I had 4 veneers places about 3 weeks ago. I was very satisfied with the color and size/shape after placement. But over the past week I noticed there is a dark spot forming on the corner of one of the veneers that was not present when they were placed. I had not had any trauma to the teeth. Is this a bonding issue? Can it be rectified without replacing the entire veneer? And should my dentist charge me for fixing this?