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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.
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... Schwartz et al., 2001), and between populations (e.g. Smith et al., 2007;Aris et al., 2020aAris et al., , 2020b. A common trend between these lines of research is the exclusive use of what are deemed as dental samples containing no evidence of pathology, stress markers, or growth of accessory enamel (defined here as: growth of enamel outside of the features typically used to define and identify human tooth types). ...
... These rates accelerate from inner enamel regions proximal to the enamel dentine junction towards the outer enamel surface (e.g. Beynon et al., 1991Beynon et al., 1998Reid et al., 1998;Lacruz & Bromage, 2006;Mahoney, 2008;Aris et al., 2020aAris et al., , 2020b. Daily secretion rates are also faster relative to their proximity to the dentine horn (Beynon et al., 1991). ...
... Analysis of DSRs for human samples have examined variations within individual teeth (Mahoney, 2008), differences between biologically male and female groups (Schwartz et al., 2001), and more recently variations between populations (Aris et al., 2020a(Aris et al., , 2020b. Despite the breadth of these studies, they have universally used teeth absent of evidence of stress, pathology, and accessory enamel growth. ...
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This study investigates enamel growth of a modern-day human upper first incisor (S197) possessing an accessory cusp. Growth rates collected from the accessory enamel are compared to data collected from the primary cusp and healthy incisors from the same population. Upper first incisors (n=12) and S197 were analysed using histological methods. Daily secretion rates (DSRs) were calculated for inner, mid, and outer regions of cuspal and lateral sites. Additional DSRs were calculated for equivalent regions of S197’s accessory cusp. S197’s primary cusp DSRs were significantly faster than the accessory cusp for all lateral regions, but significantly slower in the inner and mid cuspal regions. S197’s primary cusp DSRs were also significantly faster than the healthy incisor sample for all lateral regions, but significantly slower in the inner and mid cuspal regions. The DSRs of the healthy sample were significantly faster than those of S197’s accessory cusp for all lateral regions, but significantly slower in the inner cuspal region. This case study displays that human teeth possessing accessory cusps can present varying DSRs to healthy teeth of the same population, and that accessory enamel growth may not follow the same pattern of increasing DSRs along the length of enamel prisms.
... These single human samples were also generated as a comparative sample for equivalent hominin/hominoid data analysis, rather than in direct analysis of human enamel growth/morphological patterns. There is therefore a clear need for the further generation of developmental enamel variable data from multiple modern human populations, in order for intra-specific research of human dentition to continue -a topic that has seen a resurgence in recent years (e.g., Le Luyer, Rottier, and Bayle, 2014;Aris et al., 2020aAris et al., , 2020bAris and Street 2021). ...
... Alongside the areas of inequality in research coverage and data availability regarding micro-scopic features of human enamel, there is a growing trend in intraspecific analyses investigating whether enamel growth and thickness has varied within the human species over relatively short periods of time. To date, these analyses have found significant variations in both enamel thickness and regional DSRs between geographically similar populations differing in context by as little as 400 years (Aris et al., 2020a;2020b). This varies from older research in the field which frequently has either pooled dental samples for their growth and thickness data, or just used a single sample population, in order to create representative data sets for geographic regions or the entire human species (e.g., Beynon et al., 1991b;Lacruz and Bromage, 2006;Smith et al., 2007;Mahoney, 2008). ...
... Where the same data has been utilised in multiple published works only one is detailed; preference was given to the original source where possible (Table 3). Note: Articles using similar data which have been published to date but are not included are those which utilised the data sets provided in this article (Aris et al., 2020a(Aris et al., , 2020bAris and Street, 2021). ...
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This article represents an open repository of human enamel data collected/reconstructed from seven populations covering a 2000 year time period in Britain via five temporally distinct periods. In total data was collected from 285 permanent teeth, including maxillary and mandibular first molars, and maxillary canines and first incisors. Data was gathered through thin histological methods using standard procedures for sectioning human dental material. In regards to enamel growth, data is collected for daily secretion rates (DSRs) for the inner, mid, and outer areas of lateral and cuspal enamel. For enamel thickness average (AET) and relative (RET) enamel thickness, cuspal linear thickness (CT), and lateral linear thickness (LT) was collected. Alongside the data presented this article also provides clear and transparent explanations for all the methods involved in its production, in order to ensure understanding of the rigorous protocol and consistency associated with the data provided. The novel data is also contextualised with a compilation of equivalent data published in past articles.
... Studies of enamel daily secretion rates (DSRs) of human teeth have tended to focus on permanent molars (e.g., Aris, Mahoney, O'Hara, & Deter, 2020;Beynon, Dean, & Reid, 1991b;Lacruz & Bromage, 2006;Mahoney, 2008) and deciduous dentition (e.g., Birch & Dean, 2009;Mahoney, 2012Mahoney, , 2015. Relatively less research has been undertaken on growth rates of the anterior dentition (incisors and canines) (e.g., FitzGerald, 1998;Schwartz, Reid, & Dean, 2001). ...
... These results show the trend toward the slowing of daily enamel growth in Britain over the last 2000 years, has been consistent in both anterior and posterior teeth. Where the differences in enamel growth rates between populations were similar in the anterior teeth and first molars of the British populations, this was not the case specifically in differences between the Roman and Early Anglo-Saxon populations.In their study,Aris et al. (2020) commented on the similarities in the growth rates of the two populations, most notably in the cuspal enamel where mean rates were near identical. Conversely, in almost all anterior tooth enamel regions presented here, both male and female DSRs can be observed to vary between the Roman and Early Anglo-Saxon population. ...
... Future analysis of premolar enamel would be valuable.Comparison of DSRs for equivalent enamel regions and British populations between tooth types identifies further variation growth patterns. Comparing mean regional DSRs calculated from male and female anterior tooth samples (presented here) to mean DSRs for molar regions (see: Tables 2 and 3inAris et al., 2020) shows permanent first molar enamel, in the majority of 24 comparisons, to have been secreted at a faster rate than that of anterior teeth. In 11 of these cases molar regions grew faster, but only by a rate of ≤0.15 μm/ day. ...
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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.
... The equivalent rates in n=15 maxillary deciduous canines were slightly greater in the inner third of the enamel (3.72, 3,85, 4.39 µm/day). However, archaeological teeth may have faster rates of enamel formation than modern teeth (Aris, Mahoney, O'Hara & Deter, 2020) and a grand mean value for one third of the total enamel thickness is a considerable amount, whereas the methods employed in this study focus only on the first formed 100 µm of deciduous enamel where formation rates are slowest and where there has been shown to be least variation in rate along the EDJ (Birch & Dean, 2014;Nava, Bondioli, Coppa, Dean, Rossi & Zanolli, 2017). With this in mind, Mahoney (2015) measured daily enamel secretion rates at 25 µm intervals in a sample of recent Medieval maxillary deciduous canines. ...
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Objectives Deciduous canines are now used increasingly in archaeological and forensic studies to establish the time of birth and as a retrospective source of trace elements incorporated into enamel before and after birth. However, data on the variability of deciduous enamel formation times are scarce. Our objectives were to use daily incremental markings to estimate daily secretion rates, the timing of prenatal, postnatal and total enamel formation and any changes in enamel coverage or prism and stria orientation that occur during enamel formation. Materials and Methods Longitudinal ground sections of 81 deciduous canines were studied with transmitted light microscopy. High-resolution digital images were imported from an Olympus VS-120 virtual slide scanning system into a geographic information system (ArcGIS, ESRI USA) for quantitative and statistical analyses of linear, angular and area measurements of buccal enamel. Results Daily rates of enamel secretion close to the EDJ were faster than in permanent enamel (3.23 µm/day, SD = 0.54). Prism and stria angles subtended to the EDJ both increased through crown formation. Enamel coverage was low in the cusp and cervix but maximal ∼150 days after birth. The mean prenatal enamel formation time was 118 days (range 60−150, SD, 29.2, n = 24). The overall mean postnatal enamel formation time was 319 days (range 210–420, SD 50.6, n = 67). Conclusions Daily enamel secretion rates compared well with previous studies of deciduous enamel, however, enamel extension rates in deciduous cuspal enamel were notably lower. The variability of both prenatal and postnatal deciduous enamel formation times was greater than previously reported.
Objective This study explored differences in the regional daily growth rates of human enamel between tooth types across a temporal transect in Britain. Methods Upper permanent central incisors (n = 81), upper permanent canines (n = 69), and upper and lower permanent first molars (n = 115) from Roman, Pre-Medieval, Medieval, and Modern day populations were analysed using histological methods. Daily secretion rates (DSRs) were collected for inner, mid, and outer regions of cuspal and lateral enamel for each tooth type and temporal sample. Variation in DSRs between the tooth types, within each population, was sought using Welch’s tests. Results Numerous significant differences were observed in DSRs between equivalent enamel regions of different tooth types. The majority of differences were observed between molars and the anterior teeth, but there were no obvious trends as to which typically grew faster/slower, nor was there any consistency across the temporal samples. In contrast, comparisons between incisors and canines yielded minimal differences and variation, when significant, was found to be enamel area- and sample-specific. Conclusions This study presents evidence for a high level of variation in DSRs between anterior teeth and first molars of the permanent dentition. This variation appears sporadic with no clear trend outside of anterior tooth comparisons, where analyses of the Late Pre-Medieval and Modern-day populations highlight how DSRs within cuspal and lateral enamel can vary independently.
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Within the last two decades, the fields of dental anthropology and bioarchaeology have seen a drastic increase in the number of studies investigating the internal structures of human enamel in archaeological populations. Due to its relatively low cost and preparation time, combined with a high degree of accuracy, destructive histological analysis has become a common methodology in enamel research. However, despite its accuracy and presence within academic literature, institutions often reject applications to perform histological analysis as standard procedure. Most frequently this is justified because destructive analysis negatively impacts future research. As a result, many studies are forced to utilise published data or attempt to access the small number of dental histological slides already in existence. This paper details the processes and procedures followed during histological sampling, with the aim to provide an easily accessible reference for curators allowing them to make more informed decisions regarding requests to conduct histology on samples within their care. Moreover, this paper highlights the preservative methods available to researchers which, when employed, both limit the negative impact to future research and expand the type of material which institutions can provide access to. Access to these new materials provides curators with alternative responses to applications rather than rejecting proposals entirely. Methods include high quality resin casting, which allows for future metric and micro-wear analysis, and digital stitching methods for producing dental cross section databases which institutions can offer access to instead of further destructive sampling.
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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.
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Evidence of a periodic biorhythm is retained in tooth enamel in the form of Retzius lines. The periodicity of Retzius lines (RP) correlates with body mass and the scheduling of life history events when compared between some mammalian species. The correlation has led to the development of the inter-specific Havers-Halberg oscillation (HHO) hypothesis, which holds great potential for studying aspects of a fossil species biology from teeth. Yet, our understanding of if, or how, the HHO relates to human skeletal growth is limited. The goal here is to explore associations between the biorhythm and two hard tissues that form at different times during human ontogeny, within the context of the HHO. First, we investigate the relationship of RP to permanent molar enamel thickness and the underlying daily rate that ameloblasts secrete enamel during childhood. Following this, we develop preliminary research conducted on small samples of adult human bone by testing associations between RP, adult femoral length (as a proxy for attained adult stature) and cortical osteocyte lacunae density (as a proxy for the rate of osteocyte proliferation). Results reveal RP is positively correlated with enamel thickness, negatively correlated with femoral length, but weakly associated with the rate of enamel secretion and osteocyte proliferation. These new data imply that a slower biorhythm predicts thicker enamel for children but shorter stature for adults. Our results develop the intra-specific HHO hypothesis suggesting that there is a common underlying systemic biorhythm that has a role in the final products of human enamel and bone growth.
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The characterization and quantification of human dental enamel microstructure, in both permanent and deciduous teeth, allows us to document crucial growth parameters and to identify stressful events, thus contributing to the reconstruction of the past life history of an individual. Most studies to date have focused on the more accessible post-natal portion of the deciduous dental enamel, even though the analysis of prenatal enamel is pivotal in understanding fetal growth, and reveals information about the mother's health status during pregnancy. This contribution reports new data describing the prenatal enamel development of 18 central deciduous incisors from the Imperial Roman necropolis of Velia (I-II century CE, Salerno, Italy). Histomorphometrical analysis was performed to collect data on prenatal crown formation times, daily secretion rates and enamel extension rates. Results for the Velia sample allowed us to derive a new regression formula, using a robust statistical approach, that describes the average rates of deciduous enamel formation. This can now be used as a reference for pre-industrial populations. The same regression formula, even when daily incremental markings are difficult to visualize, may provide a clue to predicting the proportion of infants born full term and pre-term in an archaeological series.
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The tooth enamel development gene, enamelin (ENAM), showed evidence of positive selection during a genome-wide scan of human and primate DNA for signs of adaptive evolution. The current study examined the hypothesis that a single-nucleotide polymorphism (SNP) C14625T (rs7671281) in the ENAM gene identified in the genome-wide scan is associated with a change in enamel phenotype. African Americans were selected as the target population, as they have been reported to have a target SNP frequency of approximately 50%, whereas non-Africans are predicted to have a 96% SNP frequency. Digital radiographs and DNA samples from 244 teeth in 133 subjects were analysed, and enamel thickness was assessed in relation to SNP status, controlling for age, sex, tooth number and crown length. Crown length was found to increase with molar number, and females were found to have thicker enamel. Teeth with larger crowns also had thicker enamel, and older subjects had thinner enamel. Linear regression and generalized estimating equations were used to investigate the relationship between enamel thickness of the mandibular molars and ENAM SNP status; enamel in subjects with the derived allele was significantly thinner (P=0.040) when the results were controlled for sex, age, tooth number and crown length. The derived allele demonstrated a recessive effect on the phenotype. The data indicate that thinner dental enamel is associated with the derived ENAM genotype. This is the first direct evidence of a dental gene implicated in human adaptive evolution as having a phenotypic effect on an oral structure.
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Across mammalian species, the periodicity with which enamel layers form (Retzius periodicity) in permanent teeth corresponds with average body mass and the pace of life history. According to the Havers-Halberg Oscillation hypothesis (HHO), Retzius periodicity (RP) is a manifestation of a biorhythm that is also expressed in lamellar bone. Potentially, these links provide a basis for investigating aspects of a species' biology from fossilized teeth. Here, we tested intra-specific predictions of this hypothesis on skeletal samples of human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n = 25). Correlations were sought between RP, molar average and relative enamel thickness (AET, RET), and the average amount of primary bone growth (n = 7) in humeri of age-matched juveniles. Results show a previously undescribed relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET and RET, and scales isometrically. The direction of the correlation was opposite to HHO predictions as currently understood for human adults. Juveniles with higher RPs and thicker enamel had increased primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was, again, opposite to predictions. Next, we compared RP from deciduous molars with new data for permanent molars, and with previously published values. The lowermost RP of 4 and 5 days in deciduous enamel extends below the lowermost RP of 6 days in permanent enamel. A lowered range of RP values in deciduous enamel implies that the underlying biorhythm might change with age. Our results develop the intra-specific HHO hypothesis.
Objectives This study investigated the use of sexually dimorphic metrics of the first permanent maxillary molar (M¹) to determine sex in adult and immature individuals within and between populations. Methods Ten M¹ dimensions were measured in 91 adults (19–55 years) and 58 immatures (5–18 years) from two English populations, one of documented sex (Spitalfields crypt) and another of morphologically‐assigned sex (Black Gate). Preliminary statistical analysis was undertaken to explore bilateral differences and variation by age and sex, followed by multivariate analyses to predict sex from dental metrics. Results Both cross‐validated linear discriminant analysis and binary logistic regression predicted biological sex consistent with known sex in 94.6% of adults and 90.9% of immatures. When functions extracted from the Spitalfields data were used to assign sex to Black Gate adults, consistency with morphological sex varied from 83.3% to 57.7%. A new function developed on Black Gate resulted in only a 4.8% increase in maximum accuracy but reduced bias. The immature cohort comprised 19 (52.8%) males and 17 (47.2%) females. Conclusions This study demonstrates substantial sexual dimorphism in a single tooth which is commonly preserved in archaeological and forensic contexts. It successfully assigns biological sex to immatures from 5 years of age with substantially greater accuracy than any other morphological or metric method. We suggest that accurate cross‐population functions based on dentition require a trade‐off between accuracy and applicability, and that functions extracted from populations of documented sex can be used to assign sex to other archaeological and forensic remains.
Starting with the onset of the last glaciation approximately 100,000 years ago and continuing to the end of the Late Pleistocene approximately 10,000 years ago, human tooth size began to reduce at a rate of 1% every 2,000 years. Both the mesial-distal and the buccal-lingual dimensions of mandibular and maxillary teeth were undergoing the same rate of reduction. From the beginning of the Post-Pleistocene until the present, the overall rate of dental reduction doubled, becoming approximately 1% per thousand years. Buccal-lingual dimensions are now reducing twice as fast as mesial-distal dimensions, and maxillary teeth are reducing at an even more rapid rate than mandibular teeth. Late Pleistocene rates are comparable in Europe and the Middle East. The Post-Pleistocene rates are also the same for Europe, the Middle East, China, Japan, and Southeast Asia. It is suggested that the cookery at the beginning of the Late Pleistocene allowed the earlier changes to occur. The use of pottery within the last 10,000 years further reduced the amount of selection that had previously maintained usable tooth substance. Reduction then occurred as a consequence of the Probable Mutation Effect (Brace, 1963; McKee, 1984).
In this study, we investigate outer and inner variations of upper second molars (UM2) for Late Pleistocene and Early Holocene modern humans, at a key-period in our evolutionary history associated with major sociocultural, economic and environmental changes. Non-metric traits have been recorded on 89 UM2 of 66 Upper Paleolithic, Mesolithic and Neolithic individuals, and 40 UM2 have been microscanned to assess variations in enamel thickness (ET) distribution and enamel–dentine junction (EDJ) shape. Major changes are found between Mesolithic and Neolithic periods: a decrease of the metacone expression combined with an increase of the hypocone development; an increase of the heterogeneity of ET distribution between lingual and buccal cusps; and an increase of the development of the dentine horn tips corresponding to the hypocone and, to a lesser extent, to the metacone. These morphological modifications could be linked to the masticatory functional changes associated with the transition to agriculture.