sometimes new teeth will come in while the baby tooth is still there. Might want to have the vet take a look, and see if any need pulling.
I do the "Chilly Bone" which you wet and toss in freezer, but have also done an old washrag tied in a knot and wet down and frozen. Just have to make sure they don't chew off bits and eat it.
Most times though, I just give them a bully stick and let the old teeth fall out and let them gum the bully so it stimulates gums and lets new ones come in.
Makes me want to whip out the ambesol ? but not sure if that's ok or not. Have been tempted.