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Aim: The aim was to examine the influence of the heating temperature on the fabrication of vacuum-formed mouthguards., Materials and Methods: Mouthguard sheets of 3.8 mm ethylene vinyl acetate were vacuum-formed on working models at three heating temperatures: 80, 100, and 120°C. The thickness of the mouthguard was measured at the labial surface of the central incisor, and the buccal and occlusal surfaces of the first molar. Differences in the thickness of the mouthguards were analyzed by two-way analysis of variance. The fit of the mouthguard was examined at the central incisor and the first molar by measuring the distance between the mouthguard and the cervical margin of the working model. Differences in the distance between the mouthguard and the cervical margin according to the heating temperatures were analyzed by one-way analysis of variance., Results: Mouthguard thickness varied among the measured regions of the central incisors and first molars (P < 0.01). The greatest thickness was found at the labial surface of the central incisor and the buccal surface of the first molar in mouthguards fabricated with heating temperature of 120°C (P < 0.05). The best fit was obtained in mouthguards fabricated with heating temperature of 120°C (P < 0.05)., Conclusions: Heating the mouthguard sheet until the temperature reached 120°C was the best fabrication method to maintain the thickness and to obtain proper fit. It is important to control the heating temperature when fabricating vacuum-formed mouthguards., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Aim: The purpose of this study was to examine the differences of the vacuum-formed mouthguard thickness by the timing of vacuum application., Materials and Methods: The material used in this study was a mouthguard sheet of 3.8-mm ethylene vinyl acetate. Three conditions of the timing of vacuum application were examined: the vacuum was applied immediately, 5 s after, and 10 s after the sheet holder was lowered over the vacuum-forming stand. We measured mouthguard thickness at the labial surface of the central incisor, buccal surface of the first molar, and occlusal surface of the first molar. Differences in thickness in different regions of mouthguards formed under different timing of vacuum application were analyzed by two-way analysis of variance and Bonferroni method., Results: We found that mouthguard thickness differed in different regions of the central incisors and the first molars (P < 0.01). The mouthguard thickness at the labial surface of the central incisor and buccal surface of the first molar became thinner when the vacuum was applied immediately after the sheet holder was lowered over the forming stand. The thickness at the occlusal surface of the first molar did not vary with the timing of vacuum application., Conclusions: Our results suggest that the thicknesses of the labial surface of the central incisor and buccal surface of the first molar became larger when the vacuum was applied several seconds after the sheet holder was lowered over the forming stand. This finding is necessary knowledge when forming a mouthguard sheet., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: The goal of the present study was to examine the thickness of mouthguards molded under a variety of heating conditions to clarify suitable conditions during vacuum-pressure forming of ethylene vinyl acetate sheets., Materials and Methods: Mouthguards were fabricated using ethylene vinyl acetate (EVA) sheets (thickness: 4.0 mm) using a vacuum-pressure forming machine. The sheet was pressed against the working model, followed by vacuum forming for 10 s and compression molding for 2 min. Three heating conditions were investigated in which the sheet was molded when the center of the softened sheet sagged 10 mm, 15 mm, or 20 mm below the clamp (H-10, H-15, or H-20 respectively). The temperature of the sheet surface was measured using a radiation thermometer under each heating condition. The thickness of the mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in thickness due to the heating condition of the sheets were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests., Results: The temperature difference between the heated and non-heated surfaces was lowest under H-15. The thickness differences at incisal edge, labial surface, and cusp were determined. The thicknesses for H-10 and H-15 were greater than that for H-20, and the thicknesses for H-10 and H-15 were equivalent at all measurement points. No differences in thickness at the buccal surface were observed for the various heating conditions., Conclusion: The present study demonstrated that a sagging distance of 15 mm provided the most suitable forming process. The results of the present study provide a standard heating condition for EVA sheet forming., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Unevenness in softening of the plastic sheet leads to a decrease in the mouthguard thickness during thermoforming. In this study, we examined the heating methods for reducing unevenness when softening mouthguard sheets during vacuum-pressure formation., Materials and Methods: Ethylene vinyl acetate mouthguard sheets and olefin copolymer sheets (thickness: 4.0 mm) were used. The following three heating conditions were compared: condition A-the sheet was molded when it sagged 15 mm from the sheet frame (under normal condition); condition B-the heater was turned off when the sheet sagged by 10 mm from the frame, followed by the sheet molding when the sagging reached 15 mm below the frame; and condition C-the sheet was inverted after heating when the sheet sagged 10 mm and was molded when the sagging reached 15 mm below the frame. The sheet was heated and pressed over the model using a vacuum-pressure machine; then, 10 s of vacuum forming and 2 min of pressure molding were applied. The sheet temperatures were measured using a radiation thermometer. Thickness of the fabricated sheets was determined for the incisal and the molar portion using a measuring device. Thickness data for each condition were analyzed by one-way anova followed by Bonferroni's multiple comparison tests., Results: On both sheets, condition B was smallest for temperature difference between the heated and the non-heated surface, and thicknesses after molding were greatest at all measuring portions., Conclusion: By comparing changes in sheet temperatures at molding and variation in thicknesses when applying the heating method using a vacuum-pressure molding machine, we found that reduced unevenness in sheet softening occurred when the heater was turned off when the sag distance of the sheet was 5 mm less than the conventional molding, and then, the sheet was pressed when the conventional sag distance was reached., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The aim of this study was to investigate vacuum forming techniques for reduction of loss in mouthguard thickness effects of sheet grooving and thermal shrinkage of extruded sheets on molded mouthguard thickness. Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0 mm thick) using a vacuum forming machine. Sheet form was a convexing v-shaped groove toward the back, 10-40 mm from the anterior end. The sheets were placed in the forming machine with the sheet extrusion direction either vertical or parallel to the model's centerline of right and left. Molding was performed by crimping the sheet using suction when the most descending portion of the sheet sagged downwards from the clamp, 15 mm below the basal surface. Postmolding thickness was determined using a measuring device. Measurement points were the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). Differences in molded mouthguard thickness with the sheet orientation of extruded EVA sheets were analyzed by student's t-test. The sheet in parallel axis orientation with the model's centerline yielded higher thickness than vertical orientation at the labial surface and the buccal surface. The present results suggested that addition of a groove to the sheet in conjunction with placement of the sheet with its axis of orientation parallel the centerline of the working model can effectively reduce thickness loss in the molded mouthguard with the equipment and materials used in this study., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The purpose of this study was to examine the difference in the thickness and the fit of mouthguards fabricated with a vacuum-forming method of the mouthguard sheet material. The material used in this study was Sports Mouthguard (3.8 mm thickness). Two forming conditions were performed. In the first condition, the sheet was lowered over the working model after the vacuum was applied, and in the other trial, the sheet was lowered over the working model before the vacuum was applied. The sheets were formed using a vacuum former when the heated sheets hung 1.5 cm from the baseline. We measured the thickness and the fit of the mouthguard at the areas of the central incisor and first molar in both conditions. The difference of the thickness at the areas of the central incisor and first molar and the forming condition was analyzed by Two-way anova. The difference of the fit according to the forming conditions was analyzed by the Mann-Whitney U test. The results showed that the thickness of the mouthguard differed at the areas of the central incisor and first molar, but the thickness of the mouthguard did not differ according to the forming conditions. The fit of the mouthguard at the central incisor and first molar was significantly different between the forming conditions (P < 0.01 and P < 0.05). These results suggested that the fit of the mouthguard was the best without any deficiency of thickness when the vacuum was applied first and then the sheet was pressed onto the working model. These results may be useful in fabricating proper mouthguards., (© 2012 John Wiley & Sons A/S.)

Background/aim: Polyolefin sheet mouthguards are usually formed in the same manner as ethylene-vinyl acetate sheet mouthguards. However, the heating condition of the polyolefin sheet for the pressure-forming process has not been determined. The aim of this study was to examine the appropriate heating condition for polyolefin sheet mouthguards when fabricated with the pressure-formed technique.Materials and Methods: Mouthguard sheets of 3.0 mm polyolefin were pressure formed on working models at three heating temperatures: 90°C, 105°C, and 120°C. The thickness of the mouthguard was measured at the labial surface of the central incisor, and the buccal and occlusal surfaces of the first molar. The fit of the mouthguard was examined at the central incisor and the first molar by measuring the distance between the mouthguard and the cervical margin of the working model. Differences in the thickness and fit of the mouthguards according to the heating conditions and the measured regions were analyzed using two-way analysis of variance.Results: Mouthguard thickness varied among the measured regions of the central incisors and first molars (p < .01). The greatest thickness was found at the labial surface of the central incisor in mouthguards fabricated with the heating temperature of 90°C (p < .01). The greatest thickness was found in mouthguards fabricated with the heating temperature of 105°C at the buccal surface of the first molar (p < .01), and 105°C or 120°C at the occlusal surface of the first molar (p < .01). The fit was not significantly different among the three heating conditions both at the central incisor and the first molar.Conclusions: The appropriate heating condition for pressure-formed mouthguards using polyolefin sheets was 90°C to maintain the mouthguard thickness at the anterior teeth area with proper fit. [ABSTRACT FROM AUTHOR]

Background/aims: The appropriate heating conditions for polyolefin sheets have not yet been determined and polyolefin sheets are usually formed in the same manner as ethylene vinyl acetate sheets. The aim of this study was to examine the appropriate heating conditions for polyolefin sheets when fabricating vacuum-formed mouthguards.Materials and Methods: Mouthguard sheets of 3.0 mm polyolefin were vacuum formed on working models at three heating temperatures: 90°C, 105°C, and 120°C. The thickness of the mouthguard was measured at the labial surface of the central incisor, and the buccal and occlusal surfaces of the first molar. The fit of the mouthguard was examined at the central incisor and the first molar by measuring the distance between the mouthguard and the cervical margin of the working model. Differences in the thickness and fit of the mouthguards according to the heating conditions and the measured regions were analyzed by two-way analysis of variance.Results: Mouthguard thickness varied among the measured regions of the central incisors and first molars (P < .01). The smallest thickness was found at the labial surface of the central incisor in mouthguards fabricated at 90°C (P < .01). The smallest thickness was found at the buccal and occlusal surface of the first molar in mouthguards fabricated at 120°C (P < .01). The worst fit was obtained with the heating temperature of 90°C (P < .01).Conclusions: The appropriate heating temperature for polyolefin sheets was 105°C to maintain mouthguard thickness and to obtain proper fit. [ABSTRACT FROM AUTHOR]

Aim: Mouthguard thickness influences the preventive effects against dental and oral injury. The aim of this study was to examine the difference in pressure-formed mouthguard thickness according to the laminate procedure used.Materials and Methods: The materials used were mouthguard sheets of 2.0-mm and 3.0-mm ethylene vinyl acetate, and pressure formed using a pressure former. Two forming conditions for laminated mouthguards were examined: the condition 23P used the 2.0-mm sheet as the first layer and 3.0-mm sheet as the second layer. The condition 32P used the 3.0-mm sheet as the first layer and 2.0-mm sheet as the second layer. The first layer was trimmed to cover only the anterior region; then, the second layer was formed over the first layer. Mouthguard thickness was measured at the labial surface of the central incisor, buccal surface of the first molar, and occlusal surface of the first molar. Statistical analysis was performed by two-way analysis of variance and Bonferroni method to analyze the differences in thickness by measurement region of mouthguards and forming conditions.Results: Mouthguard thickness differed in different regions of the central incisors and the first molars (P < .01). The thickness at the labial surface of the central incisor became statistically significantly larger on the 32P condition than that on the 23P condition (P < .01). The thickness at the buccal surface and the occlusal surface of the first molar became statistically significantly larger on the 23P condition than that on the 32P condition (P < .01).Conclusions: The thicknesses of the labial surface of the central incisor became larger when the sheet thickness of the first layer was larger. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the influence of reheating after the vacuum forming process on the dimensional changes of a mouthguard after immersion in water and after drying. 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. The weight and volume were measured before immersion, 1, 2, 3, 6 hours after immersion, and 1, 2, 3, 4, 5, 6, and 7 days after immersion. The weight was measured just after drying, 1, 2, 3, 6 hours after drying, and 1 and 2 days after drying. The differences in the changes in weight and volume after immersion in water and change in weight after drying were analyzed by the Friedman test. The change in weight after immersion in water was not significantly different among the four conditions. The weight increased considerably within 2 hours, and then decreased slightly. The change in volume after immersion in water was large in the first 2 hours, and then it decreased. Statistically significant differences were found between the condition of rapid cooling and reheating for 5 minutes, slow cooling and reheating for 10 minutes, and reheating for 5 minutes and reheating for 10 minutes (p<0.05). The change in weight after drying was not significantly different among the four conditions. In this study, we demonstrated that reheating the mouthguard for 5 minutes could reduce its deformation after use. [ABSTRACT FROM AUTHOR]

Background/aim: Mouthguards should be provided with appropriate thickness and proper fit to exert their effects. However, mouthguard thickness becomes thinner after forming. The aim of this study was to examine the effect of using a notched mouthguard sheet and forming as the heated surface of the sheet contacts the surface of the working model.Materials and Methods: The material used was a 3.8-mm-thick Sports Mouthguard. Notches with a length of 90 and 80 mm were cut into an ethylene vinyl acetate sheet 20 mm from the anterior and posterior margins and 15 mm from the right and left margins, respectively, and the sheet was compared with the original. The sheets were then formed using a vacuum former. Original and notched sheets were heated until the temperature of the sheet reached 80°C, and the non-heated surface of the sheet was sucked down over the model. Both sheets were also heated at first until the sheet temperature reached 80°C, then turned upside down, and the heated surface of the sheet was sucked down over the model. The thickness and fit of the mouthguard were measured at the central incisor and first molar. Differences in thickness and fit according to the measurement parts and the sheet conditions were analyzed by two-way ANOVA.Results: The thickness of the mouthguard significantly differed by the measurement parts and the sheet conditions (P < 0.01), and the notched sheet maintained the required thickness. Fit differed between the measurement parts and the sheet conditions (P < 0.01), and the sheets formed as the heated surface contacted the working model showed better fit.Conclusions: These results suggest that the ideal mouthguard with appropriate thickness and proper fit can be fabricated by notching a sheet and contacting the heated surface of the sheet to the working model. [ABSTRACT FROM AUTHOR]

Background/aim: Ethylene vinyl acetate and polyolefin sheets have been used commonly for fabricating mouthguards. However, the change of the sheet temperature during heating of the polyolefin has not been clarified. The aim of this study was to examine the effects of changing the sheet temperature during heating, and to examine whether there were any differences between the sheet materials.Materials and Methods: The mouthguard materials used were 4.0 mm sheets of ethylene vinyl acetate and polyolefin. The sheet temperature of the two materials was measured when the center of the sheet was displaced by 10, 15, and 20 mm from the baseline after heating. The sheets were pressure-formed when the heating temperatures reached 100°C. Mouthguard thickness and fit were measured at the central incisor and the first molar. Differences in the sheet temperature and the thickness between the sheet materials were analyzed by two-way analysis of variance.Results: The sheet temperature of ethylene vinyl acetate and polyolefin sheets became higher as the hanging distance became larger (P < 0.01), and there were statistically significant differences between ethylene vinyl acetate and polyolefin sheets at the hanging distance of 10 and 15 mm (P < 0.01). The thicknesses of the pressure-formed mouthguard at the central incisor and the first molar were greater in the mouthguards formed by ethylene vinyl acetate sheets than those with polyolefin sheets (P < 0.01 and P < 0.05, respectively). The fit of the mouthguard was not different between mouthguards formed by ethylene vinyl acetate sheets and those formed by polyolefin sheets.Conclusions: The change of mouthguard sheet temperature during heating was different between ethylene vinyl acetate and polyolefin sheets. The ethylene vinyl acetate sheets maintained the mouthguard thickness in comparison with the polyolefin sheets at the same heating temperature. [ABSTRACT FROM AUTHOR]

Background/aim: Mouthguard sheet materials such as ethylene vinyl acetate and polyolefin have been used commonly. However, the change of the sheet temperature during heating of the polyolefin has not been determined. The aim of this study was to examine the change of the sheet temperature during heating and to examine the vacuum-formed mouthguard characteristics for the sheet materials.Materials and Methods: The mouthguard materials used were 4.0-mm sheets of ethylene vinyl acetate and polyolefin. The sheet temperature of the two materials was measured when the center of the sheet was displaced by 10, 15, and 20 mm from the baseline after heating. Sheet temperature differences by sheet materials were analyzed by two-way analysis of variance. The sheets were vacuum-formed when the heating temperatures reached 100°C using ethylene vinyl acetate sheet and polyolefin sheet. Mouthguard thickness and fit was measured at the central incisor and the first molar. Differences in the thickness and fit between the sheet materials were analyzed by two-way analysis of variance.Results: The sheet temperature of ethylene vinyl acetate sheets became higher as the hanging distance became larger (P < 0.05), but that of polyolefin sheets was not different. The thicknesses of the vacuum-formed mouthguard at the central incisor and the first molar were greater in the mouthguards formed by ethylene vinyl acetate sheets than that with polyolefin sheets (P < 0.01 or P < 0.05). The fit of the mouthguard was not different between mouthguards formed by ethylene vinyl acetate sheets and that formed by polyolefin sheets.Conclusions: The change of mouthguard sheet temperature during heating was different between ethylene vinyl acetate and polyolefin sheets. The ethylene vinyl acetate sheets maintained the vacuum-formed mouthguard thickness in comparison with the polyolefin sheets with a better fit. [ABSTRACT FROM AUTHOR]

Background/aim: The method used to form mouthguards should be carefully selected in order to obtain their full preventive benefits. The aim of this study was to examine the differences of mouthguard characteristics according to the forming methods.Materials and Methods: Mouthguard sheets of 3.8-mm ethylene vinyl acetate were vacuum-formed and pressure-formed on a working model. The sheets were formed when heating causing them to displace 15 mm from baseline. Mouthguard thickness was measured at the labial surface of the central incisor, the buccal surface of the first molar, and the occlusal surface of the first molar. The fit of the mouthguard was measured at the central incisor and the first molar. Differences in the thickness and fit between the vacuum-formed and pressure-formed mouthguards were analyzed by two-way analysis of variance and the Bonferroni method.Results: Mouthguard thickness varied between the central incisors and first molars (P<.01). The thicknesses at the labial surface of the central incisor and the buccal surface of the first molar were greater in the vacuum-formed mouthguards than in the pressure-formed mouthguards (P<.01). The fit was better in the pressure-formed mouthguards than that in the vacuum-formed mouthguards (P<.01).Conclusions: The vacuum-forming method maintained the mouthguard thickness, while the pressure-forming method obtained better fit. [ABSTRACT FROM AUTHOR]

Aim: The aim of this study was to examine the influence of the position of the working model on the formation of a pressure-formed mouthguard.Materials and Methods: Mouthguard sheets of 3.8 mm ethylene vinyl acetate were pressure-formed on working models in three positions: anterior, central, and posterior. The thickness of the mouthguard was measured at the labial surface of the central incisor and the buccal and occlusal surfaces of the first molar. Differences in the thickness of the mouthguards were analyzed by two-way analysis of variance.Results: Mouthguard thickness varied among the measured regions of the central incisors and first molars (P < 0.01). The thickness at the labial surface of the central incisor was greatest for mouthguards formed with the working model in the posterior position (P < 0.01).Conclusions: The results of this study suggest that pressure-formed mouthguards could be fabricated effectively by positioning the center of the working model 15 mm posteriorly from the center of the pressure former. The position of the working model should be considered carefully when forming a mouthguard. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to identify changes in sheet shape during thermoforming and the effect of the model position in the molding machine on fabricated mouthguard thickness.Materials and Methods: Ethylene vinyl acetate mouthguard sheets (3.8 mm thick) were used that had cross-stripes (10 × 10 mm), and the anteroposterior and bilateral lengths were used for measurements. Two forming machines were used: a vacuum- and a pressure-forming machine, and two heating conditions were investigated that defined as the time when sagging of the softened sheet was 15 mm (H-15) and 20 mm (H-20) below the clamp, and the length of each cross-stripes was measured. The area of each lattice was calculated using Bretschneider's formula to compare changes in sheet shape for each condition. Next, mouthguards were molded by forming machine where the working model was positioned under two different conditions: with the model anterior centered in the forming unit and with the model centered. The sheet thickness after fabrication was determined for the incisal and the molar portion, and dimensional measurements were obtained using a measuring device. Differences in the thickness were analyzed by two-way analysis of variance (anova).Result: In both molding machines, the change in the area under H-20 was greater than H-15. While the increase in area tended to expand from the center of the sheet in concentric circles, the difference between the central and surrounding areas was only approximately 5%. For both molding machines, differences in thickness after molding due to setting position of the model were not observed.Conclusion: 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. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the thickness of mouthguard sheet after vacuum-pressure formation based on the mouthguard sheet material. Three mouthguard sheet materials (4.0 mm thick) were compared: ethylene-vinyl acetate co-polymer (EVA), olefin co-polymer (OL), and polyolefin-polystyrene co-polymer (OS). The working model was made by hard gypsum that 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. Where the center of the softened sheet sagged 15 mm lower than the clamp, the sheet was pressed against the working model, followed by vacuum forming for 10 s and compression molding for 2 min. The thickness of mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in the change in thickness due to sheet materials were analyzed by one-way analysis of variance (anova) followed by Bonferroni's multiple comparison tests. The OL sheet was thickest at all measurement points. At the incisal edge and cusp, thickness after formation was highest for OL, then EVA and finally OS. At the labial surface and buccal surface, the thickness after formation was highest for OL, then OS and finally EVA. This study suggested that post-fabrication mouthguard thickness differed according to sheet material, with the olefin co-polymer sheet having the smallest thickness reduction. [ABSTRACT FROM AUTHOR]

The shapes of ethylene vinyl acetate (EVA) sheets are mainly square or round. The aim of this study was to elucidate a fabrication method that effectively maintains the thickness of the round sheet. Mouthguards were fabricated using EVA sheets (diameter 125 mm, thickness 4.0 mm) and a vacuum-forming machine. The sheet was pinched at the top and bottom and stabilized by the circle tray. Two heating conditions were compared: (i) the sheet was molded when it sagged 10 mm below the level of the sheet frame at the top of the post under normal conditions (N); and (ii) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use and molded when it sagged 10 mm from the sheet frame (L). Two EVA sheet shapes were compared: an ordinary sheet (O) and a sheet with a horizontal v-shaped groove 30 mm from the anterior end (G). The height of the working model was 20 mm at the incisor point and 15 mm at the first molar. The sheet temperatures of the heating and non-heated surface were measured by the radiation thermometer. Post-molding thickness was determined for the incisal and molar portion. Differences in the thickness were analyzed using two-way anova. The temperature difference among points was smaller under condition L than under condition N. Thickness after formation was higher in condition L than in condition N, and was higher in condition G than in condition O. At the labial surface and the cusp, L-G was thickest. With the present techniques, uneven softening during heating can be improved by lowering the sheet frame and consequently reducing the reduction in the thickness of the sheet. Additionally, the thickness reduction is reduced by creating a horizontal groove on the sheet, establishing the clinical efficacy of this method. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the influence of the thermal shrinkage to thickness of the mouthguard with the heating method by the setting position of a sheet and the working model using an ethylene vinyl acetate sheet prepared by extrusion. Mouthguards were fabricated with EVA sheets (4.0 mm thick) using a vacuum-forming machine. Two forming conditions were compared: the square sheet was pinched by the clamping frame attached to the forming machine (S); and the round sheet was pinched at the top and bottom and stabilized by the circle tray (R). The sheet was aligned to make the sheet's extrusion direction vertical (V) or parallel (P) to the midline of the working model. The following two heating conditions were compared: (i) the sheet was molded when it sagged 15 mm below the level of the sheet frame measured at the top of the post in condition S (S-0), or that sagged 10 mm in condition R (R-0) in the usual position; (ii) the sheet frame was lowered by 50 mm from the ordinary height (S-50, R-50). Postmolding thickness was determined using a measuring device. Measurement points were the incisal and molar portion. Differences in the change of thickness of mouthguards molded under different heating conditions and extrusion directions for each sheet shape were analyzed by two-way analysis of variance (anova). The results of this study showed that by lowering the height of the sheet frame, the difference of the sheet temperature of each part was reduced. Among all sheets, condition V produced under S-50 and R-50 had the largest thickness independently of shape sheet. Furthermore, thickness reduction is effectively suppressed by aligning the direction of the extruded sheet to be vertical to the midline of the model. [ABSTRACT FROM AUTHOR]

The purposes of this study were to clarify the suitable heating conditions during vacuum-pressure formation of olefin copolymer sheets and to examine the sheet temperature at molding and the thickness of the molded mouthguard. Mouthguards were fabricated using 4.0-mm-thick olefin copolymer sheets utilizing a vacuum-pressure forming device, and then, 10 s of vacuum forming and 2 min of compression molding were applied. Three heating conditions were investigated. They were, defined by the degree of sagging observed at the center of the softened sheet (10, 15, or 20 mm lower than the clamp (H-10, H-15, or H-20, respectively)). The working model was trimmed to the height of 20 mm at the maxillary central incisor and 15 mm at the mesiobuccal cusp of the maxillary first molar. The temperature on both the directly heated and the non-heated surfaces of the mouthguard sheet was measured by the radiation thermometer for each condition. The thickness of mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in the thickness due to the heating condition of the sheets were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. The temperature difference between the heated and non-heated surfaces was highest under H-10. Sheet temperature under H-15 and H-20 was almost the same. The thickness differences were noted at incisal edge, cusp, and buccal surface, and H-15 was the greatest. This study demonstrated that heating of the sheet resulting in sag of 15 mm or more was necessary for sufficient softening of the sheet and that the mouthguard thickness decreased with increased sag. In conclusion, sag of 15 mm can be recommended as a good indicator of appropriate molding timing for this material. [ABSTRACT FROM AUTHOR]

Aim: The aim of this study was to examine the effectiveness of layering a second piece of ethylene vinyl acetate on the original sheet before fabrication to maintain the thickness of vacuum-formed mouthguards.Materials and Methods: Two methods were used to form mouthguards. In the first, a 3.8-mm ethylene vinyl acetate sheet was laminated after 3.0-mm ethylene vinyl acetate sheet was formed at the anterior teeth area. In the second, a second piece of 3.0-mm sheet was layered on the original 3.8-mm sheet in the region mounted on the anterior teeth. Mouthguard thickness at specific sites on the central incisors and first molars was measured. The differences in mouthguard thickness according to measurement regions and forming methods were analyzed by two-way analysis of variance and a post hoc test (Bonferroni method).Results: Mouthguard thickness differed significantly among the measurement regions (P < 0.01). Mean thickness at the central incisors was significantly greater with the sheet-layering method (5.5 mm) than with the laminate method (3.9 mm) (P < 0.01).Conclusions: The results of this study indicate that adding a second layer of ethylene vinyl acetate to the original sheet effectively maintained the thickness of the mouthguard. This method is effective to maintain the mouthguard thickness and cost-effective method. [ABSTRACT FROM AUTHOR]