Your general dentist may have told you that you need to have a crown lengthening. There are two main indications for crown lengthening: biologic and esthetic.
The biologic basis for crown lengthening has to do with how close the margin of a restoration (crown, filling) is to the level of bone. If the margin is less than 3mm away from the level of the bone, your gum tissue will be unable to form a tight biologic seal around the tooth. It is this tight biologic seal which keeps bacteria out, and allows for a healthy restoration. If the margin is too close to the bone then bacteria will get into the pockets, and cause the gum tissue to be inflamed and irritated. Most important, however, is that the weakest part of your crown or filling (the margin) will be exposed to this bacteria, which could cause decay under the crown resulting in loss of your crown and possibly loss of your tooth.
The esthetic basis for crown lengthening has to do with improving the esthetics of your smile. This may involve removing excess gum tissue to expose your existing teeth, or to prepare your mouth for esthetic crowns or veneers by your general dentist.