الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
Aim of the Study:The aim of the present study was to compare the marginal integrity of occlusal veneers made from hybrid ceramic (Cerasmart) and zirconia reinforced lithium disilicate (Vita Suprinity ) under thermal cycling and cyclic loading. Materials and Methods: A standardized tooth preparation was applied to 34 human first maxillary molars using CNC machine with anatomical occlusal surface preparation with 1 mm ferrule and 1 mm deep chamfer finish line. All teeth were restored with occlusal veneers with 1.8 thickness at the cusp tip and 1.2 mm at the central groove ( CEREC AC CAD /CAM system) . Hybrid ceramic (Cerasmart) and zirconia reinforced lithium disilicate (Vita Suprinity ) were used to mill the restorations (n=17). The intaglio surfaces were HF-etched and silanated (Vita Suprinity) or airborne-particle abraded and silanated (Cersasmart). All restorations were adhesively luted with self adhesive resin cement (Rely X Unicem). All specimens were subjected to thermal cycling and cyclic loading for 25000 cycles simulate 2 months. A weight of 5Kg which is comparable to 50 N of chewing force was exerted with thermal aging between 5˚ C and 55˚ C. The marginal gap distance of the specimen was photographed using USB Digital microscope with a built-in camera connected with an IBM compatible personal computer using a fixed magnification of 45X. Shots of the margins were taken for each specimen. Then morphometric measurements were done for each shot [4 equidistant landmarks along the cervical circumference for each surface of the specimen (Mesial, buccal, distal, and lingual). Measurement at each point was repeated five times. Then the data obtained were collected, tabulated and then subjected to statistical analysis
Results:
The marginal gap mean ±SD values recorded for Vita-Suprinity group were (58.42±10.15 μm) with minimum value (46.12 μm) and maximum value (78.11 μm). Meanwhile the marginal gap mean ±SD values recorded for Cerasmart group were (44.71±9.12 μm) with minimum value (28.71 μm) and maximum value (54.73 μm).It was found that Vita-Suprinity group recorded statistically significant higher marginal gap mean value (58.42±10.15 μm) than Cerasmart group (44.71±9.12 μm) as indicated by unpaired t-test (P=0.0084< 0.05).
Conclusions
1. Hybrid ceramic restoration (Cerasmart) provided superior marginal accuracy than Zirconia reinforced lithium silicate (Vitasuprinity) restoration.
2. All occlusal veneers constructed from both tested materials (Cerasmart and Vitasuprinity ) proved to have a clinically acceptable marginal gap distances.