If black stains are deposited from outside , they can be removed by cleaning or scaling
If black stains are coming from inside the tooth crown , teeth whitening may help
If the crown itself is getting discoloured slowly , a ceramic (metal free) crown or veneer can be given to mask up , but the reason for discolouration needs to be found out first . Discoloured crowns are often due to trauma to the tooth years back ,in that case Root canal is indicated before going to cosmetic masking up with veneer or crown
Next Steps
Visit dentist to find out what kind of stain