Objective: The objective of our study is to analyse (with the help of scanning electron microscopes) the quality of the dental root surface and the appearance of dental cracks after performing apical preparations using two diffe- rent types of ultrasonic tips. Study design: We used 32 single-rooted teeth that underwent a root canal and apical resection. Afterwards, the teeth were divided into 4 groups of 8 teeth each, with preparations of the apical cavities in the following manner: Group 1: stainless steel ultrasonic tip at 33KHz. Group 2: stainless steel ultrasonic tip at 30KHz. Group 3: diamond ultrasonic tip at 30KHz. Group 4: diamond ultrasonic tip at 33 KHz. The quality of the root surface and the presence of cracks were evaluated by one single observer using a scanning electron microscope. Results: All of the teeth in our study had cracks after the apical preparations. The mean number of cracks per tooth ranged between 6.1±1.9 (group 1) and 3.5±2.4 (group 4), with a significantly higher number found in the groups that used stainless steel tips (P=.03). The types of cracks produced involved: 8 complete cracks (4.5%), 167 incomplete cracks (94.4%), and 2 intradentinal cracks (1.1%), with no significant differences observed between the different frequencies used for each group. Conclusions: Stainless steel ultrasonic tips provoked a larger number of cracks than diamond tips. The frequency of vibration used did not have any effect on the number of cracks found.