Lost fillings can in some cases be replaced temporarily by using one of the over the counter temporary cements such as Tempanol or Dentemp depending on the size and shape of the area. Crowns too can be temporarily recemented with these with these medidation. However, for recementing a crown it is probably better to choose a formulation that requires mixing a powder (zinc oxide) and a liquid (eugenol). These components are used in the dental office as a temporary cement and as a sedative filling material. Follow the directions carefully before using, and remove as much of the old cement as possible before placing the new cement into the crown.