2.1 Participants

Data for this study was taken from a sample of the 2013–2015 KNHANES, an investigation into the health of the public, the status of chronic diseases, and the status of food/nutrition. The survey was conducted by the Korea Centers for Disease Control and Prevention (KCDC). KNHANES includes secondary data which are processed to be anonymous.

The total number of participants for the 2013–2015 KNHANES was 29,321. Information from individuals aged 1 to 18 years was excluded because KNHANES did not ask persons aged under 19 years about cigarettes. Furthermore, data were excluded from four individuals who were unable to provide information about smoking or vaping cigarette. We also excluded those who were unable to provide information about age, education, marriage, region, income, alcohol status, occupation, the number of days walking per week, subjective health status, subjective stress level, subjective oral health status, dental caries, toothache within past year, or the experience of dental damage. Following all exclusions, a total of 13,551 participants (men: 5,715 and women: 7,836) were analyzed.

2.2 Variables

Participants were classified into four groups: electronic cigarette users, conventional cigarette users, ex‐users, and non‐users. Individuals who answered “Yes” to the questions about electronic cigarettes were placed in the electronic cigarette group. Individuals who reported “Yes” to the conventional cigarette question, were placed in the conventional cigarette group. Ex‐users and non‐users were determined by a “Yes” answer to a direct question (i.e., “Are you a former cigarette user?”). Additionally, analyses included demographic, socioeconomic, and health‐related characteristics. The demographic analysis consisted of age, gender, and marital status. The socioeconomic analysis consisted of education, region, household income level, and occupation. The health‐related characteristics analyzed were alcohol status, number of walking days in a week, self‐reported health status, and stress level. Dental related variables, such as self‐reported oral health status, dental caries, toothache within the past year, and the experience of dental damage were also included.

Periodontal disease was the main dependent variable in this study. Periodontal status was divided into 0 to 4 points, using the CPI, which was recommended by the WHO. A CPI score of 0 represents healthy periodontal tissue, 1 means bleeding periodontal tissue, 2 means periodontal tissue with plaques, 3 means periodontal tissue with shallow periodontal pockets (3.5 ≤ pocket depth < 5.5 mm), and 4 means periodontal tissue with deep periodontal pockets (pocket depth ≥ 5.5 mm). In this study, a score of 3 to 4 was considered to denote periodontal disease.

2.3 Statistical analysis

A chi‐square test was conducted to investigate the general characteristics of the study population. Multiple logistic regression analysis was performed to examine the association of conventional cigarette smoking and electronic cigarette vaping with periodontal disease, after accounting for potential confounding variables including demographic, socio‐economic, and health‐related characteristics. Results are reported as odds ratio (OR) and confidence interval (CI). Subgroup analyses were also performed with multiple logistic regression stratified by gender, to investigate the associations with self‐reported oral health status, education level, region, dental caries, toothache within the past year, and the experience of dental damage. The analysis used a stratified sampling variable (kstrata), clustering variable (primary sampling units) provided by KNHANES. All analyses included the use of weighted variables. Differences were considered statistically significant with a P value < 0.05. All data analyses used SAS 9.4 software.