Residual amine degradation and oxidation of residual unreacted carbon-carbon double bonds lead to the formation of yellowing compounds.[27-30] In addition, the physicochemical properties of monomers used in a resin matrix can influence stain resistance.[16] As reported by their manufacturers,

RelyX Veneer is composed primarily of bis-GMA and TEGDMA resin, Variolink II contains bis-GMA and UDMA, and Maxcem Elite contains HEMA and MEHQ monomers. As these materials age, the water sorption characteristics of the resin monomers Mitomycin C manufacturer may contribute to differences in the degree of color stability.[16, 35] TEGDMA-based resins release higher quantities of monomers into aqueous environments than bis-GMA- and UDMA-based materials do. Water uptake by bis-GMA-based resins increases in proportion to the TEGDMA concentration

DNA Damage inhibitor and decreases with the partial substitution of TEGDMA by UDMA. UDMA appears to be less susceptible to staining than bis-GMA is.[30] Furthermore, composite resins with larger filler particles may be more susceptible to discoloration. A previous study showed that the size and number of particles can also influence the values of ∆E, ∆L*, ∆a*, and ∆b*, as well as the translucency of composite resins.[29] In another study Variolink Veneer (light-polymerizing), Variolink II (light-polymerizing), Variolink II (dual-polymerizing), and Multilink (autopolymerizing) were used for cementation of 0.7-mm-thick porcelain laminate veneers. The authors reported that cements could ensure color stability when used to cement porcelain laminate veneers, but the change in opacity could affect clinical results. As a result of the study, autopolymerizing cements became more opaque with aging.[17] In the present study, the opaque shade resin cements affected both 0.5- and 1-mm-thick ceramic translucency, while the translucent resin cements were not affected by aging.

There was also no significant difference among the dual- or light-cured translucent shade resin SPTLC1 cements beneath the ceramics. Tristumulus colorimeters have been found to have precision and accuracy for the in vitro assessment of monochromatic porcelain specimens,[40] and the colorimeter used in this study was previously validated for evaluation and specification of dental porcelain color.[20, 40] The colorimeter used in this study was a small-diameter color measuring instrument. When using an instrument with a small aperture for both illumination and collection of light, the amount of reflected light is reduced, causing an inadequate L* value reading. The edge-loss effect generally occurs when illumination and color measurement are made through the same window.[40] Thus, the results of the present study may be limited; however, the specimens were prepared with a diameter (10 mm) greater than the diameter (3 mm) of the measurement tip of the colorimeter, to minimize the possible effects of edge loss.