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

The aim of this study was to evaluate the effect of different ph beverages on the surface hardness and fracture toughness of Vita Enamic and Lava Ultimate. Disc shaped specimens 2mm thickness were cut by an isomet, finished and polished according to the manufacturer{u2019}s instructions. The samples were stored in coca , coffee and artificial saliva as a control for 24 days where the solutions were changed every 12 hours. 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. It was found that Vita enamic group recorded statistically significant (P<0.05) higher hardness mean value than Lava Ultimate group.It was concluded that non-aged group recorded statistically significant (P<0.05) higher hardness mean value than aged group. where the fracture toughness was calculated by the indentation method through this equation KIC = 0.016(E/H) 0.5(P/c1.5). The data was obtained and the results were tabulated. We concluded that regarding the fracture toughness: it was found that non-aged group recorded statistically significant (P<0.05) higher fracture toughness mean value than aged group .It was found that Vita enamic group recorded statistically significant (P<0.05) higher fracture toughness mean value than Lava Ultimate group as indicated by two way ANOVA followed by pair-wise Tukey{u2019}s post-hoc tests .It was concluded that the ageing media statistically decreased the hardness of the Vita Enamic samples but it did not affect its fracture toughness. However the ageing media did not affect both the hardness and the fracture toughness of Lava Ultima

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