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Inlays, onlays and overlays: when a filling is not enough and a crown is too much

A filling made in a laboratory or by computer and bonded to the tooth can close a large cavity without cutting away as much tooth as a crown

When decay or an old filling in a back tooth gets bigger, two classic options are discussed: a new filling, or a crown (cap) that covers the whole tooth. Inlays and onlays sit between the two: they are fillings made outside the mouth and bonded to the tooth. An inlay stays within the hollows of the tooth; an onlay also covers one or more cusps (the pointed chewing peaks of the tooth); an overlay covers the entire chewing surface. Below you will find which is considered for which tooth, the difference between ceramic and composite, the 5- and 10-year results from research, and what choosing an onlay instead of a crown gains and what it puts at risk.

Short answer

Inlays and onlays are fillings made outside the mouth to fit the cavity in the tooth and then bonded to it. They are considered when the damage is too much for an ordinary filling but too little for a crown. An inlay stays within the hollows of the tooth, an onlay covers one or more cusps, and an overlay covers the entire chewing surface. A meta-analysis of ceramic inlays, onlays and overlays found survival of 92–95% at 5 years and 91% at 10 years; the most common reason for failure was fracture.

Where it sits: Between a filling and a crown; the sound walls of the tooth are preserved
Material: Ceramic (porcelain, glass ceramic), composite, gold
Survival with ceramic: 92–95% at 5 years, 91% at 10 years (meta-analysis)
Appointments: Usually two if made in a laboratory; one if made by computer in the surgery

What an inlay or onlay solves

An ordinary filling is placed in the tooth while soft and hardens inside the mouth. For small and medium-sized cavities this is enough. As the cavity grows, especially if one of the cusps has become thin or has broken, a large filling shaped inside the mouth struggles to carry the force of chewing. The classic solution at that point is to reduce the tooth on every side and make a crown to go over it. Cleveland Clinic describes inlays and onlays for exactly this in-between zone: when a tooth is too damaged to support a filling, but not damaged enough to need a crown.

The three terms are distinguished by how much of the tooth the restoration covers. An inlay stays within the pits of the chewing surface and the surfaces between the teeth, and does not extend over the cusps. An onlay covers at least one cusp; by wrapping a weakened wall from above, it aims to stop it from cracking. An overlay covers the entire chewing surface and is the closest to a crown; the difference is that the side walls of the tooth are left uncut. In research this group is called partial coverage restorations; some publications also give very thin overlays the separate name occlusal veneers, and those that partly wrap the side wall the name partial crowns.

The difference from a crown is in how much tooth is cut away. For a crown, tissue is removed from every surface of the tooth, because the restoration wraps the tooth like a thimble and gets its retention from that shape. Onlays and overlays, on the other hand, are attached to the tooth with an adhesive; a large part of their retention comes from the bonding, so sound walls can be left uncut. The margins near the gum line also often stay higher up. This has a practical consequence: if the restoration breaks or the tooth decays again in future, there is still uncut tooth tissue left for a crown.

The material options fall into three main groups. Ceramics (feldspathic porcelain, leucite-reinforced glass ceramic and glass ceramics such as lithium disilicate) look the most like natural teeth and have a surface that resists wear. Composite, that is a more durable form of filling material hardened in a laboratory or as a block, is more flexible and easier to repair inside the mouth. Gold is the oldest option; because it is not tooth-coloured, it is chosen less often today. Cleveland Clinic lists gold and porcelain for indirect fillings and writes that porcelain is a mixture of minerals such as feldspar, quartz and kaolin.

The broadest picture of how long they last comes from the 2016 meta-analysis by Morimoto and colleagues. Combining 14 studies with at least 5 years of follow-up, the authors found survival of ceramic inlays, onlays and overlays of 92–95% at 5 years and 91% at 10 years. The most common cause of failure was fracture or chipping (4%); this was followed by nerve problems needing root canal treatment (3%), new decay at the margin (1%) and the restoration coming loose (1%). The type of ceramic, porcelain or glass ceramic, did not significantly change the result; whether the tooth's nerve was alive or not, however, was associated with the outcome.

For a comparison with crowns, the 2018 review by Vagropoulou and colleagues gives a good idea. Examining nine studies, the authors report mean survival of 90.9% for inlays, 93.5% for onlays and 95.4% for crowns, and write that 5-year survival exceeded 90% for all of them. Because the studies differed greatly from one another, the authors also state that no meaningful comparison between the types could be made. In every group the most common biological problem was new decay and the most common technical problem was ceramic fracture.

The answer to the question of ceramic or composite is less clear. The 2013 systematic review by Fron Chabouis and colleagues could find only two randomised trials comparing these two materials; both looked only at inlays, there was no study including onlays, the risk of bias was high, and it found the evidence that ceramic is better in the short term very limited. Another meta-analysis from 2023 reported that, for indirect fillings that stay within the tooth, lithium disilicate and composite give similar results in the short term, but that at 5–7 years of follow-up the failure rate for composite was 18 percentage points higher than for gold fillings. In a 2025 meta-analysis, survival at 3 years was 93.7% for lithium disilicate partial coverage restorations and 89.3% for resin-matrix ceramics; the authors stress that the long-term outcome is uncertain.

The situation in a tooth that has had root canal treatment needs to be discussed separately. Protecting the cusps of root-filled back teeth by covering them is a common recommendation, but the evidence on whether this should be done with a crown or an onlay is weak. Cochrane's 2015 review found insufficient evidence to assess the difference between crowns and fillings in root-filled teeth; only one study could be included. A 2024 systematic review writes that bonded partial ceramic restorations and full crowns show similar survival in root-filled back teeth, but that there are few studies on the subject.

Which tooth suits an inlay or onlay, and which needs another solution

The decision comes from an examination and an X-ray; the lists below are to help you understand what is being looked at when you talk to your dentist. The first list covers situations where an inlay or onlay is a strong candidate, the second situations where another solution comes to the fore.

When it fits

There is a large old filling or decay, but the outer walls of the tooth are soundIf the cavity is too big for an ordinary filling but the side walls of the tooth are thick and sound, an inlay or onlay can close the cavity without cutting away as much tooth as a crown.
One or two cusps have become thin or have brokenAn onlay that covers a weak cusp from above aims to stop that wall from cracking in future. The walls that are still sound are not cut.
The chewing surface is worn or has been dissolved by acidIn back teeth shortened by wear or erosion, thin overlays can be used to rebuild the chewing surface without cutting around the tooth.
Oral hygiene is good and the risk of new decay is lowThe edge of an inlay or onlay is a joint bonded to the tooth. In research, new decay starting at the margin is among the important causes of failure; regular cleaning protects this joint.

When it doesn't

The cavity is smallFor small and medium-sized cavities an ordinary filling is usually enough and is finished in one appointment. Cutting away extra tooth for an inlay or onlay gives no benefit in this case.
There are cracks running in more than one direction, or a suspected root fractureThe direction and depth of the crack are decisive. With a fracture that extends below the gum line or down into the root, the problem lies outside the area the restoration can cover; in this case a crown or extraction is discussed.
The margins are well below the gum lineBonding needs a dry field. In a tooth where the margin lies beneath bleeding gum, the reliability of the bond falls; this area may need to be corrected first, or another solution chosen.
Many teeth have been lost across the mouth and there is advanced gum diseaseAn inlay or onlay on a tooth whose root is loose or whose bone has largely gone does not extend the life of the tooth. In this case, rather than treating teeth one by one, a plan covering the whole mouth should be discussed.

How an inlay or onlay is made

The sequence below is the typical course for an inlay or onlay made in a laboratory. With systems that design by computer and mill in the surgery, the impression and fitting can be done on the same day.

1
Examination and X-ray
The depth of the decay, what is under the old filling, whether there is a crack and the condition of the tooth's nerve are assessed. With deep decay close to the nerve, it first needs to become clear whether the nerve will stay alive; the plan for the inlay or onlay changes accordingly.
2
Removing the old filling and the decay
Under local anaesthetic, the decay and the old filling are removed. Deep areas can be filled and levelled with filling material; the aim is to make the base on which the restoration will sit flat and sound.
3
Shaping the tooth
The cavity where the restoration will sit is given angled walls. For an onlay or overlay, enough tissue is removed from the cusps to be covered to give the material a thickness at which it will not break. The sound side walls are not touched.
4
Impression or digital scan
A record of the tooth and the opposing jaw is taken with conventional impression material or an intraoral scanner. Cleveland Clinic writes that most indirect fillings need two appointments: one for the impression and one for fitting.
5
Temporary cover
During the laboratory stage, the top of the tooth is closed with a temporary filling. Not chewing hard or sticky food on that side during this period prevents the temporary filling from falling out and the tooth from breaking.
6
Try-in and bonding
The restoration is tried on the tooth, and the fit of the margins and the contact points are checked. The tooth is isolated, the surfaces are prepared and the restoration is bonded with a resin adhesive. Excess adhesive is cleaned away.
7
Bite check and polishing
Using articulating paper, the dentist checks whether the tooth touches the opposing tooth too early, and if necessary the surface is adjusted and polished. A restoration that is left high both causes pain and increases the risk of the ceramic breaking.

Options discussed instead of an inlay or onlay

More than one route is often possible for the same tooth. The choice is determined by the amount of sound tooth left, the chewing load and the condition of the tooth's nerve.

A large composite filling

It is done inside the mouth in a single appointment and can be repaired when needed. In large cavities it becomes harder to give the right shape and contact point inside the mouth; for teeth whose cusps need covering, durability should be discussed with the dentist.

A full crown

It wraps the tooth on every side. If the remaining walls are very thin or cracked, it is a reliable option. The price is that more tooth is cut away; Cleveland Clinic writes that tissue has to be removed from the outer layer of the tooth for a crown to fit in place.

A gold inlay or onlay

If aesthetic expectations are low and the tooth is not visible at the back, it is still an option. In the 2023 meta-analysis, gold indirect fillings that stay within the tooth failed significantly less often than composites at 5–7 years.

Root canal treatment followed by an onlay or a crown

If the nerve has lost its vitality, root canal treatment is done first, then the tooth is protected by covering its cusps. For these teeth there is no strong evidence showing a clear advantage for either an onlay or a crown.

Extracting the tooth and replacing it

In a tooth with a root fracture, decay too deep to save or bone that has largely gone, an inlay or onlay changes nothing. For such a tooth, extraction and what replaces it is a separate decision; for a single tooth, discuss this with your own dentist, and where many teeth are affected together, with a plan covering the whole mouth.

Problems seen with inlays and onlays

The problems seen most often in research are listed below. Some come from the material, some from the tooth itself.

Fracture and chipping

In the Morimoto meta-analysis, fracture was the most common reason for failure of ceramic restorations (4%). For people who clench or grind their teeth at night, this risk should be discussed with the dentist separately, and you should ask whether a night guard is needed.

Nerve problems and the need for root canal treatment

In the same meta-analysis, 3% of restorations later developed a nerve problem needing root canal treatment. With inlays and onlays made after deep decay, the nerve may already be under strain; the dentist should discuss this beforehand.

New decay at the margin

The bonding line between the restoration and the tooth is a place where bacterial plaque builds up. In the Vagropoulou review, new decay was the most common biological problem for inlays, onlays and crowns alike.

The bond giving way

The restoration coming loose is an uncommon but reported problem. If a restoration falls out on its own, keep it and take it to your dentist; it can often be checked whether it can be bonded back in place.

Sensitivity after bonding

In the first few days there may be mild sensitivity to cold and to biting. Cleveland Clinic writes that mild sensitivity after a filling is expected to settle within a week or two. Pain that also reacts to warm drinks, starts on its own or wakes you at night, however, is not expected.

What to expect after bonding

An inlay or onlay is not an operation; recovery is more about the tooth getting used to it. The course below is the usual one, and what your dentist tells you takes priority.

The temporary filling period
In the days between the impression and the fitting, the tooth may be mildly sensitive. If the temporary filling falls out, call your dentist rather than leaving the tooth exposed.
The day of bonding
Until the numbness wears off, do not eat on that side or have hot drinks; you could bite your lip or cheek without noticing.
The first two weeks
There may be mild sensitivity to cold and to biting, which is expected to ease gradually. If the tooth feels like the first tooth to make contact, the bite may have been left high; ask for a check without waiting.
Over the years
At regular check-ups, the restoration is examined for its margin, discolouration and cracks. If a small problem starting at the margin is noticed early, the restoration can often be repaired while staying in place.

Don't wait if

The tooth touches first when you bite, or hurts when you chew. The bite may have been left high. A small adjustment is often enough; waiting increases the risk of the ceramic breaking.
Pain starts on its own, wakes you at night or gets worse with heat. This picture suggests the nerve is under strain. See your dentist; the condition of the nerve needs to be assessed with tests.
The restoration has cracked, its edge has broken or it has come out. Keep the restoration and take it to your dentist. The exposed tooth surface may be sensitive and is open to decay.
The gum next to the tooth has swollen or a painful bump has appeared. This may be a sign of infection; see your dentist the same day. If you have swelling spreading rapidly across your face, or difficulty swallowing or breathing, call 112 or go to the nearest A&E.

What determines the scope and the cost

An inlay or onlay is a procedure on a single tooth and is planned by your own dentist; we do not give figures here. The main items that determine the scope are:

Material: Ceramic, composite or gold; the type of ceramic and the production route lead to different laboratory and material costs.
Production route: Laboratory production needs two appointments and a temporary filling; production by computer in the surgery can be finished in one appointment but needs the equipment.
Size of the restoration: Inlays, onlays and overlays involve different amounts of work depending on the area they cover.
Additional procedures: Protecting the nerve with deep decay, and root canal treatment or gum correction if needed, increase the overall scope.

Frequently asked questions

What is the difference between an inlay and an onlay?

An inlay stays within the hollows of the tooth and does not extend over the cusps. An onlay covers at least one cusp. An overlay covers the entire chewing surface. Which one is chosen depends on how much of the tooth is still sound.

Are inlays and onlays more durable than an ordinary filling?

In large cavities, a restoration made outside the mouth is preferred because its shape and contact points are more controlled. Survival of 92–95% at 5 years and 91% at 10 years has been reported for ceramic restorations. In small cavities, however, an ordinary filling is enough and an inlay or onlay gives no additional benefit.

Is an onlay or a crown better?

There is no single right answer. An onlay cuts away less tooth and preserves the sound walls; a crown, on the other hand, wraps very weak or cracked walls on every side. In one review, 5-year survival was above 90% for inlays, onlays and crowns alike; the studies were not suitable for making a comparison.

Should I choose ceramic or composite?

The evidence is limited. No clear difference between the two materials has been shown in the short term; in a 2025 meta-analysis lithium disilicate gave slightly better results than resin-matrix ceramics, but the certainty of the evidence was low; while ceramic looks better and resists wear better, composite is easier to repair inside the mouth. Make the choice with your dentist based on the position of the tooth, the biting forces and any clenching habit.

Can an onlay be placed on a root-filled tooth?

Yes. Covering the cusps is recommended for root-filled back teeth; whether this is done with an onlay or a crown depends on the remaining tooth tissue. One review writes that bonded partial ceramics and crowns show similar survival in root-filled teeth, but that there are few studies.

How many appointments does an inlay or onlay take?

If it is made in a laboratory, usually two appointments: one for the impression and temporary filling, and one for the try-in and bonding. With systems that design by computer and mill in the surgery, it can be finished in a single appointment.

Is sensitivity after bonding normal?

In the first few days there may be mild sensitivity to cold and to biting, which is expected to ease within a week or two. If the tooth touches first when you bite, or pain starts on its own or wakes you at night, see your dentist.

Can an inlay be placed on a front tooth?

Inlays and onlays are mainly used on back teeth, that is premolars and molars. For front teeth, a composite filling, a laminate veneer or a crown is discussed for a similar purpose.

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