Clinical Examinations After assessing the plaque and the gingival index (O'Leary 1972, Löe 1967) clinical measurements of full mouth pocket probing depths (PPD), bleeding on probing (BOP), gingival recessions (GR), and furcation involvement are taken. All measurements, except for furcation involvement, are taken at six sites per tooth (mesiobuccal, mid-buccal, distobuccal, mesiolingual, mid-lingual and distolingual). Measurements of PPD, BOP, and GR are performed using a standard Florida Probe® handpiece (Florida Probe Corp., Gainsville, FL, USA). Clinical measurements are taken at baseline, after 4 weeks, and after 3 months (visits 2a, 3a, and 4a). Smoking habits are determined by an objective chairside measurement of carbon monoxide concentration in exhaled air (Bedfont-Smokerlyzer®, Bedfont, UK) at visits 1 through 4. Intraoral radiographs and photographs are taken at baseline.