Thesis (Ph.D.) - Cairo University - Faculty of Oral and Dental Medicine - Department of Prosthodontics

Statement of problem: Successful restoration of large molar defects is a serious clinical problem. Studies on the strength of teeth restored with ceramic restorations of various designs have provided conflicting results. And Long-term clinical data on the survival of pressed lithium disilicate glass ceramic when used with partial coverage restorations and the effect that different technical and clinical variables have on survival are sparse. Aim: The aim of this study is to evaluate the clinical functional performance of ceramic onlay restorations with butt joint preparation design and compare them to shoulder preparation design Methodology: Thirty eight onlay ceramic restorations were fabricated for posterior teeth. Scaling and polishing were performed for all the patients two weeks before preparation. The patients were divided into two groups according to the preparation designs.Group1:( shoulder design) and Group2 :( butt joint design)Wax pattern (cad/cam wax pattern cad on) was used for the try in stage using Cad/Cam (DWX-50) machine with software (Exocad) and monolithic lithium disilicate (IPS ,E.max press) was used for the final restorations. .The try-in and the final restorations were performed using heat pressing technique.The restoration surfaces were treated using hydrofluoric acid etchting and saline coupling agent) and the cementation was done by using duel cure -adhesive resin cement (I fix due resin cement). Fracture, marginal adaptation and patient satisfaction were assessed immediately after cementation using the modified United States Public Health Service for restoration clinical assessments (MUSPHS standards). These measurements were repeated after one, three, six, nine, and twelve months respectively

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