微型种植体支抗负载对邻近牙根及牙周组织的影响

Effects of miniscrew implant anchorage on adjacent roots and periodontal tissues

背景:微型种植体植入过程中植入的位点和方向、微型种植体加载后的移动、牙齿移动后与微型种植体接触等都将导致牙根的损害。目的:观察微型种植体负载不同周期后与其邻近的牙根和牙周组织的变化,以及牙周组织中骨保护素的表达变化。方法:beagle犬2只,在犬上颌第2,3,4前磨牙和下颌第2,3,4前磨牙及第1磨牙的牙根之间的唇侧牙槽间隔邻近牙根处各植入1枚微型种植体。每只犬各植入微型种植体14枚,上颌6枚,下颌8枚,其中上颌有2枚微型种植体设置为对照组不加载,其余均为实验组加载正畸力。微型种植体植入后2周,通过镍钛螺旋拉簧为微型种植体加载150 g的水平力。分别于微型种植体负载4周、8周后处死beagle犬,完整切取牙齿连同牙槽骨,苏木精-伊红染色观察以及免疫组织化学法检测牙周组织中骨保护素的表达变化。结果与结论:当微型种植体邻近牙根时,牙根表面牙槽骨出现吸收陷窝;微型种植体负载与牙根相向的水平力后,牙槽骨吸收变的更加活跃。当微型种植体接触牙周膜时,牙根表面的牙骨质局部严重吸收甚至达牙本质层。微型种植体接触牙根后负载,大面积的牙骨质全层吸收,牙本质暴露在外并出现吸收。对照组骨保护素出现强阳性表达,8周表达显著;8周实验组的骨保护素阳性表达明显下降(P<0.01)。结果表明,微型种植体邻近牙根植入后,邻近微型种植体的牙根及牙周组织均受到不同程度的损伤。微型种植体负载与牙根相向的水平正畸力,短期内对牙周组织中骨保护素的表达影响较小,随着负载周期的延长,压力显著抑制了骨保护素的表达。提示当发现邻近牙根植入后,微型种植体不应再负载与邻近牙根相向的正畸力,而应该及时取出待牙根自行修复,避免对邻近牙根的损伤进一步加重。

BACKGROUND：Implanted site and direction of miniscrew implants, post-implantation movement of implants, contact between tooth and implant after tooth movement al can cause root damage. 〈br〉 OBJECTIVE：To investigate the changes of the root surface, periodontal tissue and osteoprotegerin expression in the periodontal tissue at periods of time after miniscrew implant loading. 〈br〉 METHODTwo beagle dogs were selected. For each dog, miniscrews were implanted into the labial alveolar bone near the roots of the maxil ary second, third, and fourth premolars and the maxil ary second, third, and fourth premolars and first molar. Fourteen miniscrew implants were in one dog, including six in the maxil ary and eight in the mandible;two miniscrews of the maxil ary acted as control group with no loading, and the rest miniscrews were as experimental group under orthodontics force. Two weeks after miniscrew implantation, 150 g force was loaded between two miniscrews with nickel-titanium closed-coil springs. The dogs were sacrificed after miniscrews loading 4 and 8 weeks respectively, the teeth were cut completely with alveolar bone tissue and decalcified to make the histological specimen. The histological changes of the root and periodontal tissue were observed by hematoxylin-eosin staining and expression of osteoprotegrin in the periodontal ligament was also inspected by using immunohistochemistry. 〈br〉 RESULTS AND CONCLUSION：When the miniscrews were adjacent to the roots, absorption lacuna occurred in the alveolar bone;after horizontal force was loaded opposite to the roots, alveolar resorption became much more animate. When the miniscrews contacted with the pericementum, some areas of the cement absorbed seriously and even reached the dentin;when sustaining pressure from the miniscrews, the whole layer of the cement absorbed and the dentin was exposed and began to be absorbed. The osteoprotegrin in the periodontal ligament of control group expressed sharply and its expression was notable at 8 weeks;while the osteoprotegrin of experimental group weakly expressed at 8 weeks, and there was significant divergence between control group and experimental group at 8 weeks （P＆lt;0.01）. The roots and periodontal tissue were al damaged variously after miniscrew implantation adjacent to the roots. When horizontal orthodontic force was loaded opposite to the roots, the expression of osteoprotegrin was influenced slightly;as the loading period prolonged, pressure dramatical y restrained the expression of osteoprotegrin. When discovering the miniscrew implant adjacent to roors, the miniscrew implant anchorage should not be used to load orthodontical force opposite to the roots but ought to be removed in order to leave the root repair autonomously and avoid further damage.