Inlays and Onlays: Between a Filling and a Crown

What inlays and onlays are

Back teeth have a chewing surface with raised points called cusps. Decay or an old filling often damages the area between and around those cusps.

• An inlay fits inside the chewing surface, between the cusps. It replaces lost tooth in the center of the tooth.
• An onlay does the same and also covers one or more cusps. It is sometimes called a partial crown.

A direct filling is shaped in the mouth in one sitting. An inlay or onlay is made to a precise fit in a lab or by a milling machine, then bonded or cemented in.

Filling, inlay, onlay, or crown

The choice depends on how much healthy tooth remains and where the damage is. The ADA describes crowns as a way to strengthen a tooth with a large filling when not enough tooth remains to hold the filling, and to protect a weak tooth from breaking. An onlay can do part of that job while keeping more of your own tooth.

A crown needs the tooth reduced on all sides so the crown fits over it. An onlay only reshapes the damaged part. That is the main reason dentists offer onlays when the tooth allows it.

For a deeper look at full crowns, see our guide to dental crowns in Colombia.

Materials

Ceramic

Tooth-colored ceramics are common for inlays and onlays. Ivoclar lists inlays, onlays, partial crowns, and occlusal veneers among the uses of IPS e.max CAD, its lithium disilicate block. It lists a mean biaxial flexural strength of 530 MPa for that material after firing.

Ceramic onlays are usually bonded with a resin cement. Bonding needs a clean, dry tooth surface, which affects how the dentist works.

How long ceramic onlays last

A 2018 systematic review by Abduo and Sambrook in the Journal of Esthetic and Restorative Dentistry pooled 21 studies of ceramic onlays. Studies of 2 to 5 years reported 91% to 100% survival. Studies longer than 5 years reported 71% to 98.5%.

Fracture was the most common cause of failure, followed by debonding and decay. Failure was more likely on root-canal-treated teeth, back teeth, and in patients who grind or clench. At least 2 mm of ceramic thickness on the chewing surface was linked to better longevity.

Composite resin

Composite can also be made into an inlay or onlay outside the mouth. Composite is the same family of tooth-colored material used for fillings, processed to a finished shape before it goes in.

Gold and other metals

Gold inlays and onlays have a long history and are still used. They are not tooth-colored, so many patients now prefer ceramic on visible teeth. Gold alloy prices also move with metal markets, which affects cost.

What the process looks like

Steps vary by office and material. A typical sequence looks like this.

1. Exam and X-rays. The dentist checks how deep the damage goes and whether the nerve is involved.
2. Preparation. Old filling material and decay are removed, and the cavity is shaped.
3. Impression or scan. The dentist takes a mold or a digital scan of the prepared tooth.
4. Fabrication. A lab makes the restoration, or an in-office milling machine cuts it from a block. Lithium disilicate is then fired to reach full strength.
5. Temporary, if needed. If a lab makes it, you wear a temporary for the days in between.
6. Seating. The dentist checks fit and bite, then bonds or cements it and polishes it.

If your dentist has an in-office mill, inlays and onlays can sometimes be done the same day. With a lab, expect at least two visits. That difference matters a lot if you are traveling for care.

What drives the cost

We could not find a reliable, current published price for inlays or onlays that we could verify for this article. Prices vary widely by city, clinic, and material. Instead of an average, here is what moves the number.

• Material. Ceramic, composite, and gold have different material and lab costs. Gold tracks metal prices.
• Size of the restoration. How many surfaces of the tooth it covers, and whether it caps cusps, affects lab work and chair time.
• Lab vs in-office milling. An outside lab adds a lab fee and a second visit. An in-office mill shifts cost to equipment.
• Extra work. Build-ups, treatment of deep decay, or a root canal are billed separately.
• Insurance rules. Plans differ in how they classify and pay for inlays and onlays. Ask your dentist to request a predetermination so you see the plan's estimate first.

US dental claims use the ADA's Code on Dental Procedures and Nomenclature (CDT), which the ADA says keeps the documentation of treatment consistent. Ask your dentist for the code on each line of your plan. Codes make quotes from different offices easier to compare.

Our guide to reading a dental treatment plan explains how to compare line items.

Getting inlays or onlays abroad

Inlays and onlays can suit a short trip, because they need no healing time between stages. The deciding factor is how the restoration is made.

• If the clinic mills in house, you may finish in one or two days per tooth.
• If it uses an outside lab, plan for a temporary and a return visit a few days later.
• Ask the clinic to confirm, in writing, how many days your plan needs.

Follow-up still matters. The ADA advises arranging care with a US dentist before you travel abroad for treatment, in case a restoration loosens or your bite feels wrong after you return. Our dental tourism safety checklist covers the rest of the planning.

Questions to ask your dentist

1. Is my tooth a candidate for an inlay or onlay, or does it need a crown? Why?
2. Which material and brand would you use, and why that one for this tooth?
3. Will it be milled here or made by a lab? How many visits will it take?
4. Will it be bonded or cemented?
5. What CDT code will you bill, and how many surfaces does it cover?
6. What did my insurer's predetermination say it will pay?
7. What is your warranty if it breaks or comes loose?