Trends in socioeconomic inequalities in oral health among 15-year-old Danish adolescents during 1995-2013: A nationwide, register-based, repeated cross-sectional study.

Abstract

Scandinavian welfare states, despite having better population oral health than less egalitarian societies, are characterized by ubiquitous social gradients and large relative socioeconomic inequalities in oral health. However, trends in these inequalities among Scandinavian children and adolescents have not been studied in detail. To describe the associations between socioeconomic position (SEP) and oral health in adolescents and to investigate the trends in these associations between 1995 and 2013. Nationwide repeated cross-sectional studies (using individual-level data) were conducted on 15-year-olds in Denmark from 1995, 2003, and 2013 (N=154,750). Dental data were obtained from the national dental register of the Danish Health Authority (Sundhedsstyrelsens Centrale Odontologiske Register [SCOR]) and data on social variables from administrative registers at Statistics Denmark. SEP measures included previous year's parental education (highest attained educational level by either of 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, represented 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. 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 3 years, clear gradients were observed in terms of caries differentials in all three SEP categories, with statistically significant associations (Type 3 P values, <.0001) even after adjustment for all other covariates. For instance, in 2013, even among adolescents with positive caries experience, being of lower occupational social class was associated with up to 2.4-fold (95% confidence interval [CI]: 2.2-2.6) higher caries experience. Between 1995 and 2013, relative inequalities increased in all SEP categories, while absolute inequalities decreased in the education and occupation categories. 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.