酸蝕會對牙齒硬組織產生不可逆的影響，造成機械性質下降。對於酸蝕後的牙齒，需要一個能有效再礦化牙本質，以增加機械性質的治療方式。而可靠且符合生理環境測量牙本質機械性質的方法，是評估的前提。目前測量牙本質機械性質的方法，多使用乾的牙本質，結果也只反應牙本質內礦物質成份的含量。但這些測量無機體所得的機械性質，不一定反應生理及含水狀態下的性質。因此，本實驗的目的，可分為三個部份：(一) 比較不同的生理狀態(潮溼與乾燥的牙本質機械性質的差異。(二)評估不同的去礦化方式對牙本質性質的影響。(三)使用不同處理方式進行再礦化，並比較其再礦化後的機械性質差異。第一部分實驗採用人類牙本質，分別進行不同機械性質測試：微小硬度試驗機測量維氏硬度(Vickers Hardness)、以動態機械分析儀(DMA)與奈米壓痕機的潛變模式測量牙齒的黏彈性。第二部分實驗分別調配1%檸檬酸(pH=3)與37%磷酸(pH =-0.7)溶液以模擬酸蝕，測定去礦化牙本質的機械性質。第三部份再礦化材料包含模擬體液、自聚式玻璃離子體、三氧礦化物、及後兩者9:1與7:3混合物。測定再礦化牙本質的機械性質。此外亦使用電子顯微鏡觀察牙本質去/再礦化後的表面型態變化。在彈性模數的測量結果，使用DMA拉伸與壓縮所測得的值過低。使用奈米壓痕計與所得數值，校正前後約為20-30GPa近。而微小硬度機與奈米壓痕計所測量之硬度，在乾燥時的數值均比潮溼時大，但在奈米壓痕計，潮溼時的數值約為乾燥時的68%，較微小硬度機的93%低。在使用不同去礦化材料的實驗，其硬度下降量檸檬酸與磷酸分別約為35%與80%。在FE-SEM下可明顯的看出檸檬酸對牙齒去礦化的作用較徹底。在再礦化一個月後，模擬體液與玻璃離子體再礦化前後並無明顯差異，但玻璃離子體/三氧礦化物兩者9:1與7:3混合物有較明顯的硬度上升。在奈米硬度測試可見兩組的乾樣本硬度上升，潛變減少；但相較之下，潮濕樣本具有較低硬度與較高潛變。在FE-SEM的斷面上，亦可看出兩者的膠原纖維之間，出現板狀的礦物質結構，亦即有再礦化的現象。總結來說，在測量牙齒的機械性質方面，奈米壓痕計提供可信的彈性模數或是硬度測量。而微小硬度結果於乾樣本與奈米硬度相近，但可能高估濕樣本的硬度與彈性模數。使用檸檬酸作為去礦化的材料，不管在硬度上或是形態上，都比磷酸具有更顯著的去礦化作用。使用混合玻璃離子體與三氧礦化物的再礦化材料，不管在機械性質的提升，或是顯微結果的證據，顯示其具有再礦化牙齒表面的能力。本研究將有助於建立符合生理狀態的牙本質機械性質測量方式，並發展非侵犯性的牙本質修復方式。

Dental erosion is the progressive chemical dissolution of tooth which is not caused by microbial degeneration. Acid attack leads to an irreversible loss of structure and decreased mechanical properties of enamel and dentin. To remineralize dentin, a reliable and integral approach to evaluate dentin property should be established. The purposes of this study were, first, to compare dentin mechanical properties under different physiological condition (wet and dry). The second part was to evaluate the influence of different demineralization treatments on dentin. The third part was to remineralize mineral-depleted dentin with various remineralization agents and evaluate the mechanical property changes. In the first part, human dentin slabs were prepared. The mechanical properties of dentin slabs were separately examined with microhardness tester, dynamic mechanical analyzer, or a nano-indenter. In the second part, dentin receiving different demineralization treatments (1 % citric acid and 37% phosphoric acid) was examined for the change of mechanical properties. On the third part, various treatments were used on demineralized dentin, including simulated body fluid (SBF), glass-ionomer cement (G), and the mixture with the mineral trioxide aggregate (M) at G/M as 9/1 or 7/3 ratios. The morphology changes were evaluated under SEM and Fe-SEM. The elastic modulus obtained by the nanoindentation test were 20-30GPa, but was too low by DMA. Both the microhardness and nanohardness in dry condition were higher than in wet condition. The ratio of nanohardness in wet and dry condition was 68%, which is lower than 93% by microhardness. The decrease amounts in elastic modulus were 35% in citric acid group and 80% in phosphoric acid group. Both groups showed similar topography under SEM, but citric acid groups showed more exposed collagen fibers under FE-SEM. After remineralization, only G9M1 and G7M3 groups showed significant increase in hardness. Under FE-SEM evaluation, G9M1 and G7M3 groups showed characteristic of remineralization. In conclusion, the nanoindentation test is suitable for both elastic modulus and hardness in evaluating the mechanical property of dentin. The application DMA on dentin may need further evaluation. Microindentation test may overestimate the elastic modulus in wet dentin. The demineralization of citric acid was more apparent both in hardness and FE-SEM morphology. G9M1 and G7M3 groups induced remineralization both in hardness and FE-SEM morphology but did not complete recover the dentinal property. The investigation may provide valuable information for the examination of dentin mechanical properties.

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