<s>[INST] I had a crown put in three years ago.  I had not noticed any pain or problem with it, yet the dentist says he needs to replace it because there is decay under it.  Is this unusual? I thought crowns were permanent.  Should I get a second opinion, and how do I go about doing that?? [/INST] Hi. Welcome to Chat Doctor . I have gone through your query and can understand your concerns. As per your complaint it is possible that if the margins of the crown is not intact and there is a gap between crown and tooth, water and food debris along with bacteria can seep into the tooth and leads to secondary Infection. In this case if the decay has not reached the nerves present in the center of tooth then you may not have pain, but the tooth can continue to decay. If this is the case you will have to get the crown removal, get the tooth filled or Root Canal treatment has to be done followed by replacing the crown. You can take a second opinion if you wish as well as you can send me a scan of the x Ray of the crowned tooth so that I can guide you how you should proceed for treatments. In case if tooth is decayed then the treatment advised to you is appropriate. Hope this information helps. Thanks and regards. Chat Doctor.  </s>