Amalgam tattoo is a grey, blue or black area of discoloration on the mucous membranes of the mouth, typically on the gums of the lower jaw. It is a healthcare caused lesion, due to entry of dental amalgam into the soft tissues. It is common, painless, and benign, but it can be mistaken for melanoma. Signs and symptoms
Amalgam tattoo usually occurs on the mandibular gingiva, often in an area in which an apicoectomy ("root-end filling") with amalgam was carried out. : 138  After the gingiva, the alveolar mucosa and the buccal mucosa are the next most common sites, although any mucosal site in the mouth is possible. It is painless, and appears as a blue-black or grey discolored macule on the surface of the mucosa. : 138 : 330 : 183  The borders of the tattoo are variable, and may be well defined, irregular or diffuse. Causes
Amalgam tattoo is caused by implantation of amalgam into the tissues. : 183  It may occur in several ways:

During placement of an amalgam filling,: 183  e.g. if abrasions on the mucosa are present which allow entry of amalgam dust
Shortly after placement of an amalgam filling, e.g.
A somatic symptom disorder, formerly known as a somatoform disorder, is any mental disorder that manifests as physical symptoms that suggest illness or injury, but cannot be explained fully by a general medical condition or by the direct effect of a substance, and are not attributable to another mental disorder (e.g., panic disorder). Somatic symptom disorders, as a group, are included in a number of diagnostic schemes of mental illness, including the Diagnostic and Statistical Manual of Mental Disorders. (Before DSM-5 this disorder was split into somatization disorder and undifferentiated somatoform disorder.) In people who have been diagnosed with a somatic symptom disorder, medical test results are either normal or do not explain the persons symptoms (medically unexplained physical symptoms), and history and physical examination do not indicate the presence of a known medical condition that could cause them, though the DSM-5 cautions that this alone is not sufficient for diagnosis. The patient must also be excessively worried about their symptoms, and this worry must be judged to be out of proportion to the severity of the physical complaints themselves. A diagnosis of somatic symptom disorder requires that the subject have recurring somatic complaints for at least six months.Symptoms are sometimes similar to those of other illnesses and may last for years. Usually, the symptoms begin appearing during adolescence, and patients are diagnosed before the age of 30 years. Symptoms may occur across cultures and gender. Other common symptoms include anxiety and depression.