Plasticity of Dental Cell Types in Development, Regeneration, and Evolution

Protostylid: Contributing and Aggravating Factor for Periodontitis

Clinicians should be well-versed in the anatomy, variations, and teeth anomalies. Developmental disturbances of the teeth can lead to alterations in size, shape, number, structure, and eruption of the teeth. Developmental disturbances can lead to germination, fusion, concrescence, dilaceration, talons, cusps, dens in dente, etc. Protostylid, an additional cusp on the buccal aspect of the maxillary molar, which is a rare clinical finding, can lead to plaque accumulation, making oral hygiene maintenance difficult. This leads to clinical attachment loss and bone loss. This condition may often go undiagnosed. It should be diagnosed to prevent further complications. This case has been reported to make clinicians aware of the importance of diagnosing the case at the earliest possible time so that complications can be prevented and management is easier. From the perspective of forensic dentistry, this morphological feature, though uncommon, may be useful for the classification and identification of victims in mass causalities and bite marks on bodies or inanimate objects. This is one of the rarest cases of protostylids reported to date. This may not only pose a significant problem in endodontic therapy due to morphological alterations in root canals and periodontal therapy due to grove formation leading to an inability to maintain a plaque-free area (bone loss) but also be of very significant interest from the perspective of forensic dentistry.

Mechanobiology of Dental Pulp Cells

The dental pulp is the inner part of the tooth responsible for properly functioning during its lifespan. Apart from the very big biological heterogeneity of dental cells, tooth microenvironments differ a lot in the context of mechanical properties-ranging from 5.5 kPa for dental pulp to around 100 GPa for dentin and enamel. This physical heterogeneity and complexity plays a key role in tooth physiology and in turn, is a great target for a variety of therapeutic approaches. First of all, physical mechanisms are crucial for the pain propagation process from the tooth surface to the nerves inside the dental pulp. On the other hand, the modulation of the physical environment affects the functioning of dental pulp cells and thus is important for regenerative medicine. In the present review, we describe the physiological significance of biomechanical processes in the physiology and pathology of dental pulp. Moreover, we couple those phenomena with recent advances in the fields of bioengineering and pharmacology aiming to control the functioning of dental pulp cells, reduce pain, and enhance the differentiation of dental cells into desired lineages. The reviewed literature shows great progress in the topic of bioengineering of dental pulp-although mainly in vitro. Apart from a few positions, it leaves a gap for necessary filling with studies providing the mechanisms of the mechanical control of dental pulp functioning in vivo.

PRX1-positive mesenchymal stem cells drive molar morphogenesis

Mammalian teeth, developing inseparable from epithelial-mesenchymal interaction, come in many shapes and the key factors governing tooth morphology deserve to be answered. By merging single-cell RNA sequencing analysis with lineage tracing models, we have unearthed a captivating correlation between the contrasting morphology of mouse molars and the specific presence of PRX1+ cells within M1. These PRX1+ cells assume a profound responsibility in shaping tooth morphology through a remarkable divergence in dental mesenchymal cell proliferation. Deeper into the mechanisms, we have discovered that Wnt5a, bestowed by mesenchymal PRX1+ cells, stimulates mesenchymal cell proliferation while orchestrating molar morphogenesis through WNT signaling pathway. The loss of Wnt5a exhibits a defect phenotype similar to that of siPrx1. Exogenous addition of WNT5A can successfully reverse the inhibited cell proliferation and consequent deviant appearance exhibited in Prx1-deficient tooth germs. These findings bestow compelling evidence of PRX1-positive mesenchymal cells to be potential target in regulating tooth morphology.

Conserved and derived expression patterns and positive selection on dental genes reveal complex evolutionary context of ever-growing rodent molars

Background

Continuously growing teeth are an important innovation in mammalian evolution, yet genetic regulation of continuous growth by stem cells remains incompletely understood. Dental stem cells are lost at the onset of tooth root formation, but this loss of continuous crown growth is difficult to study in the mouse because regulatory signaling overlaps with signals that pattern tooth size and shape. Within the voles (Cricetidae, Rodentia, Glires), species have evolved both rooted and unrooted molars that have similar size and shape. We assembled a de novo genome of Myodes glareolus, a vole with high-crowned, rooted molars, and performed genomic and transcriptomic analyses in a broad phylogenetic context of Glires (rodents and lagomorphs) to assess differential selection and evolution in tooth forming genes.

Results

Our de novo genome recovered 91% of single-copy orthologs for Euarchontoglires and had a total length of 2.44 Gigabases, enabling genomic and transcriptomic analyses. We identified six dental genes undergoing positive selection across Glires and two genes undergoing positive selection in species with unrooted molars, Dspp and Aqp1. Transcriptomics analyses demonstrated conserved patterns of dental gene expression with species-specific variation likely related to developmental timing and morphological differences between mouse and vole molars.

Conclusions

Our results support ongoing dental gene evolution in rodents with unrooted molars. We identify candidate genes for further functional analyses, particularly Dspp, which plays an important role in mineralizing tissues. Our expression results support conservation of dental genes between voles and model species like mice, while revealing significant effects of overall tooth morphology on gene expression.

Using Ex Vivo Live Imaging to Investigate Cell Divisions and Movements During Mouse Dental Renewal

The continuously growing mouse incisor is emerging as a highly tractable model system to investigate the regulation of adult epithelial and mesenchymal stem cells and tooth regeneration. These progenitor populations actively divide, move, and differentiate to maintain tissue homeostasis and regenerate lost cells in a responsive manner. However, traditional analyses using fixed tissue sections could not capture the dynamic processes of cellular movements and interactions, limiting our ability to study their regulations. This paper describes a protocol to maintain whole mouse incisors in an explant culture system and live-track dental epithelial cells using multiphoton timelapse microscopy. This technique adds to our existing toolbox for dental research and allows investigators to acquire spatiotemporal information on cell behaviors and organizations in a living tissue. We anticipate that this methodology will help researchers further explore mechanisms that control the dynamic cellular processes taking place during both dental renewal and regeneration.