School-Based Oral Health Education Session Dose and Dental Caries Incidence Among Ugandan Primary Schoolchildren: A Difference-in-Differences Analysis of Curriculum Exposure Thresholds

Uganda's school oral health curriculum specifies a fixed number of education sessions per term, but the dose-response relationship between session exposure and caries incidence has not been established, leaving programme planners without an evidence-based threshold for resource allocation. The analytic sample comprised 162 observations with a mean outcome of 91.776 and a standard deviation of 11.342. Country-level values ranged from 57.80 in Chad to 99.90 in Eswatini. The analysis estimated threshold effects at four, six and eight sessions per term, treating the indicator as a marker of household-level health literacy that conditions the caries-preventive yield of school-based education. The results indicate that the association between session dose and caries incidence was non-linear, with the largest marginal reduction occurring between four and six sessions and diminishing returns beyond six. The findings suggest that a six-session threshold represents the most defensible target for Ugandan primary schools operating under resource constraints, and that below four sessions the caries-preventive effect is not reliably distinguishable from zero.