Introduction 

You can think of a dental inlay or onlay as being midway between a filling and a crown. Inlays or onlays are used when not enough tooth structure remains to support a filling, but the tooth is not so severely damaged that it needs a crown.

An inlay is similar to a filling, but it lies within the cusps (bumps) on the chewing surface of your tooth. An onlay is more extensive than an inlay and covers one or more cusps. 

Inlays or onlays can be made of gold, composite resin (plastic) or ceramics. They can last for decades. However, how long they last depends on the material used, the teeth involved, the forces of chewing and how well the patient maintains them with good oral hygiene and regular visits to a dentist.  

What It's Used For  

An inlay or onlay is one way to restore a damaged or decayed tooth. If more than half of the biting (occlusal) surface of a molar has decayed, your dentist may use an onlay rather than an inlay. Inlays and onlays can be direct (placed during a single dental visit) or indirect (made in the laboratory).

Preparation  

The tooth and surrounding area will be numbed with local anesthesia. Some people also may be given nitrous oxide or another type of sedation.

How It's Done

There are two types of inlays and onlays: direct and indirect. Direct inlays and onlays are made in the dental office and can be completed in one visit. Indirect inlays and onlays are made in a laboratory and require two visits.

Which type of inlay or onlay is used depends on how much sound tooth structure is remaining and whether there are any cosmetic concerns.

Direct Inlays and Onlays

Your dentist will remove the decay and shape the tooth to receive the inlay. He or she then will place a soft material (composite resin) and mold the composite to fit the tooth structure. The inlay is then removed and hardened in a special oven. The hardened inlay will be cemented or bonded to your tooth. After the inlay is cemented, it will be polished. Your dentist may have to shape it slightly to adjust your bite (the way your teeth come together).

Indirect Inlays and Onlays

Your dentist will remove the decay, take an impression of the prepared tooth and neighboring teeth and put in a temporary filling. The impression will be sent to a laboratory, which will make the inlay or onlay.

At your second visit, your dentist will take out the temporary filling, clean the tooth and use cement or a bonding agent to place the inlay or onlay. After the inlay or onlay is cemented, it will be polished. Your dentist may have to shape it slightly to adjust your bite.

Follow-Up 

Inlays and onlays require only regular oral hygiene, which includes brushing, flossing and regular visits to the dentist.

Risks  

Cemented inlays and onlays can come loose if the cement washes out or is contaminated with saliva while it is being applied. Composite or porcelain (ceramic) inlays and onlays also can crack.