- Metallic stains: Caused by metals and metallic salts,  which may be introduced into the oral cavity  by    metal-containing dust inhaled by industrial workers.

 Examples of stains caused by various metals are: 

Copper dust	Greenish Stain
Iron	Brown Stain
Silver	Black Stain
Mercury	Greenish Black

DIAGNOSIS
Diagnosis is made based on the color of the stain. If the stain still remains after meticulous cleaning of the teeth by the dentist, it is understood that the stain is present within the substance of the tooth. A careful history taking can be useful in differentiating between an internal stain and an external stain.
 
TREATMENT
Many people have definite aesthetic problem from internal or external stains, where as others worry needlessly about the overall color of their teeth. In the latter instance the dentist must decide if the color of the teeth can be improved enough to justify treatment even though the patient insists on having something done. For e.g. person with light complexion may believe that their teeth are too dark when actually they are normal in color. A Sun tan, darker makeup or a darker lipstick will usually make teeth appear much whiter by increasing the contrast between the teeth and the surrounding facial features

Most external stains can be removed by thorough cleaning of teeth, with an instrument called “ ultrasonic scaler”. This instrument removes most of the stains caused by tobacco, food debris or bacteria. If a broken down filling or a cavity is the cause, filling the defect will improve the discoloration. Discoloration resistant to cleaning can be corrected or greatly improved through conservative procedures such as Bleaching, Micro abrasion or Veneering.

Stains caused by tetracycline medications are usually much difficult to treat, and might require a radical approach.