Method for effectively maintaining the thickness of mouthguards fabricated using EVA sheets and a circle tray: influence of grooved sheet and heating conditions.
The shapes of ethylene vinyl acetate (EVA) sheets are mainly square or round. The aim of this study was to elucidate a fabrication method that effectively maintains the thickness of the round sheet. Mouthguards were fabricated using EVA sheets (diameter 125 mm, thickness 4.0 mm) and a vacuum-forming machine. The sheet was pinched at the top and bottom and stabilized by the circle tray. Two heating conditions were compared: (i) the sheet was molded when it sagged 10 mm below the level of the sheet frame at the top of the post under normal conditions (N); and (ii) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use and molded when it sagged 10 mm from the sheet frame (L). Two EVA sheet shapes were compared: an ordinary sheet (O) and a sheet with a horizontal v-shaped groove 30 mm from the anterior end (G). The height of the working model was 20 mm at the incisor point and 15 mm at the first molar. The sheet temperatures of the heating and non-heated surface were measured by the radiation thermometer. Post-molding thickness was determined for the incisal and molar portion. Differences in the thickness were analyzed using two-way anova. The temperature difference among points was smaller under condition L than under condition N. Thickness after formation was higher in condition L than in condition N, and was higher in condition G than in condition O. At the labial surface and the cusp, L-G was thickest. With the present techniques, uneven softening during heating can be improved by lowering the sheet frame and consequently reducing the reduction in the thickness of the sheet. Additionally, the thickness reduction is reduced by creating a horizontal groove on the sheet, establishing the clinical efficacy of this method.
Preliminary Clinical Application of Complete Workflow of Digitally Designed and Manufactured Sports Mouthguards.
PURPOSE
To establish a complete digital workflow for the design and manufacture of sports mouthguards and to observe preliminary clinical effects.


MATERIALS AND METHODS
Eighteen healthy participants were included in this study. The self-controlled method was applied, and all participants were provided with two types of mouthguards. Digital mouthguards were designed and milled using CAD/CAM with polyetheretherketone, and conventional mouthguards were fabricated using the vacuum pressure-forming method with ethylene vinyl acetate. The order of wearing was determined using a random number table, and the washout period between was set as 1 month. Degrees of satisfaction in terms of retention, appearance, occlusal comfort, and labial comfort were evaluated. Distribution of occlusal force was tested using the T-scan analysis system. Participants were also asked to choose one mouthguard for future use.


RESULTS
The complete workflow of digitally designed and manufactured sports mouthguards was successfully established. No significant difference was noted in retention between the types of mouthguard. The appearance score (P = .025), occlusal comfort score (P = .030), and labial side comfort score (P = .003) of the digital mouthguard group were significantly higher compared to the conventional mouthguard group. T-scan analysis results showed that in centric occlusion, participants exhibited occlusal contact in the second molar alone while wearing conventional mouthguards, while the occlusal force was uniformly distributed with digital mouthguards. Sixteen participants selected the digital mouthguard for future use.


CONCLUSION
Digital design and manufacture of sports mouthguards improved the occlusal design and greatly simplified and optimized the conventional fabrication process.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.