The coloration of the lower jaw looks like it may have rotting issues as well. As long as the butter worms arent thicker then the space between his eyes he will be able to eat them as well. Do not force the teeth bones out as they could still be connected to him with tissue, tendons, or bone and that can hurt him. If all else fails take him in to have the vet look him over and remove it if needed. He may have swallowed it if he lost it when eating you could get an xray to confirm. For now I would just thuroughly examine his cage and feces to see if you can find the piece.