Average and Heterogeneous Associations between Secondhand Smoking and Tooth Loss

Secondhand smoke (SHS) is a pervasive health concern increasingly associated with tooth loss, yet studies assessing its population-level associations and potential heterogeneity are limited. This study aimed at estimating the average and subgroup-specific effects of SHS exposure on tooth loss among US adults using modern causal inference-based methods. This study analyzed cross-sectional data from 6,019 nonsmokers aged ≥20 y, representing 48.2 million individuals, in the National Health and Nutrition Examination Survey (2009 to 2018). SHS was defined by serum cotinine. This study quantified the association between SHS exposure and tooth loss using targeted minimum loss estimation, a doubly robust estimator that enhances confounding adjustment in observational data. Confidence intervals were obtained via bootstrap resampling. Heterogeneity of the association was evaluated by a data-adaptive causal forest method that identifies subgroup-specific variation. SHS exposure was associated with having 0.74 fewer teeth (average association, -0.739; 95% CI, -1.053 to -0.426) and with a 4.6-percentage higher probability of having <20 teeth (average association, 0.046; 95% CI, 0.027 to 0.065). Larger associations were observed among adults aged ≥45 y, those with lower socioeconomic position, individuals with higher sugar intake or medical comorbidities, and participants at the extremes of flossing frequency. This study found that SHS exposure was associated with greater tooth loss, with disproportionate burdens observed among adults facing socioeconomic disadvantages or chronic health conditions. These findings underscore the potential value of integrating oral health outcomes into tobacco control initiatives and guiding targeted prevention for groups at elevated risk.