Bonding neat hydrophobic-rich resins to etched dentin: A proof of concept

Objectives: To examine whether the effectiveness of current dentin-priming approaches requiring solvated hydrophilic resins may be replicated by modifying the infiltration dynamics of neat methacrylate-based monomers into dry-etched dentin using dimethyl sulfoxide (DMSO) pretreatments.

Methods: H₃PO₄-etched mid-coronal dentin surfaces from human molars were air-dried for 30 s and randomly pretreated with 50 %(v/v) ethanolic DMSO for 20 or 60 s. Untreated samples and an isolated wet-bonding group served as controls. Samples were bonded with a three-step etch-and-rinse adhesive or simply with the solvent-free hydrophobic-rich resin. Restored crown segments (n = 7/group) were stored in distilled water for 24 h and sectioned for microtensile bond strength testing. Resin-dentin beams (0.8 mm²) were tested under tension until failure (0.5 mm/min) after 24 h or 2 years of storage in artificial saliva at 37 °C. Nanoleakage evaluation and hybrid layer characterization were performed by SEM. Bond strength data was examined by three-way ANOVA followed by Tukey and Dunnett's test (α = 0.05).

Results: Pretreatments significantly affected the ability of neat and solvated resins to bond to etched-dry dentin (p = 0.001). Ageing significantly lowered bond strengths depending on resin composition and DMSO-application times (p = 0.007). While hybridization of DMSO-treated dentin with the solvated resin produced no significant reductions in bond strengths after ageing (p < 0.05) improving hybrid layer integrity, direct bonding of the neat hydrophobic-rich resin matched the long-term bonding performance of the "gold standard" wet-bonding protocol (p > 0.05).

Significance: Lowering dentin's hydration state via DMSO-dry bonding allows direct coupling of neat methacrylate-based resins, which may contribute to developing new strategies to ultimately extend the durability of resin-dentin interfaces.