Mammalian Teeth Research Articles

The Cultural and Chronostratigraphic Context of a New Leaf Point from Hohle Fels Cave in the Ach Valley of Southwestern Germany

During the summer of 2020 the excavation team at Hohle Fels Cave in the Ach Valley of southwestern Germany recovered a leaf point (in German Blattspitze) made from gray Jurassic chert. The find is well-preserved and remarkable for a number of reasons. First this is the only leaf point recovered by a modern excavation in the Swabian Jura, and is the first leaf point discovered in situ since 1936, when Gustav Riek’s crew recovered two well-preserved leaf points at the excavation of Haldenstein Cave in the Lone Valley. The leaf point and associated finds originate from archaeological horizon (AH) X, 120 cm below the base of the rich Aurignacian deposits at the site that dates with radiocarbon to ca. 42 ka cal BP. Four ESR dates made on the teeth of large mammals from AH IX overlying the new leaf point yielded an average age of 62.5 ± 4 ka BP. This date represents a minimum age for the new horizons, which based on convention would be placed in the cultural taxonomic unit of the Blattspitzengruppe. Since the Blattspitzengruppe is typically interpreted as the last Middle Paleolithic cultural unit, we were intrigued to find an assemblage containing a Blattspitze in such an early chronostratigraphic context. While in Germany the Blattspitzengruppe is usually associated with the end of the Middle Paleolithic, many researchers across Europe have described these leaf point assemblages as being transitional industries at the interface between the Middle and Upper Paleolithic. Historically, some authors have even suggested a degree of cultural continuity between leaf point assemblages of the Middle and Upper Paleolithic. Here we present the stratigraphic and chronological context of the AH X and provide a preliminary description of the material cultural record from this horizon. Keeping in mind that we so far have only excavated parts of 6 m2 of the new find horizon and the underlying find horizon AH XI, the paper provides initial observations that will need revision as the excavation proceeds. These findings suggest that leaf points represent a feature in the technological repertoire of the Late Pleistocene Neanderthals of southwestern Germany rather than a reliable cultural stratigraphic marker for the last phase of the Middle Paleolithic.

Differentiating siliceous particulate matter in the diets of mammalian herbivores

AbstractSilica is crucial to terrestrial plant life and geochemical cycling on Earth. It is also implicated in the evolution of mammalian teeth, but there is debate over which type of siliceous particle has exerted the strongest selective pressure on tooth morphology.Debate revolves around the amorphous silica bodies (phytoliths) present in plants and the various forms of siliceous grit—that is, crystalline quartz (sand, soil, dust)—on plant surfaces. The problem is that conventional measures of silica often quantify both particle types simultaneously.Here we describe a protocol that relies on heavy‐liquid flotation to separate and quantify siliceous particulate matter in the diets of herbivores. The method is reproducible and well suited to detecting species‐ or population‐level differences in silica ingestion. In addition, we detected meaningful variation within the digestive tracts of cows, an outcome that supports the premise of ruminal fluid ‘washing’ of siliceous grit.We used bootstrap resampling to estimate the sample sizes needed to compare species, populations or individuals in space and time. We found that a minimum sample of 12 individuals is necessary if the species is a browser or as many as 55 if the species is a grazer, which are more variable. But a sample size of 20 is adequate for detecting statistical differences. We conclude by suggesting that our protocol for differentiating and quantifying silica holds promise for testing competing hypotheses on the evolution of dental traits.

Pliocene - Early Pleistocene continental climate and vegetation in Europe based on stable isotope compositions of mammal tooth enamel

There is an increasing need for paleoclimate records from continental settings to better understand the climatic changes during critical periods such as the Pliocene and Early Pleistocene. Present data indicates a transition from a warmer than present-day climate to a substantially different cooler climate. This study reviews the oxygen and carbon isotope compositions of mammalian tooth enamel for the Pliocene and Early Pleistocene of South and Central Europe to reconstruct the spatial distribution and temporal changes of the vegetation and oxygen isotope composition of precipitation (δ18Oppt). In addition to a literature review, this study adds new stable isotope measurements for this period. All δ13C values indicate C3 ecosystems and reflect major changes in the water use efficiency and/or in the prevailing humidity. The reconstructed major floral types range from woodland to woodland ‒ mesic grassland in all of the investigated regions. The carbon isotope compositions of fossil mammal teeth demonstrate that the spatial distribution of vegetation was broadly similar to those of the present-day for the Early/Late Pliocene – Early Pleistocene, with the most “closed” vegetation in Central and Northern Italy, while open mesic grassland vegetation covers can be reconstructed for the Iberian Peninsula, Massif Central region (Central France) and the Carpathian Basin. The calculated δ18Oppt values give a negative temporal shift of about 1–1.5‰ from the Early Pliocene to Late Pliocene – Early Pleistocene in three regions (Iberian Peninsula, Central Italy, Carpathian Basin), potentially representing a 1.5–3.0 °C decrease in mean annual temperatures (MAT) over time. In the Massif Central region and the Carpathian Basin, the δ18Oppt values are almost the same for the Late Pliocene and Early Pleistocene, while in Northern Italy the values decreased over that period. The δ18Oppt values are in the range of present-day δ18Oppt values over the Early Pliocene and somewhat lower than present-day values for the Late Pliocene - Early Pleistocene in most of the regions. Because most other proxies indicate warmer than present-day climate for the Early Pliocene and similar to present-day climate for the Early Pleistocene, the δ18Oppt values are generally lower than expected, which can be partially explained by local effects.

Triple oxygen isotope distribution in modern mammal teeth and potential geologic applications

Reconstructing water availability in terrestrial ecosystems is key to understanding past climate and landscapes, but there are few proxies for aridity that are available for use at terrestrial sites across the Cenozoic. The isotopic composition of tooth enamel is widely used as a paleoenvironmental indicator and recent work suggests the potential for using the triple oxygen isotopic composition of the carbonate component of mammalian tooth enamel (Δ′17Oenamel) as an indicator of aridity. However, the extent to which Δ′17Oenamel values vary across environments is unknown and there is no framework for evaluating past aridity using Δ′17Oenamel data. Here we present Δ′17Oenamel and δ18Oenamel values from 50 extant mammalian herbivores that vary in physiology, behavior, diet, and water-use strategy. Teeth are from sites in Africa, Europe, and North America and represent a range of environments (humid to arid) and latitudes (34°S to 69°N), where mean annual δ18O values of meteoric water range from –26.0‰ to 2.2‰ (VSMOW). Δ′17Oenamel values from these sites span 162 per meg (–252 to –90 per meg), where 1 per meg = 0.001‰). The observed variation in Δ′17Oenamel values increases with aridity, forming a wedge-shaped pattern in a plot of aridity index vs. Δ′17Oenamel that persists regardless of geographic region. In contrast, the plot of aridity index vs. δ18Oenamel for these same samples does not yield a distinct pattern. We use these new Δ′17Oenamel data from extant teeth to provide guidelines for using Δ′17Oenamel data from fossil teeth to assess and classify the aridity of past environments. Δ′17Oenamel values from the fossil record have the potential to be a widely used proxy for aridity without the limitations inherent to approaches that use δ18Oenamel values alone. In addition, the data presented here have implications for how Δ′17Oenamel values of large mammalian herbivores can be used in evaluations of diagenesis and past pCO2 and past gross primary productivity.

Speleological and environmental history of Lida Ajer cave, western Sumatra.

Some of the earliest evidence for the presence of modern humans in rainforests has come from the fossil deposits of Lida Ajer in Sumatra. Two human teeth from this cave were estimated to be 73–63 thousand years old, which is significantly older than some estimates of modern human migration out of Africa based on genetic data. The deposits were interpreted as being associated with a rainforest environment based largely on the presence of abundant orangutan fossils. As well as the main fossil-bearing chamber, fossil-bearing passages are present below a sinkhole, although the relationship between the different fossil deposits has only been tenuously established. Here, we provide significant new sedimentological, geochronological and palaeoecological data aimed at reconstructing the speleological and environmental history of the cave and the clastic and fossil deposits therein. Our data suggest that the Lida Ajer fossils were deposited during Marine Isotope Stage 4, with fossils from the lower passages older than the main fossil chamber. Our use of stable carbon and oxygen isotope analyses of mammalian tooth enamel demonstrates that early humans probably occupied a closed-canopy forest very similar to those present in the region today, although the fossil orangutans may have occupied a slightly different niche.This article is part of the theme issue ‘Tropical forests in the deep human past’.

Stress patterns in conical teeth of reptiles and mammals: experimental and finite element analyses

A 3-Dimensional Finite Element Analysis (FEA) of conical teeth of reptiles and some mammals, suggests that under a vertical loading condition along the longer axis of tooth, horizontal tensile stresses are produced. In dental enamel, these stresses are distributed mainly in two horizontal directions, i.e. in X direction and in Z direction. The empirical observation of stresses possibly leading to the vertical failure of the teeth was obtained through Universal Testing Machine (UTM) using recent unicuspid teeth of crocodiles, varanus and canines of pig, cat and dog. The horizontal development of Hunter Schreger Bands (HSBs) has been observed in the enamel of canines of herbivore and carnivore mammals, which seems to be an effective structural strategy to counter splitting of tooth enamel under vertical loading. In contrast, the unicuspid teeth of reptiles lack the HSBs, and are more susceptible to failure. However, as reptilian teeth are continuously replaced, the damage is negligible.

Finite element analysis of crenulated and non‐crenulated hominid molars: A functional hypothesis explaining the adaptive significance of molar crenulation

AbstractObjectivesThe occlusal surface of many mammalian teeth has grooves that have been collectively called crenulations. The evolutionary significance of this trait is unknown, but it has been associated with a hard diet. It has not been explained, however, why crenulated molars may present an increased mechanical resistance. The objective of this study was to determine whether a crenulated surface dissipate mechanical stress more efficiently than a smooth one.Materials and methodsUsing μCT scans we built 3D models of lower second molars from Homo, Pan, Gorilla, and Pongo. The crenulated models from Homo and Pongo were modified to remove crenulations. Finite element analysis was used to determine the distribution of mechanical stress in all the models when a vertical force was applied.ResultsThe results show that crenulated molars have a distinctive pattern of mechanical stress, namely the stress is higher in the valleys than in the crests of the crenulations. In non‐crenulated molars, mechanical stress is more homogeneously distributed. Highly crenulated molars of orangutans show the smallest values of mean stress among the compared species. Artificially removing crenulations results in more homogeneous distribution of stresses and increased mean stress values.ConclusionsMolar crenulations may increase molar resistance by canalizing mechanical stress from the tip to the base of the cusps. The overall cusp shape also influences the distribution of stress. This mechanism may be a functional hypothesis to explain the association between crenulated molars and mechanically demanding diets.

EFFECT OF BALL-MILLING TREATMENT ON SINTERABILITY OF HYDROXYAPATITE CERAMICS INCLUDING BONE MINERALS

Biological apatite found in the bone and teeth of mammals contains various ions, such as Na+, K+, Mg2+, F- and CO32-. We have previously developed porous hydroxyapatite ceramics, containing bone minerals (bone HAp). These ceramics showed great bone-forming ability and bio-resorbability; however, their mechanical strengths were in sufficient for clinical application. Thus, we focused on the refinement of raw material powder to improve the strength of the resulting bone HAp ceramics. In particular, we clarified the effect of ball milling time on sinterability of the bone HAp powder. Among the prepared samples, the most easily sinterable powder was prepared after ball milling for 1 hour. This powder showed the smallest particle size with a particle size distribution that was close to a uniform distribution. The compressive strengths of Bone HAp ceramics from powders prepared by ball-milling for 30 minutes and 1 hour were of 55.7 MPa and 63.1 MPa, respectively.

Mammalian Tooth Enamel Functional Sophistication Demonstrated by Combined Nanotribology and Synchrotron Radiation FTIR Analyses

Mammalian Tooth Enamel Functional Sophistication Demonstrated by Combined Nanotribology and Synchrotron Radiation FTIR Analyses

Stable Isotope Analysis of Mammalian Enamel From the Early Pleistocene Site of Madigou, Nihewan Basin: Implications for Reconstructing Hominin Paleoenvironmental Adaptations in North China

The reconstruction of environmental and climatic changes in the Pleistocene is an essential contribution to our understanding of human evolutionary and behavioral adaptations. Well preserved fluvio-lacustrine sediments at Nihewan basin have yielded a rich record of Early Pleistocene Paleolithic sites and mammalian fossils which provide a unique opportunity for exploring hominin behavior and paleoecology in North China. Taxonomic studies of mammalian fossils have provided important clues to the general environmental setting and landscapes of Early Pleistocene humans in the fluvio-lacustrine basin of Nihewan, but little is known about their isotopic signatures. In this paper, mammal teeth species at the Madigou archaeological site (ca. 1.2 Ma) were selected for bulk and sequential enamel stable isotope (C, O) analysis. Results show a variety of ecological environments, including grassland and sparse forest landscapes, and distinct patterns across taxa. C3-C4 mixed vegetation predominated, but C4 vegetation was also relevant at times. Madigou early humans likely experienced cold/warm or dry/wet fluctuations in this northern China basin. We hypothesize that the environmental fluctuations and diversified landscapes may have driven flexibility in various aspects of early human technological behaviors, and allowed hominins to face the environmental challenges of northern latitudes after the initial expansion from Africa into East Asia at the onset of the Middle Pleistocene Climate Transition.

Atmospheric Pressure Plasma Activation of Hydroxyapatite to Improve Fluoride Incorporation and Modulate Bacterial Biofilm.

Despite the technological progress of the last decade, dental caries is still the most frequent oral health threat in children and adults alike. Such a condition has multiple triggers and is caused mainly by enamel degradation under the acidic attack of microbial cells, which compose the biofilm of the dental plaque. The biofilm of the dental plaque is a multispecific microbial consortium that periodically develops on mammalian teeth. It can be partially removed through mechanical forces by individual brushing or in specialized oral care facilities. Inhibition of microbial attachment and biofilm formation, as well as methods to strengthen dental enamel to microbial attack, represent the key factors in caries prevention. The purpose of this study was to elaborate a cold plasma-based method in order to modulate microbial attachment and biofilm formation and to improve the retention of fluoride (F−) in an enamel-like hydroxyapatite (HAP) model sample. Our results showed improved F retention in the HAP model, which correlated with an increased antimicrobial and antibiofilm effect. The obtained cold plasma with a dual effect exhibited through biofilm modulation and enamel strengthening through fluoridation is intended for dental application, such as preventing and treating dental caries and enamel deterioration.

Dental topographic and three-dimensional geometric morphometric analysis of carnassialization in different clades of carnivorous mammals (Dasyuromorphia, Carnivora, Hyaenodonta).

The evolution of carnassial teeth in mammals, especially in the Carnivora, has been subject of many morphometric and some dental topographic studies. Here, we use a combination of dental topographic analysis (Dirichlet normal energy) and 3D geometric morphometrics of less and high carnassialized lower teeth of carnivoran, dasyuromorph and hyaenodont taxa. Carnassial crown curvature, as indicated by Dirichlet normal energy, is high in lesser carnassialized teeth and low in higher carnassialized teeth, where it is influenced by the reduction of crown features such as cusps and crests. PC1 of the geometric morphometric analysis is linked to enlargement of the carnassial blade, reduction of the talonid crushing basin and an increasingly asymmetric cervix line with an enlarged mesial flexure in more carnassialized teeth. Distribution of PC1 values further indicates that along the tooth row of dasyuromorphs (m2-m4) and hyaenodonts (m1-m3) the most distal carnassial is the most carnassialized (principal carnassial), and in most taxa with overall higher carnassialized teeth, carnassialization successively increases from the anterior to the posterior tooth position along the tooth row. PC2 indicates that a longitudinal elongated carnassial is present in caniforms and in unspecialized feliforms, which separates these taxa in morphospace from all dasyuromorphs, hyaenodonts and specialized feliforms. An ancestral state reconstruction shows that this longitudinal elongation may be a plesiomorphic ancestral state for the Carnivora, which is different from the Dasyuromorphia and the Hyaenodonta. This elongation, enabling the presence of a longitudinally aligned carnassial blade as well as a complete talonid basin, might have provided the Carnivora with an advantage in terms of adaptive versatility.

A robust, semi-automated approach for counting cementum increments imaged with synchrotron X-ray computed tomography.

Cementum, the tissue attaching mammal tooth roots to the periodontal ligament, grows appositionally throughout life, displaying a series of circum-annual incremental features. These have been studied for decades as a direct record of chronological lifespan. The majority of previous studies on cementum have used traditional thin-section histological methods to image and analyse increments. However, several caveats have been raised in terms of studying cementum increments in thin-sections. Firstly, the limited number of thin-sections and the two-dimensional perspective they impart provide an incomplete interpretation of cementum structure, and studies often struggle or fail to overcome complications in increment patterns that complicate or inhibit increment counting. Increments have been repeatedly shown to both split and coalesce, creating accessory increments that can bias increment counts. Secondly, identification and counting of cementum increments using human vision is subjective, and it has led to inaccurate readings in several experiments studying individuals of known age. Here, we have attempted to optimise a recently introduced imaging modality for cementum imaging; X-ray propagation-based phase-contrast imaging (PPCI). X-ray PPCI was performed for a sample of rhesus macaque (Macaca mulatta) lower first molars (n = 10) from a laboratory population of known age. PPCI allowed the qualitative identification of primary/annual versus intermittent secondary increments formed by splitting/coalescence. A new method for semi-automatic increment counting was then integrated into a purpose-built software package for studying cementum increments, to count increments in regions with minimal complications. Qualitative comparison with data from conventional cementochronology, based on histological examination of tissue thin-sections, confirmed that X-ray PPCI reliably and non-destructively records cementum increments (given the appropriate preparation of specimens prior to X-ray imaging). Validation of the increment counting algorithm suggests that it is robust and provides accurate estimates of increment counts. In summary, we show that our new increment counting method has the potential to overcome caveats of conventional cementochronology approaches, when used to analyse three-dimensional images provided by X-ray PPCI.

Climatic quantification and seasonality of the late MIS 3 in North China: A perspective from carbon and oxygen isotopes of fossil mammal teeth

Marine Isotope Stage 3 (MIS 3, at 60–25 ka B.P.) was a short interstadial within the Last Glacial period. A generally warm and wet climatic condition during the MIS 3 period has been suggested by many previous studies. Quantitative climatic reconstruction and studies of seasonality, however, have been seldom attempted given the scarcity of useful proxy indicators. A full understanding the climatic characteristics during this period is hampered by their absence. This is especially the case in the East Asian monsoon region in North China, which is very sensitive to climatic change. To help fill this knowledge gap, we have determined the stable carbon (δ13C) and oxygen isotope (δ18O) compositions of tooth enamel from fossil mammals (Bubalus sp [buffalo] and Cervus elaphus [red deer], dated at ∼33–31 ka B.P.) recovered from Longquan Cave in North China. We use these data to constrain ecology, local air temperature and precipitation amounts during the late MIS 3. The average δ13C (VPDB) of tooth enamel (−14.4‰ and −8.8‰, respectively for buffalo and red deer) indicate that C3 plants comprised the main diet of animals living in this area. Pollen assemblages demonstrated that vegetation mainly consisted of grasses and herbs (∼64%) with trees only accounting for about 26%. These results indicate a landscape of open steppe with sparsely distributed trees. The reconstructed climate derived from tooth enamel δ18O was relatively colder and drier than present-day condition, with mean annual air temperature ranging from 4 to 13 °C and mean annual precipitation ranging from 360 to 670 mm. Moreover, the inferred summer and winter half-year temperatures were respectively 8–24 °C and −2 to 5 °C, which represents either similar or weaker seasonality than at the present time. The inferred cold and dry climate suggested by our study contrasts with the warm and wet conditions previously reconstructed using proxy indicators from bulk soil samples in North China. In comparison to the long-term, time-averaged climatic condition reflected by those soil proxies, the stable isotope compositions of fossil more likely recorded climatic conditions at annual or seasonal time-scale. The inferred annual cold/dry climate at Luanchuan Cave suggested by our data may indicate a short climatic cooling event from Greenland Interstadial (GIS) 5 to its following stadial. Mean annual temperature fluctuated by ∼8 °C during this interstadial-stadial cycle.

Trophic ecology of a Late Pleistocene early modern human from tropical Southeast Asia inferred from zinc isotopes

Tam Pà Ling, a cave site in northeastern Laos, has yielded the earliest skeletal evidence of Homo sapiens in mainland Southeast Asia. The reliance of Pleistocene humans in rainforest settings on plant or animal resources is still largely unstudied, mainly due to poor collagen preservation in fossils from tropical environments precluding stable nitrogen isotope analysis, the classical trophic level proxy. However, isotopic ratios of zinc (Zn) in bioapatite constitute a promising proxy to infer trophic and dietary information from fossil vertebrates, even under adverse tropical taphonomic conditions. Here, we analyzed the zinc isotope composition (66Zn/64Zn expressed as δ66Zn value) in the enamel of two teeth of the Late Pleistocene (63–46 ka) H. sapiens individual (TPL1) from Tam Pà Ling, as well as 76 mammal teeth from the same site and the nearby Nam Lot cave. The human individual exhibits relatively low enamel δ66Zn values (+0.24‰) consistent with an omnivorous diet, suggesting a dietary reliance on both plant and animal matter. These findings offer direct evidence of the broad utilization of resources from tropical rainforests by one of the earliest known anatomically modern humans in Southeast Asia.

The killer’s toolkit: remarkable adaptations in the canine teeth of mammalian carnivores

Abstract Often the first point of contact between predator and prey, mammalian canine teeth are essential for killing, dismembering and consuming prey. Yet despite their importance, few associations among shape, function and phylogeny are established. We undertook the first comprehensive analysis of canine tooth shape across predatory mammals (Carnivora, Didelphimorphia and Dasyuromorphia), integrating shape analysis with function of this fundamental feature. Shape was quantified using three-dimensional geometric morphometrics and cross-sectional sharpness. Canines vary in three main ways (sharpness, robustness and curvature) which vary with diet, killing behaviour and phylogeny. Slender, sharp canines are associated with carnivores such as felids that target the neck of their prey and primarily consume the ‘softer’ parts of a carcass. Robust, blunt canines are found in mustelids and dasyurids that typically consume ‘harder’ materials, such as bone, or bite into skulls. Differences in the killing behaviours of felids and canids probably result in more curved canines in the latter, which act as hooks to hold prey. We find functional specialization in the upper and lower canines of individuals and across the major mammalian clades. These patterns demonstrate how canine teeth are adapted to suit diverse diets and hunting styles, enabling mammals to become some of nature's most successful predators.

A worked bone assemblage from 120,000–90,000 year old deposits at Contrebandiers Cave, Atlantic Coast, Morocco

SummaryThe emergence of Homo sapiens in Pleistocene Africa is associated with a profound reconfiguration of technology. Symbolic expression and personal ornamentation, new tool forms, and regional technological traditions are widely recognized as the earliest indicators of complex culture and cognition in humans. Here we describe a bone tool tradition from Contrebandiers Cave on the Atlantic coast of Morocco, dated between 120,000–90,000 years ago. The bone tools were produced for different activities, including likely leather and fur working, and were found in association with carnivore remains that were possibly skinned for fur. A cetacean tooth tip bears what is likely a combination of anthropogenic and non-anthropogenic modification and shows the use of a marine mammal tooth by early humans. The evidence from Contrebandiers Cave demonstrates that the pan-African emergence of complex culture included the use of multiple and diverse materials for specialized tool manufacture.

Effect of HAP crystallite orientation upon corrosion and tribocorrosion behavior of bovine and human dental enamel

Due to the complexity of the oral environment, understanding the relationship between the enamel microstructure and corrosion behavior of mammalian teeth is important for the development and bionic design of novel dental materials with corrosion resistance. In this paper, enamel microstructure and its influence on corrosion and tribocorrosion behavior of bovine and human molars are studied using focused ion beam & scanning electronic microscopy (FIB-SEM), transmission electron microscope (TEM), nanoindentation, and wear testing. It was found that the regions with transversal HAP nanocrystallites have better corrosion resistance than those with longitudinal crystallites. Apart from the chemical composition, the microstructure of enamel also involves in its surface corrosion. HAP nanocrystallite orientation changes the acid permeability into the enamel surface. Transversal nanocrystallites result in zigzagged acid permeation channels to increase the difficulty of acid penetration and then improve the corrosion resistance of enamel surface. The higher the fraction of transversal nanocrystallites on a surface, the better is the corrosion resistance. These findings extend our understanding of the corrosion/wear mechanisms of dental enamel with different microstructures.

Testing the inhibitory cascade model in a recent human sample.

The Inhibitory Cascade Model was proposed by Kavanagh and colleagues (Nature, 449, 427-433 [2007]) after their experimental studies on the dental development of murine rodent species. These authors described an activator-inhibitor mechanism that has been employed to predict evolutionary size patterns of mammalian teeth, including hominins. In the present study, we measured the crown area of the three lower permanent molars (M1, M2, and M3) of a large recent modern human sample of male and female individuals from a collection preserved at the Institute of Anthropology of the University of Coimbra (Portugal). The main aim of the present study is to test if the size molar patterns observed in this human sample fits the Inhibitory Cascade Model. For this purpose, we first measured the crown area in those individuals preserving the complete molar series. Measurements were taken in photographs, using a planimeter and following well-tested techniques used in previous works. We then plot the M3 /M1 and M2 /M1 size ratios. Our results show that the premise of the Inhibitory Cascade Model, according to which the average of the crown area of M2 is approximately one-third of the sum of the crown area of the three molars, is fulfilled. However, our results also show that the individual values of a significant number of males and females are out of the 95% confidence interval predicted by the Inhibitory Cascade Model in rodents. As a result, the present analyses suggest that neither the sample of males, nor that of females, nor the pooled sample fits the Inhibitory Cascade Model. It is important to notice that, although this model has been successfully tested in a large number of current human populations, to the best of our knowledge this is the first study in which individual data have been obtained in a recent human population rather than using the average of the sample. Our results evince that, at the individual level, some factors not yet known could interfere with this model masking the modulation of the size on the molar series in modern humans. We suggest that the considerable delay in the onset of M3 formation in modern humans could be related to a weakening of the possible activation/inhibition process for this tooth. Finally, and in support of our conclusions, we have checked that the absolute and relative size of M1 and M2 is not related to the M3 agenesis in our sample. In line with other studies in primates, our results do not support the Inhibitory Cascade Model in a recent human sample. Further research is needed to better understand the genetic basis of this mechanism and its relationship to the phenotype. In this way, we may be able to find out which evolutionary changes may be responsible for the deviations observed in many species, including Homo sapiens.

Dental-Derived Mesenchymal Stem Cells: State of the Art.

Mesenchymal stem cells (MSCs) could be identified in mammalian teeth. Currently, dental-derived MSCs (DMSCs) has become a collective term for all the MSCs isolated from dental pulp, periodontal ligament, dental follicle, apical papilla, and even gingiva. These DMSCs possess similar multipotent potential as bone marrow-derived MSCs, including differentiation into cells that have the characteristics of odontoblasts, cementoblasts, osteoblasts, chondrocytes, myocytes, epithelial cells, neural cells, hepatocytes, and adipocytes. Besides, DMSCs also have powerful immunomodulatory functions, which enable them to orchestrate the surrounding immune microenvironment. These properties enable DMSCs to have a promising approach in injury repair, tissue regeneration, and treatment of various diseases. This review outlines the most recent advances in DMSCs’ functions and applications and enlightens how these advances are paving the path for DMSC-based therapies.