الفهرس 
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Abstract
The current study evaluated the effect of ultrasonic finishing on marginal accuracy, internal fit and microleakage of empress e-max crowns fabricated by two methods.
In this study, the teeth were divided into two groups according to the type of finish line as the following:
Group (c): 20 upper central incisors with a deep chamfer finish line, of a 1mm width.
Group (s): 20 upper central incisors with a shoulder finish line, of a 1mm width.
Each group was divided according to the type of finishing tool into two subgroups:
Subgroup (C I): Ten upper central incisors possessing a deep chamfer finish line were finished using low speed conventional finishing stones.
Subgroup (C II): Ten upper central incisors possessing a deep chamfer finish line. The prepared teeth were finished all around using Satelec Perfect Margin chamfer (PM) ultrasonic Kit.
Subgroup (S I): Ten upper central incisors possessing a shoulder finish line were finished using low speed conventional finishing stones.
Subgroup (S II): ten upper central incisors possessing a shoulder finish line were finished all around for each side using a Satelec Perfect Margin Shoulder (PMS) ultrasonic Kit.
The surface roughness was measured at the area of the finish lines of all prepared teeth surfaces to obtain a quantitative comparison of the two finishing protocols by using Stereo microscope.
Electron microscopic scanning was done for evaluation of the morphologic and microstructural changes after finishing.
Forty crowns were constructed using Empress e-max ceramic material using two techniques;
A) CAD/ CAM technique.
B) Heat pressing technique.
The crowns were classified according to manufacture techniques in to two groups:
Group (M); manufactured with CAD/ CAM technique.
Group (H); manufactured with Heat pressing technique.
Then the forty crowns were placed on their corresponding teeth and held on its place by jig for marginal discrepancy determination before cementation using stereomicroscope.
A measurement of the internal distance before cementation gap was done by using silicon replica technique. Then measurements of microleakage and internal distance were done after cementation by using stereomicroscope.
The results of surface roughness test showed that, the conventional finishing method demonstrated significantly higher roughness values for both finish line preparations (chamfer &shoulder). And the shoulder finish line showed a non-significant increased roughness values in both finishing methods (conventional & ultrasonic).
Results of the vertical marginal accuracy testing before cementation showed that, there was no statistical significant difference between the three groups. The highest mean of vertical gap distance was 71.04 µ for the CAD/CAM crowns with shoulder finish line and finished with conventional stones (GP S I M); while the lowest mean surface roughness value was 46.37 µ for the heat pressed crowns with chamfer finish line and finished with ultrasonic stones (GP C II H).
Results of the vertical marginal accuracy testing after cementation showed that, there was no statistical significant difference between the three groups. The highest mean of internal gap distance was 82.3871 µ for the CAD/CAM crowns with shoulder finish line and finished with conventional stones (GP S I M); while the lowest mean surface roughness value was 49.2380 µ for the heat pressed crowns with chamfer finish line and finished with ultrasonic stones (GP C II H).
Results of internal gap distance before cementation showed there was a statistical significant difference between the three groups. The highest mean internal gap distance was 114.96 µ for the conventionally finished shoulder preparations restored with heat CAD/ CAM crowns (GP SIM), while the lowest mean internal gap distance was 62.38 µ for the conventionally finished chamfer preparations restored with heat pressed crowns (GP CIH).
Results of internal gap distance after cementation showed that; there was a statistical significant difference between the three groups. The highest mean of internal gap distance was 180.3µ for the conventionally finished heat pressed crowns with shoulder finish line (GP S I H), while the lowest mean internal gap distance was 88.79 µ for the ultrasonically finished heat pressed crowns with shoulder finish line (GP S II H).
Results of microleakage showed that; Ultrasonic method showed lower values of microleakage score. There was a statistical significant difference between conventional and ultrasonic finishing regarding microleakage score. Chamfer finish line showed lower values of microleakage score. There was statistically significant difference between chamfer and shoulder finish line regarding microleakage score. There was no statistical significant difference between CAD/CAM and heat pressed techniques regarding microleakage.