Although there are multiple substances capable of staining your teeth, the staining itself falls into two possible categories—extrinsic or intrinsic. Extrinsic has an external cause and is the most common type of staining. It's caused by the surfaces of your teeth coming into regular contact with compounds that might stain them, typically via your diet and lifestyle. It's generally managed with teeth whitening. Intrinsic staining is a different matter entirely and must be managed by your dentist.

The Inside Out 

Intrinsic staining occurs when something discolors a tooth from the inside out. For example, your tooth might have experienced a form of trauma resulting from a physical impact. The tooth's pulp (its nerve) then became bruised and swollen. As it swells, it presses against the walls of its pulp chamber, which is hollow at the center of each tooth. Fortunately, the trauma didn't cause any permanent damage to your tooth's structure or its pulp, and the swelling subsided.

Through the Tooth's Outer Surfaces

As the swelling subsided, your dental pulp left remnants of blood on the walls of its chamber. This chamber is completely isolated from the rest of your mouth, so there's so saliva or comparable liquid to irrigate it. The residue then stains the walls of the pulp chamber, which can be visible through the tooth's outer surfaces. The same result is possible if the pulp was infected and inflamed but subsequently recovered. The tooth may look discolored from the outside, but you're actually seeing internal staining. And because it's internal, it can't be whitened away.

Bleaching From Within

Intrinsic staining requires help from your dentist, and there are a few options. Your dentist can make a small access cavity in the tooth to insert a specially formulated bleaching strip. This releases its active ingredients slowly, to progressively remove the tooth's discoloration from within. You may need to have the treatment repeated several times, but this method sounds too invasive, you can also simply have the staining covered.

Covering the Tooth

Your dentist can cover the discoloration with a veneer bonded to the tooth's outward-facing surface. Alternatively, the tooth can be bonded, which is simply the application of a thin layer of tooth-colored composite resin (the same material used for fillings). Either of these options will effectively mask the tooth's intrinsic staining.

An internal stain can easily be visible from the outside of the tooth. You should always have your dentist assess such a tooth—if only to make sure there's no serious damage. But the issue is likely to be nothing more than a cosmetic concern, which your dentist can assist you with.

Speak to your dentist to find out more.