Patent GB-549473-A (GB)
Title: Improvements in the preparation of dental bridge prothesis
IPC: A61C13/263
Filed: 1941-08-27
Abstract: 549,473. Artificial teeth. KARLSTROM, K. A. S. Aug. 27, 1941. Nos. 10955 and 10956. Convention dates, Sept. 28, 1940 and July 17, 1941. [Class 81 (ii)] In the preparation of working models for use in making bridgework which is secured to vital teeth by means of parallel pins united into the tooth crown, the pins are secured in correct mutual positions prior to taking an impression by uniting the pins at their projecting ends and casting an impression mass around the tooth and the united pins; the pins may be united while in the mouth or outside the mouth. As shown in Figs. 1 and 2 the tooth 1 is provided with recesses 3, 4, 5 and parallel holes for the reception of three pins 6, 7, 8 and after the pins have been inserted in the holes they are joined together at their free ends by transverse braces 9, 10, flattened heads on the pins being apertured to receive the braces which are secured together by a piece of wax 16 or other binding substance and wax or the like is then applied to the heads of the pins. The pins may be screwed or joined together in any other convenient manner. The tooth or teeth to be included in the bridge are then covered with a layer of soft wax of a thickness of 4-5 mm. and a spoon 17 containing a heated plastic mass 18 is pressed against the teeth, the spoon with the layer of wax about the teeth being removed when the mass 18 has cooled and solidified; the wax is then removed and the free space 19 filled with a heated viscose impression made of an elastic nature and the spoon reintroduced into the mouth and the mass 19 brought into close contact with the teeth into which the holding pins have been inserted, these pins being effectively anchored in the mass 19 in their correct mutual positions when the spoon is removed from the mouth. A working model of plaster is then made from the impression mass. If the pins are to be fixed together outside the mouth, the tooth is oiled, the pins are loosely inserted therein, an impression mass is pressed against the tooth and when cool and hard is removed with the pins; the pins are then oiled and inserted into a mass of molten alloy having a low melting point in a container and after the alloy has solidified the pins are removed, freed from the impression mass and reinserted in the holes in the alloy mass and secured together for insertion in the tooth when the impression is to be taken. The pins may be fixed together outside the mouth by using the devices shown in Figs. 5 and 6; after the holes, e.g., two have been bored in the tooth, a pin 30 carried by a slide 26 in a nut 29 screwing on a rod 24, is adjusted relatively to a fixed pin 31 at the end of the rod so that the two pins can be inserted in the holes in the tooth. A similar slide 33 carrying a pin holder 36 is adjusted on the screwed rod 32 relatively to a fixed holder 38 so that the pins 30, 31 can be inserted in the holes 37, 39, two loose pins being then inserted in the holes and fixed together for subsequent insertion in the tooth. When it is desired to have one or more separate teeth of the model detachable, the cavity in the impression mass 19 corresponding to the detachable tooth is first filled with paste and before the plaster sets, a headed pin 46, Fig. 8, of rectangular cross-section is inserted therein and a plate 47, sliding on the shank of the pin and with its underface oiled, is pressed against the upper side of the plaster mass 44 to produce an even upper surface thereon and after the mass has solidified the plate is removed leaving the pin embedded in the mass and the tooth can be removed from the model by the aid of the pin 46 and reinserted when required, a triangular recess, formed in the tooth by a projection 49 on the plate 47, ensuring the tooth being inserted correctly.