Effect of Inhibitor Concentrations on Polymerization Characteristics of Light-Cured Composites

Objectives: The aim of this study was to use an inhibitor to slow polymerization and evaluate its effect on contraction stress kinetics, degree of conversion (DC), and flexural strength (FS) and modulus (E) in light-cured methacrylate-based composites. Methods: An experimental composite was prepared as a blend of BisGMA:UDMA:TEGDMA (1:1:1 weight ratio) with 70wt% silanated glass fillers. Groups one through eight were made by varying the concentration of the butylated hydroxytoluene (BHT) inhibitor (0.01, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 wt%). Specimens (n=5/gp) were light activated for 60 s at 608±21 mW/cm². A tensometer was used to determine contraction stress (CS), maximum stress rate (SR), and gel time (GT). DC was determined with near-infrared spectroscopy on every tensometer specimen. Exothermic changes were measured on similar specimens cured with similar light intensity. FS and E were determined with 3-point bending (n=10). Results were analyzed by one-way ANOVA/Tukey's test at the 0.05 level of significance. Results: Group 1 showed the highest CS, SR, and the shortest GT. Groups 4-8 showed significantly less CS, SR and longer GT than group 1. Groups 6&7 showed significantly the highest DC and group 8 the lowest. Group 1 showed the highest temperature rise and the steepest slope while group 8 showed the lowest. Group 6&7 showed the highest FS but were not statistically different from groups 1-5. Group 8 had the lowest E but was not statistically different from the other groups. Conclusion: High level of inhibitors appears to be an effective method to slow polymerization and reduce CS without any compromise in DC. Slow cure did not show any negative effect on E of the resultant polymers. The reduction in CS cannot be attributed to compromised DC or E rather it may be explained by increased flow capacity of the resin.