Alternatives to high noble dental casting gold alloys type 3. An in vitro in vivo study

For economic reasons a large number of cheaper alternatives to the high noble dental casting gold alloys have been introduced on the market. The main problem with these alternative alloys is their chemical stability. This is a most important property as degradation of an alloy may release substances which can be harmful to the wearer. Thus, the corrosion behavior of four dissimilar alternative dental casting alloys together with a high-gold reference alloy was evaluated in the as-cast, hardened, and annealed conditions by means of potentiodynamic polarization analysis, partly supplemented by electron spectroscopy for chemical analysis. In order to facilitate interpretation of the results of the corrosion study, the composition and metallographic structure of specimens in the specimens in the dissimilar conditions had to be determined. The methods used were light microscopy, electron probe microanalysis, and X-ray diffractometry. Biocompatibility, which is related to the release of metal ions, was evaluated by subcutaneous implantation of specimens from the five alloys in guinea-pigs. Thus, the in vivo toxicity of the different alloys could be assessed. The chemical stability of an alloy also determines its tarnish resistance and as tarnish apart from creating esthetic problems, also may result in changes in the wetting characteristics of the alloy surface the in vivo tarnish of as-cast and annealed specimens inserted into complete mandibular dentures was estimated after up to 16 weeks. Castability, an important factor in an alloy's clinical performance, was measured as the marginal sharpness of cast simulated crowns from the five alloys. Finally, the clinical performance of crowns and bridges made from one low-gold and one silver-palladium alloy as experimental materials together with a high-gold alloy as a reference material was evaluated using specific periodontal parameters, a tarnish index, and CDA's guidelines for the assessment of clinical quality. The findings may be summarized as follows: The metallographic evaluation for the low-gold alloys Midas and Rajah indicated that these alloys may contain more than one phase. The two silver-palladium alloys Albacast and Alba V were heterogeneous in the three conditions studied. In most cases, the pre-treatment of the alloys had a decisive influence on their proneness to corrosion. The castability of the silver-palladium alloys was inferior to that of the gold-based alloys. The biocompatibility as revealed by subcutaneous implantation showed that one of the silver-palladium alloys (Albacast) produced the least tissue response, while the other one (Alba V) exhibided the worst tissue response.(ABSTRACT TRUNCATED AT 400 WORDS)