Blue line on the gum, abutting on the teeth

heavy metal toxicity (lead, bismuth, mercury, gold, silver, thallium, copper)

• Libman, as in Libman-Sacks endocarditis, was a renowned diagnostician. This article is a collection of snippets, e.g. "In cases of suspected lead intoxication, it is necessary to examine the gums of every tooth, because a lead line need not be present in all of them. For careful diagnosis, one should use a magnifying glass which will make visible the separate pigmentary deposits in the tips of the papillae, and their location a little below the margin of the gums." [101]
• Tartar deposits on the teeth accentuate formation of a bismuth line. [p. 184] [102]
• The Burton lead line is blue because of the deposition of lead sulfide. Eating eggs may accentuate the line because of their sulfur content.
    Interestingly, there is an additional intersection between chickens and lead. In areas where lead mining was formerly done, "there are occasional cases of lead poisoning among animals such as horses and cows resulting from ingestion of contaminated grass roots. Other animals are even more at risk.... One way of pinpointing the ancient lead-workings is to ask if anyone in the area keeps chickens. On lead-rich ground it is impossible to do so as the birds' penchant for eating grit means they are soon poisoned." [103]