Dental crowns are tooth-shaped caps that cover teeth that have decayed or have been damaged, such as those that have cracked. Dental cements, which are used to hold crowns onto teeth, are materials created by combining powder with liquid. Various types of dental crown cements exist to either temporarily or permanently cement a crown.
Zinc phosphate, a water-based cement, is one of the oldest dental cements used to attach crowns permanently to teeth, according to "Torres and Ehrlich Modern Dental Assisting." Mixing zinc phosphate produces an exothermic reaction, which means heat is released during the mixing. For this reason, zinc phosphate should be mixed using a spatula and a cool, dry, thick glass slab that is about 20 degrees C in temperature.
Zinc phosphate also can be used in deep cavity preparations to protect a tooth from thermal shock, which takes place when sudden temperature changes occur in a tooth. The chief component in the liquid part of zinc phosphate is phosphoric acid, which can irritate the pulp --- the part of the root of a tooth that has blood vessels and nerves. As a result, a desensitiser should first be placed in a tooth before zinc phosphate is used there.
Zinc oxide-eugenol, an oil-based cement, can be used to temporarily or permanently cement dental crowns to teeth. Zinc oxide-eugenol must be mixed on an oil-resistant paper pad that will not absorb any of the liquid. The eugenol in this cement actually soothes an irritated pulp and is good for patients who are experiencing tooth sensitivity, although eugenol has a strong odour. Removing unused or excess zinc oxide-eugenol can be difficult after it hardens, in which case a solvent called oil of orange can be used, according to "Dental Materials: Properties and Manipulation."
Glass ionomer is extremely versatile in that it can easily attach to enamel --- the hard white material that covers the crown of a tooth --- as well as metal. In fact, glass ionomer can be used to cement a metal crown. In addition, glass ionomer slowly releases fluoride when applied to a tooth, which helps to prevent recurring decay in that area.
Glass ionomer also is gentle on the dental pulp and adheres easily to a slightly moist tooth surface. This cement is easy to use when seating a dental crown because it is thin. Glass ionomer can be mixed either on a cool, dry glass slab or paper pad. However, this type of cement also exists in the form of a capsule that can be triturated, or mechanically mixed, and then expressed using a dispenser.