Dental hygiene therapy–led pit-and-fissure sealant reapplication intervals and caries increment in South African school programmes: a target-trial emulation of recall scheduling under therapist shortages

School-based pit-and-fissure sealant programmes in South Africa depend on a small dental hygiene therapy workforce whose recall capacity is fixed in the short run, so the interval at which sealants are reapplied is a rationing decision rather than a clinical preference. the present analysis treats reapplication scheduling as a target trial and characterises the operating characteristics of a before-after-control-impact design that compares caries increment under alternative recall intervals when therapists are scarce. No observational data are used or claimed; the analysis evaluates the design itself under 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 for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Fifty-two clusters are required to detect a 5-percentage-point difference at 80% power. The results show that the design is feasible only at the upper end of the cluster range, that the minimum detectable effect falls steeply as clusters increase, and that the intraclass correlation of 0.64 dominates the precision of every estimate. The contribution is a defensible scheduling-evaluation architecture that separates the recall interval from therapist supply and makes the rationing trade-off explicit before any programme commits to a recall policy.