Pit-and-Fissure Sealant Application Interval and Dental Caries Survival in Kenyan School Dental Therapy Programmes: A Target-Trial Emulation of Reapplication Windows

School-based dental therapy programmes in Kenya apply pit-and-fissure sealants at fixed intervals, but the optimal reapplication window for preventing caries has not been established. The analysis characterises the operating characteristics of the design under a declared intraclass correlation of 0.64, between-cluster standard deviation of 6.0 and residual standard deviation of 4.5. Power was estimated across 2000 design cells for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The design would require 54 clusters to detect a 5-percentage-point effect at 80% power. The framework clarifies the trade-off between reapplication frequency and programme resources, and it identifies the conditions under which a target-trial emulation can yield credible estimates of caries survival from routine programme data. The contribution is methodological: it specifies how reapplication windows can be evaluated without inventing observational data, and it provides a template for dental therapy programmes seeking to optimise sealant intervals.