Evaluation of the Physicochemical and Antibacterial Properties of Experimental Adhesives Doped with Lithium Niobate

The aim of the present study was to formulate dental adhesives with different concentrations of LiNbO(3) and to evaluate their physicochemical and antibacterial properties. A dental adhesive was formulated using methacrylate monomers and photoinitiators and used as a control filler-free group. Subsequently, three experimental adhesives doped with LiNbO(3) at different concentrations (1 wt.%, 2 wt.%, and 5 wt.%) were also formulated. All the experimental adhesives were assessed to evaluate the degree of conversion (DC), softening in solvent, immediate and long-term microtensile bond-strength (μ-TBS), radiopacity, ultimate tensile strength, and antibacterial activity. The incorporation of 1 wt.% of LiNbO(3) had no negative effect on the DC of the adhesive resin compared to the control group (p > 0.05). We observed a decrease in the percentage of softening in solvent in the group LiNbO(3) at 1 wt.% (p < 0.05). The addition of LiNbO(3) increased the radiopacity at a concentration above 2 wt.%, and there was also an increase in cohesive strength (p < 0.05). The immediate μ-TBS increased for LiNbO(3) at 5 wt.% (p < 0.05), and there was no statistical difference for the other groups compared to the control (p > 0.05). After six months, the group with 5 wt.% still presented the highest μ-TBS (p < 0.05). The adhesives showed no antimicrobial activity (p > 0.05). LiNbO(3) was successfully incorporated in dental adhesives, increasing the radiopacity and their resistance to degradation. Although LiNbO(3) offered no antibacterial properties, the reliability of LiNbO(3) incorporation in the adhesive encourages new tests to better investigate the antimicrobial action of LiNbO(3) through temperature variation.