Assessment of color stability of different resin cements having different modes of polymerization before and after aging

Abstract

Porcelain Laminate veneers (PLVs) Represent a more conservative approach compared with all-ceramic full coverage restorations and allows superior eshtetics and translucency.The Challenge with poreclain laminate veneers is to achieve ideal aesthetics with limited preparation of the enamel. Studies have shown that the luting cements underlying the porcelain restorations with different shades can influence the final shade, translicency and opacity of restorations. For poreclain laminate veneers cementation, light-cured resins have been often preferred to chemically cured or dual-cured resins because of their color stability and ‘polymerization On demand’ characteristics. The Thickness and shade of the porcelain affects the degree of polymerization of both dual and light-polymerized resin luting agents, and achieving optimal polymerization is important for long- term color stability.

The aim of this in vitro was to evaluate the effect of aging on the color stability of different resin cements and compare between the change in color content of two dual cured and one light cured resin luting cement after an aging process to determine which mode of polymerization and which resin cement has the better color stability.

In this study the dual-cured resin cements used were : RelyX ultimate and RelyX unicem and the light cured resin luting cement used was RelyX veneer, where 0.1 mm thickness of the resin cements were bonded to the unglazed surface of a 0.5 mm thickness and 10 mm diameter glass ceramic discs (IPS Empress CAD) after been smoothened and polished; by means of a cylindrical teflon mould with an internal stopper of 0.6 mm and pressed together with a glass slab under finger pressure and the excess resin cement was removed and then cured from the free surface of the mould for 20 sec according to the manufacturer’s instructions.

Thirty ceramic discs were used where each 10 discs represented a group in which one resin cement of the above was used, then the samples were detached from the glass slab and trimmed.

After that by means of a spectrophotometer (Vita Easyshade compact) the a* , b* and L * values (according to the CIE Lab system) of each sample was recorded immediately after curing , then after 24 hours then after 1000 cycles of thermal aging by means of thermocycling then after 2000 cycles and finally after 3000 cycle. Each cycle consisted of 30 sec Dwell time in a 5C0 water bath then 30 sec in a room temperature water bath and finally 30 sec in a 55 C0 water bath. Between the aging stages the samples were placed in a 37 C0 distilled water bath.

Then after aging the ∆E ( the change in color content) of each resin was calculated after each one of the aging stages by the following equation

∆E = [(∆L*)2 + (∆a*)2 + (∆b*)2]½

The general population can distinguish color differences of value (∆E>3.3) , which can be considered clinically significant , below that value it is regarded a clinical success.

The results showed that RelyX Ultimate self-etching dual-cured resin cement had the least color change in all cements after 3000 cycles of thermal aging (∆E = 2.6749) . RelyX veneer total-etch light-cured resin cement comes second after RelyX Ultimate after 3000 cycles of thermal aging (∆E = 2.9026) . RelyX unicem universal Aplicap self-adhesive, dual-cured resin cement comes last after both RelyX Ultimate and RelyX veneer after 3000 cycles of thermal aging (∆E = 3.0606).