Dental caries experience in a young adult military population

SCIENTIFIC ARTICLE Australian Dental Journal 2003;48:(2):125-129 Dental caries experience in a young adult military population M Hopcraft,* M Morgan Abstract Background: The purpose of this study was to investigate a group of young Australian adults to determine their caries experience and compare these current levels with similar aged cohorts over the past 30 years. Caries experience was also related to lifetime exposure of fluoridated water consumption. Methods: This was achieved through a crosssectional study involving Australian Army recruits seen for their initial dental examination at 1 st Recruit Training Battalion, Kapooka. A total of 499 recruits had a clinical examination with the aid of bitewing radiographs and an orthopantogram. Sociodemographic and fluoride history data were elicited via a questionnaire. Results: Mean DMFT scores for age cohorts were: 17-20 years of age DMFT 3.59; 21-25 years of age DMFT 4.63; 26-30 years of age DMFT 7.07; 31-35 years of age DMFT 9.04. Subjects with a lifetime exposure to fluoridated water had significantly lower dental caries experience (DMFT 3.80) than subjects with no exposure to fluoridated water (DMFT 5.15). Conclusions: It was found that there has been a decline in the level of caries experience in young Australian adults when the data from this study were compared to other ad hoc studies. Key words: Epidemiology, DMFT, caries, adult, fluoride. (Accepted for publication 23 April 2002.) INTRODUCTION Cross-sectional studies of military populations provide a unique opportunity to capture a sample of young adults from diverse socio-economic and geographical backgrounds and observe their levels of caries experience. Comparison with data collected over the past 60 years enables trends in the distribution and severity of caries experience in the young adult population to be observed. Data from studies of military recruits have been instrumental in the planning of community dental *Lecturer, School of Dental Science, The University of Melbourne. Associate Professor, School of Dental Science, The University of Melbourne. services, in particular the introduction of water fluoridation. The extremely poor standard of oral health in Australian troops during World War Two motivated a series of epidemiological surveys in the late 1940s and early 1950s that led to the introduction of water fluoridation in Australia in 1953. 1 The proportion of Australians with exposure to fluoridated drinking water has increased from almost zero in 1953 to around two thirds of the population by 1977, with this level remaining reasonably constant to the present day. 1,2 Most of this coverage is in urban areas, with much of regional and rural Australia still without access to fluoridated water. This increased exposure to fluoridated water is accepted as being the leading cause of decreasing caries levels in Australia. There is a limited body of research data available describing the caries experience of young Australian adults, especially in relation to their exposure to fluoridated water. 1 The purpose of this study was twofold. Firstly, to investigate a group of young Australian adults to determine their caries experience and to make a comparison of current levels of caries experience with those of similar aged cohorts over the past 60 years. Secondly, to relate caries experience to the subjects reported history of fluoridated water consumption. MATERIALS AND METHODS This paper reports the findings of a cross-sectional study of Army recruits examined at the 1st Recruit Training Battalion, Kapooka. The subjects were examined over a period of six months as they enlisted into the Army, and comprised subjects from all over Australia. Source of subjects Army recruits aged 17 to 35 years were sampled between July and December 1996 at the time of their attendance at the Kapooka Dental Unit for their initial dental examination. The majority of recruits were enlisted from Queensland (39 per cent), New South Wales (21 per cent) and Victoria (16 per cent), with the remainder from South Australia (11 per cent), Western Australian Dental Journal 2003;48:2. 125

Table 1. Sociodemographic characteristics of sample population n % n % Age Socio-economic status 17-20 years 290 58 SES 1 (Professional) 59 12 21-25 years 127 26 SES 2 (Para-professional) 131 26 26-30 years 57 11 SES 3 (Advanced Clerical) 177 36 31-35 years 25 5 SES 4 (Tradesman) 74 15 SES 5 (Labourer) 32 6 Gender Not classified 26 5 Male 357 72 Female 142 28 Exposure to fluoride Lifetime fluoride exposure 145 29 Education Partial lifetime fluoride exposure 170 34 Tertiary 54 11 No fluoride exposure 99 20 Completed Year 12 209 42 Not classified 85 17 <Yr 12 224 45 Not classified 12 2 Australia (9 per cent), Tasmania (3 per cent) and the Northern Territory (1 per cent). Clinical examination Subjects were examined by one of three calibrated dentists in a dental operatory, with a mouth mirror and sickle probe and with the aid of a dental chair light. Bitewing radiographs and an orthopantogram taken by a dental hygienist were viewed with a light box during the oral examination. Operators were trained and calibrated according to the diagnostic criteria for dental caries as set out by the World Health Organization. 3 Clinical and radiographic findings were not recorded separately. Since subjects were examined for the purpose of being made dentally fit for military purposes, it was likely that there was a bias towards the over-reporting of dental caries. Inter-examiner reliability including the use of radiographs was tested during the pilot study, with Kappa scores of 0.88-0.91. Only recruits examined by one of three calibrated operators were included in the study, giving a sample size of 499 subjects. Questionnaire Sociodemographic and fluoride history data were elicited via a questionnaire prior to the oral examination. The questionnaire asked for details of the subject s highest level of education attained, parental occupation and residential history to determine fluoridated water exposure. Statistical analysis Caries experience was expressed using the DMFT index, representing the number of decayed, missing and filled teeth per subject. Mean values for DMFT were calculated for specific age, gender, educational, socioeconomic and lifetime fluoride exposure groups. Lifetime fluoride exposure was determined by comparing the reported geographic data with information from the Commonwealth Department of Health detailing areas with artificial water fluoridation and date of commencement, and also areas of known natural fluoridation. 4 Subjects were classified as having had a lifetime exposure to fluoridated water, a partial lifetime exposure to fluoridated water, no lifetime exposure to fluoridated water or unclassified. Socioeconomic status was determined by parental occupation and grouped according to Australian Bureau of Statistics criteria. 5 Ethical review This study was reviewed and approved by Director Dental Services Army, Commandant First Recruit Training Battalion and the Australian Defence Medical Ethics Committee. Informed written consent for inclusion into the study was obtained from each participant. RESULTS Participation Table 1 presents the sample population according to sociodemographic and lifetime fluoride exposure history. The age of the subjects ranged between 17 and 35 years. Four age cohorts were used in analysis of the data 17-20 year olds, 21-25 year olds, 26-30 year olds and 31-35 year olds. Male subjects represented nearly 72 per cent of the sample population. The reported standard of education achieved was generally high, with more than half of the sample completing secondary school and nearly 11 per cent of subjects having commenced tertiary study. Fluoride exposure history Nearly 30 per cent of the sample population had a lifetime exposure to fluoridated drinking water, with 20 per cent having had no exposure to fluoridated water. Of the remainder, 34 per cent had experienced a partial lifetime exposure to fluoridated water and 17 per cent were unable to be adequately classified with regard to their fluoride exposure history, due to historical recall difficulties or the inability to obtain water fluoridation data for overseas locations. Dental caries Overall, the prevalence of dental caries was high, with only 15.2 per cent of the sample population being caries free. The frequency distribution of DMFT scores was positively skewed, with the Shapiro-Wilk test for normality rejecting the hypothesis that the data were normally distributed (p<0.001). Univariate analysis of the data was done using oneway analysis of variance (ANOVA). Where statistically significant differences were found, the Bonferroni multiple comparison test was employed to determine where these differences were. Dental caries experience increased with increasing age in an approximately linear fashion, with mean dental caries experience significantly lower in the youngest age group compared to the older age groups (Table 2). There was no significant difference in caries 126 Australian Dental Journal 2003;48:2.

Table 2. Dental caries experience (DMFT) by explanatory variable Decayed Missing Filled teeth teeth teeth DMFT SD p Age 17-20 years 1.43 0.07 2.09 3.59 3.65 21-25 years 1.69 0.21 2.72 4.63 3.55 0.072 26-30 years 1.32 1.21 4.54 7.07 5.16 <0.001 31-35 years 1.60 1.96 5.48 9.04 4.66 <0.001 F=25.12 Prob>F=0.001 Gender Male 1.53 0.29 2.61 4.43 4.10 Female 1.39 0.43 2.94 4.75 4.29 0.439 F=0.60 Prob>F=0.439 Education <Yr 12 1.47 0.53 2.85 4.85 4.22 Completed Year 12 1.36 0.14 2.41 3.91 3.89 0.020 Tertiary 1.93 0.28 3.20 5.41 4.75 >0.05 F=4.21 Prob>F=0.016 Socio-economic status SES 1 (Professional) 1.39 0.20 1.97 3.56 3.24 SES 2 (Para-professional) 1.57 0.23 2.67 4.47 3.94 >0.05 SES 3 (Advanced Clerical) 1.31 0.36 2.74 4.41 4.27 >0.05 SES 4 (Tradesman) 1.65 0.23 2.45 4.32 3.54 >0.05 SES 5 (Labourer) 1.50 1.09 4.13 6.72 5.77 0.005 F=3.20 Prob>F=0.013 Exposure to fluoride Lifetime fluoride exposure 1.25 0.19 2.37 3.80 3.52 Partial lifetime fluoride exposure 1.39 0.40 2.88 4.66 4.25 >0.05 No fluoride exposure 2.03 0.33 2.79 5.15 4.60 0.035 F=3.50 Prob>F=0.031 experience between males and females. Subjects who had completed secondary school had a significantly lower caries experience than those who had not completed secondary school, and subjects who had gone on to tertiary study had a higher mean DMFT score, although this was not significant. Dental caries experience was significantly lower in subjects classified as being from the highest socio-economic group than those from the lowest socio-economic group (3.56 DMFT compared to 6.72). Subjects with a lifetime exposure to fluoridated water had a mean DMFT score of 3.80, made up predominantly of filled teeth (62 per cent), followed by decayed teeth (33 per cent) and missing teeth (5 per cent). Subjects with a partial exposure to fluoridated water had a mean DMFT score of 4.66, with filled teeth again comprising more than half of the total DMFT score. Subjects with no exposure to fluoridated water had the highest mean DMFT score of 5.15, significantly higher than subjects with a lifetime exposure to fluoridated water. There appeared to be a linear relationship between fluoride exposure and caries experience. (In order to examine whether the bivariate associations were confounded, multivariate Poisson regression was performed using age, sex, socio-economic status and water fluoridation exposure as explanatory variables, with caries experience expressed using the DMFS index. This regression model found that, when adjusted for all other variables, the effect of a partial exposure to fluoridated water became statistically Fig 1. Caries experience in Australian adults 1945-1994. significant compared to subjects with no exposure to fluoridated water. The rate of caries experience in subjects with a lifetime of exposure to fluoridated water remained virtually unchanged from the unadjusted model to the full model. Furthermore, the effect of socioeconomic status on caries experience was diminished when confounding factors were taken into account, with the rate of caries experience in the lowest socio-economic group 2.49 times that of the highest group in the unadjusted model, and 1.89 greater in the adjusted model.) DISCUSSION It is difficult to assess time trends in caries experience in a population. Dental caries is a multifactorial disease, and changes to factors such as diet, use of topical fluorides, school based preventive programmmes and attitudes to health all have an effect on the pattern of disease over time. Longitudinal studies allow the observation of disease progression over time related to possible aetiologic and preventive factors. However, they cannot show if the prevalence of disease in a particular age group has changed over a period of time. They are also expensive and timeconsuming. Comparing data from various crosssectional studies conducted at over a period of time can show trends in caries experience, although this method has some obvious risks. Differences in methodology, population sampling and control of confounding factors mean that strict comparison from two sets of data are not possible. However, the comparison of cross-sectional studies is often the simplest way to observe changes in the distribution and development of dental caries. Figure 1 reports caries experience data for Australian adults from various studies that have been performed since 1964, including results from this study. There has been a dramatic decrease in caries experience in adults between 1964 and 1988, with a more gradual decline from 1988 to 1996. Together with this reduction in caries experience, there has also been a change in the pattern of DMFT. Andrews found a mean DMFT score of 19.13 in Royal Australian Dental Journal 2003;48:2. 127

Australian Air Force personnel in 1948, of which 57 per cent could be attributed to missing teeth. 6 Caries experience remained relatively unchanged up until 1966, with mean DMFT scores ranging from 17.97 to 19.7 for subjects aged 18-25 years of age in 1960, and 18.52 to 21.80 for subjects aged 17-29 years of age in 1966. 7,8 Most of these subjects were born before the introduction of community water fluoridation. There was a noticeable decrease in mean DMFT scores from 1966 to 1984. Thomas in 1984 found mean DMFT scores ranging from 10.94 to 15.34 for subjects aged 15-29 years of age, which for the younger cohort represents almost a 50 per cent reduction in caries experience. 9 Many of the subjects in this study were born prior to the introduction of water fluoridation. However, the large difference in caries experience from the earlier studies suggest a possible topical or posteruptive effect of fluoridated water in decreasing caries experience. Spencer et al. showed a similar level of caries experience in Melbourne adults in 1985. 10 A study of Royal Australian Navy recruits in 1988 showed a further large decrease in caries experience, with mean DMFT scores ranging from 4.33 to 8.87 for subjects aged 15-29 years of age. 11 Morgan et al. showed that that there was a significant difference in mean DMFT scores for those subjects who had lived almost exclusively in artificially fluoridated areas compared to those from non-fluoridated areas. 11 For subjects aged between 15 and 19 years of age, those who had no exposure to fluoridated drinking water had a mean DMFT score of 5.02, while those who had lived in fluoridated areas had a mean DMFT score of only 3.64, a difference of 28 per cent. For the older age group (those aged 20-24 years of age) there was a mean DMFT score of 8.32 for the non-fluoridated group and 4.27 for the fluoridated group, a difference of 49 per cent. Morgan et al. found that nearly two thirds of all caries experience was attributed to filled teeth, with only 2-4 per cent of the mean DMFT score due to missing teeth. 11 Dawson and Smales found, in an older RAAF population, a higher level of caries experience. 12 When the results of the study of Naval recruits in 1988 are compared to the present results, the trend in decreased caries experience continues. The mean DMFT scores for the overall group range from 3.59 for the youngest age group (17-20 years of age) to 9.04 for the oldest age group (31-35 years of age). The overall mean DMFT scores for subjects aged 17-20 years (3.59) and 21-25 years (4.62) is similar to the mean DMFT scores for the fluoridated groups in 1988, 15-19 years (3.64) and 20-24 years (4.27). When the present groups are analysed by fluoride exposure, the difference in caries experience becomes even more noticeable. The mean DMFT scores for the fluoridated group range from 3.06 to 9.50 for subjects aged 17-35 years, while the mean DMFT scores for the nonfluoridated group ranging from 4.32 to 13.40 for the same age group. The diagnostic criteria used in the present study vary from these other studies in that radiographs were used as an aid to diagnosis. It has been shown that the omission of bitewing radiographs underestimates the DMF count, so it is probable that DMFT scores reported here would be greater than if radiographs were not used to aid diagnosis. 13 Care must be taken when comparing sample populations over a period of time, to ensure that the subjects are representative of that particular population, and that they have not changed significantly during this period. This comparison of Army recruits to other military populations over the past 50 years is a valid one. The factor that has changed most dramatically in the population is exposure to fluoridated drinking water. Other variables such as socio-economic status and level of education were not reported in some of the previous studies. The study of Naval recruits showed that half the sample had completed four or fewer years of secondary education, which is comparable to the present study. 11 The use of statistical tests based on the t distribution assumes that the data are derived from the normal distribution. However, the frequency distribution of DMFT scores in the present study was positively skewed. This presents some difficulties with statistical analysis of the data. The t method has been reported to be reasonably robust if not more than 40 per cent of the sample population is caries free and the sample size is greater that 50. 14 The most likely effect of skewness is a loss of power and an inability to find differences that do exist. 15 Oneway analysis of variance (ANOVA) was used to analyse the DMFT data with the assumption that it would not be able to detect all differences in mean DMFT scores between groups where differences actually existed. CONCLUSIONS The sample of military recruits provides a unique opportunity to study a large population of young people from diverse socio-economic and geographical backgrounds. This population also has a wide range of differing exposures to fluoridated water, ranging from those with no exposure during their lifetime through to subjects who have moved in and out of areas with water fluoridation and those who have spent their entire life consuming fluoridated water. This allows for the study of the effect of variable water fluoridation exposure on dental caries experience. Operational service requirements dictate that military personnel maintain a high level of dental health. Dental problems have the potential to adversely affect combat efficiency, and historically have been a factor in withdrawal from duty. The dental health on enlistment of Army recruits, although not used as a screening condition for acceptability for service, can determine how quickly a member can be rendered dentally deployable. The results of this study show that there has continued to be a decline in caries experience in young adults in Australia when compared to other ad hoc 128 Australian Dental Journal 2003;48:2.

studies. However, the prevalence of dental caries still remained high in these young adults, with only 19 per cent of subjects aged 17-20 years caries free and only 4 per cent of subjects remaining caries free by the age of 30-35 years. This is despite 54 per cent of 12 year old children being caries free in 1992. 16 It appears as though there has been a delay in the onset and progression of dental caries, although the severity of disease has been markedly reduced. Subjects with a lifetime exposure to fluoridated water had significantly lower dental caries experience than subjects with no exposure to fluoridated water. The sample population is a rather restricted subset of the Australian population, made up of predominantly fit, young, well-educated males. Some caution must therefore be exercised in extrapolating these results to other populations. ACKNOWLEDGMENTS The authors would like to acknowledge the support and assistance of the staff of Kapooka Dental Company in the collection of data, especially Dr Rob Hazelwood and Dr Jacob Varughese. This research was supported by the Australian Defence Medical Ethics Committee and the Royal Australian Army Dental Corps. REFERENCES 1. Spencer AJ, Slade GD, Davies M. Water fluoridation in Australia. Community Dent Health 1996;13:27-37. 2. Spencer AJ. Time trends in exposure to optimally fluoridated water supplies among Australian adolescents. Community Dent Oral Epidemiol 1984;12:1-4. 3. World Health Organization. Oral health surveys: basic methods. 4th edn. Geneva: World Health Organization, 1997. 4. Commonwealth Department of Health. Fluoridation of water in Australia 1984. Canberra: Commonwealth of Australia, 1985. 5. Australian Bureau of Statistics. Australian Standard Classification of Occupations. 2nd edn. Australian Bureau of Statistics, 1986. 6. Andrews NH. Study of the dental status of male and female personnel who enlisted in the Royal Australian Air Force during the 1939-1945 War. Aust J Dent 1948;52:12-24. 7. Duncan BC. Dental survey of 955 males serving in the Australian Military Services, 1960. Aust Dent J 1964;9:109-115. 8. Dale JW. Prevalence of dental caries and periodontal disease in military personnel. Aust Dent J 1969;14:30-36. 9. Thomas M. Survey of the oral health status of Australian soldiers. Brisbane: The University of Queensland, 1984. DDH thesis. 10. Spencer AJ, Wright FAC, Brown DF, Hammond RH, Lewis JM. A socio-dental study of adult periodontal health. Melbourne: Department of Preventive and Community Dentistry, The University of Melbourne, 1985. 11. Morgan MV, Stonnill A, Laslett AM. Dental caries amongst Royal Australian Navy recruits, 1988. Aust Dent J 1992;37:201-204. 12. Dawson AS, Smales RJ. Dental health changes in an Australian Defence Force population. Aust Dent J 1994;39:242-246. 13. de Vries HCB, Ruiken HM, Konig KG, van t Hof MA. Radiographic versus clinical diagnosis of approximal carious lesions. Caries Res 1990;24:364-370. 14. Worthington HV. The suitability of the statistical techniques currently used to describe and analyse cross-sectional caries data. Community Dent Health 1984;1:125-130. 15. Bland M. An Introduction to Medical Statistics. 2nd edn. Oxford: Oxford Medical Publications, 1995. 16. Spencer AJ, Davies M, Slade GD, Brennan D. Caries prevalence in Australasia. Int Dent J 1994;44:415-423. Address for correspondence/reprints: Dr Matthew Hopcraft School of Dental Science The University of Melbourne 711 Elizabeth Street Melbourne, Victoria 3000 Email: m.hopcraft@unimelb.edu.au Australian Dental Journal 2003;48:2. 129