Remodeling dynamics of bone supporting rigidly fixed titanium implants: a histomorphometric comparison in four species including humans

The long-term maintenance of a rigid bone-implant interface (osseointegration) is the clinical goal of most dental implant systems, although the biological mechanism for retaining a foreign object in living bone is unclear. Little data are available on the physiological turnover (remodeling) of the supporting osseous tissue. The objective of this study was to histomorphometrically assess bone remodeling surrounding rigidly integrated titanium implants in multiple species. Implants, in place from 6 months to 5 years, were recovered from human, monkey, dog, and rabbit subjects. With the use of stereological point-hit and linear-intercept methods, indices of bone formation and resorption were determined. Remarkably similar patterns emerged among all investigated species. Repeated-measures ANOVA showed a 3 to 9 fold increase in remodeling within 1 mm of the bone-implant interface (P<0.001; data expressed as percent turnover / month, mean +/- SEM for n = 3-11). All morphometric indices (percent new bone, percent fluorochrome-labeled bone, percent resorption space) showed similar trends. These data suggest that the physiological mechanism for maintaining rigid osseous integration (osseointegration) is a sustained elevation of remodeling adjacent to the bone-implant interface.