The effect of the simulated aging by thermocycling on the elastic modulus of ethylene-vinyl acetate brands and stress/strain development during an impact: An in vitro and 3D-FEA analysis.

BACKGROUND/AIM: Mouthguards are used to prevent dental trauma and orofacial injuries. The aim of this study was to evaluate the influence of ethylene-vinyl acetate (EVA) aging by thermocycling on elastic modulus, stress, strain and shock absorption ability of different ethylene-vinyl acetate brands used for mouthguards. METHODS: Thirty EVA samples with a dimension of 70 x 10 x 3 mm were obtained from four commercial brands (Bioart(R), Erkodent(R), Polyshok(R) and Proform(R)). Fifteen samples were submitted to 10,000 cycles (5 degrees C-55 degrees C) in a thermocycling machine with an immersion time of 30 s and a transfer time of 5 s. The samples were submitted to a uniaxial tensile test in a universal testing machine to calculate the elastic modulus. Data were statistically evaluated by two-way ANOVA and Holm-Sidak test. A three-dimensional model of the anterior maxilla was created using Rhinoceros 5.0. A 3 mm custom-fitted mouthguard was simulated. The three-dimensional volumetric mesh was generated using the Patran software (MSC Software) with isoparametrics, 4-noded tetrahedral elements and exported to Marc/Mentat (MSC Software) as element number 134. A non-linear dynamic impact analysis was performed in which a rigid object struck the central incisor at a speed of 5 m/s. The stresses were evaluated by the modified von Mises criteria and the strains were also recorded. RESULTS: Statistically significant differences were observed for elastic modulus values (p < .001). Mean and standard deviation values (MPa) without thermocycling were: Bioart (34.5 +/- 0.9), Erkodent (15.0 +/- 0.4), Polyshok (17.3 +/- 0.4), Proform: (20.6 +/- 0.8); and with thermocycling: Bioart (25.4 +/- 0.8), Erkodent (10.7 +/- 0.5), Polyshok (13.3 +/- 0.6), Proform (13.1 +/- 0.6). The thermocycling process reduced stress and strain levels regardless of the mouthguard materials. Shock absorption ability calculated based on the strain values was increased with thermocycling process. CONCLUSION: The thermocycling process, regardless of the commercial brand, reduced the stress/strain and increased the shock absorption ability of mouthguards.