Dental hygiene therapy–led school sealant programmes and first-molar caries incidence in Namibian primary schools: a cluster quasi-experimental evaluation of targeting rules under hygienist scarcity

Namibia's school sealant programme must allocate a small dental hygiene therapy workforce across many primary schools, and the choice of targeting rule determines how much first-molar caries is averted per hygienist-hour. the present analysis evaluates three targeting rules—universal school coverage, school-level risk screening, and child-level risk screening—within a cluster quasi-experimental design that pairs programme schools with matched comparison schools and uses difference-in-differences to estimate first-molar caries incidence over a four-year follow-up. The analysis is framed as a target-trial emulation in which the estimand is the per-hygienist-hour caries averted under each rule, and the design parameters are fixed at a 1986–2025 observation window with 168 country-survey observations drawn from the DHS Program indicator 'Number of non-first births' (mean 6749.589, SD 4199.775, range 1438.00–16479.43). Under hygienist scarcity the binding constraint is not sealant efficacy but the targeting rule's capacity to concentrate scarce hygienist time on children who will develop first-molar caries, and that school-level risk screening dominates universal coverage whenever between-school variance in caries risk exceeds within-school variance. The contribution is a decision rule for programme managers that links workforce density to the choice of targeting rule, together with an explicit statement of the conditions under which child-level screening is worth its additional cost.