Therapy-led silver diamine fluoride protocols and caries-arrest coverage in Tanzanian school dental programmes: a stepped-wedge implementation evaluation

School-based silver diamine fluoride (SDF) programmes in Tanzania have been promoted as a therapy-led alternative to conventional restorative care, yet their evaluation has been hampered by the absence of a design that can separate programme effects from secular trends in caries arrest. the present analysis reports a replication-based evaluation of the before-after-control-impact (BACI) estimator for a stepped-wedge implementation of therapy-led SDF protocols across 8, 16, 24 and 32 school clusters, with effect sizes of 3, 5 and 8 percentage points in caries-arrest coverage. Using a declared variance structure with a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.64, power was estimated across 2000 replications per design cell.52 clusters are required to detect a 5-percentage-point effect at 80% power, and that the minimum detectable effect falls steeply as cluster count rises from 8 to 32. The intraclass correlation of 0.64 dominates the design's operating characteristics, so that even the largest cluster count examined leaves the 3-percentage-point effect underpowered. The contribution is a design-level account of what a stepped-wedge SDF evaluation in Tanzanian schools can and cannot detect, and a demonstration that therapy-led protocols require cluster counts well beyond those typical of district-level implementation if their caries-arrest effects are to be distinguished from clustering.