title: Prevalence of disc displacement of various severities among young preorthodontic population: a magnetic resonance imaging study.
abstract: OBJECTIVE
  There has been no study on the prevalence of disc displacement (DD) of different levels in children and adolescents with adequate sample size using magnetic resonance images (MRIs). This retrospective cross-sectional study was designed to investigate the relationship between increasing age and the prevalence of DD of various severities in a young preorthodontic population.
  
  
  METHODS
  Of 199 preorthodontic patients aged 6 to 15 years visiting a private orthodontic office for initial examination, 153 patients with signs and symptoms of temporomandibular joint (TMJ) disorders had MRIs of their TMJs taken for further evaluation. Of those, 302 TMJs from 151 patients' MRIs of diagnostic quality were divided into three age groups (I: 6 to 9, II: 10 to 12, and III: 13 to 15 years). DD of each patient was categorized based on its severity from stage 0 (normal) to stage 4 (total DD without reduction). The distribution of DD stages in each age group was plotted on a line graph and statistically analyzed for intergroup comparison.
  
  
  RESULTS
  A graphical representation of the results clearly demonstrated a trend for higher occurrence of more advanced DD with an increase in age. No gender difference was observed. Statistical analysis showed that DD was significantly more advanced in group II than group I (p < 0.01) and group III than group I (p < 0.01).
  
  
  CONCLUSIONS
  The study revealed a high prevalence of DD in the young preorthodontic population and significant increase in the proportion of patients with more advanced stages of DD in older patients.
authors.affiliation: Private Practice, Tokyo, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Ikeda
authors.forename: Akira
authors.initials: A
authors.lastname: Kawamura
authors.forename: Renie
authors.initials: R
authors.lastname: Ikeda
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D004204:Joint Dislocations / Q000145:classification / Q000453:epidemiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008335:Mandibular Condyle / Q000473:pathology; D015995:Prevalence; D012189:Retrospective Studies; D013701:Temporal Bone / Q000473:pathology; D019224:Temporomandibular Joint Disc / Q000473:pathology*; D013705:Temporomandibular Joint Disorders / Q000145:classification / Q000453:epidemiology*
keywords: MRI; TMJ; disc displacement; young preorthodontic patients