The aim of this study was to describe the degree and orientation of root curvature in mandibular premolars and to identify the radicular third in which the curvature originates, using digital panoramic radiographs and linear morphometry. We also aimed to detect the prevalence of excessive root curvatures or dilacerations. A cross-sectional study was developed and were included 477 digital panoramic radiographs taken during 2014 at a university radiologic center. Exclusion criteria were applied to both radiographs and teeth, so that, 118 radiographs (76 women, 42 men) and a total of 294 premolars were included in the study. From the analysis of the samples, we registered the degree of curvature, the curvature orientation (distal or mesial), the part of the root in which the curvature originates, and the prevalence of dilacerations. In curved teeth, the average angle of the curvature was 19.68°. It was found that 12.24% of the premolars have mesial orientation curves, 58.84% have distal orientation curves, and 28.92% were straight. Of the total number of curvatures, 0.48% originated in the radicular cervical third, 27.27% in the middle third, and 72.25% in the apical third. A statistically significant association was found between tooth type and orientation of the curvature (p= 0.025) and between the tooth third in which the curvature originates and the orientation of the curvature (p= 0.000). In respect to mandibular premolars, 72.09% have root curvatures (average angle: 13.9°). Most curvatures originate in the apical third (72.25%). The prevalence of dilacerations was 0% to 30.27% according to different criteria. From the results of our research we believe that knowledge of the anatomy of the tooth root is important before performing procedures in endodontics, orthodontics and other areas, for a proper planning of these dental practices.

KEY WORDS: Morphometry; Panoramic radiographs; Dilacerations; Premolars.