The term "sour filling" is not a standard or widely used term in dentistry. After receiving a dental filling, some patients report experiencing an unusual taste in their mouth, which can sometimes be described as sour . Another possible reason of sour filling could be decaying or failing dental fillings that lead to unpleasant tastes. The lady would have a lot of amalgam fillings because these fillings are known for their long lasting durability to other materials like composite resins. other possible reason is , Amalgam fillings are less expensive than newer materials like composites or ceramics . Also the lady would have suffered from a lot of cavities , So she should would have used a lot of amalgam fillings.