Age-Period-Cohort Analysis of Toothbrushing Frequency in Finnish Adults: Results From Annual National Cross-Sectional Surveys From 1978 to 2014.

Abstract Objectives No previous study has analysed age-, period-, and cohort-related long-term trends in toothbrushing frequency among adults using a nationally representative data set. Our aim was to study age, period, and cohort effects on toothbrushing among 15- to 64-year-olds in Finland from 1978 to 2014. Methods Data were gathered by nationally representative random cross-sectional samples of 15- to 64-year-old Finns annually from 1978 to 2014, during which response rates decreased from 84% to 53%. The final pooled sample size was 119,665. An age-period-cohort model was used to separate the effects of age, period, and cohort on trends in men's and women's toothbrushing frequency. Results From 1978 to 2014, the proportion of respondents who brushed at least twice a day or once a day increased from 42% to 66% and from 83% to 95%, respectively. The proportion of respondents who brushed at least twice a day increased from 27% to 53% among men and from 60% to 75% among women. Increases in at least once-a-day toothbrushing were smaller in both sexes, and in women the increase was minimal over the study years. The increase in toothbrushing frequency occurred particularly among those older than 40 years of age. In men, toothbrushing frequency increased steadily cohort by cohort (cohort effect) and within a single cohort as men in the cohort got older (longitudinal age trend). Instead, in women the cohort effect and longitudinal age trend in toothbrushing were smaller at both frequency thresholds. Conclusions On the population level, favourable changes in toothbrushing habits occurred among adult Finns from 1978 to 2014, especially in men.