Association between Smoking and Periodontal Disease in South Korean Adults

**Background:** Smoking is a well-established risk factor for numerous chronic diseases, including periodontal disease. Harmful substances in tobacco, such as nicotine, can harm gingival tissue, decrease blood flow to the gums, and compromise immune responses. Previous studies have shown smoking is associated with poor periodontal health, but the authors aimed to provide more robust evidence using a large nationwide sample and to analyze smoking cessation in finer five-year intervals rather than the ten-year intervals used in prior work.

**Methods:** Data were obtained from the 2016–2018 Korea National Health and Nutrition Examination Survey (KNHANES), a nationally representative cross-sectional survey using a stratified, two-stage, clustered sampling design. Of 16,489 total participants, 9,178 adults (≥19 years) were included after excluding those under 19 (N=3,299), those unable to undergo oral examination due to tooth loss (N=2,581), and those with missing values (N=1,440). The final sample comprised 4,161 men (45.3%) and 5,017 women (54.7%). Periodontal disease risk was assessed using the Community Periodontal Index (CPI), scored 0–4 based on pocket depth, calculus, and bleeding. Smoking status was classified as non-smoker, ex-smoker, or current smoker. Covariates included age, marital status, education, household income, region, perceived stress, occupation, alcohol use, physical activity, tooth brushing frequency, and dental checkup status. Multivariable logistic regression was used, with results reported as odds ratios (OR) and 95% confidence intervals (CI). Subgroup analyses examined pack-years and smoking cessation duration in five-year intervals.

**Key Results:** Among men, 35.7% were current smokers, 39.0% ex-smokers, and 25.3% non-smokers. Among women, 5.6% were current smokers, 6.9% ex-smokers, and 87.5% non-smokers. Periodontal disease risk (CPI positive) was present in 73.1% of men and 62.6% of women. After adjusting for covariates, current smokers had significantly higher odds of periodontal disease compared to non-smokers (males: OR 1.78, 95% CI 1.43–2.23; females: OR 1.44, 95% CI 1.04–1.99). Ex-smokers showed elevated but non-significant odds (males: OR 1.20, 95% CI 0.95–1.50; females: OR 1.19, 95% CI 0.89–1.60). Older age, lower education (middle school or less: males OR 1.63, 95% CI 1.15–2.23; females OR 1.59, 95% CI 1.18–2.14), and lack of dental checkups (males OR 1.62, 95% CI 1.36–1.93; females OR 1.60, 95% CI 1.39–1.84) were also associated with higher risk. In pack-year analysis, men with >20 pack-years had the highest risk (OR 1.84, 95% CI 1.38–2.47). For smoking cessation duration, men who quit <5 years prior had OR 1.42 (95% CI 1.04–1.96), those who quit 5–10 years prior had OR 1.69 (95% CI 1.16–2.47), and those who quit ≥10 years prior had OR 0.93 (95% CI 0.71–1.21), indicating risk reduction to near non-smoker levels after 10 years of cessation.

**Clinical Implications:** This study provides strong evidence from a large, nationally representative sample that current smoking is significantly associated with periodontal disease in both men and women. The dose-response relationship with pack-years and the reduction in risk with longer smoking cessation—particularly the finding that even quitting for less than five years reduces risk compared to continued smoking—offers a powerful motivational message for smokers. Clinicians should emphasize the oral health benefits of early smoking cessation, as periodontal disease is not only a local oral health issue but is also linked to systemic conditions including cancer, heart disease, and diabetes. The findings support the need for tailored smoking cessation policies and educational interventions that highlight the relatively rapid periodontal health benefits of quitting.