What can be done when the tooth has decay? Conservatively, dental fillings are used to replace the lost tooth structure so that further destruction of the tooth is prevented and at the same time, restore its function. Dental fillings can either be made from amalgam or silver restorations or composite resin restorations. Amalgam fillings are a mixture of metals including mercury and usually placed in the back teeth. Composite fillings, the most common way of filling teeth, are made of tooth colored resin and are bonded to the tooth structure. The choice will be up to the patient depending on their preference.