Presence of isthmi in mandibular mesial roots and associated factors: an in vivo analysis

PURPOSE: To investigate the prevalence of isthmi and middle mesial (MM) canals in the mesial roots of mandibular first molars (MFM) in a Mongoloid subpopulation and to evaluate their association with demographic and anatomic characteristics. METHODS: Cone-beam computed tomography (CBCT) images of 496 patients with 823 MFMs were selected and analyzed. The following data were collected: patient age and gender, side, presence and distribution of MM canal and isthmus, distance between mesiobuccal (MB) and mesiolingual (ML) orifices, and MB–ML root canal system (RCS) morphology. Logistic regression was used to determine the association between demographic and anatomic characteristics and the presence of isthmi in the apical third. RESULTS: The overall prevalence of isthmus and an MM canal in MFM was 64.6% and 10.8%, respectively. The highest prevalence of isthmi and MM canals was found in patients of ≤ 20 and of 41–60 years, respectively (p < 0.05). The prevalence of isthmi declines with age. A total of 41.3% of the MFMs had isthmi in the apical third of the mesial roots. Younger age, shorter MB–ML orifice distance, and Weine type II RCS increased the probability of the presence of an isthmus in the apical third (p < 0.05). CONCLUSION: The prevalence of isthmus in MFM is high in the subject population, but the prevalence of MM canals is not as high as previously reported. Demographic and anatomic characteristics could aid clinicians to better predict the presence of MM canal and an isthmus.