Crowns

Overview

A crown, as the name implies, does not sit on top of the tooth; it covers three-quarters, seven-eighths or the entire tooth. Crowns that cover three-quarters or seven-eighths of the tooth are made out of metal or porcelain, and are used when a portion of the tooth is still healthy and does not need to be covered. This article focuses on full-coverage crowns. There are a number of different materials used to construct full-coverage crowns.

Your tooth is prepared for a crown by reducing the size of the tooth, usually under local anesthesia. A small cord is then packed under your gum around the preparation to allow the crown margin to be seen (the “finish line” where the crown stops and the tooth continues: where the crown and tooth come together). The instructions for constructing the crown are made by the dentist and sent by written prescription to a laboratory by one of two methods:

  1. By far the most common method today involves an impression of your prepared tooth. The dentist uses a syringe to place a putty-like material around your tooth; the material then hardens around the tooth, creating an impression of the shape of the tooth preparation.
  2. Technology now provides dentists with the ability to scan the prepared tooth into a computer. The image is sent electronically to the laboratory for construction of the crown.
  3. Today’s technology also allows the crown to be scanned and milled from a block of material in the dental office and placed on the tooth the same day.

Why do you need a crown?

A crown is usually needed:

  • When a portion of your tooth fractures off
  • When a fracture line (a crack) runs deep into the tooth structure, causing pain when you chew (see Cracked Tooth Syndrome)
  • When a filling is too wide or when more than 50% of the biting surface is covered with a filling
  • When a root canal treatment has been performed, it is widely accepted that a tooth that has gone through root canal treatment is more brittle (because it is dead). To prevent fracture, a crown is recommended.
  • When you or your dentist want to improve the positioning of a tooth, without moving the tooth/teeth orthodontically. (see Braces)
  • When a tooth is needed to anchor a bridge (see Bridges)
  • When a tooth has tipped over time and a partial denture needs to be placed; a tooth can be prepared for a crown to upright it,, improving the placement of the removable partial
  • When a tooth has no opposing tooth to stop it and, if an upper tooth, has dropped down too far, or, if a lower tooth, has drifted up too far, a crown can be placed to bring the tooth back into the proper position
  • When a tooth has a large, old filling with defective margins (the area where the tooth and the filling come together), there is a high probability that bacteria has created decay under the filling and the filling is simply too large to be replaced, a crown is indicated to protect the life of the tooth

What are the different types of crowns?

 

All-porcelain crowns

* Zirconium crowns:

  • A zirconium core with porcelain over the top (strong) or a full zirconium crown (stronger and recommended for patients who grind their teeth; milled from a computer image)
  • Tooth-colored crowns designed to restore any of your teeth
  • Usually more expensive because they are more costly to manufacture than porcelain fused to metal crowns

* Pressed porcelain crowns:

 

  • Designed to be used in the “aesthetic zone” or the smile-line.
  • Although very beautiful, do not possess the strength of zirconium crowns.
  • Most closely resemble the enamel layer of natural teeth; their translucency and color capabilities are aesthetically outstanding.
  • Usually more expensive because they are more costly to manufacture than non-porcelain crowns

Composite with fiber-reinforcement crowns

  • Tooth-colored composite resin with fibers added to strengthen the resin
  • Do not possess the strength of zirconium or porcelain crowns
  • Not usually the most popular crowns to use to restore a tooth
  • Metal-free, making them very translucent and aesthetically pleasing

Milled Porcelain Crowns

  • An all porcelain premolar and molar crown.

    An all porcelain premolar and molar crown.

    The prepared tooth is scanned into a computer.

  • The crown is designed and a block of porcelain is placed in a milling machine and the crown design is milled in the dental office.
  • Within minutes the crown can be bonded onto the prepared tooth.
  • This is the only crown that eliminates having to place temporary crown while the lab constructs and returns the finished product.

Porcelain fused to metal crowns (PFM)

* Porcelain fused to high noble or precious metal and covered in porcelain:

  • A porcelain fused to metal crown with high gold content in the metal. Note: the metal is lighter in color.

    A porcelain fused to metal crown with high gold content in the metal. Note: the metal is lighter in color.

    A metal substructure with a higher concentration of gold

  • Designed especially for individuals who have a nickel or other metal allergy but want a tooth-colored, less expensive crown
  • May become more expensive depending on the market value of gold

* Porcelain fused to noble or semi-precious metal and covered in porcelain:

  • A metal substructure with a lower concentration of gold
  • May cause an allergic reaction in individuals allergic to some metals
  • Visually look no different than a high noble PFM crown

* Porcelain fused to non-precious or base metal and covered with porcelain:

  • Have a substructure made of non-precious metal, which contains no gold
  • Visually look no different, to the untrained eye, than crowns made with precious or semi-precious metal

* Captek crowns

  • These crowns contain gold in the substructure that is very yellow, giving the porcelain a much warmer tone
  • Most dentists and dental technicians feel the porcelain has a warmer color to it when there is a greater percentage of gold in the metal substructure.

All-metal crowns

 * Full gold crowns (FGC):

A Full Gold Crown

A Full Gold Crown

  • As the name implies, fully cover the tooth and are all gold in color
  • Kinder to the teeth they oppose because metal is softer than porcelain and it creates less wear; more appropriate for patients who grind their teeth because metal is softer against natural teeth.
  • More appropriate for patients with metal allergies because they have a higher concentration of gold and fewer base metals.

* Full semi-precious crowns:

  • Contain less gold and range in color from silvery to gold
  • Not as aesthetically pleasing as an all-porcelain crown, a PFM crown, or an FGC
  • Sometimes more cost-effective

* Full non-precious crowns:

  • Silvery in color
  • Made of base metal (no gold)

* Stainless steel crowns:

  • Not custom-made by a dental laboratory to fit your prepared tooth, but instead are a stock crown placed in one visit to your dentist.
  • Used as a short-term solution to your dental problems and are meant to be replaced at some point by a laboratory-constructed or office milled crown.