Optimal heating condition of mouthguard sheet in vacuum-pressure formation: part 3 styrene-based thermoplastic...

The aim of this study was to identify suitable heating conditions of polyolefin-polystyrene co-polymer sheets in vacuum-pressure formation, monitor the sheet temperature during molding, and examine the thickness of the fabricated mouthguard.

Mouthguards were fabricated with polyolefin-polystyrene co-polymer sheets (4.0-mm thick) utilizing a vacuum/pressure-forming device, which was subjected to vacuum forming for 10 s and pressure molding for 2 min. Four heating conditions were compared, defined by the amount of sag distance of 5, 10, 15, or 20 mm from the center of the softened sheet below the clamp. The working model was trimmed to a height of 20 mm at the cutting edge of the maxillary central incisor and to a height of 15 mm at the mesiobuccal cusp of the maxillary first molar. The radiation thermometer was used to measure the sheet temperatures of the center of the heated and non-heated surfaces under each condition. The sheet thickness after fabrication was determined for the incisal and the molar portions, and dimensional measurements were obtained using a measuring device. The differences in the sheet thickness produced by the different heating conditions were analyzed by Games-Howell's multiple comparison tests.

For condition of 5 mm sagged, the temperature on the non-heated surface did not reach a sufficient softening temperature and the thickness was smallest. Mouthguard thickness was largest in the order of 15 mm sagged condition, followed by 20 mm sagged condition and then by 10 mm sagged condition, but a statistical difference was not observed in the labial and the buccal surface among the three conditions.

This study demonstrated that for sufficient softening, it was necessary to heat the sheet to obtain a sag of 10 mm or more, and that the mouthguard thickness decreased as the sag increased.