Spatial distribution of lead in the roots of human primary teeth

Deciduous teeth from the New Hampshire birth cohort study: Early life environmental and dietary predictors of dentin elements

BACKGROUND

Sparse research exists on predictors of element concentrations measured in deciduous teeth.

OBJECTIVE

To estimate associations between maternal/child characteristics, elements measured in home tap water during pregnancy and element concentrations in the dentin of shed deciduous teeth.

METHODS

Our analysis included 152 pregnant person-infant dyads followed from the second trimester through the end of the first postnatal year from the New Hampshire Birth Cohort Study. During pregnancy and early infancy, we collected dietary and sociodemographic information via surveys, measured elements in home tap water, and later collected naturally exfoliated teeth from child participants. We measured longitudinal deposition of elements in dentin using LA-ICP-MS. Multivariable linear mixed models were used to estimate associations between predictors and dentin element concentrations.

RESULTS

We measured 12 elements in dentin including those previously reported (Ba, Mn, Pb, Sr, Zn) and less frequently reported (Al, As, Cd, Cu, Hg, Li, and W). A doubling of Pb or Sr concentrations in water was associated with higher dentin Pb or Sr respectively in prenatally formed [9% (95%CI: 3%, 15%); 3% (1%, 6%)] and postnatally formed [10% (2%, 19%); 6% (2%, 10%)] dentin. Formula feeding from birth to 6 weeks or 6 weeks to 4 months was associated with higher element concentrations in postnatal dentin within the given time period as compared to exclusive human milk feeding: Sr: 6 weeks: 61% (36%, 90%) and 4 months: 85% (54%, 121%); Ba: 6 weeks: 35% (3.3%, 77%) and 4 months: 42% (10%, 83%); and Li: 6 weeks: 61% (33%, 95%) and 4 months: 58% (31%, 90%).

SIGNIFICANCE

These findings offer insights into predictors of dentin elements and potential confounders in exposure-health outcome relationships during critical developmental periods.

Quantified retrospective biomonitoring of fetal and infant elemental exposure using LA-ICP-MS analysis of deciduous dentin in three contrasting human cohorts

BACKGROUND

Spatial elemental analysis of deciduous tooth dentin combined with odontochronological estimates can provide an early life (in utero to ~2 years of age) history of inorganic element exposure and status.

OBJECTIVE

To demonstrate the importance of data normalization to a certified reference material to enable between-study comparisons, using populations with assumed contrasting elemental exposures.

METHODS

We used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of dentin to derive a history of elemental composition from three distinct cohort studies: a present day rural cohort, (the New Hampshire Birth Cohort Study (NHBCS; N = 154)), an historical cohort from an urban area (1958-1970), (the St. Louis Baby Tooth Study (SLBT; N = 78)), and a present-day Nigerian cohort established to study maternal HIV transmission (Dental caries and its association with Oral Microbiomes and HIV in young children-Nigeria (DOMHaIN; N = 31)).

RESULTS

We report Li, Al, Mn, Cu, Zn, Sr, Ba and Pb concentrations (µg/g) and qualitatively examine As, Cd and Hg across all three cohorts. Rates of detection were highest, both overall and for each cohort individually, for Zn, Sr, Ba and Li. Zinc was detected in 100% of samples and was stably present in teeth at a concentration range of 64 - 86 µg/g. Mercury, As and Cd detection rates were the lowest, and had high variability within individual ablated spots. We found the highest concentrations of Pb in the pre- and postnatal dentin of the SLBT cohort, consistent with the prevalent use of Pb as an additive to gasoline prior to 1975. The characteristic decline in Mn after the second trimester was observed in all cohorts.

IMPACT

Spatially resolved elemental analysis of deciduous teeth combined with methods for estimating crown formation times can be used to reconstruct an early-life history of elemental exposure inaccessible via other biomarkers. Quantification of data into absolute values using an external standard reference material has not been conducted since 2012, preventing comparison between studies, a common and highly informative component of epidemiology. We demonstrate, with three contrasting populations, that absolute quantification produces data with the lowest variability, compares well with available data and recommends that future tooth biomarker studies report data in this way.

Translating Analytical Techniques in Geochemistry to Environmental Health

From human health exposure related to environmental contamination to ancient deep-Earth processes related to differentiation of the Earth's geochemical reservoirs, the adaptability of inductively coupled plasma mass spectrometry (ICP-MS) has proven to be an indispensable standard technique that transcends disciplines. Continued advancements in ICP-MS, including improved auxiliary applications such as laser ablation (LA), ion/liquid chromatography (IC), automated pre-concentration systems (e.g., seaFAST), and improved desolvating nebulizer systems (e.g., Aridus and Apex) have revolutionized our ability to analyze almost any sample matrix with remarkable precision at exceedingly low elemental abundances. The versatility in ICP-MS applications allows for effective interdisciplinary crossover, opening a world of analytical possibilities. In this communication, we discuss the adaptability of geochemical techniques, including sample preparation and analysis, to environmental and biological systems, using Pb isotopes for source apportionment as a primary example.

Multifractal analysis of human canine teeth at nano scale: atomic force microscopy studies

The aim of the present study is to explore the 3-D micromorphology of human canine teeth materials using multifractal analysis through atomic force microscopy (AFM). The 3-D surfaces of ten extracted canine teeth of a group of 40 year old men were studied (enamel, inter enamel, inter dentin, and cementum) by AFM images in tapping mode and on square areas of 1 μm × 1 μm (512 × 512 points). The AFM images and surface multifractal analysis confirm the dependency of surface micromorphology to their structure–property of these materials across the length scales of the teeth structural architecture. Surface statistical parameters and hence, multifractal approach have been considered as reliable and sensitive tools for quantifying the 3-D surface microtexture changes of human canine teeth materials. The surface of inter dentin had the most irregular topography (the width spectrum Δα = 2.8361, value bigger than all the other Δα sample values), while the most regular topography (the width spectrum Δα = 2.6804, value lower than all the other sample values) was found in cementum. It has been concluded that multifractal analyses can be used as mathematical tools to explore the 3-D micromorphology of human canine teeth materials.

The relation between structural, rugometric and fractal characteristics of hard dental tissues at micro and nano levels

Human tooth exhibits a structure of a mixture of inorganic hydroxyapatite nanocrystals and organic phases. The aim of this study is to investigate different tissues of human canine teeth surface along with the micro structure parameters of each tissue. X-ray diffraction (XRD) is used to study the amorphous or crystalline nature of each tissue with different mineral compositions and crystalline structures where the highest crystalline quality is related to enamel. The surfaces are also examined by energy-dispersive X-ray spectrometry. Moreover, crystalline quality factor is carried out to estimate the crystallinity of the tissues. Also, based on the basic Scherrer equation, the Williamson-Hall equation is applied to extend the formula for the XRD. Enamel and cementum tissues of a typical human tooth, which look similar, are composed of a large variety of wide lines with different widths through Raman spectra analysis. In addition, the applied scanning electron microscopy extracts similar morphology for all tissues with round granular structures which are denser in the cementum. Atomic force microscopy is finally used for investigation of micro-morphologies of the different tissues and the results are compared with the fractal analysis which ends to the bifractal and anisotropic nature of enamel and cementum along with monofractal and isotropic nature of dentin.

Biospecimens and the ABCD study: Rationale, methods of collection, measurement and early data

Biospecimen collection in the Adolescent Brain Cognitive Development (ABCD) study – of hair samples, shed deciduous (baby) teeth, and body fluids – will serve dual functions of screening for study eligibility, and providing measures of biological processes thought to predict or correlate with key study outcomes on brain and cognitive development. Biosamples are being collected annually to screen for recency of drug use prior to the neuroimaging or cognitive testing visit, and to store for the following future studies: (1) on the effects of exposure to illicit and recreational drugs (including alcohol and nicotine); (2) of pubertal hormones on brain and cognitive developmental trajectories; (3) on the contribution of genomics and epigenomics to child and adolescent development and behavioral outcomes; and (4) with pre- and post-natal exposure to environmental neurotoxicants and drugs of abuse measured from novel tooth analyses. The present manuscript describes the rationales for inclusion and selection of the specific biospecimens, methodological considerations for each measure, future plans for assessment of biospecimens during follow-up visits, and preliminary ABCD data to illustrate methodological considerations.

Tracing fetal and childhood exposure to lead using isotope analysis of deciduous teeth

We report progress in using the isotopic composition and concentration of Pb in the dentine and enamel of deciduous teeth to provide a high resolution time frame of exposure to Pb during fetal development and early childhood. Isotope measurements (total Pb and (208)Pb/(206)Pb, (207)Pb/(206)Pb ratios) were acquired by laser ablation inductively coupled mass spectrometry at contiguous 100 micron intervals across thin sections of the teeth; from the outer enamel surface to the pulp cavity. Teeth samples (n=10) were selected from two cohorts of children, aged 5-8 years, living in NE England. By integrating the isotope data with histological analysis of the teeth, using the daily incremental lines in dentine, we were able to assign true estimated ages to each ablation point (first 2-3 years for molars, first 1-2 years for incisors+pre-natal growth). Significant differences were observed in the isotope composition and concentration of Pb between children, reflecting differences in the timing and sources of exposure during early childhood. Those born in 2000, after the withdrawal of leaded petrol in 1999, have the lowest dentine Pb levels (<0.2µgPb/g) with (208)Pb/(206)Pb (mean ±2σ: 2.126-2.079) (208)Pb/(206)Pb (mean ±2σ: 0.879-0.856) ratios that correlate very closely with modern day Western European industrial aerosols (PM10, PM2.5) suggesting that diffuse airborne pollution was probably the primary source and exposure pathway. Legacy lead, if present, is insignificant. For those born in 1997, dentine lead levels are typically higher (>0.4µgPb/g) with (208)Pb/(206)Pb (mean ±2σ: 2.145-2.117) (208)Pb/(206)Pb (mean ±2σ: 0.898-0.882) ratios that can be modelled as a binary mix between industrial aerosols and leaded petrol emissions. Short duration, high intensity exposure events (1-2 months) were readily identified, together with evidence that dentine provides a good proxy for childhood changes in the isotope composition of blood Pb. Our pilot study confirms that laser ablation Pb isotope analysis of deciduous teeth, when carried out in conjunction with histological analysis, permits a reconstruction of the timing, duration and source of exposure to Pb during early childhood. With further development, this approach has the potential to study larger cohorts and appraise environments where the levels of exposure to Pb are much higher.

The tooth exposome in children's health research

PURPOSE OF REVIEW

The exposome concept proposes a comprehensive assessment of environmental exposures from the prenatal period onwards. However, determining exposure timing, especially over the prenatal period, is a major challenge in environmental epidemiologic studies.

RECENT FINDINGS

For decades, teeth have been used to estimate long-term cumulative exposure to metals. Recently developed high-dimensional analytical methods, which combine sophisticated histological and chemical analysis to precisely sample tooth layers that correspond to specific life stages, have the potential to reconstruct the exposome in the second and third trimesters of prenatal development and during early childhood.

SUMMARY

A retrospective temporal exposomic approach that precisely measures exposure intensity 'and timing' during prenatal and early childhood development would substantially aid epidemiologic investigations, particularly case-control studies of rare health outcomes.

Tooth matrix analysis for biomonitoring of organic chemical exposure: Current status, challenges, and opportunities

Epidemiological evidence supports associations between prenatal exposure to environmental organic chemicals and childhood health impairments. Unlike the common choice of biological matrices such as urine and blood that can be limited by short half-lives for some chemicals, teeth provide a stable repository for chemicals with half-life in the order of decades. Given the potential of the tooth bio-matrix to study long-term exposures to environmental organic chemicals in human biomonitoring programs, it is important to be aware of possible pitfalls and potential opportunities to improve on the current analytical method for tooth organics analysis. We critically review previous results of studies of this topic. The major drawbacks and challenges in currently practiced concepts and analytical methods in utilizing tooth bio-matrix are (i) no consideration of external (from outer surface) or internal contamination (from micro-odontoblast processes), (ii) the misleading assumption that whole ground teeth represent prenatal exposures (latest formed dentine is lipid rich and therefore would absorb and accumulate more organic chemicals), (iii) reverse causality in exposure assessment due to whole ground teeth, and (iv) teeth are a precious bio-matrix and grinding them raises ethical concerns about appropriate use of a very limited resource in exposure biology and epidemiology studies. These can be overcome by addressing the important limitations and possible improvements with the analytical approach associated at each of the following steps: (i) tooth sample preparation to retain exposure timing, (ii) organics extraction and pre-concentration to detect ultra-trace levels of analytes, (iii) chromatography separation, (iv) mass spectrometric detection to detect multi-class organics simultaneously, and (v) method validation, especially to exclude chance findings. To highlight the proposed improvements we present findings from a pilot study that utilizes tooth matrix biomarkers to obtain trimester-specific exposure information for a range of organic chemicals.

Levels of lead, cadmium, copper, iron, and zinc in deciduous teeth of children living in Irbid, Jordan by ICP-OES: some factors affecting their concentrations

The aim of this study was to measure the concentrations of lead (Pb), cadmium (Cd), copper (Cu), iron (Fe), and zinc (Zn) in deciduous teeth from children living in Jordan and to investigate the affecting factors. Deciduous teeth samples (n = 320, without fillings) were collected from 5- to 12-year-old children and analyzed for Pb, Cd, Cu, Fe, and Zn using inductively coupled plasma-optical emission spectrometry. A questionnaire was used to gather information on each child, such as sex, age, tooth type (incisors, canines, and molars), tooth position within the mouth (upper or lower jaw), caries status, presence of amalgam fillings inside the mouth, type of drinking water (tap water, home purified water, and plant purified water), and zone of residence (close to or far from heavy traffic roads). The mean concentrations of Pb, Cd, Cu, Fe, and Zn were 30.26, 0.55, 6.23, 34.72, and 128.21 μg/g, respectively. Our results indicate that there is a clear relation between the concentrations of the metals analyzed in this study and tooth type, tooth position within the mouth, caries status, presence of amalgam fillings inside the mouth, and type of drinking water. No significant differences in the concentrations of the five metals analyzed were observed due to sex. Our results also show that no significant difference among Pb, Cd, Cu, Fe, and Zn concentrations and age among the ages of 5-6, 7-8, 9-10, and 11-12, except for Pb, which decreases at age 11-12.

Reconstructing the life-time lead exposure in children using dentine in deciduous teeth

Data are presented to demonstrate that the circumpulpal dentine of deciduous teeth can be used to reconstruct a detailed record of childhood exposure to lead. By combining high spatial resolution laser ablation ICP-MS with dental histology, information was acquired on the concentration of lead in dentine from in utero to several years after birth, using a true time template of dentine growth. Time corrected lead analyses for pairs of deciduous molars confirmed that between-tooth variation for the same child was negligible and that meaningful exposure histories can be obtained from a single, multi-point ablation transect on longitudinal sections of individual teeth. For a laser beam of 100 μm diameter, the lead signal for each ablation point represented a time span of 42 days. Simultaneous analyses for Sr, Zn and Mg suggest that the incorporation of Pb into dentine (carbonated apatite) is most likely controlled by nanocrystal growth mechanisms. The study also highlights the importance of discriminating between primary and secondary dentine and the dangers of translating lead analyses into blood lead estimates without determining the age or duration of dentine sampled. Further work is in progress to validate deciduous teeth as blood lead biomarkers.

Elemental bio-imaging of trace elements in teeth using laser ablation-inductively coupled plasma-mass spectrometry

OBJECTIVES

In this study we present the application of a novel laboratory method that employs laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to construct two-dimensional maps of trace elements in teeth.

METHODS

Teeth were sectioned longitudinally, embedded in resin and polished to a smooth surface. Data were generated by laser ablating the entire sectioned tooth surface. Elemental images were constructed using custom-built software.

RESULTS

Quantified images of (66)Zn, (88)Sr, (111)Cd and (208)Pb, with a spatial resolution of 30 μm(2), were generated from three teeth. Concentrations were determined by single-point calibration against NIST SRM 1486 (bone meal). Zn and Sr concentrations were determined in the μg g(-1) range and Cd and Pb in the ng g(-1) range. Concentrations of Pb, Zn and Cd were higher in dentine particularly in regions adjacent the pulp.

CONCLUSIONS

Elemental bio-imaging employing LA-ICP-MS is a novel method for constructing μm-scale maps of trace elements in teeth. This simple imaging method displays the heterogeneity of trace elements throughout the tooth structure that correspond to specific structural and developmental features of teeth. As a preliminary study, this work demonstrates the capabilities of LA-ICP-MS imaging in dental research.

Evaluation of Laser Ablation Inductively Coupled Plasma Mass Spectrometry for the Quantitative Determination of Lead in Different Parts of Archeological Human Teeth

The lead content of teeth or tooth-parts has been used as a biomarker of cumulative lead exposure in clinical, epidemiological, environmental, and archaeological studies. Through the application of laser ablation inductively coupled plasma mass spectrometry, a pilot study of the micrometer-scale distribution and quantification of lead was conducted for two human teeth obtained from an archeological burial site in Manhattan, New York, USA. Lead was highly localized within each tooth, with accumulation in circumpulpal dentine and cementum. The maximum localized lead content in circumpulpal dentine was remarkably high, almost 2000 μg g(-1), compared to the mean enamel and dentine content of about 5 μg g(-1). The maximum lead content in cementum was approximately 700 μg g(-1). The large quantity of cementum found in the teeth suggested that the subjects had hypercementosis (excess cementum formation) of the root, a condition reported to have been prevalent among African-American slave populations. The distribution of lead in these human teeth was remarkably similar to the distribution that we previously reported in the teeth of present-day lead-dosed goats. The data shown demonstrate the feasibility of using laser ablation inductively coupled plasma mass spectrometry to examine lead exposure in archaeological studies.

Biomonitoring of lead exposure-alternatives to blood

Lead ( Pb) is one of the most important models for biomonitoring of exposure, with the blood Pb concentration as a predominant choice in practice and in epidemiology. In this article the alternatives for biomarkers to blood are reviewed. This overview focuses on a number of different qualities that are of importance in the evaluation of a biomarker's usefulness and performance. The qualities scrutinized included: (1) analytical accuracy and precision; (2) cost; (3) practical issues; (4) what is reflected by the biomarker; (5) relationship to exposure; and (6) relationship to effects. Data indicate that the best biomarker in some circumstances may be blood, but bone or teeth (for past exposures), feces (for current gastrointestinal exposure), or urine (for organic Pb) are sometimes more useful. A striking feature is that no generally accepted biomarker of bioavailable Pb exists, though plasma, bone, teeth, urine, and hair have all been discussed. For one of the most used applications of blood Pb, monitoring of lead workers' exposure, blood has important shortcomings in that it shows a poor response to changes in exposure at high levels. The alternative of plasma has not been sufficiently evaluated to be considered an alternative in occupational health services, although previous analytical problems are basically overcome. Possibly, urine deserves also more attention. Almost all biomarkers lack systematic data on variation within and between individuals.

Human teeth as historical biomonitors of environmental and dietary lead: some lessons from isotopic studies of 19th and 20th century archival material

The lead isotopic composition of various sections (crown, crown base, root) of teeth was determined in specimens collected from 19th century skulls preserved in museum collections and, upon extraction or exfoliation, from humans of known ages residing in Scotland in the 1990s. For most 20th century samples, calculation of accurate crown-complete or root-complete dates of tooth formation ranging from the 1920s to the 1990s enabled comparison of (206)Pb/(207)Pb ratios for teeth sections (crown base root) with corresponding decadally averaged data for archival herbarium Sphagnum moss samples. This showed that the teeth sections had been significantly influenced by incorporation of non-contemporaneous (more recent) lead subsequent to the time of tooth formation, most probably via continuous uptake by dentine. This finding confirmed that separation of enamel from dentine is necessary for the potential of teeth sections as historical biomonitors of environmental (and dietary) lead exposure at the time of tooth formation to be realised. Nevertheless, the mean 19th century value of 1.172+/-0.007 for the (206)Pb/(207)Pb ratio in teeth was very similar to the corresponding mean value of 1.173+/-0.004 for 19th century archival moss, although relative contributions from environmental sources - whether direct, by inhalation/ingestion of dust contaminated by local lead smelting ((206)Pb/(207)Pb~1.17) and coal combustion ((206)Pb/(207)Pb~1.18) emissions, or indirect, through ingestion of similarly contaminated food - and drinking/cooking water contaminated by lead pipes of local origin, cannot readily be determined. In the 20th century, however, the much lower values of the (206)Pb/(207)Pb ratio (range 1.100-1.166, mean 1.126+/-0.013, median 1.124) for the teeth collected from various age groups in the 1990s reflect the significant influence of imported Australian lead of lower (206)Pb/(207)Pb ratio (~1.04) and released to the environment most notably through car-exhaust emissions arising from the use of alkyl lead additives ((206)Pb/(207)Pb~1.06-1.09) in petrol in the U.K. from ca. 1930 until the end of the 20th century.