TITLE:
Controlling Softened State of Mouthguard Sheet during Thermoforming to Ensure Thickness
AUTHORS:
Mutsumi Takahashi, Yogetsu Bando
KEYWORDS:
Mouthguard, Vacuum Formation, Softened State, Thickness, Thermoforming
JOURNAL NAME:
Materials Sciences and Applications,
Vol.11 No.7,
July
14,
2020
ABSTRACT: Mouthguard thickness is affected by the softened state of the sheet during thermoforming. The aim of this study is to establish an effective method for controlling the softened state of the sheet to prevent the mouthguard thickness from decreasing during mouthguard fabrication using a vacuum-forming machine. Mouthguards were thermoformed using an ethylene-vinyl acetate sheet (thickness: 4.0 mm) and a vacuum-forming machine. The working model was trimmed to the anterior height of 25 mm and the posterior height of 20 mm. The following two heating methods were compared: 1) the sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post (condition T); and 2) the sheet frame was lowered to and heated at 50 mm below its usual height and the sheet was formed when it sagged 15 mm below the level of the sheet frame (condition L). For each heating method, the vacuum was applied immediately (T0, L0) or 5 s (T5, L5) after the sheet frame was lowered to the forming unit. The sheet surface temperature immediately before the vacuum was applied under each condition was measured. The differences in mouthguard thickness due to forming conditions were analyzed by one-way ANOVA and Bonferroni’s multiple comparison tests. The temperature difference between the center and the posterior depending on the condition decreased in the order T0 > T5 > L0 > L5, and that was 20°C or higher for T0 and T5, and 10°C or less for L0 and L5. At the incisal edge and the cusp, L0 and L5 were significantly thicker than T0. No significant differences were observed between conditions L0 and L5 at any measurement points. For the labial and buccal surfaces, significant differences in thicknesses among all conditions, except L0 and L5, were observed and were in the order T0