Orthodontic treatment is a long term treatment. Many studies focused on how to accelerate tooth movement and reduce the active treatment time. In Physiology, The accelerating tooth movement is a process of promoting bone remodeling induced by orthodontic force, which include alveolar bone resorption and apposition. The relative research reveal that there many local factors modulating the bone remodeling process. One of them is TGF，a multifunctional modulating factor family, promote the cell hyper genesis, differentiation, and the extra cell matrix generation, also modulate the immunosystem by combining with other growth factors. TGF-β1is one of key cellular peptide, relative to the bone remodeling including bone resorption and apposition, promote the formation of cellular matrix and protein enzyme inhibitor; Decrease MMP formation. By the aboving function TGF-β1 promote osteoblast differentiation and formation and inhibit the pre-osteoclast differentiation process . Meanwhile, in Vivo and in Vitral , TGF-β1 up-modulate vascular formation peptide and promote vascular formation.Soft laser irradiation has benn used widely in the clinical work and dentistry, with its facility of no side effect, acceptable by patients. The clinical application of soft laser in orthodontics proved that soft laser irradiation could relieve the pain from <WP=52>orthodontic force, accelerate the velocity of tooth movement, and promote alveolar bone remodeling.The purposes of our study are (1) to investigate the TGF-β1 expression level changes in PDL during the experimental rabbit tooth movement process, (2) to investigate the effect of soft laser irradiation on TGF-β1 expression level in PDL, (3) to investigate the effect of soft laser irradiation on alveolar bone remodeling.Materials and methods:The rabbits whose weights were almost 2.0 kilogram were chosen , and they were divided into normal group and experimental( 1、3、5、7、14、21 day ) group randomly . Each group had 5 rabbits, and the total number was 35. A coil spring was deposited between the maxillary first molar and the maxillary central incisor, the first molar of rabbit was considered as the orthodontic tooth and the central incisor was being the anchorage tooth. Using 80g force to make the first molar mesial movement. In every experimental group, low level laser irradiated the first molar at the right side, and the left side was considered as control. Irradiation time of low level laser ranged from 1 day to 5 day, once a day, 15 min each time. All experimental animals were irradiated 5 times except that 1 day group were irradiated one time and 3 day group were irradiated three times. 35 rabbits were perfused and sacrificed at 1 day, 3 day, 5 day, 7 day, 14 day and 21 day. All of tissue sections were processed, <WP=53>then proceeded with HE staining and TGF-β1 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 TGF-β1expression in the compression and tension side of PDL in both groups of non orthodontic treatment groups and orthodontic treatment groups. Lower expression of TGF-β1 was detected in the fibroblast, osteocell, osteoclast; with higher expression level in the osteoblast. In the 1 day group, no significant changes of TGF-β1 expression was noted, except disturbing sequence of fibroblasts shapes. In the 3 days group, osteoclast activation was noted and strong TGF-β1 expression exist in the compression side . In the 5 day group, osteoclast activation still exist, meanwhile significant osteoblast activation was found with peak level in this stage. In 7 day group, the expression level of TGF-β1 remain strong , but lower than 5 day group. And it level was stronger in the tension side of PDL than compression side. In 14 day group, expression of TGF-β1 in PDL decreased dramatically with higher expression level in the tension side. In 21 day group, TGF-β1 expression level return to the normal situa
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