Inlay, onlay or crown? What each one covers and when it fits

The short answer: they differ by how much tooth they cover

An inlay fits inside the chewing surface of a tooth. An onlay covers the inside and also one or more of the pointed chewing tips, called cusps. A crown covers the whole tooth above the gum.

All three repair a tooth that has too much damage for a plain filling. The more tooth you have left, the less your dentist needs to cover. That is why inlays and onlays are sometimes called partial crowns.

Picture the top of a back tooth like a small bowl with four or five pointed rims. Those rims are the cusps. An inlay sits in the bowl. An onlay sits in the bowl and over some of the rims. A crown fits over the whole thing.

What an inlay is

An inlay is a custom-made piece that fits into a cavity between the cusps of a back tooth, like a puzzle piece. It is made outside your mouth, from porcelain, composite resin or gold, and then bonded in.

It is a good fit for a cavity that is too big for a regular filling but leaves the cusps strong. Because it is shaped for your tooth and cemented in, it can hold the tooth together better than a large filling.

Because an inlay is made outside the mouth, it is not shaped by your dentist's hand in the chair. It is designed from a scan or impression, so the fit can be very exact. Your dentist will check it before it is bonded, so any small adjustments are made at that visit.

Inlays are most common on back teeth, such as molars and premolars, where chewing force is greatest. They are less often used on front teeth.

What an onlay is, and what a crown is

An onlay covers more. It sits inside the tooth and also over one or more cusps, and in some cases the whole chewing surface. The ADA's MouthHealthy site describes gold inlays and onlays as a durable choice, and porcelain versions are tooth-colored.

Dentists reach for an onlay when a cusp is weak or partly broken, but the rest of the tooth is sound. It protects the weak spot without removing the strong parts.

A crown is a cap that covers the entire visible tooth. To make room, your dentist shapes the tooth all the way around. According to Cleveland Clinic, crowns last about 5 to 15 years with proper care and are used for teeth weakened by decay, large fillings, cracks or a root canal.

A crown is the best choice when there are too few healthy walls left for an inlay or onlay to hold on to.

Side by side

Here is a quick way to compare them:

• Inlay: sits inside the cusps, removes the least tooth, for medium cavities
• Onlay: covers one or more cusps, for bigger damage with sound walls
• Crown: covers the whole tooth, for weak, cracked or root-canal-treated teeth
• Filling: for small cavities, done in one visit

What they are made of

Ceramic or porcelain looks most like a natural tooth and stands up to wear well. Gold is very strong and can last 20 years or more, but it is the most costly and is visible. Composite resin is another option, with a softer feel, though it can wear faster.

Your dentist will help you choose based on where the tooth is, how hard you bite, whether you grind at night and how much you care about color.

Another point is wear on the teeth around the restoration. A material that is much harder than enamel can wear down the tooth that bites against it. Your dentist keeps that in mind, especially if you grind your teeth.

What the visits look like

Inlays and onlays usually take two visits. At the first, your dentist numbs the tooth, removes decay, shapes the tooth and takes a digital scan or impression. A temporary covers the tooth while the piece is made. At the second visit, the final piece is checked for fit and bite, then bonded.

Crowns follow the same pattern. Cleveland Clinic notes that some offices can make a crown in one visit, but same-day crowns are not for everyone.

Between visits, avoid sticky and hard foods on that side. If the temporary piece comes off, call your dentist so the tooth is covered again, since an uncovered tooth can be sensitive and shift.

Why many dentists like inlays and onlays

The big benefit is that they keep more of your natural tooth. A crown needs a layer removed from every side. An onlay only needs the damaged part shaped. The less tooth you lose, the more you keep for later.

They are also well fitted, because they are made on a model of your tooth, and they can strengthen the tooth in a way a big filling cannot. They are not right for every tooth. If the walls are thin or cracked, a crown is safer.

If your dentist suggests a crown, it is fair to ask whether an inlay or onlay would work. If it would not, ask why. The answer should be about how much healthy tooth is left, and your dentist should be able to show you.

Another point is gum health. The edges of a well-made inlay or onlay often sit above or at the gum line, which makes them easier to keep clean than a crown edge that sits below it. Your dentist will check where the edges sit.

What to ask your dentist, and what we offer at KDA

Ask three things: how much healthy tooth is left, whether an inlay or onlay would work and what the plan is if the repair fails. A good dentist will show you the X-ray and explain the choice in plain words.

Kendall Dental Associates offers porcelain inlays and onlays, crowns and bridges and tooth-colored fillings. We use digital X-rays and 3D scans to plan each repair. Call 305-271-1421 or visit us at 8833 SW 107th Ave, Miami, in the Kendall Mall. We are open Monday to Friday, 8:00 AM to 5:00 PM, with emergency care available 24/7. We accept most dental insurances and most Medicare supplemental plans, and financing is available.

Bring up your habits too. If you grind your teeth, chew ice or have had a piece of a tooth break before, say so. These details help your dentist choose a material and a design that will hold up.

Common questions

This article is general information, not medical advice. Your dentist will confirm what is right for you at your exam. General information checked against: mouthhealthy.org, my.clevelandclinic.org, mouthhealthy.org.