L.A.
Melanie E is correct. My dentist told me the same thing last month when he went to replace an existing crown. Once he drilled the old one off to see what was happening to the tooth underneath, most of the tooth shattered (it was dead and x-rays indicated decay or something was going on). "crown lengthening" on a new crown was one of several options he discussed with me as a replacement. By the way, I have 7 crowns and this was the first time I was told about crown lengthening too.