Methods: Sixty standardized Y-TZP copings were manufactured with a CAD/CAM system. Out of these, twenty each were 0.4 and 0.5 mm thick, machined from fully sintered Y-TZP blocks. The remaining were 0.5 mm thick machined from partially sintered Y-TZP blocks and subsequently sintered. Ten copings from each group were cemented to epoxy resin glass laminate preparations using zinc phosphate cement (Healthcare products, UK) and the rest were cemented using a resin based luting agent (Kuraray Corp, Japan). After 24 hours, the samples were loaded to failure with a wrought carbon steel indenter of 4 mm diameter in the centre of the restoration in a universal testing machine (Instron 1193, USA) using a crosshead speed of 1mm min-1.
Results: The load to failure for each sample was recorded and Weibull plots were compiled. 90% confidence intervals show that there is a significant difference in the load to failure values for copings machined from pre sintered and fully sintered blocks, for both types of cement used. 0.4 and 0.5 mm thick copings machined in the hard state and bonded with resin showed highest characteristic strengths and Weibull moduli.
Conclusions: Weibull plots indicated good correlation of fit for all groups. Within the limitations of this study it can be concluded that the characteristic strengths of the copings are significantly affected by the machining strategy and thickness as well as the type of luting cement.(Supported by studentship from Renishaw plc, UK.)