Prioritizing model trimming to prevent thinning during mouthguard thermoforming: Influence of increased height associated with an acute model angle.

Abstract

The shape of the working model is one of the major factors affecting the thickness of thermoformed mouthguards. The aim of this study was to clarify the priority of model trimming to prevent thinning during mouthguard thermoforming. Mouthguards were thermoformed using 4.0 mm thick ethylene-vinyl-acetate sheets and a vacuum forming machine. Working models were trimmed so that the angles of the labial surface to the model base were 100°, 90°, and 80°. The posterior height was unified to 30 mm, and the anterior heights were 30 mm (A100-L), 35 mm (A90-M), and 40 mm (A80-H), respectively. When the sheet temperature reached 100°C, vacuum forming was performed. Six specimens were formed for each condition. Mouthguard thickness (incisal edge, labial surface, cusp, and buccal surface) was measured using a specialized caliper accurate to 0.1 mm. Differences in thickness reduction rate due to model shapes were analyzed by one-way ANOVA and Bonferroni's multiple comparison tests. At the incisal edge, there were no significant differences in the reduction rate of the thickness of the mouthguard according to model shapes. On the labial surface, cusp, and buccal surface, the smaller the model angle, the smaller the reduction rate of thickness, and significant differences were observed between A100-L and A80-H, and A90-M and A80-H. On the labial and buccal surfaces, A80-H was more than 7.1% thicker compared with A100-L and more than 5.6% thicker compared with A90-M, and the thickness reduction rate was reduced when the model was trimmed to an acute angle. At the cusp, A80-H was more than 4.3% thicker than A100-L and A90-M. It is useful to trim the model at an acute angle in order to prevent thinning during mouthguard thermoforming, even if the anterior height of the model is increased.