Buonian line is seen due to the exposure of?

A stippled blue line called Buonian line is seen on the gums in 50-70% of cases of lead poisoning.It appears due to the subepithelial deposits of granules at the junction with teeth, only near diy or carious teeth, within a week of exposure, especially on upper jaw. It is due to the formation of lead sulphide by the action of hydrogen sulphide formed by the decomposition of tooth. Ref: The Essentials of Forensic Medicine and Toxicology 29th Ed Page 488.