Effect of prosthetic superstructure accuracy on the osteointegrated implant bone interface.

OBJECTIVE: This study evaluated the biologic result of forces induced by a misfitting prosthetic superstructure on implants placed in a New Zealand white rabbit tibia model. STUDY DESIGN: Nine rabbits had two dental implants placed in both right and left proximal tibias. After 6 weeks, one animal was sacrificed for baseline integration data, and the remaining animals had fitting or misfitting prosthetic superstructures attached to the implants for 12 weeks. Implants were evaluated clinically, radiographically, and histomorphometrically at the scanning electron microscopic level. RESULTS: No clinical, radiographic, or histomorphometric evidence exists of integration failure with implants subjected to superstructure strain, although bone remodeling is noted. CONCLUSIONS: Given the limitations of sample size, animal model used, duration of prosthetic superstructure attachment, and loading confounders possible, the study of prosthetic framework misfit must be evaluated with another animal model, such as an intraoral primate model, to determine the relationship between clinical performance and histologic findings.

Comparison of the resistance of miniplates and microplates to various in vitro forces.

A comparison of the Luhr Mini System (Howmedica, Inc, Rutherford, NJ) and the Luhr Micro System (Howmedica, Inc) was undertaken to determine resistance to various forces using a biomechanical model. Miniplates and microplates were first tested to determine their resistance to forces of displacement on flat bend, edge bend, tension, and compression generated by a materials testing system machine. Then, miniplates and microplates were attached to fresh porcine ribs, fixed to a custom-made jig, and subjected to the same forces of displacement. The load was applied to the bone plate to permanent deformation in all tests. The mini and microplate systems resisted 14.50 and 1.14 kg, respectively, on edgewise bending, 2.65 and 1.10 kg, respectively, on flat bending, 92.03 and 16.44 kg, respectively, on tension, and 127.9 and 27.02 kg, respectively, on compression. The mini and microsystem biomechanical model resisted 1.89 and 0.94 kg, respectively, on edgewise bending, 5.20 and 0.85 kg, respectively, on flat bending, 37.60 and 15.72 kg, respectively, on tension, and 53.55 and 16.0 kg, respectively, on compression. The results suggest that the Luhr Mini Fixation System provides a significant amount of resistance to tensile and compressive forces, but is weakest when large forces are applied at 90 degrees to the flat portion of the plate. The system showed decreased force resistance in the biomechanical model except on flat bending. The Luhr Micro Fixation System has significantly less resistance to deformation, but shows no decrease in ability to resist forces of displacement in the biomechanical model.

Reliability of a facebow transfer procedure.

The three-dimensional orientation of a maxillary cast mounting from a simulated-kinematic facebow transfer was evaluated in multiple trials among three operators on a single subject. The anterior and posterior anatomic facial reference points were marked on the subject. Each operator performed a separate series of trials to reset the anterior facebow component, the two posterior facebow components, and a control series with no resetting of any facebow components relative to the subject. The x, y, and z coordinates of three reference points on the maxillary cast were determined with a machinist microscope relative to a fixed reference after each facebow transfer. A range of differences between mountings of the maxillary cast were found between trials with all three methods used. These mounting errors were due to setting of the instrument and would be expected in routine clinical use of this instrument.