GB499959A - Improvements in or relating to method of and means for making porcelain dental articles such as artificial teeth - Google Patents

Abstract

499,959. Moulding porcelain dental articles. MEYER, L. W. (Erdle & Prange, Inc.) May 31, 1937, No. 15116. [A Specification was laid open to inspection under Sect. 91 of the Acts, March 22, 1938.] [Classes 22, 70, and 87 (ii)] [Also in Group VI] Dental articles such as artificial teeth are produced by compacting moistened finely ground porcelain in a mould by prolonged vibration, removing the body from the mould, and then fire-hardening it. The mould is preferably flexible and is prepared by inverting a flask 5 over a tooth pattern 9, pouring the mould material 17 in through openings 8, and allowing it to set. The mould may be made of rubber, plasticized vinyl chloride, glue, gelatine, &c. In the case of glue or gelatine the mould may be lined with colloidal rubber solution either directly or by coating the pattern 9 which is first saturated with coagulating material such as boric acid. The pattern may be prepared from natural teeth by a duplicating machine or by taking an impression in a mixture of ground glass and silica which is fired to form an enlarged pattern. The artificial tooth is formed of ground porcelain, preferably of 200 mesh or finer, and a binder in proportions of two to one. Suitable binders comprise an organic silicate such as tetraethyl silicate, sodium silicate and hydrochloric acid, zinc oxide and phosphoric acid, magnesium oxide and magnesium chloride, zinc chloride and magnesium oxide. Plaster of Paris, 5 per cent of Nepheline Syenite, or <4>/10 per cent of boric acid, moistened with water may also be used. Plain water or water with the addition of clay, dextrin, or sugar is also suitable. The mixture of porcelain and a binder is placed in the mould 27, subjected to vibration, and allowed to set. The mould 27 is flexed to release the tooth 30, as shown in Fig. 5. If a shaded tooth is desired, porcelain of different shades is placed in the mould in batches. The top part of the tooth is ground away to form a ridge lap which fits the gum and this ridge lap may be grooved as at 35, Fig. 8, or may be coated with a mixture of glaze, shellac, and refractory grains, which forms a granular surface on firing. Metal pins may be placed in the mould and thus embedded in the tooth. As shown in Fig. 14, the flexible mould 50 may be confined in a metal container 58 which distorts it so as to alter the dimensions of the mould cavities 53. The moulded tooth, before firing, may be impregnated with paraffin wax or lacquer and may be machined or drilled or may be hollowed out to form a thin shell crown. This shell may afterwards be filled with a strong porcelain to produce a translucent effect.