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Abstract
Many studies were consistent with the present findings. Engel and Steiman (53) who stated that ultrasonic preparations appeared more centered on the canals and isthmi with fewer tendencies to gouge the canal walls in the thinnest areas of the root. Arens et al(54) emphasized the importance of preparing the root end cavity in a conservative approach, they recommended that a distance of at least 2 mm should exist between the canal walls and the cementum region on the sectioned apical surface. If this is not the case, the walls of the cavity may fracture and break after cavity preparation.
Regarding the leakage of different cavity designs, the 90° bevel resulted in better apical seal in comparison to the 45° bevel.
This was in agreement with Tidmarsh and Arrowsmith (55) who suggested that the angle of the bevel should be kept to a minimum and that the retrograde filling should extend coronally into the canal, at least to the level of the coronal end of the bevel.
This study was confirmed by Gilheany et al (56) who stated that as the bevel of the resection changed from 0 degrees to the long axis of the root to 30 degrees and then 45 degrees, the leakage rose significantly and that the miniaturized ultrasonic tips have also eliminated the need for steep bevel angles, thus exposing fewer dentinal tubules and reducing the chance of periapical leakage.