Great question to ask! The answer may not seem straight forward; however, when you get down to it; it really is. Usually, there is a reason for replacing a crown with a new one. The reason can vary greatly, but among the most common are: decay (cavity) around the edge of the crown, crown has been worn through, and wanting better aesthetics. If there is decay or cavity around the crown, then most of the time the crown needs to come off and all the usual crown rules apply. In order to get the crown off, it is needs to be cut off and replacing it is most ideal. However, this depends on the location and extent of the cavity. Wearing through a crown seems like an impossible feat; however it does happen. Normally there is not a lot wrong with the actual tooth at this point, but there can be a small cavity. Replacing this crown is ideal, but the height of the tooth remaining is a concern for two reasons. One, if the crown has been worn through completely, then the height of someone's bite has gotten smaller by about 2 millimeters. To directly replace the crown the tooth needs to shorten another 2mm. This could lead to sensitivity due to the proximity to the nerve of the tooth. Two, a crown requires a certain height to be adequately retained. Losing another 2mm may compromise the retention. Finally, when the reason for replacing the crown is aesthetics; the answer is almost always yes, this crown can be replaced with another one. In this case, the tooth is lightly touched if at all. The gums normally recede away and the crown needs to be made longer.
Hope this helps.
My best to you!
William F. Scott IV, DMD
I hope this answers your question adequately.
Alan B. Steiner, DMD