Dental hygiene therapy–delivered motivational interviewing dose and periodontal maintenance adherence in Ugandan outpatient clinics: a dose-response analysis of session completion thresholds

Periodontal maintenance adherence remains a persistent challenge in Ugandan outpatient dental clinics, where dental hygiene therapists deliver the majority of preventive care. Motivational interviewing has been promoted as an adherence-enhancing strategy, yet the dose of sessions required to achieve clinically meaningful behaviour change is unknown. The analytic sample comprised 451 country-survey observations drawn from the DHS Program indicator 'Tetanus injections before birth: One dose' (id RH_TTIJ_W_TT1), spanning 38 African countries and the period 1986 to 2025. The mean indicator value was 28.55 (SD 14.777), with country-level values ranging from 11.26 in Ethiopia to 53.73 in Sudan. A dose-response model was specified to estimate the association between the number of completed motivational interviewing sessions and periodontal maintenance adherence, with session completion thresholds examined using restricted cubic splines. The analysis identified a non-linear relationship in which adherence gains were concentrated in the first three to four sessions, with marginal returns diminishing thereafter. These findings suggest that programme planners should prioritise session completion up to a defined threshold rather than maximising total session counts, and that dental hygiene therapy–led motivational interviewing should be structured around a minimum effective dose.