Heyse Jr, Jeffrey2020-10-262020-10-262020-08https://hdl.handle.net/11299/216767University of Minnesota M.S. thesis. August 2020. Major: Dentistry. Advisor: RONALD ORDINOLA-ZAPATA. 1 computer file (PDF); vi, 43 pages.PURPOSE: To quantitively measure initial and remaining dentin wall thickness in the danger zone of the second mesiobuccal (MB2) canal of extracted human maxillary first molars after rotary instrumentation using cone beam computed tomography (CBCT) imaging. MATERIAL AND METHODS: Each tooth was scanned multiple times after instrumentation by files of increasing taper. Repeated- measures ANOVA and post hoc Tukey test were used to compare the changes in the remaining wall thickness. RESULTS: The preoperative dentin thickness in the danger zone of the MB2 area had a mean of 0.82 +/- .17mm. Multiple comparison test found significant levels of mean dentin removal in the danger zone for all groups. CONCLUSION: The Sx orifice opener does significantly reduce the remaining dentin thickness removing an average of 32% of the dentin in the distal wall. There is a safe area of dentin thickness toward the mesial wall of the MB2 danger zone.enCBCTDanger ZoneEndodonticsRotaryThesis or Dissertation