*2.3. Self-Questionnaire*

Before oral examination, participants answered self-questionnaires on sex, age, job category [19], work pattern (daytime/daytime and nighttime/flextime), and 10 questions about oral health [20], as presented below:


Furthermore, to assess whether oral status influences work performance, we asked "Have you had any problems with work performance because of oral diseases?" [7]. The answer was given in a "yes/no" format. If the answer was "yes", work performance was assessed as impaired.

### *2.4. Intervention*

The intervention group received individualized instruction for five minutes. During the study briefing, the participants set three goals for oral health behavioral modification to improve individual oral status and received advice on achieving the goals using a leaflet and a dental model. The instructors were dental hygienists or dentists who did not perform oral examinations. Moreover, we performed self-assessment questionnaires three times per year by mail (mailing method). In the mailing method, the intervention group evaluated the level of achievement of the goals, which were suggested at baseline intervention and reconsidered the direction. If the goals were achieved, new goals were established by participants.

#### *2.5. Statistical Analysis*

SPSS version 20 software (IBM, Tokyo, Japan) was used for statistical analyses. Values of *p* < 0.05 were considered to indicate significant associations. Chi-squared tests or non-paired *t*-tests were used to assess whether there were significant differences between the intervention group and the control group at both baseline and follow-up. McNemar test, McNemar-Bowker tests or paired *t*-tests were used to assess whether there were significant changes between baseline and follow-up.

### **3. Results**

Figure 1 shows the flow chart for study participants. All participants agreed to participate in this study. As the participants who did not undergo re-examination or provided incomplete data were excluded, 371 workers out of 611 workers were included in the analysis (final follow-up rate; 60.7%).

**Figure 1.** Flow chart showing the protocols for selecting analyzed workers from among those who agreed to participate in this study.

Table 1 shows the distribution of participants' characteristics at baseline. Data were not significantly different between the two groups at baseline (*p* ≥ 0.05, chi-squared tests, data not shown). The most common job category was professional and technical workers (36.9%). Daytime workers accounted for 85.4% of participants.


**Table 1.** Characteristics of participants at baseline.

<sup>1</sup> *<sup>n</sup>* (%); <sup>2</sup> Mean ± standard deviation.

In Table 2, we show a comparison of clinical variables between the two groups at baseline and at follow-up. All variables related to oral health status did not significantly differ between the two groups at baseline and follow-up (*p* ≥ 0.05, non-paired *t*-tests or chi-squared tests, data not shown).

**Table 2.** Comparison of clinical variables between the intervention group and the control group at follow-up.


<sup>1</sup> Debris index-simplified; <sup>2</sup> Percentage of bleeding on probing; <sup>3</sup> Community periodontal index; <sup>4</sup> Mean ± standard deviation; <sup>5</sup> *n* (%); <sup>6</sup> Non-paired *t*-test at follow-up; <sup>7</sup> Chi-squared test at follow-up.

The distribution of self-questionnaire answers between the intervention group and the control group is shown in Table 3. At baseline, there were no significant differences between the two groups (*p* ≥ 0.05, chi-squared tests, data not shown). After intervention, the frequency of fluoride toothpaste and interdental brushes/dental floss use was higher in the intervention group than in the control group (*p* < 0.05). There were no significant differences in work performance.

**Table 3.** Comparison of qualitative variables between the intervention group and the control group at follow-up.



**Table 3.** *Cont.*

<sup>1</sup> Chi-squared test on differences between intervention and control groups at follow-up; <sup>2</sup> *n* (%).

Changes in measured variables from baseline to follow-up in each group were also compared (Table 4). Use of interdental brushes/dental floss and dental examinations in the past year improved significantly in both groups. On the other hand, three variables (tooth brushing in workplace, using fluoride toothpastes, and experience of receiving tooth brushing instruction) showed significant improvement only in the intervention group. Work performance and oral status did not change significantly.

**Table 4.** Changes in variables in intervention and control groups.



**Table 4.** *Cont.*

<sup>1</sup> Debris index-simplified; <sup>2</sup> Percentage of bleeding on probing; <sup>3</sup> Community periodontal index; <sup>4</sup> Mean ± standard deviation; <sup>5</sup> n (%); <sup>6</sup> Paired *t*-test; <sup>7</sup> McNemar test or McNemar-Bowker test.

Oral health behavioral interventions are not invasive. Therefore, there were no study-related serious adverse events in this study. Furthermore, outcomes did not change after the trial commenced.

### **4. Discussion**

To the best of our knowledge, this was the first study to assess changes in work performance after oral health-related behavioral modification intervention. The study design was reliable as examinations were performed blinded, participants were quasi-randomly (alternate allocation) separated into either an intervention group or a control group, and the sample size was sufficiently large. Unfortunately, this intervention did not improve work performance, and there are several reasons for this. In a previous study [21], it was reported that work performance is mainly influenced by pain from oral diseases. In this study, there was a significant association between work performance and oral pain (baseline, *p* = 0.002; follow-up, *p* = 0.019; chi-squared tests; data not shown). However, there was no significant difference in the decrease in oral pain between the intervention and control groups (*p* ≥ 0.05). A previous study showed that a combination of professional oral hygiene treatment and oral hygiene instructions contributed to a decrease in gingival-related pain [22]. Thus, in the future, we should investigate whether a combination of professional oral hygiene treatment and oral health instruction improves work performance.

Oral health-related behavioral modification intervention improved oral health behavior but not oral health status. A systematic review showed that oral hygiene instruction had short-term and long-term effects [10]. The short-term effects were improving knowledge, attitudes, self-efficacy, oral health behavior, and theory constructs. The long-term effects included improving the number of decayed teeth, plaque score, BOP, and gingival condition [10]. The results of this study may be included in the short-term effects. Menegaz et al. suggested that a follow-up time of less than one year led to a lack of efficacy for educational intervention [23]. In addition, Oshikohji et al. reported that workers who had more participation time for oral examination and oral health instruction had better periodontal condition than those with less time [24]. If the duration of this study and/or the frequency of instruction was increased, oral health status might improve.

The intervention in this study was advantageous as it included some of the known factors that lead to behavioral modification. We explained why the workers should change their behavior (prompt intention formation), let the workers set goals independently (prompt specific goal setting), and checked their improvement and prompted them to reconsider their goals (prompt self-monitoring of behavior and prompt review of behavioral goals) [12,13]. Goals to improve oral status were also set based on individual situations in this study. These concepts were supported by a previous study [25]. Finally, the intervention time was short (5 min), a factor which may be effective in workplaces to improve oral health behavior.

There were 17 participants who had problems with work because of tooth or gum disease (4.6% of participants) at baseline. These conditions agree with the prevalence of poor work performance caused by oral pain in previous studies, which ranged between 1.0–7.6% [25–28]. The percentage in this study was within this range. However, the job sector of participants in this study was skewed. The percentage of workers who belonged to the tertiary industry sector was high (83%), and there were no workers from the primary industry sector. Therefore, we should exercise caution when applying our results more generally.

There were some limitations with regard to the interpretation of these results. First, although most of the participants visited a dental clinic during the study period, the type of dental health instruction they received was not confirmed. The intensity of instruction may have affected the results. Second, the follow up rate was not high (approximately 60.7%). As >20% loss would pose a serious threat [29], the high percentage of loss to follow-up may have affected our results. In the intervention group, the ratios of work performance, oral status, and oral health behavior were not significantly different between the analyzed and non-analyzed workers (188 vs. 85 workers, chi-squared test and non-paired *t*-test, *p* > 0.05). However, in the control group, the percentage of those using interdental brushes/dental floss was significantly different (183 vs. 90 workers, chi-squared test, *p* = 0.034). In the control group, use of interdental brushes or dental floss might have been improved because more workers who did not use these were not analyzed. Other limitations include the short-term scale of the study period and the fact that this was not a randomized trial.

#### **5. Conclusions**

In conclusion, oral health-related behavioral modification intervention improved oral health behavior, but not work performance in Japanese workers.

**Author Contributions:** Conceptualization, A.T.-T., S.M., D.E. and M.M.; investigation, A.T.-T., N.S., Y.S., D.F., Y.U., H.M. and A.Y.; data curation, A.T.-T. and N.T.; writing—original draft preparation, N.T.; writing—review and editing, all authors; project administration, M.M.; funding acquisition, M.M.

**Funding:** The research was funded by the "Research Fund of Clinical Study for Industrial Accident and Disease" (14020101–01) from the Japanese Ministry of Health, Labour and Welfare.

**Acknowledgments:** The authors are grateful to Junko Emi (Animal Development and Reproductive Biotechnology, Okayama University Graduate School of Environmental and Life Science Okayama, Japan) for data entry and collection, Hirofumi Mizuno (Sasaki dental clinic, Aichi, Japan) for oral examination, and Yuko Kimura (International Dental Hygienist College, Okayama, Japan) for collaboration with regard to oral health behavioral modification intervention.

**Conflicts of Interest:** The authors declare no conflicts of interest.
