Cement or cementum is at the centre of current research on the estimation of age in adult remains. Like enamel and dentine, it has a layered structure, known as annulation. These annulae or ring-like structures vary between different types of cement, found in different parts of the root, but some show a more regular spacing. Cement is laid down slowly on the surface of the root throughout life and one established idea is that these regular annulae are deposited yearly. This chapter gives a detailed description of cement structure and the evidence this provides for the changes which took place at the root surface during life.

Tremendous progress has been made since cementum analysis first applications in the 1950s. Today, with a better understanding of cementum biology, robust, replicable protocols support promising innovative research. Now, cementum should be considered within a broader evolutionary framework and cementogenesis tested from chronobiology theoretical assumptions to identify genetic or environmental variables affecting its circannual growth. With the rise of image analysis automation and optimization of species-specific standardized protocols, cementochronology is mature for site-level experiments. Also, the groundbreaking evolution of noninvasive, 3D cementochronology opens opportunities to study the fossil record, from stem-mammals to our Homo lineage. The breadth of applications across disciplines is a testament to cementochronology as a unique tool to investigate age and season at death, mobility patterns, life-history events, or mammalian evolutionwhich should be deployed broadly in anthropology. The goal of this volume is to promote collaborative efforts and stimulate interdisciplinary opportunities to renew diverse anthropology themes using cementum in anthropology.

The purpose of this volume is to gather interdisciplinary scholars to explore and implement cementochronology, the analysis of cementum growth, from a chronobiology perspective. Chronobiology, the study of biological rhythms, rests on the premise that the regular rotation of the earth around its central axis and the sun produces two fundamental periodicities to which all life has become adapted. The evolutionary "clock-shop" model posits that circadian clocks govern daily rhythmicity, and circannual clocks provide a seasonal endogenous calendar. We present current theories explaining and interpreting cyclic growth marks observed in hard tissues, especially cementum. Repeated empirical and validation studies are now available to explain cementum's annual/seasonal periodicity, even though specific molecular pathways are still needed. We present our evidence in three parts covering cementum biology, protocols, and anthropological applications and argue that cementochronology with its regular and continuous growth characteristics should have a privileged place among skeletal age indicators.

Seasonal variations directly impacted the social and economic activities of past human populations. Cementochronology is one of the methods available to address seasonality questions. It relies on the cyclic deposition rate of dental cementum observed microscopically on petrographic thin‐sections of animal teeth from archaeological contexts. However, no protocol exists to select a Region of Interest (ROI) or to identify the last cementum increment. This chapter proposes consensual biological and optical criteria for the selection of optimal ROIs and their analysis. Interobserver tests were performed to assess the criteria, as well as age and season of death, on thirty thin‐sections of modern documented reindeer teeth. Results demonstrate the accuracy, and replicability of this protocol, and emphasize the influence of training and experience for the proper implementation of cementochronology.

For human dental cementum research, sample preparation protocol is now widely tested, validated, and standardized, thanks to the low variability in teeth morphology. For non-human mammals, posterior teeth are typically preferred. However, the taxa diversity implies a significant variation in morphology or specific characteristics for certain species (equids, suids), leading to multiple unstandardized protocols. This work aims to improve protocols for producing a thin section by optimizing the parameters, minimizing the risk of errors, and offering an easily reproducible quality of thin-sections. The result of 26 experiments and 124 analyses during stages of consolidation (embedding), cutting, gluing, and finishing (grinding) allowed the co-authors' combined experience from multiple laboratories to propose standardized humans and ungulates (large teeth) protocols for the systematic analysis of dental research collections.

Non-invasive 3D methods for imaging cementum increments using synchrotron radiation sources are one of the most promising new avenues for cementum research. This technique offers the opportunity to overcome the major caveats to traditional thin section imaging, and provides volumetric datasets of sub-micrometer resolution that can be investigated in new ways. Such studies can unlock the 3D structure of cementum increments, and 3D measures may allow for new inferences on the relationship between cementum growth and life history. However, as a new field of research, synchrotron X-ray imaging of cementum must ensure reproducibility by employing quantitative approaches to develop optimal experimental procedures and settings for imaging cementum in different samples. The quantitative parameter optimisation procedure we introduce in this chapter should form a crucial part of the imaging protocol that we present here, in which we outline the major steps in preparing for, performing and concluding a synchrotron imaging experiment, based on our own experience.

The paleodemography analysis of the Early medieval Lauchheim cemetery (Germany) was conducted to reconstruct the age-at-death distribution of 789 adults with preserved teeth using the Tooth Cementum Annulation (TCA) method, and the analysis of individual morphological age markers (MAE) for those without teeth. Aggregating TCA and MAE results revealed specific mortality peaks for males in their early fifties. After a mortality peak in their early forties, females surviving their fertile age group seemed to benefit from a resilience pattern that allows them to survive longer than their male counterparts. The mean life expectancy for females was below male life expectancy, whereas the oldest age group above 70 years of age included females only. In conclusion, TCA shows a more diverse age-at-death distribution without MAE inherent effects. Thus, it could be argued that TCA allows us to complement osteological age estimations and shape age at death distributions to understand demographic processes in premodern societies better.

Acellular cementum (AC) is critical for dental attachment and periodontal function. This chapter emphasizes how insights into cementum's nature have increased through human disease and experimental animal models. X-linked hypophosphatemia (XLH) is the most common form of hereditary rickets, in which low circulating phosphate and altered vitamin D metabolism are associated with skeletal and dental mineralization defects. AC thickness is reduced in XLH, and periodontal function may be affected. Inorganic pyrophosphate is a circulating inhibitor of mineralization. The inherited disorder, hypophosphatasia (HPP), is characterized by increased pyrophosphate levels, leading to skeletal and dental hypomineralization. AC is mainly affected by HPP, and premature loss of deciduous and permanent teeth is a common result. Conversely, a decrease in pyrophosphate results in increased cementum thickness. Extracellular matrix proteins also regulate cementum formation. Bone sialoprotein (BSP) is a component of cementum. Deletion of BSP in genetically edited mice results in reduced or absent AC, leading to periodontal destruction.

This chapter summarizes cementum biology knowledge, formation, types, composition, and clinical aspects. Two main types of cementum exist on human tooth roots. Acellular cementum (AC) covers cervical root surfaces and cellular cementum (CC) covers apical and furcation regions. Cementogenesis occurs during root formation following completion of the crown. Cementum formation includes deposition and mineralization of collagen fibers on root dentin surface by cementoblasts. The slow appositional growth of AC throughout life incorporates Sharpey’s fibers to anchor teeth to the alveolar bone. CC formation is initiated around the time the tooth enters occlusion. Cementum is composed of approximately 45-50% inorganic material by weight, primarily hydroxyapatite. The organic component includes multiple types of collagens and non-collagenous proteins such as bone sialoprotein and osteopontin, that may regulate mineralization and other properties. In considering the use of tooth root cementum to estimate ages of human samples, various circumstances may affect cementum structure, growth, or other properties and should be considered during analysis.

Counting dental acellular cementum (AC) annulations is used to estimate age at death in anthropological contexts by embedding the tooth, sectioning the root, and imaging the thin sections. However, there are several published protocols creating confusion to optimize these steps. We compared three standard illumination techniques (differential interference contrast; transmitted bright field; transmitted polarized) on sections with the same thickness, field of view, on three types of samples: fresh teeth embedded in both MMA and epoxy; archeological samples embedded in epoxy. We compared the quality of AC increment visibility on longitudinal and transversal sections of the same root, to optimize the quality of AC micrographs for age estimation. Results suggest that differential interference contrast microscopy might be ideal, even though brightfield consistently provides a decent image; epoxy resin with quick polymerization time doesn't affect AC structure and allows for higher contrast than traditional MMA; transverse sections are more consistent. These results emphasize the need for cementum-specific procedures not always compatible with traditional dental analyses.

Tooth Cementum Annulation Analysis (TCA), or Cementochronology, has been evolving over recent years with great potential for applied forensic sciences. The goals of this research is to evaluate if TCA can be used to accurately determine the chronological age at time of death and season at time of death for unaccounted for US service members and in forensic anthropology in general. Fifty teeth were processed, and analyzed by two independent observers for age and season at time of death estimations. Results indicate an average of 85% estimation success within a ±4 years range of documented chronological age. The last band of cementum was identified to the correct season in average 74%, with an interobserver agreement of 78%. This pilot study thus supports age at death estimation using TCA in forensic contexts, and suggests additional validation studies for season of death estimation.

The teeth are an ideal medium for recording information on the evolution, diet, age, lifestyle, culture, social behavior, and activities of populations. The general health of an individual or a group can also be assessed by studying bucco-dental pathologies that concern the enamel, the dentin, the alveolar bone, and the cementum. However, structural changes in this last tissue are barely discernible and are much less studied than changes in other tissues. The main objective of this chapter is to review the pattern of human cementum deposition with a special emphasis on hypercementosis. The first part is devoted to present the physiological factors that modulate cementum continuous apposition. The second part is dedicated to the pathological factors that are likely to disturb growth. The last part explores a particular growth pattern of cementum, hypercementosis, and its significance in past populations.

The circannual rhythm and continuous growth of cementum throughout life have been seen by many researchers as offering an exciting window of potential information of life history recorded in the shape, texture, and chemistry of its increments. A host of studies have thus been presented studying the relationship between these factors and various life history events affecting mammal physiology, most notably pregnancy and parturition. This chapter reviews the literature that has tested this assumption directly, in animals and in humans. Also, we offer theoretical and methodological insights into future advances in cementochronology specifically for identifying and recording these life-history events.

Acellular cementum anchors the root to the alveolar socket via the periodontal ligament and grows in layers continuously throughout life, unlike enamel and dentin. Increments are deposited in a biannual light-dark pattern correlated to age and season at death in transmitted light microscopy. This study investigates the still debated structure of individual acellular increments using x-ray fluorescence and x-ray diffraction mapping with synchrotron radiation microbeams on reindeer, red deer, cattle, and human samples. Results show that Ca or Zn x-ray fluorescent intensities and cAp diffracted intensity reveal cementum band structure. Average crystallographic texture (of cAp nanoplatelets’ orientation and collagen fibril orientations) is constant for each specimen. Microtextural variation is also present across individual bands, demonstrating that the overall collagen fibril orientation undergoes subtle changes with season. Patterns of “feast or famine” and concomitant changes in amount and intensity of PDL loading might produce altered collagen (and cAp) orientations between the “good” and the “bad” seasons for ungulates but maybe not for modern human populations.

Dental hard tissues contain periodic incremental markings that can be used as an absolute temporal archive to reconstruct their growth and can incorporate trace elements into their chemical structure during formation that reflect diet, the environment, metabolism, and health. The growth history can be recovered from teeth using virtual tooth histology to resolve a continuous record of trace element composition within each of the mineralized dental tissues, to further our understanding of past life history events in extant and extinct taxa. While acellular cementum forms slowly and regularly and is ideal for recording annual increments, compensatory cellular cementum can mirror this regular growth through gradual physiological changes in anterior tooth inclination. Here, we document this growth through microstructural elemental mapping using non-destructive synchrotron x-ray fluorescence on chimpanzee dental thin sections. We evidence clear seasonal mineral fluctuations, and match the narrower, brighter incremental markings visible in TLM with peaks in mineral concentration in zinc and strontium.