Influence of Activation Mode of Dual-cured Resin Composite Cores and Low-viscosity Composites Liners on Bond Strength to Dentin Treated with Self-etching Adhesives

The objective of this study was to investigate the effect of light- or chemical initiation on the polymerization reaction of dual-cured composite core buildup materials (CM) with respect to their shear bond strength to dentin treated with self-etching adhesives (SE), in the presence or absence of a low-viscosity composite liner (LI). Two SEs (Clearfil SE Bond and Unifil Core Bond), their respective CMs (DC Core Paste and Unifil Core), and a LI (Protect Liner F) were tested. After removing the labial enamel surfaces of 8 bovine incisors, each flat dentin surface was sectioned into 4 pieces with similar surface areas (30 mm2). The dentin surfaces were wet abraded with 600-grit SiC paper and randomly divided into 8 groups. Experimental groups comprised the use of a SE and its respective CM with or without an intermediate application of the LI and with or without CM light activation. Three cylinders of CM (0.5 mm high and 0.75 mm in diameter) were applied to each bonded dentin surface (n = 12), using a tygon tubing mold. After water storage for 24 h, specimens were subjected to microshear testing. Data were statistically analyzed by two-way ANOVA and Tukey's test (5%). For both SEs, LI application and CM light activation showed significantly higher bond strengths than the groups in which an intermediate LI was not used or the CMs were only chemically cured. The bond strength of CM to dentin using SE is reduced if the LI and light activation are not employed. Keywords: adhesive systems, resin core, bond strength, dentin, composite activation