Policy problem and rationale for research: Recent years have witnessed a decline in the number of private general dental practitioners (GDPs) providing publicly funded primary oral healthcare for low-income adults as contractors on behalf of the Irish health system. This has resulted in restricted access to care for vulnerable populations. Against this backdrop, the Irish Government seeks to implement Smile agus Sláinte - National Oral Health Policy (2019) which aims to widen access to publicly funded care through greater use of GDP contractors. The current workforce and capacity challenges in primary oral healthcare are not unique to Ireland or dentistry and are symptomatic of wider health system problems. In the context of policy and change implementation, understanding complex system drivers and how they influence the capacity of the system to deliver services can help bridge a policy implementation gap. There is an absence of primary research investigating this topic in Ireland and wider research focussing on factors influencing dentists' engagement in state-funded care from a health systems perspective. The aim of this PhD thesis therefore is to understand what are the health system factors that influence private GDPs participation in state-funded, contracted primary oral healthcare and therefore the implementation of workforce changes proposed as part of oral healthcare system reforms in Smile agus Sláinte - National Oral Health Policy.

Methods: Across three sequential studies, this PhD thesis addresses the research aim from different perspectives. The first study is a documentary and secondary data analysis, the second study is a realist review, and the third study is a realist interview study. Data were collected via searches of publicly available oral healthcare datasets, systematic and non-systematic literature searching, and via qualitative realist interviews respectively. Documentary and secondary data analysis methods and realist analytical approaches were adopted.

Results: This PhD thesis demonstrates a steady decline in the number of private GDP-contractors providing state-funded primary oral healthcare for low-income adults in Ireland while the eligible population has increased, widening the gap between service demand and capacity. The three studies highlight important health systems contextual factors which influence GDPs participation and engagement in publicly funded, contracted care. In Ireland and elsewhere, oral health garners limited political and health systems priority, influencing the design, funding and resourcing of services. Oral healthcare systems, including Ireland's, continue to focus on costly, dentist-led restorative care models rather than prevention. This can lead to care rationing and cost containment within state dental contracts. Contract restrictions which limit clinician autonomy, alongside perceived low remuneration and burdensome administration can drive dentists towards the private sector. Background economic conditions and societal care preferences can also influence the wider oral healthcare `market' dynamics. Suboptimal or adversarial communication and engagement between health systems and dentists can also lead to loss of trust, deepen professional isolation among GDPs and further fuel their dissatisfaction with state-financed oral healthcare. Messaging from within GDPs' professional networks can reinforce dissatisfaction and further encourage the shift towards the private sector.

Conclusion: Private GDPs' engagement in publicly funded primary oral healthcare is influenced by a myriad of complex and inter-related health systems factors. As Ireland looks to implement Smile agus Sláinte and meet its international obligations commensurate with the WHO Global oral health action plan, the findings of this thesis provide health system leaders with evidence to leverage system change that could potentially increase or sustain GDPs' engagement in state-contracted care. Leveraging such change and increasing GDPs' engagement in publicly funded primary oral healthcare has the potential to improve access to care for vulnerable populations and reduce oral health inequalities.

P.29 Prevention and management of oral diseases - The 16th century Dutch philosopher Desiderius Erasmus is credited for coining the well-known and often cited proverb “Prevention is better than cure.” He also wrote the satirical essay, "In Praise of Folly" in which he criticises the foolishness and corrupt practices of the Christian church and wider society at the time. Five centuries on, the sentiments underlying Erasmus’ works can be applied in how oral diseases, namely dental caries, are managed across health systems globally. The aetiology of many of the world’s most prevalent oral diseases can ultimately be traced to sugar, tobacco and alcohol. As such, there is a wide body of evidence underpinning preventative modalities in oral healthcare namely oral health education and instruction, application of topical fluorides, pit and fissure sealants, smoking cessation advice and community water fluoridation (CWF). On prevention, the evidence is unequivocal that public health interventions tackling common risk factors can lessen the burden of oral diseases and other NCDs...