South Kensington
- 20 Old Brompton Road, London SW7 3DL
- Open seven days a week
- 020 7183 2362
Treatment comparison · Wimpole Street, Marylebone
Onlay or filling: matching the size of the repair to the size of the damage
A filling and an onlay sit next to each other on the scale of tooth repairs. A filling is composite resin placed straight into a cleaned cavity and set in the same visit; it is the right answer for the great majority of small and medium holes. An onlay is made outside the mouth from a scan of the prepared tooth and covers at least one cusp, the raised corners of a back tooth that take the brunt of chewing. It comes into its own when the damage has spread to those corners and a filling would be too large to rely on.
Decision guide
Which is right for you?
Choose White fillings if…
- The cavity is small or moderate and confined to the grooves or the side of the tooth.
- You want the tooth sorted in a single appointment of 30 to 60 minutes.
- You are repairing a chip or replacing a modest older filling.
- Keeping the fee low is a priority and the tooth is not under heavy load.
Choose Dental onlays if…
- A cusp has broken or is thin enough that a filling would leave it unsupported.
- An existing large filling has failed and the tooth around it has weakened.
- You grind your teeth and back-tooth fillings have not lasted well.
- You want to avoid a crown but need more coverage than a filling can offer.
At a glance
Side by side
| Feature | White fillings | Dental onlays |
|---|---|---|
| How it is made | Placed and sculpted directly in the mouth | Fabricated in a laboratory and bonded at a second visit |
| Extent of damage treated | Small to moderate cavities | Moderate to large damage involving one or more cusps |
| Strength | Adequate for small repairs; large ones can crack or wear | High; laboratory materials withstand heavy chewing |
| Tooth preparation | Only decay and weak enamel removed | Damaged cusps reshaped; remaining walls kept, unlike a crown |
| Visits | One | Two, a week or two apart |
| Fee at Wimpole Street | From £185 | From £995 |
| Expected lifespan | Around 5 to 10 years | Around 10 to 15 years or more |
| Appearance | Tooth-coloured composite matched at the chair | Porcelain or composite finished in the laboratory |
| Wear and staining | Composite may stain and wear at the edges | Resistant to both |
| Best suited to | Small cavities, minor decay and chip repairs | Cusp damage and failing large fillings |
In the chair
What the treatment involves
White fillings
Local anaesthetic is given if needed, decay is removed and the cavity is cleaned and dried. The enamel is etched, a bonding agent applied, and composite is placed in increments, each hardened with a curing light so the material sets fully and shrinks as little as possible. The dentist shapes the surface to follow the natural grooves, checks that the bite feels even and polishes the result. The appointment usually takes 30 to 60 minutes and the tooth can be used once the numbness has passed.
Dental onlays
At the first appointment the tooth is numbed, the old filling and any decay are cleared, and weakened cusps are reduced to a level the onlay can cover securely. A digital scan captures the prepared tooth and a temporary filling protects it. The laboratory then makes the onlay in porcelain, a reinforced composite or occasionally gold, matching the shade taken at the chair. A week or two later the temporary comes out, the onlay is tried in, adjusted for contact and bite, bonded with resin cement and polished. A short review may follow if the bite needs fine-tuning.
Fees
Cost and longevity at Wimpole Street
White fillings at Wimpole Street will start from £185 per tooth, the fee increasing with the size of the cavity. An onlay starts from £995, the difference reflecting the laboratory work, the material and the second appointment.
A composite filling in a heavily loaded back tooth typically lasts five to ten years, and each replacement takes a little more tooth with it. An onlay generally lasts ten to fifteen years or more, so a large cavity may pass through two fillings in the life of one onlay. For small cavities the filling is plainly the economical option; for damage involving a cusp, the onlay is often cheaper over the long run and delays or avoids the need for a crown.
All prices are indicative and are confirmed in a written treatment plan at your consultation. Fees are the same at every Medical & Dental clinic.
Weighing it up
Strengths and trade-offs
White fillings
Strengths
- Completed in one visit
- Lowest-cost tooth-coloured repair
- Minimal removal of healthy tooth
- Blends with the surrounding enamel
- Well suited to small and moderate cavities
Trade-offs
- Large fillings are prone to cracking and leakage
- May not support a weakened cusp
- Composite can stain, wear and shrink over time
- Shorter lifespan; often replaced every five to ten years
Dental onlays
Strengths
- Much stronger than a large composite filling
- Laboratory-made for a precise fit
- Covers and protects damaged cusps
- Keeps more tooth than a crown
- Resists wear and staining
- Lasts ten to fifteen years or more
Trade-offs
- Higher fee
- Two appointments with a temporary in between
- Unnecessary where a filling would do
- Needs enough sound tooth left to bond to
FAQ
Common questions
Signs include a sharp twinge when biting on something hard, a visible crack line, or an old filling that occupies more than half the width of the tooth. The dentist checks with a bite test and by examining the tooth once the old filling is removed, which is sometimes the only way to see how much sound structure remains.
Not quite. A crown wraps the whole tooth and requires every surface to be reduced. An onlay covers only the chewing surface and the affected cusps, leaving the outer walls intact. It sits between a filling and a crown in both coverage and how much tooth is removed.
Porcelain and high-strength laboratory composite are the usual choices for a natural appearance. Gold is still used occasionally on molars because it wears at a similar rate to enamel and is very durable, though it is visible.
Yes, and this is one of the commonest reasons for having one. When a large filling breaks or leaks and the tooth has lost some of its walls, an onlay replaces the filling and reinforces the cusps in one restoration.
Mild sensitivity to cold is common for a few days after a deep filling or onlay preparation and normally fades. Sensitivity when biting that persists beyond a couple of weeks should be checked, as it may point to a high spot on the restoration or a crack in the tooth.
Yes. Fillings and onlays are provided now at South Kensington and St Paul’s at the same fees, and your records move to the Marylebone clinic once it opens.
Marylebone, W1
Wimpole Street opens 1 October 2026
Register your interest and we will contact you when the Marylebone diary opens. If you would rather not wait, the same clinicians can see you at South Kensington or St Paul's now.
Related treatments at Wimpole Street
Opening 1 October 2026
Wimpole Street is not yet seeing patients. Until then, please book or call our South Kensington clinic on 020 7183 2362 or our St Paul's clinic on 020 7183 3709. Questions about the new clinic: wimpolestreet@md.co.uk.
Until we open
Need an appointment before 1 October 2026?
The same clinical team already works from two other Medical & Dental clinics. Book at either one now and, if you prefer, move your ongoing care to Wimpole Street once the doors open.
St Paul's, City of London
- 5 Ave Maria Lane, London EC4M 7AQ
- Open Monday to Friday
- 020 7183 3709
