牙釘周圍骨頭癒合之細胞分化模型

Abstract

牙釘在近年來被廣泛的使用於恢復牙齒本身的功能。然而，植牙手術後若失敗會影響到牙齒的復原狀態。如果牙釘植入牙齒後鬆脫搖擺而非穩固的卡在齒槽，可能會使得植牙手術的失敗率大大上升。初級穩定性是影響植牙後手術失敗率的一大因素。若植牙後的早期恢復狀態不佳，會導致骨長入的效率以及骨整合較差，同時也容易使得軟組織層生成於牙釘和齒槽骨之間。上述的情形均為植牙後牙釘鬆脫的可能原因。因此，本研究將探討植牙後周圍骨頭癒合的情形與手術失敗原因的關係。 研究中我們將使用細胞分化演算法並以有限元素法模擬作為我們的研究方式。該演算法中提及，影響細胞分化的刺激可分為固相及液相層面。透過此兩種刺激的結果數據再經由演算法公式運算，即可推得接下來該細胞的分化結果。 由於骨頭屬於一種孔洞材料，因此研究中我們將使用多孔彈性材質作為骨頭建模的元素並進行模擬。為了驗證我們建立的數值化模型是正確的，且又為了節省計算資源以及加速模擬的時間，我們先使用二維軸對稱模型進行建模。模擬的狀態為將牙釘植入獵犬齒槽骨並觀察其周圍骨癒合情形。為了與文獻中的實驗進行比較驗證，模擬的時程設定與實驗觀察的天數相同。研究結果顯示，我們模擬出的骨頭分化預測結果與實驗結果有極為相似的骨生長特徵。在模擬時間第21天之前，我們觀察到在初期植入牙釘後的周圍骨癒合會長出一層薄的軟組織層，然而在癒合時間過了21天之後，隨著骨頭成長提供的支撐力，軟組織也漸漸消失並分化為骨頭。 在二維數值化模型被成功驗證之後，為了解決二維模型方向性過於簡化問題，或為了研究更複雜的牙釘如：孔隙牙釘，我們將二維模型的演算法進行修改並發展出三維的數值化模型。在我們建立三維數值化模型之後，我們設計了兩種具有不同孔隙狀態的牙釘進行模擬並預測周圍骨頭生長的情形。此兩種孔隙牙釘是利用雷射積層製造的方式製作出來的Ti6Al4V牙釘，並進行動物實驗，以便與我們模擬的結果進行比較。在比較模擬與實驗結果時，我們可觀察到相似的骨頭生長特徵，同時也驗證了我們的三維數值化模型。根據這些結果，本研究開發並驗證了細胞分化演算法，其可以成功的用來模擬牙釘周圍骨頭生長的情形，並可對骨釘外形設計給予建議。

The dental implant is widely used to recover the function of the teeth. However, the surgery failure rate is influenced by the recover conditions. If the dental implant is loose rather than fixed, the likelihood of surgery failure might raise. The primary stability is one of the reasons for the surgery failure. If the recovery situation of the early-stage is poor, it may lead the worse bone in-growth ratio and osseointegration. Also, the fibrous-cartilage layer may grow between the implant and bone which can also cause the loose of dental implants. The mechano-regulation model is considered in the current study. The stimuli of the model are solid phase and fluid phase. The cell type is regulated by different criteria. Based on the porous material properties of the bone, the poroelastic material is used in 2D axisymmetric geometry. We used these model and geometry to simulate the bone healing in the beagle dogs. The time-course of cell diffusion is set the same time as the experimental data in the literature. In the simulation result, we can get similar features compared with experimental results. For example, a wavy layer of fibrous tissue forms in the beginning of the simulation. Then, the cell is getting mature gradually. On the 21th day, the bone resorption occurs between the implant thread having good agreement with the experimental results. After the success of 2D numerical model, we modified the algorithm and developed the 3D numerical model in order to simulate the bone healing around dental implants with more complicated geometry. Two additive-manufactured dental implants with the different porous style are studied in the current study. Then, we used our numerical model to study the bone healing around these two implants and compare with the results obtained from the animal tests. Our three dimensional numerical model is also verified and prove that the implant has greater size of porous giving better healing pattern and shorter healing time. The cell- differentiation method can accurately predict bone healing around the dental implant and provide design guideline for implant.