Oral mucosal lesions found in smokeless tobacco users

The risk for oral mucosal lesions associated with use of smokeless tobacco among 1,109 professional baseball players during spring training in 1988 was investigated. Leukoplakia was very strongly associated with use of smokeless tobacco in this population of healthy young men. Of the 423 current smokeless tobacco users, 196 had leukoplakia compared to seven of the 493 nonusers (OR = 60.0, 95% CI = 40.5-88.8). The amount of smokeless tobacco used (in hours per day that smokeless tobacco was held in the mouth), recency of smokeless tobacco use (hours since last use), type (snuff versus chewing tobacco), and brand of snuff used were significantly associated with risk for leukoplakic lesions among smokeless tobacco users. Ninety-eight leukoplakic areas in 92 subjects were biopsied and examined microscopically. All lesions were benign, but one specimen had mild epithelial dysplasia. The long-term significance of leukoplakia in smokeless tobacco users and their relation to oral cancer is not clear.     

Oral health effects of smokeless tobacco use in Navajo Indian adolescents

Recent reports have suggested that the use of smokeless tobacco is increasing in adolescents, and is particularly high in Native Americans, causing concern about possible effects on oral health. In this study, 226 Navajo Indians, aged 14-19, were interviewed regarding their use of smokeless tobacco (ST), cigarettes, and alcohol. Midbuccal and mesiobuccal sites on all fully erupted permanent teeth (excluding third molars) were examined for the presence of gingival bleeding, gingival recession, calculus, and loss of periodontal attachment. The oral mucosa was examined for evidence of leukoplakia. 64.2% (145) of the subjects (75.4% of the boys and 49.0% of the girls) were users of ST. Of these, over 95% used snuff alone or in combination with chewing tobacco. 55.9% used ST one or more days per week. 52.2% consumed alcohol, usually beer or wine, and 54.0% smoked cigarettes. 25.5% (37) of the users and 3.7% (3) of the non-users had leukoplakia. The duration (in years) and frequency of ST use (days per week) were highly significant risk factors associated with leukoplakia. However, the concomitant use of alcohol or cigarettes did not appear to increase the prevalence of these lesions. No consistent relationship was observed between the use of ST and gingival bleeding, calculus, gingival recession, or attachment loss, either when comparing users to non-users or when comparing the segment where the tobacco quid was habitually placed to a within-subject control segment. In view of these results, there is little doubt that smokeless tobacco is significantly related to the etiology of leukoplakia. As some evidence exists that smokeless tobacco use is a significant risk factor associated with oral carcinoma, intervention programs to discourage the use of smokeless tobacco by adolescents should be a public health priority.     

Oral leukoplakia status six weeks after cessation of smokeless tobacco use.

BACKGROUND: This study evaluated the prevalence and risk of developing oral leukoplakia in smokeless tobacco, or ST, users and the response of these leukoplakic lesions after six weeks of involuntary tobacco cessation. U.S. Air Force basic military training provided an environment of a mandatorily tobacco-free setting. METHODS: The authors designed their investigation as a case control study with a nested cohort study. The principal investigator (G.C.M.) conducted oral examinations of 3,051 male U.S. Air Force basic military trainees. Using a questionnaire, he obtained detailed information concerning subjects' ST use patterns before basic training. Clinical photos were taken of all leukoplakic lesions identified in ST users at the initial examination and again six weeks later. RESULTS: Of the 3,051 male trainees examined (mean age = 19.5 years), 9.9 percent (302/3,051) were identified as current ST users. Among current ST users, 39.4 percent (119/302) had leukoplakia vs. 1.5 percent (42/2,749) of nonusers of ST (odds ratio = 41.9, 95 percent confidence interval = 28.1-62.6). At the end of the involuntary cessation of tobacco use, 97.5 percent of these leukoplakic lesions had complete clinical resolution. The type of ST used (snuff vs. chewing tobacco), amount used (cans or pouches per day), length of use (months), number of days since last use and brand of snuff used were significantly associated with the risk of developing leukoplakic lesions among ST users. CONCLUSIONS: The important new finding from this investigation is that if a young, otherwise healthy man with leukoplakic lesions stops using tobacco for six weeks, most of his leukoplakic lesions will resolve clinically. Use of ST, specifically snuff, is strongly associated with development of oral leukoplakia in young adult men. CLINICAL IMPLICATIONS: The clinician can use these findings in deciding when to perform biopsies on leukoplakic lesions associated with ST use. This information also should be used to assist ST users in quitting this addictive behavior.     

Oral leukoplakia and adolescent smokeless tobacco use

The recent increase in smokeless tobacco (ST) use has prompted investigators to assess the health effects of ST use. This study attempted to evaluate the prevalence of oral leukoplakia among adolescent users and to determine factors associated with its presence. During their annual physical examination, 1116 teenaged football players (567 black, 546 white) answered a 34-question survey and received an oral screening examination. Results indicated that 0.5% of nonusers, 1.5% of previous users, and 13% of current users had clinically evident oral leukoplakia. Factors statistically associated with higher leukoplakia rates included history of ST use, regular ST use, years of ST use, and the weekly quantity consumed. Factors not associated included use of alcohol, use of cigarettes, type of ST used, and hours of ST use. One brand of snuff was found to be associated with a relative risk of leukoplakia higher than that of another brand of snuff. Overall, in ST users oral leukoplakia was six times more likely to develop than in nonusers. Earlier ages of ST use may lead to greater periods of use (in years) and to possible increases in deleterious long-term health effects in current adolescents.     

Smokeless tobacco and severe active periodontal disease, NHANES III

Whereas smoking is a major risk factor for periodontal disease, the role of smokeless tobacco is unclear. The purpose of this US population-based study of 12,932 adults participating in the Third National Health and Nutrition Examination Survey was to evaluate the association between smokeless tobacco use and severe active periodontal disease. Univariable and multivariable logistic regression modeling quantified the associations between tobacco use and severe active periodontal disease. All adults and never-smokers who currently used smokeless tobacco were twice as likely to have severe active periodontal disease at any site [respective odds ratios (OR(Adj)) and 95% confidence intervals: OR(Adj) = 2.1; 1.2-3.7 and OR(Adj) = 2.1; 1.0-4.4] or restricted to any interproximal site [respective OR(Adj) = 2.1; 1.0-4.2 and OR(Adj) = 2.3; 0.9-6.3], simultaneously adjusted for smoking, age, race, gender, diabetes, and having a dental visit in the past year. These results indicate that smokeless tobacco may also be an important risk factor for severe active periodontal disease.     

Oral pre-cancer and the associated risk factors among industrial workers in Japan''s overseas enterprises in the UK

BACKGROUND: Screening at industries has been advocated as a method of early detection for cancer. This study describes the prevalence of oral pre-cancerous lesions and other mucosal diseases following oral mucosal screening, and associated risk factors among Japanese industrial workers in the UK. METHODS: Oral mucosal screening was by invitation at 51 industrial locations in the UK. A self-administered questionnaire was used to record socio-behavioural factors and frequency of daily intake of fruits and vegetables. RESULTS: Four hundred and eighty-four subjects attended for oral mucosal screening (mean age 39.9 +/- 8.3 years) and their mean period of residence in UK was 5.3 +/- 4.5 years. 63.4% examined were male. 31.3% of males and 26.6% of females smoked daily. The gender differences were striking compared with Japan's national rates. A higher proportion of managerial staff was regular heavy (20+ per day) smokers. The intake of more than five portions per day of vegetables and/or fruits during the weekend was significantly higher in females than in males (P = 0.022). One hundred and six subjects (22%) were detected with oral mucosal lesions, including 16 leukoplakia lesions (3.3%) and three with oral lichen planus (1%). The rate of positive detections was higher in managers (7.5%). Odds ratios were estimated by socio-behavioural variables. Among subjects positive for oral leukoplakia, managers accounted for 68.8% (OR 5.26; 95% CI, 1.24-22.29). 87.5% of subjects detected with oral leukoplakia smoked daily and had done so for the past 10 years (OR 28.40; 95% CI, 5.63-143.28). Though regular alcohol drinking was a common feature among male leukoplakia cases, heavy alcohol misuse was not encountered. None reported an intake of five or more portions of fruits or vegetables. CONCLUSIONS: The Japanese nationals working in managerial positions in the UK and daily regular smokers in the industries visited were found to be at a high risk of oral pre-cancer. Regular dental/oral check up and tobacco education programmes are encouraged for oral cancer/pre-cancer control in industrial settings.     

The association between oral leukoplakia and use of tobacco, alcohol and that based on relative risks assessment in Kenya

A case-control study was conducted to determine the significance of tobacco, alcohol and Khat (Catlia edulis) chewing habits in the development of oral leukoplakia among Kenyans aged 15 yr and over. In a house-to-house survey, 85 cases and 141 controls matched for sex, age and cluster origin was identified and compared for these risk factors. Smoking unprocessed tobacco (Kiraiku) with a relative risk (RR) of 10.0 (95% confidence interval (CI)=2.9-38.4) and smoking cigarettes (RR = 8.4; 95% CI = 4.1-17.4) were the most significant factors. While the RR associated with smoking cigarettes alone was 4.5 (95% CI= 1.9-10.8), smoking of both products (RR= 15.2) suggested probable synergy or additive effects. Oral leukoplakia in 18 cases could not be attributed to smoking tobacco. Commercial beer, wines and spirits were relatively weak, but statistically significant, risk factors. Traditional beer, khat and chilies were not significantly associated with oral leukoplakia.     

Implications of smokeless tobacco use in athletes

After almost falling into obscurity, smokeless tobacco use began to increase almost simultaneously with the reduction in cigarette smoking that was influenced by the Surgeon General's first Report on Smoking and Health in 1964. Consumption of smokeless tobacco was stimulated by media promotion using professional athletes; and large numbers of impressionable male teenagers, assuming that it was a safe alternative to smoking, began to use this product, particularly snuff. The nicotine content of smokeless tobacco is equivalent to that of cigarettes and, therefore, will produce habituation and addiction. It may also expose the long-term user to a number of adverse physiologic effects on the cardiovascular system that are similar to those attributed to smoking. Smokeless tobacco contains N-nitrosamines that have a potential carcinogenic effect on the tissues with which they come into contact in the oral cavity. A hazard of short-term use is irreversible gingival recession. The contact of snuff with the oral mucosa can produce leukoplakia that is readily visible and will alert the dentist. The dental professional team must actively strive to prevent initiation of smokeless tobacco use and assist with cessation of this habit.     

Histopathology of smokeless tobacco lesions in professional baseball players. Associations with different types of tobacco.

We examined 142 biopsy specimens of smokeless tobacco-associated oral mucosal lesions from 133 professional baseball players. Four types of epithelial change were observed in the specimens: hyperparakeratosis, hyperorthokeratosis, pale surface staining, and basal cell hyperplasia. These types of epithelial change were associated with the type of smokeless tobacco used (snuff or chewing tobacco) but not with the duration (years) or amount (hours per day) of use. The thickness of hyperkeratosis in a specimen correlated directly with the amount of smokeless tobacco use. The use of snuff was more frequently associated with development of oral mucosal lesions than was the use of chewing tobacco, and snuff appeared to cause a greater variety and severity of epithelial change than did chewing tobacco.     

Periodontal conditions in male adolescents using smokeless tobacco (moist snuff)

Aim: The aim of this study was to evaluate the potential association of the use of smokeless tobacco (moist snuff) on the periodontal conditions of adolescents. Material and methods: A subject sample of one hundred and three 19‐year‐old male individuals (33 snuff users, 70 controls) living in Göteborg, Sweden, were clinically examined with regard to oral hygiene, gingivitis, probing pocket depth (PPD), clinical attachment loss (CAL) and gingival recession. Bitewing radiographs were obtained for assessments of alveolar bone level. Information about tobacco and oral hygiene habits was obtained by a structured questionnaire. Student 's t‐test, χ²‐test and logistic regression analysis were used for statistical analysis. Results: The mean plaque and gingivitis scores in snuff‐users were 59% (SD 21.0) and 47% (18.6), respectively, and in controls 64% (22.4) and 50% (18.3), respectively. The average PPD and CAL in snuff‐users amounted to 2.3 mm (0.3) and 0.2 mm (0.1), respectively, and in controls 2.4 mm (0.3) and 0.1 mm (0.1) (p>0.05), respectively. The mean bone level was 1.3 mm (0.2) in both groups. The prevalence of subjects showing recession was 42% among snuff‐users and 17% among controls (p=0.006). In snuff users, an average of 4% (0.9) of the teeth showed recession, compared with 1% (0.3) in controls (p<0.001). Limiting the analysis to the maxillary anterior tooth region, 33% of the snuff‐users and 10% of the controls presented recessions (p=0.002). The use of snuff entailed an OR=5.1 to have gingival recessions. Conclusion: In the present population sample of adolescents, the use of smokeless tobacco (moist snuff) was not associated with the presence of periodontal disease except for a significantly high prevalence of gingival recessions.     

Incidence rates for oral leukoplakia and lichen planus in a Japanese population

BACKGROUND: Data on the incidence rates of potentially malignant diseases of the oral cavity in different populations is meagre. This is the first study to report on the age-specific incidence of oral leukoplakia and oral lichen planus from an industrialized country. METHODS: Annual screening for oral cancer and pre-cancer was undertaken in Municipal Health Centres in Tokoname city, Japan from 1995 to 1998. A total of 9536 volunteers aged 40-95 years participated in this programme. A cohort of 6340 (67%) subjects attended annual mouth examinations following a negative screen result at entry, allowing 13 072 person-years of observations. Some associated risk factors (tobacco and alcohol misuse) and health-related variables were also evaluated. RESULTS: Over a 4-year follow-up period, 18 new oral leukoplakias (all homogenous; 11 idiopathic and seven tobacco-associated) and 24 oral lichen planus (22 reticular, one erythematous and one ulcerative) were detected at screening and confirmed by re-examination at specialist units. The age-adjusted incidence rate for leukoplakia was 409.2 (95% CI: 90.6-727.9) in male and 70.0 (95% CI: 17.9-121.8) in female per 100,000 person-years observations. For lichen planus, the corresponding rates were 59.7 (95% CI: 7.4-112.1) and 188.0 (95% CI: 96.0-280.1). The age-adjusted incidence rate for tobacco-associated leukoplakia in males was almost 12 times compared with female (560.3 vs. 45.2 per 100,000). Age-specific incidence rates for oral leukoplakia varied by age groups. New oral leukoplakias were more prevalent on gingival/alveolar ridge (33.3%) than in other oral sites, and lichen planus at buccal site (33.3%). Prevalence of smoking habits among those positive for leukoplakia (38.9%) was higher compared with the screen-negatives (26.4%) but these differences did not reach statistical significance (P = 0.232). Regular drinking was not related to occurrence of either oral leukoplakia or oral lichen planus. In cases with diabetes mellitus, relative risk for oral lichen planus adjusted by logistic regression was 6.4 (95% CI: 2.4-17.6), suggesting an association. CONCLUSIONS: The reported incidence rates for oral leukoplakia in this Japanese population are somewhat higher to those reported from India, the risk habits of the two groups being markedly different. The reported rates for oral leukoplakia and lichen planus allow estimation of service needs in specialist oral medicine clinics and for the training of primary care dentists. A high incidence of idiopathic leukoplakia found in this study raises challenges to the strategy of screening high-risk populations aimed at conserving resources.     

Nass use,cigarette smoking,alcohol consumption and risk of oral and oesophageal precancer

In a cross sectional study, conducted in Uzbekistan, an area with a high incidence of oral and oesophageal cancer, 1569 men were interviewed regarding use of nass quid, cigarette smoking and alcohol drinking. All subjects in the study had an oral examination, and oesophagoscopy was performed in 1344 men. Nass use and cigarette smoking emerged as independent risk factors for oral leukoplakia. The prevalence odds ratio (OR) for life-time nass intake equivalent rose from 1.0 in never-users to 5.17 [95% confidence interval (CI), 3.10–8.61] in the highest category; for total pack-years of cigarettes smoked the risk rose from 1.0 in never-smokers to 10.03 (95% CI, 4.9–20.6) in the highest category. There was a significant trend in risk (P < 0.001), for both factors. In the group with oral leukoplakia, the effect of nass use and cigarette smoking appeared to be additive. Cigarette smoking was also found to be an independent risk factor for oesophageal lesions and was significantly associated with chronic oesophagitis. The risk of chronic oesophagitis in the group with the highest pack-years of cigarettes smoked was approximately double that among non-smokers [Odds ratio (OR) = 2.47; 95% CI 1.34–4.56]. There was a weak association between nass use and oesophageal pathology: the highest life-time intake equivalent was associated with an OR of 1.56 (95% CI 1.09–2.23). Alcohol intake was not found to be independently associated with the presence of oral and oesophageal precancerous lesions.     

Smokeless tobacco use among men in the United States, 2000 and 2005

Background:  Compared with smoking, there is much less information about smokeless tobacco (ST) use in the United States. The purpose of this study is to characterize and compare ST use among American men in 2000 and 2005.
Methods:  We used US National Health Interview Surveys from 2000 and 2005 to estimate the prevalence of ST use, describe the demographic and socioeconomic profile of ST users and evaluate ST use according to product type and with respect to smoking.
Results:  The prevalence of ST use among American men was 4.4% in 2000 and 4.3% in 2005. Almost all ST users were white, about half were 25–44 years old and 80% lived in the South or Midwest, commonly in small metropolitan and rural areas. Educational and income levels of ST users were lower than those of never users of tobacco. One-third of ST users also smoked; cigarette consumption was lower among dual users than among exclusive smokers. In 2005, 1.3 million current ST users were former smokers but 3.2 million smokers were former ST users. ST users were evenly distributed between snuff (43%) and chewing tobacco (44%) in 2000 and 13% used both products. By 2005 snuff use was clearly dominant.
Conclusions:  The prevalence of ST use among men is low but stable; dual use of cigarettes and ST is common, and snuff has become the dominant ST product.     

Tobacco usage in relation to the anatomical site of oral leukoplakia

OBJECTIVE: Tobacco usage is the most important known aetiological factor in the development of oral leukoplakia. The purpose of this study was to investigate the possible relation of tobacco usage to the anatomical site of the leukoplakia. SUBJECTS AND METHODS: Clinical data regarding tobacco usage and localisation of leukoplakia obtained from 166 patients with oral leukoplakia. RESULTS: Leukoplakias in the floor of mouth appeared to be statistically significantly more often present in smokers than in non-smokers, compared to all other oral sites (P < 0.001; OR = 8.47 and 18.13 for men and women, respectively). On the contrary, leukoplakias on the borders of the tongue were statistically significantly more common among non-smokers, than smokers, compared to all other oral sites (P < 0.001; OR = 0.22 and 0.12 for men and women, respectively). CONCLUSION: The present study suggests that the influence of tobacco on the development of leukoplakia varies by anatomical site.     

Cigarette smoking,snuff use and alcohol drinking: coexisting risk behaviours for oral health in young males

OBJECTIVES: The use of oral moist snuff (snus) is widespread among Swedish men, but little is known about the use in adolescents. The aim of this study was to describe patterns of snuff dipping, smoking and alcohol drinking in a sample (n = 6287) of 9th grade male students participating in a census survey in the Stockholm region. RESULTS: About 20% of the sample reported use of snus, and more than two-thirds of snus users were also cigarette smokers. Among current nonusers of tobacco (66% of the sample), 14% reported frequent binge drinking, in contrast to 49% among current exclusive cigarette smokers, 60% among exclusive snus users and 69% among users of both cigarettes and snus. The estimated mean annual consumption of alcohol was 5-10 times higher among tobacco users than among nonusers, with users of snus consuming more alcohol than smokers. Compared to non- or minimal drinkers, heavy alcohol drinkers had a disproportionately higher risk to report snus use, after adjustment for smoking behaviour (OR = 16.7, 95% CI 12.9-21.7). When the analysis was restricted to users of only one type of tobacco, heavy drinkers were twice as likely to report snus, rather than cigarette, use. CONCLUSIONS: Both tobacco use and alcohol drinking have been independently associated with a variety of pathological oral conditions in adults. These behaviours coexist in early adolescence. Their effect on oral health need to be investigated in prospective studies and should be of concern to the dental professionals.     

Self-awareness of premalignant oral lesions among veterans attending six U.S. Veterans Affairs Medical Centers

Early identification is key to reducing the morbidity and mortality of oropharyngeal cancer. This study identified factors associated with self-awareness among patients newly diagnosed with a premalignant oral lesion. Data describing sociodemographics, medical/dental histories, tobacco/alcohol use and oral health were obtained by questionnaire and clinical examination of 73 veterans at six U.S. Veterans Affairs Medical Centers. Lesion types included homogenous and non-homogenous leukoplakia, smokeless tobacco lesion (STL), papilloma, lichen planus and erythroplakia. Prior to diagnosis, 29 subjects (39.7%) were unaware of their lesion. In bivariate analyses, lesion self-awareness was associated with anatomic location, multifocal/generalized appearance, pain, oral sores, and cigar use (p<0.05). Awareness varied with lesion diagnosis and was more likely with STL and less likely with homogenous leukoplakia (p<0.05). In multivariate analyses, awareness was predicted by the presence of a lesion on easily visible mucosa (adjusted odds ratio, OR=11.2) and a history of mouth sores (OR=11.2). These findings identified marked variations in patient self-awareness of oral premalignant conditions.     

Dietary factors in oral leukoplakia and submucous fibrosis in a population-based case control study in Gujarat, India

OBJECTIVES: To investigate the relationship of specific nutrients and food items with oral precancerous lesions among tobacco users.
DESIGN: A population-based case-control study. SETTING: Villages in Palitana taluk of Bhavnagar district, Gujarat, India.
SUBJECTS AND METHODS: An interviewer-administered food frequency questionnaire, developed and validated for this population, was used to estimate nutrient intake in blinded, house-to-house interviews. Among 5018 male tobacco users, 318 were diagnosed as cases. An equal number of controls matched on age (±5 years), sex, village, and use of tobacco were selected.
MAIN OUTCOME MEASURES: Odds ratios (OR) from multiple logistic regression analysis controlling for relevant variables (type of tobacco use and economic status).
RESULTS: A protective effect of fibre was observed for both oral submucous fibrosis (OSF) and leukoplakia, with 10% reduction in risk per g day^-1 ( P < 0.05). Ascorbic acid appeared to be protective against leukoplakia with the halving of risk in the two highest quartiles of intake (versus the lowest quartile: OR = 0.46 and 0.44, respectively; P < 0.10). A protective effect of tomato consumption was observed in leukoplakia and a suggestion of a protective effect of wheat in OSF.
CONCLUSION: In addition to tobacco use, intake of specific nutrients may have a role in the development of oral precancerous lesions.     

Oral lesions of 500 habitual psychoactive substance users in Chennai, India

The aim of this study was to ascertain the prevalence of oral lesions among 500 psychoactive substance users in a hospital-based population. The study group consisted of 500 consecutive patients attending TTK Hospital, a non-governmental organisation involved in rehabilitation of substance users. Patient history was recorded in a pre-determined format and clinical findings were recorded by a trained physician and dental surgeons. Psychoactive substances used by the patients were alcohol (97%), tobacco (72%), arecanut (57.2%), narcotics (6.8%), cannabis (3.2%) and benzodiazipines (1.8%). Ninety-one percent of patients had one or more oral lesions: dental caries (39%), gingivitis (37.6%), extrinsic stains (24%), oral submucous fibrosis (OSF) (8%), periodontitis (7.4%), leukoplakia (6.6%), melanosis (5.2%), nicotina palatini (2.2%) and erythroplakia (0.6%). For OSF, those using arecanut and alcohol had an odds ratio (OR) of 2.4 [95% confidence intervals (CI) 1.23-4.69, P=0.009], smokers using arecanut products and alcohol had an OR of 3.07 (95% CI 1.59-5.91, P=0.000), and smokers who chewed arecanut products and used drugs had an OR of 23.1 (95% CI 2.05-260, P=0.001) compared with the general population. Those who smoked and used alcohol, arecanut and drugs had a 20.67-fold higher risk of developing leukoplakia compared with those who did not engage in these habits. In conclusion, 91% of patients had one or more oral lesions that needed dental treatment, and most patients were not aware of their oral lesions. The high prevalence of OSF and leukoplakia in substance abusers compared with the general population emphasises the need for regular dental assessments in these patients.     

Influence of dose and cessation of kiraiku, cigarettes and alcohol use on the risk of developing oral leukoplakia

Data from a previously-reported study of oral leukoplakia-associated risk factors in a Kenyan population were further analyzed to determine the influence of dose and cessation. Specifically, risk analysis was made with respect to kiraiku (a traditional Kenyan type of home-made, hand-rolled tobacco product), cigarettes, and commercial beer. The relative risk (RR) of oral leukoplakia among those who smoked 10 cigarettes was 14.7. as compared to 6.7 among those who smoked 10 cigarettes. With regard to duration, the RR increased from 7.4 in those who had smoked for 15 years to 10.8 in those who had smoked for 30 years. Among those who had quit smoking, RR value was significant only in ex-kiraiku smokers (RR=4.9. 95% confidence interval (Cl)=2.3–20.4) and was dependent on both the duration of smoking and duration since quitting. For commercial beer, the RR was significant in consumers of >10 bottles per drinking day (RR=4.2. 95% Cl=1.0–3.9) and in those whose who drank for 5 days per month (RR=3.8, 95% Cl=1.0–15.1). Duration of beer consumption did not significantly influence the RR of oral leukoplakia. The RR in ex-beer consumers was not statistically significant. These findings suggest a dose-dependent association between oral leukoplakia and the use of tobacco and alcohol, in which the number of cigarettes smoked, the quantity of beer consumed, and the frequency of consumption were more important than the duration of use of these products. Furthermore, while oral leukoplakia due to cigarette smoking may regress completely, those due to kiraiku may persist for more than 10 years after cessation of these habits