How well does synthetic cow bone work to replace bone loss in gums?

Bone grafts: Bone from cows, or bovine bone, works very well to augment the jawbone under the gums, for example, for placement of dental implants. Technically, it's not synthetic because it comes from a living animal. There are other bone sources, including pigs (porcine bone) and unrelated human bone, which also work well. Other synthetic artificial bone substitutes are available also.

Yes: Let me clarify. The bone grafts available relating to your question are either synthetic bone or cow (bovine) bone. Both types of bone grafts, will work to replace the bone loss underneath the gums. It depends on the clinical situation.

No such thing: You either have a cow bone (allograft) or synthetic bone. Cow bone usually is harder, and actually are very good bone graft material (they are more expensive than human cadaver bone and synthetic bone). Their bone structure is similar, but more dense than our bone. Upon resorption, they would be replaced by much denser bone fill. All grafting material resorp and replaced by our real bone.