Proton microprobe determination of fluorine depth distributions and surface multielement characterization in dental enamel

Particle induced X-ray emission analysis (PIXE) and nuclear reaction analysis have been applied to multielemental analysis of human dental enamel in a proton microprobe. The PIXE technique was excercised for the characterization of multielemental lateral distributions on and just below the sample surface. For the assessment of depth distributions of fluorine the resonant nuclear reaction¹⁹F(p,aλ)¹⁶O was used. The combination of two analytical techniques comprising both atomic and nuclear interactions in a microprobe was applied to enamel samples of different origins. One sample constituted a healthy enamel and the other one enamel from a restored tooth. The microprobe in the combined mode was demonstrated to permit the establishment of lateral, concentration gradients of elements heavier than phosphorus with a resolution of 15 μm in enamel and simultaneously of depth distributions of fluorine better than 0.7 μm. The detection limits approached, 10–25 ppm for most of the elements considered. Supported by the Swedish Natural Science Research Council     

Radioactive labeling in the study of abrasion of hard tooth tissue

Labeling the surface of hard tooth tissue samples by the nuclear recoil effect in radioactive decay was applied to study abrasion caused by abrasive components of tooth-pastes.²²²Rn and its short-lived decay products were implanted into the surface in vacuum. For this purpose irradiation was applied to sample placed very close to thin²²⁶Ra source. Measuring the activity before and after abrasion was used to evaluate abrasion in the system toothbrush — various suspensions of the tooth-pastes — hard tooth tissue (enamel or dentine) in a specially designed device, dentoabrasionmeter VUS 2.     

Application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for the identification of potential diagenesis and crystallinity changes in teeth

During burial, diagenetic alteration can invalidate the paleodietary signature, which the hydroxyapatite (Ca₅(PO₄)₃OH) matrix in incremental tissues, such as tooth enamel, provides. Thus, analytical methods that can evaluate diagenetic changes are crucial in anthropological and archaeological investigations. Modern deciduous tooth enamel (exfoliated) from Solis, Mexico and Kalama, Egypt, as well as Bronze Age (circa 2200 B.C.E.) adult enamel from (present-day) Tell Abraq, U.A.E. and adult enamel from the New York African Burial Ground (NYABG) in lower Manhattan, were analyzed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The samples were compared to synthetic hydroxyapatite powder and bone ash samples. The DRIFTS spectra of tooth enamel yielded similar infra red finger print pattern to previous pellet-based FTIR spectra in both absorbance and Kubelka–Munk units. The study demonstrates that DRIFTS is a convenient alternative to pellet-based transmission FTIR in testing diagenetic changes in hard tissue for archaeological investigations. Tooth enamel samples contained a higher carbonate–phosphate ratio than synthetic hydroxyapatite and bone ash standard samples. Correlations are reported between Crystallinity Index (CI_Ab) and carbonate–phosphate ratio, strontium–calcium ratio, and fluoride peak appearance. Crystallinity indexes (CI_Ab) were in the range of 2.6–3.8 (in absorbance units) and Kubelka–Munk Crystallinity indexes (CI_KM) were in the range of 3.1–4.9.     

Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology-based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag(3)PO(4) crystals by using a strongly buffered, moderate-temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as delta(18)O, V-SMOW scale) is typically 0.2-0.3 per thousand (1 s.d.) on samples as small as 300 microg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen.     

History of individuals of the 18th/19th centuries stored in bones,teeth, and hair analyzed by LA–ICP–MS—a step in attempts to confirm the authenticity of Mozart’s skull

A cranium stored in the Stiftung Mozarteum in Salzburg/Austria which is believed to be that of Mozart, and skeletal remains of suspected relatives which have been excavated from the Mozart family grave in the cemetery in Salzburg, have been subjected to scientific investigations to determine whether or not the skull is authentic. A film project by the Austrian television ORF in collaboration with Interspot Film on this issue was broadcast at the beginning of the “Mozart year 2006”. DNA analysis could not clarify relationships among the remains and, therefore, assignment of the samples was not really possible. In our work this skull and excavated skeletal remains have been quantified for Pb, Cr, Hg, As, and Sb content by laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) to obtain information about the living conditions of these individuals. A small splinter of enamel (less than 1 mm³) from a tooth of the “Mozart cranium” was also available for investigation. Quantification was performed by using spiked hydroxyapatite standards. Single hair samples which are recorded to originate from Mozart have also been investigated by LA–ICP–MS and compared with hair samples of contemporary citizens stored in the Federal Pathologic–Anatomical Museum, Vienna. In general, Pb concentrations up to approximately 16 μg g⁻¹ were found in the bone samples of 18th century individuals (a factor of 7 to 8 higher than in recent samples) reflecting elevated Pb levels in food or beverages. Elevated Pb levels were also found in hair samples. The amount of Sb in the enamel sample of the “Mozart cranium” (approx. 3 μg g⁻¹) was significantly higher than in all the other tooth samples investigated, indicating possible Sb ingestion in early childhood. Elevated concentrations of elements in single hair samples gave additional information about possible exposure of the individuals to heavy metals at a particular point in their life.     

Determination of strontium in human tooth enamel by flameless atomic-absorption spectrometry

The determination of strontium in human tooth enamel by flameless atomic-absorption spectrometry was found to be subject to interference from the calcium/phosphate matrix of the enamel. The standard addition method was used to compensate for this interference. Hydrochloric acid and nitric acid did not affect the strontium absorption, but perchloric acid caused a significant reduction in the absorption. The sensitivity of the flameless atomic-absorption enabled 1-mg samples of enamel to be analysed. Hence, the proposed method can be used to determine the distribution of strontium through the tooth. An average recovery of 100.4% for amounts of strontium added to enamel showed that the proposed method was reliable.     

Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO2- radicals to a specific location, and one type of CO3(3-) radical was only found in enamel. Moreover, a major difference was found in the non-CO2- and non-CO3(3-) signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.     

2H stable isotope analysis of human tooth enamel: a new tool for forensic human provenancing?

Stable isotope analysis of biogenic tissues such as tooth enamel and bone mineral has become a well-recognised and increasingly important method for determining the provenance of human remains, and it has been used successfully in bio-archaeological studies as well as forensic investigations. In particular, (18)O and (2)H stable isotope signatures of bone and hair, respectively, are well-established proxies of climate (temperature) and source water and are therefore considered as indicators of geographic life trajectories of animals and humans. While the methodology for (2)H analysis of human hair, fingernails, and bone collagen is currently used to determine human provenance, i.e. geographic origin and identify possible migration patterns, studies involving the analysis of (2)H in tooth enamel appear to be nonexistent in the scientific literature. Ground tooth enamel was analysed by continuous-flow isotope ratio mass spectrometry (IRMS) coupled on-line to a high-temperature conversion elemental analyser (TC/EA). An array of tooth enamel samples from archaeological and modern teeth has been analysed under different experimental conditions, and the results of this proof-of-concept study are presented. While no significant differences in (2)H abundance were noted as a result of H exchange studies or different sample preparation protocols, no significant differences or trends in measured δ(2)H-values were observed either with regard to known differences in geographical provenance. We concluded that the δ(2)H-values obtained from tooth enamel could not be used as proxy for a person's geographical origin during adolescence.     

EPR spectroscopy of tooth enamel: the tooth radicals and the microcrystal alignment

The paramagnetic radicals induced by radiation in dental enamel are very important because they can be related to the crystalline structure of hydroxyapatite. The R-value, that is, the ratio of the amplitude of the lines of the EPR signal due to radiation, is a measure of the degree of microcrystal alignment in human tooth enamel. The aim of this study is to underline the importance of a correct evaluation of the R-value, by using the current method to increase reproducibility in EPR spectroscopy of tooth enamel. Data with and without correction show a significant difference and, consequently, they give rise to a different valuation of microcrystal alignment.     

Synchrotron X-ray diffraction characterization of healthy and fluorotic human dental enamel

With the introduction of fluoride as the main anticaries agent used in preventive dentistry, and perhaps an increase in fluoride in our food chain, dental fluorosis has become an increasing world-wide problem. Visible signs of fluorosis begin to become obvious on the enamel surface as opacities, implying some porosity in the tissue. The mechanisms that conduct the formation of fluorotic enamel are unknown, but should involve modifications in the basic physical-chemistry reactions of demineralization and remineralisation of the enamel of the teeth, which is the same reaction of formation of the enamel's hydroxyapatite (HAp) in the maturation phase. The increase of the amount of fluoride inside of the apatite will result in gradual increase of the lattice parameters. The aim of this work is to characterize the healthy and fluorotic enamel in human tooth using Synchrotron X-ray diffraction. All the scattering profile measurements were carried out at the X-ray diffraction beamline (XRD1) at the Brazilian Synchrotron Light Laboratory—LNLS, Campinas, Brazil. X-ray diffraction experiments were performed both in powder samples and polished surfaces. The powder samples were analyzed to obtain the characterization of a typical healthy enamel pattern. The polished surfaces were analyzed in specific areas that have been identified as fluorotic ones. X-ray diffraction data were obtained for all samples and these data were compared with the control samples and also with the literature data.     

Isotopic Indications of Late Pleistocene and Holocene Paleoenvironmental Changes at Boodie Cave Archaeological Site,Barrow Island,Western Australia

This paper presents the first application of mammal tooth enamel carbonate stable isotope analysis for the purpose of investigating late Pleistocene–early Holocene environmental change in an Australian archaeological context. Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope ratios were analyzed from archaeological and modern spectacled hare wallaby (Lagorchestes conspicillatus) and hill kangaroo (Osphranter robustus) tooth enamel carbonates from Boodie Cave on Barrow Island in Western Australia. δ¹⁸O results track the dynamic paleoecological history at Boodie Cave including a clear shift towards increasing aridity preceding the onset of the Last Glacial Maximum and a period of increased humidity in the early to mid-Holocene. Enamel δ¹³C reflects divergent species feeding ecology and may imply a long-term shift toward increasing diversity in vegetation structure. This study contributes new data to the carbonate-isotope record for Australian fauna and demonstrates the significant potential of stable isotope based ecological investigations for tracking paleoenvironment change to inter-strata resolution.     

Strontium isotope ratios (87Sr/86Sr) of tooth enamel: a comparison of solution and laser ablation multicollector inductively coupled plasma mass spectrometry methods

Strontium isotope ratios (87Sr/86Sr) in tooth enamel provide a means to investigate migration and landscape use in humans and other animals. Established methods for measuring (87)Sr/(86)Sr in teeth use bulk sampling (5-20 mg) and labor-intensive elemental purification procedures before analysis by either thermal ionization mass spectrometry (TIMS) or multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Another method for measuring 87Sr/86Sr is laser ablation MC-ICP-MS, but concerns have been expressed about its accuracy for measuring tooth enamel. In this study we test the precision and accuracy of the technique by analyzing 30 modern rodent teeth from the Sterkfontein Valley, South Africa by laser ablation MC-ICP-MS and solution MC-ICP-MS. The results show a mean difference in 87Sr/86Sr measured by laser ablation and by solution of 0.0003 +/- 0.0002. This degree of precision is well within the margin necessary for investigating the potential geographic origins of humans or animals in many areas of the world. Because laser ablation is faster, less expensive, and less destructive than bulk sampling solution methods, it opens the possibility for conducting 87Sr/86Sr analyses of intra-tooth samples and small and/or rare specimens such as micromammal and fossil teeth.     

Spin-flop and spin-Peierls transition in doped CuGeO3

Ni⁺⁺ ions doped inorganic CuGeO₃ sample has been studied by using electron spin resonance (ESR) technique in the temperature range of 3–300 K. The ESR spectrum of Cu⁺⁺ ion has been observed to be strongly temperature dependent for inorganic spin-Peierls (SP) Cu_0.96Ni_0.04GeO₃ samples. The ESR line width and ESR amplitude exponentially vanishes below a critical temperature, T_sp = 14 K. The one-dimensional (1D) antiferromagnetic (AF) spin chain formed of Cu⁺⁺ is broken by Ni⁺⁺ (spin-1) ion, giving uncoupled spins at the end of the chains that give extra contribution to the spectra at lower temperature and stabilizes a Néel state. The g-factor is much smaller than the expected value for isolated Cu⁺⁺ and Ni⁺⁺ ions and is much more anisotropic than for undoped samples [O. Yalçın, B. Aktaş, J. Magn. Magn. Mater. 258/259 (2003) 137 (reference therein)]. It is shown that the ground state of dimerized spins is singlet. The spin-flop (SF) phenomenon is obtained from AF state mixed condition and then ferromagnetic (FM) state. The spin-flop field slightly increases when increasing temperature in the temperature range 100–300 K. The SF transition is showed almost AF order for Cu_0.96Ni_0.04GeO₃.     

Author index for volume 52

Dehydrated samples of zeolite Y containing alkali-metal cations have been reacted with alkali-metal vapor in sealed silica tubes, and the products studied by electron-spin resonance (ESR) spectroscopy. Two distinct species were detected following the reaction of sodium-exchanged zeolite Y with sodium, potassium, or rubidium vapor. Exposure to a low concentration of metal vapor resulted in brightly colored samples with ESR signals characteristic of a stable ionic cluster species Na³⁺₄, in which an unpaired electron is trapped on four equivalent sodium cations in the sodalite cages of the zeolite. Exposure to higher concentrations of metal vapor resulted in dark-colored samples with ESR signals characteristic of small metallic particles located inside the zeolite cavities. A similar ionic cluster species K³⁺₄ was detected following the reaction of potassium-exchanged zeolite Y with sodium or potassium vapor although the potassium cluster was less stable than its sodium counterpart and an ESR signal from small metallic particles was observed at the same time. The corresponding Rb³⁺₄ ionic cluster species was not detected following the reaction of rubidium-exchanged zeolite Y with rubidium vapor; only an ESR signal from small metallic particles was observed. The narrow linewidths of the ESR signals from the small metallic particles suggest an inhibition of the spin-relaxation mechanisms in the bulk metals.     

Application of laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP–MS) to investigate trace metal spatial distributions in human tooth enamel and dentine growth layers and pulp

Human tooth enamel provides a nearly permanent and chronological record of an individuals nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196×339 m² raster pattern areas (6.6×10⁴ m²) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine–enamel junction (DEJ), dentine, and the dentine–pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. ⁴³Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA–ICP–MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.Presented in part at the 2002 Winter Conference on Plasma Spectrochemistry, Scottsdale, AZ, January 6–12, 2002. The poster was selected as an outstanding poster presentation.     

Relationship between microhardness and fluorine contents on tooth enamel determined by PIGE analysis

The remineralization effect of fluoride has been measured by surface microhardness on tooth enamel. The purpose of this study was to investigate the relationship between microhardness and fluorine concentration on tooth enamel. Twelve sound bovine enamel specimens were prepared and immersed in 0.05% NaF solution for 1, 3, 6, 24 and 36 hours, respectively. The concentration of fluorine in specimens were measured by PIGE analysis and surface microhardness of each specimen was measured by surface microhardness tester. Fluorine concentration was increased by immersing time. There was no change in microhardness of each specimen by fluorine content. The results of this study suggest that there was no relationship between the fluorine concentration and surface microhardness in sound tooth enamel. PIGE analysis can be used effectively to assess the remineralization effect of fluorine content in tooth enamel.     

Structural features of human tooth tissues affected by high dose of external ionizing radiation after nuclear catastrophe of Chernobyl plant

The application of micro-Raman spectroscopy is discussed for the analysis of structural features of human tooth tissues affected by high doses of external ionizing radiation (0.5–1.7 Gy) after the nuclear plant catastrophe in Chernobyl in 1986. The results have shown significant changes in the mineral matrix of dental enamel that lead to the decrease of tooth enamel hardness. Destruction of the collagen chain of the organic matrix has been observed for dentin and cementum.     

The vanadium content of human dental enamel and its relationship to caries

A method for the determination of vanadium in dental enamel based on neutron activation analysis is described. After rapid dissolution of the irradiated sample in perchloric acid,⁵²V is quickly separated by solvent extraction from mixed perchloric-hydrochloric medium with N-benzoyl-N-phenyl hydroxylamine (BPHA) reagent in toluene in 95% yield. The technique was applied to samples from a low caries area of Dalmatia, Zemunik (DMFT<2), and a normal area, Novigrad (DMFT>5), in the same region. No significant differences in vanadium content were found between the two areas, nor between deciduous and permanent teeth. The levels in other areas of Yugoslavia were found to be similar, with a mean concentration of 3.7±1.5 ng·g⁻¹ for 37 samples, with a nearly normal distribution; a few impacted teeth gave lower values. The method can also be adapted to the analysis of bone and biological materials generally.     

Intra‐ and inter‐tooth variation in strontium isotope ratios from prehistoric seals by laser ablation multi‐collector inductively coupled plasma mass spectrometry

Rationale

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in modern‐day marine environments are considered to be homogeneous (~0.7092). However, in the Baltic Sea, the Sr ratios are controlled by mixing seawater and continental drainage from major rivers discharging into the Baltic. This pilot study explores if variations in Sr can be detected in marine mammals from archaeological sites in the Baltic Sea.

Methods

⁸⁷Sr/⁸⁶Sr ratios were measured in tooth enamel from three seal species by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS). The method enables micro‐sampling of solid materials. This is the first time that the method has been applied to marine samples from archaeological collections.

Results

The analyses showed inter‐tooth ⁸⁷Sr/⁸⁶Sr variation suggesting that different ratios can be detected in different regions of the Baltic Sea. Furthermore, the intra‐tooth variation suggests possible different geographic origin or seasonal movement of seals within different regions in the Baltic Sea through their lifetime.

Conclusions

The method was successfully applied to archaeological marine samples showing that: (1) the ⁸⁷Sr/⁸⁶Sr ratio in marine environments is not uniform, (2) ⁸⁷Sr/⁸⁶Sr differences might reflect differences in ecology and life history of different seal species, and (3) archaeological mobility studies based on ⁸⁷Sr/⁸⁶Sr ratios in humans should therefore be evaluated together with diet reconstruction.

     

Non-destructive profiling of fluorine in teeth to large depths

A new method for non-destructive depth profiling of fluorine has been developed which extends the profiling range to much larger depths than hitherto possible. In this method the thick-target yield of 6–7 MeV gammas from the reaction of ¹⁹F(p,αγ) ¹⁶O in the tooth sample, was measured as a function of the incident energy from threshold to up to 2.7 MeV and the yield curve plotted. This curve was compared to the calculated yield curve of 6–7 MeV gammas from the same reaction but on an enamel matrix containing uniformly distributed fluorine. The difference in the shape of the two curves was only due to the non-uniform distribution of fluorine in the tooth sample, which could then be calculated. By making use of this method F-depth profiles in teeth of monkeys were determined non-destructively to a depth of 14 μm. This method is also applicable for profiling other elements through appropriate resonant or non-resonant nuclear reactions.