Universal Adhesive Bonding to Sound and Artificially Demineralized Dentin: The Role of Etching Strategy and Resin Composite Type

This study evaluated the effects of dentin substrate, adhesive strategy, and resin composite type on microshear bond strength (μSBS), with particular emphasis on three-second selective dentin etching of artificially demineralized dentin (ADD). Flat midcoronal dentin surfaces from 144 human permanent third molars were allocated according to dentin substrate, adhesive strategy, and resin composite type. ADD was produced using a 14-day pH-cycling protocol. Etch-and-rinse (E&R), self-etch (SE), and three-second selective dentin etching (SDE) strategies were evaluated with a thermoviscous bulk-fill and an injectable resin composite. μSBS was tested after 24-h water storage. Data were analyzed using three-way analysis of variance and heteroscedasticity-robust HC3 tests, with Bonferroni-adjusted pairwise comparisons. Sound dentin showed higher μSBS than ADD (p < 0.001), and adhesive strategy had a significant effect (p = 0.006). SDE showed higher μSBS than SE after Bonferroni adjustment (p = 0.0246), whereas the E&R–SE difference did not meet the adjusted significance threshold (p = 0.0503). No statistically significant difference was detected between SDE and E&R. The resin composite main effect and interactions were not statistically significant. These findings concern immediate bond strength after 24-h water storage and do not establish long-term bonding performance.