In Vivo Micro-CT Follow-up of Peri-Implant Bone-Remodelling in Early Low-Frequency-Loading

Objectives: In vivo follow-up of peri-implant bone mass using microfocus computed tomography (micro-CT) to evaluate the effect of strain with low frequency early loading on osseointegration of endosseous implants in guinea pigs.

Methods: Three series of guinea pigs (n=10) received customized TiAl₆V₄ TiO₂-blasted percutaneous implants (Astra Tech AB, Mölndal, Sweden) in both tibiae. One week after implant installation, one implant was stimulated daily for 1800 cycles with a sinusoidally varying bending moment during 4 weeks while the contra-lateral implant served as unloaded control. Loading frequency was kept constant at 3Hz, while loading force was varied (0.5, 1, 2N) resulting in calculated varying strains (133, 267, 533 µstrain) and strain rates (400, 800, 1600 µstrain/s) in the cortical peri-implant bone. In vivo micro-CT scans were taken of both tibiae: 1 week after implantation before starting stimulation (v1), after 2 (v2) and 4 weeks (v3) of stimulation. Bone mass (BM (%) bone occupied area fraction) was analysed morphometrically on longitudinal micro-CT-slices.

Results: All implants integrated well. Reconstructed micro-CT-slices clearly showed progressive bone remodelling over 4 weeks. Statistically (multivariate linear model SAS 9.1.) significant increases in BM were measured between v1 and v2 (p<0.0001) and between v1 and v3 (p<0.0001), but not between v2 en v3. A significant positive effect of low frequency stimulation on Δ BM (BM at stimulated side minus BM at control side) was observed in the distal half peri-implant marrow cavity already after two weeks of stimulation (p=0.011) (v2). Δ BM was the highest for the 1N stimulation at the 3 Hz frequency (p=0.014). Conclusions: In vivo micro-CT methodology allows performing longitudinal studies in small animals. A positive effect of early controlled mechanical loading of titanium implants on the peri-implant bone could be clearly visualized and quantified.

Acknowledgements: Research Fund K.U.Leuven (VIS/99/012 IMFIX) and E.C. (IMLOAD QLK6-CT-2002-02442)