الفهرس 
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Abstract
This study was designed to investigate, the fracture resistance and adaptation of Zirconia CAD/CAM versus heat pressed ceramic implant abutments (in vitro).
The increased esthetic demand among patients together with the recent developed of all ceramic systems, encouraged the selection of Zirconia & lithium disilcate press material for our study.
Twenty implant fixtures were inserted in epoxy resin in the mounting blocks, and divided into two main groups according to the type of abutment materials (10 specimen /group):
• ZR Group: zirconia (CAD/CAM) abutment with E.max crown.
• PR Group: E.max press hybrid abutment with E.max crown.
The restorations were fabricated using zirconia and E.max materials and protocols
Restorations were cemented to their corresponding titanium base and engaged to the mounted implant fixture, the lithium disilcate crowns were cemented to abutment in both groups with adhesive cement, then the vertical marginal discrepancies of the samples was measured at the implant / abutment interface, by using a high resolution digital microscope at fixed magnification of 70X.
Afterwards, the specimens were fatigue cycled for 250,000 cycles, and then the marginal discrepancies were re-measured with the same procedures to monitor any difference in the marginal readings before and after cyclic loading. Fractures resistances of the samples were tested using universal testing machine with static load.
The data of vertical marginal discrepancies and fracture resistance were collected, tabulated and statistically analyzed to detect any significant values among the different groups.
The following results were obtained:
The results revealed that the lowest marginal discrepancy mean value (38.2μm) was recorded by ZR-pre cyclic followed by (39.9μm) recorded by PR-pre cyclic group while a higher marginal discrepancy mean value (65.6μm) was recorded by ZR-post cyclic group. And the highest marginal discrepancy in the tested groups was recorded for PR group -post cyclic (71.1μm).
The obtained results showed that group ZR, recorded higher fracture resistance mean value (451.86 N), than those for group PR which recorded a lower fracture resistance mean value (409.34 N), with non-significant difference.
Within the limitations of this study, the following conclusions were drawn:
1. Changing the type of restoration; either pressable lithium disilcate or CAD/CAM zirconia implant abutment had no effect on the fracture resistance.
2. All the tested groups revealed failure load that exceeded the masticatory recorded in the incisors area of the oral cavity.
3. Changing the technique and the material of the ceramic abutment had no effect on the marginal discrepancies, but there was a prominent increase after cyclic loading.
4. The vertical marginal gap mean values of all tested groups obtained in this study were within the clinically acceptable level.