I had 4 metatarsal head resection in jan. now am getting callous on third metatarsal. dr. says bone regrowth. is that possible?

Yes: Bones can regrow but the question is why was it removed? Diabetic ulcer?

Bone growth possible: Yes. I believe you are speaking of a callus beneath the 3rd metattarsal. Bone re-growth is possible after surgery. An x-ray should be taken to see the orientation of the lengths of mets 2 and 4, with respect to the 3rd. If the 3rd metatarsal is longer than the second, it will bear more weight causinf a callus beneath it. An accommodative orthotic can be fabricate to alleviate this problem.

Yes possible: Some may develop a bony overgrowth at the site of bone surgery.