How can we diagnose Tooth Discoloration ? 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. Published on May 04, 2013Last Updated on May 14, 2013