Effect of investment on casting high-fusing alloys.

A definite interaction in castability was found between the three different phosphate-bonded investments and four different alloys tested in this study. 1. Casting completeness of all alloys, as measured by the length of test specimens, was affected by the investment. The high-gold content alloy, SMG II, yielded the most complete castings of all combinations teted when invested with Ceramigold. Of the nonprecious alloys, Biobond CB combined with Ceramigold II resulted in the longest samples. 2. The surface quality of Jelbon and SMG II castings was good, regardless of the investment used. Wiron S and Biobond CB varied in surface quality with different investments, Ceramigold II giving the smoothest castings. 3. All alloys, especially the nonprecious ones, should be tested for compatability with different investments before asserting their qualities or lack of qualities for clinical use.

Simplified denture repair technique.

The use of a cyanoacrylate adhesive to accurately and easily assemble the fractured segments of a denture is advocated. The repair can then be accomplished quickly without the need to pour a stone cast so that the patient does not remain without the prosthesis for extended periods. In addition, dentures once deemed unrepairable by conventional methods because they were broken into many pieces can now be salvaged.

An improved technique for the retention of polycarbonate crowns.

The following conclusions may be drawn from this study: Composite resins do not bond to polycarbonate crowns. A technique for priming the internal surfaces of polycarbonate crowns is indicated, in order to create such a bond. Priming the polycarbonate crown with methyl methacrylate monomer alone produces a bond with composite resins. Priming the polycarbonate crown with a syrup of methyl methacrylate monomer and (poly) methyl methacrylate powder appears to produce a stronger bond with composite resins than the monomer alone.

Evaluation of alternative alloys to type III gold for use in fixed prosthodontics.

A study was done to evaluate the fit of castings made from commercially available alloys promoted by their manufacturers as cheaper alternatives to type III gold for use in fixed prosthodontics. Two nickel-chromium alloys, two silver-palladium alloys, two gold-silver-palladium alloys, a 50% gold alloy, and a type III conventional gold alloy (used as a basis of comparison) were evaluated. After optimum conditions for waxing, investing, and casting were determined experimentally, four crowns (two full crowns and two three quarter crowns) were cast from each alloy. The castings were cleaned by pickling or sandblasting and placed on their respective dies. Only one casting was made from each die. Ten judges were asked to evaluate the marginal fit and completeness of each casting on its die. The judges rated each casting and the ratings were converted into rankings. Type III gold and Forticast tied and were ranked first; Paliney CB was ranked second; Alborium and Albacast tied and ranked third; Aurolite CB was ranked fourth; and Jelenko Experimental and Howmedica III tied and ranked fifth. It was found that the nickel-chromium alloys produced castings that had a tight fit and showed marginal discrepancies even under conditions designed to yield maximum expansion of the investment. These nonprecious metal castings were judged inferior in terms of fit when compared with castings made from noble metal-and precious metal-containing alloys. Existing investments and techniques were adequate for all castings except those made from the nonprecious alloys. It was concluded that low (approximately lambda 50%) gold alloys and palladium-silver-gold alloys that are commerically available can be used as substitutes for type III gold alloy without any loss inthe quality of casting fit.