When do dental crowns need to be removed and replaced, as opposed to repaired?

Doctor's Answer

The short answer is that crowns that are defective are usually replaced.

This is mainly because of the way a crown is made that is very different from a filling. A crown is made up of a thin layer of either metal, ceramic or a combination of both materials that encircles the tooth. The thickness of this layer varies from 0.5mm-2mm depending on the location on the tooth.

A filling sits within a cavity that has been prepared within the tooth as a result of decay excavation.

Most defective crowns have problems at the margin (the area where the crown meets the tooth surface, usually at the neck of the tooth). Other issues include perforation (a hole) of the biting surface, secondary decay (usually at the margins), dislodgement or fracture of the crown. The underlying tooth may also fracture requiring a new crown IF there is still sufficient tooth structure remaining.

These problems can be detected by your dentist during a routine examination that includes x-rays. X-rays can be very useful in examining hidden areas of the crown (e.g. under the gum or in between the teeth) where ill-fitting margins can harbour secondary decay.

If a crown has ill-fitting margins or decay undermining the margins, it can be almost impossible to repair predictably in the mouth. Also, doing a repair will not allow your dentist to assess how far underneath the crown the decay has penetrated. Removing the existing crown and cleaning out all decay and old filling materials inside is the best way to visualize the underlying tooth structure.

A crown with a leaking margin that is accessible from the side MAY sometimes be repaired as a temporary measure. However, these repairs are unpredictable and may fail quite soon. Also by leaving the crown on the tooth, your dentist will not be able to treat any decay associated with the leaking margin properly.

Hope this is helpful! Most dentists would not replace crowns unless there is a very serious problem with them.

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