Objectives: To evaluate the effectiveness and cost benefit of dentists prescribing of 5000ppm fluoride toothpaste compared to usual care in individuals 50+ years with high-risk of caries. Methods: A pragmatic, open-label, randomised controlled trial (CTIMP) that aims to recruit and follow-up for 3 years, 1200 participants from ~60 dental practices across the UK. Primary outcome: proportion of participants receiving dental treatment due to caries. Secondary outcomes: coronal and root caries increment, quality of life measures, and economic outcomes. Here we report recruitment rates and initial qualitative findings drawn from interviews with dentists concerning their experiences in participation and their views and behaviours concerning the prescribing of high dose fluoride toothpaste. Results: Recruitment started in February 2018, we have recruited 44 practices and 517 participants at a rate of 43 per month (target 91). Barriers of recruitment included acquiring necessary permissions in a timely fashion, funding for dentists, complex documentation needs of a CTIMP, identifying eligible participants and time-commitment required of patients. Dentists’ views and behaviour regarding high dose fluoride toothpaste prescription varied widely and could be influenced by their peers’ prescribing behaviour, where they were trained and their participation in the trial. Dentists’ views about patients also varied, some reported demands for continuous repeat prescriptions while some described reticence to use the toothpaste because of concerns of possible adverse effects of fluoride. Conclusions: The trial is important given the growing aging population and lack of evidence for the costs and effects of prescribing high dose fluoride toothpaste. Recruitment to practice-based trials is challenging and influenced by common factors and also factor that are unique to the context of each trial. This abstract is based on research that was funded entirely or partially by an outside source: UK NIHR Disclosure Statement: The submitter must disclose the names of the organizations with which any author have a relationship, the nature of the relationship, and the clinical or research area involved. The following is submitted: Iain Pretty receives funding from the Colgate Palmolive company in the form of an academic grant.