Hydroxylherderite as a Novel Filler for a Dental Adhesive

Aims: The aim of this study was to incorporate Hydroxylherderite (HEr) into an adhesive and evaluate the resulting material’s properties including degree of conversion, microhardness, mineral deposition, and cytotoxicity. Study Design: In vitro study. Methodology: Hydroxylherderite was incorporated into the adhesive at concentrations of 2% and 5% by weight. The degree of conversion (DC, n = 3) was measured using an ATR-FTIR spectrometer. After immersion in absolute ethanol for two hours, the softening of the adhesive was assessed using a microhardness tester with a Knoop indenter. After 7 and 28 days of immersion in Simulated Body Fluid (SBF), mineral deposition in the adhesive was evaluated using a Raman microscope. Cell viability in contact with the adhesive was assessed according to ISO 10993-5. Data were analyzed using paired t-tests, ANOVA, and Tukey's post hoc tests with a significance level set at 0.05. Results: The incorporation of HEr into the adhesive did not affect the degree of conversion compared to the control. DC ranged from 59.21 ± 11.11% to 63.49 ± 5.30%. The 5 wt% group showed a significant increase in initial microhardness (p < 0.05). Higher mineral deposition was observed with increased immersion time HEr concentration. All HEr concentrations maintained cell viability above 80% after 48 and 72 hours of contact. Conclusion: HEr was successfully incorporated into the adhesive resin, promoting mineral deposition without cytotoxic effects and without compromising the physicochemical properties of adhesive.