Alqahtani F, et al. - In this investigation involving 102 male individuals, researchers compared cotinine levels in the peri-implant sulcular fluid (PISF) among 35 cigarette smokers, 33 waterpipe users, 34 electronic-cigarette users, and 35 nonsmokers. PISF was collected and levels of cotinine in the PISF were measured using standard techniques. Compared to nonsmokers, scores of peri-implant plaque index and probing depth were significantly higher among cigarette smokers, waterpipe smokers, and electronic-cigarette users. Compared to cigarette smokers, waterpipe smokers, and electronic-cigarette users, peri-implant bleeding on probing was more often manifested in nonsmokers. Investigators found that the volume of PISF collected among cigarette and waterpipe smokers and electronic-cigarette users was significantly higher than nonsmokers. Findings revealed that habitual use of nicotinic products enhances cotinine expression in the PISF. Cotinine levels are comparable in cigarette and waterpipe smokers' PISF as well as users of electronic cigarettes.