MEASUREMENTS OF BONE AND FRAMEWORK DEFORMATIONS INDUCED BY MISFIT OF IMPLANT SUPERSTRUCTURES - A PILOT-STUDY IN RABBITS

This in vivo study used a 3-D photogrammetric technique to measure dis tortion of 3 unit implant frame-works and bone surrounding osseointegr ated implants after securing misfitting superstructures to the implant s. Four adult loop-eared rabbits were provided with 3 implants each in the proximal part of 1 tibia each. After a healing period of 8 weeks, a titanium frame-work was connected with a misfit to the central impl ant. Three-dimensional photographs were taken before and after securin g the central screw, which induced a calculated mean preload of 246 N. Measurements and comparisons of the topography of the frame-works and surrounding bone before and after tightening the central screw indica ted a complex and inconsistent deformation pattern. Generally, it coul d be observed that the top edge of the central cylinder showed vertica l movement towards the bone of about 150 mu m, always in combination w ith a rotation of the entire super-structure. The head of the central implant seemed to show a corresponding displacement towards the frame- work of about 50 to 200 mu m. Bone deformation uas found to be basical ly localized between the implants, where compressions of about half a millimetre were observed. This concentration of bone deformation as a result of misfit may be one contributing factor to initial marginal bo ne loss, occasionally observed after insertion of implant supported pr ostheses.