人類的自然牙主要是由牙釉質(enamel)與牙本質(dentin)所構成，兩者之材料特性皆屬於非等向性、非均質。現今牙科廣泛運用的補綴材料如樹脂、陶瓷、氧化鋯等，其材料特性多為均質且等向性的，無法確切地呈現自然牙原本的特性。牙科目前常見具非等向性系統的材料為纖維強化樹脂(fiber-reinforced composite, FRC)，臨床上通常應用在固定式局部補綴物(fixed partial denture, FPD)，提供了強度與剛性，但現階段仍沒有在單顆牙冠上的臨床應用。
本研究假設具非等向性的牙科材料且經適當排列可以提升贋復體的力學表現。在有限元素法模擬的模型設計上採用複合材料與人牙牙本質結合，樣本組別以不同纖維緊密排列區分成橫向、縱向兩組。以不銹鋼材質壓頭施予一負載應力以觀察樣本受力的變化。力學測試於萬用材料測試機上採用ball on ring的方式進行並同時施以音洩檢測以了解材料內部結構發生變化的即時狀況。
模擬結果顯示(一)經由適當排列的實驗組比起對照組其最大主應力結果都有降低的現象(二) 「FRC縱向排列」的組別其應力表現優於「FRC橫向排列」。力學試驗結果顯示：Z350與Dyract flow兩種樹脂製備之「無FRC」之樣本組別，其音洩參數「累積撞擊」、「最大負載」皆優於「含有FRC」之組別。而同樣含有FRC之組別相比，Z350「FRC縱向排列」的結果優於「FRC橫向排列」，Dyract flow組別則無明顯差異。造成數值模擬與力學實驗結果趨勢不同，認為原因其一是來自於樣本製備過程的瑕疵，使得樣本內部含有氣泡，降低整體的強度；其二，由於模擬之數值模型與實際實驗之樣本，纖維的排列緊密程度有差異，造成力學試驗時，含有纖維之樣本，反而比較早破壞。

The structures of natural teeth are composed of enamel and dentin. Both of them are anisotropic and heterogeneous. The anisotropy of enamel comes from the “hierarchical structure” and the different arrangement of enamel rods. Also the distribution of dentinal tubules and their spatial arrangement make dentin anisotropic. Most dental materials such as resin, ceramic or zirconia are homogeneous and isotropic, which can not fully mimic dentin and enamel. Fiber-reinforced composite (FRC) is one of the materials with anisotropy. It is often used for fabricating the substructure or framework of fixed partial denture (FPD) clinically to enhance mechanical performance. However, FRC system has not been applied on a single crown.
The present project was divided into two parts: Finite Element Analysis and the in vitro experiment. We hypothesize that the mechanical performance of a structure can be improved by introducing anisotropy of appropriate arrangement. The material properties of FRC composite and human dentin were assigned to the parts. Two models with different FRC arrangements were considered: parallel and vertical to the outer surface. The model with fully anisotropic material properties was set as the control group. An indenter of stainless steel was created as loading apparatus and the pressure load was applied to its top surface. The bottom of the model was fixed and the indenter was confined to move in the vertical direction only. For in vitro experiment, the specimens made by Z350 and Dyract flow were tested using the manner of “ball-on-ring” (BOR) test. Acoustic emission (AE) signals were captured to identify the occurrence of material damage.
Simulation results showed that the maximum principal stress of both longitudinal and transverse arrangement groups were higher than control groups. And the mechanical performance of longitudinal arrangement groups were better than transverse groups. The results of mechanical tests of “no fiber” groups showed that the cumulative hits were lower and the maximum load were higher of “no fiber” groups were better than “with-fiber” groups. Focused on the with-fiber and groups, Z350-Longitudinal group had better performance than Z350-Transverse group. However, the results of testing groups obtained from Dyract flow group did not show significant difference.
According to the results, the numerical simulation results were consistent to the hypothesis. While the trend of mechanical experiment results were unmatched to the numerical simulation. The reason of this phenomenon can be attributed to: 1) the preparation of specimen. 2) the difference of material properties. 3) the difference of loaded area in simulation model and test specimens.

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