Crown lengthening is a surgical procedure that re-contours the gum tissue and often the underlying bone of a tooth. Crown lengthening is often for a tooth to be fitted with a crown. It provides necessary space between the supporting bone and crown, which prevents the new crown from damaging bone and gum tissue.

Decay can frequently be found below the gum line. In order to gain access to the decay, it is necessary to reduce some of the bone surrounding the area of decay so the gum tissue can be positioned either higher up or lower down on the tooth making access to repair decay feasible. In other circumstances, the tooth may fracture below the gum line. Often the tooth requires a crown (cap) to cover over the fracture line. In order for the crown to fit over the fracture line, it is necessary to raise or lower the gum and reshape the bone accordingly so that the fracture line now becomes visible above the gum. The tooth is now ready for a crown (cap). When smiling, ideally there should be a display of upper teeth and a slight amount of gum displayed as well. In many circumstances there is an excessive amount of gum displayed (this is known as a gummy smile). In order to reduce the gum display so that there can be an ideal amount of tooth and gum showing, it is necessary to move both the gum and bone higher up on the teeth. The bone is gently sculpted to create room for the gum tissue to be ideally positioned. Hence the correct proportions of the teeth and gum are now visible.