Oral health changes in an adult Norwegian population: a cohort analytical approach

Objectives: The purpose of this analysis was to study temporal variation in oral health in an adult population. The cohort analysis comprised 1) estim ation of longitudinal, cross-sectional, and time-lag differences in caries and treatment experience of the adult population in Trondelag from 1973 to 1983 and to 1994; 2) assessment of which of the effects of age, period and cohort was the most plausible explanation for the observed differences and 3) discussion of causal and other factors underlying the effects of age, pe riod and cohort. Methods: Cohort analysis was used to study changes in oral health over time. Study participants were selected by random sampling in 1 973, 1983, and 1994 (n=1959, n=3195, n=2341 respectively). The methods of d ata collection comprised standardised clinical measurements and a self-admi nistered questionnaire. Cohort tables were established to analyse changes i n DFT from 1973 to 1983 and DFT and DFS from 1983 to 1994. Results: Four pa tterns of changes in oral health were identified from adolescence to older adulthood. They point in different directions which indicate that complex p rocesses are present. There were two and three significant changes in the s ubsets of analysis. Assumptions and conditions that allow identification of separate cohort, period, and age effects appeared not to be present. The p attern of changes was consistent with main effects of both age, period, and cohort. The effects were discussed from the perspective of the chosen fram e of explanatory factors. Conclusions: The changes in oral health between p opulations in 1973, 1983 and 1994 were the combined consequences of simulta neously occurring factors that account for both age, period and cohort effe cts.