In Vitro Analysis of Enamel Patterns Across Three Species Using Stereomicroscopy.

Background Dental enamel, the outermost layer of the tooth, stands as a unique and remarkable tissue that plays a crucial role in safeguarding teeth against various external factors. The examination and analysis of enamel rod end patterns on tooth surfaces, referred to as ameloglyphics, offer a promising avenue for dental identification and forensic investigations in forensic medicine, thereby enhancing the precision and reliability of forensic analyses. This paper aims to evaluate and compare the ameloglyphics of different species under a stereomicroscope. The species examined in this study include the beaver (genus Castor), fox (genus Vulpes), and human (Homo sapiens). Methods Teeth samples from each species (n = 3) were gathered from the tooth repository and examined under a stereomicroscope at various magnifications, both with and without graphite staining. Photographs were captured, and the enamel patterns were meticulously evaluated. Through the utilization of plot profiles, the enamel patterns of the different species were compared, and any discernible differences between them were carefully noted. Results The plot profiles of the three species were analyzed, revealing distinct characteristics. Specifically, it was observed that the plots of the genus Castor teeth and Homo sapiens teeth exhibited dispersed arrangements, whereas the plot profile of the genus Vulpes displayed a closely arranged pattern. Conclusions Within the confines of the current investigation, it can be inferred that every mammal exhibits a distinct and exclusive arrangement of enamel rods. Hence, the task of identifying a deceased individual through dental imprints may pose difficulties if the structural characteristics are not thoroughly comprehended.

Artificial neural networks reconstruct missing perikymata in worn teeth.

Dental evolutionary studies in hominins are key to understanding how our ancestors and close fossil relatives grew from the early stages of embryogenesis into adults. In a sense, teeth are like an airplane's 'black box' as they record important variables for assessing developmental timing, enabling comparisons within and between populations, species, and genera. The ability to discern this type of nuanced information is embedded in the nature of how tooth enamel and dentin form: incrementally and over years. This incremental growth leaves chronological indicators in the histological structure of enamel, visible on the crown surface as perikymata. These structures are used in the process of reconstructing the rate and timing of tooth formation. Unfortunately, the developmentally earliest growth lines in lateral enamel are quickly lost to wear once the tooth crown erupts. We developed a method to reconstruct these earliest, missing perilymata from worn teeth through knowledge of the later-developed, visible perikymata for all tooth types (incisors, canines, premolars, and molars) using a modern human dataset. Building on our previous research using polynomial regressions, here we describe an artificial neural networks (ANN) method. This new ANN method mostly predicts within 2 counts the number of perikymata present in each of the first three deciles of the crown height for all tooth types. Our ANN method for estimating perikymata lost through wear has two immediate benefits: more accurate values can be produced and worn teeth can be included in dental research. This tool is available on the open-source platform R within the package teethR released under GPL v3.0 license, enabling other researchers the opportunity to expand their datasets for studies of periodicity in histological growth, dental development, and evolution.

Meaningful measures of enamel hypoplasia: Prevalence and comparative intensity of developmental stress.

OBJECTIVES: Developmental stress causing enamel thinning is an important topic in primate biology. Because taxa differ in growth rates and enamel thickness, the goal is to provide a new method allowing direct comparison of prevalence and salience of enamel defects among samples. MATERIALS AND METHODS: Casts of ape teeth spanning the Late Pleistocene to Late Miocene from three site areas of increasing seasonality, equator (Sumatra) to 20° (Vietnam) and 25°N latitude (China), were examined for enamel defects among paleo-orangutans (n = 571, 222, respectively) and Lufengpithecus lufengensis (n = 198). Frequency of affected teeth and number of linear enamel hypoplasia were recorded. Defect dimensions were measured with a confocal microscope. Simple prevalence is compared to weighted prevalence (%), calculated by dividing "number of LEH from specific tooth groups" by "specific tooth sample size"; this quantity divided by "tooth-specific years of imbricational enamel formation." Defect dimensions are reduced to a dimensionless index termed "enamel deficit ratio" through dividing "daily enamel deficit" by "daily secretion rate." RESULTS: Weighted prevalence increases to the North, highlighting latitudinal similarities. In contrast, "enamel deficit ratio," designed to express comparative severity of developmental stress among samples, was least in the high latitude sample and differed little between paleo-orangutan samples. DISCUSSION: The actual numbers generated are not as important as efficacy of the proposed methods for other taxa. Developmental stress appears least severe in the high latitude (Lufengpithecus) sample but affects a greater proportion, compared to paleo-orangutans. Regardless of findings, the proposed solutions to improve comparability of disparate samples, yield reasonable results.

Characterization of short-period and long-period incremental markings in porcine enamel and dentine-Results of a fluorochrome labelling study in wild boar and domestic pigs.

Mammalian dental hard tissues exhibit incremental markings that reflect the periodic variation of appositional growth rates. In order to use these markings to characterize dental growth processes and to infer life-history traits, an unequivocal identification of their periodicities is required. We performed a fluorochrome labelling study on forming enamel and dentine in molar teeth of wild boar and domestic pigs to establish the periodicity and temporal correspondence of incremental markings in enamel and dentine. The dominant incremental markings in enamel (laminations) and dentine (von Ebner lines) recorded in the pig teeth are of a daily nature. In addition, long-period incremental markings with a periodicity of 2 days were recorded in enamel (striae of Retzius) and dentine (Andresen lines). The 2-day growth rhythm was also expressed at the lateral crown surface, as evidenced by the pattern of perikymata. In enamel, also markings with a sub-daily periodicity, representing an ultradian growth rhythm, were observed. Our study provides experimental evidence for the periodicity of incremental markings in porcine enamel and dentine. The findings correct previous misconceptions on incremental markings in dental hard tissues of pigs and other ungulates that had led to erroneous conclusions regarding crown formation parameters.

Conventional microscopy makes perikymata count and spacing data feasible for large samples.

OBJECTIVES: Current methods of quantifying defects of dental enamel (DDE) include either gross or low-level examination for linear enamel hypoplasia, histological analysis of striae of Retzius, or scanning electron microscopy (SEM) of a tooth or a tooth cast. Gross examination has been shown to miss many defects. Other methods can be destructive, require transporting samples, and are expensive. Here, we show that digital light microscopy (DLM) can be used for the analysis of DDE as indicated by widened perikymata spacing (WPS). This method takes advantage of high-power (100×) microscopy, but is non-destructive, can be implemented almost anywhere, and is inexpensive. MATERIALS AND METHODS: As proof of concept, we created photomontages of labial surfaces of five human canines from images made using DLM and SEM. We counted and measured the widths of all visible perikymata for each imaging modality and fit measurements to a negative curve representing the expected values for each tooth. We calculated residuals for each measurement. WPS were defined when R2 was in the 90th percentile, and were considered matched in DLM and SEM images when observed within the same decile of the tooth surface. RESULTS: There were more WPS detected in the images derived from DLM than from SEM. Overall, the data derived from the two imaging modalities provided similar information about the frequency and timing of stress during dental development. CONCLUSIONS: The method described here allows for DDE data acquisition as WPS from large samples, making feasible population-level studies that reflect sophisticated understanding of dental development.

Insights on patterns of developmental disturbances from the analysis of linear enamel hypoplasia in a Neolithic sample from Liguria (northwestern Italy).

OBJECTIVE: To assess developmental disturbances through the analysis of linear enamel hypoplasia (LEH) frequency and to infer environmental stress and life history within Neolithic communities from Liguria (Italy). MATERIALS: 43 unworn/minimally worn permanent anterior teeth of 13 individuals recovered from nearby caves and dated to c. 4800-4400 cal. BCE. METHODS: LEH defects were identified with high-resolution macrophotos of dental replicas, age at LEH was calculated via perikymata counts. LEH defects matched between two or more teeth were considered as systemic disturbances. LEH frequency by age classes was analyzed via GLZ and Friedman ANOVA. RESULTS: Number of matched defects per individual range between 2-12. The mean LEH per individual was highest in the 2.5-2.99 age category, with a significant increase relative to earlier growth stages, followed by a decline. CONCLUSION: LEH may reflect life-history in the local ecology of Neolithic Liguria, where several individuals with osteoarticular tuberculosis have been recorded. Disease burden may have triggered developmental disturbances around the time of weaning. Age at first defect was negatively correlated with age at death and positively with the total number of defects, suggesting that early stress may have affected survivorship. SIGNIFICANCE: The study contributes to the reconstruction of ecological pressures among Neolithic people of Liguria, and informs on environmental challenges during the Neolithic adaptive expansion. LIMITATIONS: The visual examination of macrophotos is prone to observer error; mid-crown tends to display more visible LEH due to tooth architecture. SUGGESTIONS FOR FURTHER RESEARCH: Apply different quantitative methods to examine severity and duration of disturbances.

Pig enamel revisited - Incremental markings in enamel of wild boars and domestic pigs.

The nature and periodicity of incremental markings in pig enamel is currently debated. To broaden the basis for a correct interpretation of growth marks in pig enamel, we analyzed their periodicity in teeth of wild boars and domestic pigs. For that, the numbers of enamel incremental markings were recorded in ground sections and compared with crown formation times for the respective teeth derived from literature data on tooth development and eruption in Sus scrofa. Our study revealed that laminations with a daily periodicity are the dominant incremental feature of pig enamel. In wild boar M3s, daily enamel secretion (apposition) rates ranged between a minimum of 6.1 µm in the inner and a maximum of 30.6 µm in the outer enamel. Long-period (supra-daily) incremental markings were present as perikymata at the outer enamel surface (OES). Contrary to the situation in primate enamel, in pig enamel the long-period incremental lines terminating in perikyma grooves were mostly structurally indistinguishable from the daily laminations. Typically, five sub-daily increments were present between successive laminations. The incremental pattern in pig enamel can be misinterpreted if the laminations are mistaken for long-period markings (striae of Retzius) and the sub-daily growth marks for daily prism cross-striations. The findings of the present study demonstrate the critical importance of correctly characterizing the incremental markings and their periodicity in enamel, and caution against an uncritical transfer of the interpretation of the nature of incremental markings in primate enamel to other mammalian taxa.

Perikymata: a non-existent term: a scientific literature invention? Terminology analysis and proposal / Periquematíe: un término inexistente. ¿una invención de la literatura? Análisis de la terminología y propuesta

SUMMARY: The constant and gradual apposition of the enamel during odontogenesis forms different histological structures on the tooth, including the perikymata, which appear on the crown surface as ridges between two imbrication lines. Although they are enameldependent structures described in various scientific texts and publications, they are not included in the enamel-dependent histological terms published in the Terminologia Histologica. The aim of this study was to analyze the term perikymata from a linguistic point of view and propose it as a new histological term. The word perikymata is derived from the Greek words perí 'around'+ kyma, 'wave', introduced by Preiswerk in 1895. Although the term is descriptive in itself, concentrating only information about the structure in a single word, as the terminology establishes, this does not indicate its location. We propose the term perikymata enamelis (perikymata of the enamel) be added. Although proposing new terms that are more in line with the International Federation of Associations of Anatomists (IFAA) and its terminology poses great challenges, a term is not just a word that makes reference to a morphological structure, it is also a unit of language, a means of communication, which in this case unites the morphological community in a single language.

RESUMEN: La aposición constante y paulatina del esmalte, durante la odontogénesis, forman en el diente distintas estructuras histológicas, uno de ellas son los perikymatas; los cuales se presentan en la superficie coronaria, como rodetes o crestas bajas, entre dos líneas de imbricación. Si bien son estructuras dependientes del esmalte, descritas en múltiples textos y publicaciones científicas, estas no se encuentran dentro de los términos histológicos dependientes del esmalte, publicados en Terminologia Histologica. El objetivo del estudio fue realizar un análisis del término perikymata desde un punto de vista lingüístico y proponerlo como nuevo término histológico. El término perikymata deriva de las palabras griegas perí 'alrededor de' + kyma, 'onda', introducido por Preiswerk en 1895, si bien el término es descriptivo por si solo concentrando la información de la estructura en una sola palabra, tal como lo establece la terminología, este no indica su ubicación. Debido a lo anterior proponemos agregar el término perikymata enamelis (periquematíe del esmalte). Aunque proponer nuevos términos que estén más acorde con los señalado por la International Federation of Associations of Anatomists (IFAA) y la propia terminología, presenta grandes desafíos; un término no sólo es una palabra que hace referencia a una estructura morfológica, sino que también es una unidad del lenguaje, un vehículo de comunicación, que en este caso une a la comunidad morfológica en un solo lenguaje.

Perikymata distribution on anterior teeth of Miocene Lufengpithecus lufengensis from Yunnan, Southern China.

OBJECTIVES: The present study investigated the distribution of perikymata on anterior teeth of Miocene Lufengpithecus lufengensis so as to broaden the comparative data of developmental variation within and among hominoids. We also compared perikymata-spacing pattern of Lufengpithecus lufengensis with hominins and extant African great apes to understand the implication of dental development. MATERIALS AND METHODS: A total of 30 anterior teeth (including 6 I1, 10 I2, and 14 C) of Lufengpithecus lufengensis were examined using a scanning electron microscope and Keyence VHX-600EOS digital microscope to document the number and distribution of perikymata on their labial surfaces. The labial crown height of each tooth was divided into 10 equal deciles and the total perikymata number in each decile was recorded. The mean number of perikymata per millimeter was then calculated for each decile. SPSS statistical software was used to perform analyses of these data, including t-tests for sexual dimorphism and plots showing the perikymata distribution in Lufengpithecus lufengensis. RESULTS: Perikymata counts of Lufengpithecus lufengensis in the first three deciles are fewer than the remaining deciles, and with perikymata becoming increasingly more closely packed as growth progresses from cusp to cervix, but decrease in density in the cervical decile. Besides, total labial perikymata counts of canines tend to display very significant sexual dimorphism. DISCUSSION: Lufengpithecus lufengensis anterior teeth are more similar in their distribution of labial perikymata to those of Australopithecus than those of other hominins and extant African great apes from previous studies.

Lateral enamel growth in human incisors from Çatalhöyük in Turkey.

OBJECTIVES: Whereas the differences in lateral enamel growth between fossil and modern populations have been well documented in recent years, few studies report on the variability in perikymata counts and distribution between modern human populations. There is a need for information on modern human populations from a wide range of geographical regions and archaeological populations to determine whether existing patterns are representative. The aim of this paper is to document enamel surface microstructures in human teeth from a previously unknown region and time period comprehensively. MATERIALS AND METHODS: Perikymata counts and distribution are assessed in a large sample of relatively unworn permanent incisors from the mid-Holocene site of Çatalhöyük in Turkey. RESULTS: All four incisor types exhibit total perikymata counts that are intermediate between values for modern samples from northern Europe and South Africa. The perikymata distribution followed the modern human pattern of a marked decrease in spacing in the cervical half of the crown. DISCUSSION: The existence of regional differences in perikymata number and distribution demonstrates the importance of documenting enamel microstructures in a wider range of modern human populations, both geographically and chronologically.

Perikymata distribution in Homo with special reference to the Xujiayao juvenile.

OBJECTIVES: This study investigates where the Xujiayao juvenile (I(1) and C(1) ) fits into the array of perikymata distribution patterns found within the genus Homo. MATERIALS AND METHODS: In addition to the I(1) and the C(1) of the Xujiayao juvenile, this study includes samples of early Homo (H. rudolfensis and H. erectus), Neandertals, early modern humans (Qafzeh), and recent modern humans from Southern Africa, Newcastle (UK), and North America (Inupiaq, AK). Three sets of analyses were undertaken, including a comparison of percentage of perikymata in the cervical half of the crown, repeated measures analysis of the percentage of total perikymata in each decile, and canonical variates analysis using both total perikymata number and the percentage of perikymata in the cervical half of the crown. RESULTS: The I(1) and C(1) of early Homo and Neandertals have a lower percentage of perikymata in the cervical half of the crown than modern human samples. Repeated measures analysis reveals clear distinctions in the distribution of perikymata between the modern human and fossil samples. Canonical variates analysis suggests greater differences between modern humans and the fossil samples than within the fossil samples, and classifies the Xujiayao teeth among modern humans. DISCUSSION: The present study further clarifies variation of perikymata distribution patterns within the genus Homo. The perikymata distribution of the Xujiayao juvenile tends to be more similar to that of modern humans than to either early Homo or Neandertals.

A comparative study of stress episode prevalence and duration among Jomon period foragers from Hokkaido.

This study reconstructs linear enamel hypoplasia (LEH) prevalence and stress episode duration among Jomon period foragers from Hokkaido, Japan (HKJ). Results are compared to Jomon period samples from coastal Honshu, Japan (HSJ) and Tigara Inupiat from Point Hope, Alaska (PHT) to provide a more comprehensive perspective on the manifestation of stress among circum-Pacific foragers. LEH were identified macro- and microscopically by enamel surface depressions and increased perikymata spacing within defects. Individuals with more than one anterior tooth affected by LEH were labeled as LEH positive. Stress episode durations were estimated by counting the number of perikymata within the occlusal wall of each LEH and multiplying that number by constants reflecting modal periodicities for modern human teeth. LEH prevalence and stress episode duration did not differ significantly between the two Jomon samples. Significantly greater frequencies of LEH were found in HKJ as compared to PHT foragers. However, HKJ foragers had significantly shorter stress episode durations as compared to PHT. This suggests that a greater proportion of HKJ individuals experienced stress episodes than did PHT individuals, but these stress events ended sooner. Similarity in stress experiences between the two Jomon samples and differences between the HKJ and PHT are found. These findings are important for two reasons. First, stress experiences of foraging populations differ markedly and cannot be generalized by subsistence strategy alone. Second, due to significant differences in episode duration, stress experiences cannot be understood using prevalence comparisons alone.