Making graphene oxide (GO)-cladded SiO spheres (SiO @GO) as inorganic fillers for dental restorative resin composites.

Objective: Graphene oxide (GO) is of great interest in dentistry as the functional filler, mainly owing to its ability to inhibit the formation of cariogenic bacteria and possess low cytotoxicity to different cells, such as human dental pulp cells, HeLa cells, etc. However, its typical brown color limits the practical application.

Methods: Here, the refractive-index-matched monodisperse SiO were used as the supporting substrates to synthesize GO-cladded SiO spheres (xSiO @ yGO) through a mild electrostatic self-assembly process, where x and y represent the amount of SiO and GO in the reaction mixture, respectively. The morphology and the optical performance of the obtained xSiO @ yGO particles were modulated by varying the mass ratio of SiO and GO (5:1, 10:1, 50:1, and 100:1). All developed hybrid particles were silanized and formulated with dimethacrylate-based resins. These were tested for curing depth, polymerization conversion, mechanical performance, in vitro cell viability, and antibacterial activity.

Results: Of all xSiO @ yGO materials, increasing the mass ratio to 100:1 made the 100SiO @GO particles appear light brown and possess the lowest light absorbance from 300 to 800 nm. The results of CIEL*a*b* system showed that all these hybrid particles exhibited obvious discoloration compared with SiO and GO, where 100SiO @GO possessed the smallest color difference. Furthermore, following the results of curing depth, polymerization conversion, and mechanical performance of dental composites, the optimal filler composition was 100SiO @GO at 5 wt% filler loading. The resultant 100SiO @GO-filled composite produced the highest flexural strength (115 ± 12 MPa) and the lowest bacterial concentration (6.7 × 10 CFU/mL) than those of the resin matrix (78 ± 11 MPa; 9.2 × 10 CFU/mL) and 5 wt% SiO-filled composite (106 ± 9 MPa; 9.1 × 10 CFU/mL), respectively, without affecting in vitro cell viability.

Significance: The facile and mild synthesis of xSiO @ yGO hybrid particles provided a convenient way to tune their optical property. The optimal 100SiO @GO particles could be considered as the promising antibacterial filler to be applied in dental care and therapy.