Method for effectively maintaining the thickness of mouthguards fabricated using EVA sheets and a circle tray: influence of grooved sheet and heating conditions.
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.
Effect of Model Height and Model Position on Forming Table on Mouthguard Thickness in Thermoforming Using Circular Frame
Effectiveness and safety of mouthguards are greatly affected by its thickness. The aim of this study was to clarify the effect of model height and model position on the forming table on the mouthguard thickness in thermoforming using a circular frame. Mouthguards were thermoformed using 4.0-mm-thick ethylene-vinyl-acetate sheets and a vacuum forming machine. The sheet was sandwiched between circular frames and fixed to the clamp of the forming machine. Working models were two types of hard gypsum models trimmed so that the height of the anterior part was 25 mm (Model A) and 30 mm (Model B). The model was placed with its anterior rim positioned 40 mm (P40), 30 mm (P30), 20 mm (P20), or 10 mm (P10) from the front of the forming table. Differences in the reduction rate of the thickness due to the model height and model positions were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Differences depending on the model height were observed at P40 at the incisal edge and P30, P20, and P10 on the labial surface, and the reduction rate of the thickness was significantly smaller in Model A (P < 0.01). As the distance from the model anterior rim to the front of the forming table was smaller, the rate of the thickness of the incisal edge and the labial surface decreases became larger. The rate of decrease in the thickness of the cusp and buccal surface was the smallest at P20. This study indicated that the difference in the thickness of the single-layer mouthguard depending on the model position on the forming table is affected by the model height. However, that is only the anterior part of the mouthguard, and the difference in thickness reduction rate is less than 5%. Additionally, in order to perform stable forming, it is useful to increase the distance from the model to the frame, and it is important to position the part whose thickness is desired to be maintained in the center of the forming table.
Mouthguard retention: is design or accuracy of fit more critical?
AIM
To examine the influence of the accuracy of fit on mouthguard retention in relation to mouthguard outline location.


MATERIALS AND METHODS
Mouthguards were fabricated on a fully dentate maxillary cast with 4-mm thick ethylene vinyl acetate sheets using a well-dried cast (VD) and on a wet cast (VW) with a vacuum-forming machine. Mouthguards were also made with a pressure-forming machine (P). The mouthguard outline was set at 4 mm from the cervical margin (control, C), the palatal outline was set at the cervical margin (Pa), and the buccal outline was extended to the buccal fold (Bu). A dislodging force perpendicular to the occlusal plane was applied at the first molar on the universal testing machine. Results were analyzed using ANOVA with Scheffe's test (P < .05).


RESULTS
Using the VW, the retentive forces were statistically smaller at Pa compared to Ca or Bu (C: 58 +/- 17 gf, Pa: 36 +/- 7 gf , Bu: 50+/-8 gf) (P < .05). There were no statistical differences between VD (C: 116+/-27 gf, Pa: 86+/-15 gf, Bu: 92+/-7 gf) and group P (C: 133+/-31 gf, Pa: 139+/-24 gf, Bu: 136+/-17 gf).


CONCLUSIONS
The results indicate that mouthguard retention is closely related to the accuracy of fit at the cervical undercut area rather than the outline location.