以動物實驗探討矯正治療中牙根與迷你骨釘碰撞之組織反應

Abstract

矯正治療中，骨性錨定扮演了重要的角色，迷你骨釘因為其體積小、使用上的多樣性、價格相對低廉、及方便植入及移除，故成為最常使用的工具。然而，迷你骨釘若植於牙根間齒槽骨部位時，在後續的矯正治療中若將牙根移向骨釘，可能會有牙根傷害之風險。本研究即利用動物實驗，探討在微觀下牙根與迷你骨釘碰觸之實際情形，以了解是否對牙根造成傷害及鄰近組織的可能反應。 本實驗以小獵犬兩隻分別在不同時間點做為研究對象，模擬臨床迷你骨釘使用狀況。實驗一先拔除其上下顎第一及第二小臼齒後植入迷你骨釘於犬齒遠心及第三小臼齒近心側（靠近但不可接觸牙根），並於三週後使用鎳鈦彈簧施予犬齒及第三小臼齒150克相互牽引力量，於第15週停止力量並嘗試固定牙根與骨釘之關係。實驗二則是多加了上顎雙側的第三門牙做為實驗對象，並分為左右兩側及設計對照組（單純矯正力量所造成的牙根吸收），施力則是持續至實驗結束。兩組實驗每隔三星期實施骨頭標定，皆於24週後將動物犧牲。接著將骨釘及其臨近的牙根樣本取下，並以樹脂包埋並切片，打薄後以顯微鏡觀察，其微觀下之螢光表現及細胞形態。 實驗結果發現：（1）碰觸處的細胞形態多為纖維母細胞、膠原纖維及微血管羅列，並未看到明顯的炎性細胞、或牙根表面的噬牙骨質細胞；（2）牙根與骨釘碰觸，會造成牙根表面的缺損情形，且呈現的則是長而淺的型態，而矯正引起之吸收則是不規則的吸收形態；（3）牙根與骨釘持續接觸時，表面傷害處尚未有修復的跡象；若是再有位移而使牙根與骨釘分開時，牙根表面會看到修復性的牙骨質生成。

Skeletal anchorage plays an important role in contemporary orthodontics. Miniscrew, which is one of the most frequently used temporal anchorage device (TADs), is famous for its small size, versatile usage, low price, and ease of insertion and removal. However, there are risks of root damage if we move a teeth to contact a miniscrew being inserted between two roots. Therefore, we used histological analysis on experimental animals to realize the possible response of root and surrounding tissues during this traumatic incidence. In dog A , both upper and lower arch first and second premolar were extracted. Miniscrew were placed over distal side of canine and mesial side of third premolar (without contacting miniscrews). Three weeks later, space between canine and third premolar was attempted to close with 150g NiTi coil spring. After fifteen weeks, active force was stopped and fixation was performed to reserve the relation between dental root and miniscrew. In dog B, force application was continued until experiment completed. Newly formed calcifying tissues were labeled with bone markers, and the experimental animals were sacrificed after 24 weeks. In order to observe the bone labeling markers and cell morphology surrounding miniscrews and tissues, samples were embedded with resin and sectioned with microtomes. Experimental findings:（1）There were fibroblasts, collagen fibers and capillaries surrounding the screws and roots. Inflammatory cells and cementoclasts were not found on the damaged root surface.（2） Long and shallow defect areas were seen on root surface if dental root was indeed in contact with the miniscrew. However, irregular resorptive concavity also could be detected as orthodontically induced root resorption.（3）Root repair was not initiated over resorptive area if dental root and miniscrew were still in contact with each other. On the contrary, reparative cementum can be found over resorbed concavity if dental root was displaced away from miniscrew surface.