Objective To evaluate the effects of ultrasonic power on root-end preparation. Methods 58 teeth were root canal prepared and filled, 3 mm of the root-end was cut off along the vertical direction of the long axis of the tooth. The samples were divided randomly into 3 experimental groups and 1 control group. In the experimental groups, root-ends were prepared with high, middle, and low 3 different ultrasonic power. The control group was not prepared. Microcracks, marginal integrity, and gutta-percha clearance rate were observed under scanning electron microscope, and recorded the operation time. Results Number of microcracks and destroy of marginal integrity were much more under high power. Low power took the minimal gutta-percha clearance rate. The greater power took the shorter operation time. Conclusion Under moderate ultrasonic power, the number of microcracks and destroy of marginal integrity were much small, clearance rate of gutta-percha were higher, and also took short operation time.
