機械張力對矯正迷你植體失敗率與MG-63類骨母細胞活性的影響

Abstract

近年來，應用迷你植體所發展出的齒顎矯正新式治療已經為傳統技術增添全新樣貌。傳統齒列矯正治療經常利用後牙、鄰牙或口外裝置作為矯正錨定，以避免治療過程中發生不符合治療目標的牙齒移位。迷你植體錨定是指在患者的顎骨或齒槽骨選擇適當區域植入迷你骨釘或迷你骨板等迷你植體，藉以提供穩定的骨性錨定，如此可完全取代傳統矯正錨定。迷你植體的優點包括可立即受力、毋需患者合作、可提升治療效率、增進成年患者接受治療之意願。植入迷你骨板需翻辦手術且術後傷口難免腫痛，迷你骨釘的植入過程則相對簡易，因此迷你骨釘的應用與研發逐漸成為矯正迷你植體的主流。迷你植體錨定可大幅擴展矯正牙齒移動範圍，極可能突破傳統治療極限，本研究首先擬評估應用迷你植體錨定及固定矯正裝置進行上顎大臼齒壓入治療的效果。在矯正治療受力過程中，多數迷你植體能成功做為穩定之骨性錨定，但也有可能發生鬆動終至失敗，若能探討相關原因並適當改善臨床流程，將有助於增進迷你植體錨定之穩定性，因此本研究也將探討影響迷你植體失敗率的臨床因素。如上所述，穩定之骨性錨定可持續抵抗矯正力量之反作用力，但是矯正醫師也須避免施力過當的風險，矯正力量過大可能傷害牙周與迷你植體周圍的骨組織及骨細胞，本研究的第二部份將透過精確控制細胞受力條件的體外實驗模式，探討高度張力刺激對於類骨母細胞的生長活性及細胞分裂週期之影響。 材料與方法: 本研究收集22位患者治療前後的上顎牙齒模型，以三維數位儀分析上顎大臼齒壓入治療的位移變化。迷你植體失敗率研究則是以回溯性方式收集323患者所使用共計851支迷你植體的資料，依序建置2個資料庫(分別為359支植體/129患者，492支植體/194患者)，以統計各種迷你植體失敗率並透過單變項分析檢測各項關於患者特徵、迷你植體本身、及植入過程的因素是否與迷你植體失敗率有所關聯，再進一步以多變項邏輯式迴歸分析探討可預測迷你植體失敗率的顯著因素。至於細胞受力實驗，則是將MG-63類骨母細胞株培養於具伸縮彈性的培養皿，施以周期性張力刺激(15%, 0.5 Hz) 24或48小時，再檢測細胞活性及細胞分裂週期變化，另以RT-PCR技術分析與細胞分裂週期及細胞自我凋亡有關的基因表現。 結果: 本研究分析22位患者合計43個上顎大臼齒與32個小臼齒治療前後的三度空間位移變化，結果證實迷你植體能有效率地完成上顎後牙過度萌出之絕對壓入治療，直接受力的第一大臼齒壓入程度平均達3mm以上。迷你植體的統計結果: 迷你骨板失敗率低於5%，迷你骨釘失敗率依其種類而異(10% ~25%)，第一個資料庫的單變項分析結果顯示下列因素顯著影響迷你植體的失敗率: 患者年齡、迷你植體種類、迷你植體種植位置、應用迷你植體進行的牙齒矯正移動型式，而多變項邏輯式迴歸分析則發現當患者年齡較輕、迷你植體種類為骨釘、種植於下顎骨，三項因素之存在皆可預測迷你植體失敗風險將顯著升高。本研究的第二個資料庫分析結果也顯示迷你骨板的失敗率明顯低於純鈦預鑽迷你骨釘及不鏽鋼自鑽迷你骨釘，單變項分析發現下列情形之迷你植體失敗率明顯著較高:迷你骨釘為自鑽型、使用於牙齒扶正、種植處骨密度較低、迷你骨釘周圍軟組織發炎、植入三週內即開始受力。多變項邏輯式迴歸分析則顯示迷你植體周圍軟組織發炎及迷你植體植入三週內即開始受力，是迷你植體失敗風險大幅升高的最顯著因素。此外，本研究經由細胞受力實驗證實高度張力刺激對MG-63類骨母細胞的生長活性所造成之傷害: 不僅細胞分裂增生受抑制，同時也造成細胞週期停滯、細胞自我凋亡，以及調控細胞分裂之基因表現降低。 結論: 迷你植體錨定確實能取代傳統矯正錨定，擴大牙齒矯正移動範圍，有效達成上顎大臼齒絕對壓入之矯正移動。探討影響迷你植體失敗的相關因素將有助於臨床醫師防範未然以降低其失敗率；雖然迷你骨板的失敗率低於迷你骨釘，但植入及取出過程皆需進行翻瓣手術。使用穩定之迷你植體作為骨性錨定時，矯正醫師更需謹慎控制矯正力量大小，以避免過大力量刺激加諸於牙齒及迷你植體周圍骨細胞的傷害效應。

Background/purpose: Mini-implant anchorage have expanded the envelope of orthodontic tooth movement and broadened the therapeutic spectrum in orthodontics. However, mini-implants failure due to loosening during orthodontic loading remained the problem and the determination of specific clinical features that affect the stability of mini-implants has become crucial. The first part of this study aimed to investigate the envelope of intrusive movement of maxillary molars in patients treated with fixed orthodontic appliances and mini-implants anchorage, and to retrospectively explore possible factors affecting the success and failure rates of orthodontic mini-implants. Mechanical loading provides an anabolic stimulus for bone. However, heavy force loading may exert excessive stress on the bone tissue surrounding mini-implants. The second part of this study aimed to examine the effects of high-level mechanical tensional force on the growth and cell cycle progression of osteoblast-like MG-63 cells in vitro. Materials and Methods: The pre-treatment and post-intrusion dental casts were digitized and analyzed using a 3-D digitizer to quantitatively assess the intrusive movement of 43 maxillary molars and 32 premolars. To investigate the failure rate of mini-implants, two databases were sequentially built-up by collecting the records of 851 mini-implants in 323 patients. The first database included 359 mini-implants (miniplates, miniscrews, and microscrews) in 129 patients. The second database included 492 mini-implants (miniplates, pre-drilling miniscrews, and self-drilling miniscrews) in 194 patients. Many clinical factors potentially associated with mini-implant failure were checked with univariate analysis, followed by multivariate forward stepwise logistic regression. In the part II study, osteoblast-like MG-63 cells were seeded onto flexible-bottomed plates and subjected to cyclic mechanical stretching (15% elongation, 0.5 Hz) for 24 and 48 h in a Flexercell FX-4000 strain unit. Cellular activities were measured by an assay based on the reduction of the tetrazolium salt, 3,[4,5-dimethyldiazol-2-yl]-2,5-diphenyl tetra-zolium bromide (MTT). The number of viable cells was also determined by trypan blue dye exclusion technique. Cell cycle progression was checked by flow cytometry. mRNA expressions of apoptosis- and cell cycle-related genes (Bcl2, Bax, cdc2, cdc25C, and cyclin B1) were analyzed using an RT-PCR technique. Results: The mean intrusive movement of the maxillary first molars was 3 to 4 mm with a maximum of over 8 mm. For the adjacent maxillary second molars and second premolars, the amount of intrusion was 2 mm and 1-2 mm, respectively. There was a significant difference among the failure rates of miniplates, miniscrews, and microscrews. The statistical results of the first database showed that the failure arte of miniplate was obviously lower than those of microscrews and miniscrews. Greater risks for failure were found in younger patients, when an implant was placed for retraction/protraction, when it was placed on the mandibular arch, when it was placed posterior to the second premolars, or when using the miniscrew/ microscrew systems. After adjusting for potential confounding effects, only 3 factors (type of mini-implant, placement on the mandibular arch, and age) were found to be statistically significant in predicting mini-implant failures. The analysis of the second database revealed that there were no significant differences in failure rates among the mini-implants for the following variables: facial divergency, location (anterior or posterior), arch (upper or lower), type of soft tissue (attached gingival or removable mucosa), and most of the cephalometric measurements which reflect dento-cranio-facial characteristics. An increased failure rate was noted for the self-drilling miniscrew, those for tooth uprighting, those inserted on bone with lower density, those associated with local inflammation of the surrounding soft tissue, those loaded within 3 weeks after insertion, and those placed in patients with greater mandibular retrusion. As to the cell culture study, the number of viable cells significantly decreased in osteoblast-like MG-63 cells subjected to mechanical stretching for 24 or 48 h. The MTT activity of stretched cells did not change at 24 h, whereas a significant decrease was noted at 48 h in comparison to the unstretched controls. The flow cytometry showed that mechanical stretching induced S-phase cell cycle arrest. Furthermore, exposure to mechanical stretching may lead to apoptotic cell death, as shown by the increase in the hypodiploid sub-G0/G1 cell population. Moreover, a decreased cdc25C mRNA level was consistently noted in stretched cells. Whereas, the mRNA expressions of Bcl2, Bax, cdc2, and cyclin B1 genes were not significantly altered compared to unstretched control cells. Conclusion: A combination of mini-implants anchorage and fixed appliances is a predictable and effective orthodontic procedure to intrude over-erupted maxillary molars. The logistic regression model revealed that severe inflammation of the surrounding soft tissue and early loading within 3 weeks after insertion were most significant in predicting mini-implant failure. The stability of miniplate was superior to those of pre-drilling or self-drilling miniscrews. However, the application of miniplate requires flap surgeries for implantation and for removal. Therefore, selection of the proper type of mini-implants should be based on the treatment needs of each individual patient. In vitro study revealed that high-level mechanical stretching induced cell cycle arrest and apoptotic cell death in osteoblast-like MG-63 cells. It suggests that heavy tensional force is a negative regulator of osteoblastic activities, thus should be minimized in orthodontic/orthopedic treatment using stable mini-implants anchorage.