Tooth Apatite Research Articles

Multiple proliferation signaling pathways are modulated by octacalcium phosphate in osteoblasts.

Octacalcium phosphate (OCP), a type of bioactive ceramics, may be associated with dentine, tooth apatite, and especially bone generation, and promotes wound healing after fracture. Recently, commercial bone grafting products containing a large amount of OCP material have been released because OCP can be synthesized in large quantities. It is reported to increase cell proliferation, but the interaction between OCP and cell signaling pathways is still unclear. In this study, first, we demonstrated OCP mediated cell signaling pathways with only purified OCP materials. OCP regulated P38, JNK (c-Jun N-terminal kinase), Src, and AKT (protein kinase B) signaling pathways. OCP crystals appeared in the characteristic ribbon shape but varied by several tens of micrometers in size. The X-ray diffraction pattern was the same as previously reported. We studied two concentrations of OCP (10 mg/ml and 20 mg/ml) to understand whether the effect of OCP on cell signaling pathways is dose dependent. We confirmed that OCP treatment affected cell proliferation and alkaline phosphatase and disrupted Src phosphorylation but did not change the total protein level. P38 phosphorylation was activated with OCP treatment and inhibited by SB203580, but P38 total protein level did not change. OCP inhibited JNK phosphorylation signaling, whereas PD98509 inhibited JNK phosphorylation with or without OCP. Interestingly, the AKT total level decreased after OCP treatment, but AKT phosphorylation increased considerably. Our results demonstrate that OCP materials modulate cell signaling pathways and increase cell proliferation.

Smart injectable self-setting bioceramics for dental applications.

A thermo-responsive injectable bioactive glass (BAG) that has the ability to set at body temperature was prepared using pluronic F127 and hydroxypropyl methylcellulose as the carrier. The injectable composite has the advantage to fill irregular shape implantation sites and quick setting at body temperature. The structural and morphological analysis of injectable BAG before and after setting was done by using Fourier Transform Infrared spectroscopy (FTIR), and Scanning Electron Microscope (SEM). The effect of an ultrasonic scaler for a quick setting of injectable BAG was also investigated. The ultrasonic scaler sets the BAG formulation three-folds faster than at body temperature and homogenized the dispersion. The in vitro bio-adhesion was studied in the bovine tooth in both artificial saliva and deionized water for periodic time intervals, i.e., day 7, 30, 90, and 180, which confirmed the apatite layer formation. The mineral density analysis was used to differentiate the newly formed apatite with tooth apatite. In the MTT assay, the experimental material showed continuous proliferation and cell growth. This indicated that injectable hydrogel promoted cell growth, facilitated proliferation, and had no cytotoxic effect. The SEM and micro-CT results (performed after in vitro bioactivity testing) showed that the injectable BAG had the ability to regenerate dentin, hence this material has the potential to be used for dental and biomedical applications including tooth and bone regeneration in minimally invasive procedures in future.

Thermophysiologies of Jurassic marine crocodylomorphs inferred from the oxygen isotope composition of their tooth apatite.

Teleosauridae and Metriorhynchidae were thalattosuchian crocodylomorph clades that secondarily adapted to marine life and coexisted during the Middle to Late Jurassic. While teleosaurid diversity collapsed at the end of the Jurassic, most likely as a result of a global cooling of the oceans and associated marine regressions, metriorhynchid diversity was largely unaffected, although the fossil record of Thalattosuchia is poor in the Cretaceous. In order to investigate the possible differences in thermophysiologies between these two thalattosuchian lineages, we analysed stable oxygen isotope compositions (expressed as δ18O values) of tooth apatite from metriorhynchid and teleosaurid specimens. We then compared them with the δ18O values of coexisting endo-homeothermic ichthyosaurs and plesiosaurs, as well as ecto-poikilothermic chondrichthyans and osteichthyans. The distribution of δ18O values suggests that both teleosaurids and metriorhynchids had body temperatures intermediate between those of typical ecto-poikilothermic vertebrates and warm-blooded ichthyosaurs and plesiosaurs, metriorhynchids being slightly warmer than teleosaurids. We propose that metriorhynchids were able to raise their body temperature above that of the ambient environment by metabolic heat production, as endotherms do, but could not maintain a constant body temperature compared with fully homeothermic ichthyosaurs and plesiosaurs. Teleosaurids, on the other hand, may have raised their body temperature by mouth-gape basking, as modern crocodylians do, and benefited from the thermal inertia of their large body mass to maintain their body temperature above the ambient one. Endothermy in metriorhynchids might have been a by-product of their ecological adaptations to active pelagic hunting, and it probably allowed them to survive the global cooling of the Late Jurassic, thus explaining the selective extinction affecting Thalattosuchia at the Jurassic-Cretaceous boundary. This article is part of the theme issue 'Vertebrate palaeophysiology'.

An integrated multifunctional hybrid cement (pRMGIC) for dental applications

ObjectiveGlass-ionomer and resin-modified glass-ionomer cements are versatile materials with the ability to form a direct bond with tooth tissues. The aim of this study was to formulate a novel class of dental bio-interactive restorative material (pRMGIC) based on resin-modified glass-ionomer cements via the inclusion of an organophosphorus monomer, ethylene glycol methacrylate phosphate, with a potential to improve the mechanical properties and also function as a reparative restorative material. MethodspRMGIC was formulated with modification of the resin phase by forming mixes of ethylene glycol methacrylate phosphate (EGMP; 0–40%wt) and 2-hydroxyethyl methacrylate monomer into the liquid phase of a RMGIC (Fuji II LC, GC Corp.). The physical properties of the cements were determined including setting characteristics, compressive strength and modulus (CS &CM), microhardness (MH) and biaxial flexural strength (BFS). Fluid uptake and fluoride release were assessed up to 60 days storage. Adhesion to sound dentine was measured using micro-tensile bond strength and surface integrity was analysed using SEM coupled with EDX. Statistical analysis was performed using ANOVA and Bonferroni post-hoc tests. ResultsThe pRMGIC cements exhibited an increase in working time with increasing EGMP concentration however were within the limits of standard clinical requirements. Although the compressive strength of pRMGIC cements were comparable to control cements in the early stages of maturation, the higher EGMP-containing cements (EGMP30 and 40) exhibited significantly greater values (p < 0.05) after 4 weeks storage (141.0 ± 9 and 140.4 ± 8 MPa, respectively), in comparison to EGMP0 (128.8 ± 7 MPa). A dramatic two fold increase in biaxial flexural strength (p < 0.001) was observed for the pRMGIC’s. Furthermore, the ability to decalcify tooth apatite resulted in enhanced interfacial adhesion due to chelation with calcium ions of tooth apatite. The inclusion of EGMP encouraged formation of reinforcing complexes within the RMGIC, thus improving physical properties, decreasing solubility and lower fluoride release. A dense microstructure was observed with increasing EGMP content. SignificanceA novel universal bio-interactive adhesive repair material will enable clinicians to offer more effective repair of the tooth-restoration complex, thus future treatments will benefit both patient and a severely constrained healthcare budget.

Determination of Molecular Species of Calcium Salts of MDP Produced in Demineralization of Tooth Apatite

Determination of Molecular Species of Calcium Salts of MDP Produced in Demineralization of Tooth Apatite

The effect of grain size on carbonate contaminant removal from tooth enamel: Towards an improved pretreatment for radiocarbon dating

It is rarely possible to directly radiocarbon date skeletal remains from hot environments as collagen rapidly degrades. Although able to survive in the majority of burial environments for longer, unburnt biological apatites frequently produce inaccurate radiocarbon dates due to contamination from carbonate in the groundwater. The location of this contamination within the skeletal material is rarely investigated, hampering development of improved radiocarbon pretreatment methods. This paper focuses on tooth enamel and aims to test whether carbonate contaminants are sitting at the crystallite boundaries, and from this to test a pretreatment to produce more accurate radiocarbon age estimates. Although the porosity of enamel is low, trace elements are thought to diffuse between enamel prisms and crystallites. Gordon et al. (2015, Science, 347 (6223), 746-750) identified magnesium substituted amorphous calcium phosphate between the apatite crystallites. This phase contains the majority of magnesium within modern rodent enamel, providing an opportunity to monitor its removal, and thus test whether carbonate contaminants are located between or on the surface of the crystallites. Modern Sus scrofa and four ancient Sus scrofa teeth have been used to demonstrate that the more finely ground the enamel, the more magnesium can be removed with an acetic acid leach, and the more accurate the radiocarbon dates. After leaching in acetic acid, teeth dating to beyond the limit of the radiocarbon method (c.50 ka) produce ages of c.20 kBP when hand ground, and c.30 kBP when mechanically ground. This suggests that some contaminants are sitting at the crystallite boundaries. However, although mechanically grinding substantially increases the amount of carbonate contamination removed in an acid leach compared to hand grinding, not all contaminants could be removed from the samples examined in this study, and radiocarbon dates on tooth apatite should still be regarded as minimum ages.

Influences on the stable oxygen and carbon isotopes in gerbillid rodent teeth in semi-arid and arid environments: Implications for past climate and environmental reconstruction

The stable isotope composition of small mammal tissues has the potential to provide detailed information about terrestrial palaeoclimate and environments, because their remains are abundant in palaeontological and archaeological sites, and they have restricted home ranges. Applications to the Quaternary record, however, have been sparse and limited by an acute lack of understanding of small mammal isotope ecology, particularly in arid and semi-arid environments. Here we document the oxygen and carbon isotope composition of Gerbillinae (gerbil) tooth apatite across a rainfall gradient in northwestern Africa, in order to test the relative influences of the 18O/16O in precipitation or moisture availability on gerbil teeth values, the sensitivity of tooth apatite 13C/12C to plant responses to moisture availability, and the influence of developmental period on the isotopic composition of gerbil molars and incisors. The results show that the isotopic composition of molars and incisors from the same individuals differs consistent with the different temporal periods reflected by the teeth; molar teeth are permanently rooted and form around the time of birth, whereas incisors grow continuously. The results indicate that tooth choice is an important consideration for applications as proxy Quaternary records, but also highlights a new potential means to distinguish seasonal contexts. The oxygen isotope composition of gerbil tooth apatite is strongly correlated with mean annual precipitation (MAP) below 600 mm, but above 600 mm the teeth reflect the oxygen isotope composition of local meteoric water instead. Predictably, the carbon isotope composition of the gerbil teeth reflected C3 and C4 dietary inputs, however arid and mesic sites could not be distinguished because of the high variability displayed in the carbon isotope composition of the teeth due to the microhabitat and short temporal period reflected by the gerbil. We show that the oxygen isotope composition of small mammal teeth strongly reflects moisture availability in semi-arid and arid environments and would provide an excellent record of palaeo-aridity in a terrestrial setting. The results illustrate that an understanding of an animal's physiology is essential for interpreting the animal's isotopic responses to external contexts, especially in arid zones.

Chemical composition of modern and fossil Hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 1: Major and minor element variation

Abstract. Bioapatite in mammalian teeth is readily preserved in continental sediments and represents a very important archive for reconstructions of environment and climate evolution. This project provides a comprehensive data base of major, minor and trace element and isotope tracers for tooth apatite using a variety of microanalytical techniques. The aim is to identify specific sedimentary environments and to improve our understanding on the interaction between internal metabolic processes during tooth formation and external nutritional control and secondary alteration effects. Here, we use the electron microprobe to determine the major and minor element contents of fossil and modern molar enamel, cement and dentin from Hippopotamids. Most of the studied specimens are from different ecosystems in Eastern Africa, representing modern and fossil lacustrine (Lake Kikorongo, Lake Albert, and Lake Malawi) and modern fluvial environments of the Nile River system. Secondary alteration effects - in particular FeO, MnO, SO3 and F concentrations – are 2 to 10 times higher in fossil than in modern enamel; the secondary enrichment of these components in fossil dentin and cement is even higher. In modern and fossil enamel, along sections perpendicular to the enamel-dentin junction (EDJ) or along cervix-apex profiles, P2O5 and CaO contents and the CaO/P2O5 ratios are very constant (StdDev ∼1%). Linear regression analysis reveals tight control of the MgO (R2∼0.6), Na2O and Cl variation (for both R2&gt;0.84) along EDJ-outer enamel rim profiles, despite large concentration variations (40% to 300%) across the enamel. These minor elements show well defined distribution patterns in enamel, similar in all specimens regardless of their age and origin, as the concentration of MgO and Na2O decrease from the enamel-dentin junction (EDJ) towards the outer rim, whereas Cl displays the opposite trend. Fossil enamel from Hippopotamids which lived in the saline Lake Kikorongo have a much higher MgO/Na2O ratio (∼1.11) than those from the Neogene fossils of Lake Albert (MgO/Na2O∼0.4), which was a large fresh water lake like those in the western Branch of the East African Rift System today. Similarly, the MgO/Na2O ratio in modern enamel from the White Nile River (∼0.36), which has a Precambrian catchment of dominantly granites and gneisses and passes through several saline zones, is higher than that from the Blue Nile River, whose catchment is the Neogene volcanic Ethiopian Highland (MgO/Na2O∼0.22). Thus, particularly MgO/Na2O might be a sensitive fingerprint for environments where river and lake water have suffered strong evaporation. Enamel formation in mammals takes place at successive mineralization fronts within a confined chamber where ion and molecule transport is controlled by the surrounding enamel organ. During the secretion and maturation phases the epithelium generates different fluid composition, which in principle, should determine the final composition of enamel apatite. This is supported by co-linear relationships between MgO, Cl and Na2O which can be interpreted as binary mixing lines. However, if maturation starts after secretion is completed, the observed element distribution can only be explained by equilibration of existing and addition of new apatite during maturation. It appears the initial enamel crystallites precipitating during secretion and the newly formed bioapatite crystals during maturation equilibrate with a continuously evolving fluid. During crystallization of bioapatite the enamel fluid becomes continuously depleted in MgO and Na2O, but enriched in Cl which results in the formation of MgO, and Na2O-rich, but Cl-poor bioapatite near the EDJ and MgO- and Na2O-poor, but Cl-rich bioapatite at the outer enamel rim. The linkage between lake and river water compositions, bioavailability of elements for plants, animal nutrition and tooth formation is complex and multifaceted. The quality and limits of the MgO/Na2O and other proxies have to be established with systematic investigations relating chemical distribution patterns to sedimentary environment and to growth structures developing as secretion and maturation proceed during tooth formation.

Reconstructing seawater Sr/Ca during the last 70 My using fossil fish tooth enamel

The chemical composition of past oceans records the combined effects of the evolution of life, climate changes and solid Earth dynamics. Variations in the rate of hydrothermal alteration of the oceanic crust, continental weathering input and burial of marine carbonates are thought to drive the seawater Sr/Ca ratio. Several methods exist for reconstructing past seawater Sr/Ca ratio which are based on the partitioning of Sr between biogenic and inorganic carbonates, and seawater. A compilation of reconstructed seawater Sr/Ca ratios shows that results at variance with each other are obtained for the last 100 My, leaving the question of the Sr/Ca composition of seawater over this period unresolved. Here, a new method for reconstructing the Sr/Ca ratio of past seawater based on the partitioning of Sr between tooth apatite of fossil fish enamel and seawater is proposed. Previously reported values of Sr/Ca and δ 18O PO4 for a collection of fish teeth and new data allow the reconstruction of the seawater Sr/Ca ratio evolution for the last 70 My using a new thermometer based on the Sr/Ca ratio in fish teeth. Calculated Sr/Ca ratios decrease from ~ 14 mmol·mol − 1 at 70 Ma to ~ 8 mmol·mol − 1 at 50 Ma and further increase to present day values during the Pliocene. The results are in agreement with values calculated from Cenozoic benthic foraminifera obtained from ODP and DSDP sites. Once the biological offsets of the partitioning of Sr between apatite and water are determined, fossil fish tooth bioapatite represents a material of choice for reconstructing the past seawater Sr/Ca considering its better resistance to diagenetic alteration than for calcite and aragonite.

Effect of Reacted Acidic Monomer with Calcium on Bonding Performance

We determined the number of reacted and unreacted 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) molecules with calcium during the demineralization process of hydroxyapatite or dentin by 10-MDP-based one-step (Clearfil Tri-S Bond, TS) or two-step self-etch adhesive (Clearfil SE Bond Primer, SE). We then examined the effects of the number of reacted and/or unreacted 10-MDP molecules on the initial bond strength and bond durability of the resultant adhesive layer. The null hypotheses were that (1) the etching efficacy of tooth apatite by 10-MDP used in TS was the same as that in SE, and (2) the unreacted 10-MDP polymer included within the adhesive layer does not affect bond durability. Addition of hydroxyapatite or dentin to the TS and SE resulted in decreases in the NMR peak intensities for 10-MDP. The peak intensity for 10-MDP showed a greater reduction in SE than in TS, consistent with the observation that SE provided significantly higher initial mean bond strengths than TS. Further, the unreacted 10-MDP polymer within the adhesive layer did not decrease the mean bond strength, despite the application of 20,000x thermo-cycling.

Apatite varieties in extant and fossil vertebrate mineralized tissues

A whole-pattern fitting of X-ray diffraction (XRD) patterns, including lattice-parameter and size–strain analysis, was elaborated and applied to a sample set of extant and fossil vertebrate tooth apatite. Recent and subfossil human tooth enamel and dentine, extant and fossil shark tooth enameloid, sarcopterygian and coelacanth tooth enamels were studied. As comparative materials, a modern coelacanth fish scale and a pharyngeal tooth of bony fish were used. It was found that the enamel apatite of human milk teeth had lattice parameter valuesa≃ 9.4 Å andc≃ 6.88 Å, which are close to the corresponding values of subfossil human teeth. The apatite of fossilized vertebrate teeth always has a loweralattice parameter (about 9.37 Å), while the lattice parametercappears to be more stable, being around 6.88 Å. The strain appears to be correlated with the lattice direction, being around ten times higher in the [hk0] direction. During fossilization, the strain diminished in the [00l] direction, but was random in the perpendicular [hk0] direction. The enamel tissues of vertebrates are built of two discrete crystallite series. About one-third of the human milk tooth enamel is composed of larger crystallites with dimensions of about 400 × 500 Å, and two-thirds of smaller crystallites with dimensions of about 50 × 150 Å. The latter range of dimensions is also characteristic for the crystallites forming the mineral part of human dentine and fish scales. Shark tooth enameloid is also built of two distinct series of apatite crystallites of different sizes and shapes. The larger crystallites (amounting to ∼15% of all crystallites) have approximate dimensions of 500 × 1000 Å, while the smaller ones are 400 × 500 Å. Both series are distinguishable in XRD patterns of modern, Jurassic and Devonian shark enamel.

골 생체조직공학을 위한 복합 세라믹 골 지지체의 제조와 생체역학적 특성

Novel porous composite ceramic bone scaffolds composed of biodegradable PHBV(polyhydroxybutyrate-co-hydroxyvalerate) and TA(toothapatite) have been fabricated for bone tissue engineering by a modified solvent casting and particulate leach-ing method with salt-contained heat compression technique. The results of this study suggest that the PHBV-TA composite scaffold, especially the scaffold containing 30 weight of TA may be a good candidate far bone tissue engineering of non-load bearing area in oral and maxillofacial region.

골 조직공학을 위한 치아인회석, 키토산, 시아노아크릴레이트를 이용한 새로운 생체흡수성 골시멘트

치아인회석, 키토산, 시아노아크릴레이트 등의 생분해성 생체재료를 이용해 새로운 생체흡수성 골시멘트를 개발하고자 하였다. 이들 골시멘트들에 대해서 중합온도, 응고시간 등의 조작특성과 압축강도, 전단강도 등의 물성을 분석하였다. 특히, 치아인회석과 키토산의 미립가루와 부틸 시아노아크릴레이트의 강력접착제를 이용한 시멘트(B)에 대해서는 직접 접촉방법과 XTT 방법을 통해 세포독성을 분석하였고, 또한 쥐를 이용한 동물실험에서 시멘트(B)의 처리그룹에 따라 생체적합성을 분석하였다. 시아노아크릴레이트를 이용한 골시멘트의 최대중합온도는 약 33<TEX>$^{\circ}C$</TEX>, 조작(응고)시간은 3-6분, 압축강도는 약 15-25㎫, 전단강도는 약 0.4-l.7 ㎫를 나타내었다. 첨가제로 사용된 Lipiodol은 골시멘트의 주사성과 강력접착제의 초기 중합지연도를 높였고, 특히 송진가루는 시아노아크릴레이트의 초기중합을 지연시켰다. 시아노아크릴레이트를 이용한 시멘트(B)의 세포독성을 분석한 결과, 대부분의 처리 그룹에서 낮게 나타났고, 특히 키토산과 치아인회석을 사용한 경우 각각 세포 독성이 더 낮게 나타났다. 그리고 골시멘트(B)의 동물 생체적합성 실험의 방사선상 및 조직학적 분석에서도 뼈 형성 및 결합이 우수하게 나타났다.

Diagenesis and the reconstruction of paleoenvironments: A method to restore original δ 18O values of carbonate and phosphate from fossil tooth enamel

Intra-tooth δ 18O variations within the carbonate (δ 18Oc) and phosphate (δ 18Op) components of tooth apatite were measured for Miocene and Pliocene hypsodont mammals from Afghanistan, Greece and Chad in order to evaluate the resistance of enamel to diagenetic alteration. Application of water-apatite interaction models suggest that the different kinetic behaviours of the phosphate-water and carbonate-water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra-individual variations are considered. Selective alteration of the oxygen isotope composition from the carbonate component of Afghan and Greek enamels suggests inorganic isotopic exchange processes. Microbially-induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from Chad, in association with extensive recrystallization. In Chad, δ 18Op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis. Mass balance calculations using average carbonate content in enamel as a proxy for recrystallization, and the lowest δ 18Op value of dentine as a proxy for the isotopic composition of the diagenetic fluid, indicate that diagenesis can alter δ 18Op by as much as 3‰ in some enamel samples. This diagenetic alteration is also responsible for a decrease in intra-individual variations of up to 1‰ in affected specimens. The effects of diagenesis on δ 18Op values of fossil enamel are not systematic, however, and can only be estimated if sequential δ 18Op and δ 18Oc analyses are performed on fossil enamel and dentine. Reconstruction of large temporal- or spatial-scale paleoclimates based on δ 18Op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects.

Isotopic evidence for paleoclimatic and paleoatmospheric variations from the Paleogene Bighorn Basin sequence

Land mammal faunas changed dramatically from the late Paleocene to the Eocene. This interval was marked by substantial paleoceanographic changes, including marine warming, and mass extinction of benthic foraminifera. Yet study of the impact of marine events on continental climates and faunas is problematic, due to imprecision in marine/continental correlation.Oxygen isotope measurements of paleosol carbonates, mammals, and bivalves from the Paleogene Bighorn Basin can be used to estimate mean annual temperature (MAT). The δ18O of paleosol carbonate is controlled by two factors: the δ18O of the groundwater from which it crystallizes, and the temperature during crystallization. Because mammals and bivalves secrete mineral in a biologically-restricted range of temperatures, their isotopic compositions serve as proxy indicators of surface water δ18O. The difference in δ18O between these proxy indicators of water and paleosol carbonate is used to calculate MAT through application of standard oxygen isotope thermometry relationships. Calculated temperatures vary significantly throughout the interval, with high values (&gt;20°) in the late Paleocene, lower values in the earliest Eocene (10–20°), and renewed warmth later in the Early Eocene.In modern temperate regions, MAT and the δ18O of precipitation are closely correlated. Estimates for Paleocene/Eocene surface waters from tooth apatite and bivalves range from −8 to −12± (SMOW). Today, precipitation with values this low is usually found in cold regions (0–10°). These temperature estimates are too low in light of other isotopic and paleobotanical indicators, which suggest very warm temperatures in the Bighorn Basin during the Paleogene. We hypothesize that vapor transport to the region was substantially different than at present. A potential model may be Amazonia, where wet season air masses lose up to 80% of their water vapor as they move across the basin, resulting in 18O-depleted rainfall despite a warm climate.Variations in δ13C provide a tool for marine/continental correlation. Carbon in tooth apatite and soil carbonate is derived from plants, which fix atmospheric CO2. Atmospheric CO2 is, in turn, in isotopic equilibrium with marine carbonate. Because of these links, marine carbonate, land plants, land mammals, and soil carbonate should exhibit coupled carbon isotope variations. In the Paleogene, when C3 plants dominated floras, isotopic variations due to shifting floral composition, such as those documented in the Miocene Siwalik Sequence, could not occur. Paleogene continental and marine carbon isotope records are tightly coupled. In particular, there is an unusual marine carbon isotope excursion immediately preceding the Paleocene/Eocene boundary, which corresponds precisely to the major paleoceanographic changes and the extinction of benthic foraminifera. Tooth apatite and soil carbonate from the Paleogene Bighorn Basin also record this excursion, which occurs at the base of the Wasatchian, where perrisodactyls, artiodactyls, and modern primates first appear. Carbon isotopes allow tight marine/continental correlation of the Paleocene/Eocene boundary, and demonstrate that major biologic and climatic events at this time were globally synchronous.

Growth increments in teeth of &lt;i&gt;Diictodon&lt;/i&gt; (Therapsida)

Growth increments circa 0.02 mm in width have been observed in sectioned tusks of Diictodon from the Late Permian lower Beaufort succession of the South African Karoo, dated between about 260 and 245 million years ago. Mean growth increments show a decline from relatively high values in the Tropidostoma/Endothiodon Assemblage Zone, to lower values in the Aulacephalodon/Cistecephaluszone, declining still further in the Dicynodon lacerficeps/Whaitsia zone at the end of the Permian. These changes coincide with gradual changes in carbon isotope ratios measured from Diictodon tooth apatite. It is suggested that the decline in growth increments is related to environmental changes associated with a decline in primary production which contributed to the decline in abundance and ultimate extinction of Diictodon.

Diets of Pliocene mammals from Omo, Ethiopia, deduced from carbon isotopic ratios in tooth apatite

Carbon isotopic ratios in tooth apatite of Pliocene fossil mammals from Omo, Ethiopia, dated at 2.0 m.y. ago reported here are consistent with dietary predictions based on modern herbivores of the African savannah. The results indicate the applicability of the technique in reconstructing dietary patterns of fossil animals including hominids.

Mineralization of the Growing Tooth as Shown by Radio-Phosphorus Autographs.

The deposition of radio-phosphorus in growing molar teeth was examined in young hamsters with the help of the autographic technic. An injection of carrier-free radio-phosphorus (P32) was given at the age of 4 days, that is, soon after the appearance of dentin and enamel in the germs of the first and second molars. The animals were sacrificed 1 hour, 6 hours, 1 day, 2 days or 4 days later. The jaws were fixed in a neutral formalin-alcohol mixture, embedded in celloidin without decalcification- sectioned as usual, autographed by coating the sections with photographic emulsion according to the “inverted method”(1), and stained with basic fuchsin. Dentin and enamel, but not soft tissues, showed autographic reactions. These were attributed to the presence of radio-phosphorus in a form sufficiently insoluble to be retained in the sections during the histological procedure. Presumably, the radio-phosphorus had become part of the complex phosphate salt making up the crystalline structures of the tooth (apatite).A...