The Histochemical And Immunohistochemical Observation And Research About The Mechanism Of Deciduous Teeth Exfoliation

The physiological absorption of the deciduous root is a unique phenomenon, and there are still many unknown mechanisms about it. The replacement of permanent teeth by primary teeth is a strictly regulated process, and during this process, there are a series of changes in the interior of the pulp,periodontium and alveolar bone of the deciduous teeth and the odontotheca of the inherited permanent tooth, which make the permanent dental germ constantly move towards the occlusal way. Meanwhile, the deciduous root is absorbed physiologically, loosened up, and eventually replaced by the new permanent teeth. Osteoclast and odontoclast play important roles during this process. It is very complex that primary teeth are replaced as it was affceted by a variety of factors:①The reforming of the bone tissue around the teeth,②Periodontal ligament cells or fibers or both working together,③Formation of the root,④The role of fluid mechanics. Cementoclast and osteoclast play an important role in the process. The mature differentiated osteoclast in the root area is called cementoclast. Cementoclast is the functional cell which can cause the absorption of the alveolar bone, and they are all multinucleated giant cells originated from blood stem cells in monocyte-macrophage cell system. Activated T cell factor (NFAT) is the transcription factor which is required by the cytokine (such as IL-2) production by antigen stimulated T lymphocyte. NFAT plays an important role in the transcription regulation of cytokine gene druing the immune response. NFAT is a Ca2 + regulated transcription factor, and has five members. NFAT1-4 is found in the cytoplasm of cells, and it can be activiated when the intracellular Ca2 + concentrations is elevatedup to a certain level resulting the activation of CaN (phosphatase calcineurin). The expression of NFAT2 mRNA was significantly increased at early stages of differentiation of the mice osteoclast [13-15]. The activation of NFAT has three steps: dephosphorylation, nuclear translocation and enhancement of the DNA affinity.Wei[6] and other reseachers also found that NFAT2 was important for the osteoclast development and differentiation in cultured cells. Recently Ikeola[7] found that NFAT1 expressed not only in precursor cells of the osteoclast, but also in the matured osteoclasts when they studied the molecular mechanism of NFAT1, NFAT2 and C-Jun, C-Fos of AP-1 family members regulared differentiation and development. Over-expression of NFAT1 results in the expression NFAT2 and the differentiation of the osteoclast in RAW264 cells. Therefore, NFAT1 is the upstream regulator of the NFAT2 during the development of the osteoclast, and high expression of C-Jun and C-Fos can significantly improve NFAT1 and NFAT2 activity in this process. This shows that the differentiation of C-Jun/C-Fos and the family members of NFAT are important for the differentiation and development of the osteoclast.We selected the extracted deciduous teeth because of stagnation, 5 teeth with complete root absorption, 5 teeth with 2/3 of root absorption, and 5 teeth with 1/2 of root absorption, 5 extracted permanent teeth because of orthodontic treatment. We also selected 5 mandible bone of mature mouse and the mouse with mixed dentition respectively. Major steps: All the primary and permanent teeth and mandibles were put into 40/L poly-phosphate buffer solution of formaldehyde and fixed for 24h (4℃), then decalcified in the EDTA solution. After this process, they were sliced,repaired,dehydrated and embedded in paraffin. Then, they were sliced into 3-5um sections, dryed and prepared for HE staining, NFATcl immunohistochemical staining and TRAP staining, using PBS solution as negative control in the control group. All of these were prepared for light microscopy observation. In 1/2 absorpted group and mandible group, NFATcl expression was significantly higher than their control group, which appeared in the cytoplasm of the osteoclast/odontoclast as yellow grains or clumps, and the control group was negative. The expression of NFATc1 in 3/4 absorpted and totally absorpted groups were slightly positive or even negative, and their control was negative. Our experiment showed the positive expression of NFAT in osteoclast during the process of the root absorption, and also strongly expressed in alveolar osteoclast and osteoblast in mice, indicating that NFAT participate in the process of the deciduous root absorption. This research has provided more theoretic proofs for the theory of root resorption and made a foundation for the future studies.