This procedure is typically needed for one of two reasons; either cosmetic or restorative. Crown lengthening can cosmetically improve the smile line by eliminating the "gummy" smile look. The restorative reason is to provide more tooth to be visible in the mouth so the tooth can be properly restored. When a tooth breaks off near the gum line or when decay occurs on the root surface crown lengthening is needed to properly restore the tooth. Crowns and/or bridges cannot be cemented with the edge of the crown near the bone, which is why crown lengthening is needed.
When performing a crown lengthening procedure, the gum and bone around the area needing treatment is reshaped to expose more of the natural tooth. For cosmetic procedures, one tooth can be treated to provide an even appearance at the gum line, or what we call the whole smile line can be treated to create a natural smile line.
If the procedure is needed to restore a tooth that is decayed or fractured near the bone, then the area around the defect is treated. The only other option would be extraction of the involved tooth.
Please see the Periodontal Gallery for the types of treatment that can be accomplished.