Associations between dental knowledge, source of dental knowledge and oral health behavior in Japanese university students: A cross-sectional study

The aim of this study was to investigate the associations between dental knowledge, the source of dental knowledge and oral health behavior in a group of students at a university in Japan. A total of 2,220 university students (1,276 males, 944 females) volunteered to undergo an oral examination and answer a questionnaire. The questionnaire assessed dental knowledge, the source of dental knowledge and oral health behavior (e.g., daily frequency of tooth brushing, use of dental floss and regular dental checkups). The odds ratio and 95% confidence interval for oral health behavior based on dental knowledge and source of dental knowledge were calculated using logistic regression models. Of the participants, 1,266 (57.0%) students obtained dental knowledge from dental clinics, followed by school (39.2%) and television (29.1%). Logistic regression analyses indicated that use of dental floss was significantly associated with source of dental knowledge from dental clinics (P = 0.006). Receiving regular dental checkups was significantly associated with source of dental knowledge; the positive source was dental clinic (P < 0.001) and the negative sources were school (P = 0.004) and television (P = 0.018). Dental clinic was the most common source of dental knowledge and associated with better oral health behavior among the Japanese university students in this study.


Introduction
In research on major chronic diseases, more emphasis has been placed on the influence of health behavior rather than standard risk factors [1]. This concept has spread to the field of PLOS ONE | https://doi.org/10.1371/journal.pone.0179298 June 8, 2017 1 / 11 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111

Study population
In April 2014, first-year students (n = 2,288) at Okayama University were invited in this study and 2,270 students received voluntary oral examinations and completed a questionnaire (response rate = 99.2%). The participants were recruited from 11 faculties (Faculties of Letters, Education, Law, Economics, Science, Pharmaceutical Sciences, Engineering, Environmental Science and Technology, Agriculture, Medicine and Dentistry). The inclusion criteria were young adults (18-24 years old), and students who received oral examinations and completed the questionnaire. The exclusion criteria were participants aged ! 25 years old and those who had provided incomplete responses in the questionnaire. Participants aged ! 25 years old (n = 25) and those who had provided incomplete responses in the questionnaire (n = 25) were excluded. Finally, data from 2,220 students (1,276 males, 944 females) were subjected to analysis. Informed consent was obtained verbally from each participant. The protocol of this study was approved by the Ethics Committee of Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences (No. 808).

Questionnaire
A self-administered questionnaire was delivered by postal mail to each participant before dental examinations were conducted. In addition to sex and age, the questionnaire included the following items.
Dental knowledge. Questionnaire items asked participants whether they could explain dental terms, such as calculus, dental plaque, dental floss, sealant, periodontal disease, temporomandibular disorder, fluoride-containing mouthwash, topical application of fluoride and 8020 movement [20]. "8020 movement" is a Japanese social campaign aiming to retain 20 or more of one's own teeth at the age of 80 [28]. Answers were given in a "yes/no" format.
Source of dental knowledge. Participants were also requested to state where they acquired dental knowledge. Participants were able to indicate up to three sources from the following: dental clinic, school, television, family, internet, newspaper, acquaintance and publication.
Oral health behavior. Participants were asked about the following oral health behavior: daily frequency of tooth brushing (! 2 times/ 1 time); use of dental floss (yes/no); and receiving regular dental checkups during the past year (yes/no) [5,6].

Oral examination
Five dentists (D.E., A.T., S.M., M.Y-T. and K.K.) examined the participants' periodontal status. The periodontal status was assessed using the Community Periodontal Index (CPI) [29] using a CPI probe (YDM, Tokyo, Japan) to evaluate six sites on each tooth (mesio-buccal, mid-buccal, disto-buccal, disto-lingual, mid-lingual and mesio-lingual). For periodontal examination, the following 10 teeth were selected: two molars in each posterior sextant and the upper right and lower left central incisors. As bleeding on probing (BOP) is an earlier and more sensitive indicator of gingival inflammation than the probing depth [30], the percentage of teeth exhibiting BOP (%BOP) among the ten examined teeth was also assessed [20]. The intra-and interexaminer reliabilities, evaluated by κ statistics, of the CPI score were > 0.8.
Statistical analyses. The unpaired t test and chi-squared test were used to determine significant differences according to sex. Secondly, the chi-squared test was used to determine significant differences according to oral health behavior.
The odds ratio (OR) and 95% confidence interval (CI) were calculated using a logistic regression model. Each oral health behavior was considered a dependent variable. The multivariate analysis included sex, age, dental knowledge and the source of dental knowledge as independent variables. Independent variables were selected when the P value was <0.05 for the chi-square test or unpaired t-test in each variable.
Lastly, we evaluated the significant differences in oral health behavior between the two groups of periodontal statuses using the chi-squared test. The CPI and %BOP were divided into the following two groups: presence of probing pocket depth (PPD) ! 4 mm (CPI codes 0, 1 or 2 vs. CPI codes 3 or 4) or %BOP (< 20 vs. ! 20) [31].
All statistical analyses were performed using SPSS (version 22.0; IBM, Tokyo, Japan) with a level of significance set at P < 0.05. Table 1 shows the differences in parameters between males and females. Males had worse oral health behavior than females (P < 0.01). Additionally, males had significantly less dental knowledge of the seven terms than females (P < 0.05). More than half of the students acquired dental knowledge from a dental clinic, followed by school and television. In contrast, newspaper, acquaintance and publication were rarely chosen as the source of dental knowledge.

Results
There were no significant differences in dental knowledge and source of dental knowledge between the two groups of tooth brushing frequency ( Table 2). There were significant differences in dental knowledge of calculus, dental floss and sealant according to use of dental floss and receiving regular dental checkups (P < 0.05). Participants who acquired dental knowledge from a dental clinic reported significantly greater use of dental floss and regular dental checkups than participants who did not (P < 0.05) However, participants who acquired dental knowledge from school or television reported significantly lower use of dental floss and regular dental checkups than participants who did not (P < 0.05).
Regarding the association between oral health behavior and dental knowledge or source of dental knowledge, the parameters that showed the significant differences in oral health behavior were partially different between males and females (Tables 3 and 4).
In logistic regression analyses, daily frequency of tooth brushing was significantly associated with sex (P < 0.001) ( Table 5). Use of dental floss was significantly associated with sex (P = 0.004); having knowledge of dental floss (P < 0.001) and sealant (P = 0.048); and dental clinic as the source of dental knowledge (P = 0.006). Regular dental checkups were significantly associated with sex (P = 0.006), having knowledge about dental plaque (P = 0.008), calculus (P < 0.001), dental floss (P = 0.016) and sealant (P = 0.008), and the source of dental knowledge (P < 0.05). The positive source was dental clinic (P < 0.001) and the negative sources were school (P = 0.004) and television (P = 0.018).
The association between oral health behavior and periodontal status is shown in S1 Table. Participants with low %BOP scores (< 20%) had significantly higher frequencies of using dental floss and regular dental checkups than participants with higher %BOP scores (! 20%) (P < 0.001) (S1 Table).

Discussion
In this study, we focused on the associations between the source of dental knowledge, dental knowledge and oral health behavior. We found that differences in the source of dental knowledge were associated with oral health behavior in university students; that is, both positive and negative associations between the sources and oral health behavior were observed. The source of dental knowledge from dental clinics contributed to good oral health behavior, i.e., use of dental floss and regular dental checkups. A previous study found that oral health education at dental clinics was effective at modifying oral health behavior [25][26][27], which was confirmed by our results. Since dentists are important sources of oral disease prevention for the general public [32], dental clinics could be the most effective location for university students to improve oral health behavior.
It is interesting to note that school and television were negatively associated with regular dental checkups (Table 5). Previous studies found that oral health education in primary or secondary school could improve oral health behavior [33][34][35][36][37][38][39]. On the other hand, other studies in school-based education programs found no improvement [40,41]. A mass media health education campaign on television could not demonstrate a significant impact on behavior [42,43]. Furthermore, a recent study suggests that oral health program without repetition could transiently improve oral health behavior, but could not sustain improved oral health behavior in the long-term [44]. Thus, oral health education should be repeated with either method to keep its positive results [41,44,45]. Taken together, the other sources except for dental clinics might not encourage regular dental checkups repeatedly. A previous study found that oral health education from school teachers or dentists was equally effective in improving oral health knowledge and the oral hygiene status of adolescents [46]. However, the outcome of oral health education programs is dependent on the teachers' instructions or motivations [47][48][49]. This finding may support our result that obtaining dental knowledge from school was negatively associated with receiving regular dental checkups.
On the other hand, multifaceted interventions such as education programs, with a combination of methods (lectures and small-group discussions), improved knowledge, skills and attitude compared to single interventions or no interventions [50]. In terms of an education program, "television", "family", "internet", "newspaper", "acquaintance" or "publication" involved no intervention, but "school" can have multifaceted interventions. This study demonstrated that school was one of the major sources of dental knowledge. However, school was negatively associated with oral health behavior. Therefore, more effective intervention to promote better oral health behavior among students should be introduced in the Japanese education curriculum.
In this study, the most common source of dental knowledge was dental clinic, followed by school. However, approximately 20 years ago, schools were the most common source of dental knowledge in Japan [24]. In other countries, more than 60% of adults obtained dental knowledge from dentists or dental clinics [32,51]. Furthermore, in the United States and other western countries, adults visited the dental clinic more often [52][53][54]. In Japan, the rate of regular Values are reported as number (percentage). *P < 0.05 dental checkups has been increasing [55]. Thus, the source of dental knowledge may change from school to dental clinics. The percentage of participants who could explain dental floss was different from that of participants who used dental floss. The previous study shows that the percentage of participants who comprehend dental floss was different to that of participants who used dental floss [56]. Thus, explainable level of dental knowledge might not completely imply oral health behavior. On the other hand, dental knowledge of dental floss was positively associated with use of dental floss, which was supported by the previous study [56]. As the relationship between knowledge and behavior can be complex, further studies are needed.
In our study, use of dental floss and receiving regular dental checkups were associated with %BOP (S1 Table); that is, participants with good oral health behavior had good periodontal status. This result supports the findings of a previous study [6]. Thus, acquiring dental knowledge from dental clinics may effectively induce good oral health behavior, which contributes to achieving and maintaining good periodontal status.
There are some limitations associated with our study. First, a causal association could not be shown because the study was cross-sectional. Second, other possible confounders, such as attitude [9][10], lifestyle [11][12][13], stress [14,15], education level [16], socioeconomic status [17,18], sense of coherence [19] and self-efficacy [5], were not included in this study. Third, we did not investigate the effects of frequency of obtaining information from the source, interaction between the assessed knowledge and the sources, frequency of dental floss use, the recall interval for the dental checkups, the experience and pattern of dental visitation, or the relation between oral health status and dental visitation pattern, which might affect oral health behavior. Finally, all participants were recruited from Okayama University students. It may limit the ability to extrapolate these findings to the general young population.

Conclusion
The source of dental knowledge from dental clinics as well as having dental knowledge were associated with better oral health behavior in university students in Japan.
Supporting information S1 Table. Association between oral health behavior and periodontal status. (DOCX)