GB426744A - Improvements in or relating to dentures and denture blanks and to processes of making the same - Google Patents

Abstract

<PICT:0426744/IV/1> Dentures or denture blanks are made from a composition comprising an artificial polymeric resin containing a vinyl halide, e.g. vinyl chloride, and a vinyl ester of an aliphatic acid, e.g. vinyl acetate, propionate or butyrate, the vinyl halide being present in the composition in the proportion of about 75--95 per cent. The resin may be obtained by the conjoint polymerization of the vinyl halide and the vinyl ester of the aliphatic acid, the polymerization preferably being effected at a temperature of below 60 DEG C. or below 40 DEG C. in the presence of a catalyst such as dibenzoyl peroxide and in the presence or absence of solvents or liquid media. After the conjoint polymerization, the resin may be purified by partially precipitating it from the solution and removing the impurities by a partial solvent, e.g. toluene, xylene or solvent mixture such as acetone-water or isopropanol-acetone, making a solution of the so treated precipitate, filtering the solution to remove insoluble impurities, and thereafter precipitating the vinyl resin from the filtered solution and drying the precipitated resin. The resin may be further purified by extraction. According to one example, vinyl acetate and vinyl chloride are polymerized in the presence of acetone and dibenzoyl peroxide. Isopropanol is added to the resulting solution of resin in acetone, a sloppy gel being precipitated. After decantation, the gel was re-dissolved in acetone and again precipitated, the precipitation and re-solution being repeated five times. The final solution in acetone was filtered in the presence of filter aids such as silica &c., and precipitated, the resulting resin being washed with water and dried. In a second example, the solution of resin in acetone obtained by the polymerization step as in the preceding example was treated to steps of partial precipitation and re-solution employing acetone-water and acetone respectively. The resin finally precipitated was washed with isopropanol and extracted with toluene three times. In the first extraction the effect of the presence of residual acetone was compensated by the addition of isopropanol. The resin was finally washed with isopropanol and dissolved in acetone, the solution being filtered and the resin being obtained as described in the last steps of the first example. In the construction of the denture blanks, thickened sections to receive the teeth, and additional thickness wherever pressure is to be applied to the blank in moulding is preferably provided, e.g. as shown in Fig. 4. Stability of the composition to light and heat may be assisted by the addition of calcium stearate, or a mixture of calcium stearate and a wax such as carnauba wax, or hydrated lime. Other additions include modifying agents such as chlorinated diphenyl derivatives, chlorinated naphthalene, ethyl abietate, natural resins, polymerized aldehyde resins and polymeric glycol esters, inert transparent or translucent filling materials such as finely ground silica, and colouring or opacifying materials such as titanium oxide, lithol red, toluidine toner, rhodamine B base, quinoline yellow base and oil reds. Water soluble colouring materials may be used if desired. The dentures may be reinforced by metal insertions. Composites containing the vinyl resins and other denture materials may be formed. Ordinary dentures may be improved by surfacing them with vinyl resin compositions. The portion of porcelain teeth to be embedded in the vinyl resin may be roughened, and in addition, may be coated with a solution of a resin which is thermosetting, which shrinks considerably, and to which the vinyl resin will adhere by partial solubility; examples of such resins are phenol-formaldehyde resins and alkyd resins of the glycerol-phthalic acid type. The Specification as open to inspection under Sect. 91 comprises also the employment of acetyl benzoyl peroxide as a catalyst in the polymerization step. This subject-matter does not appear in the Specification as accepted.