Effect of adding zinc oxide nanoparticles supported in 4A zeolite on antibacterial properties and flexural strength of self-curing acrylic resin used in removable orthodontic appliances

Self-curing acrylic resins, mainly composed of Polymethyl Methacrylate (PMMA), are widely used to manufacture removable orthodontic appliances. Self-curing acrylic resins have higher porosity than heatcuring acrylic resins leading to a susceptible place for microbial plaque colonization. Due to some of these microorganisms' activities, a very unpleasant odor is emitted from orthodontic base plates, which has adverse effects on patients' cooperation. This study aimed to investigate the antimicrobial properties of cold-curing PMMA acrylic resin containing ZnO nanoparticles supported in 4A zeolite and evaluating its mechanical properties.

The synthesized nanocomposite ZnO/4A zeolite was added to SR Triplex® Cold orthodontic selfcuring acrylic resin powder with 2wt% and 4wt% concentrations. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), energy dispersive X-ray (EDX), MAP analysis, and Dynamic light scattering (DLS) were performed to investigate the sample's characteristics. Direct test method was used to assess the antibacterial properties of the fabricated acrylic samples against three bacterial strains Streptococcus mutans, Klebsiella Pnemoniae, and Esherichia coli. Flexural strength was evaluated by a three-point bending test, and Oneway ANOVA and Tukey's post hoc test were used for statistical evaluation of data. The p-value of less than 0.05 was considered significant.

The addition of ZnO/4A in 2wt% and 4 wt% concentrations lead to more than 99% destruction of colonies in all three types of microorganisms. The mean flexural strength of acrylic specimens containing 2wt% and 4wt% of ZnO/4A significantly lower than the control group. Despite the considerable reduction, all mean values are greater than 50 MPa.

The ZnO/4A zeolite nanocomposite due to its potent antibacterial properties and minimal toxicity can reduce the unfavorable odor of orthodontic base plates consequently increases patient cooperation and reaching the desired result.