Influence of color difference of mouthguard sheet on thickness after forming

PurposeThe 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.MethodsThe 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 Pearson's product-moment correlation coefficient.ResultsShore 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 manufacturer's 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.ConclusionsThe 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.     

Investigation of vacuum forming techniques for reduction of loss in mouthguard thickness: part 2—effects of sheet grooving and thermal shrinkage

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.     

Variation in mouthguard thickness according to heating conditions during fabrication Part 2: sheet shape and effect of thermal shrinkage

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.     

Thickness of mouthguard sheets after vacuum–pressure formation: influence of mouthguard sheet material

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.     

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

PurposeThe 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.MethodsMouthguards 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. 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 Bonferroni's multiple comparison tests.ResultsThe 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.ConclusionWithin 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.     

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.     

定制牙托膜片切牙区厚度变化的影响因素

佩戴运动牙托可以缓冲外力,降低颌面部损伤的风险.运动牙托种类较多,其中个性化定制运动牙托具有较好的保护作用和较高的舒适度而备受欢迎.个性化定制运动牙托的膜片加热后可发生延展,随后发生厚度变化,尤以切牙区膜片的厚度变化更能影响其保护性能;因此,笔者就影响个性化定制运动牙托膜片切牙区的厚度变化的膜片硬度、膜片形状和膜片表面设计等膜片因素,工作模厚度和工作模摆放角度等工作模因素,加压方法,夹持托盘形状、夹持方式和夹持托盘与工作模底座的距离等夹持因素,加压时间等的研究进展作一综述.