以動物實驗探討不同方向扭力對迷你骨釘卸除扭力的影響

Abstract

迷你骨釘不同於傳統的贗復植體，植入後達到一定的初級穩定度時，便可以在臨床上立即施力，或是早期施力。新式的迷你骨釘在頭部設計成矯正器溝槽或是有方孔的設計，臨床上透過片段彎製的矯正弓絲，將弓絲綁在矯正器溝槽或是穿過方洞，做三度空間牙齒移動的控制。此時對於迷你骨釘本身會產生一扭力，但這扭力大小及方向是否會造成迷你骨釘的鬆脫，目前並無明確的答案。本研究即利用動物實驗，模擬在口腔內的迷你骨釘受到扭力的情形，了解此扭力是否會影響迷你骨釘的穩定度。 本實驗取三隻小獵犬為研究對象，分別在不同區域設計給予迷你骨釘不同方向的扭力。設計的實驗裝置給予後方迷你骨釘一扭力，左側設計給予順時鐘方向扭力，右側設計給予逆時鐘方向扭力。實驗中共計有80根迷你骨釘（直徑2.0公釐、長度11公釐）分別植入上下顎犬齒至第一大臼齒齒槽骨間，裝置作用後會給予後方迷你骨釘一扭力，並每隔三星期實施骨頭標定。前兩隻狗實驗時間為六個月，後一隻狗實驗時間為七個月。記錄植入前每支迷你骨釘的植入扭力，動物犧牲時紀錄其卸除扭力及裝置作用的時間。動物犧牲後將骨釘及其周圍骨頭樣本取下，並以樹脂包埋切片，以顯微鏡觀察骨釘周圍組織變化。透過統計多變項迴歸分析方法，針對卸除扭力、植入扭力、組織學觀察的結果加以分析。 實驗結果主要分成兩個部份:1.臨床結果：（1）黏在迷你骨釘上之矯正器,部份因施予扭力造成角度旋轉。(2)實驗組與對照組的迷你骨釘卸除扭力於統計學上雖無差異，但隨作用時間增長，其兩組迷你骨釘之卸除扭力均隨之增加。（3）給予迷你骨釘不同方向扭力，其卸除扭力比較在統計學上無差異。（4）下顎迷你骨釘之植入扭力顯著大於上顎區域。 2.組織學結果:（1）迷你骨釘與骨頭組織接觸介面中，骨釘尖端位置具有較高之骨組織接觸比例。(2)有作用力的實驗組，標定螢光綠骨頭組織在迷你骨釘周圍表現較明顯。

Miniscrews, which are different from traditional dental implants, can be loaded immediately or quite early after primary stability established. New design of its head structure , with a bracket slot , tube, or hole, can be connected to a sectional wire in order to achieve three dimenisional control of tooth movement during orthodontic treatment. However, this mechanical design would give a moment, which may endanger the stability of the miniscrews. Therefore, we used animal experiments to simulate this type of loading on miniscrews to test its effect on the miniscrew stability. Eighty miniscrews (2.0mm diamter, 11mm length) were surgically placed in maxillary and mandibular alveolar bone between canine and first molar in 3 adult mongrel dogs. At each quardrant, we bonded the brackets on the posterior miniscrews. At left side, we gave a clockwise moment to the posterior miniscrew by cantilever arm devices. At right side, we gave a counter-clockwise moment to the posterior miniscrew. The total experimental time was six months in dogs A and B, and seven months in dog C. Each dog was given metabolic bone labeling at three-week intervals. Clinically, we recorded the insertion torque, the removal torque and loading time of each miniscrews before animals sacrificed. In order to observe the tissue changes at interface of bone and miniscrews, samples were embedded with resin and sectioned with microtomes, and the results were evaluated under a microscope By multivariate logistic regression method, parameters from clinical data and histological results were analysed for their influences on removal torque. Clinical data showed: 1) In some areas, the brackets on miniscrews were rotated gradually by the given moment. 2) There was a significant positive correlation between the loading time of miniscrews and the removal torque, but not the other variables. 3) There was no significant difference in the removal torque between the clockwise- and counter-clockwise groups. 4) The values of insertion torque were significantly higher in the mandible than those in the maxilla. Histological finding showed:1) Higher bone to implant contact (BIC) ratio was found towards the tip of the miniscrews. 2) In experimental loading group, there seems to be more flurorence labeled bone tissue surrounding the miniscrews.