Root-end preparation during surgical endodontics may produce dentinal microcrack formation and/or propagation, leading to vertical root fractures.This study aimed to evaluate and compare the microcrack formation and propagation during ultrasonic root-end cavity preparation, with diamond- and zirconium nitride-coated tips using micro-computed tomography (CT).Twenty-eight extracted, mature, free-of-defect, mandibular premolars were decoronated and micro-CT scanned for the presence of preexisting microcracks. Samples were prepared till F4, were obturated, and were re-scanned to determine an increase in the number of microcracks. After 3 mm of root-end resection, the samples were randomly divided for ultrasonic root-end preparation into Group 1 ( = 12): preparation was done with ProUltra Surg tip, Group 2 ( = 12): preparation was done with KiS tip, and Group 3 ( = 4): no preparation was done. The samples were rescanned, and data collected were analyzed using ANOVA and Student's -test. The level of significance was set at 5%.Preexisting microcracks were observed in few samples. The mean percentage number increase of microcracks after root-end preparation in ProUltra Surg group was 1.25 and in KiS group, it was 0.5. The difference in mean percentage increase for the number of microcracks after root-end cavity preparation using ProUltra Surg tip and KiS tip was 0.75. However, this difference was not statistically significant ( = 0.34).Both diamond- and zirconium nitride-coated ultrasonic tips resulted in more number of dentinal crack formation and propagation when preexisting cracks were present.