Evaluation of Dentin Defect Formation during Retreatment with Hand and Rotary Instruments: A Micro-CT Study

The purpose of this study was to compare the incidence and longitudinal propagation of dentin defects after gutta-percha removalwith hand and rotary instruments using microcomputed tomography. Twenty mandibular incisors were prepared using thebalanced-force technique and scanned in a 19.9𝜇m resolution. Following filling with the lateral compaction technique, gutta-perchawas removed with ProTaper Universal Retreatment (PTUR) or hand instruments. After rescanning, a total of 24,120 cross-sectionalimages were analyzed. The numbers, types, and longitudinal length changes of defects were recorded. Defects were observed in36.90% of the cross sections. A total of 73 defects were comprised of 87.67% craze lines, 2.73% partial cracks, and 9.58% fractures.No significant difference in terms of new defect formation was detected between the retreatment groups. The apical and middleportions of the roots had more dentin defects than the coronal portions. Defects in three roots of the PTUR instrument groupincreased in length. Under the conditions of this in vitro study, gutta-percha removal seemed to not increase the incidence of dentindefect formation, but the longitudinal defect propagation finding suggests possible cumulative dentinal damage due to additionalendodontic procedures. Hand and rotary instrumentation techniques caused similar dentin defect formation during root canalretreatment