You may be wondering why that one tooth is significantly darker than the adjacent teeth. And after you've tried all the whitening tips and strips you can get, and it still looks gray. Several causes of discoloration are: extrinsic stains, these can be from smoking habits, or from food and beverages that causes staining; and intrinsic stains which causes discoloration inside out. The causes can be from a dying tooth that was caused by caries or physical trauma, or from a previ