This article applies Le Grand's distinction between knightly and knavish motivations to the behaviour of dentists in choosing whether to treat patients on the NHS or privately. Using national quantitative and discursive surveys, it shows that dentists' notions of their own interests centre on independent small-business entrepreneurship and their professional culture defines patient interest in terms of access to clinically autonomous practice based on a restorative paradigm. Government attempts to promote preventive dentistry in the context of the weakening in dentists' bargaining position as general dental health improves and the determination of the profession to protect high remuneration have led to conflict. Both knavish and knightly motives (understood from the perspective of dentists' professional culture) lead dentists to exit from the NHS. Any analysis of ‘robust’ policies, designed to accommodate both motivations, must take into account social factors such as professional cultures which influence how practitioners understand their own interests and those of their clients.