In vitro study of how the undercut amount on the model labial side affects the reduction rate of laminated mouthguard thickness.

Background/aim: An undercut on the model's labial side affects the mouthguard thickness. The aim of this study was to investigate how the undercut amount on the model's labial side affects the reduction rate of laminated mouthguard thickness.

Materials And Methods: Mouthguards were thermoformed using 3.0-mm-thick ethylene-vinyl-acetate sheets for the first and second laminates and a pressure molding machine. Working models were three hard plaster models trimmed so that the undercut amount on the model's labial side was 0°, 10°, and 20° (U0, U10, and U20). A specialized caliper was used to measure the thickness of the incisal, labial surface, and buccal surface of the first layer and the laminated mouthguards. Thickness reduction rate of the first layer or laminated mouthguard due to the model undercut amount were analyzed using one-way ANOVA. Additionally, in each model, the difference in the thickness reduction rate between the first layer and the laminated mouthguard were analyzed by Student's t-test or Welch's test.

Results: Differences in the thickness reduction rate depending on the model's undercut amount showed the same tendency between the first layer and the laminated mouthguard. Significant differences were observed between U0 and U10 as well as U0 and U20 at the incisal edge, and these were observed among all models on the labial and buccal surfaces (p < .01). On the labial surface, the rate of decrease in the laminated mouthguard thickness compared to U0 was approximately 10.4% larger for U10 and approximately 14.9% larger for U20 (p < .01). The thickness reduction rate of the laminated mouthguard was significantly smaller than that of the first layer, which was observed in all models at the incisal edge and in U10 and U20 on the labial surface (p < .01).

Conclusions: The presence of a 10° or 20° undercut on the model's labial side increases the thickness reduction rate on the labial side of the laminated mouthguard by approximately 10% or 15%.