積層製造仿生元件之模擬與結構最佳化

Abstract

牙釘植體是一種仿生醫療器具，除了被用來修復因缺牙而導致牙齒功能喪失之外，亦被廣泛的運用於骨折的治療。為了使植體能擁有長時間的療效，必須將其緊實的固定在骨頭中以抵擋外力。目前已有許多有限元素法研究指出，植體表面與周圍骨頭間接觸區域的設計可影響並刺激骨生長，其中，兩關鍵要素：細胞附著情形及生物力學刺激的影響，可以預防骨吸收與並進而增加骨生長。故能刺激周圍骨生長的植體設計即為本論文所提出的重要主題之一。 因為植體外觀的設計可以使牙釘植體獲得較高的穩定性，因此，我們模擬了許多不同的牙釘植體以進一步評估可用來固定螺釘的最佳形狀。在本論文中，植體的設計主要由四個參數所控制，包含：牙釘植體及螺紋兩者分別的高度和半徑。因此，我們透過ANSYS有限元素分析軟體來建構自動化的3-D模型，進而模擬其力學行為。此外，為了進一步探討不同植體設計下的骨生長情形，我們分析牙釘最大彈性應力、應變分佈和周圍骨的位移，並進一步使用Wolff’s Law將周圍骨頭的健康狀態分類為無用、自適應、可修復及超載四個區域，來分析植體周圍骨頭的生物力學行為。為了方便分析，我們利用MATLAB軟體來建置圖形化介面繪製出3-D反應曲面圖以比較不同牙釘植體設計對於骨整合的影響。 由於不同外形的牙釘植體會影響到周圍骨頭的應力狀態，因此，我們進一步分析一種由工研院新研發的T形牙釘植體，此種新設計的牙釘植體相關資訊非常稀少，因此我們利用一種計算模型，概念源自Wolff’s Law對於骨頭重整的定義，進一步將其用來設計T形牙釘植體的復原腔室。目前的研究結果亦可擴展到其他的醫療器具。不僅如此，T形牙釘模擬的結果也與International Team for Implantology (ITI)的牙釘植體復原腔室做比較。 因此，本論文包含了兩個對仿生醫學裝置的主要研究: (1)骨頭重整的數值化計算模型和 (2)牙釘植體的外型最佳化設計。其結果可證明何種仿生醫療器具可擁有較佳的骨長入情形且有效的降低應力遮蔽效應，進而改善植體長期植入的穩定性。

Dental implants are biomimetic medical devices applied to recover the function caused by the loss of one or several teeth. They have been also widely used for fractural bone treatments. To reach successful function for the long time, the dental implants must be well fixed into the bone to be able to resist the external forces. Theoretical finite element studies have demonstrated that a contact region between the implant’s surface and surrounding bone can be designed to induce optimal biomechanical stimulation for bone formation. Cell attachment and biomechanical stimulation are key factors to prevent bone resorption and afterward to gain bone. The design of the bones surrounding the implant’s surface that stimulates bone growth is one of the main subjects presented in this thesis. The main factor to obtain high anchorage stability is the implant’s design. Thus, different dental implant models were created for the further evaluation for the best shape to fix the screw. In this thesis, the implant design includes four optimized parameters, such as: length and width of the implant body with different shapes of the thread. Therefore, the finite element analysis (FEA) software ANSYS 15.0 was used to automatically build three-dimensional (3-D) geometries to simulate their mechanical behavior. Besides, Wolff’s Law was used to analyze biomechanical behavior at the surrounding bone for further investigation of the bone remodeling due to different implant designs. Results were collected as a volume at disuse, adaptive, repair and overload regions, total volume of the bone; maximum elastic stress, strain distribution and the displacement in surrounding bones. Graphic user interface was created by MATLAB software to build 3-D surface contour and to show how different implant designs influence the osseointegration. Stress conditions around an implant can also be improved by selecting an appropriate implant’s shape. Therefore, a new shape was taken to analyze its biomechanical behavior, such as T-shape dental implant. Also, information about this shape of the dental implant is insufficient. A numerical method of the bone remodeling process at the implant’s surrounding surface was applied to the T-shape dental implant. Theoretical methods of the bone remodeling were described. The concept of this numerical model was from the definition of bone remodeling according to Wolff’s Law. Next, this method was applied to design healing chamber of T-shape dental implant. The result of the current work can be extended to other medical devices. Moreover, a numerical model for T-shape implant design was taken into account and compared with the International Team for Implantology’s (ITI) dental implant’s healing chamber. Thus, the present thesis contains two main topics of importance for biomimetic medical devices: i) numerical model based on the bone remodeling and ii) shape optimization of dental implants. This can demonstrate which biomimetic device can allow more bone ingrowth, efficiently reduce stress shielding effect, and therefore may improve long-term implant stability.