In chin wings, bone (from the crest of the pelvis 'hip' graft) is used to buttress, 'sandwich' separated sections of bone (for elongating an area). But, in that situation, it's used to fill in a GAP left by bone separation and not to make any specific contour shape from it.
Facial implants (common ones used) are made from silicone or a material with micro-pores (used to be called 'porex') which allow bone growth within the pores. If custom ones, they are designed to fit exactly on to one's bone structure and also to give a desired shape for a 'look' one wants. The ones that are porous for bone growth within are hard to remove because they integrate with your own bone. The silicone ones are easier to remove because they don't. But with those ones, if not sewn into a really tight subperiosteal pocket, they can have micro movements with muscle movements and it is that type of friction that is associated with bone erosion, most common place for the friction is to the chin.
Although your own bone can resorb with age/over time, not sure but I think SOFT TISSUE coverage goes at a faster rate and that can give a 'gargoyle' type look over very prominent bone structure. Have you ever seen photos of Nicolai Tesla in his YOUTH and then at OLD AGE? It's like he kept his very prominent bone structure but lost all the soft tissue coverage of it with passing time.