Influence of Implant Geometry and Surface Characteristics on Progressive Osseointegration
Nico C. Geurs, DDS, MS, Robert L. Jeffcoat, PhD, Edwin A. McGlumphy, DDS, MS, Michael S. Reddy, DMD, DMSc, rjorie K. Jeffcoat, DMD
Purpose: Although no currently available technique for the measurement of osseointegration is entirely satisfactory, 3 clinical variables can be reasonably associated with the process: probing depth, micromobility, and crestal bone height. Micromobility can be quantified to some extent with the use of the Periotest, a commercially available instrument. In this investigation, the influence of surface characteristics and geometry upon Periotest value (PTV) and probing depth measurements was studied. Materials and Methods: In a multicenter trial, 120 healthy edentulous patients received 5 or 6 implants in the anterior mandible and were followed for 3 years. A total of 634 implants were placed. Every patient received at least 1 implant of each of 3 types: threaded titanium plasma-sprayed (TPS), threaded hydroxyapatite-coated (HA), and cylindric HA-coated. A randomization schedule assured that approximately equal numbers of each type of implant were placed and that they were uniformly distributed over the arch. Results: Of the 4 tested combinations of dependent and independent variables, the only statistically significant (P < .05) effect was that of coating on PTV. At 1 year after prosthetic restoration, the mean PTV for HA-coated threaded implants was –5.36 ± 1.24, compared with –4.86 ± 1.70 for TPS implants. This difference steadily declined in magnitude and significance, until, after 3 years, the groups were indistinguishable. Discussion: This study agrees with the previous observations that HA coating tends to accelerate the initial rate of osseointegration. The absence of a difference between threaded and cylindric implants confirms that the PTV responds to micromobility near the surface, on a scale much smaller than such gross geometric features. Conclusion: On the basis of these results, one may conclude that HA-coated implants exhibit a more rapid decrease in micromobility than do TPS implants of identical geometry.