The aim of this prospective interventional study is to verify the efficacy of smoking cessation on clinical and microbiological outcomes of non-surgical periodontal therapy of chronic periodontitis patients. Smokers willing to quit received periodontal treatment and concurrent smoking cessation therapy. Periodontal maintenance was performed every 3 months. A single calibrated examiner, blinded to smoking status, assessed periodontal clinical outcomes and applied a structured questionnaire in order to collect demographic and behavioural information. Further, expired carbon monoxide concentration were measured with a monoximeter. A pooled subgingival plaque sample was collected from the deepest periodontal pocket from each participant. The presence and quantification of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola were determined using (RT-PCR).

Smokers willing to quit, with 10 teeth or more, and with periodontitis (30% or more of their teeth with proximal attachment loss ≥ 5 mm) were enrolled in the study. All subjects received periodontal treatment and concurrent smoking cessation therapy. Smoking cessation therapy was performed by a team comprising physicians, nurses, a psychologist and dentists, and consisted of four 1-h counselling lectures, psychologist-assisted cognitive behavioral therapy, nicotine replacement therapy and medication (bupropion or varenicline). Smoking cessation motivation was reinforced by dentists at the maintenance sessions, by means of motivational interviewing techniques. Periodontal therapy consisted in full-mouth supra and subgingival scaling and root planing (with curettes and ultrasonic scaler); oral hygiene instruction and motivation and removal of intra-oral plaque retentive factors. Further, periodontal maintenance was performed every 3 months.

A single calibrated examiner, blinded to smoking status, assessed periodontal clinical outcomes (recession, pocket depth, clinical attachment level, plaque index and bleeding on probing). A structured questionnaire was applied in order to collect demographic and behavioral information. Expired carbon monoxide concentration was measured with a monoximeter, in order to validate smoking status. A pooled subgingival plaque sample was collected from the deepest periodontal pocket from each participant. The presence and quantification of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola were determined using real time - PCR (RT-PCR).

Inclusion Criteria:

• smokers willing to stop smoking
• >10 teeth
• periodontitis (30% or more of their teeth with proximal attachment loss ≥ 5 mm)

Exclusion Criteria:

• systemic conditions considered as risk factors for periodontal disease,
• periodontal therapy in the last 6 months
• continuous systemic use of anti-inflammatory or steroidal drugs

The outcome assessor was blind to smoking status. Before each follow-up periodontal examination (3, 6 and 12 months), the following procedures were performed by a periodontist: (1) removal of all tobacco stains from subject's teeth and/or dental polishing, with a standardized duration of up to 30 min., (2) 0.12% chlorohexidine rinse (1min.) aimed to hide any possible cigarette odour exhaled from the oral cavity. After these procedures, the examiner entered the examination room fully equipped (including a mask), in order to avoid noticing the smoking status by odour