Dental hygiene therapy supply shortages and silver diamine fluoride substitution in Tanzanian primary oral care: an instrumental-variable analysis of consumable stockouts

Tanzanian primary oral care depends on a narrow set of consumables for dental hygiene therapy, and stockouts of these items are frequent. Because stockouts are not randomly assigned, an instrumental-variable strategy is proposed, using district-level procurement delays as an instrument for consumable availability. The analysis is framed as a methodological and comparative contribution: it specifies the conditions under which the instrument is valid, derives the interpretation of the local average treatment effect, and assesses the plausibility of the exclusion restriction in the Tanzanian procurement context. The paper also reports a descriptive benchmark from the Demographic and Health Surveys Program indicator 'Percentage receiving injection given by health care provider' (FP_SPUS_W_SPH), covering 14 African countries in 2021-2025, with a mean of 91.964 and a standard deviation of 12.468. This benchmark is used only to illustrate the scale of cross-country variation in service delivery, not as an outcome of the oral care analysis. SDF substitution is a defensible interim strategy only when procurement delays are plausibly exogenous and when the substitution margin is clearly defined. The contribution is a specification of the identification conditions and a set of testable propositions for future empirical work.