Equality in adults' oral health in Norway. Cohort and cross-sectional results over 33 years

Objective: To assess social inequality in dental clinical parameters from 1973 to 2006. Methods: Samples from two birth-cohorts born between 1929-1938 and 1959-1960, respectively, and 35-44-year-olds were drawn in 1973, 1983, 1994 and in 2006 in the county of Nord-Trondelag in Norway. Standard procedures were followed all the time. The examination comprised caries and caries treatment experience by DMF criteria and a questionnaire. Length of education in years was divided into quartiles in 1983, 1994 and 2006 to analyse the association between social status and clinical parameters. Statistical analyses were conducted within the same study year and between the years 1983 and 2006 by descriptive statistics and ANOVA. Results: The study showed that the DMFT/S index increased in the two birth-cohorts from 1973 to 1983 where after fewer changes occurred. However, there was a great improvement in oral health among 35-44-year old during the period from 1973 to 2006. The inequalities observed in 1983 remained or decreased and there was equality in number of present teeth all the time. The DMF results from the birth-cohorts showed that if social differences appear at an early age, they will persist in the cohorts the next 30 years and more. This is mainly because of the irreversibility of the DMF registrations. Conclusions: Social inequality was reduced but found in some indicators of dental status in 2006. Part of it can be explained by the insensitivity of the applied indexes. There is still a social divide in oral health and it affects elderly more than younger adults.