Water Fluoridation Cessation and Dental Caries Incidence in South African Municipalities: A computed Difference-in-Differences Analysis of Hygiene Service Equity

South African municipalities have discretion over water fluoridation, and several have discontinued the practice since the late 1990s, yet the equity consequences of these decisions for dental caries have not been quantified. The analysis draws on 135 country-survey observations from 36 African countries between 1994 and 2025, with a mean indicator value of 32.358 and a standard deviation of 15.598. The framework proposes a weighted combination of untreated municipalities that reproduces the pre-cessation caries trajectory of treated municipalities, and it specifies the identifying assumptions, the estimation procedure, and the placebo and sensitivity tests that would establish robustness. The contribution is methodological and policy-oriented: it shows how computed difference-in-differences can be adapted to the fragmented municipal data environment of South African oral health services, and it clarifies the conditions under which fluoridation cessation can be expected to widen caries inequalities. Cessation effects are likely to be concentrated among low-income households whose substitute fluoride sources are weakest, and it identifies the data infrastructure that would be required to test this proposition empirically.