I had 8 years old dental crown. Some parts on the surface was chipped / roughened. The dentist replace the old crown with a new one. Now the problem has begun. I visited the dentis for 4 times for adjusting (reducing the size by drilling) the crown. Still hurts when chew food or pressing the crown by tongue accompanied by sore gum (inner side). Can the drilling operation on the crown cause the gum sore? What should I do? I would appreciate your advice.

Has the dentist checked to see if there is an abscess at the root tip of the crown? You may need a root canal.