Ex Vivo Mechanical Properties of Dental Implant Bone Cement Used to Rescue Initially Unstable Dental Implants: A Rabbit Study

Purpose: Dental implant bone cement (DIBC) was developed to rescue unstable implants at the time of placement. The purpose of this study was to compare the mechanical properties of bone-cement-implant interfaces of cemented implants that were unstable initially and bone-implant interfaces of self-threaded implants placed in rabbit femurs after various healing periods. Interfaces and failure modes were also characterized using histology and scanning electron microscopy (SEM). Materials and Methods: Eighty dental implants were placed in 20 rabbits. In each rabbit, two experimental and two control implants were placed in the right or left femur; one was in the distal epiphysis and the other in the cortical shaft. The experimental implants were cemented in loosely prepared bony sockets, while the control implants were self-threaded. The rabbits were sacrificed after varying healing periods. Magnetic pulse stability and push-in yield tests on ex vivo specimens measured secondary implant stability, 0.2% yield load, displacement, interface stiffness, and load at 100 µm. After loading tests, interfaces were evaluated with histology and SEM. Most analyses used mixed linear models. Results: The 0.2% yield load, interface stiffness, load at 100 µm, and secondary stability were significantly higher for bone-cement-implant interfaces than for bone-implant interfaces. Mechanical properties of bone-cement-implant interfaces plateaued at 1 week, with minimal change over the following 12 weeks, whereas bone-implant interfaces improved gradually. SEM and histology showed intimate bone-cement-implant interfaces without soft tissue intervention and mainly cohesive failures within DIBC. Secondary stability was significantly correlated with interface stiffness and load at 100 µm. Conclusion: The results suggest that DIBC can provide early implant stability and mechanical properties superior to those of self-threaded implants while maintaining intimate interfaces without signs of osteonecrosis or soft tissue intervention. Keywords: dental implant bone cement, primary stability, rabbit femur, secondary stability, yield load