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

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.

Shape change in mouthguard sheets during thermoforming – part 2: effect of the anteroposterior position of the model on mouthguard thickness

“…The thickness of the mouthguard is affected by the form of the model (10). However, the decrease in thickness is substantial during thermoforming.…”

“…The model was left to dry for over 48 h at about 20.5°C in an air-conditioned room (8)(9)(10)(11)(12)(13)(14)(15)(16). A working model was fabricated using a silicone rubber (Correcsil Ò ; Yamahachi Dental Mfg., Co., Aichi, Japan) impression taken from a maxillary dental model (D16FE-500A-QF; Nissin Dental Products Inc., Kyoto, Japan), into which gypsum (New Plastone Ò ; GC Co., Tokyo, Japan) was poured.…”

“…A laser pointer was fixed to a three-dimensional coordinate measuring machine (192-201; Mitutoyo Co., Kanagawa, Japan) and used to measure the sagging distance (8)(9)(10)(11)(12)(13)(14)(15)(16). A separating medium was applied (at varnish TF; Shofu Inc.) to the model in preparation for pressure molding.…”

“…Thickness reduction during formation is also greatly affected by the shape of the model (7,10). Thickness reduction during heat-softening is largely due to the increase in the sagging distance of the sheet.…”

“…Thickness reduction during heat-softening is largely due to the increase in the sagging distance of the sheet. The shape change during molding in the second stage was caused by the sheet being stretched while applying pressure or a vacuum (7,10,12,13). Previous studies have examined the reduction in sheet thickness that occurs in the first stage (12).…”