ObjectivesTo assess the extent of the association of psychosocial stress with oral health in an Ontario population stratified by age groups, and whether any association is modified by indicators of social and economic capital.MethodsWe retrieved data of 21,320 Ontario adults, aged 30–74 years old, from the Canadian Community Health Survey (CCHS: 2017–2018), which is a Canada-wide, cross-sectional survey. Using binomial logistic regression models that adjusted for age, sex, education, and country of birth, we examined the association of psychosocial stress (indicated by perceived life stress) with inadequate oral health (indicated as having at least one of the following: bleeding gums, fair/poor self-perceived oral health, persistent oral pain). We assessed the effect measure modification of indicators of social (sense of belonging to the local community, living/family arrangements) and economic capital (household income, dental insurance, dwelling ownership) on the perceived life stress-oral health relationship, stratified by age (30–44, 45–59, 60–74 yrs). We then calculated the Relative Excess Risk due to Interaction (RERI) which indicates the risk that is above what would be expected if the combination of low capital (social or economic) and high psychosocial stress was entirely additive.ResultsRespondents with higher perceived life stress were at a significantly higher risk of having inadequate oral health (PR = 1.39; 95% CI: 1.34, 1.44). Adults with low social and economic capital were also at an increased risk of inadequate oral health. Effect measure modification showed an additive effect of indicators of social capital on the perceived life stress-oral health relationship. This effect was evident across all three age groups (30–44, 45–59, 60–74 yrs), with the highest attributable proportion of social and economic capital indicators in the psychosocial stress-oral health relationship in older adults (60–74 yrs).ConclusionOur findings suggest an exacerbating effect for low social and economic capital in the relationship of perceived life stress with inadequate oral health among older adults.