Pivot tooth is another word for pivot crown.

If a tooth has suffered such severe damage by cavities that nothing is left of the crown, crown treatment is no longer be possible, since the crown cannot be securely attached. But if the roots are still intact, then good root canal treatment and restoration of the tooth stump could provide enough support for a crown. Crowns supported by such artificial structures are called pivot crowns.

This film shows a plaster cast taken from the mouth of a patient. There is hardly anything left of the tooth, only a very small part (shown in blue) protrudes from the gums. A bridge would not hold if it were set on this stump. Only restoration of the stump – shown here is black - can provide support for the bridge, and in this case the pivot tooth would not support just one single crown, but a bridge.
Good root treatment is crucial to the stability of a pivot tooth, since a part of the pivot structure is secured to the root by means of a root pivot.The picture shows a tooth which has experienced faulty root treatment. The rear root contains a pre-fabricated pivot, and root treatment did not extend all the way to the tip of the root. The front root had also not been treated properly, meaning that another root tip resection had to be performed. But this was also not performed properly: as you can see there are still some remains of the resected tooth.