Crown Retention. Sometimes, tooth decay can result in the removal of a significant amount of tooth structure above the root and surrounding bone. A small amount of the bone around the tooth can be removed to expose more healthy tooth structure in order for the crown to fit better, and to prevent gum irritation issues down the road. This is a fairly common and minor procedure.
Crown lengthening. In order for a crown to be placed on a tooth after a root canal there must be sufficient tooth structure remaining. If decay was removed down to the bone level of the tooth, bone may have to be removed to allow crown placement. This procedure is called crown lengthening.
Severe decay. If there was severe decay in the tooth, then some minor bone removal may be indicated when preparing the tooth for a crown in order to have the margin of the crown sitting on solid tooth structure.