A crown is a tooth-shaped cover placed over a tooth that is badly damaged or decayed. A crown, which many people call a cap, is made to look like your tooth.

Crowns may be placed for several reasons, but generally the tooth has been extensively damaged by decay or breakage and filling material can't replace the missing tooth structure and make the tooth strong enough. A crown may hold together parts of a cracked tooth and can be used to hold a bridge in place. Crowns also are used for cosmetic purposes to cover misshapen or badly discolored teeth.

Crowns can be prefabricated or made in a laboratory. Prefabricated crowns are made of plastic or stainless steel and can be used as a temporary restoration until a permanent crown is manufactured. In some cases, prefabricated crowns can be used as a permanent restoration.

Crowns can be all metal, porcelain fused to metal (PFM), or all ceramic. Metals include gold alloy, other alloys (palladium) or a base-metal alloy (nickel or chromium). The all-metal or PFM crowns are stronger and are better choices for back teeth. PFM and all-ceramic crowns look just like normal teeth.

Usually, crowns last at least 7 years, but in many cases they last much longer, up to 40 years or so.


Preparing the Tooth
If you need a crown, you may also need endodontic or root canal treatment on the tooth, due to extensive decay or the risk of infection or injury to the tooth's pulp. Not everyone who needs a crown will also need a root canal.
Besides the crown, your dentist may need to build up a foundation to support the crown. A foundation is needed if large areas of the natural tooth structure are decayed, damaged or missing. If you are receiving the crown after root canal treatment, your dentist may insert a post-and-core foundation.

To place a crown, your dentist must file down the tooth to make room for it. If you are receiving an all-metal crown, less tooth structure will be removed because these crowns are thinner than PFM or all-porcelain ones.

After filing down the tooth, your dentist will use a piece of thread or cord to push the gum down around the tooth, and then make an impression of the tooth. The impression material sets in five or six minutes and is removed. Your dentist will also take an impression of the teeth above or below the tooth that will receive the crown, to make sure the crown will not affect your bite.

The impressions are sent to the lab, where the crown is made. During that time, you will have a temporary crown. These crowns are usually made of plastic and are made in your dentist's office on the day of your visit. They are not meant to last. If a temporary crown is left in the mouth, the cement eventually washes out and the tooth can decay.

At a second visit, your dentist will remove the temporary crown and test the permanent one. Sometimes crowns need additional polishing or glaze or some other adjustment before they are placed. Once the crown is ready, it's cemented to your tooth.


After a Crown
You shouldn't feel any discomfort or sensitivity after a crown is placed, though if your tooth still has the nerve in it, you may have some hot/cold sensitivity. If you notice pain or sensitivity when you bite down, you should contact your dentist. Usually this means that the crown is too high on the tooth. This can be fixed easily.

You may notice a dark line next to the gumline on your crowned tooth, particularly if you have a PFM crown. This dark line is the metal of the crown showing through and is normal. A crowned tooth is not protected from decay or gum disease. You should continue practicing good oral hygiene.

Crowns, especially all-porcelain ones, can chip. This can sometimes be repaired in the mouth. Your dentist will etch the porcelain with acid and bond composite resin to it to fix the chip. If the chipping is extensive, you may need a replacement crown.

It's also possible that the cement could wash out from under the crown, but the crown does not fall out. Under these conditions, bacteria can leak in and cause decay. If your crown seems loose, contact your dental office.

Your crown may fall out, due to a lack of cement or an improper fit. If this happens, clean the crown and the tooth. You can replace the crown temporarily using denture adhesive or temporary cement sold for this purpose. Contact your dental office immediately and try to schedule a visit for the next day. If you are away from home, seek a dentist in the area who can evaluate the problem. You may need a new crown or it may be possible to re-cement the old one on the tooth.

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