The shape of the socioeconomic-oral health gradient: implications for theoretical explanations

Objectives: The nature of the relationship between status and health has theoretical and applied significance. To compare the shape of the socioeconomic -oral health relationship using a measure of relative social status (MacArthur Scale of Subjective Social Status) and a measure of absolute material resource (equivalised household income); to investigate the contribution of behaviour in attenuating the socioeconomic gradient in oral health status; and to comment on three hypothesised explanatory mechanisms for this relationship (material, psychosocial, behavioural). Methods: In 2003, cross-sectional self-report data were collected from 2,915 adults aged 43-57 years in Adelaide, Australia using a stratified cluster design. Oral conditions were (1) < 24 teeth, (2) 1+ impact/s reported fairly often or very often on the 14-item Oral Health Impact Profile; (3) fair or poor self-rated oral health, and (4) low satisfaction with chewing ability. Prevalence ratios and 95% confidence intervals (PR, 95%CI) were calculated from a logistic regression model. Covariates were age, sex, country of birth, smoking, alcohol use, body mass index, frequencies of toothbrushing and interdental cleaning. Results: There was an approximately linear relationship of decreasing prevalence for each oral condition across quintiles of increasing relative social status. In the fully adjusted model the gradient was steepest for low satisfaction with chewing (PR = 4.1, 95%CI = 3.0-5.4). Using equivalised household income, the shape more closely resembled a threshold effect, with an approximate halving of the prevalence ratio between the first and second social status quintiles for the adverse impact of oral conditions and fair or poor self-rated oral health. Adjustment for covariates did not attenuate the magnitude of PRs. Conclusion: The nature of the relationship between social status and oral conditions differed according to the measure used to index social status. Perception of relative social standing followed an approximately straight-line relationship. In contrast, there was a discrete threshold of income below which oral health deteriorated, suggesting that the benefit to oral health of material resources occurs mostly at the lower end of the across the full socioeconomic distribution.