Treatment Comparison
Compare onlays and fillings side by side — coverage, strength, longevity, cost and suitability explained clearly with real pricing from Dental Clinic London.
When a tooth has a cavity or an old restoration that needs replacing, the two most common options are a direct composite filling or a custom-made onlay. Both restore the tooth's shape, function and appearance — but they differ significantly in strength, longevity and the situations they are best suited to.
A filling is placed directly into the cavity in a single appointment — it is ideal for small to medium areas of damage. An onlay is fabricated in a dental laboratory and covers one or more of the tooth's cusps, providing far greater structural reinforcement for larger cavities. The right choice depends on the size of the cavity, the amount of healthy tooth remaining and the forces the tooth must withstand. Both are part of our restorative dentistry and general dentistry services.
Not sure which you need? Book a consultation or call us on 020 7183 0527 — your dentist will examine the tooth, take X-rays and explain the most appropriate option before any treatment begins.
At a Glance
Onlay vs filling — side by side.
| Feature | Onlay · From £995 | Filling · From £185 |
|---|---|---|
| Coverage | One or more cusps — extends over the biting surface | Within the cavity only — does not cover cusps |
| Procedure | Lab-made (indirect) — 2 appointments | Direct — completed in 1 appointment |
| Treatment Time | 2 visits, 45–60 min each, 1–2 weeks apart | 1 visit, 30–45 minutes |
| Structural Support | High — reinforces and protects weakened cusps | Moderate — fills the cavity without cusp coverage |
| Aesthetics | Excellent — porcelain shade-matched to tooth | Very good — composite shade-matched to tooth |
| Cost (DCL) | From £995 | From £185 (small) · From £325 (large) |
| Longevity | 15–25 yrs (porcelain) · 25–30+ yrs (gold) | 7–15 years |
| Suitability | Medium to large cavities, weakened cusps | Small to medium cavities |
Treatment recommendations depend on individual clinical assessment. All prices confirmed before treatment begins.
Lab-Made Restoration
An onlay is a custom-made restoration that covers one or more of the tooth's cusps — the raised points on the biting surface. It is fabricated in a dental laboratory from porcelain, ceramic or gold using a detailed impression of your tooth, then bonded permanently into place at a second appointment. An inlay is similar but smaller — it fits within the cusps without covering them. Together, inlays and onlays represent the middle ground between a filling and a full dental crown.
At Dental Clinic London, onlays start from £995 regardless of material — porcelain, ceramic or gold. The treatment takes 2 appointments, 1–2 weeks apart, each approximately 45–60 minutes. Onlays are significantly stronger and more durable than direct composite fillings, typically lasting 15–25 years (porcelain) or 25–30 years or more (gold), compared to 7–15 years for a filling.
The key advantage of an onlay is that it reinforces the tooth's weakened cusps while preserving the maximum amount of healthy structure. This makes it stronger than a filling but far more conservative than a crown, which requires reducing the entire outer surface of the tooth. An onlay is also commonly used to protect teeth that have had root canal treatment but still retain enough structure that a full crown is not required.
Direct Restoration
A dental filling is a direct restoration placed into a cavity in a single appointment. At Dental Clinic London, we use BPA-free composite resin — a tooth-coloured material that is shade-matched to your natural teeth, making the repair virtually invisible. The dentist applies the composite directly into the prepared cavity, sculpts it to match the tooth's natural shape and hardens it with a curing light.
White fillings start from £185 for a small single-surface filling, £245 for a medium two-surface filling, and £325 for a large multi-surface filling. The procedure takes approximately 30–45 minutes in a single visit. With good oral hygiene and regular check-ups, composite fillings typically last 7–15 years.
The key advantage of a filling is its simplicity and efficiency — treatment is completed in one appointment with minimal tooth preparation. Composite resin bonds directly to the tooth structure, which helps to reinforce it. However, for larger cavities where the cusps are weakened, a filling alone may not provide sufficient strength to protect the tooth long-term — and if a tooth is eventually lost, replacement options such as dental implants are significantly more complex and costly.
Understanding the Difference
This is the most important distinction. A filling replaces the decayed or damaged portion within the cavity — it fills the space but does not cover or reinforce the cusps. An onlay covers one or more cusps, effectively splinting and reinforcing the weakened parts of the tooth. For large cavities where the cusps are undermined, a filling may leave them vulnerable to fracture, whereas an onlay protects them.
For a filling, the dentist removes the decay and applies composite directly into the cavity — this is the least invasive approach. For an onlay, the decay is removed and the tooth shaped with smooth margins to accept the lab-made restoration. Both are more conservative than a dental crown, which requires reducing the entire outer surface of the tooth. The key difference is that an onlay preparation extends over the cusps, whereas a filling preparation stays within them.
An onlay is fabricated in a dental laboratory from porcelain, ceramic or gold — materials that are significantly harder-wearing than composite resin. Porcelain onlays typically last 15–25 years, gold 25–30 years or more. Composite fillings typically last 7–15 years. For larger restorations on back teeth, the longevity advantage of an onlay is considerable and can make it the more cost-effective option over the long term.
At Dental Clinic London, composite fillings start from £185 (small), £245 (medium) and £325 (large). Onlays start from £995 regardless of material. While the upfront cost is higher, the longevity of an onlay (15–25+ years vs 7–15 years) means fewer replacements over a lifetime. A new patient examination is £30. 0% finance is available on selected treatments, subject to status. View our complete pricing on the fee guide.
For small to medium cavities where the cusps are intact and the surrounding tooth is healthy, a composite filling is the most appropriate and cost-effective option. For larger cavities — especially on premolars and molars where one or more cusps are weakened, cracked or undermined — an onlay provides the structural reinforcement needed to protect the tooth long-term. Your dentist will always recommend the most conservative option that is clinically safe.
Weighing Up
Advantages
Limitations
Advantages
Limitations
Transparent Pricing
Prices at Dental Clinic London. View our complete fee guide for all treatment pricing.
| Treatment | Price |
|---|---|
| New Patient ExaminationFull assessment, X-rays & treatment plan | £30 |
| Composite Filling — Small (1 surface)Direct — single appointment, 30–45 minutes | From £185 |
| Composite Filling — Medium (2 surfaces)Two-surface restoration | From £245 |
| Composite Filling — Large (3+ surfaces)Extensive multi-surface restoration | From £325 |
| Onlay (Porcelain / Ceramic)Lab-made, custom-fitted — reinforces weakened cusps | From £995 |
| Onlay (Gold)Exceptionally durable — 25–30+ years longevity | From £995 |
| Dental Crown (for comparison)Full-coverage restoration — from zirconia or E.max | From £995 |
| Root Canal Treatment (if needed)Front from £695 · Premolar from £795 · Molar from £895 | From £695 |
All costs confirmed before treatment begins. 0% finance available on selected treatments, subject to status.
Making Your Decision
The choice between an onlay and a filling depends on the size and location of the cavity and how much healthy tooth structure remains. Here is a general guide — your dentist will confirm the best approach following examination.
If the cavity or damage extends over one or more cusps — or a large old filling is failing and the remaining cusps are weakened — an onlay is the ideal choice. It replaces the damaged portion and reinforces the cusps, providing significantly greater strength and longevity than a filling. This is the go-to option for medium to large cavities on premolars and molars where long-term durability matters.
For small to medium cavities where the cusps are intact and the surrounding tooth is healthy, a direct composite filling is the most appropriate and cost-effective option. It is completed in a single 30–45 minute appointment, bonds directly to the tooth and provides a natural-looking repair. Fillings are ideal for straightforward decay on both front and back teeth.
If longevity is your priority, an onlay is the stronger choice. A porcelain onlay typically lasts 15–25 years, and a gold onlay 25–30 years or more — compared to 7–15 years for a composite filling. For larger restorations on back teeth, the extended lifespan of an onlay often makes it the more cost-effective option over a lifetime, despite the higher upfront cost.
If upfront cost is a primary consideration, a composite filling is significantly more affordable — starting from £185 compared to £995 for an onlay. For small cavities where a filling provides adequate strength, this is the sensible choice. However, for larger restorations, the shorter lifespan of a filling (and the cost of future replacements) should be factored into the decision. Your dentist will help you weigh up the options. If the tooth later needs stronger protection, a filling can often be replaced with an onlay or a crown.
Contact our team to discuss your options — we are here to help you make the right decision for your tooth.
Common Questions
Book a new patient examination at Dental Clinic London for just £30. Your dentist will assess the tooth, take X-rays and explain whether a filling, onlay, crown or another restoration is the most appropriate option for your situation. No pressure, no obligation — just clear, honest advice.
Disclaimer
This article is intended for general educational purposes only and does not constitute personalised dental advice. Individual diagnosis and treatment recommendations require a clinical examination by a qualified dental professional. All treatment outcomes vary by patient. Prices shown are starting prices and may vary depending on complexity. Dental Clinic London is registered with the Care Quality Commission (CQC) and the General Dental Council (GDC).