Dental Traumatology 2014; 30: 472–476; doi: 10.1111/edt.12123
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 Mutsumi Takahashi, Kaoru Koide, Fumi Mizuhashi Department of Removable Prosthodontics, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan
Key words: mouthguard; thickness; sheet material shape; working model shape; ethylene vinyl acetate sheet Correspondence to: Mutsumi Takahashi, 1-8, Hamaura-cho, Chuo-ku, Niigata City, Niigata, 951-8580, Japan Tel.: +81 25 267 1500 Fax: +81 25 265 5846 e-mail: [email protected] Accepted 17 April, 2014
Abstract – The aim of this study was to evaluate the change in thickness of a working model mouthguard sheet due to different shape. Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0 mm thick) using a vacuum-forming machine. Two shapes of the sheet were compared: normal sheet or v-shaped groove 10–40 mm from the anterior end. Additionally, two shapes of the working model were compared; the basal plane was vertical to the tooth axis of the maxillary central incisor (condition A), and the occlusal plane was parallel to the basal plane (condition B). Sheets were heated until they sagged 15 mm below the clamp. Postmolding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). Differences in the change in thickness due to the shape of the sheets and model were analyzed using two-way ANOVA followed by a Bonferroni’s multiple comparison tests. The thickness of the mouthguard sheet with v-shaped grooves was more than that of the normal sheet at all measuring points under condition A and condition B (P < 0.01). The thickness of condition B was less than that of condition A, there the incisal portion in the normal sheet and the incisal edge in the sheet with v-shaped grooves (P < 0.01). The present results suggested that thickness after molding was secured by the use of the sheet with v-shaped grooves. In particular, the model with the undercut on the labial surface may be clinically useful.
Use of mouthguard is effective in reducing trauma and prevention of maxillofacial area during sports (1–5). The common mouthguard material is ethylene vinyl acetate resin (EVA), which is broadly divided into olefin- and styrene-based thermoplastic elastomers. EVA has many applications owing to its low softening temperature and affordable price, and the many color variations of EVA also contribute to its popularity (6). In general, custom-made mouthguards are produced mainly by soft welding a thermoplastic elastomer sheet over a working model in a molding device. The procedure is relatively handiness but reduced material thickness after molding (7, 8). The shape of the working model affected the thickness of the mouthguard after molding. The working model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor and reduced the height as much as possible, which was useful for ensuring the thickness of fabricated mouthguards (6, 9, 10). However, the trimming 472
form may be subject to restrictions depending on the inclination of the occlusal plane and the row of teeth. An EVA sheet should be 3–4 mm thick at the incisal and molar portions to sufficiently reduce the force of any impact (1–4, 11). However, the reduction in mouthguard thickness that occurs along the incisal edges and the labial surface is extensive, so the challenge is how well the thickness reduction in this region can be prevented. It is difficult to attain such thickness using the conventional-forming method with a single layer of sheet material (12). On the other hand, the laminated-type mouthguard can secure necessary thickness such as anterior part and occlusal surface without being affected by the dentition or occlusion (13–15). Thus, that has many advantages so as to recommend it as the best option. Although, it is difficult to convince all players to use the laminated-type mouthguard for reasons such as cost, time, or time spent to deliver the © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Thickness of mouthguards after vacuum formation mouthguard. For this reason, the fabrication of the single-layer mouthguard in ordinary equipment does not affect the thickness reduction and fit as possible, and it would be clinical useful. The thickness of fabricated mouthguard affected as a results of various factors, the shape of a working model, sheet color, and the molding device (1, 3, 9, 11, 12, 16, 17). Especially, the shape of a working model is a factor in reducing the thickness of the mouthguard that with an undercut on the side of the labial surface and the height is higher (9, 10). We have previously studied the shape of the sheet as a production method that can ensure thickness of the anterior mouthguard without affecting adaptation when using the grooved sheet (18). As a result, by applying a groove convex to the model in the anterior direction, it is possible to suppress the reduction in the thickness that occurs during heat softening and pressure forming. The aim of this study was to investigate the thickness of fabricated mouthguard what extent was possible to decrease the thickness reduction when using a model with an undercut on the side of the labial surface and mouthguard sheet with v-shaped grooves. Materials and methods
EVA sheets (Sports Mouthguardâ, 127 mm 9 127 mm 9 4.0 mm, clear; Keystone Dental Inc., Cherry Hill, NJ, USA) were used. Cross-stripes (10 9 10 mm) were painted on each sheet, and these were used as observation of the shape deformation after thermoforming. The working model was made by taking an impression of a maxillary dental model (D16FE–500A– QF; Nissin Dental Products Inc., Kyoto, Japan) using a silicone rubber impression paste (Correcsilâ, Yamahachi Dental Mfg., Co., Aichi, Japan). Hard gypsum (New Plastoneâ, GC Co., Tokyo, Japan) was then poured onto the impression, and the model was removed from the impression 60 min later. The working model was trimmed using a wet-type model trim-
(A)
Fig. 1. The shape of the working model. Condition A: The model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor; the height at the cutting edge of the maxillary central incisor is 20 mm and that at the mesiobuccal cusp of the maxillary first molar is 15 mm. Condition B: The model was trimmed, so the occlusal plane was parallel to the basal plane; the height at the cutting edge of the maxillary central incisor was 20 mm and that at the mesiobuccal cusp of the maxillary first molar was 20 mm. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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mer (Model trimmer MT–6â; Morita Co., Tokyo, Japan). Two model shapes were compared: a 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, with the tooth axis of the maxillary central incisor vertical to the basal plane (condition A); and a height of 20 mm at the cutting edge of the maxillary central incisor and 20 mm at the mesiobuccal cusp of the maxillary first molar, with the occlusal plane parallel to the basal plane (condition B) (Fig. 1). The model was well dried for more than 48 h in an air-conditioned room at a temperature of about 24.0°C. Sheets were molded using a vacuum-forming machine (Ultraformerâ, Ultradent Products Inc., South Jordan, UT, USA) (7, 18, 19). For fabrication, the model of the incisal part was placed at the center of the vacuum unit of the molding device and used EVA sheets with two shapes: the normal sheet (A–N, B–N) or a convexing vshaped groove 10–40 mm from the anterior end (A–V, B–V). The v-shaped groove was created using an ultrasonic disc cutter (Labo Sonic Cutterâ, Nakanishi Inc., Tochigi, Japan) with a width/depth of approximately 5/ 3 mm, making the sheet thickness at the v-shaped groove approximately 1 mm (Fig. 2). The formation was performed by crimping the sheet by applying suction when the most descending portion of the sheet reached 15 mm below the basal surface (8). The descending distance of the sheet was measured with a laser pointer fixed to a three-dimensional coordinate measuring machine (No. 192–201; Mitutoyo Co., Kanagawa, Japan). The sheet was crimped against the model for 2 min and cooled for at least 3 h in an airconditioned room at a temperature of 24.0°C. The sheet was molded after being heated in a molding device, and a radiation thermometer (CT–2000Dâ, Custom Co., Tokyo, Japan) in the vacuum unit confirmed cooling to room temperature. Six samples were produced under each condition. Thickness of the mouthguard sheets after fabrication was measured with a measuring device (21–111; YDM Co., Tokyo, Japan) (8, 9). The spring of the measuring
(B)
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Fig. 2. The shape of the mouthguard sheet. The gray area indicates the area of the sheet mounted on the model. Condition A–N and B–N: Normal sheet. Condition A–V and B–V: The sheet with a convex v-shaped groove 10–40 mm from the anterior end.
device was removed to prevent distortion of the material sheet during measurement. Measurement points for the incisal portion were defined at the following left and right central incisor positions: Five points were spaced equally from the proximal to the distal end of the incisal edge; 10 points were on the labial surface, including five points spaced equally from the cervical to the incisal edge along a line located one-third of the distance from the proximal edge corresponding to the five points along a line located one-third of the distance from the distal edge. Measurement points for the molar portion were defined in the left and right first molars as follows: four points were on the cusp, including the proximal and distal buccal cusps and distal lingual cusps; and 10 points were on the buccal surface, including five points spaced equally from the cervical to the tip of the cusp along a line located one-third of the distance from the proximal end corresponding to the five points along a line located one-third of the distance from the distal end. Measurement was performed once for each sample and used to determine mean thickness. Additionally, the fit of the mouthguard to the working model was observed macroscopically after formation, as recommended in a study by Mizuhashi et al. (20). Statistical analysis was performed in SPSS 17.0 software (SPSS Japan Inc., Tokyo, Japan). Differences in the thickness change of mouthguards molded in response to different conditions of the sheets and models were analyzed using the Shapiro–Wilk test for normality of distribution and Levene’s test for homogeneity of variance. Normality and equality of variance were found for each item. Data were analyzed by two-way analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test. Significance was set at P < 0.05. Results
Figure 3 shows the relationship between the mouthguard sheets and the working model after vacuum formation. The stripe of the sheet with the v-shaped groove was more elongated in the anteroposterior direction at the anterior part of the sheet than that of
the normal sheet. Compared with the model shape, the sheet molded under condition B was more elongated in the lateral direction at the side of the posterior teeth of the model than that under condition A. The fit of the mouthguard to the working model after formation was almost the same when observed macroscopically under either condition. The results of two-way ANOVA followed by Bonferroni’s multiple comparison tests are shown in Fig. 4. Thickness was significantly higher in the sheet with the v-shaped groove than in the normal sheet at all measurement points (P < 0.01). Condition A–V was thicker than A–N by approximately 0.65 mm (37%) at the incisal edge, 0.81 mm (36%) at the labial surface, 0.50 mm (25%) at the cusp, and 0.67 mm (29%) at the buccal surface (P < 0.01). Condition B–V was thicker than B–N by approximately 0.49 mm (31%) at the incisal edge, 1.01 mm (50%) at the labial surface, 0.44 mm (23%) at the cusp, and 0.67 mm (29%) at the buccal surface (P < 0.01). Thickness was significantly less for condition B–N than that for condition A–N by approximately 0.19 mm ( 11%) at the incisal edge and 0.22 mm ( 10%) at the labial surface. Thickness was less for condition B–V than for condition A–V at the incisal edge by 0.35 mm ( 15%) (P < 0.01). Discussion
Appropriate equipment and materials used for producing a mouthguard should be selected to estimate changes in thickness after molding (1, 3, 9, 11, 12, 16, 17). In particular, the shape of the working model affects the thickness at the anterior part of the mouthguard. Therefore, the working model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor and reduced the height as much as possible, which could secure the thickness of mouthguard (6, 9, 10). Many mouthguards are constructed using a plaster model which is made by taking an impression of standard maxillary dental model (8, 19). When the standard maxillary dental model was trimmed like that, the height at the cutting edge of the maxillary central incisor is 20 mm and that at the © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Thickness of mouthguards after vacuum formation (A)
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(B)
Fig. 3. Mouthguard sheet after formation. Condition A–N; Condition A–V; Condition B–N; Condition B–V.
Fig. 4. Comparison of the thickness between conditions at measurement points of the incisal portion (incisal edge and labial surface) and the molar portion (cusp and buccal surface) after formation.
mesiobuccal cusp of the maxillary first molar is 15 mm. Therefore, we investigated the thickness of fabricated mouthguard using like this shape model. When mouthguards are produced in a clinical, there are cases of large undercuts and odontoparallaxis. It is possible to be smoothly press the mouthguard sheet against the model using a model form modified that was performed blocking out in gypsum or compound at such time (6). In addition, the labiolingual tooth axis of the anterior teeth was influenced to the amount of undercut of labial surface on the model, which affects the height of the molar region by trimming the model. Mouthguard after molding becomes thinner as the height of the model is increased, so reduced the height as much as possible is desirable (9). However, labial tipping of the anterior teeth is high, and the height of the model in the anterior parts increases when trimmed © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
to reduce the undercut of these parts, which results in a thinner mouthguard after molding. Therefore, when trimmed to reduce the height of the model to some extent, the undercut remains on the labial side of the model and the model base surface is nearly parallel to the occlusal plane in many cases. Various methods have been devised to maintain the thickness of mouthguard at the anterior part (6, 19). We have previously studied the shape of the sheet as a production method that can ensure thickness of the anterior mouthguard without affecting adaptation when using the grooved sheet (18). As a result, by applying a groove convex to the model in the anterior direction, it is possible to suppress the reduction in the thickness that occurs during heat softening and pressure forming. In the present study, we investigated which items can be adjusted to alter the shape of a
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working model when using a mouthguard sheet with vshaped grooves. The result of this study, the thickness at the anterior part after formation under condition B–N was less than that under condition A–N, but there was no difference at the posterior part. The thickness change might be effect of model form; the small width in antero at the anterior part of the sheet was elongated in anteroposterior direction, and the large width at the posterior part of the sheet was less likely to affect the thickness (8). On the other hand, when using the sheet with the v-shaped grooved, the thickness at the incisal edge after formation under condition B–V was thinner than that under condition A–V, but there was no difference at the other part. There was likely the same when using the normal sheet, which showed that a reduction in the incisal edge thickness is likely to occur. Differences in thickness by the model shape is less, that is why the part of the groove was extended toward to model during vacuum forming; therefore, that could be reduced the stretch at the labial surface. In a previous study, we reported that the thickness of the groove was reduced by stretching due to its own weight during heat softening of the sheet, and further stretching of the surrounding parts was suppressed in the portion of the groove extending significantly in the model direction during vacuum forming (18). This study suggested when using the model with an undercut on the side of the labial surface, that could be able to secure the thickness of the mouthguard by using the sheet with grooved at the same level as when using a model was not remained undercut. The present findings indicate that when molding mouthguards, thickness changes can be suppressed using a sheet with a convex groove. In particular, it was suggested that the method for fabricating mouthguards was useful in the case of using a working model with a remaining undercut on the labial surface. In the present study, almost the same findings were observed macroscopically after formation under each condition. Therefore, further studies are needed to investigate the influence of fit due to different sheets or model conditions (17, 21). Conclusions
The present results suggested that thickness after vacuum formation was secured by the use of the sheet with v-shaped grooves, especially the model with an undercut on the side of the labial surface may be clinically useful. References 1. Bemelmanns P, Pfeiffer P. Shock absorption capacities of mouthguards in different types and thicknesses. Int J Sports Med 2001;22:149–53.
2. Westerman B, Stringfellow PM, Eccleston JA. EVA mouthguards–how thick should they be ? Dent Traumatol 2002; 18:24–7. 3. Geary JL, Kinirons MJ. Post thermoforming dimensional changes of ethylene vinyl acetate used in custom-made mouthguards for trauma prevention–a pilot study. Dent Traumatol 2008;24:350–5. 4. Maeda M, Takeda T, Nakajima K, Shibusawa M, Kurokawa K, Shimada A et al. In search of necessary mouthguard thickness–Part 1: from the view point of shock absorption ability. Nihon Hotetsu Shika Gakkai Zasshi 2008;52:211–9. 5. O’Malley M, Evans DS, Hewson A, Owens J. Mouthguard use and dental injury in sport – a questionnaire study of national school children in the west of Ireland. J Ir Dent Assoc 2012;58:205–11. 6. Takeuchi M, Togaya N. Effectively of thermoforming process for fabricating of intraoral apparatus. Tokyo, Japan: Sunashobo; 2006. 24–6, 52–9, 67 p. (in Japanese). 7. Ranalli DN. Prevention of craniofacial injuries in football. Dent Clin North Am 1991;35:627–45. 8. Takahashi F, Koji T, Morita O. Study on mouthguard material – thickness, relationship between the elongation and the thickness of mouthguard sheet after vacuum forming process. J Sports Dent 2004;7:12–7. 9. Takahashi F, Takahashi M, Koji T, Morita O. Study on the elongation and thickness of mouthguard sheets after vacuum forming process – the influence of the height of the working model. J Sports Dent 2008;11:64–70. 10. Takahashi M, Koide K, Mizuhashi F. Study on the thickness of mouththguard sheet after vacuum forming process –influence of the shape of the working model. J Sports Dent 2011;14:47–52. (in Japanese). 11. Westerman B, Stringfellow PM, Eccleston JA. Forces transmitted through EVA mouthguard materials of different types and thickness. Aust Dent J 1995;40:389–91. 12. Park JB, Shaull KL, Overton B, Donly KJ. Improving mouth guards. J Prosthet Dent 1994;72:373–80. 13. Dorney B, Dreve V, Richer T. Signature mouthguards. Phillip J 1994;9:311–9. 14. Padilla R, Dorney B, Baylor S. Prevention of oral injuries. J Calif Dent Assoc 1996;24:30–6. 15. Padilla RR, Lee TK. Pressure laminated athletic mouth guards–a step-by-step process. J Calif Dent Assoc 1999;27:200–9. 16. Del Rossi G, Leyte-Vidal MA. Fabricating a better mouthguard–Part I: factors influencing mouthguard thinning. Dent Traumatol 2007;23:149–54. 17. Del Rossi G, Lisman P, Signorile J. Fabricating a better mouthguard–Part II: the effect of color on adaptation and fit. Dent Traumatol 2008;24:197–200. 18. Takahashi M, Kiode K, Mizuhashi F. Difference in the thickness of mouthguards fabricated from ethylene-vinyl acetate co-polymer sheets with differently arranged v-shaped grooves. J Prosthodont Res 2013;57:169–78. 19. Mizuhashi F, Koide K, Takahashi M, Mizuhashi R. A method to maintain the thickness of the mouthguard after the vacuum forming process–changes of the holding conditions of the mouthguard sheet. Dent Traumatol 2012;28:291–5. 20. Mizuhashi F, Koide K, Takahashi M. Thickness and fit of mouthguards according to a vacuum-forming process. Dent Traumatol 2013;29:307–12. 21. Yonehata Y, Maeda Y, Machi H, Sakaguchi RL. The influence of working cast residual moisture and temperature on the fit of vacuum-forming athletic mouth guards. J Prosthet Dent 2003;89:23–7.
© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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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 Mutsumi Takahashi, Kaoru Koide, Fumi Mizuhashi Department of Removable Prosthodontics, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan
Key words: mouthguard; thickness; sheet material shape; working model shape; ethylene vinyl acetate sheet Correspondence to: Mutsumi Takahashi, 1-8, Hamaura-cho, Chuo-ku, Niigata City, Niigata, 951-8580, Japan Tel.: +81 25 267 1500 Fax: +81 25 265 5846 e-mail: [email protected] Accepted 17 April, 2014
Abstract – The aim of this study was to evaluate the change in thickness of a working model mouthguard sheet due to different shape. Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0 mm thick) using a vacuum-forming machine. Two shapes of the sheet were compared: normal sheet or v-shaped groove 10–40 mm from the anterior end. Additionally, two shapes of the working model were compared; the basal plane was vertical to the tooth axis of the maxillary central incisor (condition A), and the occlusal plane was parallel to the basal plane (condition B). Sheets were heated until they sagged 15 mm below the clamp. Postmolding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). Differences in the change in thickness due to the shape of the sheets and model were analyzed using two-way ANOVA followed by a Bonferroni’s multiple comparison tests. The thickness of the mouthguard sheet with v-shaped grooves was more than that of the normal sheet at all measuring points under condition A and condition B (P < 0.01). The thickness of condition B was less than that of condition A, there the incisal portion in the normal sheet and the incisal edge in the sheet with v-shaped grooves (P < 0.01). The present results suggested that thickness after molding was secured by the use of the sheet with v-shaped grooves. In particular, the model with the undercut on the labial surface may be clinically useful.
Use of mouthguard is effective in reducing trauma and prevention of maxillofacial area during sports (1–5). The common mouthguard material is ethylene vinyl acetate resin (EVA), which is broadly divided into olefin- and styrene-based thermoplastic elastomers. EVA has many applications owing to its low softening temperature and affordable price, and the many color variations of EVA also contribute to its popularity (6). In general, custom-made mouthguards are produced mainly by soft welding a thermoplastic elastomer sheet over a working model in a molding device. The procedure is relatively handiness but reduced material thickness after molding (7, 8). The shape of the working model affected the thickness of the mouthguard after molding. The working model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor and reduced the height as much as possible, which was useful for ensuring the thickness of fabricated mouthguards (6, 9, 10). However, the trimming 472
form may be subject to restrictions depending on the inclination of the occlusal plane and the row of teeth. An EVA sheet should be 3–4 mm thick at the incisal and molar portions to sufficiently reduce the force of any impact (1–4, 11). However, the reduction in mouthguard thickness that occurs along the incisal edges and the labial surface is extensive, so the challenge is how well the thickness reduction in this region can be prevented. It is difficult to attain such thickness using the conventional-forming method with a single layer of sheet material (12). On the other hand, the laminated-type mouthguard can secure necessary thickness such as anterior part and occlusal surface without being affected by the dentition or occlusion (13–15). Thus, that has many advantages so as to recommend it as the best option. Although, it is difficult to convince all players to use the laminated-type mouthguard for reasons such as cost, time, or time spent to deliver the © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Thickness of mouthguards after vacuum formation mouthguard. For this reason, the fabrication of the single-layer mouthguard in ordinary equipment does not affect the thickness reduction and fit as possible, and it would be clinical useful. The thickness of fabricated mouthguard affected as a results of various factors, the shape of a working model, sheet color, and the molding device (1, 3, 9, 11, 12, 16, 17). Especially, the shape of a working model is a factor in reducing the thickness of the mouthguard that with an undercut on the side of the labial surface and the height is higher (9, 10). We have previously studied the shape of the sheet as a production method that can ensure thickness of the anterior mouthguard without affecting adaptation when using the grooved sheet (18). As a result, by applying a groove convex to the model in the anterior direction, it is possible to suppress the reduction in the thickness that occurs during heat softening and pressure forming. The aim of this study was to investigate the thickness of fabricated mouthguard what extent was possible to decrease the thickness reduction when using a model with an undercut on the side of the labial surface and mouthguard sheet with v-shaped grooves. Materials and methods
EVA sheets (Sports Mouthguardâ, 127 mm 9 127 mm 9 4.0 mm, clear; Keystone Dental Inc., Cherry Hill, NJ, USA) were used. Cross-stripes (10 9 10 mm) were painted on each sheet, and these were used as observation of the shape deformation after thermoforming. The working model was made by taking an impression of a maxillary dental model (D16FE–500A– QF; Nissin Dental Products Inc., Kyoto, Japan) using a silicone rubber impression paste (Correcsilâ, Yamahachi Dental Mfg., Co., Aichi, Japan). Hard gypsum (New Plastoneâ, GC Co., Tokyo, Japan) was then poured onto the impression, and the model was removed from the impression 60 min later. The working model was trimmed using a wet-type model trim-
(A)
Fig. 1. The shape of the working model. Condition A: The model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor; the height at the cutting edge of the maxillary central incisor is 20 mm and that at the mesiobuccal cusp of the maxillary first molar is 15 mm. Condition B: The model was trimmed, so the occlusal plane was parallel to the basal plane; the height at the cutting edge of the maxillary central incisor was 20 mm and that at the mesiobuccal cusp of the maxillary first molar was 20 mm. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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mer (Model trimmer MT–6â; Morita Co., Tokyo, Japan). Two model shapes were compared: a 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, with the tooth axis of the maxillary central incisor vertical to the basal plane (condition A); and a height of 20 mm at the cutting edge of the maxillary central incisor and 20 mm at the mesiobuccal cusp of the maxillary first molar, with the occlusal plane parallel to the basal plane (condition B) (Fig. 1). The model was well dried for more than 48 h in an air-conditioned room at a temperature of about 24.0°C. Sheets were molded using a vacuum-forming machine (Ultraformerâ, Ultradent Products Inc., South Jordan, UT, USA) (7, 18, 19). For fabrication, the model of the incisal part was placed at the center of the vacuum unit of the molding device and used EVA sheets with two shapes: the normal sheet (A–N, B–N) or a convexing vshaped groove 10–40 mm from the anterior end (A–V, B–V). The v-shaped groove was created using an ultrasonic disc cutter (Labo Sonic Cutterâ, Nakanishi Inc., Tochigi, Japan) with a width/depth of approximately 5/ 3 mm, making the sheet thickness at the v-shaped groove approximately 1 mm (Fig. 2). The formation was performed by crimping the sheet by applying suction when the most descending portion of the sheet reached 15 mm below the basal surface (8). The descending distance of the sheet was measured with a laser pointer fixed to a three-dimensional coordinate measuring machine (No. 192–201; Mitutoyo Co., Kanagawa, Japan). The sheet was crimped against the model for 2 min and cooled for at least 3 h in an airconditioned room at a temperature of 24.0°C. The sheet was molded after being heated in a molding device, and a radiation thermometer (CT–2000Dâ, Custom Co., Tokyo, Japan) in the vacuum unit confirmed cooling to room temperature. Six samples were produced under each condition. Thickness of the mouthguard sheets after fabrication was measured with a measuring device (21–111; YDM Co., Tokyo, Japan) (8, 9). The spring of the measuring
(B)
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Fig. 2. The shape of the mouthguard sheet. The gray area indicates the area of the sheet mounted on the model. Condition A–N and B–N: Normal sheet. Condition A–V and B–V: The sheet with a convex v-shaped groove 10–40 mm from the anterior end.
device was removed to prevent distortion of the material sheet during measurement. Measurement points for the incisal portion were defined at the following left and right central incisor positions: Five points were spaced equally from the proximal to the distal end of the incisal edge; 10 points were on the labial surface, including five points spaced equally from the cervical to the incisal edge along a line located one-third of the distance from the proximal edge corresponding to the five points along a line located one-third of the distance from the distal edge. Measurement points for the molar portion were defined in the left and right first molars as follows: four points were on the cusp, including the proximal and distal buccal cusps and distal lingual cusps; and 10 points were on the buccal surface, including five points spaced equally from the cervical to the tip of the cusp along a line located one-third of the distance from the proximal end corresponding to the five points along a line located one-third of the distance from the distal end. Measurement was performed once for each sample and used to determine mean thickness. Additionally, the fit of the mouthguard to the working model was observed macroscopically after formation, as recommended in a study by Mizuhashi et al. (20). Statistical analysis was performed in SPSS 17.0 software (SPSS Japan Inc., Tokyo, Japan). Differences in the thickness change of mouthguards molded in response to different conditions of the sheets and models were analyzed using the Shapiro–Wilk test for normality of distribution and Levene’s test for homogeneity of variance. Normality and equality of variance were found for each item. Data were analyzed by two-way analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test. Significance was set at P < 0.05. Results
Figure 3 shows the relationship between the mouthguard sheets and the working model after vacuum formation. The stripe of the sheet with the v-shaped groove was more elongated in the anteroposterior direction at the anterior part of the sheet than that of
the normal sheet. Compared with the model shape, the sheet molded under condition B was more elongated in the lateral direction at the side of the posterior teeth of the model than that under condition A. The fit of the mouthguard to the working model after formation was almost the same when observed macroscopically under either condition. The results of two-way ANOVA followed by Bonferroni’s multiple comparison tests are shown in Fig. 4. Thickness was significantly higher in the sheet with the v-shaped groove than in the normal sheet at all measurement points (P < 0.01). Condition A–V was thicker than A–N by approximately 0.65 mm (37%) at the incisal edge, 0.81 mm (36%) at the labial surface, 0.50 mm (25%) at the cusp, and 0.67 mm (29%) at the buccal surface (P < 0.01). Condition B–V was thicker than B–N by approximately 0.49 mm (31%) at the incisal edge, 1.01 mm (50%) at the labial surface, 0.44 mm (23%) at the cusp, and 0.67 mm (29%) at the buccal surface (P < 0.01). Thickness was significantly less for condition B–N than that for condition A–N by approximately 0.19 mm ( 11%) at the incisal edge and 0.22 mm ( 10%) at the labial surface. Thickness was less for condition B–V than for condition A–V at the incisal edge by 0.35 mm ( 15%) (P < 0.01). Discussion
Appropriate equipment and materials used for producing a mouthguard should be selected to estimate changes in thickness after molding (1, 3, 9, 11, 12, 16, 17). In particular, the shape of the working model affects the thickness at the anterior part of the mouthguard. Therefore, the working model was trimmed, so the basal plane was vertical to the tooth axis of the maxillary central incisor and reduced the height as much as possible, which could secure the thickness of mouthguard (6, 9, 10). Many mouthguards are constructed using a plaster model which is made by taking an impression of standard maxillary dental model (8, 19). When the standard maxillary dental model was trimmed like that, the height at the cutting edge of the maxillary central incisor is 20 mm and that at the © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Thickness of mouthguards after vacuum formation (A)
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Fig. 3. Mouthguard sheet after formation. Condition A–N; Condition A–V; Condition B–N; Condition B–V.
Fig. 4. Comparison of the thickness between conditions at measurement points of the incisal portion (incisal edge and labial surface) and the molar portion (cusp and buccal surface) after formation.
mesiobuccal cusp of the maxillary first molar is 15 mm. Therefore, we investigated the thickness of fabricated mouthguard using like this shape model. When mouthguards are produced in a clinical, there are cases of large undercuts and odontoparallaxis. It is possible to be smoothly press the mouthguard sheet against the model using a model form modified that was performed blocking out in gypsum or compound at such time (6). In addition, the labiolingual tooth axis of the anterior teeth was influenced to the amount of undercut of labial surface on the model, which affects the height of the molar region by trimming the model. Mouthguard after molding becomes thinner as the height of the model is increased, so reduced the height as much as possible is desirable (9). However, labial tipping of the anterior teeth is high, and the height of the model in the anterior parts increases when trimmed © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
to reduce the undercut of these parts, which results in a thinner mouthguard after molding. Therefore, when trimmed to reduce the height of the model to some extent, the undercut remains on the labial side of the model and the model base surface is nearly parallel to the occlusal plane in many cases. Various methods have been devised to maintain the thickness of mouthguard at the anterior part (6, 19). We have previously studied the shape of the sheet as a production method that can ensure thickness of the anterior mouthguard without affecting adaptation when using the grooved sheet (18). As a result, by applying a groove convex to the model in the anterior direction, it is possible to suppress the reduction in the thickness that occurs during heat softening and pressure forming. In the present study, we investigated which items can be adjusted to alter the shape of a
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working model when using a mouthguard sheet with vshaped grooves. The result of this study, the thickness at the anterior part after formation under condition B–N was less than that under condition A–N, but there was no difference at the posterior part. The thickness change might be effect of model form; the small width in antero at the anterior part of the sheet was elongated in anteroposterior direction, and the large width at the posterior part of the sheet was less likely to affect the thickness (8). On the other hand, when using the sheet with the v-shaped grooved, the thickness at the incisal edge after formation under condition B–V was thinner than that under condition A–V, but there was no difference at the other part. There was likely the same when using the normal sheet, which showed that a reduction in the incisal edge thickness is likely to occur. Differences in thickness by the model shape is less, that is why the part of the groove was extended toward to model during vacuum forming; therefore, that could be reduced the stretch at the labial surface. In a previous study, we reported that the thickness of the groove was reduced by stretching due to its own weight during heat softening of the sheet, and further stretching of the surrounding parts was suppressed in the portion of the groove extending significantly in the model direction during vacuum forming (18). This study suggested when using the model with an undercut on the side of the labial surface, that could be able to secure the thickness of the mouthguard by using the sheet with grooved at the same level as when using a model was not remained undercut. The present findings indicate that when molding mouthguards, thickness changes can be suppressed using a sheet with a convex groove. In particular, it was suggested that the method for fabricating mouthguards was useful in the case of using a working model with a remaining undercut on the labial surface. In the present study, almost the same findings were observed macroscopically after formation under each condition. Therefore, further studies are needed to investigate the influence of fit due to different sheets or model conditions (17, 21). Conclusions
The present results suggested that thickness after vacuum formation was secured by the use of the sheet with v-shaped grooves, especially the model with an undercut on the side of the labial surface may be clinically useful. References 1. Bemelmanns P, Pfeiffer P. Shock absorption capacities of mouthguards in different types and thicknesses. Int J Sports Med 2001;22:149–53.
2. Westerman B, Stringfellow PM, Eccleston JA. EVA mouthguards–how thick should they be ? Dent Traumatol 2002; 18:24–7. 3. Geary JL, Kinirons MJ. Post thermoforming dimensional changes of ethylene vinyl acetate used in custom-made mouthguards for trauma prevention–a pilot study. Dent Traumatol 2008;24:350–5. 4. Maeda M, Takeda T, Nakajima K, Shibusawa M, Kurokawa K, Shimada A et al. In search of necessary mouthguard thickness–Part 1: from the view point of shock absorption ability. Nihon Hotetsu Shika Gakkai Zasshi 2008;52:211–9. 5. O’Malley M, Evans DS, Hewson A, Owens J. Mouthguard use and dental injury in sport – a questionnaire study of national school children in the west of Ireland. J Ir Dent Assoc 2012;58:205–11. 6. Takeuchi M, Togaya N. Effectively of thermoforming process for fabricating of intraoral apparatus. Tokyo, Japan: Sunashobo; 2006. 24–6, 52–9, 67 p. (in Japanese). 7. Ranalli DN. Prevention of craniofacial injuries in football. Dent Clin North Am 1991;35:627–45. 8. Takahashi F, Koji T, Morita O. Study on mouthguard material – thickness, relationship between the elongation and the thickness of mouthguard sheet after vacuum forming process. J Sports Dent 2004;7:12–7. 9. Takahashi F, Takahashi M, Koji T, Morita O. Study on the elongation and thickness of mouthguard sheets after vacuum forming process – the influence of the height of the working model. J Sports Dent 2008;11:64–70. 10. Takahashi M, Koide K, Mizuhashi F. Study on the thickness of mouththguard sheet after vacuum forming process –influence of the shape of the working model. J Sports Dent 2011;14:47–52. (in Japanese). 11. Westerman B, Stringfellow PM, Eccleston JA. Forces transmitted through EVA mouthguard materials of different types and thickness. Aust Dent J 1995;40:389–91. 12. Park JB, Shaull KL, Overton B, Donly KJ. Improving mouth guards. J Prosthet Dent 1994;72:373–80. 13. Dorney B, Dreve V, Richer T. Signature mouthguards. Phillip J 1994;9:311–9. 14. Padilla R, Dorney B, Baylor S. Prevention of oral injuries. J Calif Dent Assoc 1996;24:30–6. 15. Padilla RR, Lee TK. Pressure laminated athletic mouth guards–a step-by-step process. J Calif Dent Assoc 1999;27:200–9. 16. Del Rossi G, Leyte-Vidal MA. Fabricating a better mouthguard–Part I: factors influencing mouthguard thinning. Dent Traumatol 2007;23:149–54. 17. Del Rossi G, Lisman P, Signorile J. Fabricating a better mouthguard–Part II: the effect of color on adaptation and fit. Dent Traumatol 2008;24:197–200. 18. Takahashi M, Kiode K, Mizuhashi F. Difference in the thickness of mouthguards fabricated from ethylene-vinyl acetate co-polymer sheets with differently arranged v-shaped grooves. J Prosthodont Res 2013;57:169–78. 19. Mizuhashi F, Koide K, Takahashi M, Mizuhashi R. A method to maintain the thickness of the mouthguard after the vacuum forming process–changes of the holding conditions of the mouthguard sheet. Dent Traumatol 2012;28:291–5. 20. Mizuhashi F, Koide K, Takahashi M. Thickness and fit of mouthguards according to a vacuum-forming process. Dent Traumatol 2013;29:307–12. 21. Yonehata Y, Maeda Y, Machi H, Sakaguchi RL. The influence of working cast residual moisture and temperature on the fit of vacuum-forming athletic mouth guards. J Prosthet Dent 2003;89:23–7.
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