상온분사코팅에 의한 임플란트용 지르코니아 기판의 표면 개질

Abstract

3 mol% yttria-stabilized zirconia (3Y-TZP) ceramics have received considerable attention as non-failure materials for dental implants due to superior mechanical properties (high bending strength, fracture toughness), biological properties (biocompatibility, biofunctionality) and optical properties (high transmittance, excellent esthetics). But, manufactured zirconia implants from the computer-aided design and computer-aided manufacturing (CAD/CAM) and post-sintering process have disadvantage to low surface roughness and many surface defects due to processing characteristics. By the previous reports, zirconia implants with low bioactivity could be detached from the gums during the maintaining for a long time because of low bone-bonding ability and less cell adhesion. In this study, we tried to improve the bioactivity of zirconia substrate by the powder coating of zirconia and hydroxyapatite. For this purpose, surface coating on zirconia substrate was performed by room temperature spray processing, which could enhance bioactivity and surface roughness. We also investigated the microstructural change and surface roughness of coated surface and analyzed the bioactivity by in vitro test in SBF solution. Firstly, we controlled the processing factors for room temperature spray processing (particle size of raw material, spraying distance, and number of deposition cycle) to obtain the optimal condition for high surface roughness of coated layer. Secondly, we prepared four types of zirconia substrate with different surface morphology by the grinding on silicon carbide (SiC) abrasive papers with the number of #220, #400, #800. After performing the zirconia powder coating on substrate, we investigated the effect of surface-grinding of substrate on the surface roughness and morphology of coated layer and optimal coating condition for biological aspects. Finally, we tried to fabricate the bioactive zirconia substrate by the surface coating of hydroxyapatite powder. Also, we investigated the improvement of bioactivity of zirconia substrate by the analysis of coating layer via microstructural observation and in vitro test in simulated body fluid (SBF) solution. From the above experimental investigation, we could be obtained meaningful conclusion as follows;

Firstly, surface roughness of zirconia substrate could be enhanced by the deposition of zirconia particles using a room temperature spray processing. Coated layer have 2~3 times surface roughness, compared with an sintered zirconia substrate. Surface roughness and microstructural feature of coated layer were dependent on the processing parameters. Surface roughness of coated zirconia substrate gradually increased with the number of repeated deposition cycle and decreased with spraying distance. Coated zirconia layer had a homogeneous and dense microstructure with wave pattern, consisting of nanoscale tetragonal zirconia grains. Secondly, surface grinding by SiC abrasive paper was created large and small scratches on zirconia substrate, it affected to the surface roughness and surface morphology of coating layer formed by room temperature spray processing. Surface grinding of zirconia substrate resulted to the reduction of surface roughness on coated layer. Surface morphology and coating thickness were dependent on the substrate roughness and surface texturing, relying on the type of surface grinding. Maximum surface roughness (Ra; 0.42 µm) and film thickness (9.6 µm) of coated layer were obtained from the as-received substrate with maximum substrate roughness. In contrast, minimum surface roughness (Ra; 0.32 µm) and film thickness (3.2 µm) of coated layer were obtained from the fine grinded substrate with minimum substrate roughness. Finally, we confirmed that the bioactivity of zirconia substrate could be improved by the surface coating of hydroxyapatite powder. Hydroxyapatite coating on zirconia substrate by room temperature spray processing was induced high surface roughness by the formation of hydorxyapatite nanoparticles on coated layer and it accelerated the precipitation of nanoscale hydroxyapatite particles on the surface of coated layer during the in vitro test in SBF solution under pH 7.4 for 1 to 14 days. The newly precipitated particles were evaluated to the spherical basal type with the size 4.0~7.0 µm.