The Burton line is a clinical sign

Medical sign

A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....

 found in patients with lead poisoning

Lead poisoning

Lead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems...

. It is a thin, grey-blue line visible along the margin of the gums, at the base of the teeth.

The sign was described in 1840 by Henry Burton

Henry Burton (physician)

Dr. Henry Burton was an English physician who is remembered for describing the Burton line in 1840. He was born in London, attended Tonbridge School and studied medicine at Caius College, Cambridge where he qualified in 1826. He was a physician at St. Thomas' Hospital in London from 1828, and...

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A similar line, the "bismuth line", occurs in people who have ingested bismuth compounds; bismuth, however, is of very low toxicity.