Expression Of RANKL And OPG In The Periodontium On Pressure Side Of Experimental Rapid Tooth Movement Through Periodontal Ligament Distraction

Objectives:To establish the experimental animal model of rapid tooth movement through periodontal ligament distraction ( PDLD) with Beagles, to observe the difference of content change of RANKL and OPG in the periodontium on the pressure side between rapid tooth movement through PDLD and routine orthodontic tooth movement, which investigate the effect of RANKL and OPG on periodontium remodeling mechanism of rapid tooth movement through PDLD and provide theoretical base for clinical treatment.Methods:Eight beagles were divided into 4 groups randomly with 2 Beagles in each group: group A (1-week activating), group B (2-week activating), group C (2-week activating, 2-week retention) and group D (2-week activating, 4-week retention). The 2nd mandibular premolars were extracted on both sides of the eight Beagles, One side was chosen for PDLD and the other side for routine orthodontic tooth movement randomly. We defined the 1st mandibular premolars as the moved teeth and the 3rd mandibular premolars as anchorage teeth. The 2nd premolars of maxillary was the normal control. For PDLD side, the interseptal bone resistance was reduced, then a custom-made tooth-borne distractor was bonded. The distractor was activated 90°, twice a day for 2 weeks and followed by retention period. The NiTi spring was activated with a force of 1.47N for 2 weeks and followed by retention period on routine control side. The distance of tooth movement was measured. The dogs were sacrificed on each designed group time, dentoalveolar segment including the 1st and 3rd premolar were dissected out separately, fixed, decalcified, paraffin-embedded, sliced. The changes of periodontium on pressure side of moved tooth were observed with HE staining. The number of osteoclasts in periodontium on pressure side of moved teeth was counted with TRAP staining.The content change of RANKL and OPG in periodontium on pressure side were observed with immunohistochemical staining. The statistical analyses were performed using the SPSS13.0 statistical program.Results:1 distance of tooth movement:After 1 week activating, the distal movement of moved teeth on PDLD side was 1.47±0.55mm compared with 0.47±0.21mm on routine control side, there was significantly statistical difference of the distance of tooth movement between PDLD and routine control sides (P<0.01). After 2 weeks activating, the distal movement of moved teeth on PDLD side was 3.98±1.26mm compared with 0.68±0.59mm on routine control side, there was significantly statistical difference of the total distance of tooth movement between PDLD and routine control sides (P<0.01).2 results of HE staining:Along with the activation,the periodontium on pressure side was narrowed significantly, hyalinization and undermining resorption were discovered on the routine control side; during the retention period, hyalinization was removed gradually by osteoclasts. While the periodontium on pressure side was narrowed not significantly on the PDLD side, and the interseptal bone was compressed into the extraction socket rapidly and resorpted, with part of which joined with the extraction socket. There are a number of osteoclasts around and in the interseptal bone, and few hyalinization zone was discovered in the periodontium on pressure side of PDLD. After 6 weeks, the periodontium on pressure side of PDLD and routine control reverted to normal gradually.3 results of osteoclasts in the periodontium on pressure side with TRAP staining:Along with the activation, TRAP+ osteoclasts had increased in the periodontium on pressure side of PDLD and routine control. The TRAP+ osteoclasts increased significantly in the periodontium on pressure side and reached the peak on PDLD side in group B, and reached the peak on routine control side in group C. There were significantly statistical difference of the amounts of TRAP+ osteoclasts between PDLD and routine control sides in group A(P<0.01), group B(P<0.01) and group C(P<0.01).4 expression of RANKL,OPG protein in the periodontium on pressure side:RANKL and OPG protein expressed mainly in cytoplasm of osteoblasts, fibroblasts, bone lining cells, vascular endothelial cells and osteoclasts located in resorption lacunae. Along with the activation, expression of RANKL and OPG protein increased gradually in the periodontium on pressure side of the routine control. The expression of RANKL and RANKL /OPG ratio reached the peak on routine control side in group C, then decreased. The expression of RANKL protein and RANKL /OPG ratio reached the peak on PDLD side in group B. During retention period, the expression of RANKL protein and RANKL /OPG ratio reduced gradually on PDLD side, while the expression of OPG protein kept on a high level both on PDLD and routine control side. There were significantly statistical difference of the expression of RANKL protein between PDLD and routine control sides in group A (P<0.01),group B (P<0.01) and group C (P<0.05). There were significantly statistical difference of the expression of OPG protein between PDLD and routine control sides in group A (P<0.01), B (P<0.01), group C (P<0.01) and group D (P<0.01). There were significantly statistical difference of RANKL /OPG ratio between PDLD and routine control sides in group A (P<0.01), B (P<0.01), group C (P<0.05) and group D (P<0.01).Conclusion:1 The periodontal ligament distraction method could accelerate the tooth movement through reducing interseptal bone resistance.2 The amounts of TRAP+ osteoclasts in the periodontium on pressure side of PDLD were more than that of the routine control. Bone resorption on the PDLD side has occurred earlier and faster than that on the roution control side.3 RANKL and OPG participate the periodontium remodeling of tooth movement through PDLD and routine tooth movement. RANKL/OPG ratio regulates the differentiation and activation of osteoclast in the periodontium on pressure side during tooth movement. The content changes of RANKL and OPG and RANKL/OPG ratio in the periodontium on pressure side of PDLD are much obvious than those of routine orthodontic tooth movement, leading to the rapid remodeling of the periodontium on pressure side of PDLD tooth movement.