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

Statement of the problem: It was reported that bleaching for patients with discolored teeth adjacent to tooth colored restorations may lead to alterations in surface texture and topography, so our objective was measuring the efficacy of 10% and 20% carbamide peroxide OPF bleaching agents on fracture toughness of hybrid ceramic restorations (In-vitro study). Purpose: The aim of this study was to assess the efficacy of at home bleaching (10% and 20% carbamide peroxide OPF) with two frequencies of application at 2 months interval on fracture toughness of Hybrid ceramic restorations. Materials and methods: A total of 84 vita enamic discs were be sectioned under water irrigation applications with a precision cutting machine IsoMet 1000 into discs with dimensions 3mm thickness and 11 mm diameter as measured by digimatic micrometer. All samples (84 samples) will be divided into to two main test groups according to carbamide peroxide concentrations Group A): (42samples) bleaching with 10% carbamide peroxide- opalescence PF and Group B): (42 samples) bleaching with carbamide peroxide 20%-opalescence PF and 3 subgroups according to times of exposure for bleaching agent for each main group, subgroup I: artificial saliva, subgroup II: after first exposure to bleaching agents and subgroup III: after second exposure to bleaching. The application of bleaching agents 8 hours per day for 14 days for first exposure while control groups immersed in artificial saliva, after 14 days samples of subgroups II for two main groups (A,B) prepared for fracture toughness test ,while subgroups III for each main group (A,B) were immersed in artificial saliva for 2 months, after that exposed for bleaching agents for 14 days and prepared for fracture toughness tests.fracture toughness was measured before bleaching exposure as base line and after exposure for bleaching and saliva storage

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