생체활성 세라믹 코팅에 의한 치과용 임플란트의 표면개질

Abstract

Titanium alloys and zirconia ceramics are mainly used as dental materials due to their excellent biocompatibility, corrosion resistance, and chemical stability. However, both materials have bioinertness in body, so they could not directly bond with human bone. Therefore, their bone bonding and bone formation abilities should be improved. In this research, bioinert surfaces of titanium and zirconia substrates changed to bioactive characteristics by the surface modification. General methods to increase surface bioactivity include mechanical and chemical treatments such as sandblasting, surface corrosion by acid or alkali deposition, but it reported that mechanical and chemical damages were induced on implant surface by the formation of structural defects during treatment. Another recommended methods are surface coatings with bioactive materials, using physical and chemical processes. When implanted in the human body, the mineral part of the bone tissue binds to the implant while the coated bioactive material dissolves to promote bone conduction. It is important for the bioactive material to quickly induce the precipitation of new hydroxyapatite particles, which are essential for proper dissolution and bone bonding within the body, and create them on the implant surface. Bioactive ceramics such as calcium phosphate and silicate have been studied to modify the implant surface with bioinertness. Especially, representative calcium phosphate-based ceramics including hydroxyapatite and tricalcium phosphate have been used as artificial bone materials for a long time because they have similar composition and structure to bone. However, it is known that calcium phosphate-based ceramics have low bone-bonding ability due to low solubility in body. In the case of silicate-based ceramics, it has been reported that they exhibit high solubility and good apatite-forming ability in body. Of the silicate ceramics, wollastonite has high dissolution rate and rapid apatite-forming ability in body. But the density of the precipitated hydroxyapatite particles is low, resulting in poor implant fixing force. On the contrary, akermanite, which is one of Ca-silicate ceramics containing Mg has lower solubility than that of wollastonite. It used as a control material to low the wollastonite solubility. In this study, surface modifications of zirconia and titanium alloy were performed by wollastonite coating to improve their surface bioactivity. Also, akermanite bioceramics which is one of cacium magnesium silicate, was synthesized by solid-state reaction to apply a surface coating material with suitable bone-bonding ability. Firstly, to improve the bioactivity and roughness of zirconia substrate, wollastonite was deposited on zirconia by slurry/spin coating. Secondly, to improve the bioactivity of Ti-6Al-4V alloy, wollastonite-coated layer was deposited by room temperature spray coating. Finally, akermanite was synthesized by solid-state reaction method, and investigated the dissolution and precipitation characteristics in SBF solution. Through above three experimental studies, we reached the following conclusion. Firstly, homogeneous wollastonite coating layer on zirconia substrate could be obtained through slurry/spin coating. When repeated more than 4 cycles, the surface roughness was improved more than 10 times, compared to initial 3Y-TZP substrate. Dissolution of wollastonite and precipitation of hydroxyapatite particles were observed during the immersion period in SBF solution, indicating that the wollastonite surface coating contribute to improve the surface bioactivity of 3Y-TZP substrate. Secondly, wollastonite powder was successfully deposited on the Ti-6Al-4V alloy by the room temperature spraying process. Corrosion resistance was also improved by PEO treatment, and its wettability and bioactivity were also greatly increased by wollastonite coating. Resultly, it indicates that both of PEO treatment and wollastonite coating by room temperature spray processing were induced superior improvement of surface bioactivity. Finally, akermanite synthesized by the solid phase reaction has a good bioactivity with low solubility in SBF solution. With increasing the reaction temperature, secondary phase(Merwinite(Ca3MgSi2O8), Wollastonite(CaSiO3))was decreased, but its solubility in SBF solution also decreased. Bioactivity of akermanite was optimized at synthetic temperature of 1100℃.