So you have been told that you need a tooth crowned but it had a filling in it before. Why can’t it just be filled again? A crown or “cap” is a dental restoration that caps over the entire tooth in order to hold it together when the tooth has lost a great deal of existing tooth structure. Teeth that are in need of crowns rather than fillings have generally lost so much tooth structure that the tooth risks breakage and even possible loss of the tooth if a filling is placed. The purpose of the crown is to fit over the entire tooth and hold it together to try to prevent breakage and give a solid structure with which to chew.
A bridge is prepared similarly to crowns as they are effectively multiple crowns made in one piece meant to replace a missing tooth or teeth, usually in between the two ends of the bridge. Generally for bridges, the tooth on either end of the missing tooth is prepared for crowns and the two crowns are connected to the false tooth in the middle. These are made when the patient wants to replace the missing tooth with something that is not removable from their mouth and is not willing or able to place a dental implant. Unfortunately, since the bridge is made with purpose of replacing missing teeth, the teeth on either side of the false tooth that are prepared for crowns may not actually need the crowns due to loss of tooth structure.
Preparation for Crown and Bridge
For both a crown and the teeth holding a bridge, preparations requires numbing the tooth and removing a minimum of 1.5-2 mm of tooth structure across the top and around the sides of the tooth in order to make space to place the crown over the tooth. Impressions are made of the prepared tooth to fabricate the custom made restoration in the laboratory and a provisional or “temporary” crown is placed over the tooth for the patient to wear until the crown is completed, usually in a week or two. The patient then comes back at a later appointment to have the final restoration adjusted and cemented into place. There are milling machines that can produce crowns “while you wait” and bypass the need for the provisional restoration. These are generally functional crowns, but do give up strength that you can get from crowns that require more time to produce.
Longevity of Crown and Bridge
Crowns and bridges can last anywhere from a few years to 30+ years depending on how well the patient takes care of them and how prone a patient is to dental decay. The most common reason that someone has to replace a crown or bridge is a cavity starting at the edge of the crown, most commonly in between teeth. Therefore, maintenance requires brushing and flossing AT LEAST on a daily basis and having regular biannual cleanings and exams and annual x-rays. Prevention or early treatment is the key to longevity of these restorations.