Shape change in mouthguard sheets during thermoforming

Abstract

The results showed that shape changes of the sheet during thermoforming tend to concentrically and almost uniformly expand from the center and that it is important to center the sheet and the model when positioning the model in the forming unit.

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

“…It is necessary to know how each forming method affects the thickness and how the thickness will change after forming. The shape change that occurs during the first stage has been investigated (12) and the following was reported: (i) There was almost no change in the clamp regions; (ii) the shape change in the non-clamped areas increased by 5-10%; and (iii) the shape change tended to increase slightly more in the central portion than at the sheet periphery, and that noticeable changes did not occur in the center (the difference was only about 5%). During the molding of mouthguards, thickness reduction occurs in the heat-softening and formation stages.…”

“…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 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).…”

The Effect of Process Parameters on Thickness Distribution in Thermoforming

“…So, forming temperature, type of plastic (amorphous or crystalline), shape of mold (positive or negative), air pressure (positive or negative), shape, type and number of heaters play a critical role throughout the process [4,5,7,8]. One of the leading factors that affects the product quality is plug assist.…”