How should I fix my front yellow tooth ? (photos)

Hi, thanks for the question... You have better alternative before the crown, first: do it a root canal is the most important treatment, to remove the infection inside of your tooth and later you could do inside whitening teeth, this really helps or you could do dental veneer if the whitening don't work, the crown is the last option at this case. Regards 

Your dentist is correct--these teeth are bruised from the inside and unlike a bruise on your skin the dark color does not go away. If the tooth has a root canal it is best to bleach it internally. you can try custom trays and whitening with focusing the bleach on that tooth--this may or may not give you good results--otherwise as your dentist says--cover it up with composite or porcelain--Dr John Merrill