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The phylogenetic relationships of the small-bodied catarrhine Pliobates cataloniae (∼11.6 Ma, NE Iberian Peninsula) have been controversial since its original description. However, the recent report of additional dentognathic remains has supported its crouzeliid pliopithecoid status. Based on the available hypodigm, the molar enamel-dentine junction (EDJ) shape of P. cataloniae is compared with that of other pliopithecoids from the same basin as well as both extinct and extant hominoids to further evaluate its pliopithecoid affinities. We also quantitatively compare the EDJ shape among these taxa by means of landmark-based three-dimensional geometric morphometrics using principal component analysis (PCA), canonical variate analysis, and between-group PCA. Permutation tests are performed to test whether Pliobates variation exceeds that of extant hominoid genera. Results indicate that Pliobates is similar in molar EDJ shape to other pliopithecoids, particularly crouzeliids. The variation displayed by Pliobates upper molars is less marked at the EDJ level than at the outer enamel surface, probably owing to differential enamel wear and intraspecific differences in enamel thickness. Multivariate analyses of EDJ shape show that all pliopithecoids (including Pliobates) cluster together in the PCAs, canonical variate analyses, and between-group PCAs and occupy a different portion of the morphospaces from extinct and extant hominoids. Posterior and typicality probabilities strongly support the classification of Pliobates as a pliopithecoid, wheras permutation tests fail to reject the single-genus hypothesis for the P. cataloniae hypodigm. We conclude that P. cataloniae is a crouzeliid pliopithecoid, as recently supported by cladistic analyses of craniodental characters, and that previous cladistic results that supported a stem hominoid status are attributable to postcranial convergences with crown hominoids. Our results further highlight the potential of three-dimensional geometric morphometrics analyses of the EDJ shape for better informing fossil primate alpha-taxonomy by means of quantitatively testing hypotheses about tooth shape variation., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Objective: This descriptive observational study aimed to determine clinically relevant and applicable data of enamel thickness (ETH), considering the mesio-distal differences of anterior and posterior permanent teeth and their relationships., Material and Methods: The sample consisted of right-sided standardized radiographs of 34 individuals (21 females and 13 males), aged between 13 and 24 (average 16) years, with all permanent teeth intact and without crowding. Four periapical and four interproximal radiographs were obtained and digitized. ETH measurements (mesial to distal contact points at the dentin-enamel junction) were performed after correction for radiographic image magnification. The Students' t-test was applied to the differences between paired means, with the Pearson correlation to evaluate the correlation between them., Results: The mesial and distal ETH increased from the anterior to the posterior teeth. Incisor ETH ranged between 0.60 and 0.84 mm. Canines, premolars, and molars were more than 1.0 mm thick, and molar enamel reached values between 1.26 and 1.44 mm., Conclusion: Distal ETH was significantly greater than the mesial ETH, and progressively thicker from the anterior to posterior teeth. Interproximal reduction (IPR) of the lower central and upper lateral incisors should be avoided, reduced, or performed on their distal surfaces. There is a positive and significant correlation between ETH and the mesial and distal surfaces of the teeth. Periapical radiographs and evaluation of the remaining ETH are necessary in cases of retreatment. The location and number of tooth size discrepancies should be considered in treatment planning and appropriately compensated with IPR.

Competing Interests: Declaration of competing interest The authors declare no conflict of interest.

Objectives: Dental anthropological investigations into sexual dimorphism have conventionally concentrated on evaluating the dimensions and configuration of the enamel cap of canines. However, the morphology of the crown dentine surface can be closely linked to that of the enamel surface. This link can facilitate examination of crown morphology even when the enamel surface is slightly worn. Here, we determine if the morphology of the enamel-dentine junction (EDJ) differs within (maxillary vs. mandibular) and between a sample of male (n = 26) and female (n = 21) contemporary human permanent canines from Europe., Methods: The morphological data of the EDJ were gathered employing a template comprising 96 landmarks and sliding semilandmarks. Subsequently, the data underwent analysis through form space principal component analysis following Procrustes registration, utilizing standard 3D geometric morphometric techniques., Results: Significant differences in the morphology of the EDJ were observed between the sexes, particularly concerning the overall shape of the crown, the symmetry of the mesial and distal edges, and the development of the distal accessory ridge., Conclusions: Sex differences in the morphology of the EDJ could relate in part to retention of the canine-premolar honing complex in males. Our results indicate that analyses of the permanent canine EDJ may potentially provide a novel method for estimating the sex of adult and nonadult skeletons., (© 2024 Wiley Periodicals LLC.)

African papionins are classic paleoecological referents for fossil hominins. Enamel chips on the teeth of baboons and hominins are argued to represent responses to similar dietary habits; however, a comprehensive analysis of modern papionin chipping is lacking, leaving open the question of analog suitability. Here, we investigate patterns of antemortem enamel chipping across a diverse set of African papionin species occupying a range of ecological niches. We compare papionin chipping frequencies to estimates for Plio-Pleistocene hominins to address hypotheses of habitat and/or dietary similarities. Antemortem chips in seven African papionin species were scored on intact postcanine teeth (P3-M3) using established protocols. Chip size was scored on a tripartite scale. Papio hamadryas and Papio ursinus-two common paleoecological referents-display higher levels of chipping than Plio-Pleistocene hominin taxa (Australopithecus and Paranthropus) posited to have similar dietary habits. Papio populations occupying dry or highly seasonal habitats accumulate more large chips than Papio taxa occupying more mesic habitats, and terrestrial papionins chip their teeth more often than closely related taxa occupying arboreal niches. Chipping is present on the teeth of all Plio-Pleistocene hominins; however, chipping in baboons (P. ursinus and P. hamadryas) consistently exceeds most hominin taxa. Chipping frequencies on their own do not reliably sort taxa into major dietary groupings. We conclude that the large differences in chipping frequency may instead reflect habitat use and food processing idiosyncrasies. Less chipping in Plio-Pleistocene hominin teeth compared to modern Papio is more likely attributable to differences in dental morphology rather than diet., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Childhood is an ontogenetic stage unique to the modern human life history pattern. It enables the still dependent infants to achieve an extended rapid brain growth, slow somatic maturation, while benefitting from provisioning, transitional feeding, and protection from other group members. This tipping point in the evolution of human ontogeny likely emerged from early Homo. The GAR IVE hemi-mandible (1.8 Ma, Melka Kunture, Ethiopia) represents one of the rarely preserved early Homo infants (~ 3 years at death), recovered in a richly documented Oldowan archaeological context. Yet, based on the sole external inspection of its teeth, GAR IVE was diagnosed with a rare genetic disease-amelogenesis imperfecta (AI)-altering enamel. Since it may have impacted the child's survival, this diagnosis deserves deeper examination. Here, we reassess and refute this diagnosis and all associated interpretations, using an unprecedented multidisciplinary approach combining an in-depth analysis of GAR IVE (synchrotron imaging) and associated fauna. Some of the traits previously considered as diagnostic of AI can be better explained by normal growth or taphonomy, which calls for caution when diagnosing pathologies on fossils. We compare GAR IVE's dental development to other fossil hominins, and discuss the implications for the emergence of childhood in early Homo., (© 2021. The Author(s).)

Lufengpithecus hudienensis is a Late-Miocene hominid from the Yuanmou basin of southwestern China. Previous studies link Lufengpithecus to either the Sivapithecus-orangutan clade or a derived branch from the basal stem of the Hominidae. Despite a rich fossil assemblage, the taxonomy of L. hudienensis and its phylogenetic relationship with other hominids is still unclear. Enamel thickness in fossil and modern hominids can provide insights into taxonomy, phylogeny, and dietary reconstructions. In this study, 24 upper and lower L. hudienensis premolars were imaged using high-resolution microcomputed tomography. Three-dimensional average enamel thickness and relative enamel thickness (RET) indices, as well as whole-crown enamel distribution patterns were recorded for the L. hudienensis specimens and compared with a total of 113 specimens of fossil and extant apes and recent modern humans (RMH): fossil Pongo (n = 36), Gigantopithecus blacki (n = 21), Pan troglodytes (n = 11), Gorilla gorilla (n = 7), and RMH (n = 38). RET of the premolars of L. hudienensis was found to be similar to that of fossil Pongo, P. troglodytes, and G. gorilla, but less than Gi. blacki and RMH values. The distribution of enamel thickness shows a taxon-specific pattern for L. hudienensis, generally characterized by thicker enamel on the lateral wall than on the cusp apex, on the lingual cusp of the upper and buccal cusp of the lower premolars, with some differences with respect to fossil Pongo, Gi. blacki, P. troglodytes, and G. gorilla patterns. Additional characterizations of enamel thickness distribution patterns of the molars and other dental endostructural morphologies are needed to further explore the phylogenetic relationships of L. hudienensis with other hominids., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objectives: Dimorphism in the dentition has been observed in human populations worldwide. However, research has largely focused on traditional linear crown measurements. As imaging systems, such as micro-computed tomography (micro-CT), become increasingly more accessible, new dental measurements such as dental tissue size and proportions can be obtained. This research investigates the variation of dental tissues and proportions by sex in archaeological samples., Materials and Methods: Upper and lower first incisor to second premolar tooth rows were obtained from 30 individuals (n = 300), from 3 archaeological samples. The teeth were micro-CT scanned and surface area and volumetric measurements were obtained from the surface meshes extracted. Dental wear was also recorded and differences between sexes determined., Results: Enamel and crown measurements were found to be larger in females. Conversely, dentine and root measurements were larger in males., Discussion: The findings support the potential use of dental tissues to estimate sex of individuals from archaeological samples, while also indicating that individuals aged using current dental aging methods may be underaged or overaged due to sex differences in enamel thickness., (© 2020 Wiley Periodicals LLC.)

Objectives: Human tooth enamel retains evidence of growth in the form of Retzius lines. The number of daily growth increments between the regularly occurring lines defines their repeat interval, or periodicity. Retzius periodicity is often incorporated into enamel formation times, age-at-death reconstructions, or used to provide a basis from which to explore an underlying biorhythm. Biological anthropologists typically assume that RP remains constant within an individual and does not vary along the tooth-row. Here, we test that assumption., Materials and Methods: RP was calculated from n = 223 thin sections of human permanent teeth from individuals of British and southern African origin. Forty individuals provided multiple teeth (n = 102 teeth) and a further 121 individuals each provided a single tooth., Results: We report first evidence that RP of permanent teeth does not always remain constant within an individual. Of those individuals that provided multiple teeth, 42% (n = 17/40) demonstrated a decrease in RP along the tooth row, with most shifting by two or more days (n = 11). Across the entire sample, mean RP of anterior teeth was significantly higher than molars. Mean premolar RP tended to be intermediate between anterior teeth and molars., Discussion: Our data do not support the assumption that RP invariably remains constant within the permanent teeth of an individual. Transferring RP from molars to incisors within an individual can result in a miscalculation of formation time and age-at-death by up to 1 year. Implications for biological anthropologists and the source of the underlying long period biorhythm are discussed., (© 2020 Wiley Periodicals LLC.)

Objective: Three-dimensional relative enamel thickness (3DRET) is important for assessing hypotheses about taxonomy, phylogeny, and dietary reconstruction for primates. However, its weaknesses have not been thoroughly investigated. Here, we analyze its weaknesses and propose an index aiming at better taxonomic discrimination., Materials and Methods: The dimensionless 3D index, ratio of enamel-thickness to dentine-thickness (3DRED), which is defined as the cubic root of the ratio of 3D average enamel thickness (3DAET) to 3D average dentine thickness (3DADT), is proposed here. To compare 3DRET and 3DRED and their sensitivity to voxel size, a fossil orangutan molar was scanned 14 times with different resolutions ranging from 10 to 50 μm. Enamel thickness analysis was carried out for each resultant digital model. In addition, enamel thickness measurements of 179 mandibular permanent molars (eight genera) were analyzed, followed by investigating the relationship between 3DRET and 3DAET and between 3DRED and 3DAET., Results: Regarding sensitivity, 3DRED is more robust than 3DRET. In addition, 3DRET is correlated with 3DAET by linear curve with regression coefficients approximating or larger than 0.8 in most cases, while 3DRED shows less correlation with 3DAET. Furthermore, there are clear separations between different taxa in the bivariate plot of 3DRED against 3DAET, indicative of the taxonomic value of 3DRED., Conclusion: Under certain conditions, 3DRED promises to be a robust and reliable alternative to 3DRET in taxonomic study., (© 2020 Wiley Periodicals LLC.)

Objectives: We aimed to investigate molar enamel development in fossil orangutans from Guangxi and shed light on the evolution of Asian great apes., Materials and Methods: We collected 32 fossil orangutan molars, most of which were from Guangxi apothecaries and the Guangxi Daxin Heidong cave, and prepared histological sections of each molar. We then characterized aspects of dental development, including long period line periodicity, number of Retzius lines and lateral enamel formation time, cuspal enamel thickness, and enamel formation time., Results: The long period line periodicity in fossil orangutans ranged from 9 to 10 days (mean, 9.09 days). The molar lateral enamel formation time ranged from 1.48 to 3.17 years (540-1,152 days). Cuspal enamel thickness in fossil orangutan molars ranged from 949 to 2,535 μm, and cuspal enamel formation time ranged from 0.64 to 1.87 years. Molar enamel formation time of fossil orangutans ranged from 2.47 to 4.67 years., Discussion: Long-period line periodicity of fossil orangutans from Guangxi was within the variation range of extant orangutans, and the average long period line periodicity (9.09 days) of fossil orangutans from Guangxi in this study was lower than the values for extant orangutans (9.5 days) and fossil orangutans (10.9 days) from Sumatra and Vietnam. Orangutan enamel thickness may have gradually decreased from the Middle Pleistocene to Holocene. Crown formation time of fossil orangutans was slightly longer than that of extant orangutans, and the M1 emergence age of fossil orangutans from Guangxi was about 4-6 years. These findings might indicate the regional difference or evolutionary changes in orangutans since Pleistocene. Dental development of the Guangxi fossil orangutans were more similar to that of Asian Miocene apes, suggesting the closer evolutionary relationship of orangutans to Miocene Asian fossil apes., (© 2020 Wiley Periodicals LLC.)

Objectives: Molar crenulation is defined as the accessory pattern of grooves that appears on the occlusal surface of many mammalian molars. Although frequently used in the characterization of species, this trait is often assessed qualitatively, which poses unavoidable subjective biases. The objective of this study is to quantitatively test the variability in the expression of molar crenulation in primates and its association with molar size and diet., Methods: The variability in the expression of molar crenulation in hominids (human, chimpanzee, gorilla, and orangutan) was assessed with fractal analysis using photographs of first, second and third upper and lower molars. After this, representative values for 29 primate species were used to evaluate the correlation between molar complexity, molar size, and diet using a phylogenetic generalized least squares regression., Results: Results show that there are statistically significant differences in fractal dimensions across hominid species in all molars, with orangutan molars presenting higher values of occlusal complexity. Our results indicate that there is no significant association between molar complexity and molar size or diet., Discussion: Our results show higher levels of occlusal complexity in orangutans, thus supporting previously published observations. Our analyses, however, do not indicate a clear association between molar complexity and molar size or diet, pointing to other factors as the major drivers of complexity. To our knowledge, our study is the first one to use fractal analysis to measure occlusal complexity in primates. Our results show that this approach is a rapid and cost-effective way to measure molar complexity., (© 2020 Wiley Periodicals LLC.)

The teeth of all vertebrates predominantly comprise the same materials, but their lifespans vary widely: in stark contrast to mammals, shark teeth are functional only for weeks, rather than decades, making lifelong durability largely irrelevant. However, their diets are diverse and often mechanically demanding, and as such, their teeth should maintain a functional morphology, even in the face of extremely high and potentially damaging contact stresses. Here, we reconcile the dilemma between the need for an operative tooth geometry and the unavoidable damage inherent to feeding on hard foods, demonstrating that the tooth cusps of Port Jackson sharks, hard-shelled prey specialists, possess unusual microarchitecture that controls tooth erosion in a way that maintains functional cusp shape. The graded architecture in the enameloid provokes a location-specific damage response, combining chipping of outer enameloid and smooth wear of inner enameloid to preserve an efficient shape for grasping hard prey. Our discovery provides experimental support for the dominant theory that multi-layered tooth enameloid facilitated evolutionary diversification of shark ecologies.

Third permanent molars (M3s) are the last tooth to form but have not been used to estimate age at dental maturation in early fossil hominins because direct histological evidence for the timing of their growth has been lacking. We investigated an isolated maxillary M3 (SK 835) from the 1.5 to 1.8-million-year-old (Mya) site of Swartkrans, South Africa, attributed to Paranthropus robustus. Tissue proportions of this specimen were assessed using 3D X-ray micro-tomography. Thin ground sections were used to image daily growth increments in enamel and dentine. Transmitted light microscopy and synchrotron X-ray fluorescence imaging revealed fluctuations in Ca concentration that coincide with daily growth increments. We used regional daily secretion rates and Sr marker-lines to reconstruct tooth growth along the enamel/dentine and then cementum/dentine boundaries. Cumulative growth curves for increasing enamel thickness and tooth height and age-of-attainment estimates for fractional stages of tooth formation differed from those in modern humans. These now provide additional means for assessing late maturation in early hominins. M3 formation took ≥ 7 years in SK 835 and completion of the roots would have occurred between 11 and 14 years of age. Estimated age at dental maturation in this fossil hominin compares well with what is known for living great apes.

Objectives: Enamel thickness features prominently in hominoid evolutionary studies. To date, however, studies of enamel thickness in humans, great apes, and their fossil relatives have focused on the permanent molar row. Comparatively little research effort has been devoted to tissue proportions within deciduous teeth. Here we attempt to fill this gap by documenting enamel thickness variation in the deciduous dentition of extant large-bodied hominoids., Materials and Methods: We used microcomputed tomography to image dental tissues in 80 maxillary and 78 mandibular deciduous premolars of Homo sapiens, Pan troglodytes, Gorilla, and Pongo. Two-dimensional virtual sections were created from the image volumes to quantify average (AET) and relative (RET) enamel thickness, as well as its distribution across the crown., Results: Our results reveal no significant differences in enamel thickness among the great apes. Unlike the pattern present in permanent molars, Pongo does not stand out as having relatively thicker-enameled deciduous premolars than P. troglodytes and Gorilla. Humans, on the other hand, possess significantly thicker deciduous premolar enamel in comparison to great apes. Following expectations from masticatory biomechanics, we also find that the "functional" side (protocone, protoconid) of deciduous premolars generally possesses thicker enamel than the "nonfunctional" side., Discussion: Our study lends empirical support to anecdotal observations that patterns of AET and RET observed for permanent molars of large-bodied apes do not apply to deciduous premolars. By documenting enamel thickness variation in hominoid deciduous teeth, this study provides the comparative context to interpret rates and patterns of wear of deciduous teeth and their utility in life history reconstructions., (© 2020 Wiley Periodicals LLC.)

Teeth have been studied for decades and continue to reveal information relevant to human evolution. Studies have shown that many traits of the outer enamel surface evolve neutrally and can be used to infer human population structure. However, many of these traits are unavailable in archaeological and fossil individuals due to processes of wear and taphonomy. Enamel-dentine junction (EDJ) morphology, the shape of the junction between the enamel and the dentine within a tooth, captures important information about tooth development and vertebrate evolution and is informative because it is subject to less wear and thus preserves more anatomy in worn or damaged specimens, particularly in mammals with relatively thick enamel like hominids. This study looks at the molar EDJ across a large sample of human populations. We assessed EDJ morphological variation in a sample of late Holocene modern humans ( n = 161) from archaeological populations using μ-CT biomedical imaging and geometric morphometric analyses. Global variation in human EDJ morphology was compared to the statistical expectations of neutral evolution and "Out of Africa" dispersal modeling of trait evolution. Significant correlations between phenetic variation and neutral genetic variation indicate that EDJ morphology has evolved neutrally in humans. While EDJ morphology reflects population history, its global distribution does not follow expectations of the Out of Africa dispersal model. This study increases our knowledge of human dental variation and contributes to our understanding of dental development more broadly, with important applications to the investigation of population history and human genetic structure., Competing Interests: The authors declare no competing interest.

Objective: This study explored biological sex differences in the regional daily growth rates of human anterior enamel from modern and ancient populations in Britain., Methods: Maxillary permanent incisors (n = 80) and canines (n = 69) from Roman, Anglo-Saxon, Medieval, and Modern day populations were analyzed using histological methods. Daily secretion rates (DSRs) were collected for inner, mid, and outer regions of cuspal and lateral enamel. Modern day samples were of known sex, archeological individuals had sex determined using standard osteological methods. Variation in DSRs between the sexes, both between and within populations, was sought using parametric and nonparametric tests., Results: When all samples were pooled, there was no significant difference between males and females. Similarly no significant differences in DSRs were identified between male and females within each population. When DSRs were compared between the populations, DSRs decreased from the more ancient to the more recent populations for males, and for females. More interpopulation differences were observed in males., Discussion: This study presents evidence for the relative consistency of enamel DSRs between male and female groups within each British population. Interpopulation analyses found DSRs slowed significantly between Roman and modern day populations for both sexes, with male DSRs showing the greatest variation between populations., (© 2020 The Authors. American Journal of Physical Anthropology published by Wiley Periodicals LLC.)

Lower Eocene (Wasatchian-aged) sediments of the Margaret Formation on Ellesmere Island in Canada's High Arctic preserve evidence of a rainforest inhabited by alligators, turtles, and a diverse mammalian fauna. The mammalian fossils are fragmentary and often poorly preserved. Here, we offer an alternative method for their identification. Among the best preserved and extensive of the Eocene Arctic forests is the Strathcona Fiord Fossil Forest, which contains permineralized in situ tree stumps protruding from a prominent coal seam, but a paucity of vertebrate fossils. In 2010 and 2018, we recovered mammalian tooth fragments at the fossil forest, but they are so incomplete as to be undiagnostic by using their external morphology. We used a combination of light microscopy and SEM analysis to study the enamel microstructure of two tooth fragments from the fossil forest-NUFV2092B and 2092E. The results of our analysis indicate that NUFV2092B and 2092E have Coryphodon-enamel, which is characterized by vertical bodies that manifest as bands of nested chevrons or treelike structures visible in the tangential section under light microscopy. This enamel type is not found in other mammals known from the Arctic. Additionally, when studied under SEM, the enamel of NUFV2092B and 2092E has rounded prisms that open to one side and are surrounded by interprismatic matrix that is nearly parallel to the prisms, which also occurs in Coryphodon enamel, based on prior studies. The tooth fragments reported here, along with some poorly preserved bone fragments, thus far are the only documented vertebrate fossils from the Strathcona Fiord Fossil Forest. However, fossils of Coryphodon occur elsewhere in the Margaret Formation, so its presence at the fossil forest is not surprising. What is novel in our study is the way in which we identified the fossils using their enamel microstructure., Competing Interests: The authors have declared that no competing interests exist.

Objectives: This study explores variation and trends in first molar enamel thickness and daily enamel secretion rates over a 2000 year period in Britain., Methods: Permanent first molars (n = 89) from the Roman, Anglo-Saxon, and Medieval periods, as well as modern-day Britain, were analyzed using standard histological methods. Relative enamel thickness (RET) and linear measurements of cuspal and lateral thickness were calculated for mesial cusps. Daily secretion rates (DSRs) were calculated for inner, mid, and outer enamel regions in both cuspal and lateral enamel. Significant differences and trends were identified between samples using nonparametric statistical tests., Results: Enamel thickness differed between some populations, but no temporal trends were identified. Early Anglo-Saxon molars had significantly thinner RET than both Late Anglo-Saxon (p < .00) and Medieval (p < .00) molars. Lateral enamel from the Roman molars was significantly thinner than the modern-day sample (p = .04). In contrast, a significant slowing trend in DSRs was observed across the more ancient to modern-day samples in every measured region except the mid-lateral enamel region., Discussion: This study presents the first evidence for a gradual slowing in the daily rate that enamel is secreted in molars over the past 2000 years in Britain. However, this trend was not matched by consistent or significant positive or negative shifts in enamel thickness. These findings suggest that modern human molars of similar enamel thickness, from different modern and ancient populations, formed at different rates., (© 2020 Wiley Periodicals, Inc.)

The aim of the study was to see whether the length of the enamel secretion zone in unimpeded rat incisors, measured precisely, is in agreement with the observed decrease in enamel thickness. Unimpeded eruption of mandibular incisors of five experimental and two control rats was induced by cutting off the erupted part of the incisors three times per week for 5 weeks. The length of the zone of enamel secretion in unimpeded and impeded control incisors was measured on longitudinal and serial transverse histological sections of fixed, demineralised and embedded hemimandibles. Impeded contralateral incisors were also included in the study. The length of the zone of enamel secretion in unimpeded incisors showed an increase to 8,398 ± 558 µm, that is 161% of the length in control incisors (5,213 ± 95 µm). The contralateral incisor showed a reduction in eruption rate, in length of the secretion zone, and the whole tooth was shifted somewhat apically. The measured length of the secretion zone is in agreement with the observed thickness of enamel (98 µm) in unimpeded incisors. The reduced eruption rate and the apical shift of the contralateral incisor are probably due to an increased occlusal load., (© 2020 The Authors. Anatomia, Histologia, Embryologia published by Blackwell Verlag GmbH.)

Sexual dimorphism is an important component of the total variation seen in populations and plays a key role in taxonomic debates. In this study, microtomographic (microcomputed tomography) techniques were applied to a sample of hominin teeth from the Sima de los Huesos site (Spain). Dental tissue proportions of the permanent canines were assessed to characterize the pattern and degree of sexual dimorphism within this population. In addition, the possible similarities and differences with the Homo neanderthalensis remains from Krapina (Croatia) and with a recent modern human sample were evaluated. A combination of classical statistical approaches with more novel techniques allowed us not only to ratify the sex allocation of the individuals previously assigned in the literature but also to estimate the sex of the youngest individuals, which were not assessed in previous studies. Likewise, the sexes of certain extensively worn canines and isolated pieces were estimated. As a result, the sex ratio observed in our dental sample from the Sima de los Huesos population is 5:9 (N m :N f ). In general terms, both Sima de los Huesos and Krapina dental samples have a degree of sexual dimorphism in their permanent canine tissue proportions that does not surpass that of modern humans. The marked dimorphic root volume of Sima de los Huesos mandibular canines is the exception, which surpasses the modern human mean, although it falls within the 95% confidence interval. Therefore, our results do not support that dental tissue proportions of the European Middle Pleistocene populations were more dimorphic than in modern humans. However, the differences in canine tissue proportions are great enough to allow sex estimation with a high degree of confidence., Competing Interests: Conflict of interest We declare no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Mobility of people and goods during the Upper Paleolithic has proven difficult to reconstruct given the relative rareness of remains. Nevertheless, archaeological contexts like the Late Pleistocene horizon of Borsuka Cave (Southern Poland) represent a unique opportunity to explore patterns of objects' transportation across Central Europe. We investigated the origin of four ornaments made of European elk (Alces alces L.) incisors recovered at Borsuka Cave - the oldest known burial site in Poland, possibly a child grave. Laser-ablation plasma source mass spectrometric analyses of trace elements and Sr isotopic compositions revealed that one elk was roaming within a geologically uniform area while the others changed their pastures during their lifetimes. The non-local origin of the elk teeth is inferred from their exotic Sr isotopic compositions and the lack of evidence for the presence of elk in this territory during the Pleistocene. Instead, the elks' Sr isotopic composition show good agreement with sites near the Austria-Slovakia border region and northern Hungary, ~250 km away from the study site. We argue that the artefacts were most likely brought to Borsuka Cave by humans or by a network of exchange, so far never reported in the time range 32.5-28.8 ka cal BP for Southern Poland.

Dental enamel thickness, topography, growth and development vary among hominins. In Homo, the thickness of dental enamel in most Pleistocene hominins display variations from thick to hyper-thick, while Neanderthals exhibit proportionally thinner enamel. The origin of the thin trait remains unclear. In this context, the Middle Pleistocene human dental assemblage from Atapuerca-Sima de los Huesos (SH) provides a unique opportunity to trace the evolution of enamel thickness in European hominins. In this study, we aim to test the hypothesis if the SH molar sample approximates the Neanderthal condition for enamel thickness and/or distribution. This study includes 626 molars, both original and comparative data. We analysed the molar inner structural organization of the original collections (n = 124), belonging to SH(n = 72) and modern humans from Spanish origin (n = 52). We compared the SH estimates to those of extinct and extant populations of the genus Homo from African, Asian and European origin (estimates extracted from literature n = 502). The comparative sample included maxillary and mandibular molars belonging to H. erectus, East and North African Homo, European Middle Pleistocene Homo, Neanderthals, and fossil and extant H. sapiens. We used high-resolution images to investigate the endostructural configuration of SH molars (tissue proportions, enamel thickness and distribution). The SH molars exhibit on average thick absolute and relative enamel in 2D and 3D estimates, both in the complete crown and the lateral enamel. This primitive condition is shared with the majority of extinct and extant hominin sample, except for Neanderthals and some isolated specimens. On the contrary, the SH molar enamel distribution maps reveal a distribution pattern similar to the Neanderthal signal (with thicker enamel on the lingual cusps and more peripherally distributed), compared to H. antecessor and modern humans. Due to the phylogenetic position of the SH population, the thick condition in molars could represent the persistence of the plesiomorphic condition in this group. Still, more data is needed on other Early and Middle Pleistocene populations to fully understand the evolutionary meaning of this trait., Competing Interests: The authors have declared that no competing interests exist.

Objectives: The objective of this study was to explore potential relationships between neonatal line (NNL) width and early life history variables such as maternal health, gestation, the birth process, and perinatal health., Materials and Methods: Histological thin sections of deciduous canines were studied from 71 children from the Avon Longitudinal Study of Parents and Children (ALSPAC). The width of the NNL was measured in three locations on the tooth crown using spatial mapping techniques (ArcGIS) from digital images from an Olympus VS-120 microscope. Life history variables were collected prospectively through a combination of clinical observations and questionnaires., Results: Infants born late term or post term had narrower neonatal lines than those born prematurely or at full term. Infants born in Autumn (September to November) had narrower NNLs than those born at other times of year. NNLs in infants born to mothers with hypertension were wider than those without. Infants resuscitated at birth or born to obese mothers had narrower NNLs than those that were not. There was no association between NNL width and either the type or duration of delivery., Discussion: The NNL in enamel is an irregular accentuated line, but the factors underlying its formation and width remain unclear. In contrast to some previous studies, we found no association between wider NNLs and long or difficult births. Instead, we found that the width of the neonatal line NNL varied in relation to parameters that reflected the prenatal environment and length of gestation., (© 2020 Wiley Periodicals, Inc.)

Mammals and reptiles have evolved divergent adaptations for processing abrasive foods. Mammals have occluding, diphyodont dentitions with taller teeth (hypsodonty), more complex occlusal surfaces, continuous tooth eruption, and forms of prismatic enamel that prolong the functional life of each tooth [1, 2]. The evolution of prismatic enamel in particular was a key innovation that made individual teeth more resilient to abrasion in early mammals [2-4]. In contrast, reptiles typically have thin, non-prismatic enamel, and shearing, polyphyodont dentitions with multi-cusped or serrated tooth crowns, multiple tooth rows, rapid tooth replacement rates, or batteries made of hundreds of teeth [5-9]. However, there are rare cases where reptiles have evolved alternative solutions to cope with abrasive diets. Here, we show that the combined effects of herbivory and an ancestral loss of tooth replacement in a lineage of extinct herbivorous sphenodontians, distant relatives of the modern tuatara (Sphenodon punctatus) [10], are associated with the evolution of wear-resistant and highly complex teeth. Priosphenodon avelasi, an extinct sphenodontian from the Cretaceous of Argentina, possesses a unique cone-in-cone dentition with overlapping generations of teeth forming a densely packed tooth file. Each tooth is anchored to its predecessor via a rearrangement of dental tissues that results in a novel enamel-to-bone tooth attachment. Furthermore, the compound occlusal surfaces, thickened enamel, and the first report of prismatic enamel in a sphenodontian are convergent strategies with those in some mammals, challenging the perceived simplicity of acrodont dentitions [11-15] and showcasing the reptilian capacity to produce complex and unusual dentitions., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Enamel thickness remains an important morphological character in hominin systematics and is regularly incorporated into dietary reconstructions in hominin species. We expand upon a previous study of enamel thickness in mandibular molars by examining a large maxillary molar sample of Plio-Pleistocene hominins (n = 62) and a comparative sample of extant nonhuman apes (n = 48) and modern humans (n = 29). 2D mesial planes of section were generated through microtomography, and standard dental tissue variables were measured to calculate average enamel thickness (AET) and relative enamel thickness (RET). AET was also examined across the lingual, occlusal, and buccal regions of the crown. This study confirms previous findings of increasing enamel thickness throughout the Plio-Pleistocene, being thinnest in Australopithecus anamensis and peaking in Australopithecus boisei, with early Homo specimens, exhibiting intermediate enamel thickness. Agreeing with previous findings, 2D plane of section enamel thickness is found to be a poor taxonomic discriminator, with no statistically significant differences observed between fossil hominins. For fossil hominins, modern humans, and Pongo, the occlusal region of enamel was the thickest, and the lingual enamel thickness was greater than buccal. Pan and Gorilla present the opposite pattern with enamel being thinnest occlusally. Comparison at each molar position between the maxilla and mandible revealed very few significant differences in fossil hominins but some evidence of significantly thicker maxillary enamel (AET) in modern humans and thinner maxillary enamel in Pan (RET)., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Characterizing dental development in fossil hominins is important for distinguishing between them and for establishing where and when the slow overall growth and development of modern humans appeared. Dental development of australopiths and early Homo was faster than modern humans. The Atapuerca fossils (Spain) fill a barely known gap in human evolution, spanning ~1.2 to ~0.4 million years (Ma), during which H. sapiens and Neandertal dental growth characteristics may have developed. We report here perikymata counts, perikymata distributions and periodicities of all teeth belonging to the TE9 level of Sima del Elefante, level TD6.2 of Gran Dolina (H. antecessor) and Sima de los Huesos. We found some components of dental growth in the Atapuerca fossils resembled more recent H. sapiens. Mosaic evolution of perikymata counts and distribution generate three distinct clusters: H. antecessor, Sima de los Huesos and H. sapiens.

Enamel macro- and microstructure has been studied in the teeth of Merck's rhinoceros (Stephanorhinus kirchbergensis Jäger, 1839), woolly rhinoceros (Coelodonta antiquitatis Blumenbach, 1799), and rhinoceroses from the Tetyukhinskaya (44°35' N, 135°36' E) and Sukhaya (43°09' N, 131°28' E) caves in southern Primorye. The teeth from the caves were identified as the teeth of Merck's rhinoceros. Radiocarbon dating and accompanying animal species enabled the dating of Merck's rhinoceros remains to the Late Pleistocene (marine isotope stages 5-2). These finds mark the extreme eastern boundary of the Merck's rhinoceros species range in the Late Pleistocene. The living range reached the Pacific Ocean coast during a certain time interval within this epoch. This was due to the abundance of tree and shrub vegetation in the area during the Late Pleistocene.

To investigate the prevalence of different patterns of cemento-enamel junction (CEJ) morphology under swept-source optical coherence tomography (SS-OCT). One hundred extracted human teeth were used consisting of incisors, premolars, and molars. Each sample was observed for every 500 μm circumferentially along CEJ and OCT images of the pattern were noted. Microscopic observations were done for the representative sample using confocal laser scanning microscope (CLSM) and transmission electron microscope (TEM). The OCT images exhibited four CEJ patterns: edge-to-edge (type I), exposed dentin (type II), cementum overlapping enamel (type III), and enamel overlapping cementum (type IV). The prevalence of CEJ patterns was further statistically considered for mesial, distal, buccal, and lingual surfaces. The real-time imaging by SS-OCT instantly determined CEJ morphology. CLSM and TEM observation revealed morphological features along CEJ, which corresponded to OCT images of CEJ anatomy. OCT results showed 56.8% of type I pattern predominantly found on proximal surfaces, followed by 36.5% of type II pattern on buccal and lingual surface, 6.4% of type III pattern, and 0.3% of type IV pattern. There was a significant difference in prevalence of CEJ patterns among different types of teeth, but there was no statistically significant difference among the four surfaces in each type of teeth. OCT is a non-invasive diagnostic tool to examine the CEJ patterns along the entire circumference. OCT observation revealed even minor dentin exposure that would need clinical and home procedures to prevent any symptoms.

Gummivory poses unique challenges to the dentition as gum acquisition may often require that the anterior teeth be adapted to retain a sharp edge and to resist loading because they sometimes must penetrate a highly obdurate substrate during gum extraction by means of gouging or scraping. It has been observed previously that the enamel on the labial surface of the teeth used for extraction is thicker relative to that on the lingual surface in taxa that extract gums, while enamel is more evenly distributed in the anterior teeth of taxa that do not regularly engage in extractive behaviors. This study presents a quantitative methodology for measuring the distribution of labial versus lingual enamel thickness among primate and marsupial taxa in the context of gummivory. Computed microtomography scans of 15 specimens representing 14 taxa were analyzed. Ten measurements were taken at 20% intervals starting from the base of the crown of the extractive tooth to the tip of the cutting edge across the lingual and labial enamel. A method for including worn or broken teeth is also presented. Mann-Whitney U tests, canonical variates analysis, and between-group principal components analysis were used to examine variation in enamel thickness across taxa. Our results suggest that the differential distribution of enamel thickness in the anterior dentition can serve as a signal for gouging behavior; this methodology distinguishes between gougers, scrapers, and nonextractive gummivores. Gouging taxa are characterized by significantly thicker labial enamel relative to the lingual enamel, particularly towards the crown tip. Examination of enamel thickness patterning in these taxa permits a better understanding of the adaptations for the extraction of gums in extant taxa and offers the potential to test hypotheses concerning the dietary adaptations of fossil taxa., (© 2019 S. Karger AG, Basel.)

It is well recognized that enamel microanatomy in mammals reflects biomechanical demands placed upon teeth, as determined by mechanical properties of species' diets, use of teeth as weapons, and so forth. However, there are limited options for researchers wishing to perform large-scale comparisons of enamel microstructure with adaptive questions in mind. This is because to date there has been no efficient method for quantification and statistical analysis of enamel complexity. Our study proposes to apply a method previously developed for quantification of 3D tooth cusp morphology to the problem of quantifying microstructural enamel complexity. Here, we use image compression ratio (ICR) as a proxy variable for enamel complexity in 2D enamel photomicrographs taken using circularly polarized transmitted light microscopy. ICR describes the relationship between a digital image captured in an uncompressed file format and the identical image that has had its file size compressed using computer algorithms; more complex images receive less compression. In our analyses, ICR analysis is able to distinguish between images of teeth with simple, radial enamel and teeth with complex decussating enamel. Moreover, our results show a significant correlation between ICR and enamel complexity ranks assigned via visual assessment. Therefore, our results demonstrate that ICR analysis provides a viable methodology for efficient comparison of overall enamel complexity among dental samples. Anat Rec, 302:2279-2286, 2019. © 2019 American Association for Anatomy., (© 2019 American Association for Anatomy.)

This study evaluated enamel mineral content and surface microhardness before and after bleaching treatment using 10% carbamide peroxide (CP) containing calcium (Ca) or amorphous calcium phosphate (ACP). Thirtysix bovine slabs were randomly allocated into 3 groups (n = 12) according to bleaching treatment: G1 Opalescence PF 10% (CP), G2 NiteWhite ACP (CP+ACP), and G3 Opalescence PF (10%) with calcium (CP+CA). The bleaching agent was applied on enamel surface for 6 h/day over a period of 21 days. Enamel surface was evaluated by Knoop microhardness (KNH) and micro energydispersive Xray fluorescence spectrometry (μEDXRF) at baseline and at after bleaching treatment. Data were statistically analyzed by repeated measures ANOVA and Tukey's test (α = 0.05). There was a significant decrease in microhardness after bleaching treatments for all study groups, but no difference between bleaching gels. There was no difference in the Ca/P ratio measured by μEDXRF for all groups at the study times, but the mean value was lower in group CP+CA than in group CP+ACP. Group CP was similar to both CP+ACP and CP+CA. It can be concluded that enamel microhardness decreased after the bleaching process, regardless of the presence of calcium or ACP, but there was no significant change in the Ca/P ratio of enamel after bleaching for each tested gel. This indicates that the bleaching gels have erosive potential, causing softening of enamel without promoting surface loss, regardless of the presence of calcium of ACP ions.

Dental functional morphology, as a field, represents a confluence of materials science and biology. Modern methods in materials testing have been influential in driving the understanding of dental tissues and tooth functionality. Here we present a review of dental enamel, the outermost tissue of teeth. Enamel is the hardest biological tissue and exhibits remarkable resilience even when faced with a variety of mechanical threats. In the light of recent work, we progress the argument that the risk of mechanical degradation across multiple scales exhibits a strong and continued selection pressure on the structural organization of enamel. The hierarchical nature of enamel structure presents a range of scale-dependent toughening mechanisms and provides a means by which natural selection can drive the specialization of this tissue from nanoscale reorganization to whole tooth morphology. There has been much learnt about the biomechanics of enamel recently, yet our understanding of the taxonomic diversity of this tissue is still lacking and may form an interesting avenue for future research., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.)

The fossil record of middle and late Miocene Eurasian hominoids has expanded considerably over the past few decades, particularly with the recovery of numerous isolated teeth and jaws. Scholars have turned to assessments of internal tooth structure and growth to make sense of the evolutionary radiations of these primates as well as their affinities to the living great apes (hominids). Here we characterize full-dentition enamel thickness and dental development in several juvenile Rudapithecus hungaricus individuals using multiple imaging modalities. Relative enamel thickness (RET) values for the anterior teeth and premolars of Rudapithecus are broadly akin to those of gorillas and chimpanzees and are thinner than those of orangutans. First molar RET values are most similar to chimpanzees, while posterior molar values are closer to thicker-enameled orangutans. When compared to Miocene hominoids, Rudapithecus shows an intermediate molar RET condition that is especially similar to other dryopithecines. Long-period line periodicity values are comparable to African apes and most Miocene hominoids, and lower than living and fossil orangutans. The mean cuspal daily secretion rate is similar to that of several other Miocene hominoids but is greater than extant great apes. Cusp-specific molar crown formation times generally exceed those of chimpanzees, are lower than those of orangutans, and are broadly like those of other Miocene apes. While Rudapithecus appears to have a somewhat unique pattern of enamel thickness and dental development relative to individual great ape genera, these structural and developmental features are consistent with its designation as a hominid., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The 2D arrangement of rows of enamel rods with alternating (decussating) tilt angles across the thickness of the inner layer in rat and mouse incisor enamel is well known and assumed to occur in a uniform and repetitive pattern. Some irregularities in the arrangement of rows have been reported, but no detailed investigation of row structure across the entire inner enamel layer currently exists. This investigation was undertaken to determine if the global row pattern in mouse mandibular incisor enamel is predominately regular in nature with only occasional anomalies or if rows of enamel rods have more spatial complexity than previously suspected. The data from this investigation indicate that rows of enamel rods are highly variable in length and have complex transverse arrangements across the width and thickness of the inner enamel layer. The majority of rows are short or medium in length, with 87% having < 100 rods per row. The remaining 13% are long rows (with 100-233 rods per row) that contain 46% of all enamel rods seen in transverse sections. Variable numbers of rows were associated with the lateral, central and mesial regions of the enamel layer. Each region contained different ratios of short, medium and long rows. A variety of relationships was found along the transverse length of rows in each region, including uniform associations of alternating rod tilts between neighboring rows, and instances where two rows having the same rod tilt were paired for variable distances then moved apart to accommodate rows of opposite tilt. Sometimes a row appeared to branch into two rows with the same tilt, or conversely where two rows merged into one row depending upon the mesial-to-lateral direction in which the row was viewed. Some rows showed both pairing and branching/merging along their length. These tended to be among the longest rows identified, and they often crossed the central region with extensions into the lateral and mesial regions. The most frequent row arrangement was a row of petite length nestled at the side of another row having the same rod tilt (30% of all rows). These were termed 'focal stacks' and may relate to the evolution of uniserial rat and mouse incisor enamel from a multilayered ancestor. The mesial and lateral endpoints of rows also showed complex arrangements with the dentinoenamel junction (DEJ), the inner enamel layer itself, and the boundary area to the outer enamel layer. It was concluded that the diversity in row lengths and various spatial arrangements both within and between rows across the transverse plane provides a method to interlock the enamel layer across each region and keep the enamel layer compact relative to the curving DEJ surface. The uniserial pattern for rows in mouse mandibular incisors is not uniform, but diverse and very complex., (© 2019 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

The mandibular third premolar (P 3 ) exhibits substantial differences in size and shape among hominoid taxa, and displays a number of discrete traits that have proven to be useful in studies of hominin taxonomy and phylogeny. Discrete traits at the enamel-dentine junction (EDJ) can be accurately assessed on moderately worn specimens, and often appear sharper than at the outer-enamel surface (OES). Here we use microtomography to image the P 3 EDJ of a broad sample of extant apes, extinct hominins and modern humans (n = 100). We present typologies for three important premolar discrete traits at the EDJ (transverse crest, marginal ridge and buccal grooves), and score trait frequencies within our sample. We find that the transverse crest is variable in extant apes, while the majority of hominins display a transverse crest which runs directly between the two major premolar cusps. Some Neanderthals display a unique form in which the transverse crest fails to reach the protoconid. We find that mesial marginal ridge discontinuity is common in Australopithecus anamensis and Australopithecus afarensis while continuous marginal ridges largely characterize Australopithecus africanus and Paranthropus. Interrupted mesial and distal marginal ridges are again seen in Homo sapiens and Neanderthals. Premolar buccal grooves, previously identified at the OES as important for hominin systematics, are again found to show a number of taxon-specific patterns at the EDJ, including a clear difference between Australopithecus and Paranthropus specimens. However, their appearance may be dependent on the morphology of other parts of the crown such as the protoconid crest, and the presence of accessory dentine horns. Finally, we discuss rare variations in the form of dentine horns that underlie premolar cusps, and their potential homology to similar morphologies in other tooth positions., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background: Physiological disruptions to early human development have implications for health and disease in later life. Limited research has explored how prenatal factors influence dental development in children of mothers with known pregnancy conditions. Enamel in human deciduous teeth begins forming in utero and is highly susceptible to physiological upsets experienced perinatally. The moment of birth itself is marked in deciduous enamel by the Neonatal Line (NNL) as a baby transitions from the uterine to external environment. This study evaluates the effect of maternal health factors that include stress and alcohol consumption on NNL in teeth from Australian children., Study Design and Subjects: Mothers (n = 53) were interviewed about their health during pregnancy and experience of birth. Sixty-five deciduous teeth (incisors, molars, one canine) from their children were donated for histological examination. Neonatal line thickness was measured from thin sections and evaluated against maternal and neonatal factors using statistical analyses, controlling for tooth type and birth number., Results and Conclusions: The only maternal factor of a statistically significant effect on NNL thickness was alcohol consumption. Children of mothers who drank occasionally during pregnancy had a thicker NNL when compared to children of mothers who abstained. These results suggest that maternal lifestyle factors influence NNL formation possibly due to physiological changes that disrupt calcium homeostasis during enamel deposition. We highlight large intra-specific variation in human NNL expression. The potential of dental sampling in identifying children with prenatal exposure to alcohol is suggested., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Objectives: Stable isotope analysis has often been used in neonatal remains from archeological contexts to investigate the presence of a signal of breastfeeding and weaning in past populations. Tooth histology on the other hand might be used as an indicator of birth survival. This pilot study aimed to investigate the feasibility of using stable nitrogen (δ 15 N) and carbon (δ 13 C) isotope values from neonatal bone collagen to elucidate if values deviating from the adult female average could indicate breastfeeding and co-occur with the presence of a neonatal line (NNL). The combination of these independent indicators might be useful in clarifying the fate of individuals who died around birth., Materials and Methods: Bone collagen from 21 archeological human and animal specimens was extracted and analyzed via mass-spectrometry for δ 15 N and δ 13 C. A verification of the stable isotope results was undertaken using tooth histology on three individuals who were investigated for the presence of a NNL as an indicator of live birth and short survival., Results: The biological age of the human samples varied between 8.5 lunar months (Lm) and 2 postnatal months (Pm) of age. All except one individual exhibited elevated δ 15 N values compared to the female average. The histological analyses revealed no NNL for this and two further individuals (n = 3)., Discussion: The results indicate that elevated nitrogen values of very young infants relative to a female average in archeological contexts are not necessarily associated with a breastfeeding onset signal, and therefore cannot be used exclusively as a proxy of birth survival. The elevation might be possible due to various reasons; one could be nutritional, in particular maternal stress during pregnancy or a metabolic disorder of mother and/or her child. In those cases, the evaluation of a NNL might reveal a false breastfeeding signal as seen for two individuals in our sample who have elevated nitrogen values despite the fact no NNL could be observed. Overall, our data support the growing awareness that bone collagen δ 15 N values of neonates/infants should not be used as a proxy for breastfeeding or birth survival on its own., (© 2019 Wiley Periodicals, Inc.)

Objective: The aim of the study was to compare the neonatal line width as well as the composition of the pre-natal and post-natal enamel in deciduous teeth of children with cerebral palsy (CP) to deciduous teeth of healthy children., Design: 58 extracted or normally exfoliated deciduous teeth were collected for the study, 29 teeth from children with cerebral palsy and 29 pair matched teeth from healthy children who served as controls. The teeth were cut along the bucco-lingual/palatal axis and polished up to a thickness of 50-100 microns. The sections were examined using a light microscope and scanning electron microscope (SEM). The neonatal line was identified in 25 teeth and measured in width and the enamel concentrations of calcium, phosphorus, silicon, magnesium, sodium, oxygen, and carbon were measured in the pre-natal and post-natal enamel using ESD program., Results: The neonatal line was significantly narrower in the deciduous teeth collected from children with cerebral palsy. In both groups, the concentration of magnesium and sodium in the pre-natal enamel was significantly higher than in the post-natal enamel. Magnesium and sodium levels were significantly higher in pre-natal enamel in the CP group compared to the pre-natal enamel of the control group., Conclusions: The neonatal line was narrower in the deciduous teeth collected from children with cerebral palsy than in those collected from healthy children. Children with cerebral palsy have a higher concentration of magnesium and sodium in the enamel that developed before birth., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Objectives: This study explores the outer and inner crown of lower third and fourth premolars (P 3 , P 4 ) by analyzing the morphological variation among diverse modern human groups., Materials and Methods: We studied three-dimensional models of the outer enamel surface and the enamel-dentine junction (EDJ) from μCT datasets of 77 recent humans using both an assessment of seven nonmetric traits and a standard geometric morphometric (GM) analysis. For the latter, the dental crown was represented by four landmarks (dentine horns and fossae), 20 semilandmarks along the EDJ marginal ridge, and pseudolandmarks along the crown and cervical outlines., Results: Certain discrete traits showed significantly different regional frequencies and sexual dimorphism. The GM analyses of both P 3 s and P 4 s showed extensive overlap in shape variation of the various populations (classification accuracy 15-69%). The first principal components explained about 40% of shape variance with a correlation between 0.59 and 0.87 of the features of P 3 s and P 4 s. Shape covariation between P 3 s and P 4 s expressed concordance of high and narrow or low and broad crowns., Conclusions: Due to marked intragroup and intergroup variation in GM analyses of lower premolars, discrete traits such as the number of lingual cusps and mesiolingual groove expression provide better geographic separation of modern human populations. The greater variability of the lingual region suggests a dominance of functional constraints over geographic provenience or sex. Additional information about functionally relevant aspects of the crown surface and odontogenetic data are needed to unravel the factors underlying dental morphology in modern humans., (© 2019 The Authors. American Journal of Physical Anthropology published by Wiley Periodicals, Inc.)

Natural bio-ceramics have attracted extensive interests due to its high strength and high toughness, which can hardly be achieved in artificial ceramics simultaneously. In this work, the microstructure and properties of the wild boar's tusk enamel were investigated. The enamel was found to exhibit a hierarchical structure ranging from the hydroxyapatite (HAP) fibers (single or poly-crystals, nano-scale), enamel rods (micro-scale), enamel types (meso-scale) to enamel patterns (macro-scale). It is worth mentioning that the high-density and high-order hierarchical nanotwins were observed in the HAP fibers. The mechanical properties of the wild boar's tusk enamel showed strong anisotropy and were higher along the longitudinal direction than along the transverse direction. The mechanical properties varied from the dentin-enamel junction (DEJ) to the outer surface. The elastic modulus increased with the distance from the DEJ and then kept invariant. The nano-hardness increased in inner enamel but decreased in outer enamel. There was a peak of nano-hardness in inner enamel area. The fracture toughness showed an opposite tendency. It exhibited high values in inner enamel, but fell in the outer enamel zone. The irregular, decussating texture of the enamel, as well as the nanotwins/hierarchical nanotwins was considered as the main reason for its excellent mechanical properties. These unique structures of the wild boar's tusk enamel are expected to cast light on the design of medical materials and provide some guidelines to improve their mechanical properties., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Objectives: Previous studies have revealed that human permanent dental tissue proportions differ significantly between males and females, with females having relatively thicker enamel relative to overall crown area than males. The aims of this study are to investigate sexual dimorphism in permanent mandibular molars and to determine whether such differences can be used to estimate sex in modern humans reliably., Materials and Methods: The permanent mandibular molars used in this study (n = 51) originate from 36 individuals of known sex from a Spanish anthropological collection. Eight variables were assessed from two-dimensional (2D) mesial planes of section obtained from microtomographic scans. Binary stepwise logistic regression was then applied to the data., Results: Male molars possess significantly greater quantities of dentine than females, both absolutely and proportionally. Females differed significantly from males by having greater relative enamel thickness. Logistic regression identified the proportion of dentine (relative dentine area [RDA]) as the most important sex discriminator, which can be used to correctly classify specimens with an overall accuracy rate of 74.36%., Discussion: These results confirm that sexual dimorphism in mandibular molar size is a result of males having a greater amount of dentine, both absolutely and proportionally. The findings suggest that 2D measurements of RDA may be useful for sex determination, although further research is required to test the reliability of these predictive techniques across different populations., (© 2019 Wiley Periodicals, Inc.)

The most mineralized tissue of the mammalian body is tooth enamel. Especially in species with thick enamel, three-dimensional (3D) tomography data has shown that the distribution of enamel varies across the occlusal surface of the tooth crown. Differences in enamel thickness among species and within the tooth crown have been used to examine taxonomic affiliations, life history, and functional properties of teeth. Before becoming fully mineralized, enamel matrix is secreted on the top of a dentine template, and it remains to be explored how matrix thickness is spatially regulated. To provide a predictive framework to examine enamel distribution, we introduce a computational model of enamel matrix secretion that maps the dentine topography to the enamel surface topography. Starting from empirical enamel-dentine junctions, enamel matrix deposition is modeled as a diffusion-limited free boundary problem. Using laboratory microCT and synchrotron tomographic data of pig molars that have markedly different dentine and enamel surface topographies, we show how diffusion-limited matrix deposition accounts for both the process of matrix secretion and the final enamel distribution. Simulations reveal how concave and convex dentine features have distinct effects on enamel surface, thereby explaining why the enamel surface is not a straightforward extrapolation of the dentine template. Human and orangutan molar simulations show that even subtle variation in dentine topography can be mapped to the enamel surface features. Mechanistic models of extracellular matrix deposition can be used to predict occlusal morphologies of teeth., Competing Interests: The authors have declared that no competing interests exist.

Objectives: We provide the description and comparative analysis of six new teeth from the site of La Ferrassie. Our goal is to discuss their taxonomic attribution, and to provide an updated inventory of Neandertal and modern human remains from La Ferrassie in their associated archeological context., Materials and Methods: We use external and internal anatomy, classic morphometrics, and geometric morphometrics. The teeth from La Ferrassie are compared to several samples of contemporary Neandertals and upper Paleolithic modern humans and to recent modern humans., Results: Three specimens are classified as Neandertals, two as modern humans, and one remains unclassified., Discussion: Based on the previously known fossil samples and the new teeth reported here, there are currently a minimum of four adult and five immature Neandertal individuals coming from the "Grand Abri" and a minimum of two modern human adult individuals: one from "Grand Abri" and one from "Grotte." It is noteworthy that the spatial distribution of the recovered Neandertal remains is not restricted to the area where the LF1-LF 8 were found but now covers the full extension of the excavated area. Moreover, while both Neandertal and modern human occupations have yielded isolated human remains, the partial-to-complete skeletons only belong to Neandertals. These considerations open new perspectives for the understanding of the occupation and use of the La Ferrassie site., (© 2019 Wiley Periodicals, Inc.)

Several human dental traits typical of modern humans appear to be associated with the prolonged period of development that is a key human attribute. Understanding when, and in which early hominins, these dental traits first appeared is thus of strong interest. Using x-ray multiresolution synchrotron phase-contrast microtomography, we quantify dental growth and development in an archaic Homo juvenile from the Xujiayao site in northern China dating to 161,000-224,000 years or 104,000-125,000 years before present. Despite the archaic morphology of Xujiayao hominins, most aspects of dental development of this juvenile fall within modern human ranges (e.g., prolonged crown formation time and delayed first molar eruption). For its estimated age-at-death (6.5 years), its state of dental development is comparable to that of equivalently aged modern children. These findings suggest that several facets of modern human dental growth and development evolved in East Asia before the appearance of fully modern human morphology.

Background: Ceramic crown that fires the layering porcelain on zirconia corping is starting to be used due to aesthetic requirements. However, many ceramics are used, but wear characteristics are often unknown., Objective: This study was performed to investigate the wear of human enamel by porcelains, and to determine the influence of porcelain hardness, surface roughness and crystal of porcelain on the enamel wear., Methods: Enamel specimens were prepared from extracted human molar teeth. Porcelain specimens were prepared from Deguceram Gold, Vita Omega 900, and Cercon Ceram Kiss. Enamel wear volume was calculated and the porcelain wear depth, surface roughness and Vickers hardness was measured. Moreover, the observation of a crystal by scanning electron microscope and the crystal by X-ray diffraction were identified., Results: Omega 900 showed the smallest enamel wear volume and porcelain wear depth. The Vickers hardnesses of Omega 900 and Cercon Ceram Kiss were almost identical. Leucite was detected from Deguceram Gold and Omega 900, and Silica and Silicon Nitride were detected from Cercon Ceram Kiss., Conclusions: The enamel wear is influenced not by the hardness of the porcelain but by the surface roughness, the size and shape of the crystal.

Objectives: We describe 14 unpublished and nine published teeth from the Mousterian level of Portel-Ouest (Ariège, France), dated to 44 ka. In a comparative context, we explore the taxonomical affinities of those teeth with Neandertals and modern humans which are both known to exist at that time. We further make some paleobiological inferences about this human group., Methods: The comparative analysis of Neandertals and modern humans is based on nonmetric traits at the outer enamel surface and the enamel-dentine junction, crown diameters and three-dimensional (3D) enamel thickness measurements of lower permanent teeth. The crown and roots are explored in detail based on the μCT-scan data to identify the multiple criteria involved in the paleobiological approach., Results: Nonmetric traits and 3D enamel thickness tend to be more similar to Neandertals than modern humans, notably for C 1 , P 4 , and M 2 (included in all analyses) as well as volume of the pulp cavity in roots of the anterior permanent teeth. The Portel-Ouest sample corresponds to a minimum of seven juveniles, one or two adolescents and one adult, which exhibit recurrent linear enamel hypoplasia (up to five events for one individual), the torsiversion of one anterior tooth and irregular oblique wear in some anterior deciduous teeth., Discussion: This morphological study confirms that the remains from Portel-Ouest are Neandertals, associated with a Mousterian complex. Furthermore, we found the expected pattern of mortality and stress for a Neandertal group, that is, various age categories and developmental defects (nonexclusive to Neandertals), while adults are underrepresented and juveniles are overrepresented. Further excavations would contribute finding new remains and maybe complete this demographic profile., (© 2018 Wiley Periodicals, Inc.)

Objective: The aim of this study was to evaluate the mineral content and morphology of primary tooth enamel prepared using an Er:YAG laser at different power settings. Materials and methods: The buccal surfaces of 45 noncarious primary molars were assessed in this study. The surfaces were cleaned and the teeth were randomly divided into nine groups ( n  = 5 each) to evaluate the effects of Er:YAG laser treatment at different energy levels: 200 mJ, 2 Hz; 200 mJ, 3 Hz; 200 mJ, 10 Hz; 250 mJ, 2 Hz; 250 mJ, 3 Hz; 250 mJ, 10 Hz; 300 mJ, 2 Hz; 300 mJ, 3 Hz; and 300 mJ, 10 Hz. The mean percentage weight (wt%) of calcium (Ca), phosphorous (P), fluoride (F), magnesium (Mg), potassium (K), and sodium (Na) in the primary tooth enamel was calculated for each group using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy before and after laser application. The enamel morphology was also evaluated using SEM. The obtained data were statistically analyzed by one-way analysis of variance and Tukey's honest significant difference test. Results: The mean wt% of Ca, P, and F in the enamel exhibited a significant change after laser treatment ( p  < 0.05); the wt% of Mg, K, and Na remained unchanged ( p  > 0.05). There was no association between the power setting of the laser and changes in the wt% of minerals in the enamel ( p  > 0.05). SEM showed that enamel irradiated at different energy levels exhibited a characteristic lava flow appearance, and more surface irregularities were observed with the 250-mJ setting than with the 200-mJ setting. Conclusions: Our findings suggest that the mineral content and morphology of the enamel of primary teeth are affected by Er:YAG laser irradiation.

Objectives: Dental tissue proportions of human permanent canines is one of only a few sexually dimorphic features that is present in childhood and maintained in adults, offering the opportunity for this to be used in sex determination. This study assesses dental tissue volumes and surface areas of maxillary permanent canines in a sample of known sex to provide new data and to explore the potential of these variables as reliable sexual estimators., Materials and Methods: The teeth studied here derive from 56 individuals (27 females and 29 males) of known sex and age, and of different geographic origins. The teeth were scanned and three-dimensional (3D) measurements (volumes and surface areas) were obtained. In addition, a discriminant function analysis was applied., Results: The results presented here concur with those previously published in relation to both size and dental tissue patterns. Male maxillary canines have a greater dentine component, whereas female enamel is thicker, leading to a difference in dental size in favor of males. Discriminant functions were calculated using these histological variables successfully identifying sex in between 87.5% and 93.75% of the known-sex hold-out sample, with 92.3% correctly assigned when all functions were applied together., Discussion: The present study supports that methods for sex determination based on dental tissue measurements can achieve high allocation accuracies, being especially useful in the case of subadults or when no other appropriate method is available., (© 2018 Wiley Periodicals, Inc.)

Scholars have debated the taxonomic identity of isolated primate teeth from the Asian Pleistocene for over a century, which is complicated by morphological and metric convergence between orangutan (Pongo) and hominin (Homo) molariform teeth. Like Homo erectus, Pongo once showed considerable dental variation and a wide distribution throughout mainland and insular Asia. In order to clarify the utility of isolated dental remains to document the presence of hominins during Asian prehistory, we examined enamel thickness, enamel-dentine junction shape, and crown development in 33 molars from G. H. R. von Koenigswald's Chinese Apothecary collection (11 Sinanthropus officinalis [= Homo erectus], 21 "Hemanthropus peii," and 1 "Hemanthropus peii" or Pongo) and 7 molars from Sangiran dome (either Homo erectus or Pongo). All fossil teeth were imaged with non-destructive conventional and/or synchrotron micro-computed tomography. These were compared to H. erectus teeth from Zhoukoudian, Sangiran and Trinil, and a large comparative sample of fossil Pongo, recent Pongo, and recent human teeth. We find that Homo and Pongo molars overlap substantially in relative enamel thickness; molar enamel-dentine junction shape is more distinctive, with Pongo showing relatively shorter dentine horns and wider crowns than Homo. Long-period line periodicity values are significantly greater in Pongo than in H. erectus, leading to longer crown formation times in the former. Most of the sample originally assigned to S. officinalis and H. erectus shows greater affinity to Pongo than to the hominin comparative sample. Moreover, enamel thickness, enamel-dentine junction shape, and a long-period line periodicity value in the "Hemanthropus peii" sample are indistinguishable from fossil Pongo. These results underscore the need for additional recovery and study of associated dentitions prior to erecting new taxa from isolated teeth., Competing Interests: The authors have declared that no competing interests exist.