In the past, whenever a large filling or crown was used to restore a badly broken down tooth, a patient could usually expect to experience temperature sensitivity on that tooth for up to a month afterwards. New adhesive cements and insulating liners have almost eliminated this problem completely. Some of the new advanced polymer-resin cements are so strong that they allow dentists to cement crowns on to very small tooth segments. Previously, teeth such as these used to require root canals and posts before crowns could be attached to them. Many of these new cements and liners contain fluoride, which prevents decay from forming years after a restoration has been placed.