Burton's line

Burton's line, also known as the Burton line or Burtonian line, is a clinical sign found in patients with chronic lead poisoning. It is a very thin, black-blue line visible along the margin of the gums, at the base of the teeth.^[1][2] It is caused by the reaction between circulating lead and sulphur ions produced by oral bacteria, forming deposits of lead sulfide in the gums.^[3]

Burton's line
Differential diagnosis	Chronic lead poisoning

The sign was described in 1840 by Henry Burton:^[4]

The edges of the gums attached to the necks of two or more teeth of either jaw, were distinctly bordered by a narrow leaden-blue line, about the one-twentieth part of an inch in width, whilst the substance of the gum apparently retained its ordinary colour and condition.

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