What is an onlay?
In certain clinical cases onlays are indicated instead of conventional fillings to restore damaged teeth. Fillings are soft to begin with and are moulded in the tooth which has been shaped to take and hold the filling and then set hard. Onlays are made outside the mouth, usually in a dental laboratory on a model of your teeth and then bonded or cemented to the tooth in the surgery.
An onlay sits on the tooth and builds up its shape. Onlays can be made in tooth-coloured porcelain, gold or a white filling material called composite. Every material has different properties, advantages and disadvantages and the choice of the best material for every case depends on a number of clinical factors.
An onlay is prepared by the dentist and made by a dental technician.
What will my dentist do?
- Normally give you a local anaesthetic to numb the area.
- Remove any old filling material and any decayed or damaged tooth structure.
- Use a putty-like material to record the shape of the tooth being repaired and the teeth around it – this is called taking an 'impression'.
- Give the impression to an experienced highly trained dental technician to custom make an onlay to fit accurately your tooth.
- Use a temporary filling to protect the tooth that is being repaired while you wait for the onlay to be made.
- Bond or cement the onlay in place on your next visit approximately 2 weeks later – the dentist may make small adjustments, so that the tooth is comfortable to bite on.
When is an onlay indicated?
Onlays are indicated for back teeth (premolars+molars) in cases where:
- a large part of the crown of the tooth is missing or damaged
- buccal and/or lingual cusp of the tooth are thin and fragile and under high risk of fracture
Is it uncomfortable or painful to have an onlay made?
No. The procedure is not painful because a local anaesthetic is used during the preparation of the tooth and the taking of the impression.
What are the benefits?
- Onlays are very strong and usually last much longer than fillings.
- They are especially suitable for the chewing surfaces of back teeth and can mimic better the shape of occlusal and interproximal surfaces of natural teeth.
- Better contact points with adjacent teeth make onlays better cleansable and minimise the chance of tooth getting secondary decay long term.
What role does the dental technician play?
- The dental technician plays an important part in the making of an onlay. It takes skill and experience to fabricate an onlay from the impression that the dentist provides. The onlay must be very precise in its colour and dimensions.
- The impression that is received from the dentist is used to make a plaster or stone cast of the prepared tooth or teeth. The cast is a copy of the tooth or teeth.
- It allows the technician to make an onlay over the exact copy of a prepared tooth.
- The technician will use the same shade/colour guide as the dentist, to ensure that the replacement onlay will match the colour of the adjacent teeth.