Inlay and Onlay Guide: Differences From Fillings and Crowns, Gold, Ceramic and Resin Materials, and the Treatment Process

An inlay is an indirect restoration in which a piece made outside the mouth to match the cavity left after decay removal is fitted and bonded, and an onlay is a slightly larger version that also covers part of the pointed cusps of the chewing surface. They are used when the damage is too large for a direct resin filling but a crown would waste too much of the remaining tooth. Gold, ceramic and resin materials are available, treatment usually takes two or more visits, and cost varies with material and dental clinic.

Published 2026-11-08 · Updated 2026-11-08 · DentalStatics editorial team

Key facts

Indications for gold inlays	Teeth with large cavities that are hard to restore with amalgam or composite resin, and replacing amalgam with large defects (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Number of visits	2 or more, for impression and bonding (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Gold inlay service period	Many people use them for 10 years or more (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Tooth-colored inlay materials	Composite resin and porcelain (ceramic); porcelain is widely used on molars too (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Reaction after treatment	Sensitivity may occur early on, and root canal treatment may be needed if severe (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)

How do inlays and onlays differ from fillings and crowns?

A resin filling is a direct restoration in which material is placed and hardened right in the mouth, whereas inlays and onlays are indirect restorations bonded as pieces made by a dental lab or milling equipment from an impression. The National Health Information Portal explains that indirect restorations can be more precise and stronger than direct restorations.

A crown wraps the entire crown of the tooth, while an inlay covers only the inside of the cavity and an onlay only part of the cusps, leaving more healthy tooth. If the remaining tooth wall is thin or cracked, a crown may be better than an inlay.

Resin filling: small cavities, completed in one visit
Inlay: medium-sized cavities, restores only the inside of the cavity
Onlay: cavities that damage the cusps, covers part of the chewing surface
Crown: when much of the tooth crown is damaged or after root canal treatment

How do gold, ceramic and resin inlays differ?

According to KDCA materials, gold inlays do not dissolve in saliva or corrode, are resistant to breaking under chewing force, and show little volume change after bonding. On the other hand, they differ in color from the tooth and are hard to use in visible places, and because they conduct heat well, a base material to protect the nerve is needed.

Tooth-colored inlays are made of composite resin or porcelain. Resin inlays wear the opposing teeth less and are elastic so impact is less transmitted, while porcelain inlays excel in color and biocompatibility. In exchange, treatment costs are relatively higher and they may break if you grind or clench your teeth.

What is the order of inlay treatment?

At the first visit, after anesthesia, the decay is removed, the shape of the cavity is refined, and an impression is taken. While the lab makes the inlay, a temporary filling material is placed in the cavity. At the second visit, the temporary material is removed, the inlay is tried in, then bonded with dental cement and the bite is adjusted.

More recently, a method is also used in which the tooth is scanned with a camera instead of using impression material, and the inlay is milled from the designed data. The National Health Information Portal explains that the precision of this method is increasing with technological advances.

What should you be careful about while waiting for the inlay and after it is bonded?

Temporary filling material does not bond firmly to the tooth, so it is best to avoid tough foods and very hot or cold foods. If you go without the temporary material, the tooth may shift slightly and the finished inlay may not fit, so tell the dentist right away if it comes out.

For the first few days after bonding, you may feel sensitivity to cold. If the sensitivity gradually worsens or you have pain even at rest, the nerve may be inflamed and needs checking. The inlay margin is a place where secondary decay easily forms, so care for it carefully with floss.

How do you choose an inlay material and compare costs?

Priorities differ by location: for a small molar that shows when you smile, a tooth-colored inlay may be considered, while for a back molar with strong chewing force that is rarely seen, a gold inlay may be considered. Grinding habits, how prone you are to cavities and the thickness of the remaining tooth wall also affect material choice.

Inlay costs differ by material and dental clinic. The Health Insurance Review and Assessment Service publishes uninsured medical fees by institution on its website and the Geongang-eum app, so searching by treatment item shows the price range at local clinics in advance. When you get a quote, check whether it includes the temporary filling and bonding.

Common myths and facts

Myth: Even for a small cavity, an inlay lasts longer.

The National Health Information Portal lists small, shallow cavities and cavities limited to the chewing surface as cases not suited to gold inlays. For small cavities, methods that remove less tooth, such as resin, are considered first.

Myth: Ceramic inlays are weak and cannot be used on molars.

The National Health Information Portal explains that porcelain strong against external force has been developed and porcelain inlays are widely used on molars. However, severe grinding can break them, so the choice takes bite force into account.

Frequently asked questions

Are inlays covered by health insurance?

Inlays are an uninsured treatment not covered by health insurance, so prices differ by material and dental clinic. For cavity treatment, the materials covered for a long time were amalgam and the like, and composite resin is covered only for permanent teeth up to age 12.

Is sensitivity after an inlay normal?

Sensitivity to cold for a few days right after bonding is a common reaction. However, if it gradually worsens or you have pain on your own at night, there may be nerve inflammation and you should be examined.

Should I choose an onlay or a crown?

If part of a cusp is broken but the remaining tooth wall is strong, an onlay can preserve more of the tooth. For a molar that has had root canal treatment or a tooth with widespread cracks, a crown that wraps the whole tooth is sometimes recommended.

Can children have inlays?

The National Health Information Portal lists young patients as a case not suited to gold inlays. For permanent-tooth cavities up to age 12, light-cured composite resin filling is covered by health insurance, so that method is often considered first.

Can an inlay that came out be bonded back?

If there is no decay or fracture in the inlay that came out and in the tooth under it, it may be bonded back. Do not throw away the piece; bring it to the dentist, who will decide after looking at its condition.

References

Korean version →