I have a porcelain crown and the bottom part is wearing off and the metal cap is becoming exposed. is this harmful? also how does the dentist fix that

Over time: The biting surfaces of teeth ; crowns wear, more in some individuals than others. Over the time the gums may recede, ; again more in some individuals than others. Your dentist can evaluate both the health of your bone ; gums as well as your bite in order to determine both the severity of these issues ; whether or not any treatment is appropriate. The only fix is a new crown for cosmetic reasons.

Fractured porcelain: You are fine as long as the metal portion of the crown is intact. However, eventually you will wear through the metal. You should see your dentist to evaluate why the porcelain fractured and whether there are any problems with the tooth itself. At some point, the crown should be re-made both for cosmetic purposes and to adjust for the reason the porcelain fractured.

Porcelain won't wear: Off the side you are probably seeing the metal margin. If that is the case, your dentist can tell for sure, no treatment is necessary. But, it can't be replaced to update the cosmetic. If it is fractured porcelain and still supports the bite and adjacent teeth, it can be smoothed off or replaced, your choice.

Crown is not 4 ever: An older crown may eventually show signs that it’s time for a replacement. A damaged crown won’t protect the underlying tooth properly, so if an old crown has suffered damage, it’s time for a replacement. If you don’t replace the defective crown, you might be risking decay and further damage to a natural tooth.