Vulnerable and socially excluded groups in society persistently experience significantly worse oral health and poorer access to dental services than the mainstream population. Action to tackle these unfair, unjust and avoidable inequalities in oral health needs to be informed by an understanding of the broad range of interacting factors that ultimately influence oral health across society and specifically the most vulnerable and marginalised. Failure to understand the underlying factors that create and perpetuate the oral health equity gap risks the development and implementation of ineffective interventions that do not achieve meaningful improvements in oral health for the most vulnerable. This paper presents a theoretical framework that combines a broad public health perspective on oral health inequalities, combined with more specific factors determining the oral health of vulnerable and marginalised groups. Actions to improve access to dental services and policies to combat oral health inequalities among vulnerable adult populations are then presented.