Not sure I like the TITLE heading of the post as I would not extrapolate what ever 'smarts' I might have to this particular field which you are more interested in than I am. I'm not really a 'bone only or bust type' as to patently reject the concept of implants made from bio-compatible materials just because they are 'not your own bone'. Besides, I don't want to preclude others from answering your question too.
Maybe there is someone on here who's direct field of study is/was biology. Although I had some pre-med courses at MIT, I got alienated by the 'Be a doctor, be a doctor and make lots of money' types and subsequently gravitated to 'Materials', things like making Samurai swords, Crystallography, laser labs, labs having to do with bio-compatible materials, hanging out with walter Lewin and cross registering at Harvard in Fine Arts with stint at the Fogg in curation.
That said, my 'take' on this:
There are materials that become infiltrated or surrounded by 'your own bone' but they REMAIN there. For example a porous hydroxyappetite block of what ever shape needed whether it be a buttress between separated bones or an 'onlay' as in implant to shape face will always remain there AS HA material even though your own bone (or other tissue) grows into it or surrounds it. So, what ever SHAPE it makes will always be there even when you get old and are making more osteoCLASTS than osteoBLASTS.
Biological materials (as opposed to bio-compatible ones that remain permanent) such as bone taken from a living being (or once alive) high up on the food chain (mammal to man) can be used as a bone BUTTRESS in direct contact with the cut surfaces of your bone (sandwiched between) can eventually be replaced by your own bone providing the osteoCLASTS direct themselves to degrading the material and the osteoBLASTS infiltrate it fast enough to keep it's SHAPE.
They are using Calcium phosphate and depending on re-mineralization of it with your own bone to maintain the shape and form of the implant generated with it. But I can't tell you if their claim that your osteoBLASTS will take over in time to maintain the SHAPE of the implant before your osteoCLASTS dissolve the thing.
Also, it looks like they're not getting very far with it. Implants made from THAT particular material (Calcium phosphate) happen to be THE ones that are NOT available despite being listed as 'available soon' for, (I think a few years) and despite their saying they get a lot of INTEREST in those, I didn't see their even including questions about it in their FAQ section.
