Bio-Oss is a made from OX-bone (well, cattle). It's called a 'XENO-graft' because it's FORIEGN to your own species (human). It's main advantage over an 'AUTO-graft' (not only bone from your own species but bone from your SELF) is that it doesn't require a separate operation to harvest it. It's often used for putting in tooth implants so there is a bone matrix for the implant to go into and also so your own bone grows into the matrix. In that way, the bone density of the area they need to screw the implant into, increases.
I have NO IDEA how they can differentiate the rate of resorption of bio-oss vs rate of resorption of your own bone in a situation where your own bone grows into the BO matrix. As long as the net bone density to the area grafted with the stuff increases is all that matters.
A bone GRAFT really isn't exactly an 'onlay' as is a 'stick on' face implant unless it's harvested from 'compact' bone (cortical) bone , outer surface of bone. The other type of bone is the inside bone, (cancellous) or spongy. Compact bones are made of osteons while spongy bones are made of trabeculae. Compact bones are tough and heavy while spongy bones are light. Compact bones fill the outer layer of most of the bones while spongy bones fill the inner layer of the bones.
Bone GRAFTS used in such things as chin wings and zygo osteos are NOT 'onlays' or 'stick ons'. They are 'in betweens' as in in between the bones cut and separated by the osteotomy. They are bone BUTTRESSES to the cut surfaces so that bone cells can grow into the CHANNELS (pores) of the bone buttress. That is what bone GRAFTING refers to when the reference is chin wings and zyg osteos. So the cancellous or 'spongy' bone is used for those. For the graft to take, the cut surface of your face bones must make direct contact with the bone graft, otherwise, your cut face bones with exposed surfaces RESORB if there were no buttress between them.
So, if you want an ONLAY (or even a bone buttress) for face augmentation, it isn't going to happen with 'your own bone' without a bone harvest. If you are AVERSE to materials used for onlays (face implants) that have no chance of resorbing (eg. silicone, PEEK, medpore, titanium, onlay augmentation isn't going to happen either. If you want something like CATTLE BONE (Bio-Oss) to be uses as a face augment ONLAY, I doubt that's going to happen either BECAUSE it's meant to be SURROUNDED by your own bone so it can grow into it. If one side of it didn't have direct bone contact (like the outer surface of an implant onlay used in face implants), it would tend to resorb. (exposed surface).
In short, a bone graft, (usually made from cancellous bone) meant to be SURROUNDED by your own bone so your own bone grows into it's channels, can't be used as an ONLAY because an onlay, by definition, would have an exposed outer surface that would tend to resorb.
The only material I can think of that is actually MADE FROM BONES (animal bones) that would not resorb if used as face implant onlays is porcellian as in 'bone china' made from the inorganic mineral containing ash of burned bones. However, how bio-compatible 'tea cup' face implants would be, I don't know. But they certainly would be breakable.
