Laboratory and clinical perspectives of universal adhesives

The continuous evolution of adhesive dentistry has led to the development of universal adhesives (UAs) aimed at simplifying clinical procedures while maintaining effective bonding. However, degradation of the resin-dentin interface remains a major limitation due to enzymatic activity and the intrinsic complexity of dentin. This doctoral research investigated strategies to improve hybrid layer stability and bond performance through four approaches: (1) the use of glutaraldehyde-based desensitizing agents as dentin primers; (2) application of the Immediate Dentin Sealing (IDS) technique for indirect restorations; (3) evaluation of the effects of endodontic irrigants on adhesive performance; and (4) incorporation of bioactive materials into adhesive systems to promote remineralization and enzymatic protection. Extracted human teeth were sectioned to obtain standardized dentin specimens. Universal adhesives were applied using etch-and-rinse, self-etch, or selective enamel etching strategies. In selected groups, Gluma Desensitizer was applied prior to bonding, IDS protocols were performed, or dentin was pre-treated with NaOCl, EDTA, or CHX. Adhesive performance was evaluated using microtensile and shear bond strength tests immediately and after aging procedures. Hybrid layer morphology, nanoleakage, and tubule occlusion were assessed through SEM and confocal microscopy, while in situ and gelatin zymography were used to evaluate MMP activity. Bioactive formulations containing ion-releasing components were also investigated. Statistical analysis was performed using ANOVA with a significance level of p < 0.05. Glutaraldehyde-based pretreatment improved bond strength and reduced nanoleakage, likely due to collagen stabilization and reduced enzymatic activity. IDS significantly enhanced bond strength and hybrid layer uniformity. NaOCl negatively affected adhesion, whereas EDTA and CHX showed more favorable effects on substrate preservation. Bioactive materials promoted ion exchange and apatite-like precipitation, suggesting a protective effect against hybrid layer degradation. Overall, the findings support a biofunctional approach to adhesive dentistry, integrating chemical bonding, enzymatic inhibition, and remineralization to improve long-term adhesive stability.