Discomfort or sensitivity: Your newly crowned tooth may be sensitive immediately after the procedure as the anesthesia begins to wear off. If the tooth that has been crowned still has a nerve in it, you may experience some heat and cold sensitivity. Your dentist may recommend that you brush teeth with toothpaste designed for sensitive teeth. Pain or sensitivity that occurs when you bite down usually means that the crown is too high on the tooth. If this is the case, call your dentist. He or she can easily fix the problem.
Chipped crown: Crowns made of all porcelain can sometimes chip. If the chip is small, a composite resin can be used to repair the chip with the crown remaining in your mouth. If the chipping is extensive, the crown may need to be replaced.
Loose crown: Sometimes the cement washes out from under the crown. Not only does this allow the crown to become loose, it allows bacteria to leak in and cause decay to the tooth that remains. If a crown feels loose, contact your dentist's office.
Crown falls off: Sometimes crowns fall off. Usually this is due to an improper fit, a lack of cement, or a very small amount of tooth structure remaining that the crown can hold on to. If this happens, clean the crown and the front of the tooth. You can replace the crown temporarily using dental adhesive or temporary tooth cement that is sold in stores for this purpose. Contact your dentist's office immediately. He or she will give you specific instructions on how to care for the tooth and crown for the day or so until you can be seen for an evaluation. Your dentist may be able to re-cement the crown in place; if not, a new crown will need to be made.

Allergic reaction: Because the metals used to make crowns are usually a mixture of metals, an allergic reaction to the metals or porcelain used in crowns can occur, but this is extremely rare.
Dark line on crowned tooth next to the gum line: A dark line next to the gum line of your crowned tooth is normal, particularly if you have a porcelain-fused-to-metal crown. This dark line is simply the metal of the crown showing through. While not a problem in itself, the dark line is cosmetically unacceptable and your dentist may have to replace the crown.