Many times when a single tooth has a dark color it is due to a trauma or a root canal treatment. Since the dark color comes from within the tooth, it requires “internal whitening”, which is a different approach to the whitening of sound teeth. In these teeth the broken down blood cells, bacteria or root canal filling material( as shown in the image) create a dark staining inside the tooth. The treatment has to start with removing the cause, followed by the application of a special mixture of sodium perborate. The reason I use a different whitening agent, for these delicate teeth is that while peroxide, the ingredient in whitening gel,  penetrates the tooth enamel and dentin layers, the sodium perborate whitening products, do not penetrate the enamel. This way the sodium perborate is  safer, since it does not “escape” from inside the tooth, leading to a great outcome with little effect on surrounding areas.