Determining peri-implant bone strength: Is CT the way forward?

Objectives: The goal of this study was to use micro-CT and novel bilayered tissue engineering bone scaffolds as a means for providing a non-destructive, but predictive quantification of bone quality needed to support implant placement.

Methods: Novel high porosity hydroxyapatite scaffolds were prepared by template coating and sintering. Scaffold architectures produced were either trabecular (TA) having mean pore sizes of 450, 340, 250 and 200 µm or bilayered (BL) with three outer cortical to inner trabecular volume ratios: 70:30, 45:55 and 60:40 (n=6). The bilayered scaffolds were representative of mandibular trabecular bone with cortical end plates. Scaffold porosity was measured using pycnometry, and morphometric analysis was performed on Micro-CT images (9 µm resolution). Scaffolds were then tested to failure under compression in a hydrated environment at 37°C.

Results: The scaffolds had a mean porosity of 86% (TA) and 76% (BL). The ultimate strength, elastic moduli and toughness for the scaffolds ranged between 0.16-0.7 MPa, 34-138 MPa and 0.2-7.8 kPa for TA scaffolds and 0.44-1.83 MPa, 45-199 MPa and 9.8-68.6 kPa for BL scaffolds. Bone volume density (BVTV), bone surface:volume, trabecular pattern factor (TbPf) and trabecular thickness (TbTh) all showed significant correlation (p<0.01 level) with strength, modulus and toughness. BVTV best predicted strength (R²=0.84), TbPf (R²=-0.64) and TbTh(R²=0.64) best predicted elastic modulus while TbTh(R²=0.60) best predicted toughness (Pearsons correlation).

Conclusion: Morphometric parameters^[1] and mechanical parameters^[2] measured were similar to the values reported for different grades of mandibular bone, proving the validity of using tissue engineered scaffolds. Statistically significant correlations between the morphometric CT parameters and mechanical test data allows a non-destructive, but quantitative prediction of bone strength, thereby enabling a more efficient evaluation of bone quality for implant placement.

^[1] M.I. Fanuscu, et al. Clin Oral Impl Res. 2004; 15:213-8.

^[2] C.E. Misch, et al. J Oral Maxillofac Surgery 1999; 57:700-06.