Comparison of plasma‐sprayed hydroxyapatite coatings and zirconia‐reinforced hydroxyapatite composite coatings: In vivo study

Abstract The clinical use of plasma‐sprayed hydroxyapatite (HA) coatings on metal implants has been widely adopted because the HA coating can achieve the firmly and directly biological fixation with the surrounding bone tissue. However, the long‐term mechanical properties of HA coatings has been concern for the long‐term clinical application. Previous research showed that the concept of adding ZrO₂ as second phase to HA significantly increased the bonding strength of plasma‐sprayed composite material. The present work aimed to explore the biological properties, including the histological responses and shear strength, between the plasma‐sprayed HA and HA/ZrO₂ coating, using the transcortical implant model in the femora of canines. After 6 and 12 weeks of implantation, the HA coating revealed the direct bone‐to‐coating contact by the backscattered electron images (BEIs) of scanning electron microscope (SEM), but the osseointegration was not observed at the surface of HA/ZrO₂ coating. For new bone healing index (NBHI) and apposition index (AI), the values for HA implants were significantly higher than that for HA/ZrO₂ coatings throughout all implant periods. After push‐out test, the shear strength of HA‐coated implants were statistically higher than HA/ZrO₂ coated implants at 6‐ and 12‐week implantation, and the failure mode of HA/ZrO₂ coating was observed at the coating‐bone interface by SEM. The results indicate that the firm fixation between bone and HA/ZrO₂ has not been achieved even after 12‐week implantation. Consequently, the addition of ZrO₂ could improve the mechanical properties of coatings, while the biocompatibility was influenced by the different material characteristics of HA/ZrO₂ coating compared to HA coatings. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 652–660, 2004