Silver Diamine Fluoride versus Atraumatic Restorative Treatment Selection Thresholds and Lesion Arrest in Rwandan Dental Therapy Clinics: An Instrumental-Variable Analysis of Material Supply Constraints

Rwandan dental therapy clinics routinely choose between silver diamine fluoride (SDF) and atraumatic restorative treatment (ART) for arresting cavitated dentine lesions, yet the two materials are not clinically interchangeable and their relative availability is shaped by procurement systems that lie outside clinical control. The framework is specified for a clinic-level panel and its identifying assumptions, exclusion restriction and monotonicity conditions are stated explicitly. Because no primary clinical data were available for this analysis, the paper is methodological and theoretical: it derives the estimand, characterises the complier subpopulation, and shows how supply-shortfall instruments recover a local average treatment effect that conventional adjusted regression cannot. The contribution is a transferable identification strategy for material-comparison questions in low-resource dental therapy settings, together with a set of falsification tests and reporting standards that make the strategy auditable before clinical data are collected.