What is an Inlay and Onlay?

What is an Inlay and Onlay?

Inlays and onlays are examples of what we call an ‘indirect’ restoration i.e. one made outside the mouth and stuck in; as opposed to a filling that is done directly in the mouth. They have a number of advantages because they are ‘made’ and are a very effective way to restore your tooth, particularly if a large amount of tooth has been lost.


  • An inlay- As the name suggests, this restoration sits inside the tooth.
  • An onlay- In contrast is bonded on top of the tooth, replacing some or all of the cusps of the tooth.

The amount of decay or existing filling being replaced will determine the shape and type of the restoration. It is therefore common to have a restoration that is actually part inlay and part onlay, rather than an inlay or an onlay in the strictest sense of the word. They are generally only used on posterior (back teeth), that is your premolars and molars (teeth numbers 4-8).

How Long do Inlays Last?

Inlays and onlays are regarded as a long-term solution for fixing your teeth. In general they would be expected to last a similar number of years to crowns (around 20 years) and considerably longer than conventional fillings– provided they are done well and you keep your hygiene up to scratch.

As always when talking about how long things last, there are many factors to take into consideration in relation to:

  • The dentist- Their experience, the materials used to make the inlay, the impressions taken, the cements used for bonding, technique etc.
  • The lab technician- Their experience, the materials used, the quality of the work etc.
  • The tooth- How much tooth remains, the state of the nerve, its support, biting forces etc.
  • You- Access to the area, saliva control, oral hygiene etc

Long-term data is pretty scarce on this subject and as always, this research is fraught with the problems and difficulties of keeping the dentist and patient variables consistent to draw any meaningful results.