Q: “Burton's line” named after the physician who first described it, is a thin bluish purple line at the tooth and gum interface. This line is a clinical sign of which metal toxicity?
Answer: Lead toxicity
Although 'Burton's line', also known as 'lead line' is not a hallmark sign of lead toxicity but in view of pertaining history and other symptoms like colicky abdominal pain, it calls for Blood Lead Level (BLL) check up. Also, presence of basophilic stippling on blood smear can be an associated finding.
Burton’s line occurs due to the interaction of the circulating lead and the sulphur ions released by oral micro flora. This causes the deposition of lead sulphide at the tooth gum interface.
See related article with picture here