Exposure to tobacco smoke is generally accepted as a major environmental risk factor for periodontal diseases. As reviewed by Gelskey,[11
] smoking meets most of the criteria for causation proposed by Hill. The specificity of the association between smoking and periodontitis is evident from the studies of Bergstrom et al
] Jansson et al
] and Tomar et al
] who have shown that disease progression slows down in patients who quit smoking when compared to those who continue to smoke.
In most investigations, tobacco smoke exposure was examined exclusively via a self-administered questionnaire, the validity of which is often questioned because of underestimation.[7
] On the other hand, self-reported measures are likely to be imprecise indicators of intake of tobacco smoke.[7
] A quantitative assessment of tobacco smoke exposure through evaluation of its metabolites would help overcome such drawbacks. Hence, in our study, semi-quantitative assessment of salivary cotinine levels was done.
Markers of exposure to cigarette smoke include carbon monoxide (carboxyhemoglobin), thiocyanate ion, nicotine, and cotinine.[15
] A general consensus is that cotinine has the prerequisites of specificity, retention time in the body, and detectable concentration levels that make it the analyte of choice for quantifying tobacco smoke exposure.[16
] At present, cotinine is generally regarded as the best marker for monitoring tobacco exposure in either actively or passively exposed individuals. Moreover, cotinine has a much longer half-life of 18-20 h, making it more appropriate for use as an exposure marker.[15
] In studying the long-term effects of tobacco smoke exposure, cotinine levels may represent an alternative measure to complement, confirm, or better quantify self-reported smoking status.[17
] However, few studies have demonstrated an association between cotinine level in body fluids and periodontitis.[7
] Hence, in our study, cotinine levels were assessed.
Noninvasive samples, like saliva, are of particular importance in field settings. Saliva and blood cotinine levels are highly correlated, with a ratio of 1.1-1.4 for saliva to blood.[18
] An investigation by Bernert et al
] reported that the serum levels of cotinine were more closely correlated with unstimulated saliva (> by 4%) than with stimulated saliva (> by 41%). Hence, unstimulated salivary cotinine levels were assessed in the current study.
Cotinine has been measured in the biologic matrices using various methods like chromatography, colorimetry, raidoimmunoassay, ELISA, etc.[19
] ELISA with monoclonal antibodies has been proven useful in detecting cotinine in saliva.[20
] Studies of ELISA tests for urine cotinine showed almost total agreement with the confirmatory tests like gas chromatography.[21
] The NicAlert cotinine test strips (NCTS) used in this study contain cotinine-specific monoclonal antibodies and is an immunochromatographic strip that works on the principle of ELISA. It is designed to provide a semi-quantitative estimate and can be assessed conveniently by non-specialists, based solely on visual inspection. Studies by Fiona Cooke et al
] have shown that NCTS are a valid alternative to the more expensive and time-consuming gas chromatographic tests when testing saliva to verify tobacco smoke exposure. NCTS detect exposure to nicotine from all sources. NCTS have a specificity of 95%, sensitivity of 93%, positive predictive value of 95%, and a negative predictive value of 93%.
On evaluation of gingivitis and bleeding on probing, in smokers and non-smokers, most investigations have found that smokers had less bleeding on provocation than non-smokers.[23
] GI was higher in Group A than in Group B, and the difference was found to be statistically significant (P
=0.016). These findings are in consistence with the data of Newbrun et al
] The mean GBI was higher in Group A than in Group B and the difference was statistically significant (P
<0.001). These findings are also in consistence with the report of Newbrun et al
] Decreased gingival bleeding in smokers has been explained as being due to nicotine, which causes vasoconstriction of peripheral blood vessels such as in forearm, skin, and hands.[24
] Lang et al
] demonstrated that the absence of bleeding on probing was an indicator of periodontal stability. However, the lack of bleeding on probing in smokers with advanced periodontal disease represents a false-negative predictor, thus making the presently accepted clinical significance of bleeding on probing of uncertain value in smokers.[24
One of the variables commonly associated with prevalence and severity of periodontitis is plaque. In our study, there was no significant difference in PI between the two groups. These results are in consistence with the findings of Bastian and Waite.[26
] This implies that the harmful effects of smoking on periodontal health may not be associated with plaque accumulation and poor oral hygiene.[27
PPD and CAL estimate the degree of periodontal destruction, and therefore are measures of periodontal morbidity. Further, as these measures are normally found from a large number of single measurements in the individual, they must be considered to provide robust and reliable data.[28
] In the present study, mean±SD for PPD was 5.09±0.55 mm for Group B and 4.03±1.13 mm for Group A, and mean±SD for CAL was 6.03±1.31 mm for Group B and 4.49±0.97 mm for Group A. They were found to be significantly more in Group B than in Group A, in spite of the plaque scores showing no significant statistical difference. Similar findings have been reported in studies by Bergstrom et al
] These findings which were independent of plaque levels suggest that the effect of tobacco smoke exposure on periodontal conditions may be direct rather than being related to plaque infection.[27
In general, the reason attributed to the increased PPD and CAL in patients exposed to tobacco smoke is twofold. Both bacterial flora and host take part in the pathogenesis of periodontal diseases, and since no difference has been found in the periodontal pathogens between smokers and non-smokers,[27
] it would appear that the deleterious effects of tobacco on the host occur through two mechanisms. On one hand, it systemically causes alteration of the immune response, and on the other hand, it acts locally through release of cytotoxic metabolites and vasoactive substances. These are produced by the combustion of tobacco and in turn affect the fibroblasts and vascular response.[30
In the present study, GR was significantly more in Group B than in Group A, with P
<0.0001. These results are in agreement with the results of Martinez Canut et al
] and Gunsolley et al
] who have reported that GR was twice as severe in smokers as in non-smokers. Recession in smokers could be due to vasoconstriction and less inflammatory response caused by nicotine.[24
Our study also shows that Group B has significantly higher levels of salivary cotinine when compared to those of Group A. On correlation of periodontal parameters with those of salivary cotinine among Group B subjects, it was found that GI (P
=0.019), PI (P
=0.002), GBI (P
<0.001), PPD (P
<0.001), CAL (P
=0.027) and GR (P
=0.018) positively correlated with cotinine. This shows that as the salivary cotinine levels increased, the severity of periodontal parameters also increased. Tobacco smoke interacts with and compounds the effects of various systemic conditions, resulting in greater disease severity. These results are in consistence with the results of Gonzalez et al
] This finding also establishes a quantitative direct association between the level of tobacco smoke exposure and severity of periodontitis.
Our results show that categorization of subjects as smokers and non-smokers may not be sufficient to evaluate the role of smoking in the severity of periodontal disease. This is because smokers represent a highly heterogeneous (as they show variations in the types and methods of tobacco exposure, rate of metabolism, etc.) group of subjects. Therefore, a quantitative and more objective method to describe such a group would provide a better analytical tool to evaluate the association between tobacco smoke exposure and periodontal disease. On the other hand, biochemical markers are difficult to estimate and are not dependent on social pressures, recollection, or brand of tobacco used.[17
Our data provide evidence to show that the use of cotinine levels is an objective, reliable, and quantitative method for measuring tobacco use. Our findings also confirm the relation between tobacco smoke exposure and periodontal disease, and establish a quantitative direct association between the level of tobacco smoke exposure (as determined by salivary cotinine) and severity of periodontal disease.
The findings indicate that NCTS are a valid alternative to the more expensive, laborious, and time-consuming gas chromatographic studies. NCTS also have the potential for use in large population-based trials, for evaluating the effectiveness of cessation programs, and in population prevalence studies. Immediate and personalized feedback from a point-of-care test such as NCTS improves compliance and also improves quit rates. It also helps in reinforcing cessation of smoking.[22
The most important limitation of the present study is its cross-sectional design, as all information pertaining to periodontal disease and tobacco smoke exposure were collected simultaneously. A single spot evaluation of cotinine level may not reflect its long-term average, which may attenuate associations with self-reported measure of exposure to smoke.[33
] Instances where non-smokers can test positive for cotinine and come under Group B include environmental tobacco smoke (ETS) exposure, passive smoking, dietary factors, etc.[17
] In addition, individual metabolism, rate of absorption, time of smoking, and smoking habits, as well as ethnic differences,[34
] all play a role in the estimation of tobacco exposure. Also, the sample included only males, and hence the results cannot be generalized. Longitudinal studies involving larger population and evaluation of more specific markers such as anabasine and anatabine are required.