Thesis (M.Sc.) - Cairo University - Faculty of Oral and Dental Medicine - Department of Prosthodontics

The aim of this study is to determine the effect of surface finish and the effect of different pH media on the fracture toughness and surface hardness of Vita Suprinity. 76 plates of 3mm thickness were cut by an isomet cutting machine. All the specimens were sintered and then auto-glazed according to manufacturer's instructions. Half of the specimens was finished using a coarse grit diamond stone and then polished using the special polishing kit for Vita Suprinity. The specimens were washed using distilled water in an ultrasonic cleaner. The other half was left with its glazed surface without any surface treatment. The samples were stored in 2% citric acid solution and artificial saliva as a control for 8 hours and 14 days respectively in an incubator at 37oC where the saliva was changed every 2 days. Surface hardness and fracture toughness were measured before and after storage where the surface hardness was measured through Vicker{u2019}s indentation: three indentations were made in each sample and the mean was calculated for each using this equation HV=1.854 P/d2 Fracture toughness was calculated by the indentation method through this equationKIC = 0.016(E/H) 0.5 (P/c1.5). The basis of the indentation technique is a series of cracks that form under heavy loading for a certain duration in a brittle material around a Vickers diamond indenter. When viewed superiorly the cracks appear to emanate from each of the corners of the indentation. The size of these cracks expressed by the surface dimension 2c,3 increases with an elevating indentation load and is an inverse function of fracture toughness. The data was obtained and the results 5were tabulated

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