i think it is the electric currents taking minerals out through electrolysis and disrupting the nerves. mercury holds up so well because it actually inhibits bacterial growth around the edges and last 20+ years instead of five for composites. composites are no panacea. but then, i know how to prevent cavities by avoiding fluoride and substances which coat the teeth and keep them from being in contact with mineral rich saliva. oil pulling is a godsend.