Study Of The Relationship Between Cbfa1 And The Mechanism Of The Bone Remodeling In The Process Of Orthodontic Tooth Movement

The orthodontic force is transfered to the periodontal ligament and alveolar bone in the tooth movement of the orthodontic treatment. Then a series of biological effect happens in the periodontal tissue and that induces the rebuilding , especially for the alveolar bone. At last the tooth moves . The periodontal ligament is the physiological medium of the orthodontic treatment, a aberrant periosteum lying between the alveolar bone and the tooth cement, having the ability of bone resorption and formation. The proliferation,differentiation and movement of cells, including osteoblast ,osteoclast,fibroblast,non differentiation mesenchymal cell in periodontal ligament play the main role in the rebuilding of periodontal tissue. The alveolar bone is the plasticitied tissue made up of cell and matrix. The cells ,osteoblast,osteoclast ,osteocyte ,bone lining cell, locate at the surface of the bone ,except for the osteocyte that lies in the calcified bone matrix. In the process of the bone remodeling ,the osteoblast,osteoclast,etc have reciprocity and restriction by secreting many kind of cell factors, and control the bone resorption and formation. Komori et al had proved that a kind of differential transferred factor ,cbfa1(core binding factor a1,cbfa1)decided the process of the differentiation of the non differentiation mesenchymal cell to the osteoblast. Cbfa1 has a DNA combining zone ,which is constituted of 128 amino acids alike the runt gene of the drosophila. Cbfa1 can not only combine to DNA alone by the runt region,also form into heterogenous dimmer by combining to cbfβ,that can improve the appetency of the combination of the cbfa1 and DNA. The recent research have showed that many genes relating to the mineralization ,such as I collagen and osteocalcin have the combining zone of cbfa1 in the promoter.Cbfa1 is the indispensable factor of the differentiation of osteoblast and the development of bone ,by regulating the gene expression of the grow factor and ECMP. Cbfa1 can differentiate the nonosteoblast or proosteobalst into the osteoblast by upregulating the expression of the related gene. In addition ,cbfa1 can regulate the ability of the osteoblast and gene expression of the other grow factors, thereby control the physiological process of the formation and development of the bone . In general ,bone formation and bone resorption happen at one time and the reciprocity between the osteoblst and proosteoclast is the precondition of the osteoclast formation. OPG , a kind of glycoprotein secreting by the osteoblast,is a restrain factor of the differentiation of osteoclast and bone resorption .cbfa1 has played the tache role in the bone formation and resorption by regulating expression of OPG . In a word ,cbfa1 has expressed in the osteoblast ,fibroblast and periodontal ligament cells ,having affinity to the differentiation of osteoblast and bone formation in the physiological remodeling of periodontal tissue and taking part in the early healing of tooth extraction socket and the development of teeth. The purposes of our study are (1) to have qualitative and quantitative analysis of cbfa1 in PDL during the experimental rat tooth movement process, (2) to investigate the action mechanism of the cbfa1 in the osteoblast differentiation and the controlled factor to cbfa1(3) to investigate thefeasibility of cbfa1 as the way of accelerating tooth movement Materials and methods: 42 male wistar rats whose weights were almost 225 gram were chosen ,and they were divided into normal group and experimental( 1,3,5,7,14,21 day ) group randomly . Each group had 6 rats. A coil spring was deposited between the maxillary first molar and the maxillary central incisor, the first molar of rat was considered as the orthodontic tooth and the central incisor was being the anchorage tooth. Using 50g force to make the first molar mesial movement. 42 rats were perfused and sacrificed at 1 day, 3 day, 5 day, 7 day, 14 day and 21 day. All of tissue sections were processed, then proceeded with HE staining and cbfa1 immunohistochemical staining. Observing the histological changes of periodontal tissue, and the result was analyzed by the Computer Image Analyzing System and treated by statistics test. Results: There are cbfa1 expression in the compression and tension side of PDL in both groups of non orthodontic treatment groups and orthodontic treatment groups. In the normal PDL of non orthodontic treatment groups ,cbfa1 expressed lower ,especially in the osteoblast lying in the surface of alveolar bone and a few fibroblast ,distributing equally. In the 1 day group, disturbing sequence of fibroblasts in the compression and tension side was detected , and active proliferation of the PDL cells in the tension side and unevenness of the alveolar bone in compression side; cbfa1 expression was little stronger than the normal situation .In the 3 day group, the fibroblast was stretched in the tension side, and a few osteoblast andHowshiop's lacunae was noted in the compression side ;cbfa1 expression was stronger and the number of positive cell increased, distributing in the osteoblast ,PDL cell in the surface of the alveolar bone and the osteoblast in the marrow of the alveolar bone. However,cbfa1 expression was still low in the PDL cells adjacent to the tooth cement .In the 5 day group, the single line of cube shape osteoblast was detected in the surface of bone in tension side ,and the fibroblast was stretched to shuttle shape ,a flat nucleus. The osteoblast and Howshiop's lacunae increased in compression side;cbfa1 expression was strong and number of the positive cells increased in tension side, and the expression was stronger than the 3 day group in compression side. In the 7 day group, cbfa1 expression was the same in osteoblast of the surface of alveolar bone but little decreased around the blood vessel in the tension side ;in the compression side, a great deal of osteoblast and Howship's lacunae and strongly expression of cbfa1 was noted . In the 14 day group,cbfa1 expression was decreased greatly in the tension side , but bone resorption continued in the compression side and the expression of cbfa1 attained to the peak level. In the 21 day group,cbfa1 expression was decreased to the same to the normal station in the tension and compression side. The peak level of the cbfa1 expression in compression side was later than the tension side ,but alike to decrease to the normal station in 21 day. Cbfa1 expression in the surface of alveolar bone was lower in compression side than tension side, and the number of positive cells was less too. Conclusion: the change of cbfa1 expression in PDL is the a complex of biology reaction, that is induce by mechanical forces on alveolar bone. Under...