Dynamic behavior of implants as a measure of osseointegration

Research into the formation, destruction, and adaptation of bone around imp lants would benefit from a sensitive, nondestructive, noninvasive, and quan titative technique to assess the bone-implant interface. It is hypothesized that osseointegration can be quantified by sensing the mechanical impedanc e (or micromobility) of the implant when it is subjected to minute vibrator y forces superimposed upon a quasi-static preload. To test this hypothesis, a total of 24 identical threaded, titanium root-form implants (10X3.75 mm, Osteo-Implant, New Castle, PA) were placed in the mandibles of 4 Walker ho unds and allowed to heal submerged for 3 months. The implants were exposed and characterized for osseointegration using clinical observations, quantit ative radiography, and a custom-designed impedance instrument. Subsequently , arbitrarily selected implants were ligated to induce bone loss and examin ed monthly over a 6-month study period. Following the terminal examination and euthanasia, quantitative histologic measurements were made of bone adja cent to the implant, including estimates of both crestal bone height and th e percent bone (bone fraction). Linearized dynamic parameters (effective st iffness and effective damping) correlated well with radiographic and histol ogic measures of bony support (r(2) values ranged from 0.70 to 0.89). Moreo ver, the presence of nonlinear stiffness was clearly associated with a bimo dal "clinical impression" of osseointegration (P < .0003, 1-way analysis of variance). These results confirm that, in this animal model, mechanical im pedance can be used as a measure of implant osseointegration.