title: Timing of developmental stages in permanent mandibular teeth of Finns from birth to age 25.
abstract: OBJECTIVE
  The aim was to provide radiographic data on postnatal development of the 8 mandibular teeth to serve as reference norms in clinical dentistry, forensic dentistry, anthropology, and research.
  
  
  METHODS
  Developmental stages of teeth were assessed from a total of 2795 radiographs, mostly panoramic, of 1970 Finns (966 M and 1004 F) from birth to age 25. The grading was based on Demirjian's 8 mineralization stages and the crypt stage.
  
  
  RESULTS
  Timing of development in individual mandibular teeth is presented in two ways: as age at attainment of each developmental stage and as age of subjects in a developmental stage. Initiation of mineralization was visible in 1st molars at 0.20 years, in central incisors at 0.22 years, lateral incisors at 0.37 years, and canines at 0.56 years of age. Timing was usually earlier in girls than in boys. Differences were greatest in canines, where females were advanced by 1.74 years at the closure of the apex. Root development in 3rd molars showed an opposite trend, where apical closure was 1.19 years earlier in men. In 3rd molars, age at apical closure in females was 21.50 years, among the highest reported. In general, the early developmental stages had the shortest duration and the last stages the longest.
  
  
  CONCLUSIONS
  Timing of postnatal development of individual mandibular teeth in Finns resembled developmental schedules reported for other Caucasian population groups. Any differences were mostly small and inconsequential.
authors.affiliation: Department of Orthodontics, Institute of Dentistry, University of Helsinki, Finland. marjatta.nystrom@helsinki.fi
authors.forename: Marjatta Elina
authors.initials: ME
authors.lastname: Nyström
authors.forename: Helena Meri
authors.initials: HM
authors.lastname: Ranta
authors.forename: Jaakko Sakari
authors.initials: JS
authors.lastname: Peltola
authors.forename: Jorma Matti
authors.initials: JM
authors.lastname: Kataja
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D019229:Dentition, Permanent; D005260:Female; D005387:Finland; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging*; D015588:Observer Variation; D011859:Radiography; D012737:Sex Factors; D013997:Time Factors; D014070:Tooth / Q000000981:diagnostic imaging / Q000254:growth & development*