Do universal adhesives applied with different modes affect remineralized enamel surfaces? A SEM study

The aim of this study is to evaluate the effect of different application modes of different universal adhesives on enamel shear bond strength after remineralization on white spot lesions and to evaluate the changes in the remineralized surface with SEM/EDX analysis. 144 bovine enamels were obtained for shear bond strength testing, and 120 enamel were obtained to evaluate the effect of adhesives on Ca/P ratios. Demineralization and remineralization values were measured using DIAGNOdent Pen and randomly distributed into 12 groups (n = 12). Universal adhesives (G-Premio Bond, Clearfil S³ Universal Bond) were applied to intact, demineralized, remineralized enamels according to total-etch and self-etch modes, then resin composite (R = 1 mm, h = 2 mm) was placed and polymerized. Changes in Ca/P ratio with the removal of adhesives from enamels were evaluated by EDX. Data were analyzed with three-way ANOVA test and post hoc Tukey HSD test. According to the data, there are statistically significant differences in universal adhesives, application modes, bond strength, and Ca/P ratios between different enamel surfaces. For both adhesive systems, highest bond strength was obtained on sound enamel samples with the total-etch adhesive mode. In remineralized enamel, bond strength in total-etch mode decreased when G-Premio Bond was used compared to self-etch system and increased when Clearfil S³ Universal Bond was used. Use of Remin Pro, a remineralization agent containing xylitol, hydroxyapatite and fluoride, increased bonding on enamel surface compared to demineralized enamel, and this effect is close to bonding to intact enamel surface. Universal adhesives change the Ca/P ratios on remineralized surface. To increase the bond strength on this surface layer, it can be recommended to remineralize the surface before adhesive treatments because of the weakened bond strength. In both universal adhesives, bonding to remineralized tooth enamel produced bond strength values similar to those on intact tooth enamel. Bond strength increases when the Remin Pro remineralization agent is applied to tooth enamel surfaces. Applying universal adhesive with mild-acidity in the self-etch mode, rather than a total-etch mode to remineralized enamel increased bond strength. Applying a light-acidity universal adhesive in the total-etch mode increased the bond strength. Using orthophosphoric acid in remineralized enamel should be exercised carefully.