Tooth trauma can cause a tooth to darken. The darkening is caused by injury to the tooth, but it doesn't necessarily mean that the injury is serious. Sometimes, a tooth darkening is basically equivalent to a bruise. There's been some minor damage to the tooth pulp, the living part of the tooth.

What causes a tooth to darken?

Aging: As you age, the outer layer of enamel on your teeth gets worn away exposing the yellow dentin. Your tooth dentin also grows as you age, which decreases the size of the pulp. The translucency of the tooth reduces, making it look darker. Genetics: Thicker and whiter enamel runs in some families.

What does it mean when one tooth is darker than the rest?

When a tooth goes dark, this means that the nerve has been damaged. Our bodies have a natural defense mechanism that causes the nerve to lay down an increased amount of internal tooth structure which could make it look a different color than the rest of the teeth.