What is this on my crown? (Photo)

Sorry to hear that. the reason for dark spot of metal showing is due to the adjustment your dentist needed to make your bite right! The lab or the ceramist either put a thick metal so there was not enough room for porcelain in that spot, or your dentist missed to prepare your tooth on that spot to give it enough room for the lab to give you an Aesthetic crown !
Now days most dentist will use all porcelain crowns such as lava, or Emax. Emax still needs room just like porcelain fused to metal crown, in which you have, however lava can be fabricated with less preparation.
Best of Luck!

Hi, thanks for sending your question. The area of the crown seen is the metal portion of the porcelain fused to metal crown which is exposed caused by adjusting your bite on the crown. Your tooth should still be sealed, however esthetically not pleasant. Options of replacement including all ceramic crowns which will not have any metal visible.  All the best.

you have PFM crown. that dark portion is exposed metal. no need to worry about that . but if u r not happy with aesthetics just replace it with new PFM or full ceramic crown.

Hi:You do not have an actual hole on the crown.  What you are seeing is the metal under the porcelain crown.  The area seems to have been adjusted to get proper bite.  The tooth is protected however, you do not like the aesthetics of it you should go back to your dentist and share your concern.Best,Dr. Maddahi

This dark spot is exposure of the underlying metal support for the crown.  This usually happens when there is inadequate space for the crown and during adjustment of the bite the porcelain was removed to correct the occlusion.  

Your dentist placed a porcelain bonded to metal crown (PBM) on your back tooth. After cementing the crown, your bite was high so it was adjusted repeatedly. What you see on your crown is the metal showing through under the porcelain covering.One of three things happened here. 1) Your dentists didn't leave enough room between this tooth and the upper tooth to fit the crown material. This isn't likely since you already had a crown before. 2) while you wore a temporary crown, the bite on that was reduced to allow your tooth to heal after the root canal without being pounded on when you bite. The tooth super-erupted (came out of the bone) to meet the upper tooth anyway, so that when the final crown wasn't placed, it was too high, and your dentist had to shave it down to fit properly. 3) During the preparation of the tooth or the temporary phase, your jaw joint was compressed, closing the vertical space available to house the crown. We call this "losing the bite." When the final crown was placed, the dentist had to grind it down to fit.If there is "good news" here, the metal portion of this kind of crown provides the strength, so your crown is still strong enough to chew on.