Therapy-led tobacco cessation brief intervention integration and periodontal treatment outcomes in Kenyan dental clinics: an interrupted time-series analysis

Tobacco use is a principal modifiable risk factor for periodontal disease, yet cessation counselling remains weakly embedded in routine dental care in Kenya. The intervention combined therapist-delivered 5A counselling, nicotine replacement therapy referral, and structured follow-up at each periodontal maintenance visit. Segmented regression with Newey-West standard errors was used to estimate level and slope changes in two co-primary outcomes: mean probing pocket depth and the proportion of patients achieving a five-year periodontal stability threshold. A total of 2,847 patient-episodes were analysed. Immediately after integration, mean probing pocket depth fell by 0.41 mm (95% CI 0.27 to 0.55; p < 0.001) and the stability proportion rose by 6.8 percentage points (95% CI 3.1 to 10.5; p < 0.001). Twelve months after integration, the slope of pocket depth change had steepened by 0.06 mm per month (95% CI 0.03 to 0.09; p < 0.001), and the stability slope had improved by 0.9 percentage points per month (95% CI 0.4 to 1.4; p < 0.001). Self-reported abstinence at six months rose from 4.2% to 19.7%. The findings indicate that therapist-led cessation integration produces measurable periodontal benefit, but that the effect is contingent on sustained follow-up and on the availability of nicotine replacement therapy. Cessation should be treated as a periodontal therapy component rather than an adjunctive public-health add-on.