Fracture toughness and hardness of vita suprinity CAD/CAM with and without cyclic loading and thermocycling : An in vitro study / Noura Mokhtar Nasr Sheded Alsedawy ; Supervised Samir Ziden , Ashraf Taher

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

The aim of this study is to evaluate the fracture toughness and hardness of Vita Suprinity with and without cyclic loading and thermocycling (An in-vitro study) -24 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. -All specimens were stored in distilled water at 37oC for 24 hours in sealed containers in incubator. -Half of the specimens were exposed to thermal cycling with number of cycles was 500 cycle (46) , Dwell times were 25 s. in each water bath with a lag time 10 s. and The low-temperature point was 5 0C). The high temperature point was 55 0C. (46-47) and also were exposed to cyclic loading in chewing simulator machine in which Twelve specimens of experimental ceramic group were exposed to the mouth-motion fatigue at load of 50 N for 20,000 cycles with a frequency of 1.6 Hz -The other half was left with its glazed surface without any aging procedure thermocycling and cyclic loading. -Surface hardness and fracture toughness were measured before and after storage where the surface hardness was measured through Vicker{u2018}s indentation: three indentations were made in each sample and the mean was calculated for each using this equation. HV=1.854 P/d Fracture toughness was calculated by the indentation method through this equation. KIC = 0.016(E/H)-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 {u2015}c,{u2016} increases with an elevating indentation load and is an inverse function of fracture toughness. The data was obtained and the results were tabulated

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