RESUMEN
While root canal anatomy in Middle Eastern populations is well-studied, research on isthmi in mandibular permanent teeth from this region is limited. This retrospective study used cone-beam computed tomography (CBCT) to examine isthmi prevalence and location, as well as root canal morphologies (per Vertucci's classification) in mandibular permanent teeth from a subpopulation in Ardabil, Iran. The study is aimed at enhancing our understanding of dental anatomical variations in Middle Eastern populations. A total of 3566 teeth from 384 CBCT scans were evaluated in this retrospective study. Mandibular teeth were evaluated on sagittal, coronal, and axial sections regarding the presence of isthmus and root morphology (Vertucci's classification). CBCT scans of 197 males (51.3%) and 187 females (48.7%) were evaluated, with a mean age of 41.1 ± 11.4 years. Isthmi were most prevalent in molar mesial roots, typically located in the middle third for anterior teeth and first premolars and cervical third for posterior teeth. While gender did not play a significant role, the presence of an isthmus in the mesial root of the left second molars was associated with a younger mean patient age (p < 0.05). Root morphology varied across tooth types. Central and lateral incisors predominantly showed Vertucci's Types I and III. Canines and premolars were mostly Type I, with some variation. Molar mesial roots frequently exhibited Types IV and II, while distal roots were predominantly Type I. Statistically significant differences were found between morphology and gender in the first left premolar (Type I more common in women; Type V in men; p < 0.001) and in the right canine (Type I more prevalent in men; Types III and V more prevalent in women; p < 0.001). The results revealed wide variations in root canal morphology and a relatively high prevalence of isthmi in the study population. Our findings suggest a potential difference in tooth anatomy based on sex and a relationship between age and the presence of isthmi.