Adaptation and Biomechanical Performance of Custom-Fit Mouthguards Produced Using Conventional and Digital Workflows: A Comparative In Vitro Strain Analysis.

BACKGROUND/OBJECTIVES: The use of different models for the fabrication of custom-fit mouthguards (MTGs) can affect their final thickness, adaptation, and shock-absorption properties. This study aimed to evaluate the adaptation, thickness, and shock absorption of ethylene-vinyl acetate (EVA) thermoplastic MTGs produced using conventional plaster or three-dimensional (3D) printed models. MATERIALS AND METHODS: A typical model with simulated soft gum tissue was used as the reference model to produce MTGs with the following two different protocols: plast-MTG using a conventional impression and plaster model (n = 10) and 3DPr-MTG using a digital scanning and 3D printed model (n = 10). A custom-fit MTG was fabricated using EVA sheets (Bioart) plasticized over different models. The MTG thickness (mm), internal adaptation (mm) to the typodontic model, and voids in the area (mm2) between the two EVA layers were measured using cone-beam computed tomography images and Mimics software (Materialize). The shock absorption of the MTG was measured using a strain-gauge test with a pendulum impact at 30° with a steel ball over the typodont model with and without MTGs. Data were analyzed using one-way analysis of variance with repeated measurements, followed by Tukey's post hoc tests. RESULTS: The 3DPr-MTG showed better adaptation than that of the Plast-MTG at the incisal/occlusal and lingual tooth surfaces (p < 0.001). The 3DPr-MTG showed a thickness similar to that of the Plast-MTG, irrespective of the measured location. MTGs produced using both model types significantly reduced the strain values during horizontal impact (3DPr-MTG 86.2% and Plast-MTG 87.0%) compared with the control group without MTG (p < 0.001). CONCLUSION: The MTGs showed the required standards regarding thickness, adaptation, and biomechanical performance, suggesting that the number and volume of voids had no significant impact on their functionality. Three-dimensional printed models are a viable alternative for MTG production, providing better adaptation than the Plast-MTG at the incisal/occlusal and lingual tooth surfaces and similar performance as the MTG produced with the conventional protocol.

Effect of different materials for conventional and 3D-printed models on the mechanical properties of ethylene-vinyl acetate utilized for fabricating custom-fit mouthguards.

BACKGROUND/AIM: The interaction between the ethylene-vinyl acetate (EVA) with distinct materials utilized for obtaining dental models can affect the performance of resulting mouthguards. This study attempted to evaluate the effect of different materials for conventional (dental stone) or 3D-printed (resin) models on EVA's physical and mechanical properties and surface characteristics. MATERIAL AND METHODS: EVA sheets (Bioart) were laminated over four model types: GIV, conventional Type IV dental stone model (Zhermak); ReG, resin-reinforced Type IV dental stone model (Zero Stone); 3DnT, 3D resin printed model (Anycubic) without surface treatment; 3DT, 3D-printed model (Anycubic) with water-soluble gel (KY Jelly Lubricant, Johnson & Johnson) coating during post-curing process. The EVA specimens were cut following the ISO 37-II standard (n = 30). Shore A hardness was measured before and after plasticization on the contact (internal) or opposite (external) surfaces with the model. The breaking force (F, N), elongation (EL, mm), and ultimate tensile strength (UTS, MPa) were measured using a universal testing machine. Macro-photography and scanning electron microscopy were adopted for classifying the EVA surface alteration. Data were analyzed by one-way ANOVA with repeated measures, followed by Tukey's test (α = .05). RESULTS: Plasticization significantly decreased Shore A values for the tested EVA regardless of the model type (p < .001). Higher F, El, and UTS values were verified for the EVA with 3DT and GIV models compared to ReG and 3DnT (p < .001). 3DnT models resulted in severe surface alteration and a greater reduction of the mechanical properties of the EVA. CONCLUSION: The interaction of EVA with 3D resin-printed models without surface treatment or resin-reinforced Type IV dental stone models significantly affected the physical and mechanical properties of this material. The utilization of water-soluble gel coating during the post-curing process of 3D resin printed models improved the mechanical properties of the EVA, similarly when this material was plasticized over conventional Type IV dental stone model.

Effect of surface treatment of ethylene vinyl acetate on the delamination of custom-fitted mouthguards.

BACKGROUND/AIM: Contamination of ethylene vinyl acetate (EVA) during mouthguard fabrication can cause delamination. The study evaluated the effects of different EVA surface treatments on the contact angle, laminate bond strength, and elongation capacity. MATERIALS AND METHODS: Specimens of two bonded EVA plates were prepared (n = 30). The Shore A hardness of standardized EVA plate specimens was measured before and after thermo-plasticization. The EVA plates were randomly allocated to one of five different surface treatment groups: no treatment (control); isopropyl alcohol, 100%; chloroform, 99.8%; self-cure acrylic resin monomer (methacrylate, ethylene glycol dimethacrylate, and chemical initiator-amine type); and ethyl alcohol, 70%. The maximum breaking force and elongation at the site of fracture were recorded using a universal testing machine. The contact angle surface was measured using ImageJ software. Scanning electron microscopy of the EVA surface was performed. The laminate bond strength was obtained by dividing the maximum breaking force by the bonding area between the two EVA plates. The laminate bond strength and maximum elongation data were analyzed by one-way ANOVA, followed by the Tukey's and the Dunnet test. The failure mode data was analyzed using the chi-square test (α = .05). RESULTS: EVA surface treatment significantly influenced the laminate bond strength and maximum elongation (p < .001). The control group had a higher contact angle and significantly lower laminate bond strength and maximum elongation than the other groups (p < .001). The acrylic resin monomer and chloroform-treated specimens had similar laminate bond strength and maximum elongation. The acrylic resin monomer group had a significantly lower contact angle (p < .001). CONCLUSIONS: All treatments had a significantly higher laminate bond strength and maximum elongation than the control group. The acrylic resin monomer and chloroform groups had a significantly higher laminate bond strength and maximum elongation and the acrylic resin monomer group had a lower contact angle than the other groups. The chloroform should be avoided due its hazardous effects.