How 2 remove bits of tooth left in the gum after an extraction?

Mechanically: If they are large parts buried in the gum, you will need local anesthesia. If they are really small pieces sort of stuck on the gum, a little topical anesthesia can be enough to allow them to be removed.

OUCH!: It will probably be difficult due to pain. Also if it is a piece of tooth, you should go back to your dentist. If it is just a "scale) of bone, it will probably come out by itself.Topical anesthesia will help some.

Small Surgery: The only way to remove them is to go in an get them. I assume you don't want to do this yourself, so have a dentist or oral surgeon get you numb in that area and go after those two tooth fragments. However, in some cases, the tooth bits can be left where they are. So, again, see a dentist, find out exactly what's happening, & discuss your options. Don't start digging around in your gums yourself!

Quite common: they work themselves out in a week or two. If concerned, see your dentist for small intervention.