Income-related inequalities in the association of smoking with periodontitis: a cross-sectional analysis in Tokyo Metropolitan Districts.

OBJECTIVE: Socio-economic status (SES) and smoking are risk factors for periodontitis; however, their interaction has not been determined. We investigated the effect of modification of SES and smoking with periodontal conditions. MATERIALS AND METHODS: Data on the social background, smoking status, and dental examination of 1033 individuals residing in the Tokyo Metropolitan District were analyzed. The outcomes were the number of remaining teeth and the proportion of teeth with probing pocket depth (PPD) >/= 4 mm and >/= 6 mm. Multilevel linear and Poisson regression analyses were performed after adjusting for possible confounding factors, including SES, assessed by the average income of the residential area. RESULTS: The mean number of remaining teeth was 24.6 +/- 4.8, and the proportion of teeth with PPD >/= 4 mm and >/= 6 mm was 31.2 +/- 28.5% and 12.2 +/- 18.1%, respectively. After adjusting for confounding factors, the lowest-income population had significantly lesser teeth (coefficient: - 0.46, 95% CI - 0.89, 0.02, p = 0.039) and a higher proportion of teeth with PPD >/= 4 mm than the highest-income population (ratio of means: 1.22, 95% CI 1.03-1.44, p = 0.013). Significant interactions were observed; income inequalities in periodontitis were significant only among current smokers. CONCLUSION: Inequality in socio-economic status is associated with oral health inequalities. The adverse effects of smoking on periodontitis might be greater in the low-income population. CLINICAL RELEVANCE: The low-income population, especially current smokers, had significantly more compromised oral health than the high-income population. In addition to the emphasis on smoking cessation, the promotion of universal health coverage for dental care is necessary to reduce oral health inequalities.