A Study On The Expression And Significance Of Vascular Endothelial Growth Factor During The Replacement Of Primary And Permanent Teeth

The replacement of primary and permanent teeth is one of the important process in the growth and development of animals' teeth and maxillofacial region. To children, it is a normal physiological process in oral cavity. The formation of erupt pathway and resorption of deciduous teeth roots are the previous condition of teeth eruption and replacement. Osteoclasts play an important role in these processes. Osteoclasts not only absorb primary dentition roots and alveolar bone, but blaze a way in development of permanent teeth germs and the formation of erupt pathway. These mechanisms are not fully clarified. So it is significant to study the activation, differentiation, maturation and express of osteoclasts for the understanding and control of teeth eruption and replacement.VEGF is a kind of multifunctional cell factor, which is excreted by thrombocyte, huge nucleolus cells, Endothelial cells, osteoblast or tumorous cells. VEGF is one of the highly specified endothelial cell mitogens, it helps in the endothelial cell multiplication, vascular formation, acceleration of vascular permeability and the maintance of vascular tissue. VEGF plays an important role not only in the process of vascular formation, but also in the bone metabolism as a kind of bone growth factor. It can improve OC diferrentiation and bone marrow activation, similar to the function of M-CSF. It has been proved that, VEGF helps in the balancing between bone formation and absorption, as well as in ECM reconstruction and vascular proliferation. In this study, we observed the VEGF expressed by the rat osteoclasts cultured in vitro. We also observed VEGF expression in deciduous teeth roots, alveolar bone and permanent teeth germs during three stages of the dogs' teeth replacement, including primary dentition roots stability, primary dentition roots resorption, and permanent dentition. Cell culture, immunohistochemical technique, in situ hybridization method and image analysis are mainly adopted. We hope to discuess function of VEGF. The main content and results of our researches are listed below:Part1 VEGF expression during the replacement of dogs' primary and permanent teethImmunohistochemical technique and in situ hybridization method were used. In this study we observe the VEGF expression under three states of the dogs' teeth: primary dentition roots stability, primary dentition roots resorption, permanent dentition.1 dogs' primary dentition roots stability stage: In these phase, the deciduous teeth roots were not absorbed biologically and alveolar absorption lacunae around deciduous tooth root are not found. The permanent teeth germs were developing and dentin and enamel matrix started to form. In the immunohistochemical and in situ hybridization experiments, VEGF positive signals were seen in the multinucleated osteoclasts, osteoblasts. These results indicated that osteoclasts probably participate in the differentiation and maturate of osteoclasts, thus affect bone reconstruction. VEGF positive signals were seen in ameloblasts, odontoblasts of the permanent teeth germs. These results indicat that VEGF takes part in the development of dogs' permanent teeth germs .2 dogs' primary dentition roots resorption stage: Dogs' deciduous teeth roots were undergoing absorption biologically and there were a lot of absorbed lacunae on the roots. The multinucleated osteoclasts were localized in the absorbed lacunae of the alveolar bone near the germs. Dentin and enamel of the permanent teeth germs went on forming and calcifying. In the immunohistochemical experiment, the VEGF-positive cells were the cementoclasts on absorpted root surface, the osteoclasts and osteoblasts in alveolar bone, as well the ameloblasts and odontoblasts of the permanent teeth germs. At the same time, we found odontoclasts in the lacunae of absorbed roots were dyed positively. In this stage, osteoclasts dyed strongest. In the in situ hybridization experiment, VEGF-positive cells were identified as osteoclasts. In this phase, osteoclasts enhance the excreting of VEGF, so alveolar bone and primary tooth roots are absorbed. The VEGF positive signals were observed on osteoclasts in alveolar bone, odontoclasts, osteoblasts, ameloblasts, odontoblasts of the permanent teeth germs in the in situ hybridization experiment. In this phase,osteoclasts enhance excreting of VEGF.3 dogs' permanent teeth dentition stage: Dogs' deciduous teeth shed and permanent teeth erupted. Osteoclasts were weak positive in immunohistochemical and in situ hybridization experiment. Dyeing degree of these positive cells increased significently. The results indicated osteoclasts' secreting low and the alveolar bone are rebuilding.Part2 VEGF expressed by SD rats'osteoclasts cultured in vitro Osteoclasts were cultured in vitro and identified: Marrow cells from SD mouse were harvested and cultured in the culture system with 1,25(OH)2D3, IL-1β. Osteoclast precursors are stimulated to differentiate in the culture system and observed by convert microscope. Multinucleated cells were observed on the 6th day. Osteoclasts cultured for 9 days were used for identification by the unique dying. The cells which were TRAP-positive and had bone absorptive lacuna by bone slice in one culture system were identified as osteoclast-like cells. Osteoclast-like cells were positive in VEGF immunohistochemical and in situ hybridization experiment. These positive results confirmed that osteoclasts cultured in vitro express VEGF and VEGFmRNA. The results indicated VEGF takes part in differentiation and maturate of osteoclasts.