Oral diseases affect approximately 3.9 billion people globally (Watt et al., 2020). Dental caries and periodontal disorders are among the top ten most prevalent diseases worldwide (Peres et al., 2019). Out-of-pocket payments and exclusion from most national health systems have created a disparity for access and use of dental services by adults. The affordability of dental services is a challenge for most populations globally (Peres et al., 2019). Within Australia dental services are not covered by the public funding systems including Medicare and most adults must pay out-of-pocket for treatment (Duckett et al., 2019). To produce research that is both theoretically and methodologically sound this thesis explored literature for the barriers to access and use of dental services to develop and empirically test an explanatory causal model for the use of dental services by Australian adults. After presenting background material in the form of a published scoping review (paper 1), the primary empirical study findings are presented in this thesis. From the scoping review cost (affordability of dental treatment) was identified as the primary possible causal factor that reduced the access and use of dental services by adults globally.