Synthesis, characterization and evaluation of experimental dental composite resin modified by grapefruit seed extract-mediated TiO₂ nanoparticles: green approach.

Dental composite resins often face challenges related to secondary caries, polymerization shrinkage and fracture failure. This study aimed to synthesize an experimental composite resin modified with grapefruit seed extract-mediated titanium dioxide nanoparticles (GSE-TiO₂NPs) and evaluate its antibacterial activity and mechanical and physical properties. Green synthesis of TiO₂ nanoparticles was conducted utilizing GSE. The chemical profile of GSE was identified through gas chromatography-mass spectrometry. The as-prepared nanoparticles were incorporated into experimental composites at concentrations of 10 wt.% (10 wt.% GSE-TiO₂NPs group) and 20 wt.% (20 wt.% GSE-TiO₂NPs group), with an unmodified composite as the control group. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the morphology and size of synthesized nanoparticles, with SEM revealing uniform particle distribution in the composite. Antibacterial activity against Streptococcus mutans was assessed using the agar disc diffusion method. Mechanical properties, including flexural strength (FS) and flexural modulus (FM), were evaluated according to ISO 4049 standards. Microhardness was tested according to the American Society for Testing Materials (ASTM E-384:1999) criteria. Polymerization shrinkage was measured using the strain gauge method. Modified composites exhibited significantly greater antibacterial activity against S. mutans compared to the control (p < 0.001). The 10 wt.% GSE-TiO₂NPs group demonstrated increased FS and FM values compared to the control group (p < 0.05). All groups surpassed the clinically acceptable microhardness threshold without significant differences (p = 0.588). Polymerization shrinkage was reduced in the modified groups (p < 0.01), with the 20 wt.% GSE-TiO₂NPs group showing the lowest value (13.06 ± 0.92%). Incorporating GSE-TiO₂NPs into composite resins enhances antibacterial activity, improves mechanical properties, and reduces polymerization shrinkage, suggesting a promising approach for developing advanced dental materials with integrated natural bioactive components.