The metrics used for orthopedic implants just don't match up with what we see in maxillofacial surgery because the face works so differently from weight bearing joints. Maxillofacial implants have to do multiple things at once: they need to help people chew properly, maintain clear speech, keep airways open, and look good aesthetically. Plus they have to fit into thin, uneven bones around sensitive areas like sinuses, blood vessels, and teeth.