Andrew Y. Xu

Date of Graduation


Document Type


Degree Type



School of Dentistry



Committee Chair

Takashi Komabayashi

Committee Co-Chair

Michael D Bagby

Committee Member

Anthony T Borgia


Introduction: Mechanical cleaning and shaping is an important component to the long term success of endodontic therapy. A larger diameter canal preparation allows for more penetration of antimicrobial solutions into the root canal system with resultant improved disinfection. The objective of this study was to determine the residual dentin thickness (RDT) of the distal wall of mandibular mesial roots after mechanical preparation by using 4% constant tapered Nickel-Titanium rotary (NTR) files with various tip sizes as evaluated utilizing microcomputed tomography (microCT).;Methods: Twenty-five mandibular molars were mounted at the cemento-enamel junction (CEJ) in modified polypropylene 50 ml centrifuge tubes using a non-radiopaque methyl methacrylate acrylic resin. All specimens were preoperatively scanned with microCT-40 (Scanco Medical, Switzerland). Images from the microCT-40 were transferred to ImageJ RTM image analyzing software (NIH, Bethesda, MD) to assess the initial dentin thickness of the distal wall measured 7mm from the apices of the mandibular molar mesial roots. Canals were then instrumented to length with 4% tapered NTR files (EndoSequenceRTM) with varying apical sizes based upon group designation, either size 35.04, 40.04, 45.04, 50.04, 55.04. Each specimen was measured after canal preparation in a manner identical to the pre-instrumentation measurement using ImageJ RTM. Pearson correlation test was used to determine the correlation between preoperative mesio-buccal (MB) and mesio-lingual (ML) distal wall dentin thickness. The Kruskal-Wallis test was used to detect the amount of dentin that was removed and corresponding RDT among the five groups.;Results: Preoperatively, distal wall dentin thickness of MB and ML canals was found to be highly correlated (Correlation = 0.743). A statistically significant difference was observed between the five groups with respect to dentin that was removed (p = 0.031) and the resulting RDT (P = 0.001). The median value of RDT for Groups A, Group B, Group C, and Group E were found to be close to 1mm with the exception being Group D (0.596 mm).;Conclusion: Root anatomy and preoperative dentin width thickness are the biggest factors that determine the amount of dentin removed by the files in the mid-root of the canal during mechanical root canal preparation.