The effect of amine-free initiator system and polymerization type on long-term color stability of resin cements: an in-vitro study

Background This in vitro study evaluated the effect of amine-free initiator system and polymerization type on long-term color change of amine-free light-cure and dual-cure resin cements. Methods Sixty disk-shaped specimens (10 x 1 mm) were prepared from six different amine-free resin cements; NX3 Nexus light-cure (LC) and dual-cure (DC), Variolink Veneer (LC) and Variolink II (DC), Relyx Veneer (LC) and Rely X Ultimate (DC). A feldspathic porcelain specimen (12 x 14 x 0.8 mm) was obtained from a CAD/CAM block (Cerec Blocks; Sirona Dental Systems GmbH, Bensheim, Germany) for color testing. The feldspathic specimen was placed on the resin cement disk and all measurements were performed without cementation. A spectrophotometer was used for color measurements. Specimens were subjected to thermal aging (5 degrees C and 55 degrees C; 5000 and 20,000 cycles). Specific color coordinate differences (Delta L, Delta a, and Delta b) and the total color differences (Delta E-00) were calculated after immersion in distilled water for different periods. Normality of data distribution was tested by using the Kolmogorov-Smirnov test. Data were statistically in a model of repeated measures, using multivariate tests and Tukey's multiple comparison tests at a significance level of p < 0.05. Results increment E-00 values of resin cements were influenced by cycle periods, significantly (p < 0.05). The highest Delta E00 values for long term were obtained in the NX3 (DC) (3.49 +/- 0.87) and the lowest in the NX3 (LC) (1.41 +/- 0.81). NX3 (LC), Variolink (DC), RELY X (LC) resin cements showed clinically acceptable color change after long-term aging ( increment E-00 < 1.8). Conclusion Light-cure resin cements should be preferred for long-term color stability of full ceramic restorations.