Fig. 4.

Bootstrapped mediation models testing the indirect effects of physical activity (a) and physical fitness (b) on dentine caries (ICDAS > 3) through salivary IgA concentration from stimulated saliva, adjusted for gender, BMI, and additional covariates related to lifestyle and oral health behavior (tooth brushing frequency, tobacco use, snacking, and household income). Path a represents the association between the exposure (physical activity/fitness) and the mediator (SIgA), path b the association between SIgA and dentine caries, and c the total effect of the exposure on dentine caries. Path c′ represents the direct effect after accounting for the mediator. The indirect effect is calculated as a × b. Standardized regression coefficients (β) are shown along each path, with p-values in parentheses, and bootstrapped confidence intervals (BootCI) for the indirect effect