Patent GB-680483-A (GB)
Title: Method and apparatus for forming artificial teeth
IPC: A61C13/00
Filed: 1950-05-11
Abstract: 680,483. Moulding artificial teeth. DENTISTS' SUPPLY CO. OF NEW YORK. May 11, 1950 [July 30, 1950; Sept. 15, 1949] , No. 11784/50. Class 87 (ii). [Also in Group VI] An artificial tooth made from synthetic resin and having body and enamel portions of different visual characteristics is made by moulding the body portion from relatively opaque resin and subsequently moulding the enamel portion on to the body portion, the enamel resin being forced as a viscid liquid from a loading chamber formed in a mould into a mould cavity which is connected with the chamber and contains the body portion. As described, first body portions of teeth are formed in one step (see below) or in three steps (a), (b), (c). In (a), a mould comprising two circular parts 20, 26, is heated between two hot platens in a heating press, Fig. 1, (not shown), to, say, 350‹ F. The mould parts co-operate to form eight mould cavities C, and the part 26 has a loading chamber 31. (b) The mould is removed from the heating press and immediately loaded (while hot) with moulding powder, e.g. methyl methacrylate, which may be shaken or vibrated down through the gates 30 into the mould cavities, Fig. 2, (not shown). (In a modified procedure, the mould is loaded cold with moulding powder and then heated.) (c) The loaded mould, at a temperature of, say, 335‹ F., is placed in a cooling press, Fig. 3, comprising two cooling platens 44, 46, a close-fitting plunger 38 is placed in the chamber 31, and pressure is applied to the plunger by means of piston 40. The resin is thus forced through the gates into the mould cavities, where it is cooled. An enamel portion is then applied to each body portion 36 by (d) removing the mould, with the body portions, from the cooling press and replacing the mould part 20 by two other mould parts 50, 52, Fig. 4. The body portions remain in the mould part 26, and spaces 55 for the reception of the enamel are left between the portions and the mould part 50. (e) The reconstituted mould of Fig. 4 is then inverted, the enamel material in the form of a flowable viscid liquid or gel or dough is placed in a chamber 56 in mould part 50. (f) A plunger 60 is placed in chamber 56 and the whole is placed in a heating press, Fig. 5, where a piston 40' depresses plunger 60 to force the enamel into spaces 55. If the enamel is of thermosetting material, heat is maintained until the material has set. The teeth are allowed to cool in the press or are removed (in the mould) to a cooling press, Fig. 6, (not shown). Modification: (1) To obviate the necessity for accurate measuring of the bodyforming powder, the piston 40 may be of smaller diameter than plunger 38, which may thereby be pushed below its flush position and retained there by a locking device. (2) The body positions may be made in one step by loading the resin powder into a cold mould and applying heat and pressure simultaneously as in Fig. 5. Either the body resin or the enamel resin may be acrylic or a thermosetting cross-linked polymer, or the enamel resin may be a copolymer of an olefinically unsaturated monomer and an unsaturated polyester. Specifications 664,243 and 666,968 are referred to.