Morphologic Changes of Apical Foramen and Microcrack Formation after Foraminal Enlargement: A Scanning Electron Microscopic and Micro-computed Tomographic Analysis

Introduction: The aim of the present study was to evaluate the morphologic changes on the apical foramen and the formation of dentinal microcracks after foraminal enlargement in straight and curved root canals using scanning electron microscopic (SEM) and micro computed tomographic (micro-CT) analyses. Methods: Sixty teeth were selected and divided into 2 experimental groups: GI (incisors/straight group, n = 30) and GM (molars/curved group, n = 30). Each group was divided into 2 subgroups (n = 15) according to the analysis performed: SEM or micro-CT analysis. The incisors and mesiobuccal canal of molars were instrumented with Reciproc Blue R25 instruments (VDW, Munich, Germany) using standardized shaping procedures in the apical foramen and 1 mm beyond. The occurrence of foraminal deformation was analyzed by scanning electron microscopy. The z test was used for statistical analysis (P<.05). Micro-CT imaging was used to observe the presence of microcracks in the root apical third. Afterward, pre- and postoperative cross-sectional images were screened to identify the presence of dentinal defects. Results: The curvature of the canal did not influence the occurrence of foraminal deformation either for instrumentation in the foramen or for instrumentation beyond the foramen (P>.05). It was also observed that the increase in the working length did not influence the appearance of new deformations in the GI/SEM and GM-SEM groups (P>.05). Qualitative micro-CT analysis showed the presence of dentinal defects in 0.8% (112) and 1.5% (208) of the cross sections of incisors and molars, respectively, from a total of 13,987 slices. All dentinal defects identified in the analysis of any postoperative scans were already present in the corresponding preoperative images. Therefore, no new microcracks were observed after root canal preparation. Conclusions: The preparation of straight and moderately curved root canals with Reciproc Blue, regardless of the working length, did not influence the occurrence of apical foramen deformations and did not cause the formation of dentinal microcracks.