six equal groups each of 12 (A, B, C, D, E, and F). According to the manufacturer instructions, Excite adhesive in groups A, B and C, and prompt L-pop in groups D, E and F was used. A and D groups were not exposed to light, but the exposure time in groups B, E and C, F was 20s, and 40s respectively. After one week of storage in 37°C water, synergy composite resin was applied and then was exposed to light. The specimens were loaded by shear force with 1 mm/min cross head speed. Data were analyzed by two-way analysis of variance (ANOVA). The means shear bond strength of groups A,B,C,D,E, and F were 3.9, 13.45, 18.1, 8.3, 24.81, 24.99 Mpa, respectively. The differences between shear bond strength of groups A, B and C and between groups B, D were statistically significant (p=0.0001). However, the differences between groups E, F were not statistically significant. In all exposure times, the bond strength of Prompt L-pop was significantly higher than that of Excite. According to the results of this study, increase in the light exposure led to the higher bond strengths in Excite groups. In Prompt L-pop groups, 20s exposure time was adequate and by increasing the light exposure time, shear bond strength was not affected. Without light exposure in both materials, the least bond strength for the composite resins was not attainable.