Due to decay or trauma, a tooth may fracture or become weakened. When this happens, the remaining tooth structure to support a crown restoration is often inadequate. Provided there is considerable bone support around the remaining root and a healthy root canal system, the tooth may be able to be retained and restored via a procedure called "crown lengthening".
During this procedure. a slight amount of supporting bone is removed around the tooth which ultimately "lengthens" the tooth structure available above the gum line. The increase in tooth length and form, provides a suitable substructure to retain a final crown restoration.
Not all teeth can be crown lengthened effectively, and sometimes removing bone around the tooth will result in an unesthetic or unmaintainable result. A radiograph and clinical examination is necessary with your doctor to detemine if crown lengthening is possible.