Dental Adhesive Resins With Bioactive Nitrogen-doped Titanium Dioxide Nanoparticles

Objectives: Polymerization shrinkage, poor adhesive infiltration and incomplete enveloping of dentin matrix are critical limitations of current dental adhesive resins. One approach to solving these problems is the development of a bioactive and bond-promoting adhesive resin containing nitrogen-doped titanium dioxide nanoparticles (N_TiO2). The objective of this study was to investigate the spontaneous and light-stimulated deposition of hydroxyapatite on the surfaces of N_TiO2-containing and unaltered dental adhesive resins.
Methods: Experimental adhesive resins were synthesized by adding 20%(v/v) N_TiO₂ (synthesized at Oak Ridge National Laboratory) to OptiBond Solo Plus (Kerr Corp.). Thin-films (n=12/group; d=12mm, t=15mm) were fabricated and light-cured (40s, 457±15nm) on acid-etched glass cover slips in preparation for bioactivity testing. The thin-films were then light-irradiated (405±15nm) for 1, 3 or 8 hours either in air or submerged in water (2.5mL). Specimens were then UV-sterilized and immersed in sterile Dulbecco’s Phosphate-Buffered Saline with Calcium and Magnesium aqueous solution (D-PBS, 40mL/specimen, 60°C), and then stored at 37°C in dark conditions for 7 days. Solutions of D-PBS were subsequently replenished at 72 and 120 hours. Specimens were air dried in dark conditions (minimum of 24 hours) and were sputter-coated with either iridium or gold in preparation for SEM and EDS analyses, respectively. Chemical compositional data was analyzed using General Linear Models and SNK post hoc tests (α=0.05).
Results: Mean deposition values for calcium and phosphorous ranged from 0.60 and 1.13wt% [Control, irradiated 1 hour in water] to 6.73 and 6.13wt% [20%(v/v) N_TiO2, irradiated 8 hours in air], respectively. Statistically significant differences were found for the material*irradiation time*irradiation condition interaction (p<0.05).
Conclusions: Experimental adhesive resins containing 20%(v/v) N_TiO2 that were subjected to light-irradiation in air for 8 hours were demonstrated to have the highest light-stimulated bioactivity among the materials and irradiation durations tested. As hypothesized, light-irradiation in air increased the bioactivity of adhesives containing metaloxide nanoparticles.