The aim of this prospective cohort study was to examine whether oral hygiene knowledge, and the source of that knowledge, affect oral hygiene behavior in university students in Japan. An oral exam and questionnaire survey developed to evaluate oral hygiene knowledge, the source of that knowledge, and oral hygiene behavior, such as the frequency of tooth brushing and regular dental checkups and the use of dental floss, was conducted on university student volunteers. In total, 310 students with poor tooth brushing behavior (frequency of tooth brushing per day [≤ once]), 1,963 who did not use dental floss, and 1,882 who did not receive regular dental checkup during the past year were selected. Among these students, 50, 364, and 343 in each respective category were analyzed in over the 3-year study period (follow-up rates: 16.1%, 18.5%, and 18.2%, respectively). The odds ratios (ORs) and 95% confidence intervals (CIs) for oral hygiene behavior were calculated based on oral hygiene knowledge and the source of that knowledge using logistic regression models. The results showed that dental clinics were the most common (> 50%) source of oral hygiene knowledge, and that a more frequent use of dental floss was significantly associated with dental clinics being a source of oral hygiene knowledge (OR, 4.11; 95%CI, 1.871–9.029; p < 0.001). In addition, a significant association was seen between dental clinics being a source of oral hygiene knowledge and more frequent regular dental checkups (OR, 13.626; 95%CI, 5.971–31.095; p < 0.001). These findings suggest the existence of a relationship between dental clinics being the most common source of oral hygiene knowledge and improved oral hygiene behavior in Japanese university students.

The purpose of this cross-sectional study was to investigate the association between sleep quality and duration, and periodontal disease among a group of young Japanese university students. First-year students (n = 1934) at Okayama University who voluntarily underwent oral health examinations were included in the analysis. Sleep quality and duration were assessed by the Japanese version of the Pittsburgh Sleep Quality Index. Dentists examined Oral Hygiene Index-Simplified (OHI-S), probing pocket depth (PPD), and percentage of sites with bleeding on probing (BOP). Periodontal disease was defined as presence of PPD ≥ 4 mm and BOP ≥ 30%. Overall, 283 (14.6%) students had periodontal disease. Poor sleep quality was observed among 372 (19.2%) students. Mean (± standard deviation) sleep duration was 7.1 ± 1.1 (hours/night). In the logistic regression analysis, periodontal disease was significantly associated with OHI-S (odds ratio [OR]: 2.30, 95% confident interval [CI]: 1.83–2.90; p < 0.001), but not sleep quality (OR: 1.09, 95% CI: 0.79–1.53; p = 0.577) or sleep duration (OR: 0.98, CI: 0.87–1.10; p = 0.717). In conclusion, sleep quality and duration were not associated with periodontal disease among this group of young Japanese university students.

The aim of this cross-sectional study was to evaluate the association between the influence of occupational stress and coping style on periodontitis among Japanese workers. The study sample included 738 workers (age range: 19–65 years) at a manufacturing company in Kagawa Prefecture, Japan. To analyze occupational stress and coping style, all participants answered a self-report questionnaire composed of items on their work environment and oral health behavior. Oral examinations were performed by calibrated dentists. Among all workers, 492 (66.7%) workers were diagnosed with periodontitis, and 50 (6.8%) were diagnosed with a high stress-low coping condition. Significant differences (p < 0.05) were observed between the periodontitis and non-periodontitis groups in terms of age, gender, body mass index, smoking status, daily alcohol drinking, monthly overtime work, worker type, and stress-coping style. Logistic regression analysis showed that a high stress–low coping condition was associated with an increased risk of periodontitis (odds ratio: 2.79, 95% confidence interval: 1.05–7.43, p = 0.039). These findings suggest that a high stress-low coping condition is associated with periodontitis among the 19–65 years of age group of Japanese workers.

The long-term effects of secondhand smoke (SHS) on dental caries among Japanese young adults remain unclear. The purpose of this cross-sectional study was to evaluate whether household exposure to SHS is associated with dental caries in permanent dentition among Japanese young adults. The study sample included 1905 first-year university students (age range: 18–19 years) who answered a questionnaire and participated in oral examinations. The degree of household exposure to SHS was categorized into four levels according to the SHS duration: no experience (−), past, current SHS < 10 years, and current SHS ≥ 10 years. Dental caries are expressed as the total number of decayed, missing, and filled teeth (DMFT) score. The relationships between SHS and dental caries were determined by logistic regression analysis. DMFT scores (median (25th percentile, 75th percentile)) were significantly higher in the current SHS ≥ 10 years (median: 1.0 (0.0, 3.0)) than in the SHS—(median: 0.0 (0.0, 2.0)); p = 0.001). DMFT ≥ 1 was significantly associated with SHS ≥ 10 years (adjusted odds ratio: 1.50, 95% confidence interval: 1.20–1.87, p < 0.001). Long-term exposure to SHS (≥10 years) was associated with dental caries in permanent dentition among Japanese young adults.