矯正用迷你骨釘植入後之生物體反應

Abstract

齒顎矯正治療中，錨定（anchorage）的控制始終扮演重要的角色。矯正植體（迷你骨釘與迷你骨板）因能提供良好的骨性錨定，近年來已成為矯正治療日漸普及的輔助工具。然而，植入迷你骨釘於齒槽骨部位時，難免有牙根傷害之潛在風險。本研究即在探討微觀下迷你骨釘與牙根之實際接觸情形，以及鄰近組織的可能反應；並探討當迷你骨釘接觸牙根時，軟組織包埋骨釘與否，對骨釘成功率之影響。 本實驗包含三部分，以小獵犬兩隻做為研究對象，模擬臨床迷你骨釘使用狀況。實驗一以實驗狗下顎兩側作為實驗部位，實驗組（4支）植入時刻意與牙根接觸，並設定留置不同時間；對照組一（4支）植入時亦刻意與牙根接觸，但植入後立即移除；對照組二（4支）植入時不與牙根接觸，並設定留置不同時間。實驗二以同隻實驗動物上顎兩側，探討受力狀態下迷你骨釘對牙根造成之影響。實驗組植入迷你骨釘1支於第三小臼齒之牙根分岔間，並使迷你骨釘與牙齒牙根接觸；對照組植入迷你骨釘1支於對側同樣部位，但使迷你骨釘不與牙齒牙根接觸。並拔除上顎兩側第二小臼齒。迷你骨釘植入三週後，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。實驗一及實驗二皆於24週後將動物犧牲。實驗三植入10支迷你骨釘，植入時皆刻意接觸牙根。實驗組以皮瓣包埋迷你骨釘頭部，對照組則將骨釘頭部露出。18週後將動物犧牲，量取卸除扭力。 實驗結果發現：（1）迷你骨釘若接觸牙根，可能造成程度不一之牙根傷害，骨釘孔洞周圍呈現顯著炎性反應。（2）若迷你骨釘未直接接觸牙根，但骨釘周圍有顯著炎性反應，鄰近牙根也可能出現不規則之發炎性吸收。此間接吸收現象於骨釘植入三週後即可發現。（3）牙根吸收處可能發生牙骨質修復反應。植入後三週內即可見此修復發生。牙根修復反應亦常表現在新生齒槽骨沿牙根缺損外形填入，並維持牙周韌帶寬度之恆定。（4）本實驗中成功之迷你骨釘皆未接觸牙根，周圍炎性反應少，骨釘周圍局部或大範圍與骨組織有直接接觸。失敗之迷你骨釘則多傷及牙根，骨釘周圍發炎反應嚴重，由一圈厚層軟組織包圍。鬆脫在三週內即可能發生。（5）當迷你骨釘接觸牙根時，骨釘頭部為軟組織包埋與否（迷你骨釘與口內環境相通與否），與骨釘卸除扭力並無顯著關聯。

Anchorage control is important in orthodontic treatment. Orthodontic implants, including miniscrews and miniplates, have drawn attention in recent years for values providing absolute anchorage to achieve diverse treatment goals. However, there are potential problems of damaging adjacent roots and their consequences during miniscrew insertion into alveolar regions. Therefore, miniscrew/root contact and the possible tissue response, including root repair, were investigated histologically in current study. Furthermore, whether complete soft tissue coverage of miniscrews would affect the miniscrew performance was also investigated. Two mongrel dogs were used. In experiment I, 12 miniscrews were surgically placed in the mandible. Among them, 4 miniscrews (experiment group) were placed with intentional root contact and were then retained for different time durations, 4 (control group 1) were also placed with intentional root contact but were removed immediately after insertion, and the rest 4 (control group 2) were placed without root contact and were retained for the same time durations as in experiment group. In experiment II, 2 miniscrews were placed in the maxilla to investigate the tissue response around the miniscrews and the adjacent roots when the teeth were under orthodontic force. One miniscrew of experiment group was placed with intentional root contact with upper third premolar, and 1 of control group was placed without root contact at the contralateral side. After extraction of upper second premolars , third premolars were then protracted with Ni-Ti coil spring attached to canines during week 3 to week 15. This animal was sacrificed after 24 weeks of experiment. In experiment III, 10 miniscrews were placed with intentional root contacts; half of them covered with gingival flap after insertion, and half of them kept exposed. The animal was sacrificed after 18 weeks and the removal torque of the miniscrews were measured at that time. Results: (1) The roots with miniscrew damage showed significant inflammation response of surrounding tissue. (2) Root resorption was observed occasionally even if the miniscrews did not contact with the roots directly. This kind of root resorption might be seen as soon as three weeks following miniscrew insertion. (3) Root repair was noted with cementoblasts lining along the resorption surface, which could be seen three weeks following miniscrew insertion. Alveolar bone filled into the lesion when the root damage was large so that the contour of alveolar bone followed that of the damaged root, with the width of periodontal ligament space kept constant. (4) Miniscrews with clinical success were largely those which had no direct contact with adjacent roots, showing little inflammation response in surrounding tissue and some extent of direct bone contact around the miniscrews. On the contrary, most of the failed miniscrews were those which had direct contact with adjacent roots, exhibiting severe tissue inflammation and being covered with thick layers of soft tissue. Failure of miniscrews could be seen as soon as three weeks after insertion. (5) There was no statistically significant relation between the soft tissue coverage of screw head and removal torque according to Mann-Whitney test and Kruskal-Wallis test.