A Study on the Pressing of Thermoplastic Hard Resin for Oral Appliance: Part 1

Appropriate Temperature on the Surface of the Sheet

Abstract

Purpose: The most appropriate way to form the thermoplastic hard resin made of the PET for oral appliance (PRT-sheet) has not been established yet. This study aimed to determine the most suitable temperature to form a PET-sheet to obtain optimal fit.
Method: PET-sheet (125×125×1.5 mm) was heated at each 10°C increment between 120°C and 160°C on the plaster model (M-Model) and given pressure immediately thereafter until the sheet temperature became 50°C. The trial temperature depended on the static load examination (load: 400 gf). Plaster was poured into the mold (sheet taken off), and that which hardened was taken out (W-Model). Images of M-Model and W-Model were obtained by flatbed scanner, and superimposed. The distance between the formed PET-sheet and the plaster model was evaluated for the fit using image analytic software.
Results: In the outside-center group (O-C) and outside-edge group (O-E), the gap became shorter with higher softening temperature, whereas in the inside-center group (I-C), the gap became longer. The gap was not different in the inside-edge group (I-E). There was no difference between C-E and O-C. However, the gap in the edge was significantly longer than that in the center (p<0.05).
Conclusion: The most suitable temperature to form PET-sheets for obtaining maximum fit is in the range 130–150°C with consideration of their ductility with heat.