Theses and dissertations (Health Sciences)
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Item An evaluation of the colours of base metal alloy oxide layers, and its effects on the shade of base metal alloy metal-ceramic restorations(1997) Somers, Grant Brandon; Waddell, J. N.Globally, difficulties are being experienced by the dental world to match manufactured prosthetic restorations with natural tooth colour. The primary objective of this study was therefore to evaluate the colour of five different metalceramic base metal alloy oxide layers, and the effects of each oxide layer on the shade of the porcelain applied to its surface. The increase in the cost of gold alloys in the dental industry has influenced manufacturers to provide alloys which are cost effective and have adequate mechanical properties for the manufacture of metal ceramic restorations. Five base metal alloys used in the fabrication of metal-ceramic restorations were selected. The selection of the base metal alloys was based on popularity in the industry, availability and cost. The following five base metal alloys were selected for the investigation: Wiron 99 (nickel-chrome) Ceradium V (nickel-chrome-beryllium) Remanium CD (nickel-chrome) \x95 Wirobond (cobalt-chrome) Heranium (nickel-chrome) Bond-on-4 (low noble content alloy {control group; which was gilded}) II Thirty specimens for each alloy group (180 in all) were cast, using the lost wax technique. Three ceramic layers (notably the opaque, dentine and a glaze layer) were applied to the 20mm in diameter surface of each specimen. .\xB7t Finally both sample groups were tested against a custom shade guide the colour being compared specifically with the Vita A 1 shade. The reason for the inclusion of the shade guide was that, clinically, most shade selections are made by comparing the patient's tooth shade with a manufactured shade guide. A wide selection of shades are available to the ceramist. A certain school of thought that recommends that the metal surfaces of semi-precious metals be gilded with a gold gilding paste before the application of ceramics. in order to block out the dark oxide colour and enhance the colour of the ceramic to a more aesthetic and warmer colour. Therefore, prior to the opaque firing of the control group (Bond-on-4), a gilding layer of Spectra Seal Paste was applied to the surface of each specimen. Following each application of ceramic, the appropriate firing cycles were used to fire the ceramic. The following factors affected the selection of the shade of ceramic used in this study: the shade which is most influenced by the dark oxide layer the more popular shades of ceramic ( the A class of shades). It was established, through a review of the literature (Crispen, 1991), that the most objective form of testing colour at the time of the study, was the use of a reflectance spectrophotometer. This form of testing had been proved to be cost effective and was consequently used in this investigation. III Thesurve