INTRODUCTION
Smoking significantly impacts human health, accounting for 24% and 7% of all deaths among men and women, respectively, in developed countries, and leading to an average life expectancy reduction of approximately 8 years1. In addition to reducing life expectancy, smoking has numerous other negative health effects, including systemic inflammatory responses2; osteoporotic fractures3; increased risks of lung, oral, laryngeal, bladder, renal, pancreatic, gastric, cervical, hepatic, penile, and colorectal cancers; and increased risks of coronary artery, cerebrovascular, and peripheral vascular diseases4. Additionally, smoking has a significant impact on oral health, with smokers experiencing dental pain, orofacial pain5, tooth loss, and periodontitis6,7. Given that permanent teeth do not regenerate once they have grown8, maintaining good oral health is of utmost importance9.
Prolonged exposure to smoking leads to an increase in the acidity of the saliva, reducing its buffering capacity and thereby hindering the natural cleansing process in the mouth. Consequently, excessive plaque build-up occurs, which increases the incidence of dental caries10. Furthermore, smoking stimulates the release of epinephrine and constricts peripheral blood vessels, reducing blood flow to the gums, and contributing to the development of periodontal disease11. Additionally, smoking impairs neutrophil function and reduces the serum antibody response against bacteria that cause periodontal disease, significantly affecting oral health12. Repeated exposure to electronic cigarettes can cause inflammation of oral epithelial cells and accelerate aging, thereby increasing the risk of oral diseases13. Therefore, evaluating the impact of e-cigarettes and dual smoking on oral health is essential. Although many existing studies have focused on regular cigarette smokers, research on the association between oral health and vaping, pack-years, and duration of smoking cessation in ex-smokers is lacking. Additionally, oral health symptoms, such as tooth loss, toothache, periodontitis, and chewing difficulties, have been examined14-17. However, as patients experiencing one oral health issue often tend to have other related problems, conducting a detailed analysis to account for overlapping cases of oral health issues is necessary.
Therefore, this study aimed to examine the association between smoking behavior and oral health problems in adults. Our findings offer a comprehensive understanding of the association between various smoking behaviors, such as smoking frequency/amount and cessation duration, and their specific associations with oral health. Additionally, this study aimed to contribute to the development of targeted interventions and strategies to improve oral health in both current and ex-smokers.
METHODS
Data and study population
This study analyzed a secondary dataset from the Korea National Health and Nutrition Examination Survey (KNHANES), spanning 3 years from 2019 to 2021, conducted by the Korea Centers for Disease Control and Prevention Agency18. The KNHANES is a statutory survey on health behaviors, prevalence of chronic diseases, and dietary and nutritional intake status of the population, conducted based on Article 16 of the National Health Promotion Act18. The purpose of the survey was to generate nationally representative and reliable statistics on the health status, health behaviors, and dietary and nutritional intake of the population, and to use these data as a basis for setting and evaluating the goals of the National Health Promotion Comprehensive Plan, developing health promotion programs, and informing health policies.
The KNHANES collects data through household member verification, health interview, health examination, and nutrition surveys. The sampling frame for the KNHANES is based on the most recent Population and Housing Census data available at the time of sample design, which allows for the extraction of a representative sample of the target population comprising all residents aged ≥1 year in the Republic of Korea. The household member verification survey is a preliminary survey conducted to identify all dwelling units and households within the selected sample areas, and to select households (and their members) to participate in the health interview, examination, and nutrition surveys. This survey updates information on the target areas and households since the construction of the sampling frame, enabling the selection of current survey participants based on the updated information. Household member verification survey data are also used to schedule visits to mobile examination centers (for the nutrition survey, household visits are conducted), distribute survey results, and calculate response rates and sampling weights18,19. The respondents completed the questionnaires, and all collected data were anonymized. Since the KNHANES adheres to the Declaration of Helsinki and offers publicly accessible data, ethical approval was not necessary.
Of the 21309 survey participants, those aged <19 years and those who did not participate in the KNHANES smoking questionnaire were excluded (n=3647). Participants with missing data were also excluded (n=3938). Consequently, a final sample of 13724 participants, including 6150 men and 7574 women, were analyzed (Figure 1).
Variables
The dependent variable was oral health problems, evaluated through self-reported questions. We considered individuals to have oral health problems if they had any one of toothache and chewing difficulties. Toothache was defined as pain, throbbing, or aching in the teeth over the past year, or pain in the teeth when consuming hot or cold beverages or foods. Chewing difficulties were defined as experiencing discomfort while chewing food due to issues with the teeth, dentures, gums, or other oral problems.
Individuals were classified as current smokers if they were currently smoking any of the following20-23: regular cigarettes, heated tobacco products, or electronic cigarettes. Ex-smokers were those who had smoked in the past, but did not smoke any of these products. Non-smokers were defined as those who had never smoked any of the aforementioned products. Also, current smokers were defined as regular cigarette smokers if they smoked only regular cigarettes; e-cigarette smokers, only vaping; and dual smokers, both types of cigarettes.
All analyses were conducted while controlling covariates, including demographic (age, region), socioeconomic (marital status, education level, household income, occupational classification), health-related (current alcohol consumption status, physical activity level, body mass index, diagnosis of hypertension or diabetes), and other factors (survey year). Covariates were selected based on biological plausibility, previous literature, and their potential to confound the association between smoking behavior and oral health problems.
Statistical analysis
Descriptive analysis was employed to examine the general characteristics of the sample population and reported as frequencies (n) and percentages (%). The chi-squared test was used to evaluate and compare the general characteristics of the study population. Subsequently, a multiple logistic regression analysis was performed to investigate the association between smoking behavior and oral health problems.
Subgroup analysis stratified occupation categories to demonstrate the association between the occupation of current smokers or ex-smokers and their oral health problems. Additionally, a subgroup analysis stratified by smoking type, cessation status, and pack-years was employed to elucidate the association between oral health problems and the type of cigarettes smoked, smoking cessation duration for ex-smokers, and smoking duration for current smokers. Finally, we performed an additional analysis by categorizing and examining each symptom of oral health problems in detail. This allowed us to conduct a more granular assessment of individual issues. Furthermore, a significant interaction effect was observed between sex and smoking status (p=0.0294), indicating that the association between smoking behavior and oral health problems differed by sex. Given this significant interaction, we conducted sex-stratified analyses to further explore these differences. In this study, all estimates were calculated using sample weighting procedures, with clusters and strata assigned to the participants. The results are presented as adjusted odds ratios (AORs) with 95% confidence intervals (CIs). Statistical significance was assessed using two-sided p-values, with a threshold of p<0.05. All analyses were conducted using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA), with statistical significance set at a p<0.05.
RESULTS
The characteristics of the study population are presented in Table 1. Of the 13723 participants, 6150 were men and 7573 were women; among them, 2211 (36.0%) men and 2903 (38.3%) women reported having oral health problems. Among the men with oral health problems, 424 were non-smokers (19.1%), 974 were ex-smokers (44.1%), and 813 were current smokers (36.8%); among the women with oral health problems, 2472 were non-smokers (85.1%), 210 were ex-smokers (7.2%), and 224 were current smokers (7.7%). The chi-squared test revealed a significant association between smoking status and oral health problems in participants of both sexes (p<0.0001).
Table 1
General characteristics of the study population in a secondary analysis of the KNHANES dataset, 2019–2021 (N=13723)
Table 2 presents the results of the multiple logistic regression analysis adjusted for all covariates and stratified by sex to examine the association between smoking status and oral health problems. Among men, ex-smokers and current smokers had AORs of 1.39 (95% CI: 1.18–1.63) and 1.60 (95% CI: 1.35–1.89), respectively, compared with non-smokers. Among women, ex-smokers and current smokers had AORs of 1.47 (95% CI: 1.18–1.83) and 1.91 (95% CI: 1.33–2.71), respectively, compared with non-smokers.
Table 2
Multiple logistic regression results showing the association between smoking behaviors and oral health problems, adjusted for covariates, based on the KNHANES dataset (2019–2021) (N=13723)
[i] AOR: adjusted odds ratio. Adjusted for all covariates: age, marital status, education level, household income, region, occupation category, current alcohol consumption status, physical activity, body mass index (BMI), diagnosis of hypertension, diagnosis of diabetes and survey year. ® Reference categories.
Table 3 presents the subgroup analysis stratified by occupation categories. Among both men and women in the pink-collar group, a strong association was observed between both ex-smoking and current smoking and oral health problems (ex-smokers: AOR=1.65; 95% CI: 0.87–3.11; current smokers: AOR=1.70; 95% CI: 0.99–2.93). Among current smokers, those unemployed showed a significant association with oral health problems. Additionally, among women, current smokers in the white-collar group demonstrated higher AORs.
Table 3
Subgroup analysis results stratified by occupational categories and adjusted for all covariates, using data from the KNHANES dataset (2019–2021) (N=13723)
[i] AOR: adjusted odds ratio. Adjusted for all covariates: age, marital status, education level, household income, region, occupation category, current alcohol consumption status, physical activity, body mass index (BMI), diagnosis of hypertension, diagnosis of diabetes and survey year. ® Reference category.
Table 4 presents the results of the subgroup analysis stratified by smoking type, cessation status, and pack-years. When analyzing the association based on smoking type, among both men and women, the odds of oral health problems were high for regular cigarette smokers and e-cigarette smokers; however, regular cigarette smokers had higher AORs than e-cigarette smokers (regular cigarette smokers: men, AOR=1.56; 95% CI: 1.31–1.86; women, AOR=1.96; 95% CI: 1.53–2.52; e-cigarette smokers: men, AOR=1.36; 95% CI: 1.05–1.74; women, AOR=1.64; 95% CI: 1.06–2.53). Among ex-smokers, participants of both sexes showed decreased ORs for oral health problems as the duration of smoking cessation increased (<10 years: men, AOR=1.55; 95% CI: 1.26–1.90; women, AOR=1.43; 95% CI: 1.03–1.98; ≥30 years: men, AOR=1.19; 95% CI: 0.89–1.58; women, AOR=1.05; 95% CI: 0.54–2.02). Furthermore, an analysis of pack-years among ex-smokers and current smokers (excluding non-smokers) demonstrated a clear correlation, with oral health problems increasing as pack-years accumulated (<10 years: men, AOR=1.31; 95% CI: 1.09–1.57; women, AOR=1.66; 95% CI: 1.37–2.00; ≥20 years: men, AOR=1.88; 95% CI: 1.56–2.26; women, AOR=2.10; 95% CI: 1.19–3.73).
Table 4
Subgroup analysis results examining smoking type, cessation status, and pack-years, adjusted for covariates, based on the KNHANES dataset (2019–2021) (N=13723)
[i] AOR: adjusted odds ratio. Adjusted for all covariates: age, marital status, education level, household income, region, occupation category, current alcohol consumption status, physical activity, body mass index (BMI), diagnosis of hypertension, diagnosis of diabetes and survey year. ® Reference category.
Figure 2 presents the subgroup analysis of the causes of oral health issues using predicted probabilities. Among both men and women, current smokers exhibited a higher probability of experiencing toothache compared to ex-smokers. The estimated probability of toothache among male current smokers was 67.85%, compared to 60.63% for male ex-smokers. Similarly, female current smokers had a 65.87% probability of experiencing toothache, whereas female ex-smokers had a probability of 62.41%. Regarding chewing problems, the probabilities varied by smoking status and sex. Among men, ex-smokers had a slightly higher probability of chewing problems (57.98%) compared to current smokers (57.26%). However, among women, current smokers had a significantly higher probability of experiencing chewing problems (65.28%) compared to ex-smokers (57.63%). These results indicate a significant association between smoking and oral health issues, particularly for current smokers, with greater differences observed in women for chewing problems.
DISCUSSION
This study found that smoking increased the risk of oral health problems in individuals of both sexes. These results support previous studies indicating that cigarette smoking and other types of tobacco use can cause various oral health problems, including bleeding upon brushing, tooth stains, bad breath, and oral cancer24,25. According to previous findings, individuals with a history of smoking have a higher incidence of oral health problems than non-smokers, and current smokers are at an even greater risk than ex-smokers. This is in line with previous studies showing that the cessation of tobacco use has a beneficial effect on the outcomes of periodontal therapy and halts the progression of periodontal disease26. Therefore, smoking cessation is necessary to prevent oral health problems.
In addition, the risk of oral health problems was found to be higher in female than male participants. Both current and ex-smokers among female participants exhibited a greater susceptibility to oral health problems. For instance, studies have shown that women have more difficulty maintain long-term smoking cessation, as stress and adverse life events affect their ability to quit27. Research also suggests that women are more likely than men to continue smoking in the presence of financial hardship and are less likely to quit smoking in response to health-related issues28. As women find it more difficult to quit smoking, compared with men, special attention, including stress management, is required. However, this finding does not imply that male smokers disregard oral health issues. Evidence from previous studies indicates that men are more likely to ignore their oral health and often delay visiting dentists until faced with acute problems29. This behavior contributes to a higher male-to-female ratio for oral cancer, largely due to more tobacco use among men29. Thus, initiatives aimed at improving oral health awareness and preventive care among male smokers are crucial.
According to the results of the independent subgroup analysis, individuals in pink-collar jobs within the service industry demonstrated a relatively stronger association between smoking and oral health problems than those in other occupations. This is consistent for both sexes, as well as for both current and ex-smokers. From the present study’s findings, this is hypothesized to be due to an increased likelihood of smoking due to job-related stress24, as pink-collar workers, such as teachers, are under a high level of stress30. These results further suggest that among current smokers, unemployment correlates with oral health problems. Additionally, among female current smokers, those in the white-collar group had higher ORs.
Significant results were also observed in the analysis of associations based on smoking type, duration of smoking cessation, and pack-years. The group that smoked both e-cigarettes and regular cigarettes had a higher risk of oral health problems than did smokers who only smoked one of the two types of cigarettes. Furthermore, e-cigarettes have a negative effect on oral health31-33; however, vapor use may be considered a healthier alternative to cigarette smoking in terms of periodontal health34. Additionally, pain in the teeth and gums is more often perceived by cigarette smokers than by electronic cigarette smokers and non-smokers35. Considering this, people who smoke only vapor are healthier than those who smoke regularly. For dual smokers, quitting both cigarettes, or only regular cigarettes, is likely to be effective for oral health. The longer the ex-smokers abstained from smoking, the better was their oral health; moreover, smokers had poorer oral health and longer pack-year history. This finding supports the idea that early smoking cessation reduces the risk of oral health problems.
Finally, the analysis conducted by stratifying the relationship between smoking and oral health problems by disease type revealed significant results. Patients with toothache were more strongly affected by smoking than those without toothache. This is in line with a previous study demonstrating that current smokers were at an increased risk of experiencing toothache in the past 6 months36. A similar trend was observed for chewing problems. Among women, current smoking showed a stronger association with chewing problems. In addition to the oral health problems addressed in this study, many other diseases are strongly associated with smoking24,25.
Strengths and limitations
This study has several strengths. First, we utilized data from the KNHANES, a nationally representative survey reflecting the characteristics of South Koreans and their health behaviors. The survey used random cluster sampling, to allow statistical generalization of the research findings to all the population. Second, the inclusion of recent data (2019–2021) is significant, encompassing current smoking status, e-cigarette use, smoking history, and cessation attempts and plans. Third, while previous studies examined the association between smoking status and oral health, focusing on regular cigarette smokers, the present study included e-cigarette smokers also. This study has some limitations. First, this study was cross-sectional, so a temporal relationship cannot be ascertained. Also, smoking may not have preceded oral health problems, so further prospective cohort studies are needed to confirm our findings. Second, the KNHANES uses self-report surveys, which can introduce issues of reliability and accuracy of health-related, socioeconomic, and smoking status information and recall bias that can potentially lead to the underestimation of smoking prevalence. Third, potentially residual confounding variables may remain, despite attempts to include as many independent variables related to smoking and oral health problems. Fourth, the overall state of oral health is not solely based on the presence of toothache or chewing problems; individuals may still have poor oral health due to other oral issues. Fifth, we only analyzed the presence and types of problems; owing to limitations in the KNHANES data, information on the degree or frequency of pain was not collected. Finally, the study findings are limited to South Korea, as data were exclusively from the KNHANES and differences may exist due to variations in cultural, socioeconomic, and healthcare factors. Thus, there is a need to include a more diverse, international population to enhance the validity of our findings to other countries.
CONCLUSIONS
This study found that smoking negatively affects oral health. A comparison between ex-smokers and current smokers indicated that smoking cessation could reduce the risk of oral health problems. Therefore, the government should consider active smoking prevention efforts and try and implement smoking prevention activities for adults in educational settings. Dual smokers are recommended to quit both e-cigarettes and regular cigarettes. By implementing these factors, the oral health of smokers can be improved, and oral health problems can be mitigated.
