Heathwood Dental Practice, Crowthorne, Berkshire. Tel. 01344 776933

What is a Crown?

A crown is a type of dental restoration that fits over a tooth, much like a thimble does over a finger. In doing so, it recreates the natural shape of the tooth as well as helping to reinforce and strengthen the underlying tooth structure.

What is an Onlay?

An onlay is similar to a crown in that it fits over the tooth. However, whilst a crown usually covers all the tooth structure visible above the gum, an onlay can be used to overlay the missing tips of a tooth without necessarily extending all the way to the gum.

Why would you need a crown or onlay?

There are a number of reasons why a crown or onlay would be needed;

  • They are useful in the restoration of teeth which have been weakened by decay, large fillings and root canal treatments.
  • Since a crown sits over a tooth, they can also be used to improve the appearance of a tooth.
  • To restore the shape, appearance and function of a tooth fractured in an accident.
  • To help hold a bridge or denture in place.

Types of Crown

  • Gold (precious metal) - These are very useful for onlays and some crowns. They are strong and long lasting. However, aesthetically they are more visible due to their colour. This is balanced by the fact that they can be made very thin; thus less tooth needs to be cut away during the preparation stage, meaning that more tooth is preserved. In addition, the alloy used is 'biomimetic'. This means that they mimic natural tooth structure as they are quite inert, as well as being of similar hardness to natural tooth. As a result, the restoration is quite sympathetic to the tooth biting against it.
  • Porcelain bonded to precious metal - Most crowns are made of an underlying thimble of gold alloy overlayed with porcelain to produce a strong, long lasting natural looking restoration. Due to their superior aesthetics, they are the first choice for most people. However, in order to produce this, more tooth needs to be cut away. Also, porcelain is harder than natural tooth which means it is less sympathetic to the tooth biting against it.
  • Porcelain crowns - This is a modern technology used to create crowns made entirely of porcelain. The resulting teeth look exremely natural, as the natural translucency of a tooth can also be reproduced. They are best used on the front teeth where aesthetics are vitally important.

How long is it going to take?

Preparation of a tooth for a crown, combined with the moulds taken of the teeth, and production in surgery of a temporary plastic crown usually takes an hour. If needed, more than one tooth can be done at a time though, and your dentist can advise you as to the overall length of apointment needed.
Usually two weeks later, a second shorter appointment of roughly 30 minutes is needed to fit the final crown.

How is it done?

An x-ray is taken to confirm the quality of the underlying tooth, and local anesthetic is used to numb the area. The shape of the tooth is modified by the dentist to allow space for a crown to fit over the remaining structure. This is then recorded by a mould which is sent to a qualified (British) dental laboratory who manufacture the crown for your tooth. You may be asked to to attend the laboratory to have the colour of your crown porcelain matched to your natural teeth.