Influence of Air-Abrasion Pretreatments and Adhesive Composition on Bond Durability to Natural Sclerotic Dentin

Background: Bonding to sclerotic dentin remains one of the most challenging procedures in restorative dentistry due to tubular occlusion and hypermineralization, which limit resin infiltration. This study evaluated the influence of adhesive system, surface treatment, storage time, and substrate position on microtensile bond strength (µTBS) to natural sclerotic dentin. Methods: Sixteen extracted human molars with sclerotic dentin were selected and randomly assigned to nine experimental groups according to the adhesive system and surface treatment. Three adhesives were tested: a two-step self-etch adhesive (Clearfil SE Bond 2, Kuraray Noritake Dental, Tokyo, Japan) and two universal adhesives, one containing 10-MDP (G-Premio Bond, GC Corp., Tokyo, Japan) and one without 10-MDP (iBond Universal, Kulzer GmbH, Hanau, Germany). Each adhesive was applied under three conditions: no pretreatment (control), Al2O3 air-abrasion, and Bioglass 45S5 (ProSylc®, Velopex International, London, UK) air-abrasion. Composite build-ups were performed, and the specimens were sectioned into 1 mm2 beams for microtensile testing either after 24 h or after 6 months of storage in distilled water at 37 °C of hypertonic solution. The effect of beam position (central vs. peripheral) was also analyzed. Bond strength was measured by µTBS testing, and the results were analyzed using multifactorial ANOVA and Tukey’s test (α = 0.05). Failure modes were examined under stereomicroscopy, whereas optical microscopy was used for qualitative evaluation of representative fractured interfaces. Results: Significant main effects were found for adhesive system and surface treatment (p < 0.001), with a notable interaction between them (p < 0.05). Al2O3 air-abrasion produced the highest bond strengths, particularly for the self-etch adhesive containing functional monomers (53.4 ± 6.1 MPa), representing a 53% increase over the untreated control. Bioglass air-abrasion did not enhance adhesion and led to irregular hybrid layers. The position of the beams affected only one universal adhesive, with higher µTBS in peripheral regions. After six months of water storage, bond strengths remained stable across most groups, indicating good hydrolytic resistance of the interfaces. Conclusions: Both the adhesive system and the surface treatment significantly influenced bonding effectiveness to sclerotic dentin. The combination of Al2O3 air-abrasion with an MDP-containing self-etch adhesive achieved the most durable and homogeneous bond interface. providing a clinically reliable protocol for restorative treatments in sclerotic dentin. Within the limitations of this in vitro study, this combination may represent a potentially useful strategy for improving adhesion to sclerotic dentin, although further investigations are required to confirm its clinical applicability.