THE IMPLANT FIXATION PROPERTIES OF TITANI UM EXPERIMENTAL DEVICES OF DIFFERING SURFACE TEXTURE IN METAPHYSEAL CANINE BONE - A BIOMECHANICALAND HISTOLOGICAL ANALYSIS

The alternative to the anchoring of an endoprosthesis by means of ceme nt is the biological fixation by an ingrowth of bone into the implant surface (osseointegration). We examined the implant fixation propertie s of titanium experimental devices with 3 different surface structures after press-fit implantation into the bony bed of 12 dogs. One third of the 48 implants had a micro-structured surface roughened by grit-bl asting, one third a roughened surface with an additional macro-groove structure (combination surface), and the remaining third a porous hydr oxyapatite (HA) coating. Twelve weeks after implantation the bony ingr owth was evaluated biomechanically by measuring the force required to pull out the implant from the surrounding bone and histologically by m orphometric assessment of microradiographs. In the pull-out-experiment the shearing forces were significantly lower (p<0.01) in the devices with a roughened surface in comparison to the devices with a micro-and macro-structured surface and the HA surface. Thus, there was no signi ficant difference between the forces required to pull out the devices with the porous HA surface and those with the combination surface. The histomorphometric assessment of bone density in the immediate vicinit y of the implant and the extent of the direct contact surface of the b one implant resulted in no significant difference in all 3 groups. We did not find an interposing layer of fibrous tissue at the interface. We can demonstrate that roughening of the surface in combination with a groove structure creates a better bond between implant and bone than a roughening alone. The grooves, which are vertical to the changing s tress on the implant and the tensile force, influence both the primary and secondary stability, as there is ingrowth of bone tissue into the m. Titanium experimental devices with a bioactive, porous, hydroxyapat ite coating do not exhibit a more stable osseointegration after 12 wee ks than this simple surface structure.