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

This study evaluated differences among various ultrasonic instruments in the development of root-end cracks following retropreparation of endodontically treated teeth. 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. 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. The results of the study suggested that more cracks may be evident microscopically in root-ends prepared with stainless steel ultrasonic instruments although this was not statistically significant. (author)