| 摘要: | 矯正釘為齒顎矯正最常搭配使用的技術之一。矯正釘在植入齒槽後即可施加牽引力，矯正釘初期穩定度越佳則更能夠承受牽引力，進一步提高矯正釘成功率，因此初期穩定度相當重要。由於對矯正釘植入齒槽骨後難以進行受力情形追蹤，因此有限元素分析法被廣泛用於矯正釘初期穩定度的評估。齒槽骨與矯正釘表面間的壓配合應力對初期穩定度有重大影響，過去的文獻中對其他生醫植入物初始穩定度評估會在有限元素分析中設定壓配合應力，然而沒有文獻針對矯正釘初始穩定度的評估提出合理的壓配合應力設定方式。本研究將透過扭力實驗量測使矯正釘滑動的臨界力矩，藉以利用預壓力的方式來建立具壓配合應力的有限元素分析模型。並探討不同植入深度(5.2 mm、7.2 mm)旋入及旋出扭力實驗之力矩趨勢。在有限元素分析中，分別對有、無壓配合應力模型施加不同傾角與方位角的側向力以探討矯正釘及骨頭的生物力學響應，進行矯正釘初期穩定度評估。最後，比較及討論不同壓配合應力模擬方式之差異。本研究使用 2 mm 公稱直徑市售矯正釘，植入人造骨後產生滑動所需的力矩為 142.2 N⋅mm。有限元素分析模型中，要模擬此矯正釘與骨頭間的壓配合應力所需設定的預壓力為 135.5 MPa。分析結果顯示，相較於一般模型，有壓配合應力模型中矯正牙釘位移變為原本的 0.72 ~ 0.77 倍，而骨頭的應力與應變則是分別增加為 6.52 ~ 10.34 倍與 9.82 ~ 10.32 倍，其中應變數值大於 4000 με小於 25000 με此應變會影響骨整合但不會立刻破壞骨頭。有限元素分析時若不考慮壓配合應力，則骨頭應力及應變與矯正釘的初期穩定度會被低估。有、無壓配合應力模型在側向力傾角為 0°時皆產生矯正釘位移最大值。側向力傾角為 0°時骨頭等效應變、最大主應力、最小主應力皆大於側向力傾角為-30°、+30°者，無壓配合應力模型則無上述趨勢。此外，壓配合應力模型預壓力大小與作用位置的相關性弱。本研究之限制包括採用等向性材料性質、壓配合應力模型中預壓力大小對應到的應力鬆弛時間較短、預壓力作用位置與大小等，這些問題皆需要進一步探討。
;In recent years, mini-implants have been one of the most commonly used techniques in orthodontic surgery. Orthodontic force can be applied to the mini-implant right after the fixation on alveolar bone. As the primary stability of mini-implant becomes higher, the capability of force resistance will also increase, and this influences the success rate significantly. However, observing mini-implant fixation state after implantation is difficult, so finite element analysis has been widely used for mini-implant stability assessment.
Primary stability is significantly influenced by press-fit stress on the contact surface between alveolar bone and mini-implant. The studies showed the method sets up press-fit stress in primary stability assessment on a variety of biomechanical implants. However, there is no evidence showing standardized methodology to set up press-fit stress in mini-implant primary stability assessment. This study demonstrated the torque test to measure critical moment enabling mini-implant sliding in order to set up press-fit stress finite element analysis models by adding pre-stress, and discussed insertion torque and removal torque with different implantation depths (5.2 mm, 7.2 mm). Forces with different direction angles and elevation angles will be applied to finite element analysis models with and without press-fit stress respectively to gain insight into biomechanical response, and further assess mini-implant primary stability by comparing simulation results with different kinds of press-fit stress setup. The torque value causing commercially available mini-implants whose diameter is 2 mm to slide is 142.2 N⋅mm. The pre-pressure value, simulating the pressure between mini-implants and bone is 135.5 MPa. The results show that deformations of Mini-implants are 23 ~ 27% lower, stress of bone is 5.95 ~ 9.72 times greater, and strain of bone is 9.14 ~ 9.83 times greater in models with press-fit stress than in those without press-fit stress on average. The value of strain is greater than 4000 μ which will affect osseointegration in the long term, and smaller than 25000 μ which can prevent bone from immediate fracture. In particular, bone strain and stress, as well as mini-implant primary stability, are likely underestimated in models lacking Press-fit Stress. The maximum value of mini-implant deformation occurred at a 0° elevation angle in both models. Bone strain and stress maximum values are found to be greater in the 0° force elevation angle model than in the -30°+30° ones with press-fit stress. The trends were not found in models without press-fit stress, however. Besides, the correlation between pre-pressure and its location is weak. The limitations of this study include the usage of isotropic material properties; time of stress-relaxation is short corresponding to pre-pressure value in press-fit stress models; correlation of pre-pressure and its applied location. The above problems need to be further investigated. |
