Patent GB-600314-A (GB)
Title: Improvements in or relating to moulds for reproducing articles such as artificial teeth, tooth patterns and models, and to articles formed in such moulds
IPC: A61C13/08
Filed: 1944-08-21
Abstract: A method of making a mould for reproducing an article such as an artificial tooth, tooth pattern, or model therefor, the reproduction having intensified surface features as compared with the original article, comprises disposing a hot viscous liquid, e.g. plasticized polyvinyl chloride, capable of setting to a resilient solid on cooling around either the original article (if it has an adsorptive surface) or around a model thereof having an adsorptive surface, applying super-atmospheric pressure to said liquid during at least a portion of the setting period thereof, and removing the article or model thereof after the liquid has set to a resilient mass.  In an example, plaster casts of natural teeth are set up in a flask and melted polyvinyl chloride at 150 DEG  C. poured over them.  The flask is immediately put in a pressure chamber and an air pressure of 300 lbs./sq. inch applied for 30 minutes.  The pressure is then gradually released over a period of 90 minutes.  The models are left in the mould for 15 hours and then removed and the mould allowed to stand for 24 hours before using.ALSO:A method of making a mould for reproducing an article such as an artificial tooth, tooth pattern, or model therefor, the reproduction having intensified surface features as compared with the original article, comprises disposing a hot viscous liquid capable of setting to a resilient solid on cooling around either the original article (if it has an adsorptive surface) or around a model thereof having an adsorptive surface, applying super-atmospheric pressure to said liquid during at least a portion of the setting period thereof, and removing the article or model thereof after the liquid has set to a resilient mass.  The liquid may be a molten mass of plasticized polyvinyl chloride, e.g. "Korogel." Reproductions cast in the mould so produced are p  larger than the original or model which was used to make the mould, and have intensified ridges, hollows and cracks.  The mould may be used as a "finish mould," porcelain tooth material being cast therein and then removed and fired, or a plaster reproduction may be cast in the mould and then used to produce other moulds from which porcelain teeth may be made.  When porcelain teeth thus made are fired, the shrinkage and loss of detail caused by firing are compensated for by the previous enlargement and intensification of detail.  The original article (having an adsorptive surface) may be made of plaster of Paris, Portland cement, powdered clay, biscuited dental porcelain, diatomaceous earth, or magnesium, zinc or calcium oxide.  Articles made of glass, vitrified porcelain and metals, and natural teeth are unsuitable.  A non-suitable article may be rendered suitable by providing it with a non-vitreous ceramic surface.  In an example, plaster casts of natural teeth are set up in a flask and melted polyvinal chloride at 150 degrees C. poured over them.  The flask is immediately put in a pressure chamber and an air pressure of 300 lbs/sq. inch applied for 30 minutes.  The pressure is then gradually released over a period of 90 minutes.  The models are left in the mould for 15 hours and then removed and the mould allowed to stand for 24 hours before using.  Plaster casts are then made in the cavities of the mould and are found to be on the average over 8 per cent larger than the original teeth, and with intensified surface detail.  The process may be repeated, using these casts and so on to any degree of enlargement required, and permanent (e.g. metal) moulds may be made at any stage desired. Pneumatic means for applying pressure are described in the Specification, but other means (e.g. mechanical) may be used.