Dental hygiene therapy same-day chairside HbA1c feedback and periodontal referral completion in South African diabetic clinics: a cluster-randomised implementation trial

Implementation trials in dental hygiene therapy often propose before-after-control-impact (BACI) designs to evaluate same-day chairside HbA1c feedback coupled with periodontal referral, yet the operating characteristics of such designs in South African diabetic clinic settings remain uncharacterised. Power was estimated across 2000 replications per design cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The analysis indicates that 54 clusters are required to detect a 5 percentage point effect at 80% power, a requirement that exceeds the largest cluster count examined. Minimum detectable effect curves decline steeply between 8 and 24 clusters but flatten thereafter, and the density of estimated power across replications shows substantial overlap between adjacent design cells. The results imply that BACI designs for chairside HbA1c feedback in this context are underpowered at feasible cluster counts, and that implementation trials should either adopt alternative estimators, increase cluster counts, or reframe the target effect around the upper end of the plausible range.