Abstract Introduction: Dental caries remains a prevalent condition with significant health and economic repercussions. To address persistent oral health disparities and reduce the burden of dental caries among preschoolers in Sweden, this study aims to evaluate the clinical and economic impact of implementing a theory-based behavioural intervention delivered by health promoters in clinics serving children at elevated risk for caries. Methods: A retrospective cohort design was applied, comparing clinics using a theory-based behavioural intervention led by health promoters with clinics using the Recommended Programme for Caries Treatment (RPCT). The cohort were children aged 3–6 years identified as being at increased caries risk in Region Västra Götaland during 2021–2023. Three analytic approaches were employed: (1) budget impact analysis (BIA) to measure net costs and resource shifts; (2) difference-in-differences (DiD) to compare mean decayed, extracted or filled teeth (deft) in intervention versus control clinics; and (3) cost-effectiveness analysis (CEA) to estimate the incremental cost-effectiveness ratio (ICER). Results: The BIA showed that the theory-based behavioural intervention led by health promoters incurred higher initial personnel costs than the RPCT but required fewer clinical hours – an opportunity cost that, if redeployed to clinical activity, could partially offset these expenses. The DiD showed that, over 3 years, clinics implementing the intervention achieved a statistically significant reduction of 0.26 deft among 6-year-olds. The CEA estimated the ICER to be 2142 SEK (199 EUR) per deft prevented, which improved to 513–810 SEK (48–75 EUR) when the economic value of the liberated work hours was included. Conclusion: A theory-based behavioural intervention led by health promoters reduced caries risk among high‐risk preschoolers and may enable improved resource allocation, contingent on the redeployment of freed hours. Despite higher initial personnel costs, the approach demonstrated favourable cost-effectiveness over time, supporting its integration into public dental care systems.