Effect of sheet extrusion direction on laminated mouthguard thickness: An in vitro study

The thermal shrinkage that occurs when the extrusion molding sheet is heated affects the mouthguard thickness. The aim of this study was to investigate the effect of sheet extrusion direction on laminated mouthguard thickness.

Mouthguards were pressure formed using the extruded sheet and a plaster model. For the first layer, a 3.0-mm-thick sheet was used. For the second layer, a 2.0- or 3.0-mm-thick sheet was used. In each of the first (F) and second (S) layers, the sheet extrusion direction was either vertical (V; FV, SV) or parallel (P; FP, SP) to the model midline. Thickness differences depending on the extrusion direction of the first layer was analyzed by Student's t-test. Differences in the laminated mouthguard thickness depending on the extrusion direction of the first or second layer and the sheet thickness of the second layer were analyzed by three-way ANOVA.

The first layer was significantly thicker in FV by about 0.20 mm than in FP at the incisal edge, labial surface, and cusp (p < .01). No significant difference was observed between SV and SP in the laminated mouthguard. However, at the incisal edge, labial surface, and cusp of the laminated mouthguard, FV were significantly thicker by 0.17 mm or more than FP under all laminating conditions (p < .01). A 3.0-mm-thick laminating condition was thicker than a 2.0-mm-thick laminating condition by 0.47 mm or more at the incisal edge, labial, and buccal surfaces, and by 0.34 mm or more at the cusp.

The laminated mouthguard thickness can be secured by molding the first-layer sheet so that the extrusion direction is vertical to the model midline. In the second layer, the extrusion direction did not affect the laminated mouthguard thickness, and a thicker sheet material should be used.