Evaluation of root-end microcrack formation following retropreparation using different ultrasonic instruments

OBJECTIVE: This study evaluated differences among various ultrasonic instruments in the development of root-end cracks following retropreparation of endodontically treated teeth. MATERIALS and METHODS: Three ultrasonic tips were compared: stainless steel, zirconium nitride and diamond. Fifty-seven single rooted extracted teeth were cleaned, shaped and obturated. Their crowns were removed. A 3 mm resection of the root-tip was completed using a straight fissure bur.The teeth were examined under a light microscope. The teeth that developed cracks after resection were discarded. The teeth were divided into three groups of 19 teeth each and a retropreparation was completed with one of the ultrasonic tips for each group. Teeth were again examined under a light microscope. The photomicrographs of the teeth before and after were compared. RESULTS: Examination of the specimens revealed that in the stainless steel group, 26% (5/19) of teeth developed cracks, in the zirconium nitride group, 10.5% (2/19) of teeth developed cracks and in the diamond group, 10.5% (2/19) of teeth developed cracks. The differences in crack formation among the three groups were not statistically significant. CONCLUSION: The results of the study suggested that more cracks may be evident microscopically in rootends prepared with stainless steel ultrasonic instruments although this was not statistically significant.