Crown vs Onlay vs Large Filling — Which Is Right for You?
When a tooth is badly broken or decayed, you may have more than one choice. This guide explains a large filling, an onlay and a full crown. It helps you decide with your dental team.
Why might a damaged tooth need more than a simple filling?
A small area of decay or damage can usually be fixed with a simple filling. But sometimes a large part of the tooth is missing. This can be from a lot of decay, a broken corner (cusp), a crack or an old filling that is failing. Then a simple filling may not be strong enough for chewing.
In this case, your dental team may talk to you about three choices:
- A large direct filling. This is done in the chair in one visit, with a white filling material (composite resin).
- An onlay (indirect restoration). This is made to fit in a laboratory. It covers part of the tooth.
- A full crown (cap). This is made in a laboratory. It fits over the whole visible tooth.
Each choice has real benefits and real limits. The right one depends on how much of your tooth is left and where it is in your mouth. It also depends on other things your dental team will check.
Option 1 — Large direct filling (composite resin)
A direct filling is done in one visit. Your dental team removes any decay and shapes the hole (cavity). They build up the tooth with layers of white filling material (composite resin). A blue light hardens each layer.
Good points:
- Done in one visit, with no wait for a laboratory
- No need for a temporary filling
- Tooth-coloured and looks natural
- In most cases, less of the tooth is removed than for a crown
- Costs the least. It is usually £120–£300 privately (NHS Band 2 in England: £76.60 where available). Your treatment plan will confirm your exact cost. Fees vary between practices and depend on how complex your case is.
Downsides and risks:
- Large white fillings are more likely to break or wear over time than ones made in a laboratory
- The filling shrinks a little as it sets. This can sometimes cause sensitivity or small gaps at the edges.
- Not ideal when very little of the tooth is left, as the filling has nothing strong to stick to
- May need replacing sooner. A large white filling lasts 5–10 years on average.
- It is hard to do well in some cases. The result depends on the shape of the tooth and on keeping it dry.
How long it lasts: 5–10 years for a large filling. Smaller fillings often last longer.
Option 2 — Onlay (indirect restoration)
An onlay is made to fit your tooth in a dental laboratory. It covers one or more of the biting points (cusps) of a back tooth. It keeps as much of your own tooth as possible. It sits on top of and around part of the tooth, like a partial crown.
Onlays are made of porcelain (ceramic), gold alloy or composite resin. Ceramic onlays blend in well. Gold onlays are very hard-wearing.
Good points:
- Less of your tooth is removed than for a full crown
- Stronger and longer-lasting than a large direct filling
- Made to fit your tooth and your bite exactly
- Porcelain onlays look very natural
- Usually last 10–20 years with good care
Downsides and risks:
- Needs two visits, usually 1–2 weeks apart. The tooth is shaped at the first visit. The onlay is fitted at the second.
- A temporary filling is placed between visits. It can sometimes come off.
- Costs more than a direct filling. It is usually £600–£1,200 privately. Your treatment plan will confirm your exact cost. Fees vary between practices and depend on how complex your case is.
- If the tooth is very badly broken, an onlay may not cover enough. You may need a crown instead.
- Small risk of sensitivity after the tooth is shaped
How long it lasts: 10–20 years, and sometimes longer if you keep your teeth clean.
Option 3 — Full crown (cap)
A crown fits over the whole visible part of a tooth, like a thimble over a finger. It covers and protects the whole tooth. To fit one, your dental team trims the tooth down on all sides. They take a mould (impression), and a laboratory makes the crown. You wear a temporary crown in the meantime.
Crowns can be all-ceramic (porcelain), ceramic fused to metal, gold alloy or zirconia. Zirconia is a very strong white ceramic. Your dental team will talk about which material suits where your tooth is and how it is used.
Good points:
- The strongest protection for a badly broken tooth, or for one that has had root canal treatment
- Covering the whole tooth stops a weak tooth from breaking further
- Very hard-wearing. Crowns usually last 10–20+ years.
- Modern ceramic crowns look very natural
- Usually advised after root canal treatment on back teeth, to lower the risk of the tooth breaking
Downsides and risks:
- A lot of your natural tooth has to be removed. This cannot be undone.
- Needs two visits, with a temporary crown in between
- Costs more. It is usually £800–£1,500 privately (NHS Band 3 in England: £332.10 where available). Your treatment plan will confirm your exact cost. Fees vary between practices and depend on how complex your case is.
- Small risk of sensitivity or an irritated nerve after the tooth is shaped. Rarely, root canal treatment may be needed later.
- If the crown fails, you have more options if some natural tooth was kept. This depends on how much tooth was left before the crown.
- Porcelain can chip or crack under very heavy biting forces
How long it lasts: 10–20 years or more. This depends on the material and on how well you clean your teeth.
Key factors that guide the decision
Your dental team will think about several things before they advise you:
- How much natural tooth is left. The more of the tooth that is whole, the less needs to be removed.
- Whether the tooth has had root canal treatment. Back teeth that have had it almost always need a crown to stop them splitting.
- Where the tooth is. Back teeth (molars and premolars) take more biting force than front teeth.
- How much damage there is, and what kind. Cracks, several missing cusps or a very large old filling all affect the choice.
- Your bite. If you grind your teeth (bruxism), stronger materials and full cover may be advised.
- Your long-term goals. A crown costs more. But it may last best if the tooth is badly weakened.
Sometimes your dental team may advise against a large filling. This is not because it costs less. It is because it really does carry a higher risk of the tooth breaking. Protecting a weak tooth properly can avoid more complex (and costly) treatment later.
What if the tooth cannot be saved at all?
Sometimes a tooth is too damaged or decayed to repair with any of these options in a way that is likely to last. Your dental team will talk about this honestly with you. If the tooth cannot be saved, the choice moves to taking it out (extraction) and then replacing it. Your dental team can give you a separate leaflet about this, Replacing a Missing Tooth — Your Options.
Your dental team should always explain how likely each repair is to work before you agree to treatment.
Questions to ask your dental team
Use these questions to guide your talk:
- How much of my tooth is still healthy and strong?
- Is an onlay a real choice for this tooth, or do I need a crown?
- What is the risk if I choose the option that removes less tooth (and costs less)?
- Has this tooth had root canal treatment? Does that change your advice?
- Which material would you advise for the crown or onlay, and why?
- How long is each option likely to last for me?
- If I have the filling now, how likely is it that I will need a crown later anyway?
NHS charges are set nationally and reviewed each April. Any NHS charge shown here is the England charge from 1 April 2026. Charges differ in Scotland, Wales and Northern Ireland. Private fees are a guide. Your dental team will confirm the exact cost on your treatment plan before you agree to go ahead. NHS availability varies by area. Not all treatments are available on the NHS. Your dental team will talk with you about the best option for your case.
This leaflet is for general information only and does not replace professional dental advice. It is intended to support — not replace — the discussion with your dental team about your individual options, risks, and treatment plan. Your dental team will confirm what is suitable for your specific circumstances before you agree to any treatment.
Sources
- Crowns, Fixed Bridges and Dental Implants: Guidelines. British Society for Restorative Dentistry, 2013.
- Dental treatments. NHS website (nhs.uk), reviewed July 2026.
Links checked 18 October 2026.
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