The antibiotic tetracycline can be a life-saver. It kills a wide spectrum of bacteria. But if it’s taken while the teeth are forming, it deposits in the dentin of the teeth and gives them a permanent gray or brown stain. Sometimes the teeth will be darkened in horizontal bands. Sometimes the darkening is moderate. While tooth whitening will lighten this stain, it has only a mild effect on it and won’t eliminate it, and whitening will never get rid of the banding. The best treatment is porcelain veneers. The photo below shows a very dark color, and you can see the horizontal banding: