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The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Side-effects from dental materials are a minor problem, but should be recognized. In recent questionnaire surveys about side-effects, the incidence was estimated to be 1:300 in periodontics and 1:2600 in pedodontics. None of these reactions was related to dental casting alloys. In prosthodontics, the incidence was calculated to be about 1:400, and about 27% were related to base-metal alloys for removable partial dentures (cobalt, chromium, nickel) and to noble/gold-based alloys for porcelain-fused-to-metal restorations. The complaints consisted of intra-oral reactions (such as redness, swelling, and pain of the oral mucosa and lips), oral/gingival lichenoid reactions, and a few instances of systemic reactions. In orthodontics, the incidence was 1:100, and most reactions (85%) were related to metal parts of the extra-oral anchorage devices. Even though the extensive use of base-metal alloys has been of major concern to the dental profession, relatively few case reports substantiate this concern. Allergy to gold-based dental restorations has been more commonly reported. Palladium-based alloys have been associated with several cases of stomatitis and oral lichenoid reactions. Palladium allergy seems to occur mainly in patients who are very sensitive to nickel. All casting alloys, except titanium, seem to have a potential for eliciting adverse reactions in individual hypersensitive patients. Tolerance induction may be a possible benefit of the use of intra-orally placed alloys. In non-sensitized individuals, oral antigenic contacts to nickel and chromium may induce tolerance rather than sensitization. A variety of systemic diseases and reactions has been claimed to be caused by dental materials. The claims are generally poorly documented.

The cytotoxic potentials of three Ni-Cr based alloys and an Fe-Cr based alloy were assessed. In tissue culture, casting of all four test materials and powders of the Fe-Cr based material did not elicit adverse cellular changes. However, cultures containing Ni-Cr powders showed prominent zones of lysis and cell alteration. The cytotoxic potential of products obtained from the surfaces of casting alloys may offer an expedient means for estimation of long-term clinical toxicity.