Influence of the feldspathic ceramic thickness and shade on the microhardness of dual resin cement.

This study evaluated the microhardness of a dual resin cement under the influence of thickness and shade of a feldspathic ceramic. Ninety-five bovine incisors were selected; the crowns, with the roots removed, were embedded in a polystyrene resin and were randomly divided into 19 groups (n=5). On the buccal surface, a standardized cavity, 4.0 mm in diameter and 1.0 mm in depth, was prepared. Ceramic restorations (Noritake Ex 3) were manufactured with 4.0 mm diameter and 1, 2 and 4-mm thicknesses at shades A1, A2, A3, A3.5 and A4. A dual resin cement (Rely X-ARC) was inserted into the prepared cavity. A mylar strip was positioned over the prepared cavity, and light curing was performed for 40 seconds following the protocols: controls-without insertion of the restoration at distances of 0.0, 1.0, 2.0 and 4.0 mm. The remaining groups had the restorations positioned between the resin cement and light source during polymerization. The Vickers hardness test was performed on the cement layer with 50 g of load application for 30 seconds, with 5 indentations for each sample. Two-way ANOVA (5 x 3) and Tukey test (alpha = 0.05) were used to compare the results. The chemical curing of the dual resin cement was not sufficient to compensate for the energy attenuation promoted by the interposition of A3.5 and A4 ceramic material with 4-mm of thickness. The thickness had a greater influence on the cement microhardness than the ceramic restoration shade.