Dental caries remains a significant health problem in England, effecting 11% of 3-year-olds and 23% of 5-year- olds. Children with dental caries suffer pain, infection and poor oral health-related quality of life. There are different approaches for the management of childhood dental caries but it remains the most common reason for a hospital admission in the UK for children aged 5-9 years, costing the NHS £50 million in 2015-2016. While current approaches have been extensively investigated, their ability to: 1) control pain and infection; 2) prevent hospital admissions, and 3) be implemented within the current NHS contractual arrangements, remains unsatisfactory. Silver diamine fluoride (SDF) is an alternative and non-invasive approach that is applied topically (simple to manage for children) and has proven efficacy in arresting caries progression in primary teeth, principally from studies conducted outside Europe. Its use in primary dental care practice in the UK is limited despite acknowledged need.

However, the clinical and cost effectiveness of SDF has not been compared to usual care in the UK, so it is unknown which treatment is more effective. Before a pragmatic randomised controlled trial (RCT) can be conducted into the clinical and cost effectiveness of SDF compared to usual care, there are several uncertainties related to recruitment, retention and fidelity that require investigation in a feasibility study.

Research Question Is a randomised controlled trial (RCT) to compare the effectiveness of silver diamine fluoride (SDF) to usual care for the treatment of caries in children's primary teeth feasible in UK primary dental care? Aim The overall aim is to establish whether conducting a RCT to compare SDF to usual care for the treatment of caries in children's primary teeth is feasible.

Methods This mixed-method study is a feasibility study with an embedded process evaluation, to compare SDF with usual treatment in primary dental care in the UK. It will be individually randomised, with at least eight dentists, each in a different dental practice and a sample size of 80 participants. There will be ten participants per dentist and equal arm allocation. Follow-up will be for one year. The study will inform whether an RCT is feasible by resolving several key uncertainties. Acceptability and implementation of SDF and the research processes will be explored. Patient and Public Involvement and Engagement (PPIE) representatives will be involved throughout, further informing design including recruitment/retention strategies, participant documentation, analysis, engagement and dissemination.

Inclusion Criteria:

• Children aged 2-6 years
• Cavitated dentinal caries in any primary tooth
• No carious involvement of the tooth pulp
• No dental infection secondary to a non-vital tooth
• Parent/carer able to complete consent forms (with the support of an interpreter if necessary)

Exclusion Criteria:

• Allergy to any treatment component
• Caries effecting the pulp
• Infection secondary to a non-vital tooth
• Conditions requiring special considerations for the child's dental management where randomisation would not be appropriate for example a medical history including cardiac defects, oncology, hereditary bleeding, or being immunocompromised.
• Dental anomalies effecting the carious teeth involved: amelogenesis imperfecta, dentinogenesis imperfecta, molar incisor hypomineralisation, abnormal morphology such as double teeth.