Antimicrobial properties of PMMA resin containing graphene

Purpose/aim: Modern prosthetic dentistry is increasingly focusing on digital procedures, including CAD/CAM technologies. In this context, PMMA is being widely employed as material for prosthetic and restorative devices. Secondary caries is still the main reason for the failure of dental resin-based restorations. Therefore, an antimicrobial activity expressed by these materials is regarded as beneficial for their longevity. This study aimed to test the physical, chemical, and microbiological behavior of a PMMA resin for CAD/CAM applications containing graphene. Materials and methods: Specimens (n = 48) were made from < 50 ppm graphene-containing PMMA disks and from conventional PMMA disks for CAD/CAM applications. Specimens were finished with abrasive paper up to 4000 grit, and a half was subjected to soaking in absolute ethanol for 24 h. This protocol was introduced to evaluate the microbiological behavior of the tested samples after softening of the surface, thus accelerating aging of the surfaces of restorative resins. Material characteristics were assessed in terms of surface roughness, microhardness, ultimate tensile strength, solubility, and water sorption. Elution of methyl-methacrylate after specimen treatment was determined using HPLC. After 24 h pre-incubation with sterile human saliva, the Fig. 1 microbiological behavior of the materials was assessed using two models: Streptococcus mutans biofilm formation in a continuous-flow bioreactor simulating shear forces (30ml/h) for 24 h, and artificial oral microcosm based on mixed plaque inoculum developed using the same setup for 24 h. The viable biomass adhering to the specimens’ surfaces was measured using a tetrazolium dye-based test. Statistical analysis included verification of normality of distribution and homoscedasticity, then multi-way ANOVA and Student’s t-test ( = .05). Results: Finishing protocol produced no significant differences in surface roughness between tested materials. Ethanol treatment significantly reduced surface microhardness in both materials, but to a lesser extent on graphene-containing PMMA. No difference in ultimate tensile strength was found between materials. Graphene-containing PMMA showed significantly lower water sorption and solubility compared to conventional PMMA. After ethanol treatment, a significantly lower amount of leachates was identified for graphenecontaining PMMA. Graphene addition significantly reduced biofilm formation compared to control in both microbiological models (Fig. 1). Interestingly, specimen treatment produced the opposite (S. mutans model) or no effect (artificial oral microcosm) on biofilm formation. Conclusions: Graphene-additioned PMMA is a promising material from both mechanical and microbiological point of view. Ethanol treatment influenced surface characteristics of the materials, leaving on graphene-additioned PMMA a surface more prone to bacterial colonization.