An x-ray will normally show early developments of an ulcer on the root apex. If there is one, it is highly likely that you will require a root canal treatment. This will usually change the dimension of the tooth preparation, so the crown is ideally made on a mould taken after this procedure. If the crown is already on its way, I recommend you have it temporarily cemented using a temporary cement. This allows the dentist to work on the tooth, should the situation not settle down. The crown can then be glued in permanently some weeks or months later. If the permanent crown is fitted permanently and the tooth does not settle, then a root canal treatment can be done, through the crown, by basically drilling right through it. This means damage to the porcelain and a somewhat inferior product. Hope that helps, let me know if you need any further advice. Regards Wolfgang