Background: Scandinavian welfare states, despite having better population oral health when compared to less egalitarian societies, are characterized by ubiquitous social gradients and large relative socioeconomic inequalities in oral health. However, time trends in these inequalities among Scandinavian children and adolescents have not been studied in detail.Objectives: To analyze the associations between socioeconomic position (SEP) and dental caries experience in adolescents and to investigate the time trends in these associations between 1995 and 2013.
Methods: Nationwide repeated cross-sectional studies using individual-level data were conducted on all adolescents in Denmark who became 15 years old in 1995, 2003, and 2013 (N=154,750). Dental data were obtained from the SCOR register of the Danish Health Authority while data on social variables were acquired from administrative registers at Statistics Denmark. SEP measures included previous year’s parental education (highest attained educational level between the parents), income (equivalized household disposable income), and occupational social class (highest recorded occupational class between the parents). Covariates were immigration status, country of origin, number of children and persons in the family, and household type. The outcome was dental caries experience, determined by the decayed, missing, and filled surfaces (DMFS) index. Negative binomial regression models were used to examine the association between DMFS count and each of the explanatory variables separately, while accounting for cluster-correlated family data. Furthermore, hierarchical multiple regressions of DMFS on SEP indicators—using the zero-inflated negative binomial (ZINB) distribution as the outcome distribution—were estimated while successively adjusting for the potential effects of the included covariates.
Results: Caries prevalence declined from 71% in 1995 to 63% in 2003 and 45% in 2013. Separate assessment of each covariate showed statistically significant graded associations between each covariate and DMFS count at all time points. Similarly, in the ZINB models, in all three years, clear gradients were observed in terms of caries differentials in all three SEP categories, with statistically significant associations (Type 3 p values, <0.0001) even after adjustment for all other covariates. For instance, in 2013, even in the latent class of adolescents with positive caries experience, being of subordinate occupational social class was associated with up to 2.4 (95% CI: 2.2–2.6)-fold increase in the amount of caries experience. Between 1995 and 2013, steadily increasing relative inequalities were observed in all three SEP categories, while absolute inequalities decreased in the education and occupation categories.
Conclusion: Considerable progress has been made in reducing dental caries rates among Danish adolescents; however, this progress has benefited the disadvantaged social groups less than the better-off groups.