I did also here this from someone else that posted on this forum below. I believe that the substance was something called malanate, but I'm not certain of this. If you are very concerned about the exact composition of the fillings, I would suggest doing some research. When you call the dentist, make this inquiry. Ask the dentist for the exact chemical composition of the material used in the filling. I didn't do it, so I'm not sure of the exact material used in my teeth. But, my dentist assured me that he uses the most bio-compatible materials. But, if it is a major concern for you, I would do more research. Find out exactly what the chemical is that Hulda Clark is referencing and also whether the dentist uses that chemical in the filling.