Optimal heating condition of ethylene-vinyl acetate co-polymer mouthguard sheet in vacuum-pressure formation.

Abstract

The goal of the present study was to examine the thickness of mouthguards molded under a variety of heating conditions to clarify suitable conditions during vacuum-pressure forming of ethylene vinyl acetate sheets. Mouthguards were fabricated using ethylene vinyl acetate (EVA) sheets (thickness: 4.0 mm) using a vacuum-pressure forming machine. The sheet was pressed against the working model, followed by vacuum forming for 10 s and compression molding for 2 min. Three heating conditions were investigated in which the sheet was molded when the center of the softened sheet sagged 10 mm, 15 mm, or 20 mm below the clamp (H-10, H-15, or H-20 respectively). The temperature of the sheet surface was measured using a radiation thermometer under each heating condition. The thickness of the mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in thickness due to the heating condition of the sheets were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. The temperature difference between the heated and non-heated surfaces was lowest under H-15. The thickness differences at incisal edge, labial surface, and cusp were determined. The thicknesses for H-10 and H-15 were greater than that for H-20, and the thicknesses for H-10 and H-15 were equivalent at all measurement points. No differences in thickness at the buccal surface were observed for the various heating conditions. The present study demonstrated that a sagging distance of 15 mm provided the most suitable forming process. The results of the present study provide a standard heating condition for EVA sheet forming.