In oral surgery, bone-grafting materials have been applied to provide sufficient bone for successful implant insertion. Although autologous bone is still the gold standard, commercially available bone grafts play an important role because of the limited availability of autologous bone and the wish of patients and clinicians to avoid discomfort related to the harvesting procedure. As the bone grafts can be fully integrated into the remodelling process, the tissue can regenerate completely.
The commercially available bone graft materials differ in composition and structure, and significant differences in their behaviour can be expected. A clinical comparison of several grafting materials is rare. To this end, we harvested trepanned biopsies exactly at the site of implant placement from eleven patients treated with Bio-Oss® (Geistlich Pharma AG, Wolhusen, Switzerland), BoneCeramic (Institute Straumann AG, Basel, Switzerland) with an absorbable collagen membrane (Bio-Gide® Geistlich Biomaterials, Wolhusen, Switzerland) and easy-graftÔ (SUNSTAR Degradable Solutions AG, Schlieren, Switzerland). These cylindrically shaped specimens were non-destructively visualized using micro computed tomography in absorption contrast mode. Subsequently, hematoxylin and eosin stained histological images were obtained. Dedicated software was developed to identify the counterpart of the two-dimensional histological slices in the three-dimensional micro computed tomography data, cf. Fig. 1 and ref[1]. It was validated by the manual search of a medical expert. Once satisfactory congruence was reached, a joint histogram was generated to segment the tissues, i.e. old and newly formed bone as well as soft tissues and the remaining bone-grafting material.
The differences of the bone-grafting materials in density and composition are clearly reflected in their local X-ray attenuation. As not only conventional micro computed tomography but also the synchrotron radiation-based technique was applied, the density resolution or contrast of the data was sufficient to discriminate bone in different mineralization stages and bone-grafting materials in various stages of degradation. Nevertheless, intensity-based segmentation can prove challenging, since the X-ray attenuation coefficients of the components overlap. The combination with histology, however, allowed identifying many anatomical features and the grafting material, which can neither be obtained from the histological nor from the high-resolution, high-contrast X-ray tomography data alone[2]. The volume of newly formed bone and of the remaining bone-grafting materials was determined. A direct comparison of the materials implanted in patients is, however, still questionable and the number of cases has to be increased significantly. Therefore, our study is preliminary and methodically oriented.
References:
[1] N. Chicherova, K. Fundana, B. Müller, P. C. Cattin: Histology to CT data matching using landmarks and a density biased RANSAC, Lecture Notes in Computer Science 8673 (2014) 243-250
[2] A. Stalder, B. Ilgenstein, N. Chicerova, H. Deyhle, F. Beckmann, B. Müller, S. E. Hieber: Combined use of micro computed tomography and histology to evaluate the regenerative capacity of bone grafting materials, International Journal of Materials Research 105 (2014) 679-691