Experimental Study On Orthodontic Tooth Movement Through Alveolar Bone Regenerates Following Mandibular Distraction Osteogenesis in Dogs

本研究的目的是评估正畸牙齿移动到犬下颌骨牵张成骨形成的未成熟或成熟的新牙槽骨的影响。6只成年雄性比格犬在第3和第4前磨牙之间使用定制的口内骨载牵张器对双侧下颌进行了10mm的延长。固形期2周（1组）或12周（2组）后，以100g正畸力将第3前磨牙离体至游离骨内，持续12周。同时，第2前磨牙离体（对照组）。牙齿移动完成后，处死狗进行组织学评价。第1组第3前磨牙与第2组和对照牙比较，第1组牙移动速度明显快于对照组（P< 0.05）。组1的牙齿移动量显著大于对照组（P< 0.01）。临床和影像学显示，第1组后缩回的第3前磨牙在牙齿移动完成时表现为远端倾斜和向再生牙内挤压，牙齿活动度提高，远端根压力侧硬膜板和水平牙槽骨丢失，侧根吸收。在组1的组织学切片中，观察到大量的侧根吸收从牙釉质-骨水泥交界处延伸到根尖，牙本质厚度减少到对照组的近一半。这些结果表明，由于较高的正畸力或较高的骨再生重塑活性，正畸牙齿移动到未成熟的纤维分散骨中会发生严重的牙根吸收。需要进一步的研究来优化牵张成骨后牙齿通过再生牙槽骨移动的时机和力度。

The purpose of this study was to evaluate the effects of orthodontic tooth movement into immature or mature new alveolar bones created by distraction osteogenesis in the canine mandible.Six adult male beagles underwent 10 mm of bilateral mandibular lengthening by using custom-made intraoral bone-borne distractors between the 3rd and 4th premolars. After 2 weeks (Group 1) or 12 weeks (Group 2) of consolidation period, the 3rd premolars were distalized into the distracted bones at 100g of orthodontic force for 12 weeks. At the same time, the 2nd premolars were distalized (Control) . After the tooth movement was completed, the dogs were sacrificed for the histological evaluation.When compared the 3rd premolars in Group 1 to those in Group2 or Control's teeth, Group 1 showed that the rate of tooth movement was significantly faster(P<.05). The amount of tooth movement in Group 1 was significantly larger than that of Control (P<.01). Clinically and radiographically, the retracted 3rd premolars in Group 1 at completion of tooth movement showed distal tipping and extrusion into the regenerate, higher tooth mobility, loss of lamina dura and horizontal alveolar bone on the pressure side of the distal root, and lateral root resorption. In the histological sections obtained from Group 1, a large amount of lateral root resorption extended from enamel-cement junction to the root apex was observed and the thickness of the dentin reduced into nearly half of that of Control.These results demonstrated that severe root resorption would occur by orthodontic tooth movement into immature fibrous distracted bones, because of the higher magnitude of orthodontic force or the higher remodeling activity of bone regenerate. Further studies are needed to optimize the timing and the force magnitude for tooth movement through regenerate alveolar bone after distraction osteogenesis.