Reduction in base metal alloy thickness will permit additional porcelain depth and improved aesthetics but unfortunately little information exists regarding the thickness to which base metal alloys may be reduced in comparison to noble metal alloys for metal ceramic restorations. Even with comparison of noble metal alloys the aesthetic benefits are restricted to improving aesthetics in base metal restoration further, since noble metal alloys are generally regarded as providing superior aesthetics to base metal restorative alloys. Purpose: The objective of this study was to determine whether a significant reduction in thickness could be achieved using a base metal alloy as compared to a noble metal alloy and the thickness to which base metal alloy substructures could safely be reduced while still providing the same resistance to fracture of the porcelain. Material and methods: Tensile strength tests (N) of the modulus of rupture of the porcelain were performed on 40 base metal alloy (Wiron 99, Bego, Germany) and 12 noble metal alloy rectangular specimens (5.8 mm wide and 15.0 mm long) bonded to a standardized 1.0 mm thickness of dentine Creation porcelain. The base metal alloy thickness varied in 0.1mm increments from 0.1 to 0.4 mm. The results were compared to 12 noble metal alloy (Bio Y 81, Argen, South Africa) specimens of recommended minimum thickness (0.3 mm). Data for the results was obtained using a universal tensile testing instrument, which was set to operate at a cross head speed of 0.5mm (Instron Mini 44, Instron corporation U.S.A). The applied force (N) that measured the modulus of rupture of each specimen was printed from a computer connected to the Instron Mini 44 that operated on a 95% level of confidence. Instron Agents (Durban, South Africa) performed the calibration and setting up of the machine prior to testing the specimens. Results: The results indicated a permissible 33.33% reduction in the base metal alloy specimens as compared to the noble metal alloy control specimens. This was deduced from the reduction in alloy thickness of up to 0.2 mm for base metal alloy specimens as compared to the 0.3 mm noble metal alloy specimens. The recommended thickness to which the base metal alloys could be reduced without distortion of the alloy was also 0.2 mm. The one-way ANOVA showed a level of significance of (α=05).
Marginal Adaptation of Metal Ceramic Crowns Cast from Four Different Base Metal Alloys before and after Porcelain Application
