Kaoru Koide

Differences in the thickness of mouthguards fabricated from ethylene vinyl acetate copolymer sheets with differently arranged v-shaped grooves: part 2 - effect of shape on the working model.

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 Bonferronis 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.

Thickness and fit of mouthguards according to a vacuum-forming process.

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.

Influence of color difference of mouthguard sheet on thickness after forming.

PURPOSE The aim of this study was to determine the color difference of mouthguard in hardness, water sorption and thickness after forming EVA sheets. Six different colors of sheets were tested for each of three manufacturers. METHODS The materials used in this study were mouthguard sheets made by three manufacturers. Each manufacturer supplied six colors: clear, white, yellow, blue, red, and black. Shore A hardness and water sorption were measured based on ISO 7619 and 1817, respectively. The thickness after formation was measured by using a measuring device. The differences in hardness, water sorption and thickness after formation were analyzed by two-way analysis of variance. The correlation between the hardness and changes in thickness was analyzed using Pearsons product-moment correlation coefficient. RESULTS Shore A hardness was different depending upon various colored sheets and manufactures. There were differences in the water sorption depending upon some colored sheet among manufacturers. There was a significant difference in the thickness after formation was found to be dependent upon few colors of the sheets on one manufacturers product on the anterior teeth and on three products on posterior teeth. A negative correlation between the hardness and the change of thickness was found in two products. CONCLUSIONS 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.

Difference in the thickness of mouthguards fabricated from ethylene-vinyl acetate co-polymer sheets with differently arranged v-shaped grooves

PURPOSE To investigate the form of mouthguard sheets that best retains its thickness. METHODS Mouthguards were molded using ethylene-vinyl-acetate (EVA) sheets and a suction-type molding device. Five sheet conditions were compared. These were I-N (Incisal part of the cast positioned at the center - Normal sheet), I-H (Incisal part positioned at the center - Horizontal v-shaped groove 30 mm from the anterior end), I-C (Incisal part positioned at the center - Convexing v-shaped groove toward the back 10-40 mm from the anterior end), C-N (Center part positioned at the center - Normal sheet), and C-C (Center part positioned at the center - Convexing v-shaped groove toward the back 10-30 mm from the anterior end). Post-molding thickness was determined for the incisal (incisal edge and labial surface) and molar portion (cusp, central groove, and buccal surface). Sheets were heated until they sagged 15-mm below the clamp. Scheffé multivariate comparison was performed to compare changes in post-molding thickness among sheet conditions. RESULTS Post-molding thickness of mouthguard material differed significantly between the two portions; rates of thickness reduction were smaller for I-C and C-C compared with other conditions. There were no significant differences between I-C and C-C at any measurement points. CONCLUSION The present results suggested that thickness reduction of the EVA sheet material after vacuum-forming may be decreased at both incisal and molar portions if the v-shaped groove with a v-shaped cross section was given in the frontal teeth region of the sheet at the apparatus and materials for this study used.

Variation in mouthguard thickness due to different heating conditions during fabrication

PURPOSE The aim of this study was to evaluate the change in thickness of the mouthguard sheet due to different heating conditions during fabrication. METHODS Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0-mm thick) using a vacuum-forming machine, and six conditions which varied the height of the frame above the surface, reversing the sheet while heating, and controlled power on-off of the heater when a specified level of sagging had been attained were used to determine optimal conditions. The working model was trimmed to a height of 20-mm at the incisor and 15-mm at the first molar. Post-molding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp, central groove, and buccal surface). Differences in the change in thickness due to heating condition were analyzed using Scheffés multiple comparison tests. RESULTS The heating condition which the sheet frame was lowered to and heated at 50mm below the top of the post, the heater was turned off when the sheet sagged by 10mm, and the sheet was molded when the sagging reached 15 mm showed the thickest, what the decrease in the thickness reduction was approximately 0.40-0.44 mm at the incisal, and that was 0.35-0.40 mm at the molar portions. CONCLUSION When molding a mouthguard using an EVA sheet, the thickness of the incisal and molar portions of the mouthguard can be maintained by adjusting the height of the sheet frame and heating conditions, which may be clinically useful.

Variation in mouthguard thickness due to different heating conditions during fabrication: Part 2

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.

Optimal heating conditions for forming a mouthguard using a circle tray: Effect of different conditions on the thickness and fit of formed mouthguards

PURPOSE The aim of this study was to determine the optimal heating conditions for sheet forming using a circle tray by comparing the thickness and fit of mouthguards formed under different conditions. METHODS Mouthguards were fabricated using ethylene vinyl acetate sheets (4.0mm thick) and a vacuum forming machine. The working model was trimmed to a height of 20mm at the incisor and 15 mm at the first molar. Two forming conditions were compared: square sheets were pinched by the clamping frame attached to the forming machine; and round sheets were pinched at the top and bottom and stabilized by a circle tray. Each condition was defined when the sheet sagged by 10-mm or 15-mm below the level of the clamp. The thickness of the sheet was determined for the incisal and molar portion. Additionally, the difference in fit according to the forming conditions was measured by examining the cross section. Differences in the thickness or the fit due to forming conditions were analyzed using two-way analysis of variance (ANOVA) followed by Bonferronis multiple comparison tests. RESULTS The thickness after formation was thicker at the 10-mm condition than that of 15-mm, and the fit at the 15-mm condition was better when that of 10-mm with square and round sheets. CONCLUSION Within the limitation of this study, it was suggested that when forming a mouthguard using a 4.0-mm EVA sheet and a circle tray on a vacuum forming machine, the sheet should be formed at a sagging distance of 10-mm.

Influence of sheet material shape on the thickness and fit of mouthguards

The aim of this study was to evaluate the influence of sheet material shape on the thickness and fit of mouthguards. Mouthguards were fabricated using ethylene vinyl acetate sheets (4.0 mm thick) and a vacuum-forming machine. The working model was trimmed to a height of 20 mm at the incisor and 15 mm at the first molar. Three forming conditions were compared: Square sheets were fabricated while being secured by the clamping frames attached to the forming machine; round sheets were fabricated while secured by a circle tray; and square sheets were fabricated while secured by a circle tray. Each condition was defined when the sheet sagged by 15 mm below the level of the clamp. The thickness of the sheet was determined for the incisal and molar portion. Additionally, the difference in fit according to the forming conditions was analyzed. Differences in the material thickness or the fit due to forming conditions were analyzed using one-way analysis of variance (anova). Round sheets resulted in the thinnest mouthguard at the incisor and molar region and produced the best fit. For square sheets, no significant difference in thickness was observed between the clamping frame and circle tray methods. The fit of the mouthguard at the first molar was better when using square sheets fabricated by a circle tray than those fabricated by the clamping frame. In conclusion, when molding a mouthguard using square sheets, the thickness reduction was less and fit was better with using a circle tray, which may be clinically useful.

Thickness and fit of mouthguards adjusted by notching thermoplastic sheets under different heating conditions

This study examines the thickness and fit of mouthguards by notching thermoplastic copolymer ethylene vinyl acetate (EVA) sheets and then heating them to various degrees. The material used was a 3.8-mm-thick sports mouthguard. Notches with a length of 90 and 80 mm were cut into an EVA 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 formed using a vacuum former when the sheets were heated until they hung 1.5, 2.0, 2.5, and 3.0 cm from the baseline. We measured the thickness and fit of the mouthguard at the central incisor and first molar. Differences in thickness and fit according to the measurement parts, sheet type, and heating conditions were analyzed by three-way anova. The measurement parts and sheet type significantly differed (P < 0.01), and the notched sheet maintained the required thickness. Fit differed among the measurement parts and by heating conditions (P < 0.01), but was not affected by the notching. The mouthguard fit was optimal when the sheets were heated to a hanging distance of 3.0 cm. These results suggest that the thickness and fit of the EVA sheet could be maintained by notching and heating the sheet to a hanging distance of 3.0 cm. These findings could be useful for fabricating appropriate mouthguards.

Optimal heating condition of ethylene-vinyl acetate co-polymer mouthguard sheet in vacuum-pressure formation.

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 Bonferronis 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.