- 學位論文
由各種脊椎動物牙齒琺瑯質之機械性質來探討生物礦物化材料優異性能的線索
Exploring the Bio-mineralized Microstructures and Mechanical Properties of Various Vertebrata Dentition: Lesson from the Evolution
摘要
人類牙齒琺瑯質由微量的蛋白質及較多的氫氧基磷灰石所組成，這樣具有黏彈性的有機物及堅硬的無機物以微觀的方式所組成的材料卻能形成又硬又韌又有彈性的牙齒，令人對其複合方式深感好奇。目前人類尚未研究出同時具有如此優秀特性的複合材料，但大自然卻早已發展出具有如此結構的生物組織-牙齒，若能探討人類牙齒具有如此優秀機械性質的原因，必能對前瞻複合材料的研究有極大的貢獻。 經由先前的研究發現人類牙齒琺瑯質表面由許多的重複微結構-釉桿柱所組成，而量測琺瑯質橫截面時亦發現其具有功能梯度的特性，使之在抵抗撞擊的同時又能有效分散能量，防止牙齒碎裂。先前的研究已觀察出牙齒具有如此優異的機械性質，但單單觀察人類牙齒卻不足於探討形成牙齒具有如此優異性質的原因。因不同生物的牙齒可能會因食性、生活環境及使用方式的不同，而造成個別琺瑯質之微結構特徵有所差異，根據這些不同結構所形成的不同機械物理特性可以為前瞻工程材料的發展提供線索。因此本研究選擇二趾樹櫴、北美負鼠、臭鼬、斑鬣狗、美洲黑熊、羊駝、白鯨、水獺、蝙蝠、鮭魚、牛、鹿、人、貓、海豚、鱷魚等十六種不同的動物牙齒，研究琺瑯質表面微觀形貌及橫截面的機械性質，比較彼此之間的差異性，探討牙齒微觀組織具有優秀機械性質的原因。 要觀察琺瑯質有機物與無機物的複合情形，須以微觀的量測儀器方可做到[1,2]，因此本實驗將透過原子力顯微鏡(Atomic Force Microscope, AFM)、奈米壓痕儀(Nano-Indentation)等儀器的幫助，量測十六種現生動物牙齒琺瑯質之表面硬度、截面功能梯度變化、耐磨耗性等機械性質；因研究物種眾多，亦可藉牙齒微觀結構的差異性來探討其演化的足跡。 透過原子力顯微鏡觀察牙齒琺瑯質表面形貌，可發現哺乳類動物已發展出規則排列的釉桿柱結構，其中更可看出草食動物的釉桿柱排列堆積較雜食、肉食密集；再以奈米壓痕儀進行探討，亦可發現表面硬度以草食、雜食、肉食的順序漸減，演化前期及琺瑯質已產生退化的動物牙齒硬度值則最低；在耐磨耗測試上也可發現硬度高的琺瑯質較耐磨耗，演化前期及退化後的琺瑯質抗磨耗性較低。在牙齒橫截面部分進行硬度量測，可發現從牙齒表面到DEJ處，琺瑯質硬度成遞減的梯度變化，高冠齒化的牙齒截面變化率明顯高於其他動物，演化前期及退化後的琺瑯質則較無明顯趨勢。 關鍵詞：釉桿柱排列、奈米壓痕硬度、功能梯度
並列摘要
In the enamel of human tooth, hydroxyapatite makes up the large majority whereas the minority consists of protein and others. We are keen to know how the material of viscoelastic, organic and hard inorganic builds up the teeth that is hard, tough and has elastic feature in a microscopic way. Humans have not yet developed such a composite material that has so many excellent properties, but nature has already developed a biological tissue – teeth. If we can investigate the reason why human teeth have excellent mechanical properties, it will be beneficial for the development of artificial composite materials significantly. Our previous studies found that the enamel surface of human teeth is composed of many repetitive microstructure – rod. In addition, the cross-section has characteristic of functional gradient, making it resistant to impact and can effectively disperse energy and prevent chipping at the same time. Exploring the underpinning that make the mechanical properties of human teeth so amazing would shed illuminating light on the development of engineering materials. Because different organisms may have distinct diet, living conditions and manner of use, resulting in the change of micro-structure. Therefore this study chose sixteen dead animals—the two toed sloth, north American opossum, skunk, hyena, American black bear, lama, beluga whale, beaver, bat, salmon, ox, deer, human, cat, dolphin and crocodile. In addition, we measured the enamel’s surface morphology and mechanical properties in cross-section, comparing the difference between them, as well as discussing the reason about the dental microstructure having such excellent mechanical properties. To observe the complex micro-structure in enamel, this study used atomic force microscope (AFM) and nano-indentation to measure the mechanical property of enamel’s surface hardness, wear, and function gradient in cross-section. Because many species are compared, this study can also explore the relationship of the biological evolution and tooth microstructure development. Observing the surface morphology of tooth enamel through AFM, this study can find mammals have developed regular arrangement of enamel rods. The rod of herbivorous mammals is arranged more densely than omnivorous and carnivorous mammals. Result from nano-indentation reveal that surface hardness decreasing by the order of herbivorous, omnivorous and carnivorous. The lowest tooth hardness belonged to the animals in the early evolution and enamel has decreased in animals. The abrasion test revealed that high hardness enamel has a good wear resistance, enamel belonging to the animals in the early evolution and enamel has decreased in animals have a lower wear resistance. Hardness was measured in the cross-section, we can see a gradient decreasing from tooth surface to dentin enamel junction (DEJ). The high crowned teeth’s rate of hardness change was significantly higher than other animals, and enamel belonging to the animals in the early evolution and enamel has decreased in animals did not show this trend. Keyword：arrangement of enamel rods、hardness of nano-indentation、function gradient
參考文獻
延伸閱讀
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