Biomedical Engineering Reference
In-Depth Information
as the bone is restored. It has excellent tissue affinity and is osteoconductive. In other words,
TCP is gradually converted to HA in vivo, and there is a mechanism whereby, as resorption
of the artificial bone progresses, it is simultaneously replaced with new bone that forms as a
result of invasion by osteoblasts. Thus, the artificial bone, which has excellent osteoconduc‐
tivity and biocompatibility, is ultimately replaced by bone. In the present study, the main
component of artificial bone was fine α-TCP powder, which was made into a non-sintered
hardened body of TCP through the use of a sclerosing solution. Such hardened bodies of TCP
are likely to be biochemical precursors of HA, and not only do they have excellent biocom‐
patibility like HA, but they are also artificial bones that are resorbed and replaced in vivo. It
therefore appears likely that the artificial bones grafted in the present study will be replaced
by bone.
Another feature of the present method is that the artificial bone is fabricated from a wax-up
made by the surgical operator prior to surgery, using the 3-D cast. This means that the present
method is able to reproduce the required shape more faithfully than conventional methods of
fabrication. This results in better compatibility than existing types of custom-made artificial
bone, so that practically no adjustments are necessary during the surgical procedure. Conse‐
quently, further reduction in the time needed for the surgical procedure can be expected. With
the present patients, bone grafts were made to bone defects resulting from tumor or congenital
anomalies. Where the graft was made to bone that had been grafted or lengthened, the surface
of the bone presented an extremely complex form, and it is likely that there would have been
limited compatibility with conventional methods. Furthermore, with the present method, the
CAD artificial bone data can be readily used to fashion the inner surface of the artificial bone
that makes contact with the host bone, allowing this region to be shaped freely. The present
method allows the surgical operator to fabricate the custom-made artificial bone into the shape
that patient's desires, and this aspect of the method is likely to make it extremely useful in
clinical practice. The conformity of the artificial bone during the procedure was extremely
good, so that there was no need for the complicated modifications to the shape that are
necessary with conventional grafts of artificial bone. The raw material used with the present
method is α-TCP, and the product is a non-sintered hydroxyapatite compact. Because its
resorbability is better than that of artificial bone made from a sintered body, it is expected that
the present artificial bone can be replaced by bone at an earlier stage. While the present artificial
bone is not as strong as artificial bone made from a sintered body, it can withstand a force of
20 MPa, and this is unlikely to be a problem for use on non-load-bearing regions of facial bone.
Furthermore, since artificial bone made from a sintered body is reported to shrink by around
15% during sintering, problems remain with regard to conformity and reproducibility. With
the patients in the present study, union of the artificial bone and the host bone was found in
some places on the CT images starting at around 3 months after surgery. This is probably
because union of the present artificial bone with host bone is more rapid than with conven‐
tional types of artificial bone, since it is highly biocompatible and non-sintered. This is a huge
advantage of non-sintered artificial bone. The most important aspect of artificial bone from
the point of view of the surgical procedure of reconstruction is the fixing of the artificial bone.
When calcium phosphate makes contact with the surface of bone, fibrous connective tissue
appears at an early stage, causing union with the bone. However, any postoperative disturb‐
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