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Theses and dissertations (Health Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/12

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    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
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    The performance of base metal ceramic alloy restorations with reference to variances in thickness in metal and porcelain in order to establish optimal thickness ratios to maxize strength and aesthetic characteristics
    (2000) Le Roux, Andre Rayne; Coertze, Dirk J.; Somers, Grant
    The greatest problem in maximizing strength and aesthetic characteristics of metal ceramic restorations arises when there is a lack of available space to allow sufficient thickness of metal alloy and porcelain. This generally results in the metal alloy being reduced to its minimum to allow adequate porcelain thickness. The minimum thickness to which noble metal alloys can safely be reduced, is generally accepted to be 0.3 mm due to previous clinical time-dependent trial and error. Agreement regarding the minimum thickness to which base metal alloys can safely be reduced is still under dispute possibly because base metal alloys have not had the same duration of clinical exposure. The objectives of the present study were: 1. To determine the influence thickness variations of the base metal alloy would have on strength characteristics of metal ceramic restorations and thereby establishing the minimum thickness to which base metal alloys can safely be reduced. 2. To determine the influence thickness variations of porcelain would have on strength and aesthetic characteristics of metal ceramic restorations and thereby establish the minimum thickness to which the porcelain thickness can safely be reduced. 3. To determine which base metal alloy to porcelain thickness ratios would be most suited in order to maximize strength and aesthetic characteristics in metal ceramic restorations where the amounts of available space for the alloy and porcelain are varied. For objective (1) Tensile strength tests to determine and compare the ability of various alloy thickness to resist porcelain fracture were performed in Newtons. For objective (2) Tensile tests to determine and compare the ability of various porcelain thickness to resist porcelain fracture were performed in Newtons.
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    Perceptions of the professionalization of dental technology
    (2010) Skea, Denise Angela; Bass, Gregory Hylton; Young, Karin
    This study investigates the perceptions of dentists, dental technicians and dental patients with regard to the professionalization of dental technology as it is currently constituted in South Africa. The origin of dental technology worldwide lies in a trade and has historically been performed by craftsmen under the instruction of dentists. In South Africa during the early 1900s dental technology was practised in much the same way but the need for formalization of this field had been recognised. By 1945 dental technology was regulated by the Dental Mechanicians Board, which enabled only registered technicians to practise dental technology within South Africa. This field continues to be practised similarly at present. In order to establish the professional development of dental technology it is necessary to consider this field within a framework of desired professional attributes. This framework is provided by Greenwood (1957), who defines a profession by the following five attributes: systematic theory, professional authority, community sanction, ethical codes and a professional culture. Owing to the varied implementation and regulation of dental technology worldwide, little research into the professionalization of this field has been conducted to date. For the purpose of this study, dentists, dental technicians and dental patients in KwaZulu-Natal were interviewed in semi-structured interviews. The main themes emerging from this study were identified and considered with reference to the framework within which this study has been positioned. This study concludes that dental technology, as it is currently constituted in South Africa is perceived to be a profession by dentists, dental technicians and dental patients. .The term profession, however, is poorly understood by all three sample groups. Despite being considered a profession, dental technology is not considered to encompass all the attributes of a profession. Dental technology is therefore identified as a developing profession that positions this field somewhere along the professionalization continuum between a profession and a business.