A crown (sometimes called a cap) is a dental restoration that completely covers or encircles a natural tooth root or is affixed to an implant. They are needed when a natural tooth has a large cavity that threatens the health of the natural tooth or when an endodontic treatment (root canal) has been performed. Additionally, crowns can be placed on an implant when a tooth has been lost or had to be removed. Crowns are bonded to the natural tooth using a dental cement, improving both the strength and appearance of the tooth.
Preparation: Prepping a tooth for a crown involves the irreversible removal of much of the natural tooth structure to give space for the crown itself. This is done by removing the enamel (and with it the cavity) typically down to the dentin. How much of the enamel that is removed depends on the material that will be used for the crown. Then, an impression is taken that is then sent to a lab where the crown is fabricated.
Types of Crowns: There are many methods and different types of materials used in fabricating crowns.
Full Gold Crown: A full gold crown is composed of a single piece of alloy and though it is called ‘a gold crown’ it is typically composed of several metals such as gold, silver and/or platinum (noble metals) and/or copper and tin (base metals). Crowns that are made using noble metals are of better quality and can only be labeled ‘high noble’ when the crown is at least 60% noble metal with at least 40% of the noble metal being gold. Gold is often used in dental restorations because its properties and strength resemble that of natural teeth.
Porcelain-fused-to-metal crowns (PFMs): PFMs are crowns that consist of a metal shell upon which a porcelain veneer is fused to it using a high heat oven. The metal shell provides the strength while the porcelain gives the crown a natural tooth-like appearance allowing it to be used for front teeth giving a natural look. The metal shell can be made of either noble metals or base metals and the porcelain can be colored to match the existing adjacent teeth.
Restorations without Metal: Though traditionally crowns have been entirely made of gold or porcelain that is fused to noble or non-noble metal for extra strength, today there are a variety of new technologies and composites that allow crowns to be made entirely from high-strength ceramics, porcelain and other materials. While there are many two popular forms of modern crowns are the all-ceramic crowns made by the CAD/CAM method of fabricating and Zirconium Crowns (Zirconia). Both are very strong as well as that they can be easily color matched to the other teeth resulting in a natural looking tooth that can be placed anywhere in the mouth.
A dental bridge (also known as a fixed partial denture) is a type of dental restoration that is used to ‘bridge’ a gap created by one or more missing teeth by joining permanently to the teeth on either side of the gap. The teeth on either side of this space can be either natural teeth, or more commonly they are crowns. Bridges vary greatly depending on how they are fabricated as well as the way that they are attached to the adjacent teeth. Like crown, bridges are made from a variety of materials including gold, porcelain fused to metal, non-metal composites and in some cases porcelain alone. When to use bridges instead of single crowns and implants depends on the condition of the patient’s bone and remaining teeth. One should discuss all the options available with their dental professional.