Particle characterization of different air-abrasion techniques and their impact on dentin topography and bonding performance of a universal adhesive.

OBJECTIVE: To evaluate the effects of different air-abrasion protocols on dentin surface properties and bonding performance of a universal adhesive applied with etch-and-rinse (ER) or self-etch (SE) strategies. METHODS: One hundred and twenty-six human molars were allocated according to airborne-particle abrasion protocols: control (no air-abrasion), dry abrasion (25 µm and 50 µm Al₂O₃), moist abrasion (29 µm and 53 µm Al₂O₃), and moist bioglass. Particles were characterized by SEM, FTIR and size distribution. Before bonding, dentin surfaces were characterized by FTIR-ATR, 3D profilometry, and SEM (tubule density and smear layer thickness). Bonding performance was assessed by micro-Raman spectroscopy of hybrid layers (immediate), nanoleakage, and microtensile bond strength (µTBS), immediate and after thermocycling (n = 8). Data were analyzed using ANOVA and post hoc tests (α = 0.05). RESULTS: Dry air-abrasion produced fewer chemical alterations and lower smear layer deposition (p < 0.05), whereas moist abrasion increased mineral loss and smear layer persistence (p < 0.05). Surface roughness increased after Al₂O₃ abrasion, while bioglass resulted in smoother surfaces (p < 0.05). The ER strategy promoted higher dentinal tubule exposure than SE (p < 0.05). Dry Al₂O₃ abrasion, particularly 50 μm with ER, showed the highest immediate μTBS, lower nanoleakage, and more stable bonding after thermocycling (p < 0.05). In contrast, moist-abrasion protocols, especially bioglass, reduced μTBS and increased nanoleakage (p < 0.05). SIGNIFICANCE: Dry air-abrasion with 50 µm aluminum oxide improves immediate dentin bonding over moist protocols, particularly with ER strategy. No pretreatment enhances bonding after thermocycling compared to air-abraded dentin.