Morphological changes of apical foramen and microcracks formation after foraminal enlargement: a scanning electron microscopy and micro-computed tomography analysis

ABSTRACT Introduction The aim of the present study was to evaluate the morphological changes on the apical foramen and formation of dentinal microcracks after foraminal enlargement in straight and curved root canals, using scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) analyses. Methods Sixty teeth were selected and divided into two experimental groups: GI (incisors - straight group/n=30) and GM (molars – curved group/n=30). Each group was divided in two subgroups (n=15) according to the analysis performed: SEM or microCT. The incisors and mesio-buccal canal of molars were instrumented with Reciproc Blue R25 instruments, using standardized shaping procedures, in the apical foramen and 1mm beyond. The occurrence of foraminal deformation was analyzed by SEM. Z test was used for statistical analysis (P 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>0.05). It was also observed that the increase in working length did not influence the appearance of new deformations in GI-SEM and in GM-SEM (`P>0.05). 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 was observed after root canal preparation. Conclusion The preparation of straight and moderately curved root canals with Reciproc Blue, regardless the working length, did not influenced the occurrence of apical foramen deformations and did not caused the formation of dentinal microcracks.