Environmental pollution is a major concern worldwide, resulting in growing exposure of the human population to harmful substances which threat human health [1].

Cadmium (Cd) and lead (Pb) are common pollutants. They are toxic even at low levels and are associated with adverse health effects. Cd accumulates mainly in the kidneys, followed by the liver, bones and teeth, while Pb is incorporated in calcified tissues, such as bone and teeth [2], [3].

Adverse effects of heavy metal exposure can start as early as from the embryonic period [4]. Pb and Cd can potentially impair normal fetal bone growth by competing with calcium for deposition into bone due to similar chemical characteristics [5], [6]. Postnatal metal exposure on infants can also occur through breastfeeding [7]. Children are at greater risk of poisoning than adults due to their rapid growth and absorbing metals and their influence on nutrient intake [8].

Several earlier studies provided insight into the potential role of Pb and Cd in dental caries. Pb and Cd can adversely affect enamel and dentin formation which makes the tooth more susceptible to dental decay [9], [10], [11], [12]. Furthermore, Pb and Cd negatively impact salivary gland development and function, resulting in reduced salivary flow [13], [14]. Previous studies reported controversial results on the role of Pb and Cd levels on dental caries when adjusting by other confounding variables, such as socioeconomic status and oral health behaviors [15], [16], [17], [18].

Metals deposited in teeth during mineralization are to a large extent retained. Primary teeth may thus be used as indicators of long-term heavy metal exposure during early life [19], [20]. Several studies showed that salivary Pb and Cd may directly reflect blood Pb and Cd levels and indicate recent exposures [21], [22], [23], [24], [25].

The most important biomarkers for monitoring exposure to toxins in humans are blood and urine [21]. Children are afraid of the blood draw procedure [22] and collecting urine sample is not easy either [26]. However, saliva and primary exfoliated teeth are easily collectable and present non-invasive methods [21], [23]. These biomarkers have been known to be reliable and more feasible than the collection of urine or blood in epidemiological studies assessing sensitive populations, such as young [27].

Pb and Cd poisoning is a silent disease in Iran, and everyone is at high risk of exposure and toxicity [28], [29]. Tehran, a metropolitan area, is an overcrowded city and has been threatened by several major sources of air, water and soil pollutants [30]. There is no study on the relationship between heavy metals levels in saliva and teeth and primary dental caries in this province.

Environmental pollution by heavy metals might affect general and oral health, in highly populated and polluted living areas. The objective of this study was to evaluate the association between lead and cadmium levels and dental caries in exfoliated/extracted primary teeth and in saliva, salivary pH controlled by background determinants, socioeconomic status and oral health behaviors. It was null hypothesized that no association exists between Pb and Cd levels and dental caries.