Biomedical Engineering Reference
In-Depth Information
induce neither inflammatory nor foreign-body reactions [603].
The biological response to implanted calcium orthophosphates
follows a similar cascade observed in fracture healing. This cascade
includes a hematoma formation, inflammation, neovascularization,
osteoclastic resorption and a new bone formation. An intermediate
layer of fibrous tissue between the implants and bones has been
never detected. Furthermore, calcium orthophosphate implants
display the ability to directly bond to bones [3-7, 39, 43, 49-56, 58,
525, 589]. For further details, the interested readers are referred to
a good review on cellular perspectives of bioceramic scaffolds for
bone tissue engineering [408].
One should note that the aforementioned rare cases of the
inflammatory reactions to calcium orthophosphate bioceramics
were caused by “other” reasons. For example, a high rate of wound
inflammation occurred when highly porous HA was used. In that
particular case, the inflammation was explained by sharp implant
edges, which irritated surrounding soft tissues [601]. Another
reason for inflammation produced by porous HA could be due
to micro movements of the implants, leading to simultaneous
disruption of a large number of micro-vessels, which grow into
the pores of the bioceramics. This would immediately produce an
inflammatory reaction. Additionally, problems could arise in clinical
tests connected with migration of granules used for alveolar ridge
augmentation, because it might be difficult to achieve a mechanical
stability of implants at the implantation sites [601].
4.6.2
Osteoinduction
Before recently, it was generally considered, that alone, any type
of synthetic bioceramics possessed neither osteogenic [604] nor
osteoinductive [605] properties and demonstrated a minimal
immediate structural support. When attached to healthy bones, an
osteoid [606] is produced directly onto the surfaces of bioceramics
in absence of a soft tissue interface. Consequently, the osteoid is
mineralized and the resulting new bone undergoes remodeling
[607]. However, several reports have already shown osteoinductive
properties of certain types of calcium orthophosphate bioceramics
[177, 459, 504, 608-621]. Namely, bone formation was found to
occur in dog muscle inside porous calcium orthophosphates with
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