Patent GB-696063-A (GB)
Title: Artificial teeth, and method and apparatus for forming the same
IPC: B29C45/16
Filed: 1950-02-13
Abstract: 696,063. Moulding artificial teeth. DENTISTS' SUPPLY. CO. OF NEW YORK. Feb. 13, 1950 [Feb. 23, 1949], No. 3671/50. Class 87 (ii). A synthetic resin tooth which has been made by moulding, e.g. by injection as described in Specification 666,968, is subjected to a second moulding operation. The tooth is placed in a mould cavity and there subjected to heat and pressure whilst other synthetic resin is urged by pressure from a reservoir through a transfer passage towards the cavity, the heat being sufficient to soften the tooth and the other synthetic resin. The tooth is then cooled under pressure. By.this means any elastic memory the tooth may have, e.g. as a result of having been made by injectionmoulding, is eliminated, and if the mould cavity is smaller than the cavity in which the tooth was originally moulded, the tooth is derisified. The invention is described in connection with the second moulding of a cluster of posterior teeth 90, Fig. 5, which have been injection-moulded by the method described in Specification 666,968 and have body portions 26, Fig. 4, and enamel portions 30. The cluster shown has been removed from the'initial mould together with the runners 44, 46. The mould, Fig. 11, comprises two parts 72, 74 having mating mould cavities 92 therein of the same shape but slightly smaller than the teeth 90. Each mould cavity communicates by means of a passage 94 with a reservoir 96 formed in the upper face of the mould part 74. Within the reservoir fits a plunger 76. In operation, first the reservoir is charged with material, e.g. acrylic, of the same composition and colour as the tooth body parts 26; this is done either by placing the plunger 76 having a resin preform 101 attached thereto as at 102 in the reservoir or by filling granulated powder into the reservoir. The empty mould parts 72, 74, with the plunger lying on the resin in the reservoir, is placed between the platens 62, 64, Fig. 7, of a heating press, where the mould and resin are heated to, say, 330‹F. for polymethyl methacrylate. The mould is then removed from the press and opened, and two cold tooth clusters are placed in the mould. One of these clusters is shown in Fig. 11. The runners 44 fit into recesses 98, 100 in the mould parts. The mould with the teeth therein is then put back into the heating press. As the hot mould closes, the runners 46 are softened and sealing surfaces 92 surrounding the cavities sever the runners from the teeth. When the mould has closed completely, the press is opened, the mould removed and a pressure plate 78 is placed on the plunger. The mould is put back into the press (Fig. 9) and pressure is applied to the resin in the reservoir and thence to the teeth, the teeth being thus pressed at about 1000 pounds per sq. inch and at 330‹F. Some flow of resin may take place from the reservoir to the mould cavities. The mould is then removed and placed between the platens of a cooling press Fig. 10 (not shown) where the teeth are cooled more quickly than the resin in the reservoir, under a pressure of, say, 1100-2300 pounds/sq. inch so that resin may flow into the cavities as the teeth shrink during cooling. The mould is then removed from the cooling press, the pressure plate 78 is removed, two studs 80, 82 are screwed into holes 108, 110 in the plunger, and the mould is placed in a device, Fig. 12, for extracting the plunger from the mould. This device comprises a stationary plate 114 on which the mould is hung by means of the studs 80, 82, and a pinion-and-rack-operated pressure head having two projections 120 which engage the mould and force it off the plunger, the resin breaking within the passages 94 and the plunger, with resin keyed to it, being left suspended on plate 114. Anterior teeth may be moulded Figs. 1, 3, 6 (not shown). The teeth may be of thermoplastic or thermosetting resin or a mixture of the two. Specification 254,075, [Group 87 (ii)], also is referred to.