Multifunctional dental resin composites enabled by QPEI-and TA-functionalized ZnO nanofillers with antibacterial and calcium-phosphate deposition properties.

To impart antibacterial activity and calcium-phosphate deposition capability to dental resin composites (DRCs) and thereby reduce the risk of secondary caries, zinc oxide nanoparticles (ZnO NPs) were surface-functionalized with quaternized polyethyleneimine (QPEI) and tannic acid (TA), yielding two functional nanofillers, termed ZQ and ZT, respectively. The modified nanoparticles were incorporated into DRCs, and their physicochemical properties, cytocompatibility, antibacterial performance, and calcium-phosphate deposition behavior were systematically evaluated. The results demonstrated that composites containing 2 wt% functionalized nanoparticles (DZQ2 and DZT2) achieved the most balanced overall performance. Both materials satisfied the ISO 4049 curing-depth requirement and exhibited enhanced mechanical properties, favorable hydrolytic stability, and good cytocompatibility, with cell viabilities exceeding 80%. Functional evaluation revealed distinct biological effects associated with the two surface modification strategies. DZQ2 exhibited strong antibacterial activity against Streptococcus mutans (88.14 ± 1.70%), whereas DZT2 promoted greater calcium-phosphate deposition, showing a higher Ca/P ratio (1.08) than DZQ2 (0.83) after 28 days of immersion in artificial saliva. Overall, surface functionalization of ZnO nanoparticles provides an effective strategy for tailoring the biological performance of dental resin composites. The developed materials combine favorable physicochemical properties, antibacterial activity, and calcium-phosphate deposition capability, demonstrating potential as multifunctional restorative materials for reducing the risk of secondary caries.