title: An In Vitro Study of the Number of Distal Roots and Canals in mandibular First Molars in Iranian Population.
abstract: BACKGROUND
  The purpose of this study was to evaluate the number of distal roots and canals in mandibular first molars and their internal anatomy radiographically within Iranian population.
  
  
  METHODS
  A total of 310 distal roots of mandibular first molars were incorporated in this study and evaluated in terms of number of roots and number and types of canals. Root canal systems were studied in vitro by means of radiography and based on Vertucci's classifications.
  
  
  RESULTS
  It was shown that 4.5% of the teeth in this study had two distal roots, of which, 100% indicated type I for both distobuccal and distolingual roots. Among all the teeth, 43.2% had two canals, 24.2% two apical foramina, and 38.7% two orifices in their distal roots. According to Vertucci's classification 54.9% of the teeth were type I, 19% type II, 1.9% type III, 14.2% type IV, 4.2% type V, 1% type VI, 0.3% type VII and 0% type VIII.
  
  
  CONCLUSIONS
  In as many as 43.2% of all teeth assessed in this study, bicanaled distal roots were observed, dentists are always recommended to search for the second canal in distal roots of mandibular first molars. In case the second canal in the distal root is missed, failure of endodontic treatment will be anticipated. A rectangular type access cavity design allows better visualization and negotiation of the probable second canals within the distal roots of mandibular first molars.
authors.affiliation: Department of Endodontics, School of Dentistry/ Dental Research Center, Tehran University of Medical Sciences, Tehran, Iran and Iranian Center for Endodontic Research.
authors.forename: Hasan
authors.initials: H
authors.lastname: Razmi
authors.forename: Noushin
authors.initials: N
authors.lastname: Shokouhinejad
authors.forename: Mohsen
authors.initials: M
authors.lastname: Hooshyar
keywords: Anatomy; Molar; Population; Root Canal