Powder Metallurgical Fabrication of Artificial Tooth Root of Hydroxyapatite/Ti with Bio-mimetic Structure

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Slurry dipping method was employed for the processing of hydroxiapatite/Ti biomimetic materials because of its capability of shape forming and microstructural control. The graded layers of both constituents were formed according to an optimum composition profile for the thermal stress reduction which will occur during high temperature processing, and for the optimum bio compatibility. Such graded layers were successfully formed by slurry dipping. Dispersion, sedimentation, viscosity, rheology, as well as yield value, of the slurries were investigated in detail in connection with properties of dispersion medium, dispersion reagent, binder and raw powders. Low- and high-viscosity slurries were investigated to enlarge a possibility of film thickness control. For the low-viscosity slurry it is necessary to suppress the sedimentation of dispersion particles, while for the high-viscosity slurry it turned out to be important to clarify the flow characteristics of the slurry for the determination of the yield value, which is needed for the precise control of the dip-coated layer thickness. The high-viscosity slurry was free from sedimentation, and the control of the film thickness with viscosity and yield value was rather easier. The consolidation process of the dip-coated layer, including drying and debinding, followed conventional powder metallurgical techniques, with particular attention on an issue pertaining to the sintering shrinkage which is characteristic to composition grading. In the present investigation the process conditions were optimized to get a sound graded layer for a better bio-compatibility. In general, however, the optimum process condition depends on material species, shape and size of the objects to be processed, and in applying the present process conditions to actual tooth root production a modification will be necessary with more or less practical and technical study.