[Application of Animal Model Training in Preclinical Skills Teaching for Graduate Students of Dentistry].

Objective: To explore the potential application value of animal model training in improving the comprehensive clinical ability of postgraduate students of dentistry and to provide reference for new methods of preclinical skills teaching. Methods: A total of 40 postgraduate students of dentistry were assigned to two groups, an experimental group and a control group. The control group took the routine teaching course on root canal treatment for the right mandibular first molar, using a simulated model of human head. The experimental group also took a teaching course on root canal therapy for the right mandibular first molar, but an animal model was used for the group. After the course was completed, the instructor conducted comprehensive evaluation of the students' psychological quality, patient communication skills, diagnosis and treatment logic, speed of performing procedures, and treatment plan design. A questionnaire survey was conducted to examine the students' attitudes toward and evaluation of animal model training. Results: The scores for psychological quality (0.430±0.024 vs. 0.115±0.036), patient communication skills (0.878±0.065 vs. 0.115±0.036), diagnosis and treatment logic (0.630±0.066 vs. 0.372±0.033), speed of performing procedures (0.8975±0.019 vs. 0.055±0.080), and treatment plan design (0.539±0.036 vs. 0.396±0.017) of the experimental group were significantly higher than those of the control group ( P<0.0001). The total score of the experimental group (3.374±0.184) was significantly higher than that of the control group (1.053±0.082) and the difference was statistically significant ( P<0.001). 95% of the students in the control group and 100% of those in the experimental group were willing to participate in animal model training to improve their level of diagnosis and treatment skills for dental and endodontic diseases, showing no statistically significant difference ( χ 2=1.026, P=0.3112). In the experimental group, 30% of the students believed that their psychological qualities had been improved, 50% believed that their procedure skills had been improved, and 20% believed that animal model training had expanded the scope of their theoretical knowledge. Conclusion: Adding animal model training can improve dentistry graduate students' comprehensive abilities, including their psychological quality, patient communication skills, diagnosis and treatment logic, speed of performing procedures, and treatment plan design. In addition, it helps students familiarize themselves in advance with animal experimental operations for basic research, thus helping them acquire dual professional skills.

Function of Orofacial Stem Cells in Tooth Eruption: An Evolving Perspective.

Tooth eruption is closely linked to the normal development of dentition and proper establishment of occlusion. Disturbances in tooth eruption may affect oral physiological functions, facial contour and aesthetics; it is therefore important to understand the eruption process. This process is a complex biological event involving dynamic changes at the tissue and cellular levels. It is guided by anatomical structures as well as biological and molecular factors that result in the movement of the tooth to its final functional position in the oral cavity. Evidence increasingly suggests that stem cells contribute to tooth development and eruption. Multiple stem cell populations have been discovered in teeth and in their supporting tissues, such as dental follicle precursor cells, orofacial bone-/bone marrow-derived mesenchymal stem cells, periodontal ligament stem cells, stem cells from the apical papilla and dental pulp stem cells. These stem cells exhibit distinct differentiation capacities and are closely linked to alveolar bone remodelling, periodontium development and root formation during the eruption process. The present review summarises the current knowledge of the characteristics and functions of orofacial stem cells in tooth eruption, with a particular focus on recent discoveries concerning their lineage allocation and regulatory mechanisms.

Osteogenesis, Osteoclastogenesis and their Crosstalk in Lipopolysaccharide-induced Periodontitis in Mice.

OBJECTIVE: To determine the crosstalk of osteogenesis and osteoclastogenesis of alveolar bone in lipopolysaccharide (LPS)-induced periodontitis in mice. METHODS: A representative periodontitis model was established by treating mice with LPS, and osteoblasts and osteoclasts were cultured. Osteoblasts and osteoclasts were cocultured to determine the effects of LPS on the crosstalk of osteogenesis and osteoclastogenesis. Quantitative polymerase chain reaction (qPCR) was performed to determine the expression of osteoclastogenesis makers underlying the potential mechanisms. RESULTS: The morphological and pathological changes in alveolar bone were observed in LPSinduced mice and LPS dose-dependently suppressed osteogenesis. The mRNA expression of cathepsin K, as a marker of osteoclasts, was accordingly downregulated in the coculture. The mRNA expression of osteoprotegerin was increased, while that of receptor activator of nuclear factor-κB ligand (RANKL) was decreased with an increased concentration of LPS. Moreover, the mRNA expression of toll-like receptor 4 (TLR4) was upregulated by LPS, whereas TLR4 knockout partially recovered osteoclast differentiation in the upper layer of the coculture. CONCLUSION: LPS dose-dependently suppressed osteogenesis but had a bidirectional effect on osteoclastogenesis. The combined effects of LPS on osteogenesis, osteoclastogenesis and their crosstalk via TLR4 account for alveolar bone loss in periodontitis.

Spatial signalling mediated by the transforming growth factor-ß signalling pathway during tooth formation.

Tooth development relies on sequential and reciprocal interactions between the epithelial and mesenchymal tissues, and it is continuously regulated by a variety of conserved and specific temporal-spatial signalling pathways. It is well known that suspensions of tooth germ cells can form tooth-like structures after losing the positional information provided by the epithelial and mesenchymal tissues. However, the particular stage in which the tooth germ cells start to form tooth-like structures after losing their positional information remains unclear. In this study, we investigated the reassociation of tooth germ cells suspension from different morphological stages during tooth development and the phosphorylation of Smad2/3 in this process. Four tooth morphological stages were designed in this study. The results showed that tooth germ cells formed odontogenic tissue at embryonic day (E) 14.5, which is referred to as the cap stage, and they formed tooth-like structures at E16.5, which is referred to as the early bell stage, and E18.5, which is referred to as the late bell stage. Moreover, the transforming growth factor-ß signalling pathway might play a role in this process.

Phenotypic research on senile osteoporosis caused by SIRT6 deficiency.

Osteoporosis is a serious public bone metabolic disease. However, the mechanisms underlying bone loss combined with ageing, which is known as senile osteoporosis, remains unknown. Here we show the detailed phenotype of this disease caused by SIRT6 knock out (KO) in mice. To the best of our knowledge, this is the first study to reveal that SIRT6 is expressed in both bone marrow stroma cells and bone-related cells in both mouse and human models, which suggests that SIRT6 is an important regulator in bone metabolism. SIRT6-KO mice exhibit a significant decrease in body weight and remarkable dwarfism. The skeleton of the SIRT6-KO mouse is deficient in cartilage and mineralized bone tissue. Moreover, the osteocalcin concentration in blood is lower, which suggests that bone mass is markedly lost. Besides, the tartrate-resistant acid phosphatase 5b (TRAP5b) concentration is much higher, which suggests that bone resorption is overactive. Both trabecular and cortical bones exhibit severe osteopenia, and the bone mineral density is decreased. Moreover, double-labelling analysis shows that bone formation is much slower. To determine whether SIRT6 directly regulates bone metabolism, we cultured primary bone marrow stromal cells for osteogenesis and osteoclastogenesis separately to avoid indirect interference in vivo responses such as inflammation. Taken together, these results show that SIRT6 can directly regulate osteoblast proliferation and differentiation, resulting in attenuation in mineralization. Furthermore, SIRT6 can directly regulate osteoclast differentiation and results in a higher number of small osteoclasts, which may be related to overactive bone resorption.

Bivalent histone modifications during tooth development.

Histone methylation is one of the most widely studied post-transcriptional modifications. It is thought to be an important epigenetic event that is closely associated with cell fate determination and differentiation. To explore the spatiotemporal expression of histone H3 lysine 4 trimethylation (H3K4me3) and histone H3 lysine 27 trimethylation (H3K27me3) epigenetic marks and methylation or demethylation transferases in tooth organ development, we measured the expression of SET7, EZH2, KDM5B and JMJD3 via immunohistochemistry and quantitative polymerase chain reaction (qPCR) analysis in the first molar of BALB/c mice embryos at E13.5, E15.5, E17.5, P0 and P3, respectively. We also measured the expression of H3K4me3 and H3K27me3 with immunofluorescence staining. During murine tooth germ development, methylation or demethylation transferases were expressed in a spatial-temporal manner. The bivalent modification characterized by H3K4me3 and H3K27me3 can be found during the tooth germ development, as shown by immunofluorescence. The expression of SET7, EZH2 as methylation transferases and KDM5B and JMJD3 as demethylation transferases indicated accordingly with the expression of H3K4me3 and H3K27me3 respectively to some extent. The bivalent histone may play a critical role in tooth organ development via the regulation of cell differentiation.