Impact of Tobacco Cessation on the Oral Microbiome and Salivary Inflammatory Biomarkers: A 12-Month Prospective Cohort Study of Periodontal Healing Dynamics

Introduction: Smoking is a major modifiable risk factor for periodontitis, and quitting is expected to help. What remains unclear is how fast the subgingival microbiota and the host inflammatory response recover once a person stops. Objective: To follow clinical periodontal status, salivary inflammatory markers and the oral microbiome for 12 months in heavy smokers who entered a structured cessation programme together with non-surgical periodontal therapy (NSPT). Methods: Eighty-four smokers (≥15 cigarettes/day) with Stage II–III, Grade B/C periodontitis received nicotine patches, cognitive-behavioural counselling and full-mouth NSPT. Assessments took place at baseline (T0) and at 1, 3, 6 and 12 months (T1, T3, T6, T12). Abstinence was verified by exhaled carbon monoxide (≤6 ppm), and participants were classified at 12 months as continuous abstainers (CA, n = 52) or non-responders/relapsed smokers (NR, n = 32). Subgingival plaque was profiled by 16S rRNA gene sequencing (V3–V4), and salivary IL-1β, MMP-8, TNF-α and IL-10 were measured by multiplex bead immunoassay. Results: In abstainers, mean probing pocket depth fell from 4.62 mm at baseline to 2.92 mm at T6 and 2.78 mm at T12, whereas non-responders improved only from 4.58 to 3.81 mm. Bleeding on probing rose transiently in abstainers (peak 48.6%) before dropping to 14.2% at T12. Salivary MMP-8 and IL-1β declined by 58.4% and 42.2% at T6 and by 71.7% and 57.0% at T12 in abstainers; changes in non-responders were smaller and not statistically significant. Red-complex species decreased within 3 months (p < 0.001), and Shannon diversity increased by T6 (p = 0.002), with a shift towards Streptococcus and Veillonella. Conclusions: Within the limits of a non-randomised comparison, sustained abstinence was accompanied by an early fall in salivary markers of tissue breakdown and a slower reorganisation of the subgingival community. These data support routine, biochemically verified cessation support as part of periodontal care.