Bone response to orthodontic loading of endosseous implants in the rabbit calvaria: early continuous distalizing forces

The purpose of this experimental study was to evaluate the effect of early orthodontic loading on the stability and bone-implant interface of titanium implants in a rabbit model. Twenty-four short threaded titanium fixtures w ere inserted in the calvarial mid-sagittal suture of 10 rabbits. Two weeks following insertion, 20 implants (test group) were subjected to continuous distalization forces of 150 g for a period of 8 weeks. The remaining four i mplants (control group) were left unloaded for the same follow-up interval. Clinically, all implants except for one test fixture were stable, and exhi bited no mobility or displacement throughout the experimental loading perio d. Histologically, all stable implants were well-integrated into bone. No d ifferences could be found between the pressure and tension surfaces of the test implants relative to bone quality and density within a range of 1000 m u m from the fixture surface. Similarly, qualitative differences were not o bserved between the apical and coronal portions of test fixtures. Morphomet rically, a mean percentage bone-to-implant contact of 76.00 +/- 18.73 per c ent was found at the test pressure sides, 75.00 +/- 11.54 per cent at the t est tension sides, and 68.00 +/- 15.55 per cent at the control unloaded sur faces. No statistically significant differences in the percentage of bone-t o-metal contact length fraction were found between test pressure surfaces, test tension surfaces, and unloaded control surfaces. Marginal bone resorpt ion around the implant collar or immediately beneath it was found in roughl y the same percentage of analysed sites in the test and control fixtures. I n contrast, slight bone apposition was demonstrated at the implant collar o f the test pressure surfaces, while no apposition or resorption were observ ed in the test tension zones. This study suggests that short endosseous imp lants can be used as anchoring units for orthodontic tooth movement early i n the post-insertion healing period.