If you need to whiten a traumatized tooth, such as a tooth that has been ravaged by disease or damaged by blunt force trauma, you may have to treat it differently than you would any other tooth. Here are some of the options available for whitening a traumatized tooth:
Do not write off external dental bleaching just because your tooth is traumatized; there are cases where external bleaching can still help. External bleaching is usually viable as long as the tooth is still vital and damage to its internal tissues is minimal. This is why, if you wish to whiten a traumatized tooth, the first thing your dentist will do is take a radiograph of your tooth and determine its vitality. After that, the dentist can determine whether external bleaching is sufficient or not.
The thing with a discolored, traumatized tooth is that sometimes it only seems discolored because of the dead tissues inside it. Blood clots and dead tissues can show through your tooth's enamel, which is translucent. If that is the case, then you should see some improvement if the dentist treats and cleans up your tooth's root (endodontic treatment). This is usually the case with teeth that have experienced physical trauma; for example, if the teeth were damaged during a fall, and they now have blood clots inside them.
In some cases, it may be necessary to commission an internal bleaching of the affected tooth. If you also need endodontic treatment, then the dentist will also bleach the tooth's root at the same time before covering it up. The dentist will give you endodontic treatment as usual, and then introduce a bleaching agent inside the tooth, leave it there for some time, and then take it out before restoring the tooth.
Lastly, there are severe cases that cannot be resolved with cleaning, external or even internal bleaching. If you have such a case, and bleaching cannot help, then the next best course of action is to cover up the imperfections with suitable materials. Examples of such cover-up treatments include dental veneers, dental crowns, and dental bonding, among others. All of them have their pros and cons, so your dentist will evaluate your condition and advise you on which treatment suits your case best.
A consultation with your dentist will shed more light on how you can improve your smile; the dentist may even come up with further treatments in addition to the ones discussed above. Professionals like Hughes Thomas R can offer more information.