Dental resin composites with improved antibacterial and mineralization properties via incorporating zinc/strontium-doped hydroxyapatite as functional fillers

This study intends to improve the antibacterial and mineralization performance of photocurable dental resin composites (DRCs) to reduce the possibility of repair failure caused by secondary caries. To the end, functionalized hydroxyapatite (HAp), including Zn-doped (Zn/HAp) and Sr-doped HAp (Sr/HAp), were added into the bisphenol A glycidyl methacrylate and triethylene glycol dimethacrylate mixture, providing the DRCs with antibacterial and mineralization capacity, respectively. By controlling the total amount of inorganic filler at 70 wt%, these HAp powders were introduced into the resin matrix with barium glass powder (BaGP), while the ratios of HAp to aGP varied from 0:70 to 8:62. And the 8 wt% of HAp could be pure HAp, Zn/HAp, Sr/HAp, or Zn/HAp +Sr/HAp in different ratios (i.e. 2:6, 4:4, 6:2). Though the fillers varied, the obtained DRCs displayed similar micro-morphology, flexural strength (∼110 MPa) and modulus (∼7 GPa), and Vickers hardness (∼65). When the doping amounts of Sr²⁺/Zn²⁺reached 15 mol% of Ca²⁺in the Sr/HAp and Zn/HAp, the DRCs displayed a high antibacterial activity by killing ∼95%Staphylococcus aureus, and induced rich mineral deposition on surface in simulated body fluid. The incorporation of the Zn/HAp and Sr/HAp into the DRCs did not cause significant cytotoxicity, with L929 fibroblasts remaining >99% viability as cultured in extracts made from the DRCs. Therein, the DRC preparations containing both Zn/HAp and Sr/HAp have achieved improvements in both the biomineralization and antibacterial performance, as well as, having sufficient mechanical properties and excellent biocompatibility for dental restoration.