Sensitivity of composite materials to ambient light and clinical working time

Abstract

Introduction. The aim of this study was to determine sensitivity of composite materials to ambient light by a modified standard ISO 4049:2000 and clinical working time. Materials and Methods. The following materials were tested: nano-hybrid Herculite XRV Ultra (Kerr), micro-hybrid Herculite XRV (Kerr), Zmack (Zhermack), SuperCor (SpofaDental) and Valux Plus (3M ESPE). Five samples in each group were exposed to ambient light of 8000 lx, which comprised dental unit light and natural light. After 60 sec of exposure, each sample was visually examined for signs of inhomogeneity meaning that material did not pass the test. Clinical working time was studied by applying a custom-built, standardized indenter into composite specimens of about 2 mm thickness during the same exposure to ambient light. Completion of polymerization was tested by dissolving samples in ethanol and measuring the difference in thickness before and after the test. Results were statistically analyzed using ANOVA at the significance level of 0.05. Results. Only Herculite XRV Ultra passed the test of sensitivity to ambient light, while other materials showed signs of inhomogeneity. Herculite XRV Ultra showed significantly longer working time than other composites, the average was 250 sec (p<0.05). The mean values of working time for other materials ranged between 117-131 sec and there was no significant difference between them (p>0.05). Conclusion. Due to the lower sensitivity to ambient light and significantly longer clinical working time compared to micro-hybrid composites, Herculite XRV Ultra can be recommended for clinical procedures that require prolonged working time with material in plastic condition.