Inlays and Onlays: Indirect Restorations for Larger Cavities
Inlays and onlays are indirect restorations: made outside the mouth to fit a damaged back tooth, then bonded or cemented in place. An inlay sits within the cusps; an onlay covers one or more. They may suit a cavity too large for a filling where a crown would remove more tooth than needed. Options at Deepcar Dental Care include composite and ceramic inlays and onlays, each taking 2 visits.
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Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
Dr Ibraheem Ijaz, principal dentist at Deepcar Dental Care, reviewed this page. He is a General Dental Practitioner, GDC 301711, and his registration can be checked on the General Dental Council's online register.
What are inlays and onlays?
An inlay or onlay is a restoration made outside the mouth to fit a prepared back tooth, then fixed in place. Dentists call it an indirect restoration.
The difference between the two is cuspal coverage: whether the restoration covers the cusps, the raised points on a back tooth's biting surface. A 2020 systematic review (Bustamante-Hernández and colleagues) classes inlays as not covering the cusps, onlays as covering at least one, and overlays as covering all of them.
A University of Bristol Dental School patient guide describes inlays and onlays as similar to fillings but constructed outside the mouth, in a dental laboratory, then cemented onto the tooth. The 2020 Bustamante-Hernández review adds that computer-aided design and manufacture (CAD/CAM) with intraoral scanners is an alternative way to make them, explained on our page about computer-designed restorations.
What gap do inlays and onlays fill?
Inlays and onlays sit between a filling and a crown, for a back tooth with too much damage for a filling to repair well. The Bristol Dental School guide lists very large cavities among situations where a white filling is not appropriate, and says an inlay or onlay may be considered if the tooth needs further reinforcement.
Covering the cusps matters most when they are weak. A 2016 Dental Update review (MacInnes and Hall) explains that cusp-covering restorations help preserve a weakened tooth against biting forces, and calls them a minimally invasive alternative to a conventional crown.
An indirect restoration is not automatically better than a filling. SCENIHR, a European Commission scientific committee, noted in 2015 that fitting a metal or ceramic indirect restoration removes more sound tooth than a direct filling, because of the technique's requirements. A 2016 systematic review (Angeletaki and colleagues), drawing on two trials, found no statistically significant difference in failure between direct and indirect composite inlays at 5 or 11 years, though staining at the edges slightly favoured direct inlays at 11 years, and said more long-term studies are needed. Smaller cavities are covered on our page about white fillings.
How much tooth does an onlay keep compared with a crown?
An onlay usually removes far less tooth than a crown, which needs the whole tooth shaped. A 2002 laboratory study (Edelhoff and Sorensen) weighed how much of the tooth above the root different preparations removed on resin model premolars and molars. Its onlay figures are as reported in a 2022 systematic review (Wang and colleagues).
| Preparation design (laboratory study, model teeth) | Share of the tooth above the root removed |
|---|---|
| Adhesive (bonded-bridge) and inlay designs | About 5.5% to 27.2% |
| Onlay or partial crown | About 35.5% to 46.7% |
| Full crown | About 67.5% to 75.6% |
These are laboratory figures, so a real tooth's share depends on its damage, and tooth shape also changed the amount removed. Where too little sound tooth remains to support an onlay, a crown, which covers the whole visible tooth, may be needed instead. Our page on having a crown fitted explains when, and comparing a crown with an onlay weighs the two side by side.
What are inlays and onlays made of?
Materials for inlays and onlays include composite resin, ceramic and gold alloy, and the table shows how each is made and fixed.
| Material (general guidance) | What it is | How it is made | How it is fixed |
|---|---|---|---|
| Composite resin | Tooth-coloured resin, the material family used for white fillings | Built up outside the mouth, or made by CAD/CAM | Bonded with a resin cement (adhesive cementation) |
| Ceramic, such as feldspathic porcelain or lithium disilicate | A tooth-coloured, glass-based ceramic | Made by CAD/CAM, pressed, or built up in layers | Bonded with a resin cement (adhesive cementation) |
| Gold alloy | Gold-coloured metal alloy | Cast by a dental technician from an impression of the tooth | Cemented to the tooth |
How matching the colour of a restoration works for tooth-coloured materials has its own page, and materials for crowns are set out in crown materials compared.
Inlay and onlay materials at Deepcar Dental Care
Options at Deepcar Dental Care include composite inlays and onlays and ceramic inlays and onlays.
Questions about this treatment? Book online or call the practice.
How is an inlay or onlay fitted?
In general, an inlay or onlay is fitted in two stages, because it is made outside the mouth to fit the prepared tooth:
- Decay or an old filling is removed and the tooth is shaped, a step called preparation.
- The shape of the prepared tooth is recorded with an impression (a mould) or a digital scan.
- The inlay or onlay is made outside the mouth to fit that shape.
- The finished piece is checked for fit and bite, then bonded or cemented to the tooth.
Inlay and onlay appointments at Deepcar Dental Care
At Deepcar Dental Care, an inlay or onlay takes 2 visits. Across the practice, rubber dam is used routinely, and topical numbing gel is applied before every injection.
How long do inlays and onlays last?
In systematic reviews, most inlays and onlays were still in place after 5 years. No study figure predicts how long one tooth's inlay or onlay will last.
For ceramic, a 2016 meta-analysis of 14 studies (Morimoto and colleagues) estimated 5-year survival of glass-ceramic and feldspathic porcelain inlays, onlays and overlays at 92% to 95%, and 10-year survival at 91%. Failures were most often fractures or chipping (4%), then complications in the tooth's nerve (3%), new decay (1%) and debonding (1%).
For composite, the evidence is thinner. A 2016 systematic review (Angeletaki and colleagues) found only one trial of composite onlays, placed directly or indirectly, reporting 87% overall survival at 5 years. A 2020 meta-analysis of ceramic, hybrid and composite onlays (Bustamante-Hernández and colleagues) estimated overall survival at 94.2%, in studies following onlays for 2 to 15 years, and found survival lower over time and for composite onlays, but its authors say the low quality of the studies means the conclusions must be interpreted with caution.
Across materials, a 2018 review of 9 studies (Vagropoulou and colleagues) found them too varied to compare restoration types or materials meaningfully, and noted a relatively high failure rate from decay and ceramic fractures. Decay was the main biological complication, then fracture of the tooth or root, then nerve complications. Ceramic fracture was the main technical complication, then loss of retention and porcelain chipping.
For onlays against crowns, Wang's 2022 meta-analysis (one trial, five observational studies) found no statistically significant survival difference between tooth-coloured onlays or partial crowns and full crowns at 1 and 3 years, and says longer trials are needed.
How much do inlays and onlays cost?
Inlays and onlays have no line on the Deepcar Dental Care fee list, checked on 25 October 2026. Restorative fees in general are covered on our page about what it costs.
When should you speak to your dentist about an inlay or onlay?
See a dentist about a broken tooth or toothache, including in a tooth with an inlay or onlay. NHS guidance gives these actions:
- A chipped, cracked or broken tooth: see a dentist, and keep any piece that has broken off in milk or saliva to take with you. Do not go to a GP, who cannot give dental treatment. If you have no dentist or cannot get an emergency appointment, call 111.
- Toothache that lasts more than 2 days, does not go away with painkillers, or comes with a high temperature, pain when you bite, red gums, a bad taste in your mouth, or a swollen cheek or jaw: see a dentist. If you have no dentist or cannot get an emergency appointment, call 111 or visit 111 online.
For urgent dental care, call your dentist; if they are closed, their answerphone may say what to do. Go to A&E if toothache comes with swelling around your eye or neck, or swelling in your mouth or neck makes it difficult to breathe, swallow or speak. Do not drive to A&E: ask someone to drive you, or call 999 and ask for an ambulance.
What other restorative treatments are there?
Inlays and onlays are one way of repairing and rebuilding damaged teeth, keeping natural teeth rather than replacing them with implants. Fillings, crowns, bridges and dentures are among the options in this section, and our decision guide helps with working out which option suits.
Frequently asked questions
Is an onlay the same as a partial crown?
The terms overlap. A 2022 systematic review (Wang and colleagues) groups onlays with partial crowns, and defines an onlay as a partial-coverage restoration that restores one or more cusps and part or all of the biting surface. A full crown, by contrast, covers the whole visible tooth.
Is an onlay stronger than a filling?
It can be, for a tooth that has lost a lot of structure. In the background to their 2022 systematic review, Wang and colleagues say onlays restore such a tooth's shape and protect it better than direct fillings or inlays. Whether a tooth needs that protection depends on how much sound tooth remains, which a dentist checks.
Are inlays and onlays available on the NHS?
NHS guidance says Band 3 treatment in England may include restoring damaged teeth with inlays and onlays. Band 3 costs £332.10 and includes everything in Bands 1 and 2. The cost depends on the treatment the dental professional thinks you need, and some people can get free NHS dental treatment.
What should you do if an inlay or onlay comes out?
Contact a dentist to have the tooth and restoration checked. NHS guidance lists refixing inlays, crowns and bridges among the treatments an urgent NHS dental appointment in England can include, at £27.90, and says further treatment afterwards may have additional costs. Whether a loose inlay or onlay can be refixed or needs replacing depends on what the dentist finds.
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Deepcar Dental Care is at 334 Manchester Road, Deepcar, Sheffield, S36 2RH, open from 8am to 8pm, Monday to Sunday. Free parking is directly outside, and the practice is on the ground floor and wheelchair accessible. Patient feedback is on the practice's reviews page.
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