Flexural strength evaluation of self-cured acrylic resin used in removable orthodontic appliances following addition of immobilized silver nanoparticles on clay

Abstract

Introduction:Self-curing acrylic resins, mainly composed of polymethylmethacrylate (PMMA), are widely used to manufacture removable orthodontic appliances. One of the major problems of removable orthodontic appliances is their potential for microbial plaque accumulation due to surface porosities, which increases the bacterial activity of cariogenic oral flora. This is especially true about cold-cure acrylic resins, which have lower polymerization degree and more porosity than heat-cure ones. Therefore, one of the goals of dental material studies is to add antimicrobial materials to acrylic baseplates. Several studies have been conducted on the antimicrobial properties of nanoparticles and their applications in dental materials, including orthodontic materials. Silver nanoparticles are one of the most important products of nanotechnology. While nanoparticles can induce antimicrobial capability, they can also alter the mechanical properties of acrylic resin. Among the mechanical properties of acrylic resin, flexural strength has got great importance. Recently, some methods for stablization of silver nanoparticles have been used.One of these methods is loading silver nanoparticles in the porous matrix structure of mineral aluminosilicates.The aim of this study is to evaluate the flexural strength of self-curing PMMA acrylic resin containing specific concentrations of silver nanoparticles supported in clay(Ag/Clay NPs). Materials and Methods: The synthesized nanoparticleswere added to Triplex Cold orthodontic self-curing acrylic resin powder with 0.2 wt%, 0.5 wt%, 1 wt% and 1.5 wt% concentrations.X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), energy dispersive X-ray (EDX), MAP analysiswere performed to investigate the sample's characteristics.Flexural strength of the fabricated acrylic sampleswas evaluated by the three-point bending test. One-way ANOVA and Tukey's post hoc test were used for statistical evaluation of data and the p-value of less than 0.05 was considered significant. Results: The addition of Ag/Clay nanoparticles to Triplex Cold self-curing acrylic resinwith concentrations of 0.2 wt% and 0.5 wt%, has caused no significant change in the flexural strength compared to the control group. The mean flexural strength in the group containing 0.2% Ag/Clay nanoparticles was higher than other groups. Nevertheless, increasing the concentration of nanoparticles to 1 wt% and 1.5 wt% has led to a significant decrease in the flexural strength. Evaluating the biocompatibility of synthesized nanoparticles on alveolar adenocarcinoma (A549) cancer cells using the MTT method has showed that with the increase in the percentage of nanoparticles, the toxicity increases to some extent, but the cell viability is stillmore than 80%, which shows the non-toxicity of nanoparticles in the percentages and concentrationsinvestigated in the present study. Conclusion: The addition of silver nanoparticles supported in clay with concentrations of 1wt %and more has led to a significant decrease in flexural strength compared to the control group, however, all values were greater than 50 MPa and in accordance with ISO 20795-2:2013.