A Novel High-Strength Dental Resin Composite Based on BaSi₂O₂N₂ for Caries Restoration

Dental resin composite (DRC) is the most widely used restorative material for caries filling treatments. However, DRC has limitations, including incomplete curing and suboptimal mechanical properties, which restrict its clinical application. In this study, we combined the mechanoluminescent material BaSi₂O₂N₂:Eu²⁺ (BSON) with DRC to create a novel DRC (BD) capable of emitting blue light under occlusal force. This study explored a resin composite with enhanced curing efficiency and improved mechanical properties. Characterization of the mechanical properties demonstrated that, as the BSON doping ratio increased (2, 4, 8, 16, and 32 wt %), the compressive strength, flexural strength, and surface hardness of BD initially increased and then decreased. The composite doped with 4 wt % BSON (BD₄) exhibited the best mechanical properties. Compared to DRC, BD₄ showed an 11% increase in compressive strength (211.9 ± 13.9 MPa), a 36% increase in flexural strength (71.9 ± 8.4 MPa), and a 7% increase in surface hardness (111.0 ± 6.4 HV). Based on these findings, BD₄ was selected for further experiments. The study of luminescent properties revealed that the mechanoluminescent wavelength of BD₄ (470-720 nm) partially overlapped with the wavelength range of the light-curing unit (420-490 nm). Additionally, after cyclic loading, BD₄'s compressive strength and degree of conversion (DC) improved. After applying a cyclic load of 300 N for 240 s, BD4's compressive strength increased by 70% (142.2 ± 1.2 MPa), and the DC increased by 8% (74.4%). Moreover, biocompatibility evaluations showed that the cell survival rate of L929 fibroblast cells exceeded 90%. Thus, we developed an effective strategy to enhance DRC by incorporating BSON, resulting in a resin composite with superior mechanical properties, enhanced curing efficiency, and favorable biocompatibility, offering a promising new solution for caries restorations.