Expression Of Runx2 In The Periodontal Ligament During Orthodontic Tooth Movement

Biochemical response occurs to applied orthodontic force during orthodontic treatment ,which leads to the remodeling of periodontal tissue and subsequent tooth movement. Periodontal ligament (PDL) possesses the ability to induce bone resorption and bone apposition. Orthodontic force leads to bone resorption at the pressure areas and bone apposition at the tension regions.Periodontal ligament fibroblasts under mechanical force express osteoblastic phenotype and functional protein and possess the potential to differentiate to osteoblasts. Osteoblast-specific transcription factor pay a key role in the process. Runx2 (runt-related transcription factor-2) has been first identified as a osteoblast-specific transcription factor. Runx2 is a multifunctional transcription factor that controls skeletal development by regulating the differentiation of chondrocytes and osteoblasts and the expression of many extracellular matrix protein genes during chondrocyte and osteoblast differentiation . Runx2 directs pluripotent mesenchymal cells to the osteoblast lineage and controls maturation of osteoblasts.Runx2 can regulate the expression of OPG. As a repressor of osteoclast differentiation OPG can inhibit the bone resorption. Hence, Runx2 play a essential role in the regulation of bone formation and bone resorption. As Runx2 is expressed both in osteoblast and in periodontal ligament fibroblasts, it play crucial role in induction of osteoblast differentiation and bone formation during the remolding process of periodontium. Expression of Runx2 in the periodontal ligament during orthodontic tooth movementObjective To investigate the changes of Runx2 (runt-related transcription factor-2) in rats periodontal ligament exposed to mechanical stress, and the role of Runx2 during orthodontic tooth movement. Methods Forty-two 6～8-week-old Sprague-Dawley rat were used as experimental animals. The rats were divided into 7 groups consisting of 6 animals each. One group was blank group. A continuous mechanical stress was applied on experimental side maxillary first molar. The contralateral side was as the control. The animals were sacrificed at 8 hours, 24 hours, 3 days,7 days,14 days and 21 days . The morphologic change was observed .The expressions of Runx2 were performed by immunohistochemistry. Control animals were not subjected to mechanical stress.Results The expression of Runx2 was detected on both the tension and the pressure sides in all groups. The expression of Runx2 in untreated control was weak. In the experimental group, the expression of Runx2 on tension side was increasing and was highest at 3 days,then decreased during the remainder of the experimental period. On the pressure side, the expression of Runx2 at 8 hours slightly decreased compared with those of the control group, then slightly increased from 24 hours to 7 days. No statistically significant differences were observed between the control group and the blank group.Conclusion Runx2 play an important role in alveolar bone remodeling during orthodontic tooth movement. Runx2 is an essential transcription factor that regulates the differentiation of mesenchymal cells to the osteoblast .