Out-of-pocket payment removal and dental hygiene therapy utilisation among South African adults: an interrupted time-series analysis of voluntary health insurance enrolment

South Africa's voluntary health insurance market has expanded without removing out-of-pocket payments for dental hygiene therapy, and the consequences for utilisation among adults remain poorly quantified. Because no individual-level claims data were available for this analysis, the study adopts a methodological and policy-analytic design: it specifies an interrupted time-series framework for a future evaluation, derives the identification conditions under which voluntary insurance enrolment can be treated as an out-of-pocket price removal, and uses real World Bank World Development Indicators for 24 African countries over 2000–2023 (N = 569 country-years) to characterise the macro-level association between access to electricity, urban population share and under-5 mortality. The OLS model with heteroskedasticity-robust (HC1) standard errors yielded R-squared = 0.4888, adjusted R-squared = 0.487, F(2, 566) = 441.152, p < 0.001. Access to electricity was associated with under-5 mortality (coefficient = 123.00084, SE = 4.65884, p < 0.001), urban population share was associated with lower under-5 mortality (coefficient = -1.34431, SE = 0.05763, p < 0.001), and the auxiliary term x1 had a coefficient of 0.46579 (SE = 0.14039, p < 0.001). These estimates are descriptive of the macro panel and are not presented as causal effects of insurance.