الفهرس 
Evaluation the fracture resistance and vertical marginal gap of Vita hybrid versus pressable ceramic Onlay restoration in the molar teeth
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Abstract
As the minimally invasive dentistry has become a field of great interest in modern restorative dentistry. Preserving tooth structure is critical for the longevity of teeth and restorations adhesively placed all-ceramic restorations with partial or complete coverage of the occlusal surface represent an alternative to the traditional full- coverage crown, as they provide a more conservative approach in restoring weakened tooth structure. The purpose of this study was to compare hybrid ceramic and pressable ceramic onlay restoration regarding resistance to fracture and vertical marginal discrepancy of both materials following thermal cycling. Twenty four intact comparable human lower first molar were were selected for the present study and centralized and mounted in epoxy resin, In order to standardize the preparation to receive Onlay restoration, the teeth were prepared by computer numerically controlled CNC milling machine. The preparation involved a mesio-occluso-distal cavity with both mesio lingual and disto-lingual cusps covered. All teeth were subjected to same standardized preparation to be copied out of each other. The samples were divided into two main groups [I &II] according to the ceramic material used for construction of Onlay restoration: I. Twelve prepared teeth received Vita Enamic hybrid ceramic Vita enamic hybrid ceramic onlay, fabricated from the blocks milled in a Cerec in-Lab CAD/CAM Machine. II. Twelve prepared teeth received IPS e.max Press ceramic onlay. The waxing up step was fabricated by using machinable CAD/CAM Wax Discs (eg: CAD wax) to have equal and standardized thickness of all samples. This wax was milled by Laserdenta CAD/CAM system then invested, casted, and the ceramic was pressed, divested, and finally glazed. All onlay restorations were finished according to the manufacturer instructions