Changes and trends in attack distributions and progression of dental caries in three age cohorts in Finland.

BACKGROUND Several factors are claimed to have contributed to the decline in dental caries that has occurred over recent decades in many industrialised countries. METHODS A retrospective cohort design follow-up study of trends in dental caries in three age cohorts born a decade apart is reported from Finland. Subjects born in the 1960s, 1970s and 1980s (n = 1275) were monitored annually through their patient records, and changes in the distribution, extent and rate of caries attack (caries leading to restorations or extractions) were analysed. Logistic and Poisson regression techniques were employed to detect trends and Kaplan-Meier survival methods were used for the rate analyses. RESULTS A marked decrease in caries was observed and the proportion of disease-free subjects increased gradually towards the younger cohorts. Logistic regression analysis showed clear trends, in that the odds ratios (ORs) for the cohort effect were 8.93 [95% confidence interval (CI) = 7.95-10.04] and 4.32 (95% CI = 3.92-4.75) in the 1960 and 1970 cohorts, respectively, relative to the 1980 cohort, and that for the age (year) effect was 1.44 (95% CI = 1.42-1.46). Similar types of cohort and age effects (p < 0.0001) were found in the disease progression analyses. The rate analyses showed statistically highly significant differences between the three cohorts (p < 0.001) for both sexes. The caries decline was a lasting one, in spite of the delay in restorations observed in the youngest cohort. DISCUSSION The results indicate a vast and continuous trend in the incidence of dental caries leading to restorations and extractions. Significant changes in the rate and extent of disease progression have taken place, which will inevitably affect the future public health agenda.