| Objective The microstructure and their mechanical properties of normal physiological enamel and dentin of primary and permanent teeth were observed in order to study the correlation between the structures and the properties, to provide information for bionics and designs of dental materials.Methods Test samples were randomly divided into four groups (permanent enamel, permanent dentin, primary enamel, and primary dentin). Topographies of all samples were observed by a Scanning electron microscope (SEM, JSM—6701F). The X-Ray Powder Diffraction (XRD, Rigaku D/Max-2400) were used to study the element and phase composition. In addition, the mechanical properties, such as the micro-hardness and elastic modulus were researched by the microscopic hardness (MH-5-VM) and nanometer indentation (NANOTEST600). In order to study the hydrophilic between the normal physiological enamel and dentin with primary and permanent teeth, the contact angles were studied with a Contact angle meter (CA-A) In our experiments. A reciprocal sliding friction and wear tester was performed to investigate the friction and wear behaviors of enamel and dentin of primary and permanent teeth by sliding against Si3N4ball under the lubrication of artificial saliva. The morphology of samples was obtained by AFM and the roughness and Young’s modulus were calculated by JPK DP Data processing of version4.0software.Results The structures with disorder and many tiny holes were found in the twisted glaze layer of permanent teeth enamel and around the dentinal tubules. For the crystallinity and the size of their crystal, the permanent teeth> primary teeth, and enamel> dentin, and the permanent enamel (Vickers Microhardness Number=423.1) has the highest hardness, and lower to the primary enamel (347.89) and the lowest was the dentin of primary (52.09) and permanent teeth (36.27). The highest value of modulus of elasticity was found in the dentin of primary teeth. Much more appetency were found on the surface of natural teeth to artificial saliva than that on the surface of natural teeth to water, and the appetency between the primary teeth and water is greater than that between permanent teeth and water. In addition, there was no statistical significance of the appetency between the enamel and dentin of primary teeth to artificial saliva. It was found that the friction and wear behaviors of the natural teeth were strongly dependent on the microstructures. The permanent teeth enamel showed the best wear resistance、slight abrasion and scuffing. But the primary teeth enamel showed the flaw and slight scuffing on its surface. Corrosive-abrasive characteristics appeared on the enamel of permanent and primary teeth, the Primary teeth dentin showed similar friction and wear behaviors as the Permanent dentin; so due to its weak and fragile microstructures, more severe scuffing and abrasion were founded on surface. In permanent teeth groups, the enamel rods arrange more tightly than those in primary teeth groups. The roughness of primary enamel (1203±39.5nm) was higher than permanent teeth (954.6±30.5nm). The Young’s modulus of enamel in primary teeth (80.4±7.7GPa) was lower than permanent teeth (90.8±2.2GPa). The roughness of dentin in primary teeth (1695±67.6nm) is higher than permanent teeth (1210±45.3nm) and the Young’s modulus of dentin in primary teeth (19.8±1.9GPa) was lower than the permanent teeth (23.1±1.0GPa)Conclusion The different of mechanical properties between the normal physiological enamel and dentin of primary and permanent teeth may be determined by their different microstructures. The mechanical characteristics of primary and permanent teeth are closely related to their microstructures. However, it is necessary to understand the micro-mechanical properties of nature teeth for the research and design of the biomimetic dental restoration materials. |
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