A leaking filling basically means that the filling has separated from the tooth structure which will cause bacterial infestation which will cause decay. A metalic taste is known to happen, but may not be noticed in many cases.The only way to be sure is to have a dental examination.The dentist will run his explorer over the surface of the filling. If it catches, this means there is seperation between the filling and the tooth (Leakage).ilver filling doesnot bond to the tooth but instead fits into the cavity.over a period of time the margins of the filling will have a gap with the tooth structure.usually you will feel sensitivity to cold food stuffs if there is leakage,food getting stuck or discolouration of the tooth is also possible.