An onlay is a custom restoration that replaces part of a tooth, including one or more of its cusps, while a crown covers the whole visible tooth. Onlays are used when damage is too large for a filling but there is still enough healthy tooth that a full crown is not needed, so they usually preserve more natural tooth. Which one is right depends on how much sound tooth is left and where the cracks are, which a dentist can tell after an exam.
What is an onlay?
Teeth can be repaired in two ways. A direct filling is placed and shaped in the mouth in one sitting. An indirect restoration is made outside the mouth, usually from porcelain or ceramic, and then bonded in place. Inlays and onlays are indirect restorations.
The difference between the two is the cusps, the raised points on the chewing surface of back teeth. Cleveland Clinic explains that an inlay fills the area between the cusps, while an onlay also covers at least one cusp. Both fit into the existing tooth like a puzzle piece and are permanently bonded.
What is a crown?
A crown is a tooth-shaped cap that fits over the entire visible part of the tooth. To make room for it, the dentist removes a layer of enamel from all sides, then bonds or cements the crown over what remains. The ADA describes crowns as a way to strengthen a tooth with a large filling when there is not enough tooth left to hold it, to protect a weak tooth from breaking, to restore one that has already broken, and to cover a dental implant.
Onlay vs crown: what are the main differences?
- Coverage: an onlay replaces the damaged part of the chewing surface, including one or more cusps. A crown covers the whole tooth above the gum.
- Tooth preserved: an onlay usually keeps more healthy tooth structure, because only the damaged part is shaped. A crown requires reshaping all around the tooth.
- When used: Cleveland Clinic describes inlays and onlays as the option when a tooth has too much damage for a filling but not enough to warrant a crown.
- Protection: a crown holds the whole tooth together, which matters when there are cracks running down the sides or very little tooth is left.
- Visits: both are often made in a lab over two visits, with a temporary in between. Some offices use CAD/CAM milling to make either one in a single appointment.
When does an onlay make more sense?
Onlays are often considered when an old large filling has failed or a cusp has broken off, but the walls of the tooth around it are still sound. Replacing just that part keeps more of the natural tooth, and the margin often sits above the gumline where it is easier to keep clean. If the tooth needs more work later, there is still enough tooth left to place a crown.
When is a crown the better choice?
A crown is usually the safer option when the tooth is badly broken down, when cracks extend across several walls, or when a back tooth has had a root canal. Cleveland Clinic notes that most people who have root canal therapy also need a crown for strength and support. Crowns are also used to restore implants, to anchor a bridge and to cover teeth that are severely worn or discolored.
How long do onlays and crowns last?
Cleveland Clinic gives crowns a range of five to 15 years with proper care, with the material, your bite and your oral hygiene all affecting where in that range a crown falls. Onlays are made from similar materials and are subject to the same kinds of wear, and their lifespan varies from case to case. What shortens the life of both is the same: decay at the edges, grinding and clenching, and chewing very hard things.
What should you ask your dentist when choosing?
- How much healthy tooth is left, and are there cracks running down the sides?
- Has the tooth had, or is it likely to need, a root canal?
- Where will the edge of the restoration sit, and how easy will it be to clean?
- What material do you recommend for this tooth and why?
- How does my insurance treat onlays compared with crowns?
The answers usually make the choice clear. You can read more about how both are made on our onlays and crowns page.
Common Questions
- Is an onlay better than a crown?
- Neither is better in general. An onlay keeps more of your natural tooth when the damage is limited, while a crown gives more protection when the tooth is badly broken or root-canal treated.
- What is the difference between an inlay and an onlay?
- An inlay sits within the cusps of the tooth, like a large filling made in a lab. An onlay extends over at least one cusp, so it can rebuild part of the biting surface.
- Does getting an onlay or crown hurt?
- Both are done with local anesthetic, so the preparation itself should not hurt. Some sensitivity for a few days afterwards is common and usually settles.
- Does insurance cover onlays?
- Coverage varies by plan, and onlays and crowns are not always treated the same way, so it is worth checking your benefits before treatment.
Sources
- Restorative Dentistry, Cleveland Clinic
- Dental Fillings, Cleveland Clinic
- Dental Crowns, Cleveland Clinic
- Crowns, American Dental Association (MouthHealthy)
This guide is general information, not a diagnosis. A dentist can tell what applies to you after an exam.