EFFECT OF SURFACE-ROUGHNESS OF HYDROXYAPATITE-COATED TITANIUM ON THE BONE-IMPLANT INTERFACE SHEAR-STRENGTH

We have investigated the bone-implant interface shear strength of hydr oxyapatite (HA)-coated Ti-6Al-4V (HA-coating A) (roughness average, R( a) = 3.4 +/- 0.5 mu m) and HA-coated Ti-6Al-4V with a rougher surface (HA-coating B) (R(a) = 8.4 +/- 1.8 mu m). There was no significant dif ference between HA-coating A and HA-coating B implants with respect to the bone-implant interface shear strength as determined in push-out t ests using the transcortical model in adult dogs. The bone-implant int erface shear strength of bead-coated porous Ti-6Al-4V was significantl y greater than that of both HA-coating A and HA-coating B implants. Th e failure site, as determined by scanning electron microscopy, was the coating-substrate interface, not the coating-bone interface. This ind icates a need to protect the HA coating from the direct shear forces. HA coating enhances early bone growth into the porous surface of the i mplant. Long-term fixation should depend on bone anchoring to this por ous surface. Hydroxyapatite coatings must be developed which do not ob struct the pores of the surface of the implant.