In vitro evaluation of secondary caries development in enamel and root dentin around luted metallic restoration

Materials that release fluoride have been recommended for patients with high caries risk, but there is no conclusive evidence of their effect on fixed prostheses abutments. This study evaluated the influence of a resin-modified glass-ionomer cement on in vitro caries development in enamel and root dentin around metallic restoration. The cervical portion of 12 human third molars were sectioned in four blocks that were randomly divided into four Groups (n = 12; 1 block from each tooth/group): ZP (restoration + zinc phosphate cement), GI (restoration + resin-modified glass-ionomer cement), C1 (no restoration and no pH cycling), and C2 (no restoration and pH cycling). In ZP and GI, metallic restorations were luted at the crown-root junction. ZP, GI and C2 were submitted to a pH-cycling model. All blocks were sectioned, embedded and polished. Enamel and root dentin demineralization were evaluated through cross-sectional microhardness Knoop measures at 20 to 80 microns of depth (from the outer surface) and at 20 to 220 microns of distance from the cavity margins. Mineral loss values were calculated from Knoop hardness numbers. Data were analyzed by ANOVA, Tukey's test and regression analysis. Groups ZP, GI and C2 showed demineralization in relation to C1, which was more superficial in enamel than in root dentin. In root dentin, mineral loss in ZP and GI was smaller than in C2. Distance from the cavity margins was not significant. There was no difference between resin-modified glass-ionomer cement and zinc phosphate cement regarding artificial secondary caries development in both dental substrates.