Title of article : Shape change in mouthguard sheets during thermoforming — Part 2 : Effect of the anteroposterior position of the model on mouthguard thickness The authors ’ full and complete names , degrees , and institutions

Background/Aim: Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of model position in the molding machine on the reduction of mouthguard thickness. Materials and Methods: Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming by a pressureor a vacuum-forming machine. The working model was trimmed to the height of 25-mm at the maxillary central incisor and A cc ep te d A rt ic le This article is protected by copyright. All rights reserved. 20-mm at maxillary first molar. For both pressure and vacuum forming, the model was placed with the anterior rim of the model positioned 40, 30, 25, 20, or 10 mm from the front of the sheet frame. An additional test was done at 50 mm for vacuum forming. The sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper. The difference of the model position on the reduction of thickness in each forming device and sheet material were analyzed by one-way analysis of variance and Bonferroni’s multiple comparison tests. Result: The reductions of thickness at the incisal edge and labial surface were about -60% and -50%, respectively, for the distance of 25 mm from the front of forming table. That position was the same as the height of the anterior part of the model for each molding machine and sheet material. The anterior thickness after molding became greater as the distance between the model and the sheet frame became smaller. Conclusion: The results showed that the thickness reduction was large when the distance from the model to the frame was small. This demonstrates the importance of centering the sheet and the model to achieve the most stable molding when positioning the model in the forming unit.