Trends in dental caries of deciduous teeth in Iran: a systematic analysis of the national and sub-national data from 1990 to 2017

Despite being largely preventable and due to its ubiquitous nature, child dental caries remains the most prevalent child affliction around the globe, affecting up to 60–90% of school-aged children in most industrialised countries [1‐4]. This results in a high economic and disease burden on countries. Iran is no exception: child dental caries has been estimated to have caused more than 1500 years lived with disability in 2017 [4] and more than $10 M in productivity losses in 2015 [5]. With this considerable burden, oral disorders tend to be overlooked among other health conditions and are rarely seen as a priority in health policy [1, 6, 7]. Other physiologically influential factors include factors affecting tooth germ formation, natural protective factors, such as saliva, and exposure to a low fluoride level [8‐10].

Oral diseases are chronic and progressive in nature [6, 11]. For example, dental caries affects very young children but is a lifelong condition that tracks across adolescence, adulthood, and into later life [6]. Poor oral health can negatively impact a child’s ability to eat, speak, sleep, and socialise, resulting in adverse impacts later in life [12, 13]. In addition to affecting children’s quality of life [14] and school performance [15], dental caries places a considerable burden on health care provision. For instance, most hospital admissions for children in England between 1997 and 2006 were primarily due to dental caries [16].

After 1960, an evident decline in caries prevalence occurred in Western European countries [17]; children’s and adolescents’ habit of brushing their teeth with fluoride toothpaste was the most crucial factor in this decline [18, 19]. However, this is not the case in developing countries where the oral health system is not fully established.

In developed countries, regular child dental health surveys have been established several decades ago (such as in the UK [20], Australia [21], and Canada [22], but in developing countries there are no regular, precise, and adequate national data in the literature. For example, the three latest child dental health surveys in Iran date back to 2004, 2013, and 2016, and the results of the survey in 2016 showed that the mean decayed, missing, and filled teeth (dmft) of Iranian school children aged 6 and 12 was 5.84 which is seven and nearly two times that of the UK’s [23] and Turkey’s [24] children, respectively. This highlights the need to make or change policies to reduce dental caries in children.

However, policy-making could not be done effectively without proper data and understanding of the current situation, which helps us in making informed decisions and improving future policy planning. This study aims at estimating the national and sub-national dental caries trend in deciduous teeth among the Iranian population at different ages by sex from 1990 to 2017. The findings of this descriptive report will serve as a baseline for monitoring the progress of policies seeking to address oral health status in Iran.

The Burden of Oral Disorders (BOD) is a part of a more extensive study (National And Sub-national Burden of Diseases: NASBOD) aiming to assess dental caries, periodontal disease, and severe tooth loss. We scrutinised all the relevant literature; either published, unpublished, or grey literature. After that, we ascertained the eligible studies using three phases including title, abstract, and full-text. Data extraction was performed after assessing the quality of data using a form based on the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) Statement [25]. Finally, data analyses and estimations were conducted using an age-spatio-temporal hierarchical model. The protocol for this study has been published earlier [26]. Full details of the methods of the current study are available in the protocol. Here, we will discuss the most critical aspects of our methodology more rigorously.

This study provides a unique opportunity to look at children’s oral health and disease in Iran over three decades. This paper has focused on one disease, caries. Dental caries is the most prevalent health condition globally, imposing a high health and economic burden on countries. Knowing the past situation and comparing it with the current status is crucial to evaluating nationwide oral health programs (if any) and providing a better point-of-view for further oral health policies. However, there are no publicly available nationwide trend data regarding child dental health in Iran, and this study endeavoured to fill in this gap.

The results highlight a high mean number of dmft across all child age groups, which has continuously increased since 1990 (more than 15%). The number of mt has been almost unchanged during these three decades, and an increased number of dt and ft is responsible for increasing dmft. The highest increase in dmft and dt was in 1–4-years age group with more than 35% and 36% increase, respectively. Overall, the highest dmft was found among the 10–14-years age group which was not unexpected, as dmft is a cumulative index.

As shown in Fig. 3, this increase in dmft gradually spreads from northwest to middle, south, and southeast of Iran and can be attributed to the shift in dietary habits of the Iranian children. This shift could also be worsened by the low frequency of daily tooth brushing and flossing among children in Iran [37, 38]. According to one study, only 2.7% of children (6 to 14 years old) brush and floss on a daily basis [39]. As depicted in Fig. 4, dmft was higher among boys compared to girls in 1990 in almost all provinces. Despite the fact that dmft increased among all age and both sexes, this difference remained until 2017. Also, an interesting finding is that although dt is higher among boys in almost all age groups and all provinces, ft is not significantly different among them. This means that girls experience tooth decay less than boys, and when they do so, they receive better or at least equal treatment. It should be noted that our data did not include any study on children with disabilities, and as this vulnerable population experience higher rate of tooth decay and also have lower access to care [40], future national surveys should include this population accordingly.

While the number of dental schools and dentists has increased dramatically during the last two decades [41], seemingly it had little or no positive impact on Iranian children’s dental health, at least in the short term. In contrast, dmft has increased. The number of ft, which is a result of dental procedures, has increased slightly. The reasons could be various, including families’ better economic situation, a shift in families’ mindset towards the importance of their children’s dental health, and a higher number of available dentists [41]. However, the mean of dt is more than 13 times the ft mean in 2017, which implies the oral health system has failed to provide adequate oral health care to Iranian children.

National and international studies have shown that increasing child dental caries burden has not occurred in every country. For example, the GBD 2017 study has stated that the Global age-standardized prevalence [− 7.9% (− 6.6%, − 9.8%)], incidence [− 2.2% (− 0.4%, − 3.9%)], and Disability-Adjusted Life Years (DALYs) [− 9.0% (− 7.3%, − 11.0%)] rates of untreated caries in deciduous teeth has decreased from 1990 to 2017 [4]. The UK’s child dental health survey 2013 has also shown that the prevalence of caries and dmft for children in England, Wales and Northern Ireland is continuing to decrease but the rate is slowing [42]; from 4.0 in 1973 to 0.7 in 2013 for 5-year-old children [20]. The mean dmft has also decreased in German 6- to 7-years-olds, from 2.89 in 1994/95 to 1.73 in 2016 [43]. Not only in industrialized countries, but some developing countries have also reported that the mean dmft of their children has decreased. For example, based on a survey in Turkey, it has been reported that the mean dmft for 5-year-olds has decreased from 1988 to 2004 (dmft = 3.7 in 2004) [24] which was much lower than dmft for the 5–9-years age group in 2000 and 2010 in Iran (4.78 and 4.97, respectively). However, some middle-eastern countries have also high dmft; for example, in a meta-analysis, it was estimated that the mean dmft for Saudi Arabian children was 5.0 [44]. In some other middle-eastern and north African countries such as Sudan, Tunisia, and Libya, dmft was lower. Furthermore, unlike Iran, the dmft trend in Iraq and Kuwait has been decreasing [45]. This indicates the unfavorable child dental health situation in Iran, and oral health policy-makers should consider that.

There is strong evidence that fluoride can prevent dental caries in children. Fluoride can be delivered via drinking water [46], toothpaste [18], and mouth rinses [47]. There was a fluoride mouthwash program in Iranian schools during the 2000s but it did not continue and was never evaluated in terms of cost-effectiveness [48]. It is known that supervised use of fluoride toothpaste and mouth rinses will result in a higher decrease in dental caries in children [18, 47]. In-office preventing measurements such as fluoride varnishes and gels and pit-and-fissure sealants also decrease child dental caries in the population [47‐49]. Furthermore, oral health education alone or in combination with supervised tooth brushing with fluoridated toothpaste could have a beneficial effect on dmft [50]. Lowering the amount of sugar in the diet is also linked with lower dental caries [51]. Public Health England suggests a targeted supervised tooth brushing program, targeted fluoride varnish program, water fluoridation, targeted provision of toothbrushes and paste by post, and targeted toothbrushes and paste provision by post and by health visitors as programs that can effectively reduce tooth decay in 5-year-olds. Among them, water fluoridation has the highest return on investment; £12.71 return on investment after five years and £21.98 return on investment after ten years for each pound spent. It is not surprising that our study showed that child dental caries is lowest in Bushehr (dmft = 3.89), Sistan and Baluchistan (dmft = 4.24), and Hormozgan (dmft = 4.40) provinces where the amount of fluoride in their drinking water is naturally high [52]. Finally, dental hygienists have a critical role in prevention and health promotion [53, 54] whom are not trained regularly in Iran for more than 10 years with no policy to utilize them in the oral health system.

Although our study is not an analytical one comparing provinces based on socioeconomic factors, Kurdistan with the second-lowest human development index (HDI) had the highest dmft versus Sistan and Baluchistan with the lowest HDI had the second-lowest dmft in Iran [55, 56]. Considering the pattern of sugar consumption and water fluoride has differed among Iranian provinces, perhaps it hides the direct effect of the HDI and can be one of the related causes of this conflict. It has been previously shown that child dental caries follows a socioeconomic gradient [57, 58] and any oral health promotion program considers target socioeconomic factors [59]. These factors are so important that even with providing free dental care services for everyone and equal attendance, there would still be inequalities in dental caries experience [60]. At the same time, they could make inequalities in attendance as well [61]. Hence, we should make a change from providing dental care to a plan with mostly preventive oral health programs.

Dental caries not only affects body weight, growth and quality of life in children [62] but also can affect their later life [63]. Furthermore, dental caries shares common risk factors with various systemic conditions such as obesity, as in both conditions, sugar consumption is the main risk factor [64‐66]. Data from Iran’s Agriculture Ministry show that the import of raw sugar was five-fold in 2006 compared to the previous year, and for the consequent years, sugar import has been higher than its export. We believe this could be one of the main causes of increasing dmft of the Iranian children and all other age groups. It is previously suggested to adopt a common risk factor approach in oral health policies [67, 68].

The trend of the child’s dental caries in Iran showed that high dmft in 1990 has increased continuously by more than 15%. Although the dmft was higher among boys compared to girls, however, this index has increases in all age groups, both sexes, and almost all provinces. This implies the urgent need to population-based interventions (such as supervised tooth brushing and improving dietary habits of this population) and changing the direction of oral health system policies. Although oral health was integrated in the national health reform plan since 2014 (which includes children under 14), however, studies with appropriate design to determine the cost-effectiveness of this plan are still lacking. This study’s results can be a backbone to inform oral health policy makers towards designing nationwide, transparent, and accurate oral health surveys and improving national oral health policies.