What causes greying discoloration of permanent teeth?

Medication: Tetracycline/ and othe meds can cause a discoloration of the teeth.

Trauma to teeth: Discoloration of permanent teeth could be from having a root canal done on the tooth or a tooth that has had trauma to it in the past. Sometimes the discoloration can occur several years later after the trauma has occurred which would indicate the that nerve of the tooth is dying. Other causes of grey discoloration may be from tetracycline antibiotics that the patient may have taken as a child.