الفهرس 
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Abstract
This in vitro study aimed to compare between the fracture resistance of one-piece and two-piece post-core-crown restorations using two different materials; hybrid ceramic and zirconia.
A total of twenty artificial human maxillary canines with clear anatomic root and pulp space were selected for the study. All the specimens were embedded in an auto polymerizing acrylic resin using a split mold. The crowns of the canines were cut off 2 mm coronal to the cervical line. The remaining coronal tooth structure was prepared with a 6° taper creating a 1mm. deep chamfer finish line.
ISO standardized #1,2,3, and 4 peso drills were used for preparing the post space. The drills were used in sequence from size#1 to #4, leaving unprepared 5mm. in the canal’s apical portion creating a standard post space of 12 mm. length from the coronal surface.
The twenty teeth were randomly divided into two main groups (n=10) according to the type of restoration as follows:
group I: Ten CAD/CAM fabricated one-piece post-crown.
group II: Ten CAD/CAM fabricated two-piece: post-core and separate crown.
Each group was further subdivided into two subgroups (n = 5) according to the material used, hybrid ceramic or zirconia, as follows:
• Subgroup IA: Five CAD/CAM fabricated one-piece hybrid ceramic restorations.
• Subgroup IB: Five CAD/CAM fabricated one-piece zirconia restorations.
• Subgroup IIA: Five CAD/CAM fabricated two-piece hybrid ceramic restorations.
• Subgroup IIB: Five CAD/CAM fabricated two-piece zirconia restorations.
Polyvinyl siloxane impression material was used to make impression of the prepared teeth. The impression was then scanned using an extra-oral scanner to fabricate the restorations using CAD/CAM technology. The finished restorations were luted to their respective teeth using dual-cure resin cement.
Artificial aging of the specimens was done using thermocycling and load cycling machines. Specimens were then subjected to fracture resistance test using the universal testing machine.
All statistical results were recorded, tabulated, and analyzed.