a device for treating plastic parts for use in dental and orthodontic applications includes a pressure receptacle which has walls which define a hollow interior with an opening which is closable by a cover or lid . a support for material to be treated is placed within the hollow interior at a spaced location in the interior walls and adjacent a heating device which is advantageously an electric heating element . the device includes a rotatable fan which is advantageously mounted on the vessel as a shaft which extends through the vessel interior and carries a rotatable fan which is rotated so as to direct a gas such as air past objects held on a support and past the heater which maintains the circulating gases at a temperature which permits polymerization of the parts . the heating air is continuously circulated and it is heated by the heater sufficiently to maintain a selected polymerization temperature .