Exploring the Bio-mineralized Microstructures and Mechanical Properties of Various Vertebrata Dentition: Lesson from the Evolution

• Main Authors: Huang,Jia-Ling, 黃佳玲
• Other Authors: Jeng,Yeau-Ren
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/k8supq

碩士 === 國立中正大學 === 機械工程學系暨研究所 === 102 === 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