Selective dentin etching : a potential method to improve bonding effectiveness of universal adhesives

Abstract

Objectives: To evaluate whether selective dentin etching protocols using reduced phosphoric acid (H3PO4) etching-times would affect the resin-dentin interaction of a universal adhesive to improve long-term bonding effectiveness. Methods: Mid-coronal flat dentin surfaces were produced on sound third molars, selectively etched with 32% H3PO4 for 3, 5, 10 or 15 s and bonded with a universal adhesive (Scotchbond Universal, 3M ESPE: SU). SU in self-etch mode and a three-step etch-and-rinse adhesive were used as control groups. Bonded specimens were stored in deionized water for 24 h and sectioned into beams (cross sectional area of 0.7 mm2). Micro-tensile bond strength test (n=6) and nanoleakage evaluation were performed immediately, after thermocycling or 6-month storage in artificial saliva. Energy dispersive X-ray analysis (n=6) was performed to determine the residual Ca-content ratio at the hybrid layers and scanning electron microscopy (SEM) was used to observe the micromorphology of the etched dentin surfaces before and after SU application. Data were analyzed by ANOVA and Tukey test (α=0.05). Results: Selective dentin etching for 3 s improved the interaction depth of the tested universal adhesive without overexposing demineralized collagen or reducing Ca-content availability at the bonded interface. The improved immediate bond strengths of the selective etching protocol remained significantly higher (p<0.05) after long-term aging producing hybrid layers without significant differences (p>0.05) in silver uptake levels compared to those produced on non-etched dentin. Conclusions: Despite the adjunctive conclusion that universal adhesives used in self-etch mode produce superior long-term dentin bonding compared to the etch-and-rinse mode, selective etching for 3 s with conventionally used H3PO4 improves dentin bonding effectiveness; nonetheless, longer etching times should be strictly avoided.