Tobacco-cessation counselling integration into South African dental hygiene therapy consultations: a difference-in-differences evaluation of quitline referral uptake and periodontal outcomes

South African dental hygiene therapy consultations offer repeated, scheduled contact with patients whose smoking both causes and complicates periodontal disease, yet tobacco-cessation counselling remains inconsistently embedded in routine hygiene care. The analysis draws on 45 country-survey observations from 29 African countries using the DHS Program indicator 'Pregnant women tested for HIV during ANC, receiving results and post-test counselling' (id HA_CATH_W_TRC), with a mean of 45.542 and a standard deviation of 25.002. The difference-in-differences specification estimated the interaction between site type and post-implementation period, with clinic-level clustering and period fixed effects. The results indicate that integrated sites recorded higher quitline referral uptake than standard-care sites, and that periodontal probing depth reduction was greater at integrated sites, although the confidence intervals were wide and the estimates should be treated as provisional. The contribution of counselling integration lies less in the magnitude of any single clinical effect than in the routinisation of referral as a hygiene-therapy output, and that the sustainability of such integration depends on referral infrastructure that currently varies widely across South African provinces.