評估矯正治療中運用迷你骨釘穩定性及危險性

Abstract

壹、中文摘要 隨著社會經濟發展及美觀要求增加，牙齒矯正之需求日增。在矯正治療中，控制牙齒的移動是成功矯正的決定因素。尋找良好的錨定，一直是矯正醫師最大的難題。近年來在矯正治療中，以迷你骨釘與迷你骨板提供矯正錨定作用，已受到相當的重視。而迷你骨釘植入齒槽骨後是否對鄰近牙根造成潛在性傷害，是我們關心的問題。 本研究第一部分計畫利用動物實驗模擬與臨床相似的狀況，設計實驗來探討迷你植體於手術時可能對牙根造成的影響。實驗中共計有84根迷你骨釘（直徑2.0公釐、長度11公釐）植入6隻實驗狗上下顎齒槽骨中，並每隔三星期實施骨頭標定。實驗一依不同時間點將迷你骨釘植入下顎齒槽骨，使骨釘接觸或不接觸牙根。實驗二則將迷你骨釘植入上顎牙齒PM3牙根間，使骨釘接觸或不接觸牙根，並於犬齒及牙齒PM4施予150g力量移動牙齒。收集迷你骨釘植入扭力、卸除扭力、每隔3星期臨床檢查、組織學變化資料並加以分析。 實驗結果顯示：（1）下顎比上顎迷你骨釘有較大植入扭力，接觸牙根比沒接觸牙根迷你骨釘有較大植入扭力。（2）卸除扭力在牙齒接觸情形、迷你骨釘動搖度及植體存留時間（3星期與24星期間）有統計學差異。（3）接觸牙根的迷你骨釘有較高的骨釘失敗率。（4）組織觀察：失敗的迷你骨釘周圍被厚薄不一軟組織包圍並有發炎反應。當發炎反應存在會造成附近牙根吸收。而在螢光顯微觀察下亦可發現被吸收牙根會有修復作用產生，如含細胞牙骨質產生硬組織沈積。 本研究第二部分為收集臨床使用骨釘矯正病患相關資料及卸除扭力，以探討可能影響卸除扭力的因素。在實驗中共有20位病患及35支迷你骨釘卸除扭力及骨釘相關資料被收集分析。實驗結果顯示，75%迷你骨釘卸除扭力數值大於0.5kgcm。此外，下顎骨釘卸除扭力比上顎數值高，且有統計學差異，而年齡、性別、骨釘長度、骨釘留置時間及施力等待時間與卸除扭力無明顯相關。

Abstract With more psychosocial and facial concerns, there is an increasing demand for orthodontic treatment to improve facial esthetics, speech, and chewing function. The success of orthodontic treatments relies on the precision of tooth movement with proper anchorage control. Recently, implant anchors such as miniscrews and miniplates have been used for absolute anchorage during orthodontic treatment. However, the potential problem of damaging the adjacent roots while mini-implants placement is a major concern. Therefore, we use animal experiments simulating orthodontic tooth movement to evaluate the risks of placing the miniscrews. Eighty-four miniscrews were surgically placed in maxillary and mandibular alveolar bone at each side of 6 adult beagle dogs with metabolic bone labeling at three-week intervals. In experiment 1, the miniscrews were placed, retained for different time points and then removed in mandibular area with or without hitting the adjacent teeth. In experiment 2, a NiTi coil for orthodontic force (150g) was used to pull the maxillary fourth premolar (PM4) and the canine towards each other for 6 months after a miniscrew was placed in the furcation of PM3 with or without intentional root damaging. The insertion torque, clinical measurements every three weeks, the removal torque, and the histological findings were analyzed. In the animal study, we demonstrated that (1) the values of insertion torque were significantly higher in the mandible than those in the maxilla. The miniscrews contacting with the roots showed a significantly higher insertion torque than those without contact. (2) For removal torque: there was a significant difference of the removal torque measurements for the following variables: the mobility of miniscrew, the state of root contact, and the duration of miniscrew in place (3 weeks vs. 24 weeks). (3) The miniscrews contacting with the root was at greater risks for failures. (4) From histological findings: the failed miniscrews were surrounded with more soft tissue with inflammation. When more inflammation was present, it seems that the adjacent roots experienced more surface resorption. However, some of the inflammation induced root resorption could be repaired with surface deposition of mineralized tissue, likely the cellular cementum, or being partially filled with alveolar bone, both labeled with fluorophore markers. The other purpose of this study was to measure the removal torque of the immediately loaded miniscrews in orthodontic patients after clinical usage and to find the possible factors associated with this value. From twenty patients with malocclusions, 35 miniscrews were removed and the removal torque was measured with a torque gauge. Removal torque values were subjected to statistical analysis for possible association of different clinical characteristics. The removal-torque value of 75% miniscrews was above 0.5kgcm. These values were significantly higher in the mandible than those in the maxilla. However, we could not detect a significant association between the removal-torque value and the following variables: age, gender, screw length, healing time and time in function. For uprighting tipped molars using anchorage from miniscrew, excessive torque in the counterclockwise direction may loosen it. From our measurement, the miniscrews should be able to sustain an uprighting moment in order for a more precise tooth movement.