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

Statement of problem: endodontically treated premolars usually present an inadequate remaining coronal structure as a result of cavity preparation and present a higher risk for biomechanical failure than vital teeth. Purpose: the purpose of this in vitro study was to compare the fracture resistance of endodontically treated teeth restored with lithium disilicate crowns retained by glass fiber posts and lithium disilicate endocrowns with two margin designs (butt joint & ferrule design). Materials and Methods: twenty seven, non-carious, human maxillary premolars freshly extracted for orthodontic reasons were endodontically treated. They were randomly assigned into 3 groups (n=9), in which teeth were standardizing prepared using CNC milling machine to receive all-ceramic restorations. Group A: Glass fiber post and resin core and conventional crown with (1 mm wide deep chamfer and 2 mm axial wall heights) ferrule. Group B: Endocrown with butt joint design (without ferrule). Group C: Endocrown with (1 mm wide deep chamfer and 2 mm axial wall heights) ferrule. All crowns and endocrowns restorations were fabricated from lithium disilicate ceramic material (IPS E-max press, Ivoclar-Vivadent),in this study CAD CAM wax was used to produce same thickness of all restorations .The ceramic restorations were made according to manufactures instructions and adhesively cemented (Ultimate Clicker 3M ESPE). Specimens were mounted in a universal testing machine (Model 3345; Instron Industrial Products, Norwood, MA, USA). Each specimen was loaded to failure at a cross head speed of 1.0 mm / min. Mode of failure was also examined. Data were analyzed using one way ANOVA followed by pairwise Tukey{u2019}s post-hoc tests were performed to detect significance between groups. The level of significance was set at 5% for all statistical analyses

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