Crown

A crown refers to the placement of an artificial crown on a tooth. It acts as a 'cap' that fits over the tooth which mimics a real crown of tooth.

Purpose

  • To restore the original shape and function of teeth.
  • To improve the esthetics of teeth, such as shape, size and colour.
  • To fix a bridge onto the teeth.
    A fixed bridge is supported by crowns on either/both side.
    Photograph of upper front teeth showing that there is a missing tooth and its adjacent teeth have been treated. Underneath it is a bridge ready to be fitted into the space and the real teeth.
  • To protect teeth from fracture.
    Tooth that has undergone root canal therapy and with a large filling is more brittle. It can be protected from fracture when a crown is placed.

Materials

  • Porcelain

  • Metal alloy

    Properties

    • Durable.
    • High wear resistance.
    • Metal alloy crown can be quite thin --- only a small amount of tooth substance needs to be removed to accommodate it.

    Disadvantage

    • Metallic colour, poor esthetics.

    Application

    • Used at high stress bearing area where good esthetics is not a must. For example, posterior teeth.
      Photograph of a gold alloy crown.

  • Procedures for metal alloy crown.

    • Remove a thin layer of tooth substance on all surfaces of the crown.
    • Take impressions of the upper and lower teeth and record the bite. Construct a temporary crown to protect the prepared tooth.
    • Fabricate the metal alloy crown in the dental laboratory.
    • Remove the temporary crown and clean the tooth surface.
    • Cement the crown onto the tooth.
      Animation of the process of producing a gold alloy crown.

    Porcelain fused to metal

    Properties

    • Esthetic --- colour of outer surface is similar to natural tooth.
    • Strong and durable because of the metal alloy base.
    • Hard.

    Disadvantage:

    • Relatively more tooth substance needs to be removed from the facial surface of the tooth.

    Application

    • Used on anterior teeth.
      Photograph of the appearance of two upper front teeth before replacement with crowns.Before treatment.
      Photograph of the appearance of two upper front teeth after replacement with porcelain crowns.After treatment.

    Procedures for porcelain fused to metal crown

    • A thin layer of the tooth is removed.
    • Take impressions of the upper and lower teeth and record the bite. Construct a temporary crown to protect the prepared tooth.
    • Fabricate the porcelain fused to metal crown in the dental laboratory.
    • Remove the temporary crown and clean the tooth surface.
    • Cement the crown onto the tooth.
      Animation of the process of producing porcelain crown.

  • Stainless steel

    Properties

    • Stainless steel crown is not custom-made. It is preformed into certain sizes.
    • Since the crown is not custom-made, the procedures of fitting are simple and the time taken is relatively short.

    Disadvantages

    • Silvery colour, unesthetic.
    • Non-stress bearing, not lasting.
    • Causes tooth decay and gum disease easily --- since the crown margin is not closely adapted to the tooth, the margin is prone to accumulation of dental plaque.

    Application

    1. Used on molars of deciduous teeth.
      Photograph showing a stainless steel crown was placed on a deciduous molar.
    2. As temporary crown before the permanent crown is ready for use.

    Procedures for stainless steel crown.

    • Remove a thin layer of the tooth surface structure.
    • Choose the right size stainless steel crown and try it in the tooth.
    • Trim the crown according to the contour of the tooth.
    • Clean the tooth surface.
    • Cement the crown onto the tooth.
      Animation of the process of producing stainless steel crown.