Catechol-based polydopamine modification of a dentin adhesive: effects on surface wettability, microhardness recovery, and mineral deposition

Abstract This study aimed to evaluate the influence of polydopamine (PDA), a bioinspired catecholamine polymer, on the functional performance of a commercial etch-and-rinse dentin adhesive when incorporated at 2% and 4% (v/v). Although PDA has demonstrated promising biomimetic and mineralisation-promoting properties in various biomedical and dental applications, its effects on the physicochemical performance of commercial etch-and-rinse dentin adhesives have not been comprehensively investigated. The study, therefore, focused on the effects of PDA incorporation on degree of conversion, pH, hydrophilicity, microhardness recovery, and mineral deposition potential. PDA was synthesised via self-polymerisation in Tris buffer (pH 8.5) and incorporated into Prime & Bond Elect adhesive at 2% and 4% (v/v). The degree of conversion was analysed using Fourier-transform infrared spectroscopy before and after light-curing. Hydrophilicity was assessed via contact angle measurements of adhesive droplets on acid-etched bovine dentin surfaces at 2 and 5 s. Microhardness was evaluated on demineralized dentin at baseline, after bonding, and following 7-day ageing in artificial saliva. Scanning electron microscopy (SEM) was used to qualitatively assess surface morphology and mineral-like deposition on deeply demineralised dentin after 14 days. pH values were measured using a microelectrode pH meter. Statistical analysis was performed using ANOVA with a significance level of p < 0.05. The results showed that PDA incorporation did not affect polymerisation, with comparable degrees of conversion values among all groups ( p = 0.984), and adhesive pH remained unchanged. Dentin hydrophilicity improved with PDA modification; at 5 s, contact angles decreased from 38.1 ± 4.7° (control) to 29.8 ± 1.7° (2% PDA) and 22.5 ± 3.6° (4% PDA), demonstrating a concentration-dependent increase in wettability. Microhardness decreased after etching in all groups ( p < 0.05), followed by partial recovery in the PDA-modified groups after ageing in artificial saliva. SEM revealed minimal surface deposition in the control, moderate mineral-like deposits in the 2% PDA group, and more extensive mineral-like surface deposition in the 4% PDA group. EDX confirmed the presence of calcium and phosphorus within the deposits, supporting their calcium phosphate-containing nature. It was found that incorporation of PDA, particularly at 4%, enhanced dentin surface hydrophilicity, promoted calcium phosphate-containing surface deposition, and improved microhardness recovery. Polymerisation efficiency and adhesive acidity were not adversely affected. These findings suggest that PDA is a promising biomimetic modifier for commercial dentin adhesives. However, further bond strength, long-term ageing, and clinical studies are needed to confirm its clinical potential.