Micro-computed tomography evaluation of three-dimensional analysis of first mandibular and second maxillary premolars apical constrictions

Apical constriction is the narrowest diameter of the root canal system that commonly is used as a reference point by clinicians as apical termination in endodontic treatment. We investigated the three-dimensional (3D) analysis of shape, size, and location of apical constriction in first mandibular and second maxillary premolars. Total 66 samples of extracted premolar teeth (due to orthodontic treatment) were selected. Selection criteria were complete root development, no restoration, no signs of root fracture or resorption, no radicular or coronal caries, and no endodontic treatment. After placement for 1 h in 3% hydrogen peroxide, and then storage in 70% alcohol, each tooth was scanned using a Bruker Skyscan 1173 micro-CT. The teeth were made transparent to reveal the root canal system morphology in 3D. The shape, size, and location of apical constriction were analyzed. Most apical constriction shapes in first mandibular and second maxillary premolars were convergent and branched constrictions, with most locations tending to be apical. Mean distance between apical constriction and apical foramen was 0.619 and 0.647 mm in first mandibular and second maxillary premolars, respectively. The variation in shape, size, and location of apical constriction should be considered by dentists performing endodontic treatment.