Background/Aims Mouthguards can reduce the risk of sports‐related injuries but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of the thermoforming technique that moves the model position just before vacuum formation. Materials and Methods Ethylene vinyl acetate sheets of 4.0‐mm thickness and a vacuum forming machine were used. The working model was placed with its anterior rim positioned 40 mm from the front of the forming table. Three forming conditions were compared: (a) The sheet was formed when it sagged 15 mm at the top of the post under normal conditions (control); (b) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use, and the sheet was formed when it sagged 15 mm (LH); and (c) the sheet frame at the top of the post was lowered and covered on the model when it sagged 15 mm. Subsequently, the rear side of the model was pushed to move it forward 20 mm, and it was then formed (MP). Sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper accurate to 0.1 mm. Thickness differences among forming conditions were analyzed by one‐way ANOVA and Bonferroni's multiple comparison tests. Results A significant difference was observed for all measurement points, and the thickness after formation increased in the order of control, LH, and MP. Particularly on the labial surface, MP was able to yield about 1.7 times the thickness (about 3.1 mm) of the control. Conclusion The forming method of moving the model forward just before vacuum formation was effective for suppressing the mouthguard thickness reduction, which is capable of securing the labial thickness at 3 mm or more with a single layer.

The results showed that shape changes of the sheet during thermoforming tend to concentrically and almost uniformly expand from the center and that it is important to center the sheet and the model when positioning the model in the forming unit.

Background/Aim Wearing a mouthguard reduces the risk of sports‐related injuries, but the material and thickness of the mouthguard have a substantial impact on its effectiveness and safety. The aim of this study was to establish a thermoforming technique in which the model position is moved just before formation to suppress the reduction in thickness. The aim of this study was to assess the effects of model height and model moving distance on mouthguard thickness. Materials and Methods Ethylene‐vinyl acetate sheets of 4.0 mm thick and a vacuum forming machine were used. Three hard plaster models were trimmed so that the height of the anterior teeth was 25 mm, 30 mm and 35 mm. Model position (MP) was 40 mm from the front of the forming unit. The sheet was softened until it sagged 15 mm, after which the sheet frame was lowered to cover the model. The model was then pushed from behind to move it forward, and the vacuum was switched on. The model was moved at distances of 20 mm, 25 mm or 30 mm whereas a control model was not moved. Thickness after formation was measured with a specialized caliper. Differences in mouthguard thickness due to model height and moving distance were analysed by two‐way ANOVA and Bonferroni's multiple comparison tests. Results Sheet thickness decreased as the model height increased. Each MP condition was significantly thicker than the control in each model. There was no significant difference among MP conditions except for the buccal surface. Conclusions Moving the model forward by 20 mm or more just before formation is useful to secure the labial thickness of the mouthguard. This thermoforming technique increased the thickness by 1.5 times or more compared with the normal forming method, regardless of model height.

The results showed that the thickness reduction was large when the distance from the model to the frame was small. This demonstrates the importance of centering the sheet and the model to achieve the most stable molding when positioning the model in the forming unit.

No abstract

The purpose of this study was to determine changes in the thickness of mouthguard sheets under different heating conditions during fabrication. Mouthguards were fabricated with polyolefin-polystyrene co-polymer (OS) and olefin co-polymer (OL) sheets (4.0-mm thick) utilizing a vacuum-forming machine under the following three conditions: (A) the sheet was moulded when it sagged 15 mm below the sheet frame (i.e. the normally used position); (B) the sheet frame was lowered to and heated at 30 mm below the top of the post and moulded when it sagged by 15 mm; and (C) the sheet frame was lowered to and heated at 50 mm below the top of the post and moulded when it sagged by 15 mm. The working model was trimmed to a height of 20 mm at the incisor and 15 mm at the first molar. Post-moulding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp, central groove and buccal surface). Dimensions were measured, and differences in the change in thickness due to heating condition were analysed using the Kruskal-Wallis test. Under condition C, OS and OL decreased in thickness from 0.36-0.54 mm to 0.26-0.30 mm, respectively, at the incisal portion and from 0.34-0.66 mm to 0.17-0.47 mm, respectively, at the molar portion. It may be clinically useful when moulding a mouthguard to maintain the thickness of the incisal and molar portions by adjusting the height of the sheet frame.

The aim of this study was to evaluate the change in thickness of a working model mouthguard sheet due to different shape. Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0 mm thick) using a vacuum-forming machine. Two shapes of the sheet were compared: normal sheet or v-shaped groove 10-40 mm from the anterior end. Additionally, two shapes of the working model were compared; the basal plane was vertical to the tooth axis of the maxillary central incisor (condition A), and the occlusal plane was parallel to the basal plane (condition B). Sheets were heated until they sagged 15 mm below the clamp. Postmolding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). Differences in the change in thickness due to the shape of the sheets and model were analyzed using two-way anova followed by a Bonferroni's multiple comparison tests. The thickness of the mouthguard sheet with v-shaped grooves was more than that of the normal sheet at all measuring points under condition A and condition B (P < 0.01). The thickness of condition B was less than that of condition A, there the incisal portion in the normal sheet and the incisal edge in the sheet with v-shaped grooves (P < 0.01). The present results suggested that thickness after molding was secured by the use of the sheet with v-shaped grooves. In particular, the model with the undercut on the labial surface may be clinically useful.

The present study suggests that the Shore A hardness and thickness after formation varied depending upon the colors of the EVA sheets and manufactures. A correlation between the hardness and change of thickness was observed in two manufactures that suggests that the hard sheets tend to reduce in thickness greater than that in softer ones.