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%.

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

BACKGROUND/AIM: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Effect of sheet extrusion direction on laminated mouthguard thickness: An in vitro study.

BACKGROUND/AIM: The thermal shrinkage that occurs when the extrusion molding sheet is heated affects the mouthguard thickness. The aim of this study was to investigate the effect of sheet extrusion direction on laminated mouthguard thickness. MATERIALS AND METHODS: Mouthguards were pressure formed using the extruded sheet and a plaster model. For the first layer, a 3.0-mm-thick sheet was used. For the second layer, a 2.0- or 3.0-mm-thick sheet was used. In each of the first (F) and second (S) layers, the sheet extrusion direction was either vertical (V; FV, SV) or parallel (P; FP, SP) to the model midline. Thickness differences depending on the extrusion direction of the first layer was analyzed by Student's t-test. Differences in the laminated mouthguard thickness depending on the extrusion direction of the first or second layer and the sheet thickness of the second layer were analyzed by three-way ANOVA. RESULTS: The first layer was significantly thicker in FV by about 0.20 mm than in FP at the incisal edge, labial surface, and cusp (p < .01). No significant difference was observed between SV and SP in the laminated mouthguard. However, at the incisal edge, labial surface, and cusp of the laminated mouthguard, FV were significantly thicker by 0.17 mm or more than FP under all laminating conditions (p < .01). A 3.0-mm-thick laminating condition was thicker than a 2.0-mm-thick laminating condition by 0.47 mm or more at the incisal edge, labial, and buccal surfaces, and by 0.34 mm or more at the cusp. CONCLUSIONS: The laminated mouthguard thickness can be secured by molding the first-layer sheet so that the extrusion direction is vertical to the model midline. In the second layer, the extrusion direction did not affect the laminated mouthguard thickness, and a thicker sheet material should be used.

Effective thermoforming method for maintaining mouthguard thickness with a circular sheet using a circular frame.

BACKGROUND/AIM: Mouthguard thickness is important to prevent oral and facial trauma during sports. The aim of this study was to establish an effective thermoforming method for maintaining mouthguard thickness with a circular sheet using a circular frame. MATERIALS AND METHODS: Mouthguards were thermoformed using 4.0-mm-thick ethylene vinyl acetate sheets and a vacuum forming machine. Each sheet was pinched at the top and bottom and stabilized by a circular frame. Two heating conditions were compared: (1) condition N, where the sheet was formed when it sagged 10 mm below the level of the sheet frame at the top of the post, and (2) condition L, where the sheet frame was lowered 50 mm below the ordinary level and heated, and the sheet was formed when it sagged 10 mm. In each heating method, two forming conditions were compared: (1) when the sheet softened, the sheet frame was lowered and formed (condition C; N-C, L-C), and (2) after the sheet frame was lowered, the model was moved forward 20 mm and then formed (condition MP; N-MP, L-MP). Six mouthguards were fabricated for each condition. Thickness differences due to heating conditions and forming conditions were analyzed by the two-way ANOVA and Bonferroni's multiple comparison test. RESULTS: At the incisal edge and at the labial and buccal surfaces, significant differences were observed among all conditions, and the thicknesses were in the order N-C < L-C < N-MP

Examination of thermoforming techniques to secure mouthguard thickness of the labial and buccal sides with a single sheet: An in vitro study.

BACKGROUND/AIM: Mouthguards must have an appropriate thickness to prevent oral trauma during sports. The aim of this study was to establish a thermoforming technique to secure the labial and buccal thicknesses of the mouthguard with a single sheet. MATERIALS AND METHODS: Mouthguards were thermoformed using 4.0-mm thick sheets manufactured by extrusion molding, a plaster model, and a vacuum forming machine. Two sheet installation conditions were compared: the sheet extrusion direction was either parallel (P) or vertical (V) to the model's centerline. In each extrusion direction, two forming conditions were compared: (1) the sheet was formed when it sagged 15-mm below the sheet frame at the top of the post (control group; C-P, C-V); and (2) the sheet frame was lowered 50-mm below the ordinary level and heated, the frame was lowered when it sagged 15-mm, and the model was moved forward 20-mm before formation (experimental group; E-P, E-V). Difference in thickness (incisal edge, labial surface, cusp, and buccal surface) due to sheet extrusion direction and forming conditions were analyzed by two-way ANOVA and the Bonferroni method. RESULTS: At all measurement sites, a significant difference in thickness depending on the sheet extrusion direction was observed in the experimental group (p < .01), but not in the control group. Difference in thickness depending on the forming condition was observed at all measurement sites, and the thickness was in the order C-P, C-V < E-P < E-V. Thicknesses of E-P and E-V were 3.01 ± 0.03 mm and 3.25 ± 0.02 mm on the labial surface, and 2.81 ± 0.02 mm and 3.02 ± 0.02 mm on the buccal surface. CONCLUSIONS: It was possible to obtain 3 mm or more thickness on the labial and buccal sides with a single sheet by adjusting the sheet extrusion direction and the heating method of the sheet, and by applying the thermoforming method where the model is moved forward just before formation.

Effects on the thickness of single-layer mouthguards with different model positions on the forming table and different sheet frame shapes for the forming device.

BACKGROUND/AIM: Effectiveness and safety of mouthguards are greatly affected by their thickness. The aim of this study was to clarify the influence of the frame shape of the forming device on how the model position on the forming table affects the anterior and posterior mouthguard thickness. MATERIALS AND METHODS: Mouthguards were thermoformed using 4.0-mm-thick ethylene-vinyl-acetate sheets and a vacuum forming device. Square sheets were fixed with the square frame of the forming device. Circular sheets were fixed to the forming device with a circular frame. The model was placed with its anterior rim positioned 40, 30, 20, or 10 mm from the front of the forming table. The model position was marked on the forming table so that it was constant under each condition. Six mouthguards were fabricated for each condition. Mouthguard thicknesses of the incisal edge, labial and buccal surfaces, and the cusp were measured. Differences in the rate of thickness reduction due to frame shapes and model positions were analyzed by two-way ANOVA. RESULTS: Difference in the thickness reduction rate depending on the frame shape was observed on the labial and buccal surfaces, and it was significantly greater with the circular frame than with the square frame (p < .01). In the anterior region, the thickness reduction rate tended to increase as the model position was moved toward the front of the forming table. The thickness reduction rate of the posterior portion was lowest when the model's molar was positioned at the center of the forming table. CONCLUSIONS: The labial thickness of the mouthguard was not affected by the frame shape if the distance from the model to the frame was larger than the model height. However, the buccal thickness was thinner with the circular frame than with the square frame regardless of the model position.

Effect on thickness of a single-layer mouthguard of positional relationship between suction port of the vacuum forming device and the model.

BACKGROUND/AIM: Wearing a mouthguard reduces the risk of sport-related injuries, but the thickness has a large effect on its efficacy and safety. The aim of this study was to investigate the effect on the thickness of a single-layer mouthguard of the positional relationship between the suction port of the vacuum forming device and the model. MATERIALS AND METHODS: Ethylene-vinyl-acetate sheets of 4.0-mm-thickness and a vacuum forming machine were used. Two hard plaster models were prepared: Model A was 25-mm at the anterior teeth and 20-mm at the molar, and model B was trimmed so the bucco-lingual width was half that of model A. Three model positions on the forming table were examined: (a) P20, where the model anterior rim was located in front of the suction port, (b) P30, where the model anterior rim and front edge of the suction port were close, and (c) P43, where the model anterior rim and palatal rim were located on the suction port. Six mouthguards were fabricated for each condition. Thickness differences due to model form and model position were analyzed. RESULTS: Thickness differences due to model form were observed at the incisal edge and labial surface, and model A was significantly thicker than model B in P43 (P<.01). The thickness of the incisal edge and labial surface was significantly greatest in P43 for model A, but in P30 for model B. CONCLUSIONS: The effect of the model position on the forming table on suppressing the labial thickness reduction of the mouthguard depended on the bucco-lingual width of the model. It is important to position the model anterior rim away from the sheet frame if the bucco-lingual width of the model is large and to place the model anterior rim in front of the suction port if the width is small.

Effect of acute angle model on mouthguard thickness with the thermoforming method and moving the model position just before fabrication.

BACKGROUND/AIM: The effectiveness and safety of mouthguards are affected by their thickness. The aim of this study was to investigate the effect of an acute angle model on the mouthguard thickness with the thermoforming method in which the model position was moved just before fabrication. MATERIALS AND METHODS: Mouthguards were thermoformed using 4.0 mm thick ethylene vinyl acetate sheets and a vacuum forming machine. Three hard plaster models were prepared: 1) the angle of the labial surface to the model base was 90°, and the anterior height was 25 mm (model A); 2) the angle was 90°, and the anterior height was 30 mm (model B); and 3) the angle was 80°, and the anterior height was 30 mm (model C). 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 (MP). The model was moved 20 mm whereas a control model was not moved. Mouthguard thickness was measured using a specialized caliper. The differences in mouthguard thicknesses due to model forms and forming conditions were analyzed by two-way ANOVA and Bonferroni's multiple comparison tests. RESULTS: The MP tended to be thicker than the control in all models. In the controls, model C was significantly thicker than models A and B at the labial and buccal surfaces. In MP, model A was significantly thicker than models B and C on the labial surface. On the labial and buccal surfaces in MP, model C was significantly thicker than model B. CONCLUSIONS: This study suggested that in the thermoforming method in which the model position was moved just before fabrication, reducing the height was more effective than changing the angle of the model to ensure the appropriate thickness.

Fabrication method to maintain mouthguard thickness regardless of the model angle.

BACKGROUND/AIM: The safety and effectiveness of mouthguards depend on the sheet material and thickness. The aim of this study was to investigate the fabrication method for a mouthguard with appropriate thickness using a single sheet regardless of the model angle. MATERIALS AND METHODS: Mouthguards were thermoformed using 4.0 mm thick ethylene vinyl acetate sheets and a vacuum forming machine. The working models were three hard plaster models trimmed so that the angle of the anterior teeth to the model base was 90°, 100°, and 110°. The model position 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. Next, the vacuum was turned on and held for 30 seconds for the control. Under the forming conditions in which the model position (MP) was moved, after the model was covered with the sheet, a scissors handle was positioned at the rear of the model and used to push it forward 20 mm, and then, the vacuum switch was turned on for 30 seconds. Six specimens were formed for each condition. Mouthguard thickness after formation was measured using a specialized caliper. The differences in mouthguard thickness due to forming conditions and model angle were analyzed. RESULTS: The MP was significantly thicker than the control in each model (P < .01). The mouthguard thickness tended to decrease as the model angle increased. The average thickness of the labial surface in the MP was 3 mm or more and was not affected by the model angle. CONCLUSIONS: This study suggested that the fabrication method in which moving the model forward by 20 mm just before formation could produce a mouthguard with approximately 3 mm thickness on the labial side with a single sheet regardless of the model angle.

Thermoforming technique for suppressing reduction in mouthguard thickness: Part 2 Effect of model height and model moving distance.

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.

Movement of model position just before vacuum forming to ensure mouthguard thickness: Part 2 Effect of model moving distance.

BACKGROUND/AIM: Wearing a mouthguard during sports reduces the risk of dental injury via absorbing impact forces, and the effectiveness and safety of the mouthguard are closely linked to the mouthguard material and thickness. The aim of this study was to clarify the suppression effect of the thickness reduction of the mouthguard when changing the moving distance of the model forward in a stepwise manner. MATERIALS AND METHODS: Ethylene-vinyl acetate sheets of 4.0 mm thick and a vacuum forming machine were used. The working model was placed at a position 40 mm from the front of the forming unit. The sheet was softened until it sagged 15 mm, and the sheet frame was lowered and covered the model. The model was then pushed from the back to move it forward, and the vacuum was switched on. The model was moved 10 (MP-10), 20 (MP-20), or 30 mm (MP-30). The control model was not moved. The thickness after formation was measured with a specialized caliper. Differences in the mouthguard thickness caused by the forming conditions were analyzed by one-way ANOVA and Bonferroni's multiple comparison tests. RESULTS: Significant differences were observed between the control and each MP condition (P < 0.01). Reduction rate of the thickness decreased as the moving distance of the model increased. In particular, the thickness difference depending on the forming conditions was greater at the labial site. The reduction rate of MP-30 was 33.8 ± 0.8% smaller than that of the control. CONCLUSION: The thickness reduction in mouthguards was mitigated by moving the model forward just before vacuum forming. The reduction was smaller as the moving distance of the model increased. This study suggested that moving the model 20 mm or more forward just before vacuum forming could secure the labial thickness of 3 mm or more.

Effects of gum chewing training on oral function in normal adults: Part 1 investigation of perioral muscle pressure.

BACKGROUND/PURPOSE: The strength of the intraoral and extraoral muscles that assist the function of tooth and jaw movement during mastication is important for performing oral function. The aim of this study was to investigate the usefulness of gum chewing training to improve the swallowing and feeding function. MATERIALS AND METHODS: In experiment 1, the differences in maximum tongue pressure (TP) and cheek pressure (CP) at the measurement time point for both groups with and without training were examined. We instructed subjects to perform gum chewing training 3 times daily for 3 months. TP and CP were measured before training and at 1, 2, and 3 months after starting training. In experiment 2, the changes of TP and CP based on the sex and duration of training were examined. The effect of the training was evaluated before training, at 2 weeks and 1, 2, and 3 months after starting training, and at 1 and 3 months after cessation of training. RESULTS: Experiment 1 showed TP and CP increased with the progress of continuous training. In experiment 2, TP and CP were higher in men than in women and markedly increased at 2 weeks and 1 month in both sexes. After cessation of training, TP and CP tended to decrease, but there was no significant difference between 3 months after starting training, and also significantly higher than before training. CONCLUSION: This study suggested that gum chewing training is a useful to improve the swallowing and feeding function.

Thermoforming technique for maintaining the thickness of single-layer mouthguard during pressure formation.

BACKGROUND/AIM: Using mouthguards can reduce the risk of injury when playing sports, 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 moving the model position just before formation in the pressure forming technique to maintain the thickness of a single-layer mouthguard. MATERIALS AND METHODS: A 4.0-mm-thick ethylene vinyl acetate (EVA) mouthguard sheet (diameter: 125 mm) and a pressure forming machine were used. The working model was placed with its anterior rim positioned 40 mm from the front of the forming table. The sheets were placed in the forming table with the sheet extrusion direction either vertical (V) or parallel (P) to the model's centerline. Two molding methods were compared: (a) The sheet was formed when it sagged 15 mm (control) and (b) the sheet was covered on the model when it sagged 15 mm, next the model was pushed forward 20 mm, and the sheet was then formed (MP). Mouthguard thickness was measured for the labial surface, palatal surface, cusp, and buccal surface using a specialized caliper. Thickness differences according to molding methods and sheet extrusion directions were analyzed by two-way ANOVA. RESULTS: The thicknesses of the labial surface, cusp, and buccal surface were significantly larger in MP than in the control (P < 0.01). In particular, the thickness differences caused by the molding method were large on the labial and buccal surfaces: For the control, the thicknesses were 1.9 ± 0.03 and 2.1 ± 0.02 mm, whereas for MP, they were 3.2 ± 0.03 and 2.9 ± 0.03 mm, respectively. CONCLUSION: The molding method of moving the model forward just before formation was useful as a thermoforming technique for maintaining the thickness of single-layer mouthguards during pressure forming with 4.0-mm-thick EVA sheet. This method produced labial and buccal thicknesses of 3.2 ± 0.03 and 2.9 ± 0.03 mm.

Thermoforming method to effectively maintain mouthguard thickness: Effect of moving the model position just before vacuum formation.

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.

Effect of the anteroposterior position of the model on fabricated mouthguard thickness: Part 2 Influence of sheet thickness and material.

AIM: 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 thickness of molded mouthguards when the model position on the forming table was changed stepwise in the anteroposterior direction for different sheet thicknesses and materials. MATERIALS AND METHODS: Ethylene vinyl acetate sheets and olefin copolymer sheets with 4.0 or 2.0 mm thick were used for thermoforming by a pressure-forming machine. The working model was trimmed to the height of 25 mm at the maxillary central incisor and 20 mm at first molar. The model was placed with its anterior rim positioned 40, 30, 25, 20, or 10 mm from the front of the sheet frame. Sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper. The differences of the model position on the thickness reduction were analyzed by two-way analysis of variance and Bonferroni's multiple comparison tests. RESULTS: Thickness reductions at the incisal edge, labial surface, and buccal surface were about -60%, -50%, and -40%, respectively; for a distance of 25 mm up to the height of the anterior part of the model and the frame from the model rim, the 4.0 and 2.0 mm sheets showed similar thickness reduction. When the model was moved forward, the anterior thickness reduction of the 2.0-mm-thick sheet increased to larger than that of the 4.0-mm-thick sheet. CONCLUSION: The thickness reduction of the mouthguard was not affected by the sheet material and thickness when the distance from the model to the frame was the same. However, when the distance between the model and the frame decreased, the thickness reduction of the adjacent portion of the model increased, such that the influence was larger in thin sheets.

Influence of continuous use of a vacuum-forming machine for mouthguard thickness after thermoforming.

BACKGROUND/AIMS: Mouthguards can reduce the risk of sports-related injuries such as tooth fracture or avulsion, 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 continuous use of a vacuum-forming machine on mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming with a vacuum-forming machine. The working model was trimmed to a height of 23 mm at the maxillary central incisor and 20 mm at maxillary first molar. During molding, the model was placed at the center of the vacuum unit. Three molding conditions were investigated (i) molding was carried out after the sag at the center of the softened sheet was 15 mm below the clamp (control); (ii) sheet heating started 5 minutes after the control, and molding in the same way as the control (AF5); and (iii) sheet heating started 10 minutes after the control, and molding in the same way as the control (AF10). Under each condition, vacuum forming was conducted for 30 seconds. Sheet thickness after fabrication was determined for the incisal edge, labial surface, cusp, and buccal surface using a special caliper accurate to 0.1 mm. The differences of the molding conditions on the thickness in each sheet material were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. RESULTS: For both sheet materials, significant differences between the control and AF5 were observed at all measurement points (P<.01), but not between the control and AF10. Compared with the control, AF5 was thinner and AF10 was a similar thickness. CONCLUSION: The continuous use of a vacuum-forming machine led to a reduction in the thickness of the mouthguard. Intervals of 10 minutes are necessary to achieve consistent molding.

Effect of thermal shrinkage during thermoforming on the thickness of fabricated mouthguards: Part 2 pressure formation.

BACKGROUND: The aim of this study was to examine the effect of thermal shrinkage, which occurs during thermoforming of ethylene vinyl acetate (EVA) sheets on the thickness of mouthguards fabricated by pressure formation. MATERIALS AND METHODS: Mouthguards were fabricated from 4.0-mm-thick EVA sheets by utilizing a pressure-forming machine. Two molding conditions were compared: The sheets were placed in the thermoforming machine with the sheet extrusion direction either vertical or parallel to the model's center line. The working model was trimmed to the height of 20 mm at the cutting edge of the maxillary central incisor and 15 mm at the mesiobuccal cusp of the maxillary first molar. The sheet was pressed against the working model for 2 min where the center of the softened sheet sagged 15 mm lower than the clamp. After fabrication, the thickness of mouthguard sheets was determined for the incisal (incisal edge and labial surface) and molar (cusp and buccal surface) portions, and dimensional measurements were made. Differences in molded mouthguard thickness with the sheet orientation of extruded sheets were analyzed by Mann-Whitney U-test. RESULT: In comparison with the parallel axis orientation, the sheets in vertical orientation with the model's centerline yielded significantly higher thickness measurements at the incisal edge, labial surface, and the cusp (P < 0.01, respectively). CONCLUSION: The results suggest that the EVA sheet produced by extrusion molding in vertical axis orientation with the model's centerline can effectively reduce loss of thickness in mouthguards after pressure formation.

Shape change in mouthguard sheets during thermoforming - part 2: effect of the anteroposterior position of the model on mouthguard thickness.

BACKGROUND/AIM: 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 model position in the molding machine on the reduction in mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming by a pressure- or a vacuum-forming machine. The working model was trimmed to the height of 25 mm at the maxillary central incisor and 20 mm at maxillary first molar. For both pressure forming and vacuum forming, the model was placed with the anterior rim of the model positioned 40, 30, 25, 20, or 10 mm from the front of the sheet frame. An additional test was carried out at 50 mm for vacuum forming. The sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper. The difference of the model position on the reduction in thickness in each forming device and sheet material was analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. RESULT: The reductions in thickness at the incisal edge and labial surface were about -60% and -50%, respectively, for the distance of 25 mm from the front of forming table. That position was the same as the height of the anterior part of the model for each molding machine and sheet material. The anterior thickness after molding became greater as the distance between the model and the sheet frame became smaller. CONCLUSION: 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.

Evaluation of reliability of perioral muscle pressure measurements using a newly developed device with a lip piece.

PURPOSE: We examined the reliability of measurements using a newly developed perioral muscle pressure measuring device with a lip piece in healthy adults. METHODS: Subjects were 40 healthy men (25.8 years) with normal stomatognathic function. Perioral muscle pressure measuring device with a lip piece was used to measure upper lip, lower lip and tongue pressure, and a balloon-based measurement device was used to measure tongue and cheek pressure. Each measurement was taken twice with a 1-min interval between the two measurements. We determined intra-rater reliability by using the intra-class correlation coefficient as a test of relative reliability. As a test of absolute reliability, Bland-Altman analysis was used to assess systematic bias and the 95% confidence interval of the minimal detectable change was calculated. Additionally, the coefficient of variation was calculated. The Spearman-Brown formula was calculated the number of measurements needed to achieve a confidence coefficient ≥0.9. Each set of measurements was followed by a second set that were taken 1 week later. RESULTS: All measurements showed high values of intra-class correlation coefficient. Upper lip, tongue, and cheek pressure can be determined based on a single measurement, while lower lip pressure requires averaging twice. No systematic bias was observed. The coefficients of variation of measurements were almost the same between the two devices. CONCLUSION: Measurements were highly reliable regardless of the type of perioral muscles. Our findings suggest that the method described in this study is useful as a quantitative chair side method for examining perioral muscle pressure.

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

BACKGROUND: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.