鯊魚牙齒之多尺度結構觀察與機械性質研究

Multi-scale Structural Characterization and Mechanical Investigation of Shark Teeth

方浩任(Hao-Jen Fang)

指導教授 ： 陳柏宇

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

斑馬鯊是一種食殼性的底棲鯊魚，以具有堅硬外殼的水中生物為食，例如軟體動物與甲殼動物。此外，斑馬鯊也會吃其他硬骨魚的肉。在食用這兩種不同的獵物時，斑馬鯊魚的牙齒會經由一種特定的機制，重新調整牙齒的角度用於穿刺肉類或用於磨碎貝殼。
為了瞭解這種具有高磨耗性牙齒的食殼性動物，此研究針對斑馬鯊牙齒做化學成分分析，微結構觀察與機械性質的量測。該結果也與尖吻鯖鯊牙齒做比較，該牙齒細長如針，通常用於穿刺獵物。在比較當中，我們可以從中了解不同形貌與功能的牙齒的異同。
結果顯示，此兩種鯊魚牙齒皆由相似的化學成分所組成，並也因此具有相似的機械性質。而在類琺瑯質上，其機械強度皆與海底動物的外殼差異不大。在缺少機械強度的優勢下，斑馬鯊藉由調整牙齒的角度及齒列分布來減低食用貝類所造成的磨損。這兩種鯊魚不同之處在於類琺瑯質束的方向排列，而造成排列不同的原因與捕獵時牙齒內所受應力分佈有關，對於斑馬鯊而言，由於其獨特的獵食機制，其類琺瑯質束的方向排列同時具有用於穿刺與磨碎的特色。為了適應環境並生存，鯊魚牙齒演化出獨特結構與優化之性能。

關鍵字

鯊魚牙齒 ； 獵食機制 ； 食殼性 ； 類琺瑯質 ； 象牙質

並列摘要

Zebra sharks are durophagous sharks, which consume the hard-shell bearing prey, such as mollusks and crustaceans. Besides, zebra sharks also feed on bony fish. In feeding on these two types of prey, zebra sharks undergo the teeth reorientation through a unique mechanism for puncturing and grinding. To understand the design strategy of high wear resistance in the durophagous fish, zebra shark teeth were investigated by chemical composition analysis, microstructure characterization, and mechanical property evaluation. The needle-like shortfin mako shark teeth, which were used for puncturing fish prey, were also studied and compared with zebra shark teeth. The results revealed that both sharks were constructed with similar chemical composition; thus, they showed the similar mechanical properties, with the hardness and reduced modulus comparable to that of the conch shell in enameloid. Without the superior mechanical properties, zebra sharks utilize dentition and teeth reorientation to prevent the damage from grinding and wearing during feeding shellfish. The difference between sharks is the orientation and distribution of enameloid bundles, which is be related to the external loading condition during feeding. Zebra shark teeth showed the mixture of the characteristics from puncturing and grinding due to its tunable feeding mechanism. Shark teeth have evolved unique structures as well as optimized properties to adapt their living environment and fulfill functionalities.

並列關鍵字

shark teeth ； feeding mechanism ； durophagy ； enameloid ； dentin

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