One indication of this procedure is a situation where during placing a filling or cementing a crown it is revealed that the margin of the healthy dental tissue is located under the gum and it cannot be isolated to avoid exposure of this area to salvia, blood or gingival crevicular fluid. Teeth treated under these conditions have always a higher risk of returning of dental caries.
It is also important that the x-ray shows that between the margin of the prosthesis/filling and the bone ridge there is at least 3–4 mm of healthy dental tissue. If the filling/crown margin is too close to the bone ridge, there will be no room for attachment of soft tissue (it has to adhere to the surface of a tooth root) and the gum in this region remains inflammatory or bone is lost in the area to accommodate the soft tissue zone.
Surgical extension of a crown is also used if during placing a prosthesis it is revealed that there is too little healthy dental tissue to achieve a stabile tooth crown.
Also there is aesthetic indication regarding front teeth (so-called gummy smile) where too much gum is exposed in addition to teeth while smiling.