title: Middle mesial canals in mandibular molars: incidence and related factors.
abstract: BACKGROUND
  Although the internal anatomy of mandibular molars has been extensively studied, information about middle mesial (MM) canals is limited. The primary aim of this retrospective study was to evaluate the incidence of MM canals in mandibular first and second molars. The secondary aim was to correlate the incidence of MM canals with variables of molar type, sex, age, ethnicity, and presence of a second distal canal.
  
  
  METHODS
  All mature permanent first and second mandibular molars treated from August 2012 to May 2014 were included in the analysis. After completion of root canal instrumentation in all main canals, the clinician inspected the isthmus area of the mesial root using the dental operating microscope. If there was a catch point in this area with a file or explorer, the operator spent more time attempting to negotiate an MM canal.
  
  
  RESULTS
  Seventy-five mandibular first and second molars were treated during the specified period. Fifteen (20%) teeth had negotiable MM canals. The incidence of MM canals was 32.1% in patients ≤ 20 years old, 23.8% in patients 21-40 years old, and 3.8% in patients > 40 years. Analysis of data revealed a significant difference in the distribution of MM canals among different age groups (P < .05). The differences in the distribution of MM canals based on sex, ethnicity, molar type, and presence of a second distal canal were not significant.
  
  
  CONCLUSIONS
  The incidence of negotiable MM canals overall and their frequency of identification in younger patients were higher than in previous reports.
authors.affiliation: Department of Endodontics, Prosthodontics and Operative Dentistry, School of Dentistry, University of Maryland, Baltimore, Maryland.
authors.forename: Ali
authors.initials: A
authors.lastname: Nosrat
authors.affiliation: Department of Endodontics, Prosthodontics and Operative Dentistry, School of Dentistry, University of Maryland, Baltimore, Maryland.
authors.forename: Raney J
authors.initials: RJ
authors.lastname: Deschenes
authors.affiliation: Department of Endodontics, Prosthodontics and Operative Dentistry, School of Dentistry, University of Maryland, Baltimore, Maryland.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Tordik
authors.affiliation: Department of Endodontics, Prosthodontics and Operative Dentistry, School of Dentistry, University of Maryland, Baltimore, Maryland.
authors.forename: M Lamar
authors.initials: ML
authors.lastname: Hicks
authors.affiliation: Department of Endodontics, Prosthodontics and Operative Dentistry, School of Dentistry, University of Maryland, Baltimore, Maryland. Electronic address: afouad@umaryland.edu.
authors.forename: Ashraf F
authors.initials: AF
authors.lastname: Fouad
mesh_terms: D000293:Adolescent; D000328:Adult; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000503:physiopathology; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging / Q000503:physiopathology; D008396:Maryland; D008853:Microscopy; D008963:Molar / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000503:physiopathology; D012189:Retrospective Studies; D012389:Root Canal Obturation; D012390:Root Canal Therapy; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000503:physiopathology; D055815:Young Adult
keywords: Dental operating microscope; isthmus; mandibular molar; middle mesial canal; root canal anatomy