A resin adhesive with balanced antibacterial and mineralization properties for improved dental restoration

Objective Aiming to develop an adhesive formulation that achieves a harmonious equilibrium between antibacterial efficacy and mineralization potential, 2-methacryloyloxy ethyl phosphorylcholine (MPC), N,N-dodecylvinylimidazole (DCV), and Sr-doped hydroxyapatite (Sr/HAp) nanorods were incorporated as functional constituents into the adhesive matrix, employing carefully optimized proportions. Methods The adhesive formulation comprised a blend of bisphenol A glycerolate dimethacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), and 1,6-hexanediol dimethacrylate (HDDMA) monomers. The effects of MPC and DCV additions, ranging from 1% to 4% (wt%), on various aspects such as adhesive curing kinetics, bonding strength, water contact angle, mechanical properties, and antibacterial activities against Streptococcus mutans (S. mutans) and Human Saliva Bacterial Flora (HSBF), was investigated both individually and in combination. Following the determination of the optimized MPC/DCV ratio, the effect of Sr/HAp on the mineralization potential of the adhesives was evaluated by soaking the samples in 1.5 times simulated body fluid (SBF) at 37 °C for 3 days followed by examination using scanning electron microscopy (SEM). Additionally, biocompatibility assay was conducted using L929 fibroblasts. Results The introduction of MPC and DCV did not interfere the C C conversion degree of the resin blends in all the preparations. Notably, the incorporation of 3 wt% MPC demonstrated a significantly enhancement in the hydrophilicity of the adhesive, resulting in reduced bacterial adsorption. The addition of 3 wt% DCV exhibited potent antibacterial properties against attached bacteria. Furthermore, the introduction of 8 wt% Sr/HAp displayed a positive effect on mineral deposition on the adhesive surface. Importantly, all adhesive formulations demonstrated negligible cytotoxicity. Although a decrease in bonding strength was observed upon the introduction of MPC/DCV, the supplementation of Sr/HAp exhibited a reinforcing effect, effectively compensating for the decline. This beneficial outcome can be attributed to a substantial improvement in the flexural strength/modulus of the composite adhesive. Significance The adhesive, simultaneously having ability in inhibiting bacteria adsorption, killing bacteria and promoted mineralization, holds great potential in achieving strong bonding strength for dental restoration applications to minimize repair failure.