What is "phossy jaw"

n. A disease resulting from exposure to white phosphorus causing degeneration of the teeth and jaw.

Phossy jaw, formally phosphorus necrosis of the jaw, is an occupational disease of those who work with white phosphorus, also known as yellow phosphorus, without proper safeguards. It was most commonly seen in workers in the match industry in the 19th and early 20th century. Modern occupational hygiene practices have eliminated the working conditions which caused this disease.