title: An in vitro assessment of type, position and incidence of isthmus in human permanent molars.
abstract: Root canal anatomical complexities, such as isthmus, may limit the action of the endodontic instruments, irrigant solutions and intracanal medications, leading to endodontic treatment failure.
  
  
  OBJECTIVE
  This in vitro study assessed the type, position and incidence of isthmus in human permanent molars.
  
  
  METHODS
  One hundred and twenty eight upper and lower first and second permanent molars were analyzed. The roots were embedded in transparent resin, and then split at different distances from the apex (1.0-2.5-4.0-5.5-7.0 mm). Following the sample examination in stereomicroscope, the data were submitted to chi-square statistical test at a 5% significance level.
  
  
  RESULTS
  The highest isthmus incidence was at 7.0 mm from the root apex in all samples, except the distal root of lower molars (at 5.5 mm). In upper and lower molars, type V (complete isthmus with a continuous opening between the two main root canals) was the most common classification of isthmus (28.8%). In the mesial root of first and second mandibular molars, type IV had the highest incidence (36% and 23.9%, respectively).
  
  
  CONCLUSIONS
  It was concluded that isthmus was widely found in flat roots, with a low percentage in areas close to the apex. In upper and lower molars, these structures were most frequently found at 7 mm from the apex.
authors.affiliation: Department of Restorative Dentistry, Endodontics Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Fernando José Camello de
authors.initials: FJ
authors.lastname: Lima
authors.affiliation: Department of Restorative Dentistry, Endodontics Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Francisco
authors.initials: F
authors.lastname: Montagner
authors.affiliation: Department of Restorative Dentistry, Endodontics Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Rogério Castilho
authors.initials: RC
authors.lastname: Jacinto
authors.affiliation: Biostatistics Division, Department of Social Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Glaucia Maria Bovi
authors.initials: GM
authors.lastname: Ambrosano
authors.affiliation: Endodontics Division, Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Brenda Paula Figueiredo de Almeida
authors.initials: BP
authors.lastname: Gomes
mesh_terms: D019412:Anatomy, Cross-Sectional; D016009:Chi-Square Distribution; D003786:Dental Pulp Cavity / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D019229:Dentition, Permanent; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008963:Molar / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D009811:Odontometry; D011859:Radiography; D012016:Reference Values; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging