Influence of Reheating after the Vacuum Forming Process on Deformation of the Mouthguard.

The aim of this study was to investigate the influence of reheating after the vacuum forming process on deformation in each part of the mouthguard after immersion in water. The mouthguard sheets were pressed on the working model for 2 minutes, and then subjected to four conditions: rapid cooling, slow cooling, reheating for 5 minutes, and reheating for 10 minutes. Then, the mouthguard was trimmed along the shape of the bottom of the working model and immersed in water. Deformation of the mouthguard was determined by measuring the distances between the buccal and palatal borders of the mouthguard and between the buccal and palatal cervical margins at the central incisor, second premolar, and second molar. The distances were measured before immersion, and on days 1-7 after immersion. The differences in the ratio of changes in the distances on the mouthguard after immersion in water were analyzed by Friedman test. The distances at the border of the mouthguard were significantly different at the central incisor, second premolar, and second molar in the four conditions (p<0.01 or p<0.05). The change in the distance at the second premolar was largest, and rapid cooling and slow cooling resulted in greater deformation in an inward direction. There were no significant differences in the distances at the cervical margins of the mouthguard. The residual stress occurring in the forming process was reduced by reheating the mouthguard for 5 minutes and 10 minutes, and deformation of the mouthguard after immersion in water was small, especially at the second premolar. Results of this study suggested that the method of reheating the mouthguard after forming would be effective to fabricate a well-fitting mouthguard that is comfortable to wear. [ABSTRACT FROM AUTHOR]