Loading improves anchorage of hydroxyapatite implants more than titanium implants

Roentgen Stereophotogrammetric Analysis (RSA) studies have shown that the quality of the early fixation of implants has a dominant effect on their long-term function. To evaluate methods to improve their fixation, we examined the influence of mechanical loading and surface coating on the quality of the bone-implant interface. We compared the fixation of a cylindrical, stable 6.0 mm implant initially surrounded by a 0.75 mm concentric gap, after 4 weeks of loaded or unloaded conditions. Two types of surfaces were analyzed: plasma sprayed hydroxyapatite (HA) and plasma sprayed titanium (Ti). The histomorphometric evaluation showed that HA implants had greater bone coverage than Ti implants, and this coverage was further increased under loaded conditions only for HA. Furthermore, loading reduced the fibrous tissue coverage for the HA implants, while it increased fibrous tissue coverage for Ti implants. These findings were in agreement with pushout results showing that HA implants had greater shear strength, stiffness, and energy than Ti implants, and (except for energy) these parameters were further increased under loaded conditions only for HA. In addition, because the two implant surfaces exhibited a different relative response to load, it is important to evaluate new surfaces under the more clinically relevant loaded condition.