Determination of gold alloy loss during the production of cast dental restorations.

Values for the loss of high gold content dental alloy during the fabrication of three types of cast dental restorations were determined. The mass changes measured were for the melting, casting and cleaning processes and the docking and laboratory finishing procedures involved in producing the final restoration. The casting yield from the alloy cast was also determined. Five Brisbane dental laboratories participated and 407 cast restorations were assessed. The mean mass loss for the melting and casting process was 0.109 g (SD 0.326) per cast restoration, and 0.827 per cent (SD 1.805) of the total mass of alloy melted. The data were analysed in four categories: alloy crowns, metal-ceramic crowns, metal-ceramic bridges, and combined. The mean total mass loss per restoration from docking and finishing for each of the four groups of cast dental restorations examined was 0.329 g, 0.350 g, 0.927 g and 0.363 g; 13.11, 28.30, 22.07 and 22.18 as a per cent of the mass of the docked casting respectively. The yield of casting masses from the alloy cast were 19.97, 9.11, 29.10 and 13.71 per cent respectively, with all differences significant at the 0.001 level. These values indicate that the recommendation for 50 per cent addition of new alloy for each cast is impractical. The wide spread of the data precludes the establishment of a precise agreed value between dentists and technicians for expected loss. However, the use of the median or mean would provide a value which might be an equitable indicator in the long term. Alternatively, working values can be developed for individual dentist/technician partnerships.