Reference values reflecting the findings of natural concentrations of teeth in a well-defined group of individuals, are indispensable, if one is to interpret results generated for clinical utility. Hence, a comprehensive compilation of literature survey is attempted to make available as a reference guideline for tooth element concentrations. Presently, the reference values are proposed for 19 elements. Several factors that are found influencing element levels, are common to any biosample and are broadly grouped under four categories namely, the factors of teeth, donor, environment and analytical methods. How best the influencing factors to be considered during analysis, are discussed. It is elucidated that standardized method of analysis with quality assurance and precision will reduce the ambiguity of comparison of inter-laboratory measurement. When the merits and demerits of element measurements are evaluated, it is recognized that except a hurdle of difficult specific sampling, many advantages make teeth an attractive material for environmental health monitoring of population and for assessment of element status of deficiency and excess due to differential exposure. The available data of tooth elements are lesser in comparison to data of blood and hair; further studies are required for reference values of others elements and for distribution pattern in different conditions, parts and types of teeth.
Reference or baseline values of teeth are determined to explain adequately functions of various elements and the changes that occur in their concentrations in pathologic states and to conduct large scale epidemiologic studies. At present, human teeth are widely analyzed for levels of elements that are compared with available levels of other studies. In such cases also, the well-founded reference values are needed. A meticulous appraisal of literature values published by Iyengar et al. [
In majority, multi-elements are analyzed in teeth because of easy analytical procedure with inter-laboratory quality assurance; in specific cases, single element e.g. lead or fluoride or other bone seeking elements are exclusively determined and their levels (ppm/ µg/g ± SD, Standard Deviation, or otherwise mentioned) are here elucidated.
Being one of the most important environmental pollutants, lead (Pb) is a common choice of selection. In table 1 are shown lead levels of deciduous and permanent teeth estimated in the subjects of several places [
In permanent teeth of resident subjects, less than 10 µg/g level of Pb were reported in Kyoto (1.2), Graz, Austria (1.7 µg/g), Klina, Kosovo (3.2) and Kuwait (5.6 females and 6.8 males). Higher levels were also observed in Mitrovica (22.3), in Virginia (43.2 ± 1.0 (enamel) and 38.9 ± 1.4 (dentine)).
Besides lead, other elements estimated in deciduous and permanent teeth of subjects from different places are shown in
The estimated mean concentrations of cadmium are 0.028 (non-urban children), 0.03 (urban children), 0.04 (children from Poland), 0.054 (control adult subjects) and 0.55 (children from Jordan).
S N | Subjects | Place | Tooth Type | Mean Level (ppm/µg/g ± SD) | Method | Ref. |
---|---|---|---|---|---|---|
1 | Children | Sao Paulo Brazil | DT | 1.3 | ICP-MS | [ |
2 | Children | Pribram, Czech Republic | DT | 1.43 | AAS | [ |
3 | Children | suburban areas of Turkey | DT | 1.30 - 1.77 | AAS | [ |
4 | Children (5 - 7 yr) from Poland | Non-urban | DT | 1.77 ± 1.79 | AAS | [ |
Urban | 1.47 ± 1.7 | |||||
5 | Male & Female children | Merida, Venezuela | Healthy DT | 3.10 ± 0.97 | AAS | [ |
6 | Children | Urban & suburban Ankara | DT | 3.42 | AAS | [ |
7 | Children | Karachi | DT | 5.78 | AAS | [ |
8 | Children of 5 to 12 yr | Jordan | DT | 30.26 | ICP | [ |
9 | Preadolescent Negro children | Charleston SC, USA | DT | 92.4 ± 41.9 | AAS | [ |
10 | 6-yr-old children 9-yr-old children | Finland | DT incisors DTcanines | 8.1 ± 5.3 4.1 ± 2.6 | PIXE | [ |
11 | Children | zinc-lead smelter area of Dariba, India | Incisors Canine Molars of DT | 40.67 ± 21.06 46.77 ± 50.10 39.56 ± 34.33 | AAS | [ |
12 | Women | Kyoto | PT | 1.2 ± 0.5 | XRF & ICP | [ |
13 | Females | Kuwait | PT dentin | 5.6 ± 4.6 | AAS | [ |
Males | 6.8 ± 4.7 | |||||
14 | Residents | Mitrovica (Kosovoa) | PT | 22.3 | ICP-MS | [ |
Klina (Kosovoa) | 3.2 | |||||
Graz (Austria) | 1.7 | |||||
15 | 10-12 yr old children | Virginia | PT | 43.2 ± 1.0 (e) 38.9 ± 1.4 (d) | NAA | [ |
16 | All subjects, (children & adult) | Hoboken (industrial) | PT | 35.35 ± 6.0 | AAS | [ |
Brussels (urban) | 17.72 ± 4.16 | |||||
Arlon (rural) | 21.45 ± 4.35 | |||||
17 | Lead-poisoned children | DT dentine | 601 ± 225 | ASV | [ | |
Children | Suburban Boston | 84.4 ± 56.6 | ||||
Healthy children | Iceland | 35.9 ± 29.5 |
Note: Atomic Absorption Spectrophotometry (AAS), Inductively Coupled Plasma-Mass Spectrophotometry (ICP-MS), Proton Induced X-Ray Emission Spectrophotometry (PIXE), Anodic Stripping Voltametry (ASV), X-Ray Fluorescence Spectrometry (XRF).
No | Subjects | Place | Tooth Type | Element | Levels (ppm)/ (µg/g ± SD) | Method | Ref. |
---|---|---|---|---|---|---|---|
1 | Children 5 - 7 yr old | Non-urban | DT | Cd | 0.028 ± 2.5 | AAS | [ |
Urban | 0.03 ± 2.63 | ||||||
2 | Normal subjects | PT | As | 0.060 | NAA | [ | |
3 | Children | North Carolina | Incisors-DT | F | 792 ± 402 | Ion specific electrode | [ |
molars-DT | 768 ± 489 | ||||||
4 | Healthy Children | Southern Poland | DT | Mn Fe Cu Cr | 4.39 ± 3.72 51.0 ± 23.9 4.62 8.97 ± 1.94 | AAS | [ |
5 | Children | Dalmatia & Novigrad, Yugoslavia | Enamel of caries free teeth | V | 3.7 ± 1.5 ng∙g−1 | NAA | [ |
6 | Adults | Finland | PT | Ni | 0.9 ± 0.7 pg/g | AAS | [ |
7 | Children of 5 to 12 yr | Jordan | DT | Cd Cu Fe Zn | 0.55 6.23 34.72 128.21 | ICP | [ |
8 | Women | Kyoto | Enamels of molar teeth (PT) | Hg Cu Zn | 1.7 ± 0.2 ng/g 0.9 ± 1.1 150 ± 24.6 | ICP-MS | [ |
9 | 6-yr-olds children 9-yr-old children | Finland | DT incisors DT canines | Zn Sr Zn Sr | 150 ± 29 63 ± 18 142 ± 22 85 ± 13 | PIXE | [ |
10 | Male and Female children | Merida, Venezuela | Healthy DT | Sr Cu Zn | 38.37 ± 4.82 1.21 ± 0.86 85.33 ± 12.98 | AAS | [ |
11 | Subjects from high Sr areas Subjects from low Sr areas | Fort Recovery Delphos Rochester | PT | Sr | 564.0 485.5 80.2 | AAS | [ |
The average dentin fluoride concentrations per exfoliated primary tooth were 792 ± 402 for incisors and 768 ± 489 for molars of children from North Carolina [
The concentration of Ni 0.9 ± 0.7 [
A value of 4.0 manganese measured in enamel by Little and Steadman [
A range of 20.0 to 44.0 of iron in sound enamel was reported by Little and Steadman [
Derise and Ritchey [
Strontium concentrations observed by others in different tooth types are 1.21 ± 0.86 in healthy deciduous teeth of children from Venezuela [
The values 0.47 ± 0.04 and 0.25 ± 0.03 were determined respectively in enamel and dentin of permanent teeth of Virginia children [
Very low copper values of 0.26 and 0.21 were found respectively in the enamel and dentin [
The estimated Zinc levels of deciduous teeth were 128.2 in Jordan children of 5 to 12 year old [
The determined Al values were 86.6 ± 2.5 in enamel and 63.4 ± 1.5 in dentin of permanent teeth of Virginia children with the enamel having the higher concentration [4/16]. Similar values in enamel (86.13) and dentin (68.06) [
Byrne and Vrbic [
Tooth levels of 19 elements are compiled; considering their physiological roles at deficiency or excess status of essential, non-essential and toxic effects and the normal concentrations between deficiency and excess, the proposed reference values (ppm) are 10.0 (Pb), 1.0 ng/g (Hg), 0.05 (Cd), 0.05 (As), 100.0 (F), 0.5 pg/g (Ni)150.0 (Zn), 10.0 (Cu) 10.0 (Ca), 2.0 (Cr) 0.5 (Se), 150.0 (Sr), 2.0 (Mn), 10.0 (Co), 2.0 (Ba), 2.0 ng/g (V), 5.0 (I), 20.0 (Fe) and 10.0 (Al).
Many factors of individual subject, teeth, environment and method of analysis are associated with levels of elements measured (
A statistically insignificant difference of tooth lead levels were shown between boys and girls [
Lead levels of teeth were higher in the hypertensives and diabetics, whereas copper levels were lower in the hypertensives from Mysore, India [
There was a significant increase in tooth lead levels with advancing age of the subjects from Coruña, Spain [
The concentrations of Pb and Cd in teeth from smokers (Pd 31.89 and Cd 0.49) were significantly higher than those from nonsmokers (Pb 24.07 and Cd 0.37) of four Jordan cities such as, Amman, Zarqa, Al-Mafraq and Irbid [
The socio-demographic factors may affect the lead level in children; certain
SN | Factors/characters influencing element levels in teeth | |||
---|---|---|---|---|
Individual | Tooth | Environment | Analytical method | |
Sex Age Diet Smoking Health status Others | Types Caries filling materials Others | Region & place of residence Urban & rural exposure Others | Sampling procedures Methods of digestion Instruments used Others |
factors viz., family income per capita per month, number of sibling and parental education, were not significantly correlated with higher tooth lead levels [
Sound primary and permanent enamel: The concentrations of F, Sr, and K were significantly (P < 0.05) higher in sound enamel of permanent teeth than that of sound enamel of primary teeth, whereas the concentrations of Al, Si, and Cu were significantly (P < 0.05) higher in sound enamel of primary teeth than the sound enamel of permanent teeth [
Concentrations of Si and Cu were not significant (P > 0.05) between the sound and carious enamel of primary and permanent teeth, but concentrations of F, K, and Si were significantly (P < 0.05) higher in sound enamel of primary teeth than that of the concentrations of carious enamel of primary teeth [
Lead (31.02) and cadmium (0.52) concentrations in teeth of Jordanian patients with amalgam fillings were significantly higher than those from patients without the fillings (Pb 26.87 and Cd 0.41) [
Human tooth, having basically made up of two parts, the crown and the root, has a complex system of heterogeneous, specialized tissues viz., enamel, dentin, cementum and pulp. Its tissues are similar to those materials making up bone and has also contain organic matter and various trace elements distributed in varying proportions in its structure. The major inorganic components are calcium, phosphate, carbonate, magnesium and sodium. Elemental distribution can provide information about 1) physiology, 2) environmental influence, 3) dietary habits, 4) contamination by metallic amalgams used as restorative material and 5) correlation of chemical composition and local variations with mechanical characteristics of enamel.
1) Enamel
It is one of the most essential structures of tooth, both from a functional and esthetic point of view. Its mineralization is a gradual process, still continuous at 6 months post-natally in the primary mandibular incisors, while demineralization depends on the degree of mineralization and the chemical content of the enamel exposed. In enamel, this mineral phase is not subject to turnover, since it consists of biological mineral hydroxyapatite, where various ions may be substituted into the crystal lattice only during the development. Thus, the enamel encapsulates a permanent record of the trace element environment during the development of a tooth.
2) Dentin
Dentine is the next underlying layer of enamel. The pulpal dentine, this last being a thin layer of new dentine lining the interior of the pulp cavity and deposited slowly during the whole life of the tooth. The bulk of the pulp is similar in composition to connective tissue, containing various types of cells, collagen fibers, nerve trunks, lymphatic and blood vessels. There is no active metabolism of elements after the completion of dentin that is surrounded by enamel and cementum, and is not affected by the oral environment [
Many studies revealed higher levels of elements in the subjects from industrial areas or urban, particularly lead in the children and adult from Belgium [
Various analytical techniques of AAS, ICP-MS, ASV, XRF, PIXE, NAA, etc., have been used for tooth element analysis after sampling and preparation through acid digestion. Many of the factors influencing trace element levels can be minimized by adopting correct and uniform sampling procedure and appropriate controls. One of the important conditions for ensuring the realistic evaluation of population exposure is the examination of sufficiently large population groups and use of certified reference materials for quality assurance [
Several factors affect tooth levels of elements and at the same time in certain cases, both positive and negative influences as well as limited numbers of factors have so far been pointed out. Even then, a detailed consideration of maximum number of the influencing factors will improve quality of analysis and make relevant for comparison within the studies.
・ There are many advantages which make teeth as an attractive bio-analytical material: easy to sample, to preserve and to store without the risk of any change in composition. Tooth composition changes more slowly than soft tissues in response to these factors due to a homeostatic mechanism which prevents either depletion or excess.
・ The potential for using lead in whole deciduous teeth, enamel or dentin as an indicator of past exposure of children to lead have been well recommended in many studies [
・ The tooth levels of lead could be considered as a proxy for skeletal lead which could be analyzed with more difficulties than tooth element analysis [
・ The advantage of deciduous tooth lead over blood lead analysis lies in the incorporation of lead into the tooth during several years from uterus to exfoliation, compared with blood that has recent exposure [
・ Measurement of lead in deciduous teeth seems to be an index of exposure during the peak years of lead ingestion even after blood lead has returned to lower levels [
・ Milk teeth could be used to investigate the passive exposure from transfer of plutonium from the mother’s blood plasma to the fetus, since enamel is formed during pregnancy [
・ Temporary teeth are free from restorations and hence they are free from one source of external contamination and preferable to permanent teeth which are filled with materials.
・ Since there is minimal turnover of lead during tooth life, the level can be related to the quantity of ingested lead [
・ Lead content of teeth is considerably greater than that of bone, since bone lead loss is related to resorption and change in the bone level, while tooth lead level is permanent [
・ Lead measurements of archaeological skeletal tissues have shown that enamel is a unique tissue in the body in preserving a reliable record of childhood Pb exposure long after death and burial [
・ Uptake of trace levels of Cd, Zn, Pb and Cu during formation of the deciduous tooth could be known.
・ Serum zinc is a reasonable indicator of the current status. On the other hand, deciduous teeth have been suggested as indicators of long-term, cumulative zinc absorption in early life [
・ Deciduous teeth showed significantly high lead levels compared to blood; they reflect cumulative exposure and prove to be better indicators of body burden and for predicting neurotoxicity of lead [
・ For legal considerations, analysis of teeth provides a viable alternative to bone for the study of geographical variations in bone-seeking radionuclide contamination [
・ There is an interest to analyze the chemical composition of enamel from patients with different developmental disorders or syndromes and evaluate possible differences compared to normal composition.
・ Past research has relied mostly on fluoride in hair, fingernails or toenails, urine, saliva, blood, bone and enamel as a biomarker of exposure [
・ Fluoride concentration of dentin has been suggested as a biomarker for cumulative exposures [
・ Incremental growth structures in enamel may provide a basis for interpreting the chronology of dietary transitions during infancy and childhood [
・ Enamel biopsy by removal of a layer of enamel by acid etching on a limited surface area of tooth, an easy sampling, facilitates wider adoption [
・ A number of problems arise in the analysis of inorganic elements of dental tissues in small, well-defined morphological areas [
・ Examination of elements could not be practiced as a routine form of screening and also not from specific subjects [
・ It is not always easy to collect exfoliated teeth from a population, besides the fact that the collection of deciduous teeth by itself will not provide the researcher with important information regarding the past history of the child, which is more easily collected when the child is examined and a questionnaire is filled by the parents.
・ Another drawback of studies on exfoliated teeth is the frequent use of many different teeth from many different regions, which makes comparisons difficult.
・ The hardness of enamel and the isolating properties of the hard tissues make the use of various probe techniques difficult. Further, many of elements have such low concentrations that few methods are appropriate for analysis.
・ Deciduous teeth, however, are not a uniform mass of calcified tissues. Despite the fact that most studies have dealt with whole tooth element content so far, teeth are anatomically complex being composed of different calcified tissues that harbor different concentrations of elements according to their own developmental characteristics [
Taking into consideration of the above two aspects, advantages are more and multifarious, while the limitations are technical and could be minimized following standardized techniques with quality assurance, except the inability of specific, immediate sampling.
In this presentation, it is concluded that generally, the baseline levels are to be reported in a specific sample groups whose values are compared with random sample groups of other population studies. In such case, standardized analytical methods must be the common condition to avoid much deviation and to identify the influence of factors [
Both deficiency of essential elements and excess of non-essential and pollutant elements could be assessed in the teeth, even at nanogram level with highly sensitive analytical techniques. Besides single element like lead, fluoride, or radioactive elements, several elements are at a time determined; rare cases of elements of poisoning, fossil hominid and endemic region could be assessed in teeth for forensic and historical importance. Though health problems of major elements are investigated less, trace elements have been observed in relation to deficiency or excess level, since there are possibilities of decreasing or increasing trends of narrow ranges of trace elements due to exposure gradients. Hence, primary concern of trace element status and health implication could be resolved with tooth element analysis. Poor health implication with 1) deficiency or excess of elements, 2) route and sources and 3) biomarkers of element effects, the triangular prediction criteria, are to be further explored for a number of elements.
Several factors influence element levels and considering the factors before sample selection is preferable to considering after sampling. Besides the influencing factors, relative element levels in teeth are to be considered, when heavy metals can replace calcium in hydroxyapatite crystals and evaluation of cadmium and lead levels in tooth should be based not only on the absolute content of these metals but also on the ratio of these metals to calcium [
Either deciduous or permanent teeth, is employed alternatively. Among the four parts (enamel, dentin, pulp and cementum), any one or two, are selected for studies. When teeth are of four types (incisor canine, premolar and molar) and location of them are also four (upper, lower, left and right regions), sample type availability is mostly random; in such case the choice of selection of their type is to reduce much variation and preferable to any one type, but further studies are required to compare and contrast distribution pattern of elements in all the four parts and types, to identify other factors known to affect tooth elements and to recognize the relationship among element level of body store, exposure sources and functional aspects for prediction of health implication.
The author thanks sincerely The Principal, RIE, Mysore and The Director, NCERT, New Delhi for moral support.
Sukumar, A. (2018) Human Exposure Assessment of Element Pollution for Environmental Health Implications: Teeth as a Biomonitoring Tool. Journal of Geoscience and Environment Protection, 6, 37-53. https://doi.org/10.4236/gep.2018.63005