In 1845 the American Society of Dental Surgeons banned the use of mercury fillings because of health concerns.*
Do these health concerns persist today?  Check out these videos:  Video 1 — Mercury FIllings    Video 2 — Neuron Degeneration
 
(*) Source:  Ring ME (2005). “Founders of a profession: the original subscribers to the first dental journal in the world”. The Journal 
of the American College of Dentists 72 (2): 20–5.