Change of shade by light polymerization in a resin cement polymerized beneath a ceramic restoration

Objectives The aim of this in vitro study was to examine the effect of the color changes of a resin cement material (Variolink II) polymerized beneath a simulated ceramic restoration (IPS Empress II) by two different light polymerizing units. Methods A conventional halogen light and a light emitting diode unit were used to polymerize resin cement with catalyst. A pressable ceramic block (10 mm in diameter, 2 or 1 mm in height) was used as an interface between the polymerizing light tip and resin cement. Colorimetric values of the specimens before and after polymerization were measured using a spectrophotometer (Easy Shade). The CIE L*a*b color system was used for the determination of the color difference. Differences between measurements were calculated as ΔE*ab. Repeated measurements analysis of variance (ANOVA) was used to analyze the data (polymerization of resin cement, polymerizing unit and ceramic thickness) for significant differences. The Tukey HSD test and paired two-tailed tests were used to perform multiple comparisons (α = .05). Results L*a*b values of ceramic system were affected by the polymerization of resin cement (before and after) (P < .01). The a* value was affected by polymerization unit (P < .05), however L* and b* values were not affected by the light polymerization unit (P > .05). The b* value was affected by ceramic thickness (1 or 2 mm) (P < .05), but L* and a* values were not affected by ceramic thickness (P > .05). The specimens polymerized beneath 1 mm ceramic thickness with conventional halogen light induced a significantly higher color changes than any other specimen (P < .05). Conclusions The results of this in vitro study suggest that light polymerization of the resin cement (Variolink II) used in this study is an important factor for the color of the definitive restoration and should be considered during shade selection and fabrication.