Optimizing phosphoric acid etching times across different formulations: Impact on dentin structure, roughness, and adhesive performance after 4 years

Abstract

Objective: To evaluate the effect of etching times with commercial phosphoric acids on the demineralization pattern, dentin roughness, chemical mapping, nanoleakage (NL), and resin-dentin microtensile bond strength (μTBS) when used with an etch-and-rinse adhesive, assessed immediately and after 4 years of water storage. Methods: Four commercial phosphoric acids were tested: Ultra-etch [ULE, 35 %], Scotchbond Universal Etchant [SUE, 32 %]; Dentsply Dental Conditioner [DDC, 37 %] and Total Etch [TTE, 37 %]. Occlusal dentin from 188 molars was etched for 3 and 15 seconds. Demineralization patterns were observed via SEM, roughness was measured using optical profilometry, and chemical mapping was obtained through micro-Raman spectroscopy. Resin-dentin bonded beams were prepared for NL and µTBS testing at baseline and after 4 years of water storage. Data were statistically evaluated with three-way ANOVA and Tukey's test (α = 0.05). Results: After 15-second etching, ULE exhibited significantly less demineralization compared to DDC and TTE, while SUE had an intermediate effect (p = 0.001). No differences were observed among groups after 3-second etching (p > 0.05). ULE and SUE showed lower tubular density than DDC and TTE (p = 0.001). Roughness and chemical mapping indicated lower demineralization at 3 seconds for all groups (p < 0.002), except ULE, which showed similar at both 3 and 15 seconds (p > 0.05). NL and μTBS values were higher for ULE and SUE, regardless of etching times and aging period (p < 0.05). ULE demonstrated the best control over demineralization, followed by SUE, both enhancing resin-dentin bonding performance. Significance: A 3-second phosphoric acid etching time produces sufficient dentin substrate modification for adhesive infiltration, maintaining bond strength and reducing nanoleakage—even after 4 years. The formulation of the acid significantly influences the demineralization pattern and adhesive performance.