Modern Teeth Research Articles

Microscopic evaluation of the structure of modern tooth brushes synthetic bristles at various useful lives (clinical and laboratory study)

Microscopic evaluation of the structure of modern tooth brushes synthetic bristles at various useful lives (clinical and laboratory study)

Age estimation in older adults: Use of pulp/tooth ratios calculated from tooth sections.

Accurate age estimates are foundational for bioarchaeological research, yet the ability to accurately age older adult skeletons remains elusive. This study uses a new version of pulp/tooth area calculations to investigate chronological age of older archaeological individuals. Pulp/tooth area ratios were calculated on modern control teeth (n = 10) that were first radiographed and then sectioned for comparative analysis. Pulp/tooth area ratios were determined on sectioned teeth using ImageJ software for: (a) modern individuals of known age (n = 26); (b) individuals from Belleville, Ontario, Canada (1821-1874) with documented age (n = 50); and (c) Belleville individuals with skeletally estimated age (n = 122). Calculations from tooth sections on modern teeth (n = 10) resulted in a mean absolute error (MAE) of ±3.9 years, whereas the radiographic method for the same teeth had an MAE of ±14.45 years. Results indicate that sectioned pulp/tooth area ratios are a significant predictor of chronological age (p < .005), with MAEs of ±4.53 years for Belleville and ±3.77 years for modern individuals. There were no statistically significant differences in age estimations between modern and archaeological individuals, or with respect to tooth type, sex, or intra/inter-observer estimations. This study provides a new more accurate method for estimating age-at-death, particularly for individuals in the 50+ age category. Sectioning the teeth and directly measuring exposed pulp chambers results in age estimations that were within ±4.15 years for both modern and archaeological individuals, thus presenting a method that will enhance the ability to age older individuals.

AMS-14C analysis of modern teeth: A comparison between two sample preparation techniques

AMS-14C analysis of modern teeth has become important for forensic studies. 14C content in human teeth reflects the 14C atmospheric concentration during its formation and allows the calculation of the actual year of birth. Through AMS, it is possible to measure the 14C concentrations in a tissue with high precision. However, there is a debate about which should be the best fraction for teeth carbon dating: collagen or enamel. This work focuses on the results obtained from enamel and collagen extracted from Mexican people in order to compare them. Collagen from dental pieces donated from people older than 60-years-old have been included to understand the turnover process and usefulness of collagen to determine the date of birth. Our results indicate that when a single dental piece is available, enamel method allows the determination of the tooth formation date. Dating collagen of the same tooth helps to discriminate if the formation date belongs to the left or the right side of the peak bomb, but also corroborates, the ages obtained through enamel analysis.

Tooth Growth in Ancient and Modern Times Inferred from Perikymata Growth Intervals; Modeled Statistically

Tooth growth is essential to health and survival. In humans the growth rate can be inferred from the width of perikymata growth intervals. We hypothesized that in ancient times teeth grew faster than in modern humans. We measured the intervals between perikymata ridges on the surfaces of teeth and in thin sections of molars (which we used as standards) in ancient, prehistoric and modern humans. We compared statistically the results from ancient and modern specimens and assessed the impact of dietary factors and sociality on tooth growth. We found that ancient teeth grew faster than modern teeth (wider intervals) because of environmental, nutritional and life style influences. This apparently conferred evolutionary advantages for human survival. Our results gleaned from combining measurements of sections of teeth with modeling of web-available images suggest that life styles of modern humans have lead to smaller teeth.

Dynamic Modelling of Tooth Deformation Using Occlusal Kinematics and Finite Element Analysis.

BackgroundDental biomechanics based on finite element (FE) analysis is attracting enormous interest in dentistry, biology, anthropology and palaeontology. Nonetheless, several shortcomings in FE modeling exist, mainly due to unrealistic loading conditions. In this contribution we used kinematics information recorded in a virtual environment derived from occlusal contact detection between high resolution models of an upper and lower human first molar pair (M1 and M1, respectively) to run a non-linear dynamic FE crash colliding test.MethodologyMicroCT image data of a modern human skull were segmented to reconstruct digital models of the antagonistic right M1 and M1 and the dental supporting structures. We used the Occlusal Fingerprint Analyser software to reconstruct the individual occlusal pathway trajectory during the power stroke of the chewing cycle, which was applied in a FE simulation to guide the M1 3D-path for the crash colliding test.ResultsFE analysis results showed that the stress pattern changes considerably during the power stroke, demonstrating that knowledge about chewing kinematics in conjunction with a morphologically detailed FE model is crucial for understanding tooth form and function under physiological conditions.Conclusions/SignificanceResults from such advanced dynamic approaches will be applicable to evaluate and avoid mechanical failure in prosthodontics/endodontic treatments, and to test material behavior for modern tooth restoration in dentistry. This approach will also allow us to improve our knowledge in chewing-related biomechanics for functional diagnosis and therapy, and it will help paleoanthropologists to illuminate dental adaptive processes and morphological modifications in human evolution.

Inferring chronological age from DNA methylation patterns of human teeth.

Current methods to determine chronological age from modern and ancient remains rely on both morphological and molecular approaches. However, low accuracy and the lack of standardized protocols make the development of alternative methods for the estimation of individual's age even more urgent for several research fields, such as biological anthropology, biodemography, forensics, evolutionary genetics, and ancient DNA studies. Therefore, the aim of this study is to identify genomic regions whose DNA methylation level correlates with age in modern teeth. We used MALDI-TOF mass spectrometry to analyze DNA methylation levels of specific CpGs located in the ELOVL2, FHL2, and PENK genes. We considered methylation data from cementum, dentin and pulp of 21 modern teeth (from 17 to 77 years old) to construct a mathematical model able to exploit DNA methylation values to predict age of the individuals. The median difference between the real age and that estimated using DNA methylation values is 1.20 years (SD = 1.9) if DNA is recovered from both cementum and pulp of the same modern teeth, 2.25 years (SD = 2.5) if DNA is recovered from dental pulp, 2.45 years (SD = 3.3) if DNA is extracted from cementum and 7.07 years (SD = 7.0) when DNA is recovered from dentin only. We propose for the first time the evaluation of DNA methylation at ELOVL2, FHL2, and PENK genes as a powerful tool to predict age in modern teeth for anthropological applications. Future studies are needed to apply this method also to historical and relatively ancient human teeth.

Stable carbon and oxygen isotopic evidence for Late Cenozoic environmental change in Northern China

Stable carbon and oxygen isotope ratios of 311 enamel samples from a diverse group of herbivorous mammals including Equidae, Rhinocerotidae, Bovidae, Rodentia and Ochotonidaewere were analyzed in order to reconstruct the Late Cenozoic history of vegetation and environmental change in the Yushe Basin in North China. The δ13C values of bulk and serial enamel samples from large mammals show a wide range of variation from −13.3‰ to 1.4‰, with a mean of −7.4‰±3.5‰ (n=294). This indicates that large herbivorous mammals in the area had a variety of diets since 6.5Ma, ranging from pure C3 to mixed C3–C4 and pure C4 diets. In contrast, the δ13C values of small mammals vary from −11.9‰ to −7.6‰, with a mean of −9.7±1.1‰ (n=17), indicating that rodents and ochotonids were feeding mostly on C3 plants. Variations in δ13C values within and between species reflect the variations in the habitat and the vegetation consumed by the animals. In general, horses had higher amounts of C4 grasses in their diets than other contemporary taxa such as bovids, rhinos, rodents and deer, suggesting that horses exploited more open habitats such as grasslands while deer, rhinos and rodents may have preferred more C3 vegetation, which is more indicative of forested environments. The carbon isotope data show that C4 grasses have been an important component of horses' diets and of local ecosystems since ~6.5Ma, confirming that the “late Miocene C4 expansion” occurred in North China as it did in Africa, Indian subcontinent and the Americas. This supports a global factor as a main driver of the late Miocene C4 expansion. The combined carbon and oxygen isotope data reveal major shifts in climate to drier and/or warmer conditions after ~5.8, ~4.1, ~3.3, and ~2.5Ma, and significant shifts to relatively wetter and/or cooler conditions after ~6.4, ~5, ~3.5Ma. The shifts to drier and/or warmer climate after ~5.8Ma and ~2.5Ma coincide with two major fauna turnover events. Intra-tooth δ13C and δ18O values are negatively correlated within individual modern teeth and some fossil teeth, displaying the characteristic pattern of the summer monsoon regime and confirming a strong monsoon influence in the area since at least the early Pliocene. The data also suggest that the C4 abundance in the area has fluctuated over the past 6.5Ma in response to changes in climate, with more C4 grasses during warmer and/or drier periods and a reduced C4 component at cooler and/or wetter times.

Strontium isotope analysis of curved tooth enamel surfaces by laser-ablation multi-collector ICP-MS

Laser ablation multi-collector ICP-MS (LA-MC-ICP-MS) is increasingly applied to measure the strontium isotope composition (87Sr/86Sr) of fossil or modern tooth samples in order to address questions about mobility. Recently, concerns have been raised that an analytical bias due to instrumental isotopic mass fractionation might be introduced when this method is used to sample across naturally curved tooth enamel surfaces.We address this concern by reanalyzing data that were originally produced using 750μm linear LA-MC-ICP-MS scans on the external, slightly curved surfaces of fossil hominin teeth (Australopithecus and Paranthropus) from South Africa. By re-integrating the first and last 1/3 of the data along the original 750μm linear scans, we compared 87Sr/86Sr results produced by sections of each scan with varying degrees of laser focus. The results show no evidence of any analytical scatter between strontium isotope values for the different sections of the curved tooth surfaces and results for the different sections of each linear scan agree well within the precision of the method (external 2σ ± 0.0004). Furthermore, each analytical session was bracketed by analysis of a curved rodent (Otomys sp.) tooth in-house standard with up to ±100μm vertical change along the 750μm linear scan. Long-term, average LA-MC-ICP-MS 87Sr/86Sr results for one such Otomys tooth standard (0.72989±0.00029, n=71) agree well with the solution MC-ICP-MS analysis of the same tooth (0.72976±0.00002). New LA-MC-ICP-MS 87Sr/86Sr ratios, using both a 213nm and solid-state 193nm laser ablation system, for sets of consecutive 750μm linear scans along the curved, outer tooth enamel surface on another single Otomys tooth in-house standard agree within ±0.0004 regardless of progressively more extreme vertical change during analysis (±10μm to ±900μm).These results are similar to LA-MC-ICP-MS Sr isotope analyses, using the same instrumentation and methodology, of an in-house, polished, flat clinopyroxene mineral standard (LA: 0.70482±0.00029, n=155; solution: 0.70495±0.00003).We conclude that, provided the stable 86Sr/88Sr ratio is used in conjunction with the exponential law to constantly correct for instrumental isotopic mass fractionation during acquisition, curved tooth enamel surfaces represent no impediment to accurate LA-MC-ICP-MS strontium isotope analyses.

The Discolouration of Human Teeth from Archaeological Contexts: Elemental Analysis of a Black Tooth from a Roman Cranium Recovered from the River Witham, Lincoln, UK

A human cranium was recovered from the River Witham, Lincoln, UK, at Stamp End Lock during a police operation in 2002. Although extensive trauma was noted, the skull was not of forensic interest since radiocarbon dating revealed that the individual had lived during the Roman occupation of Lincoln, almost 2,000 years ago. The skull had unusual black “metallic” staining on the occlusal surfaces of the teeth. As this kind of staining is relatively uncommon, it was investigated to determine the possible cause. An individual tooth was subjected to two elemental analyses: inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). A small sample (n=21) of modern teeth was also analysed for comparison to determine “normal” ranges of certain elements. Analysis of the ancient tooth shows very high levels of manganese (275 µg/g) and iron (1540 µg/g) compared to modern teeth values (1.90 µg/g Mn and 40.81 µg/g Fe). These results were consistent with the black staining arising from iron and manganese infiltrating bone and dental tissue from the depositional environment, and not a consequence of diet, pathological process or cultural practices.

Iron deposition in modern and archaeological teeth

Iron surface concentrations and profile maps were measured on the enamel of archaeological and modern teeth to determine how iron is deposited in tooth enamel and if it was affected by the post-mortem environment. Teeth from Australian children who died in the second half of the 19th century were compared with contemporary teeth extracted for orthodontic purposes. Surface analysis of the teeth was performed using the 3MV Van Der Graff Accelerator at The Australian Nuclear Science and Technology Organisation (ANSTO), Sydney, Australia. A small sample of teeth were then cut in the mid sagittal plane and analysed using ANSTO High Energy Heavy Ion Microprobe. Maps and linear profiles were produced showing the distribution of iron across the enamel. Results show that both the levels and distribution of iron in archaeological teeth is quite different to contemporary teeth, raising the suggestion that iron has been significantly altered by the post-mortem environment.

Comprehensive stable isotope investigation of marine biogenic apatite from the late Cretaceous–early Eocene phosphate series of Morocco

Fossil biogenic apatites were studied for their geochemical composition across the late Cretaceous–early Eocene Moroccan phosphate series in the Ouled Abdoun and Ganntour basins in Morocco in order to characterize paleoenvironmental conditions and to improve stratigraphy. The vertebrate remains show particularly good structural, mineralogical and chemical preservations, which relate to the favorable depositional environment of the phosphorite. The main studied fossils – shark tooth enameloid and dentine, and coprolites – show large range in δ13C values from −14 to +6‰, which can be coupled to different carbon sources. Enameloid yielded mostly positive δ13C isotopic compositions that are comparable with values reported from modern teeth. Coprolites have the lowest δ13C values that reflect burial conditions with intensive organic matter recycling.The large variation in δ18OPO4 values of the shark teeth can be related to ecological differences. However, the mean δ18OPO4 data reflect important temporal variation along the series, together with the corresponding average δ13C values. Comparisons with the global isotope records allow identifying the Early Eocene Climatic Optimum in the top of the Ouled Abdoun series (above Bed 0′). The isotope data further suggest a sedimentary gap during the latest Thanetian and the Paleocene Eocene Thermal Maximum. The top of the Paleocene series (Bed IIa) can be dated to late Selandian–early Thanetian, with the recognition of the Early Late Paleocene Event (ELPE). The Eritherium Bone Bed, that yielded the earliest known placental mammals from Africa, would be located below the ELPE and therefore, cannot be younger than late Selandian.The isotope data from the older Paleocene (Bed IIb) and Cretaceous (upper Bed III) beds in the Ouled Abdoun Basin can be correlated with the latest Danian–early Selandian and the latest Maastrichtian global isotope record, respectively. Based on the δ18OPO4 data, the Cretaceous layers of the Ganntour Basin cover most of the Maastrichtian period except the very early part. All these early Paleogene and Cretaceous chemostratigraphic ages, however, need further confirmations from other proxies. Yet, the interpretations are in general agreement with the biostratigraphy derived from the selachian fauna.

Chemical composition of modern and fossil hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 2: Alkaline earth elements as tracers of watershed hydrochemistry and provenance

Abstract. This study demonstrates that alkaline earth elements in enamel of hippopotamids, in particular Ba and Sr, are tracers for water provenance and hydrochemistry in terrestrial settings. The studied specimens are permanent premolar and molar teeth found in modern and fossil lacustrine sediments of the Western Branch of the East African Rift system (Lake Kikorongo, Lake Albert, and Lake Malawi) and from modern fluvial environments of the Nile River. Concentrations in enamel vary by two orders of magnitude for Ba (120–9336 μg g−1) as well as for Sr (9–2150 μg g−1). The variations are partially induced during post-mortem alteration and during amelogenesis, but the major contribution originates ultimately from the variable water chemistry in the habitats of the hippopotamids which is controlled by the lithologies and weathering processes in the watershed areas. Amelogenesis causes a distinct distribution of MgO, Ba and Sr in modern and fossil enamel, in that element concentrations increase along profiles from the outer rim towards the enamel–dentin junction by a factor of 1.3–1.9. These elements are well correlated in single specimens, thus suggesting that their distribution is determined by a common, single process, which can be described by closed system Rayleigh crystallization of bioapatite in vivo. Enamel from most hippopotamid specimens has Sr/Ca and Ba/Ca which are typical for herbivores. However, Ba/Sr ranges from 0.1 to 3 and varies on spatial and temporal scales. Thus, Sr concentrations and Ba/Sr in enamel differentiate between habitats having basaltic mantle rocks or Archean crustal rocks as the ultimate sources of Sr and Ba. This provenance signal is modulated by climate change. In Miocene to Pleistocene enamel from the Lake Albert region, Ba/Sr decreases systematically with time from 2 to 0.5. This trend can be correlated with changes in climate from humid to arid, in vegetation from C3 to C4 biomass as well as with increasing evaporation of the lake water. The most plausible explanation is that Ba mobility decreased with increasing aridification due to preferential deposition with clay and Fe-oxide-hydroxide or barite on the watershed of Lake Albert.

Tooth Cementum Annulation for Estimation of Age‐at‐Death in Thermally Altered Remains

Assessment of tooth cementum annulations (TCA) is acknowledged for its potential as a more accurate method for estimating age-at-death than conventional macroscopic methods typically employed. Thermal alteration of remains in a forensic context is not uncommon; however, the use of TCA in heat-treated remains has hitherto received no quantitative assessment of accuracy. This study applies TCA to a sample of modern teeth of known demographics after experimental heat treatment at 600, 800 and 1000°C. Cementum annulations do survive thermal alteration; however, their visibility is dependent on exposure temperature. Physical and chemical changes resulted in TCA being applicable to only 63.3% of samples. An overall correlation to known age of r = 0.522 (p < 0.05) was found, while correlations of r = 0.868 (p < 0.01), r = 0.249, and r = -0.185, were found for 600, 800, and 1000°C subsets, respectively. These results indicate that in teeth exposed to temperatures >600°C, TCA no longer yields accurate enough results to be of use in forensic investigations.

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.

Late Pleistocene environmental change interpreted from δ13C and δ18O of tooth enamel from the Black Creek Swamp Megafauna site, Kangaroo Island, South Australia

Stable carbon and oxygen isotope ratios of tooth enamel carbonate were collected from both fossils (50–100 ka) Tammar Wallaby ( Macropus eugeneii) and Western Grey Kangaroo ( Macropus fuliginosus) from a Late Pleistocene fossil deposit situated on Kangaroo Island, South Australia. δ 13C and δ 18O data were also obtained for modern equivalents of both species located proximal to the excavation site. Trace element compositions were collected for Sr, Ba, V, Cu, Zr, Y, La, Ca, Nd, and U for modern and fossil teeth, and for local soils. δ 13C data for fossil kangaroo and wallaby range between − 5.0 and − 18‰, while less 13C enriched values between − 18 and − 25‰ are observed in modern tooth enamel. Early-formed molars are 13C depleted by ∼ 2.5‰ compared to late-formed molars, consistent with isotopic offsets observed in modern molars, and with offsets observed from preservation of original biogenic compositions. Overall, carbon isotopes indicate a shift in diet and environmental conditions from C4-inclusive mixed habitats (woods and open grasslands) during the Late Pleistocene, to C3-only wooded and closed canopy habitats today. δ 18O values range between 23 and 30‰ and are indistinguishable for fossil and modern tooth enamel. Oxygen isotope compositions of plants and mammals correlate positively with local water compositions, and negatively with relative humidity. Thus, the lack of oxygen isotope differences for the Late Pleistocene vs. modern day teeth may be attributed to combined lower temperatures (decreasing local water δ 18O) plus decreased relative humidity (increasing plant and mammal δ 18O) in the Late Pleistocene. Trace element data from fossil and modern teeth and from fossil deposit sedimentary material indicate post burial chemical alteration. Excepting Ba and possibly Cu, concentrations of all other elements analysed (Sr, V, Zr, Y, La, Ce, Nd, and U) increased significantly relative to modern teeth (over an order of magnitude shift, with p ≤ 0.01 for t-tests and Mann–Whitney tests). This diagenetic process may have occurred during the Last Glacial Maximum (LGM), a period of localised wet conditions when significant amounts of soluble soil organic matter accumulated at the fossil site. Trace element analysis of local soils indicates that, relative to soils, teeth strongly prefer Sr and U [ K D(fossil tooth/soil) ∼ 10], and exclude Zr, Cu, and possibly V and Ba [ K D ≤ 0.5]. Surprisingly, Rare Earth Elements (REEs) indicate K D values of ∼ 1. These data imply that Ba is a poor indicator of chemical alteration, while Sr, U, Zr, V, Y, and REEs are particularly sensitive to alteration. Comparisons with other palaeoclimate data suggest that the environmental change on Kangaroo Island from Late Pleistocene to present was greater than on the Nullarbor Plain.

Laser-Induced Breakdown Spectroscopy Microanalysis of Trace Elements in Homo Sapiens Teeth

Two of the main items from which to retrieve data in anthropology are teeth and bones. Identification of trace elements in their composition allows valuable information to be obtained about alimentary habits and community life conditions of groups and individuals. Conventional methods used to determine the presence of trace elements require sample preparation, with partial or total destruction of the pieces, which in most cases are unique. In this work we show the possibilities of laser-induced breakdown spectroscopy (LIBS) as a nearly nondestructive tool in anthropology and paleontology for the measurement of the presence and distribution of trace elements in teeth. We applied LIBS to the determination of strontium and magnesium in dentin and enamel of Neolithic, middle age, and modern Homo sapiens teeth. Mg/Ca and Sr/Ca distribution maps of dentin and enamel in modern teeth were created using the data obtained. Ablation threshold fluences of dentin and enamel were also measured using the photoacoustic signal induced by laser ablation. Significant variations were found in the Mg/Ca and Sr/Ca ratios in the tooth dental tissue and between the teeth of the groups and individuals studied. These results can be useful for evolutionary anthropology studies as they can provide information regarding early nutrition, seasonality, and residential mobility.

Long-term changes of mercury levels in ringed seal ( Phoca hispida) from Amundsen Gulf, and beluga ( Delphinapterus leucas) from the Beaufort Sea, western Canadian Arctic

Mercury (Hg) concentrations were determined in the canine teeth of ringed seals ( Phoca hispida) harvested during the 13th–14th, late 19th and early 21st Centuries in Amundsen Gulf, Northwest Territories, Canada. Most historical and pre-industrial teeth contained undetectable Hg levels (i.e. < 1.0 ng/g DW), whereas samples from 2001–03 contained up to 12 ng/g DW in an age-dependent pattern. Assuming a median [Hg] value in 13th–14th Century teeth of half the detection limit (i.e. 0.5 ng/g DW), geometric means of Hg in modern teeth were 9–17 times those of seals in the 14th Century, equivalent to an anthropogenic input of 89–94% of total Hg in modern seals. These results corroborate a previous study of beluga ( Delphinapterus leucas) in the nearby Beaufort Sea. While the seals' trophic position (inferred from δ 15N values) did not change over time, modern δ 13C values were lower by about 2‰ than in the 14th and 19th Centuries. This could be due to increased dissolution of anthropogenically derived CO 2 in the ocean from the atmosphere, but could also indicate more offshore pelagic feeding by modern seals, which might be a factor in their Hg exposure. New tooth [Hg] data are also presented for the Beaufort Sea beluga, using recently-discovered museum samples collected in 1960/61, which showed that most of the anthropogenic contribution to beluga Hg had already taken effect by 1960 (reaching ∼ 75% of total Hg). Taken together, the long-term seal and beluga data indicate that whereas Hg levels in the marine ecosystems of the western Canadian Arctic were probably unchanged from pre-industrial times up to the late 19th Century, there was a significant, many-fold increase in the early to mid-20th Century, but little or no change after about the early 1960s.

Stable isotopes of modern herbivore tooth enamel in the Tibetan Plateau: Implications for paleoelevation reconstructions

Fossil tooth enamel from herbivores is considered one of the best proxies for paleoclimate and paleoelevation reconstructions, due to its low susceptibility to diagenetic alteration. A synthesis of oxygen and carbon isotope analyses of modern tooth enamel from herbivores such as Tibetan yaks, asses and antelopes is assessed. The average δ13C(PDB) value of herbivore tooth enamel in the Lhasa and south Qiangtang terrains is −11.3% ± 1.1%, whereas in the north Qiangtang and Hoh Xil terrains value is −10.2% ± 1.4% consistent with the current C3-dominant ecotype in the Tibetan Plateau. In addition, the average δ18O(PDB) values from tooth enamel show a northward systematic increase from −11.8% ± 3.4% in the Gyirong Basin, to −11.1% ± 1.1% in the Lhasa and southern Qiangtang terrains, and then to −9.0% ± 1.1% in the northern Qiangtang and the Hoh Xil areas, similar to those of the local river water and precipitation variation trends. It is suggested that δ18O(PDB) values of tooth enamel should not be used directly to evaluate the paleo-elevation of the Tibetan Plateau, because oxygen isotopic composition from tooth enamel is a combination of drinking water (precipitation- and river-sourced) and diet (plant-sourced). Moreover, an empirical relationship between oxygen isotope of tooth enamel and modern river water, and as well as elevation is recommended, which can be used in future studies of Tibetan Plateau paleoelevation.

Laser-assisted in-office bleaching using a neodymium:yttrium–aluminum–garnet laser: an in vivo study

The desire for perfect and white teeth can be accomplished in aesthetical dentistry by modern tooth bleaching methods. Within the scope of a clinical study, laser assisted in-office bleaching was applied to the teeth of 20 individual patients with a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (lambda = 1.064 microm, average power 4 W, pulse repetition rate 10 Hz, pulse duration 320 micros). The treatment was carried out in a split-mouth design, each patient having two appointments with 1 week in between. Laser activation of the bleaching agent was performed on teeth 14-11 and 34-31 per session, with a total irradiation time of 30 s per tooth. The initial and the final color of the teeth were ascertained by VITA Colorsticks and the dental chromatometer ShadeEye NCC. Whitening was detected in the laser-activated and in the non-activated quadrants. Statistical evaluation showed that the additional activation of the bleaching agent by the Nd:YAG laser had produced no significant influence on the whitening (P > 0.05). The results achieved in this study should be scrutinized critically. They give cause for one to reconsider the treatment conditions or the laser parameters used, or even to query the application of the Nd:YAG laser in general during in-office bleaching.

The use of strontium isotopes as an indicator of migration in human and pig Lapita populations in the Bismarck Archipelago, Papua New Guinea

This paper examines the potential use of strontium isotopes ( 87Sr/ 86Sr) for identifying migration within Lapita populations and their commensal animals, specifically the pig ( Sus scrofa). Lapita people (ca. 3300–2200 BP) were the initial colonists of the island groups to the east of the Solomon Islands, spreading from Papua New Guinea to Tonga and Samoa within a few centuries. Mobility is assumed to have been an important mechanism for maintaining cultural solidarity between Lapita communities. It has been previously argued that Lapita populations became progressively more sedentary over time after the initial colonising events. Two Lapita sites, Kamgot and Balbalankin, from the Anir Islands in the Bismarck Archipelago are included in the analysis and fall within the Early (ca. 3300–3000/2900 BP) and Middle (ca. 3000/2900–2700 BP) Lapita periods respectively. Ten tooth enamel samples from Lapita human and pig teeth as well as modern teeth were analysed for strontium isotopes. The mean values for the individuals from both sites were higher than the geological value obtained for the Anir Islands reflecting the incorporation of marine-derived strontium into their tooth enamel taken up in their diet. Although the sample sites have similar environments there was a difference between the local ranges of the strontium isotopic data. One Lapita age pig and one potentially modern pig from Kamgot fell well outside the local distribution for the site and were considered to be non-local. The extreme distribution of the two outliers suggests they came from two geographically separate locations. The results from the Anir Islands when compared with strontium results from other prehistoric Pacific Island populations suggest there is sufficient variation between island groups in terms of the biologically available strontium to justify further research. The present results are discussed in terms of using pigs as a proxy for human mobility as well as an indicator for the ‘local’ range of an archaeological population by treating human and pigs as separate populations. Strontium isotopes therefore provide the opportunity to investigate migration in Lapita populations on a finer scale than was previously possible.