Many patients have fillings (composite or amalgam) in the places where the brackets are bonded. Braces can be bonded onto a filling, but to get a good bond the surface needs to be prepared first – either by roughening it slightly with a dental drill or by applying a special bonding material.
Once the braces come off, the filling is polished. If it is sound and functional, there is no need to replace it.
This answer is for general information. Your own case needs an examination by an orthodontist.