Effects of Ultrasonic Removal of Fractured Files from the Middle Third of Root Canals on the Resistance to Vertical Root Fracture.

ABSTRACT

INTRODUCTION: This study aimed to analyze the effects of ultrasonic removal of fractured files from the middle third of root canals on the vertical root fracture resistance. METHODS: This study was an extension of a previous study assessing the effects of fractured file removal on dentinal microcracks. It included 18 bilaterally matched pairs of human mandibular incisors prepared and analyzed in the previous study. Briefly, 1 member of each pair was assigned to an ultrasonic or a control group. In the ultrasonic group, K-files were fractured in the middle third of canals followed by ultrasonic file removal and canal preparation. In the control group, the root canals were simply prepared. Micro-computed tomographic imaging was performed before and after treatment, and the cross-sectional root images were screened for microcracks. For the present study, 3-dimensional reconstruction was performed for volumetric assessments. The fracture resistance was measured using a universal testing machine. All data were statistically analyzed. RESULTS: Fracture loads were significantly smaller in the ultrasonic group (P < .05). The percentage increase in the canal volume significantly influenced the root fracture resistance (P < .05), whereas microcracks had no significant effect (P > .05). CONCLUSIONS: Ultrasonic removal of fractured instruments from the middle third of root canals lowers the vertical root fracture resistance, with increased dentin removal being the primary cause.