title: Age, period, and cohort analysis of regular dental care behavior and edentulism: a marginal approach.
abstract: BACKGROUND
  To analyze the regular dental care behavior and prevalence of edentulism in adult Danes, reported in sequential cross-sectional oral health surveys by the application of a marginal approach to consider the possible clustering effect of birth cohorts.
  
  
  METHODS
  Data from four sequential cross-sectional surveys of non-institutionalized Danes conducted from 1975-2005 comprising 4330 respondents aged 15+ years in 9 birth cohorts were analyzed. The key study variables were seeking dental care on an annual basis (ADC) and edentulism. For the analysis of ADC, survey year, age, gender, socio-economic status (SES) group, denture-wearing, and school dental care (SDC) during childhood were considered. For the analysis of edentulism, only respondents aged 35+ years were included. Survey year, age, gender, SES group, ADC, and SDC during childhood were considered as the independent factors. To take into account the clustering effect of birth cohorts, marginal logistic regressions with an independent correlation structure in generalized estimating equations (GEE) were carried out, with PROC GENMOD in SAS software.
  
  
  RESULTS
  The overall proportion of people seeking ADC increased from 58.8% in 1975 to 86.7% in 2005, while for respondents aged 35 years or older, the overall prevalence of edentulism (35+ years) decreased from 36.4% in 1975 to 5.0% in 2005. Females, respondents in the higher SES group, in more recent survey years, with no denture, and receiving SDC in all grades during childhood were associated with higher probability of seeking ADC regularly (P < 0.05). The interaction of SDC and age (P<0.0001) was significant. The probabilities of seeking ADC were even higher among subjects with SDC in all grades and aged 45 years or older. Females, older age group, respondents in earlier survey years, not seeking ADC, lower SES group, and not receiving SDC in all grades were associated with higher probability of being edentulous (P<0.05).
  
  
  CONCLUSIONS
  With the use of GEE, the potential clustering effect of birth cohorts in sequential cross-sectional oral health survey data could be appropriately considered. The success of Danish dental health policy was demonstrated by a continued increase of regular dental visiting habits and tooth retention in adults because school dental care was provided to Danes in their childhood.
authors.affiliation: Dental Public Health, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, China.
authors.forename: Kar-Yan
authors.initials: KY
authors.lastname: Li
authors.forename: May Chun Mei
authors.initials: MC
authors.lastname: Wong
authors.forename: Kwok-Fai
authors.initials: KF
authors.lastname: Lam
authors.forename: Eli
authors.initials: E
authors.lastname: Schwarz
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D003718:Denmark; D003729:Dental Care / Q000523:psychology / Q000706:statistics & numerical data*; D003753:Dental Health Surveys; D005260:Female; D015438:Health Behavior; D006291:Health Policy; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009066:Mouth, Edentulous / Q000453:epidemiology*; D015995:Prevalence; D012571:School Dentistry; D012737:Sex Factors; D012923:Social Class; D013029:Space-Time Clustering; D055815:Young Adult