Evidence Based Practice in Dentistry

It is well known that smoking contributes to the development of lung cancer and cardiovascular disease, and there is weighty evidence that it has a considerable influence on oral health. Smoking has many negative effects on the mouth, including staining of teeth and dental restorations, reduction of the ability to smell and taste, and the development of oral diseases such as smoker’s palate, smoker’s melanosis, coated tongue, and, possibly, oral candidosis and dental caries, periodontal disease, implant failure, oral precancer and cancer. From a qualitative point of view the latter is obviously the most serious tobacco-related effect in the mouth. Quantitatively, however, importance has been attached to periodontitis, which affects a large proportion of the population, and during recent years more attention has been given to implant survival rates. Dentists have an important role to play in preventing the harmful effects of smoking in the mouth, and consequently smoking counselling should be as much a part of the dentist’s job as plaque control and dietary advice. Copyright © 2003 S. Karger AG, Basel Introduction The role of smoking in the development of lung cancer and cardiovascular disease is well known. Since the initial suspicion of the relation between smoking and lung cancer in the 1950s [1], the famous study of British doctors, among many others, established a causal relationship between smoking and death from major diseases, including cancer of the lung and other types of cancer, respiratory diseases such as obstructive pulmonary disease, vascular diseases, and peptic ulcers [2, 3]. As part of the healthcare system dentists have an obvious interest in these diseases, but it could be argued that other members of the health system have more important roles to play as far as these and many other smoking-related diseases are concerned. However, since there is weighty evidence that smoking has a considerable influence on oral health, it is not unreasonable that dentists should play an important role in preventing the harmful effects of smoking on human tissues in general and oral tissues in particular. The oral effects of smoking range from harmless stains of teeth and dental restorations to serious diseases such as oral cancer (table 1). From a qualitative point of view the latter, obviously, is of utmost importance, since the fiveyear relative survival rate for intraoral cancer is about 50% [4]. Quantitatively, however, importance has been attached to other diseases or issues related to smoking such as periodontitis, which affects a large proportion of D ow nl oa de d by : 54 .7 0. 40 .1 1 11 /2 7/ 20 17 5 :2 1: 04 A M Tobacco and Oral Diseases Med Princ Pract 2003;12(suppl 1):22–32 23 Table 1. Effects of smoking on the mouth Discolorations of teeth and restorations Coated/hairy tongue Reduced ability to taste and smell Smokers’ melanosis Smokers’ palate Dental caries Oral candidosis Increased failure rates for dental implants Periodontal disease Smokers’ white patch/leukoplakia Oral cancer Table 2. Oral cancer: age-standardized (world population) incidence rates per 100,000 [9] Population Men Women Denmark 6.5 2.1 UK: England and Wales 3.2 1.3 France: Bas-Rhin 21.0 2.1 US: Iowa 8.2 2.6 China: Shanghai 1.8 1.3 Hong Kong 4.1 2.0 Japan: Osaka 3.0 1.3 Thailand: Chang Mai 4.7 2.5 India: Trivandum 8.2 2.5 the population, or implant survival, which has come into focus more and more during recent years. There are several general reviews and informational booklets for dentists on the effects of smoking in the mouth [5, 6]. Within the European Union (EU) the Working Group on Tobacco and Oral Health distributed informational material to dentists in EU countries and published a comprehensive review from a consensus meeting organized by the Working Group [7]. Part of this consensus paper has been cited at www.whocollab.od.mah.se/ expl/tobacco.html. The aim of this article is to provide a concise, didactic update on the effects of smoking on oral health, with an emphasis on recent evidence and achievements. When possible, reference is given to detailed and comprehensive reviews of available literature in the field. Also provided are practical and realistic guidelines for dentists to help their patients in their efforts to quit smoking. Oral Cancer The majority of oral cancers, constituting 2–3% of all cancers worldwide [8], are squamous cell carcinomas developing from the mucosal surface epithelium (fig. 1) [4]. Oral cancer affects mostly middle-aged or elderly people and is more common in men than in women [8]. The incidence varies worldwide (table 2) [9]. In this report, oral cancer is used synonymously with squamous cell carcinoma originating from the mucosal surface epithelium. Numerous studies in various populations have shown that smokers have a substantially higher risk of oral cancer than nonsmokers [10–16]. The studies are primarily concerned with the use of cigarettes, but pipe and cigars seem to carry an equal or even higher risk [13, 16]. There is a clear dose-response relationship, with risk decreasing after smoking cessation. In some studies it was shown that 10 years after quitting, former smokers have the same risk of oral cancer as people who never smoked, whereas other studies show that the risk decreases dramatically but remains at a level somewhat higher than that found in people who never smoked [12, 17]. Ethnic differences in the incidence and mortality of oral cancer exist, but the information available is scarce [18, 19]. The relationship between the use of smokeless tobacco and oral cancer has been discussed at length. The apparent discrepancies between different researchers probably derive from the fact that there are great differences in habits and products around the world, which makes a general statement on this subject impossible. Snufff-habits as they appear in Scandinavia carry none or very low risks of oral cancer [20, 21], but the use of other types of smokeless tobacco in other parts of the world seems to pose a substantial cancer risk [22]. Although the underlying mechanisms are not known in detail, it is plausible that smoking could lead to cancer since carcinogens in tobacco smoke can induce changes in DNA. In recent years much attention has been given to smoking-related mutations in a tumor suppressor gene coding for the protein p53. This protein is important in regulating cell proliferation and has a role in the repair of DNA damage [23]. Mutations in the gene may lead to an accumulation of DNA damage in the cells, which may play an important role in the development of cancer. Many studies on the relationship between smoking and oral cancer have been appropriately controlled for various confounders such as diet (low intake of fresh fruit and vegetables increases the risk of developing oral cancer [24, 25]), social status, and, not the least important, alcohol abuse. Smoking and excessive alcohol intake synergistiD ow nl oa de d by : 54 .7 0. 40 .1 1 11 /2 7/ 20 17 5 :2 1: 04 A M 24 Med Princ Pract 2003;12(suppl 1):22–32 Reibel cally increase the risk of developing oral cancer [10, 12, 14]; it has been estimated that between 75 and 90% of all cases are explained by the combined effect of smoking and alcohol use. This could be because alcohol dissolves certain carcinogenic compounds in tobacco smoke and/or alcohol increases the permeability of the oral epithelium [26]. In Greece, where the incidence of oral cancer in general is low, a study showed a similar synergistic effect between tobacco and alcohol [27], and in a study on 300 patients at an addiction unit in Hungary, 8 oral carcinomas were diagnosed (2.7%, mean age 39 years) [28]. All of the 300 patients had a daily smoking and alcohol habit; about half of them smoked more than 20 cigarettes a day and consumed the equivalent of 2–3 liters of wine daily. Thus, screening of risk groups, defined primarily by tobacco and alcohol habits, seems well founded. There is overwhelming and consistent evidence that smoking causes oral cancer. A recent study, however, showed that only one third of patients who had undergone treatment for oral cancer [29]! Thus, the public needs to be informed of the risks, in particular during their visits to the dental office.