Dental hygiene therapy–led silver diamine fluoride application and caries arrest in Ethiopian primary schools: a cluster-randomised pragmatic trial of classroom delivery under supply constraints

Silver diamine fluoride (SDF) arrests cavitated dentine caries without drilling, which makes it attractive where dental equipment is scarce, but classroom delivery by dental hygiene therapists has not been evaluated under the supply conditions of Ethiopian primary schools. No observational data are used or claimed: the analysis characterises the design under a declared variance structure with between-cluster standard deviation 6.0, residual standard deviation 4.5 and intraclass correlation 0.64, estimated across 2000 replications per design cell. Power rose with cluster count and effect size, and fifty-four clusters were required to detect a five-percentage-point difference at 80% power. The minimum detectable effect at 80% power fell as clusters increased. The results imply that a classroom-delivered SDF trial in this setting is feasible only at cluster counts well above those typical of school oral health studies, and that the intraclass correlation of 0.64, not the effect size, is the binding constraint on precision.