We found good oral health, both physical, i.e., when assessed by a dentist, and perceived by the individual, in the Japan self-defense forces (JSDF). When searching the literature to compare our results, we found only a limited number of oral health reports in military populations [1
]. We did not find a study assessing OHRQoL in military populations even though this concept has been increasingly recognized as an important component of health.
Our results suggest that the magnitude of correlations between physical characteristics of oral health and perceived oral health is small in this military population. However, because both "dimensions" of oral health affect the military personnel's readiness, assessment of physical and perceived health is necessary and we recommend including a measure of perceived oral health when military personnel oral health is examined. The only limited information available is on the missing tooth number of the military populations in other countries. They reported that the average number of missing teeth for the Croatian army[1
] was 2.3 for 650 recruits and 5.1 for 262 professionals (all male, averaged age = 32.7 years, age range 18 to 54 years) and that for Danish military [18
] was 0.02 to 0.5 (all male, average age = 25.2, age range 19 - 49 years). Our results are lower than the Croatian results and higher than the Danish results. However, the Danish subjects were younger and we found an age influence on the missing number of teeth which is also supported from studies done in civilian populations.
When compared with non-military populations, it was reported that 76.7% of the population did not have any missing tooth in New Zealand [20
]. Some studies reported lower numbers such as 62.3% in India [21
] and 53.5% in Israel [17
]. Although direct comparison with our study findings is not possible due to the difference in age and gender distribution and tooth counting system, these data provide a general framework of how prevalent tooth loss is in the general population. Japanese population-based studies reported that 49% of subjects had intact dental arch with no missing teeth and the average number of missing teeth was 1.3 (age range 15 - 59 years) [6
], which is higher than the result of this study.
Regarding denture status, the other key characteristic of physical oral health that we investigated, the Danish Military study (n = 223, all men, average age = 25.2 years, age range 19 - 49 years) reported no subject used removable dentures, which is lower than the current study result (4%). This might be due to the difference in the age of the studied populations. The denture status investigations in population based samples in Germany [12
] and Malaysia[13
] reported that 19% used removable partial dentures and 5% used complete dentures in Germany (average age = 43.3 years), that 18% used removable partial dentures and 12% used complete dentures in Finland (age > 30 years), and that 16.7% used removable dentures in Malaysia (age data not available). Again, a direct comparison is difficult to make because of methodological study differences. However, in absolute terms, the 4% figure of denture wearers in the JSDF is low. In the Japanese general population, the prevalence of removable denture users in the same age group as our study population is 7.0% [6
] or 9.4% [22
]. These numbers are substantially higher than the result of the current study.
As mentioned above, there is no report on OHRQoL in the other military populations in the literature. When compared with studies on non-military based populations, the frequencies of the impact experienced by our subjects were in general lower than previously reported. For example, the percentage of positive responses to each item ranged from 4.5 to 10.8% in a Finnish study [23
] (age range 30 - 64 years), which is higher than our study results. Average OHIP14 summary scores of population-based studies in New Zealand (age 32 years old, male 51.1%) were 8.0 units [20
], 5.1 - 7.7 in Sweden (age range 20 - 60 years, male 50%) [24
], 7.1-7.4 in Australia (age <69 years, male 41.4%) [25
], 4.7 to 5.7 in United Kingdom (age <69 years, male 45.7%) [25
], and 2.4 to 4.5 in Finland (age range 30 - 64 years, male 44.3%) [23
], and 11.0 in Malaysia (gender and age data not available) [13
]. Once again, although direct comparison is difficult due to the age and gender differences, the OHIP14 summary score in JSDF (4.6 +/- 6.7) is low in absolute terms compared with other populations. This suggests that JSDF personnel perceive their oral health as only minimally impaired.
The significant association between missing tooth number and OHIP scores was in agreement with previous studies [2
], which suggest a patient with more missing teeth is likely to suffer from more OHRQoL impairments. However, and also in agreement with previous studies, the correlation between the key characteristics of physical oral health and how subjects perceive their oral health is not substantial. The prevalence and severity of oral impacts also increased by usage of removable dentures, which is associated with a significant elevation of the OHIP score, as previously reported [12
]. It should be noted that the number of missing teeth, which itself has a significant effect on OHRQoL, is larger in those who use removable dentures. Therefore, the presence of removable partial dentures does not necessarily cause impaired OHRQoL. It is just an indicator of impaired OHRQoL. In fact, removable dentures may improve perceived oral health in subjects with missing teeth because of its effect on oral functions such as chewing, speaking, appearance and psychosocial well-being - our study because of its cross-sectional design cannot evaluate the directionality of the denture status-OHRQoL relationship. Tooth loss' impact on OHRQoL can be compensated best with fixed partial dentures or implant dentures. When the number of teeth drops below a certain level and the tooth loss cannot be treated by fixed partial dentures, very likely the removable dentures, even if done to the highest standard in the profession and even if the dentures' quality impact on the OHRQoL[10
] is maximized, cannot completely recover lost OHRQoL due to tooth loss. There is a significant cut off point of OHRQoL when a patient moves from the situation where he or she has intact dentition or missing teeth are replaced by fixed partial dentures to the situation where subjects use removable dentures [27
]. The clinical implication for military personnel as well as nonmilitary subjects - is that tooth loss should be prevented as much as possible but when it happens, a major deterioration of oral health can be avoided when the magnitude of the tooth loss can still be compensated with fixed prosthodontics and extensive tooth loss, and the use of removable partial denture can be avoided.