like bex had mentioned mercury is very hard to detect ,as for myself my blood test results always came back as very low mercury ,but I knew something was causing my symtoms , I finally deicided to have my 9 amalgam filling removed ,I have been improving since then ,the good thing you have on your side is you only have to replace one filling ,but make sure that you use a dentist that uses safe removal protocols ,the I.A.O.M.T can give you a list of dentists in your area that use these protocols there number is 863.420-6373 or www.IAOMT.ORG