Inlays and Onlays

A filling made in the mouth may be enough

Many cavities, including fairly large ones, can be filled directly in the mouth with tooth-coloured composite. Two recent reviews compared direct composite fillings with laboratory-made composite inlays and onlays in large back-tooth cavities, and reached different conclusions³. One found no significant difference; the other reported fewer failures with direct fillings⁴. Both rated the certainty of their evidence as very low, and neither covers ceramic onlays. No cavity size has been identified at which a filling stops being enough; the choice depends on how much of the walls and cusps remains.

An inlay or an onlay may suit

• Inlay: there is a large cavity or an old filling that needs replacing, but the remaining walls of the tooth are sound.
• Onlay: one or more cusps are weakened, cracked or broken and need covering, while the rest of the tooth is sound.

Whichever restoration is chosen, decay in the tooth and any gum disease around it are treated first. For gum disease, see our page on gum diseases.

A crown may suit better

A crown may be recommended for a tooth that is badly damaged or broken, weakened by a large filling, root-filled, worn down or cracked⁵. A crown is fixed in place and you cannot take it out yourself, and the tooth is shaped all round to make room for it. See our page on dental crowns for details.

Back teeth after root canal treatment

A root-filled back tooth can be restored with a filling, an onlay that covers the cusps, or a crown. A 2015 Cochrane update searched for studies up to 2015. It found only one small study comparing a crown with a filling, and did not find any study⁶ comparing an inlay or onlay with a crown. So no option can be said to be always the best; the decision rests on how much sound tooth is left. For root canal treatment, see our page on root canal treatment.

When extra care is needed

• Clenching or grinding. According to a review of ceramic onlays, ceramic onlays appear to fail more often⁷ in people with this habit. The same review also found failure more often on root-filled teeth and on teeth further back in the mouth. Tell your dentist if you clench your teeth.
• A high risk of decay. One analysis looked at 2,816 composite fillings in back teeth followed for at least 5 years. Failure was more common⁸ in people at high risk of decay and in fillings that covered more surfaces of the tooth. That study was about fillings made in the mouth; even so, preventing decay matters for every restoration.

The right option is decided at an examination, with X-rays where needed.

• Leaving it alone. If the tooth has no decay, crack or pain that needs treatment, leaving it alone is also an option. An old filling that is still sound, for example, does not need replacing just because it is old. If there is decay or a fracture, waiting will not solve it; ask your dentist how long you can wait.
• Repairing the old filling. Studies comparing the repair of defective direct fillings with their replacement found no significant difference⁹ in the risk of failure. Only 3 studies were included in that review; the risk of bias was high and the certainty of the evidence very low.
• A filling made in the mouth. Tooth-coloured composite is shaped directly in the tooth and hardened with light. No laboratory is needed.
• Inlay. A piece made outside the mouth to fit the tooth is bonded into the space between the cusps.
• Onlay or overlay. The weak cusps are covered as well. The aim is to protect the biting surface of the tooth without reducing it as much as a crown does.
• Crown. It covers the whole visible part of the tooth. It is considered when little sound tooth is left.

Which materials are used?

• Ceramic. Tooth-coloured glass ceramics and porcelain. One of these, lithium disilicate, is best known under the brand name e.max.
• Resin-matrix ceramic and composite. Resin-based materials reinforced with ceramic particles.
• Gold. Gold and porcelain fillings are made in a dental laboratory to fit the tooth¹⁰; gold is sometimes used on molars.

The material depends on the state of the tooth, your bite and your habits. Our sources do not rank one material above another.

Laboratory-made inlays and onlays are made to fit the tooth and usually need two appointments¹⁰. Your dentist plans the time between the appointments. Whether a local anaesthetic is needed is decided by your dentist according to the extent of the work.

How much of the tooth is removed depends on the decay, the old filling and any cracks. According to a review of ceramic onlays, at least 2 mm of ceramic on the biting surface⁷ has been linked with longer survival. So has a tooth shape that helps hold the onlay in place. This does not mean the same amount is removed from every tooth.

Risks and disadvantages

• It cannot be undone. Tooth is removed for an inlay or an onlay; the enamel and dentine removed do not grow back. From then on the tooth always depends on a restoration.
• Fracture and chipping. The most common reason ceramic inlays and onlays fail is fracture or chipping of the restoration¹¹. Less often, the restoration comes loose or decay starts at its edge. Even when the cusps are covered, a crack in the tooth can progress.
• The nerve of the tooth. A review pooled 37 studies. The teeth in these studies were alive at the start and were treated with indirect restorations such as crowns, partial restorations or bridge supports. In about 5 in every 100 of these teeth¹² the nerve lost its vitality. In studies with more than ten years of follow-up, the figure was about 7. The certainty of this evidence is low. If that happens, the tooth needs root canal treatment to save it. The review does not show that this risk is lower for an onlay than for a crown.
• Decay. An inlay, an onlay or a crown does not protect the tooth from decay. New decay can start at the edge where the restoration meets the tooth.
• Sensitivity. After the treatment the tooth may be sensitive to hot and cold for a while.

Benefits

• In a laboratory study on plastic model teeth, full crown preparations removed about two thirds to three quarters¹ of the crown of the tooth. For inlays and small bonded preparations the figure was about 5 to 27 per cent. A 2025 review, citing the same laboratory study, gives about 36 to 47 per cent¹³ for partial coverage restorations. These are laboratory values and give only a sense of scale. The studies do not show that leaving more tooth makes the tooth itself last longer.
• The restoration is made in a laboratory to fit the tooth, and ceramic ones are tooth-coloured.
• On a tooth that does not need a crown, the cusps can be covered without reducing the whole visible part of the tooth.

After an inlay or onlay is bonded, you can usually return to your normal day the same day. The tooth may be sensitive for a while. If you had a local anaesthetic, do not eat until it has worn off. If your bite feels high in the first few days, tell your dentist; it can be adjusted.

Daily care

• Brush your teeth twice a day with fluoride toothpaste, and clean between your teeth every day with floss or an interdental brush.
• Do not bite hard objects such as ice, pens or nutshells.
• If you clench or grind your teeth, tell your dentist; they may suggest a night guard.
• Keep to your regular check-ups.

If you are thinking about whitening, discuss it beforehand. Whitening does not lighten ceramic and composite restorations¹⁴ the way it lightens natural teeth; next to whitened teeth, the restoration can look darker. See our page on teeth whitening for details.

In short: no single number of years can be given. The rates below come from different patient groups and follow-up periods; they are not enough to rank the options against each other. Staying in the mouth does not mean there were no problems or no repairs during that time. No filling lasts forever¹⁰; over time it can break, wear or change colour.

Ceramic inlays and onlays. A meta-analysis pooled studies with more than five years of follow-up. Of every 100 glass-ceramic and porcelain inlays, onlays and overlays, about 92 to 95 were still in the mouth after five years¹¹. After ten years the figure was about 91. Another review of ceramic onlays found large differences⁷ between the results of individual studies.

Partial coverage in randomised trials. A meta-analysis of randomised trials looked at ceramic onlays and partial crowns on back teeth. It estimated three-year survival at about 94 in every 100 restorations in lithium disilicate and 89 in resin-matrix ceramic¹³. None of the trials had defined survival formally. The difference was not significant and the certainty of the evidence was low. According to the authors, the long-term performance of these restorations is uncertain.

Onlay or crown? Studies comparing onlays or partial crowns with full crowns on back teeth found no significant difference² in survival at one and three years. Most of these studies were not randomised, the group sizes were very unbalanced and follow-up was short. Another review rests on only 3 studies and focuses on back teeth with MOD cavities, which involve three surfaces (front, biting and back). It writes that an onlay may be an advantageous alternative to a crown, but that the evidence is not enough to draw meaningful conclusions¹⁵.

Crowns. A 2026 review looked at single crowns on natural teeth. The four material groups reported here are monolithic lithium disilicate, layered zirconia, porcelain fused to metal and monolithic zirconia. Of every 100 crowns in these groups, about 97 to 99¹⁶ were still in the mouth after five years.

Root-filled teeth. In a review of bonded onlays and overlays on root-filled teeth, with no comparison group, 121 of 1,254 restorations failed¹⁷. Failure was about 4 in 100 restorations in studies lasting 2 to 4 years. It was about 11 to 21 in 100 in studies lasting 7 years or more. According to the authors, in most failures the tooth appeared restorable; however, some of the failures involved loss of the tooth¹⁷.

The outcome depends on the tooth, the bite, the material, the fit of the restoration and how it is cared for.

See your dentist if any of the following happens after the restoration:

• Sensitivity that lasts longer than a week or keeps getting worse, or pain that starts with heat and lingers
• Pain when you bite, or a bite that feels high
• A crack, chip, looseness or the restoration coming out (keep the piece and do not glue it back yourself)
• Food catching at the edge of the restoration, bleeding gums or a dark line at the edge
• The temporary filling falling out
• Pain that starts on its own or wakes you at night

Emergencies. Throbbing pain, swelling in the face or a fever mean you should see a dentist without delay. If a swelling makes it hard to breathe or swallow, or spreads quickly across your face or neck, do not wait for a dental appointment. Go to an emergency department or call 112.

This page carries no prices. A treatment plan is prepared for you after an examination. The main factors that shape it are:

• Which of a filling, an inlay, an onlay or a crown suits the tooth
• The chosen material
• Any treatment needed first: decay, gum treatment or root canal treatment
• A night guard, if needed
• Repair or replacement that may be needed over time

Ask for your plan in writing, including what it covers and what will be done if the restoration breaks or comes out.