Stressful Events and Oral Health Related Quality of Life Aboard: a Longitudinal Study

Background: Stressful events may affect self-perceived general and oral health. While the working environment is known to expose military personnel to chronic stress, oral health reports in these populations is limited. Methods: This longitudinal study aimed to investigate the association of oral health related quality of life (OHRQL) and stress in the military population aboard a training ship for 6 months. The participants included were 259 crew and 227 cadets. Two anonymous questionnaires, the perceived stress scale (PSS-14) and the oral health impact prole (OHIP-14), were applied at baseline and follow-up (six-month later). Socio-demographic characteristics were also obtained. Results: Multivariate Poisson regression analysis showed that PSS-14 predicted higher OHIP-14 scores at baseline and follow-up. At follow-up, besides PSS-14 (RR: 2.03; 1.42-2.90), being part of the crew group represented an increase of 87% on the OHIP-14 scores (RR:1.87; 1.27-2.74). Older individuals were 24% less likely to present higher OHIP-14 scores (RR:0.76; 0.58-0.99) than younger ones. Conclusion: Oral health related quality of life has worsened over time in this military population, and stress was an associated factor of that.


Introduction
Occupational stress occurs when the demands of the environment go beyond the worker's coping skills, causing excessive wear on the body and interference with productivity (1). Furthermore, living under stress or stressful events may cause an individual to become vulnerable to health problems, and also to physiological, emotional, and behavioral symptoms (2).
Job stress may affect one's perception of general health, because individuals under stressful situations adopt unhealthy behaviors, like being more likely to smoke, less inclined to brush their teeth, and less likely to visit a dentist (3). It can also worsen self-perceived oral health, increasing the risk of periodontal diseases, dental caries, and oral cancer (4).
Self-perceived oral health status includes subjective measurements that re ect the individual's own assessment of oral health status and treatment needs (5,6). Speci c tools, which consider the impact of oral health conditions on quality of life, have been developed to measure how changes in oral health compromise the quality of life and the well-being of individuals (7).
Military activities have been linked to a variety of physical and physiological symptoms, such as post-traumatic stress which results in poor individual-level outcomes (8). This happens often to military personnel because their unique working environment exposes them to chronic stress and experiences of extreme violence may be anticipated under certain conditions (9).
There are no studies about the consequences of the stressful condition of military environments in the self-perceived oral health status so far. Evaluating work stress effects on quality of life aboard can help managers implement programs or strategies that help them cope with problems and avoiding the negative impact on the military`s health.
This study aimed to assess the oral health related quality of life (OHRQL) and stress in military populations and to investigate the association of OHRQL and stress in this group.

Study design
This was a longitudinal prospective census-type study that assessed the oral health related quality of life and stress in a military population submitted to a training cruise over six months. Additionally, the association between OHRQL and stress was investigated.

Data collection
On a scheduled work day, the military personnel aboard were invited to attend a meeting in the auditorium, where they were given instructions and objectives of the study before it began. Irrespective of age, sex, function or personnel aboard, they were invited to participate in the survey, being assured of con dentiality of the information provided. When they agreed to enroll, the informed consent was signed. The option to refuse to participate was a clear option.
This study was approved by Marcílio Dias Navy Hospital Research Ethics Committee, in Rio de Janeiro, Brazil, protocol 10751419.8.0000.5256/2019, and followed the ethical standards established by the Declaration of Helsinki.

Demographic and social data
The demographic and social data obtained were related to sex (male; female), personnel aboard (crew; cadets), age (in years), and education (high school; higher education). The age was divided into four age ranges: 20 to 29; 30 to 39; 40 to 49; and over 50 years old.

Questionnaires
One examiner applied two anonymous questionnaires: A) perceived stress scale, and B) oral health impact pro le. comprises of 14 questions with responses varying from 0 to 4 for each item, and ranging from never, seldom, sometimes, fairly often, and very often, respectively, based on their occurrence one month before the survey. PSS-14 scores are obtained by reversing the scores on positive items, for example 0 = 4, 1 = 3, 2 = 2, 3 = 1, and 4 = 0, and then summing across all 14 items. Items 4, 5, 6, 7, 9, 10, and 13 are the positively stated items (10,11). The scores ranged from 0 to 56, 28 being the operational cutoff value (10,12). Participants were labeled as "stressed" when scoring upper bound and as "non stressed" when scoring less than 28.

B) Oral health impact pro le
The oral health impact pro le (OHIP-14) intends to measure the physical, psychological, and social impact of oral conditions one month before the survey and are composed of 14 items that assess seven different dimensions (functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap). Each item has a set of possible answers rated on a 5-point Likert scale (4 = always, 3 = frequently, 2 = sometimes, 1 = seldom, and 0 = never). OHIP-14 scores can range from 0 to 56 and are calculated by summing the ordinal values for the 14 items (13).
PSS-14 and OHIP-14 were applied at two moments: a) baseline, two days before the annual MTC got started; and b) follow-up, the last day of the mission, in July and December of 2019, respectively.

Data analysis
Descriptive statistics were performed for the demographic and social data.
After the questionnaires were completed, the means of PSS-14 and OHIP-14 at baseline and follow-up were obtained.
The personnel aboard were separated into two groups: crew and cadets, and it was veri ed if the mean of each questionnaire was different between these groups at baseline and follow-up.
Scores for each item of OHIP-14 were compared for the whole military population and separately for the crew and cadets group, at baseline and follow-up, to identify which of them had changed the most during MTC.
The sum of PSS-14 was categorized as "non stressed" (sum < 28) or "stressed" (sum ≥ 28). Then, it was investigated whether the categorized variables of PSS-14 were different between both groups at baseline and follow-up.
Crude and multivariable Poisson regression with robust covariance was used to test the association between personnel aboard, age range, education, and PSS-14 with OHIP-14 scores at baseline and follow-up.
Statistical differences between groups were evaluated using the Chi-Square test for categorical variables and the T-test or the Mann-Whitney U test for continuous variables with a signi cance level of 5%. All data processing and analyses were performed using the software SPSS version 21.0 ("Statistical Package for the Social Sciences", SPSS Inc., Chicago, USA).
were found between the baseline and follow-up. Comparing the means of the questionnaires, OHIP-14 presented greater scores at follow-up ( Table 1).
The internal consistency of OHIP-14 measured by Cronbach's alpha coe cient was 0.90 and could not be improved by deletion of any individual question. Excellent internal consistency was also found for PSS-14 (0.86). Data expressed as an absolute number (%).
Questionnaires` data expressed as mean ± SD. SD: standard deviation.
At baseline, the means of PSS-14 and OHIP-14 were higher for the crew group than cadets, reaching statistical signi cance (p = 0.003, and ≤ 0.001, respectively). At follow-up, the means for OHIP-14 were higher for the cadets group (p = 0.03). No differences between the groups were found for PSS-14 at follow-up. The cadets' OHIP-14 mean was higher at follow-up than at baseline (p = 0.02) ( Table 2). Data expressed as mean ± SD. SD: standard deviation.
p1: comparison in the crew group between baseline and follow-up.
p2: comparison in the cadets group between baseline and follow-up.
p3: comparison at baseline between crew and cadets.
p4: comparison at follow-up between crew and cadets.
Exploring each item of OHIP-14, mean scores of 7 items among the 14 were signi cantly higher at follow-up in the cadets group (Table 3). Otherwise, only items 2 and 11 showed differences between the baseline and follow-up in the crew group (0.18 ± 0.44 versus 0.47 ± 0.77, p = 0.01, and 0.53 ± 0.84 versus 0.87 ± 1.12, p = 0.04, respectively; data not showed). An additional table le shows this in more detail [see Additional le 1].
None of the items of PSS-14 showed differences between baseline and follow-up, regarding the crew and cadets groups. Data expressed as mean ± SD. SD: standard deviation.
Regarding the PSS-14 cutoff, at baseline, 83.6% of the studied population was categorized in "non stressed" and 16.4% in "stressed", while at follow-up, 84.1% was labeled as "non stressed" and 15.9% as "stressed" (available in supplement).

Regression
The results from crude Poisson regression analysis (Table 4) showed that the OHIP-14 scores, at baseline, were signi cantly associated with: a. being part of the crew group (1.8 times more than the cadets group); b. age range (participants with higher age range were 25% more likely to present higher OHIP-14 scores); c. lower level of education (1.5 times more than those with higher education); and d. PSS-14 (individuals categorized as "stressed" were 2.4 times more likely to present greater means of OHIP-14 than those categorized as "non stressed").

Discussion
Based on this longitudinal study which evaluated a military population with similar demographic and social characteristics, it was found that oral health related quality of life got worse over time on a training cruise.
At baseline, the mean scores of PSS-14 and OHIP-14 were higher for crew compared with the cadets group. This can be explained by the arduous work that the crew group completed to prepare the ship for MTC, six months before leaving. On the other hand, at the same time, cadets were at Naval School for classes and theory instruction, and they were not living in the ship environment. At follow-up, there were no differences between both groups regarding PSS-14. This is not in accordance with an Indian study performed in a private medical college. Medical students reported a higher level of perceived stress with a mean PSS-14 scores of 27.53. Different methodologies are the main reason for the contradictory data found in the study, like the predominance of females (67.08%), the mean age group of 19.7 years, and because the survey was conducted among during the rst and second years of graduation (14). Similar results were found in a Pakistan study (mean scores was 30.84) (10), but this study used different tools to measure stress, which limits the comparability between them.
Using the PSS-14 cutoff, only 16.4% of the whole military population were labeled as "stressed". Comparing mean scores and times, the results were similar at follow-up, although the crew group was more stressed than the cadets group at baseline.
Self-perceived oral health in the crew group was different compared to the cadets after the whole population was used to the routine aboard. Comparing changes in OHIP-14 for each group, the mean of the cadets group was higher statistically signi cant at follow-up than baseline.
Exploring each item of OHIP-14, the mean scores of both questions "Have you felt that your sense of taste has worsened?" and "Have you been a bit irritable with other people?" were signi cantly higher at follow-up than baseline in both groups. Other items of OHIP-14, as "Have you been self-conscious?", "Have you felt tense?", "Has your diet been unsatisfactory?", "Have you found it di cult to relax?", and "Have you been a bit embarrassed?" were higher in the cadets group, showing that the perception of oral health was impaired in the ship`s environment. This may induce mood swings and impair interpersonal relationships. In a Thailand study with military personnel, the oral problems that could possibly affect quality of life and work were assessed using questionnaires, and it was concluded that toothache/hypersensitivity was among the most common oral problems. In addition, the majority of military personnel admitted that oral problems affected quality of life and duty performance more than other factors, such as sleep deprivation and technical skills for work (15).
In order to evaluate the relationship between stress and self-perceived oral health status and to measure the impact of stress in self-perceived oral health, regression analysis was used. Our results showed that stress was a predictor of greater OHIP-14 scores. A Lithuanian study, among high school students, found a positive relationship between the prevalence of oral and/or systemic conditions with higher stress levels, even though the questionnaires they used were different from ours (16). The signi cant impact of stress (B = 0.35, p < 0.001) on the OHRQL, applying a multiple linear regression, was also demonstrated in a Portuguese study in elderly patients (17).
Our regression analysis showed that older individuals were 24% less likely to present higher OHIP-14 scores than younger ones. Likewise, lower age contributed to higher OHIP-14 scores in a Portuguese study mentioned above (17).
There is a limited number of oral health reports in military populations (17)(18)(19)(20)(21). A study conducted among Croatian military personnel, during a periodic annual evaluation, sought to determine the predictive value of dental readiness in OHRQL. OHIP-14 was applied, and a direct and positive relationship was found between a satisfactory dental condition and the quality of life recognized from self-perceived oral health. In addition, it was concluded that patients with better oral conditions were among the youngest and those with less time in military duty, which can be explained by their motivation to improve oral health in order to be permitted to participate in international peacekeeping missions (22).
In subjects from the Japanese military during the annual medical examination in 2008 (mean aged 35.7 ± 10.1, range 15-59 years), the correlation between the number of missing teeth and the OHIP-14 scores were assessed. Only 0.2 to 1.9% reported frequent negative impacts with a mean OHIP-14 scores of 4.6 +/-6.7. Thus, the results suggested that the magnitude of correlation between physical characteristics of oral health and perceived oral health was small in this military population (21).
Some limitations may be considered when interpreting our ndings. One of them is that it s ¬possib ≤ → extrapolatetherest ̲ s → otherships, giventhepartica ̲ rityoffeaturesofeachvessel and theirmissions. A ¬herp∮ istpairedtestswe s crew during missions. The application of questionnaires, per se, involve limitations because of the respondents` interpretation of questions or desire to report their emotions in a certain way; we cannot rule out information bias. The study only involved military personnel and comprised mostly of males who were physically and mentally t.
There are some implications associated with the ndings of this study. The following are suggested strategies based in the results of study: ensure physical activity programs aboard; train health staff technically and make sure supervisors support subordinate`s needs; encourage religious assistance aboard; emphasis the ship's mission to military staff; organize social and corporate events aboard; establish a suitable place for oral hygiene; organize a periodic oral hygiene demonstration by a dentist aboard; and add dental supplies in to the welcome kit delivered aboard.

Conclusion
This longitudinal study showed that oral health related quality of life has worsened over time in the studied military population. Stress was an associated factor with it. The need to adjust management styles was highlighted as well as the need to prepare the staff to navigate stressful situations more effectively.

Declarations
Ethical Approval and Consent to participate: This study was approved by Marcílio Dias Navy Hospital Research Ethics Committee, in Rio de Janeiro, Brazil, protocol 10751419.8.0000.5256/2019, and followed the ethical standards established by the Declaration of Helsinki.