探討不同脊椎動物牙齒琺瑯質微結構對微觀機械性質的影響

Exploring the Effect of the Microstructures of Different Vertebrata Tooth Enamel on Micromechanical Property

林耿鋒(Keng-Feng Lin)

指導教授 ： 鄭友仁

國立中正大學/工學院/機械工程學系/碩士(2012年)

摘要

從遠古的石器時代，人們就已經懂得以鹿角塑型製成工具。一直到現在，人類都深深地著迷於生物組織特殊的結構特徵及優異的機械性質。但許多生物組織結構需要微觀尺度的觀察，經由隨時空演進，顯微鏡技術與分析儀器的進步，我們能夠更進一步瞭解這些生物材料，甚至能夠以微觀的尺度量測和分析這些材料的化學組成、微結構特徵與機械性質，並將這些數據予於精確的圖像化。
為了探討材料組織的特性，我們透過奈米科技的發展及原子力顯微鏡（Atomic Force Microscope, AFM）及奈米壓痕（Nano-Indentation）、破裂韌性（Fracture Toughness）等微觀尺度檢測儀器的進步，以微觀力學觀察的途徑。本論文將透過AFM、Nano-Indentation和Fracture Toughness等方式量測，依其不同食性、生活方式及環境等分類，量測現生動物人類、牛、鹿、貓、海豚以及鱷魚等六種生物牙齒琺瑯質之硬度、楊氏係數、抗磨耗度等機械性質，再佐以其個別的琺瑯質的微結構特徵，探討生物在不同的食性、生活環境、使用方式等情況下，所導致牙齒在演化上之差異與生物演化上之關聯性。
經原子力顯微鏡(AFM)觀察表面形貌後，我們發現只有哺乳類動物琺瑯質微結構晶體呈規則排列的特徵，其中又以草食性哺乳類動物的臼齒在高冠齒化的過程中，結構晶體排列更緊密的堆疊，可強化其材料性質，故我們以奈米壓痕儀量測表面硬度，可發現明顯被強化其硬度值最高，硬度次1之為雜食性動物，最軟的為肉食性動物，在韌性量測上與硬度則呈現相反的趨勢。最後再對於琺瑯質之橫截面做硬度量測，可以發現哺乳類與DEJ至牙齒表面的距離呈梯度變化，與DEJ距離有正相關，反之非哺乳類則沒有此關聯，我們將數據以線性趨勢法求出線性斜率，可觀察出草食性哺乳類動物的高冠齒琺瑯質截面的材料性質變化率比其他雜、肉食哺乳類動物琺瑯質來的大，其斜率大小與表面硬度同現象。

關鍵字

琺瑯質 ； 微結構 ； 脊椎動物 ； 力學性質

並列摘要

Various animals have different dietaries and lifestyles; these might cause the variations of evolution of teeth. As one of the most important organ for dietary, teeth are valuable bio-composites. Tooth enamel is the hardest and most highly mineralized substance of mammals. This study aims to relate the bio-mineralized microstructures of various vertabrata dentition of variations to their mechanical properties.
The developments of nano-scale measuring instruments such as Atomic Force Microscope (AFM), Nano-Indentation and Fracture Toughness provide powerful means to understand the characteristics of bio-composites. From different dietaries, this study chose six animals- human, cattle, deer, cats, dolphins and crocodiles. Nano-scale measuring instruments such as Atomic Force Microscope (AFM) was used to investigate morphologies. Nano-Indentation was used to the mechanical properties such as hardness and toughness of the tooth enamel.
The findings show that the enamel of amniota exhibit orderly architectural structure as compared to non-amniota and they lead to higher hardness. Herbivorous mammal molars have highly densed orderly architectural structure then carnivorous mammal molars and higher proportion of protein between rods arrangement of the herbivorous mammal molars. As a result, the hardness herbivorous mammal molars display higher hardness. In addition eating herbage cattle is higher than that of bark eating the deer. Our measurements of the cross-section of enamel from tooth surface to DEJ show that higher gradient of mechanical property of herbivorous mammal molars may contribute to their stronger mechanical property. The trend of fracture toughness is contrary to the surface hardness.

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