title: Evaluation of isthmus prevalence, location, and types in mesial roots of mandibular molars in the Iranian Population.
abstract: BACKGROUND
  Management of canal isthmus is considered as an important factor for successful endodontic treatment. Accordingly, this study was designed to determine the prevalence, location, and types of isthmus in mesial root canals of extracted mandibular molars in a sample of Iranian population.
  
  
  METHODS
  In this cross-sectional descriptive study, 60 extracted molars with two mesial canals were included. The samples were initially decoronated and then, roots were sectioned horizontally at 2, 4, and 6 mm levels from the apex via a low-speed handpiece with a thin metallic disk and finally prepared and stained with Indian ink. All sections were examined using a stereomicroscope at a magnification of ×30. Prevalence, location, and types of isthmus were evaluated based on the classifications by Kim and Teixeira and all data were statistically analyzed by the chi-squared test. The statistical significance level was established at 0.05.
  
  
  RESULTS
  Eighty-three percent of extracted mandibular molars had an isthmus at the mesial root. This prevalence increased with distance from the apex, that is, 92% at 6 mm from the apex and 70% at 2 mm from the apex. A statistically significant difference was found between the sections at 2 and 6 mm from the apex (P < 0.05), but no other significant differences between other levels (P > 0.05).
  
  
  CONCLUSIONS
  Isthmus is very common in the mesial roots of the mandibular permanent molars in the Iranian population, with the highest prevalence in the 6 mm distance from the root apex. Therefore, detection, cleaning, and filling of these apical 6 mm isthmuses are of great benefit in modern endodontics.
authors.affiliation: Department of Endodontics, Dental branch, Islamic Azad University, Tehran, Iran.
authors.forename: Payman
authors.initials: P
authors.lastname: Mehrvarzfar
authors.affiliation: Department of Endodontics, Dental branch, Islamic Azad University, Tehran, Iran.
authors.forename: Nahid Mohammadzade
authors.initials: NM
authors.lastname: Akhlagi
authors.affiliation: Department of Endodontics, Dental branch, Islamic Azad University, Tehran, Iran.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Khodaei
authors.affiliation: Department of Endodontics, Dental branch, Islamic Azad University, Tehran, Iran.
authors.forename: Golnaz
authors.initials: G
authors.lastname: Shojaee
authors.affiliation: Department of Endodontics, Dental branch, Islamic Azad University, Tehran, Iran.
authors.forename: Sara
authors.initials: S
authors.lastname: Shirazi
keywords: Isthmus; mandibular molars; mesial root; root anatomy