Methods: Female rats were anesthetized, the tail was disinfected and ligatured. The tail was amputated between C4-C5 vertebrae. Into the exposed surface of C4, a 5mm deep, 1mm wide central cavity was drilled. Then a wider and shallower concentric hole was made (2.0x3.5mm) to create an “empty” cylinder. Screw-type titanium implants (1.2mm) were introduced into the deeper thin hole. Following implant insertion, the skin was repositioned over the implant and tightly sutured. The surgical wound was protected aseptically by a plastic film layer. To inhibit osteoclast activity in this model, some animals were treated with zoledronic acid, an amino-bisphosphonate. Animals were sacrificed at different time points. The axial removal force of the implant was evaluated on the extracted vertebra with a force measurement system. New bone formation was also tested using a microCT instrument. Statistical analysis was performed by ANOVA.
Results: The strength of osseointegration increased gradually with time as measured by the force needed to extract the implant. It reached a plateau at 36 weeks after implantation (extraction force on week 6: 30±5,9N, on week 16: 107,9±22,7N). microCT investigations confirmed these functional observations showing a gradual increase of bone hard tissue structure during the investigated period. Bisphosphonate treatment increased new bone formation around the implant by about three times at week 6 and significantly increased the extraction force.
Conclusion: Our newly developed rat OSSI model allows us to quantitatively study osseointegration and new bone formation around implants.
Supported by TAMOP-4.2.1/B-09/1/KMR-2010-0001 and OTKA-CK80928