Dental caries is the most prevalent disease of childhood.1 The prevalence of dental caries in 5–11 year old Australian children in 2003–2004 ranged from 43.9% to 66.2%,2 whereas the prevalence of the most frequent general health condition, asthma, was 11.3% among children aged 0–17 in 2004–2005.3
Dental caries affects both the primary and permanent dentition. Because the disease is chronic and cumulative, as the population ages there is an accumulation of numbers of teeth per individual with caries experience and of people experiencing the disease. The rate at which this occurs in the primary and permanent dentition may differ between populations and across time, and the correlation between the two dentitions may make it difficult to measure these differences. For instance, caries in the primary dentition is a strong predictor of caries in the permanent dentition and a strong indicator of future disease is prior disease experience.4–6 The disease per se can be said to be the same in the two dentitions; there is demineralization, followed by cavitation and broadly, the same actors are involved. However, the disease seems to be more aggressive in the primary dentition. This could be a result of a thinner enamel layer combined with a set of other factors, such as a diet higher in sugars and/or the inability of a younger child to properly brush their teeth on their own. Also of interest is the period of mixed dentition in which both permanent and primary teeth are in mouth – roughly between the ages of 6 and 12. At age 6 most of the teeth are primary and at age 12 most of the teeth are permanent, thus these two age groups are of particular interest.
Temporal trends showed a global decline in dental caries since the 1970s, yet recent data indicate an increase of the disease in both the primary and permanent dentition.7 Changes in caries trends can be attributed to events occurring between the periods, such as changes to social determinants including public policies which affect birth cohorts at one point in time or during a period of time. Different changes in caries trends between the primary and permanent dentition can also be due to the effect of age. However, it is difficult to separate these effects; period and cohort effects confound each other and are likewise confounded by age.8 Therefore, the aims of this report are to: (1) examine 30-year trends for caries experience in the primary dentition of 6 year old children and the permanent dentition of 12 year old children enrolled in the school dental service (SDS); and (2) evaluate the role of period, cohort and age effects on caries experience in both the primary and permanent dentition. Decay experience is measured by the number of decayed, missing or filled deciduous (dmft) or permanent (DMFT) teeth.
The Child Dental Health Survey (CDHS) is an ongoing national surveillance survey for children’s dental health in Australia. The objectives of the survey are to document the annual prevalence and severity of dental caries among 5–17 year old children and to monitor trends in caries over time. The target population is all children enrolled in SDSs operated by Australian states and territories.
Data were derived from routine examination of children attending the SDS. There are some variations among states and territories in priority age groups, nature of services and the extent of enrolment in SDSs. In some instances, results from states have been excluded due to lack of representativeness of the sample or unavailable data. For greater detail, the reader is referred to year-specific CDHS reports. Caries was measured by the mean count of clinically detectable decayed, missing, and filled teeth. The methodology used for diagnosis and reporting of caries experience follows those published by the World Health Organization (WHO) for oral epidemiological studies.9
Data are weighted following standard procedures for stratified samples. The stratum-specific weights are divided by the national estimated resident population (ERP) and total sample size to achieve numerical equivalence between the weighted sample and the original number of processed records. Data are also weighted by time since last dental examination so that children on longer recall intervals, who often have better oral health, are not under-represented in the analysis.
Cohort was measured by year of birth, period by the year of data collection, and age was measured as chronological age (ages 6 and 12, equivalent to primary and permanent dentition, respectively). Because cohort, period and age are dependent on each other and therefore, the effect of one confounds the effect of another,8 several approaches were taken to examine differences in caries experience due to these effects: (1) changes in the trend of caries experience from 1977 to 2006; (2) comparison between caries experience for birth cohorts of children; (3) cross-sectional differences, i.e. in a given survey year, examining the difference in the mean number of decayed, filled or missing teeth due to caries in both primary and permanent dentition. Synthetic birth cohorts were formed for children born in 1971, 1977, 1983 and 1989. Synthetic cohorts are formed from cross-sectional data; the same group of children were not followed through time but instead each year a sample of children was drawn from the population.
In accordance with WHO standards, caries experience on primary teeth was estimated by dmft at age 6 and caries experience on permanent teeth expressed by DMFT at age 12.
In both the primary and permanent dentitions, there was a steep decline in caries experience between 1977 and 1983 (Fig 1). For the primary dentition, it soon levelled off but increased again between 1995 and 2001. In the permanent dentition, there continued to be a decline in caries experience until 2001, yet over time the decline in caries experience became smaller. Between 1980 and 1990, 6 year olds begin to show more dental caries than 12 year olds.
Of concern is the rapidly increasing caries experience in the primary dentition since the turn of this century. For example, 6 year old deciduous dmft increased by 44%, from 1.58 in 1996 to 2.27 in 2005. There is also an increase in prevalence by 2005–2006; more than 50% of 6 year old children attending SDS suffered from caries.
The permanent caries experience of 12 year olds decreased from a mean DMFT of 4.80 in 1977 to a low of 0.89 in 1998. However, since then we have seen little improvement and rather, an increasing trend is becoming apparent. For example, 12 year old DMFT increased by almost 25% from 0.89 to 1.11 between 1998 and 2005. Similar to the trend in deciduous dentition, the proportion of 12 year old children with permanent caries experience has steadily increased. An increase in prevalence is also observed in the permanent dentition with nearly 50% of 12 year old children affected with caries in 2006.
Figure 2 shows the caries experience at 6 and 12 years old for four birth cohorts: those born in 1971, 1977, 1983 and 1989. All cohorts showed more disease at age 6 (i.e. in the primary dentition) than at age 12 (i.e. the permanent dentition). There was a steady decrease for all cohorts but steeper in the 1983 and 1989 birth cohort, indicating a steeper decline in the experience of dental caries, i.e. a healthier transition between the two dentitions.
Cross-sectional differences in caries experience between synthetic cohorts during the same calendar time are observed in Fig 3. For instance, in 1983 the top data point represents the permanent DMFT of 12 year olds born in 1971 and the bottom data point represents the primary dmft of 6 year olds born in 1977. The difference between caries experience in the permanent and primary dentition, represented by the vertical lines, decreases between calendar years 1977 and 1983. Until 1983, 12 year olds experienced more disease than 6 year olds (i.e. higher prevalence of disease in the permanent dentition than in the primary dentition). By the 1989 calendar year, this trend is reversed with 6 year olds experiencing more disease than 12 year olds. From this time, the difference in primary and permanent caries experience between birth cohorts (represented by the length of the vertical lines) continued to increase. The reduction in the point estimate for 6 and 12 year olds indicates earlier cohorts had greater caries experience. In the primary dentition, the 1977 and 1983 birth cohorts showed the most similar levels of disease. For the permanent dentition, the most similar estimates of caries prevalence occur among the 1983 and 1989 birth cohorts.
The reduction of caries experience in school children from 1977 up to now in Australia represents a significant achievement in dental health. This is evidence of the success of public health programmes such as water fluoridation in some jurisdictions, extended fluoridated toothpaste use in the population and the existence of the SDSs. However, since 1997 there has been a clear increasing trend for caries in the deciduous dentition of Australian children attending SDSs. After 5 years (between 1996 and 2001) of stable permanent DMFT scores below 1, from 2004 an increasing trend has become apparent. By 2006, there was a 28% increase in deciduous caries experience.
A trend of increasing caries experience has been reported in other countries. In the United States, the recent National Health and Nutrition Examination Survey (NHANES) reported no reduction in the prevalence and severity of dental caries in primary teeth during a 10-year period.10 That is in contrast to the caries reduction reported in previous studies.10 Data reported from Norway for the period 1985–2004 showed a 15-year trend of decreasing caries in permanent teeth of 12 year old children. Beginning in 2000, an increase of 3.3% per year was reported.11 In Mexico, caries prevalence for 6–9 year olds increased by over 20% between 1999 and 2000.12 This analysis confirms there has been an increase in disease experience in the Australian child population. Nevertheless, this initial analysis is insufficient to clarify the reasons for the changing patterns and caries increase in the primary and permanent dentitions.
Several potential explanations for the rise in caries experience in Australian school children have been proposed.13 It is likely there is a shift between protective and risk factors.14 It is likely that the protective effect given by exposure to fluorides may have changed. Although there has been an increase in population coverage by community water fluoridation since the 1990s, there has been an even greater increase in the consumption of bottled, filtered and tank water versus tap water.15 The reported reduction in fluorosis also suggests declining exposures to discretionary fluorides,16 such as the introduction of low fluoride content toothpaste. Changes to dietary patterns could explain the observed changes in dental caries experience over time, e.g. the increasing trend in soft drink consumption could contribute to increased risk for dental caries.17 Changes in oral health promotion efforts, such as an increase in school vending machines could contribute to the observed trends.
Another reason which might partly account for the change in caries experience among Australian school children is the introduction of a copayment for children who do not hold a healthcare card to have care at the SDS or changes in SDS coverage from whole population to targeted population due to limited budgets. There is a drop in the proportion of children enrolled in the SDS in South Australia, e.g. from 80% in the early 1990s to 66% in 2003. The SDS child population might be less representative than it was when enrolment rates were higher. However, there are currently no clear indications of systematic differences over time and between children attending SDSs and those not attending. Future studies are needed to examine differences between children receiving dental care under different programme schemes.
The above explanations would likely influence both the primary and permanent dention but do not fully explain the differences in trends between the two dentitions. In particular, before 1987 caries experience in the permanent dentition was higher than that in the deciduous dentition. However, the reduction in permanent teeth was greater than in deciduous teeth. Between 1980 and 1990, caries prevalence in the deciduous dentition became higher than in the permanent dentition. The results of this analysis point to cohort and period effects to explain differences between primary and permanent dentition trends.
Other factors to consider could be differences in clinical practices and healthcare for younger children compared to older children (i.e. 6 and 12 year olds). For example, fissure sealants are placed on the permanent teeth but not on the primary dentition, and the same generally holds for fluoride varnish applications. The effect of age also needs to be considered, e.g. oral hygiene practices may be more difficult to establish in younger children and primary teeth may be at increased risk of disease due to their anatomical features.
Finally, it could be argued that in general the results are due to variation in data collection methods. However, the consistency of the changes through time and in all states and territories suggests that this explanation is unlikely. Weighting and analytical methods have been consistent through the time, including the period of steady increase in caries scores.
Although the CDHS is efficient in providing valuable and ongoing information on the oral health of school-aged children, it has limited data on clinical indicators, potential risk and protective factors to allow a thorough analysis of the role of social context, behaviour and biology on the changing disease patterns.
A renewed emphasis on child population oral health requires a strengthening of this evidence with more thorough population data. The last national survey of child oral health was conducted in 1987–1988. A new oral health survey among Australian children would greatly supplement the continued CDHS surveillance efforts by providing data to represent all children, not just those enrolled in the SDS.
This article used data from the Child Dental Health Survey which was funded by the Australian Institute of Health and Welfare. We also wish to acknowledge the time and effort contributed by the state and territory health authorities in the collection and provision of the data used in this report, along with the continued cooperation of individual dentists and dental therapists.