title: Twenty-year cohort study of health gain from orthodontic treatment: temporomandibular disorders.
abstract: BACKGROUND
  Temporomandibular disorder (TMD) is a common condition. Studies of TMD in relation to orthodontic treatment did not show an association, but longitudinal studies from adolescence to adulthood are lacking. The aim of this study was to investigate the relationship between orthodontic treatment and TMD with a longitudinal study design.
  
  
  METHODS
  This prospective cohort study was conducted in South Wales, United Kingdom. The baseline investigation was carried out in 1981 and involved children aged 11 to 12 years (n = 1018). Follow-up investigations were done in 1984 (n = 792), 1989 (n = 456), and 2000 (n = 337).
  
  
  RESULTS
  Overall TMD prevalence increased from the baseline (3.2%) to age 19 to 20 (17.6%) and decreased by age 30 to 31 (9.9%). TMD prevalence was higher in females at all follow-up points, except the baseline. Overall, incidences of TMD were 11.9%, 11.5%, and 6.0% at the first, second, and last follow-ups, respectively. Females were more likely to develop TMD than males (hazard ratio [HR], 2.1; 95% CI, 1.3 and 3.3), and those with high self-esteem were less likely to develop TMD (HR, 0.6; 95% CI, 0.4 and 0.8). There was no association between orthodontic treatment and new TMD onset. The incidences of persistent TMD were 20.0%, 34.9%, and 28.0% at the first, second, and last follow-ups, respectively. Females were more likely to have persistent TMD than males (HR, 2.5; 95% CI, 1.0 and 6.1). There was no association between orthodontic treatment and persistent TMD. The only significant predictors of TMD in adults aged 30 to 31 were female sex (odd ratio, 3.0; 95% CI, 1.1 and 8.2) and TMD in adolescence (odds ratio, 4.5; 95% CI, 2.0 and 10.0).
  
  
  CONCLUSIONS
  Orthodontic treatment neither causes nor prevents TMD. Female sex and TMD in adolescence were the only predictors of TMD in young adulthood.
authors.affiliation: Aberdeen Pain Research Collaboration, Division of Applied Medicine, School of Medicine and Dentistry, University of Aberdeen, Aberdeen, Scotland. Tatiana.Macfarlane@abdn.ac.uk
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Macfarlane
authors.forename: Pamela
authors.initials: P
authors.lastname: Kenealy
authors.forename: H Anne
authors.initials: HA
authors.lastname: Kingdon
authors.forename: Bengt O
authors.initials: BO
authors.lastname: Mohlin
authors.forename: J Richard
authors.initials: JR
authors.lastname: Pilley
authors.forename: Steve
authors.initials: S
authors.lastname: Richmond
authors.forename: William C
authors.initials: WC
authors.lastname: Shaw
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D015331:Cohort Studies; D005157:Facial Pain / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D005544:Forecasting; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008310:Malocclusion / Q000453:epidemiology; D009971:Orthodontics, Corrective / Q000706:statistics & numerical data*; D015995:Prevalence; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology; D012008:Recurrence; D012307:Risk Factors; D012649:Self Concept; D012737:Sex Factors; D013705:Temporomandibular Joint Disorders / Q000453:epidemiology*; D014852:Wales / Q000453:epidemiology; D055815:Young Adult