Oral Health and Function in Older Adults with Intellectual Disabilities: Measurement Innovation for Epidemiological and Population Health Research

Abstract

Summary Background Oral health is increasingly recognised as integral to systemic wellbeing, functional capacity and survival in ageing populations. However, adults with intellectual disabilities remain largely excluded from oral health surveillance and longitudinal epidemiological research. As a result, their oral health status and its interaction with multimorbidity, frailty and premature mortality remain insufficiently understood. This exclusion reflects both methodological barriers and structural inequities in health research and policy. Aim The overarching aim of this thesis was to generate disability-inclusive oral health evidence by developing and validating a structured clinical oral health assessment tool and embedding it within a nationally representative longitudinal ageing cohort to examine oral health status, oral�systemic associations and mortality risk among older adults with intellectual disabilities in Ireland. Methods The thesis adopted a post-positivist epidemiological framework informed by critical realism and an equity-oriented lens. It comprised three interconnected components. First, scoping review synthesised international evidence on oral health and pneumonia in adults with intellectual and developmental disabilities. Second, the Modified Oral Status Survey Tool (MOSST) was developed and psychometrically evaluated to enable structured clinical oral health assessment by trained non-dental clinicians. Content validity was established through international expert review and public and patient involvement. Inter- and intra-rater reliability exceeded recommended epidemiological thresholds (� > 0.85), and feasibility testing demonstrated high acceptability within field conditions. Third, MOSST was embedded within Wave 5 of the Intellectual Disability Supplement to The Irish Longitudinal Study on Ageing (IDS-TILDA), enabling cross-sectional and longitudinal analyses of oral health, systemic conditions and mortality. Multivariable regression models examined associations between oral indicators and systemic outcomes. Cox proportional hazards models assessed associations between tooth loss and all-cause and respiratory-related mortality. Results The scoping review identified biological plausibility for oro-respiratory pathways but highlighted a fragmented and methodologically limited evidence base. MOSST demonstrated strong content validity, high reliability and feasibility within a national ageing cohort. Population-level analyses revealed a substantial burden of untreated caries, compromised gum condition, reduced functional dentition and incomplete prosthetic rehabilitation among older adults with intellectual disabilities. Clear demographic and contextual patterning were observed by age, level of intellectual disability and residence type. In adjusted multivariable models, absence of functional dentition was significantly associated with constipation and osteoporosis, while indicators of poor oral cleanliness and disease burden were associated with respiratory illness. Longitudinal survival analyses demonstrated that tooth loss and absence of functional dentition were independently associated with increased risk of both all-cause and respiratory-related mortality, even after adjustment for age, gender, level of intellectual disability and multimorbidity. Discussion These findings demonstrate that oral health among older adults with intellectual disabilities is neither inevitable nor clinically peripheral but structurally patterned and epidemiologically consequential. By embedding a validated disability-adapted oral health assessment within a longitudinal cohort, this thesis advances inclusive epidemiological infrastructure and enables examination of oral-systemic and oral-mortality pathways previously absent from disability research. The results support conceptualisation of oral health as a modifiable determinant within multimorbidity and frailty trajectories and highlight the role of structural inequities in shaping oral health outcomes. Conclusions This thesis makes three principal contributions: (1) development and validation of a disability-inclusive oral health assessment tool suitable for large-scale surveillance; (2) generation of the first nationally representative, clinically assessed oral health dataset for older adults with intellectual disabilities in Ireland; and (3) empirical demonstration of oral�systemic and oral�mortality associations within a longitudinal disability cohort. The findings support integration of oral health into ageing research, public health monitoring and rights-based disability policy, reframing oral health inequity as a structural issue rather than an inherent feature of disability.