PURPOSE: To simplify an operation and to shorten time for manufacturing the title seal by heating and softening the title seal material with polyester acetic propionic cellulose as its substantial component, creating a model from the obtained seal, and shifting the model to an engagement seal as a personal tray.

CONSTITUTION: The seal material is polyester acetic propionic cellulose, and a fine particle having an approximately 150μ dimension is obtained by freezing and finely grinding the material. A heater 18 is a device in which heating plates 19a and 19b respectively having conductive heating members in them are opposed to each other and opened or closed with a hinge 21 as the center of the opening and closing action, and the heater 18 can rise the temperature of itself up to its maximum temperature 105°C so that the heater 18 can immediately heat the seal material up to 72-82°C. In order to select a tray 20, measurement is executed using a divider, etc., the necessary amount of seal material 27 is placed in the heater 18, the heating plates 19a and 19b are closed, and the seal material 27 is dried and heated. The seal material composed of the fine particles is melted and unified by the heating. The unified seal material is positioned in the tray 20. Since the seal material is not hardened yet even after the positioning of the seal material ends, the above-mentioned process is shifted to the next process. The tray is inserted into an oral cavity and press-welded to a prescribed position.