What do rates of deposition of dental cementum tell us? Functional and evolutionary hypotheses in red deer

Interobserver variation affects accuracy of inference in life history studies using cementochronology

Objective

Cementochronology is a method for assessing chronological age and identifying other life-history parameters (LHPs) from incremental lines of acellular extrinsic fibre cementum (AEFC) in most mammalian teeth. The aim of this study is to question the accuracy of this technique when used as a stand-alone age estimation method, and to examine how the number of observers may alter accuracy.

Design

This research is based on an extant clinical study conducted on 10 human teeth with the patients' anamnestic data. Nine observers used cementochronology to count AEFC incremental lines from 82 digital images. The counting was performed at three non-standardised areas on each image, totalling 246 counts per observer. Resultant observer counts were compared using the coefficient of variation method.

Results

The mean deviation of cementum estimated age from known chronological age of the participants in the study is 5.2 years.

Conclusion

Our study shows that further critical examination of the current cementochronology technique is essential, due to the subjectivity of line counting. The number of skilled observers in the study may improve the overall accuracy of the technique. These issues have wider implications, as many researchers rely on accurate scientific inferences being made by cementum-based studies to support or refute overarching demographic models and grand evolutionary narratives grounded by life history theory. Until this issue is resolved cementochronology should only be used alongside other age estimation methods.

Insights into the molecular characteristics of embryonic cranial neural crest cells and their derived mesenchymal cell pools

Neural crest cells (NCCs) are central to vertebrate embryonic development, giving rise to diverse cell types with unique migratory and differentiation capacities. This study examines the molecular characteristics of cranial neural crest cell (CNCC)-derived mesenchymal cells, specifically those from teeth which in deer show continuous but limited growth, and antlers, which exhibit remarkable regenerative capabilities. Here, through single-cell RNA sequencing analysis, we uncover shared gene expression profiles between adult antlerogenic and dental mesenchymal cells, indicating common developmental pathways. We identify a striking resemblance in transcriptomic features between antlerogenic progenitor cells and dental pulp mesenchymal cells. Comparative analysis of CNCC-derived and non-CNCC-derived mesenchymal cell pools across species reveals core signature genes associated with CNCCs and their derivatives, delineating essential connections between CNCCs and CNCC-derived adult mesenchymal pools. Furthermore, whole-genome DNA methylation analysis unveils hypomethylation of CNCC derivate signature genes in regenerative antlerogenic periosteum, implying a role in maintaining multipotency. These findings offer crucial insights into the developmental biology and regenerative potential of CNCC-derived mesenchymal cells, laying a foundation for innovative therapeutic strategies in tissue regeneration.

Population differences in dental cementum growth rates: Implications for using cementum thickness as a method for age estimation

OBJECTIVES

Age at death estimation is a key element to many research questions in biological anthropology, archeology, and forensic science. Dental cementum is a tissue of choice for the estimation of age at death in adult individuals as it continues deposition for the entirety of an individual's life. Previous works have devised regression formulas correlating cementum thickness to age at death. However, interpopulation variances are unknown, and it is therefore not clear whether regressions based on a single population are applicable to individuals with different ancestries.

MATERIALS AND METHODS

Here, we use a sample (n = 52) of teeth from individuals with known age at tooth extraction/death of European, African, and East Asian ancestry to assess whether there are interpopulations differences in cementum growth rate. We measured growth rate in four different areas (2nd and 5th decile of both the lingual and buccal aspect of the root) of each tooth and used nonparametric tests to evaluate population differences in growth rate between homologous regions of the teeth.

RESULTS

The results of the analyses show that, even after controlling for tooth size, individuals of European ancestry have significantly lower growth rates than those of both African and East Asian ancestry across all four tooth areas.

DISCUSSION

These results call into question the applicability of the regression formulas derived from European ancestry individuals to individuals of other ancestries.

Acellular Extrinsic Fiber Cementum Is Invariably Present in the Superficial Layer of Apical Cementum in Mouse Molar

The cementum is a highly mineralized tissue that covers the tooth root. The regional differences among the types of cementum, especially in the extrinsic fibers that contribute to tooth support, remain controversial. Therefore, this study used second harmonic generation imaging in conjunction with automated collagen extraction and image analysis algorithms to facilitate the quantitative examination of the fiber characteristics and the changes occurring in these fibers over time. Acellular extrinsic fiber cementum (AEFC) was invariably observed in the superficial layer of the apical cementum in mouse molars, indicating that this region of the cementum plays a crucial role in supporting the tooth. The apical AEFC exhibited continuity and fiber characteristics comparable with the cervical AEFC, suggesting a common cellular origin for their formation. The cellular intrinsic fiber cementum present in the inner layer of the apical cementum showed consistent growth in the apical direction without layering. This study highlights the dynamic nature of the cementum in mouse molars and underscores the requirement for re-examining its structure and roles. The findings of the present study elucidate the morphophysiological features of cementum and have broader implications for the maintenance of periodontal tissue health.

Spatiotemporal cellular dynamics and molecular regulation of tooth root ontogeny

Tooth root development involves intricate spatiotemporal cellular dynamics and molecular regulation. The initiation of Hertwig's epithelial root sheath (HERS) induces odontoblast differentiation and the subsequent radicular dentin deposition. Precisely controlled signaling pathways modulate the behaviors of HERS and the fates of dental mesenchymal stem cells (DMSCs). Disruptions in these pathways lead to defects in root development, such as shortened roots and furcation abnormalities. Advances in dental stem cells, biomaterials, and bioprinting show immense promise for bioengineered tooth root regeneration. However, replicating the developmental intricacies of odontogenesis has not been resolved in clinical treatment and remains a major challenge in this field. Ongoing research focusing on the mechanisms of root development, advanced biomaterials, and manufacturing techniques will enable next-generation biological root regeneration that restores the physiological structure and function of the tooth root. This review summarizes recent discoveries in the underlying mechanisms governing root ontogeny and discusses some recent key findings in developing of new biologically based dental therapies.

A simple, low-cost method to age mammals? An alternative to cementum annuli analysis

One of the most common and ubiquitous methods to age mammals is by counting the cementum annuli in molars, premolars, incisors, or canines. Despite the ubiquity and perceived simplicity of the method, cementum annuli analysis can be time-consuming, expensive, inaccurate, and imprecise, and require specialized equipment. Using beavers (Castor canadensis) as a test species, we developed a straightforward method to age mammals that requires little specialized equipment. The method consists of: (1) digitizing longitudinally sectioned teeth and measuring the proportion of tooth surface area comprised of cementum ("proportion cementum"), (2) evaluating the relationship between proportion cementum and specimen age (determined from either known-age samples or cementum annuli analysis), and (3) using the modeled relationship to estimate the age of other individuals based solely on proportion cementum. The relationship between proportion cementum and age was strongly correlated (R 2 = .97-.98 depending on observer), similar between observers, and similar between known-age specimens and those aged via cementum annuli analysis. Using this proportion cementum method, two independent observers accurately predicted the age of 80%-84% of specimens within 0.5 year and 96%-98% within 1 year. We suggest this aging method will likely work with most mammal species given the relatively consistent deposition of cementum throughout mammals' lives and has promise to be a simple and quick alternative to cementum annuli analysis regardless of whether one develops proportion cementum models using known-age specimens or those aged via alternative methods.

Possibility of Human Gender Recognition Using Raman Spectra of Teeth

Gender determination of the human remains can be very challenging, especially in the case of incomplete ones. Herein, we report a proof-of-concept experiment where the possibility of gender recognition using Raman spectroscopy of teeth is investigated. Raman spectra were recorded from male and female molars and premolars on two distinct sites, tooth apex and anatomical neck. Recorded spectra were sorted into suitable datasets and initially analyzed with principal component analysis, which showed a distinction between spectra of male and female teeth. Then, reduced datasets with scores of the first 20 principal components were formed and two classification algorithms, support vector machine and artificial neural networks, were applied to form classification models for gender recognition. The obtained results showed that gender recognition with Raman spectra of teeth is possible but strongly depends both on the tooth type and spectrum recording site. The difference in classification accuracy between different tooth types and recording sites are discussed in terms of the molecular structure difference caused by the influence of masticatory loading or gender-dependent life events.

Anti-tumour activity of deer growing antlers and its potential applications in the treatment of malignant gliomas

A recent study showed that antlers have evolved a high rate of growth due to the expression of proto-oncogenes and that they have also evolved to express several tumour suppressor genes to control the risk of cancer. This may explain why deer antler velvet (DAV) extract shows anti-tumour activity. The fast growth of antler innervation through the velvet in close association to blood vessels provides a unique environment to study the fast but non-cancerous proliferation of heterogeneous cell populations. We set out to study the anti-cancer effect of DAV in glioblastoma (GB) cell lines in comparison with temozolomide, a chemotherapeutic drug used to treat high-grade brain tumours. Here we report, for the first time, that DAV extract from the tip, but not from mid-parts of the antler, exhibits an anti-tumour effect in GB cell lines (T98G and A172) while being non-toxic in non-cancerous cell lines (HEK293 and HACAT). In T98G cells, DAV treatment showed reduced proliferation (37.5%) and colony-formation capacity (84%), inhibited migration (39%), induced changes in cell cycle progression, and promoted apoptosis. The anticancer activity of DAV extract as demonstrated by these results may provide a new therapeutic strategy for GB treatment.