Introduction: Dental caries among children is a major global health problem and is a particular public health challenge in Saudi Arabia. Dental caries cause pain, infection and negatively impact quality of life. As part of population oral health improvement efforts in Saudi Arabia, this project aims to evaluate the effectiveness of a supervised toothbrushing programme in kindergartens.

Methods and analysis: This study is a cluster randomised controlled trial. Enrolment began in September 2022, for two academic years (2022-2024) on 20 randomly selected kindergartens in Riyadh. The data collection phase will be completed in September 2024. Ten kindergartens are randomly allocated to supervised toothbrushing and 10 to treatment as usual, which is an annual oral health awareness visit. The primary endpoint will be the worsening of obvious decay experience as measured by decayed (into dentine), missing and filled teeth (d3mft) from baseline to the second year of follow-up. The secondary endpoint will be the increase in the number of teeth affected. A priori subgroups of the region of Riyadh, school type (public, private), child sex and presence/absence of prior decay at baseline, will be analysed. We require 244 evaluable endpoints using a power of 80% to meet the sample size requirement. In addition, questionnaires on behaviours, quality of life, process monitoring and cost analysis are being deployed.

Ethics and dissemination: Ethics approval for this study was given by the King Fahad Medical City Institutional Review Board in the Saudi Ministry of Health (22-083E/March 2022). The data analysis has been approved by the University of Glasgow Medical Veterinary and Life Sciences Research Ethical Committee (200220194/March 2023). The results of this study will be disseminated through presentations at scientific conferences and in scientific journals.