Meet Our Dental Team
Our experienced dental team is fully qualified and registered with the GDC, delivering safe, high-quality care in line with the highest professional standards.
Because our patients deserve nothing less.
When a tooth has been damaged by decay, a crack, or a fracture, you may be wondering whether a filling or an onlay is the most appropriate treatment. Both are designed to restore the tooth and protect it from further damage — but they differ in strength, durability, and the size of damage they are best suited to treat.
A dental filling is placed directly in the tooth during a single appointment and is ideal for small to moderate cavities. An onlay is a custom-made restoration fabricated in a laboratory, designed to treat larger areas of damage — particularly when the cusps of the tooth are affected. The right option depends on the extent of the damage and the amount of healthy tooth structure remaining.
This guide explains the key differences to help you understand your options. The most suitable treatment will always depend on a clinical assessment by your dentist.
| Feature | Dental Filling | Dental Onlay |
|---|---|---|
| Type of Restoration | Direct — placed and shaped in the mouth in one visit | Indirect — custom-made in a dental laboratory |
| Size of Damage Treated | Small to moderate cavities and decay | Moderate to large damage — too extensive for a filling |
| Strength and Durability | Good for small restorations — may weaken over time in larger cavities | Very strong — custom-made for a precise, durable fit |
| Tooth Preservation | Minimal preparation — preserves natural tooth structure | Conservative — covers damaged area including cusps without full crown |
| Treatment Time | Single appointment (30–60 minutes) | Two appointments (impression + fitting) |
| Cost (at Our Practice) | From £92.50 (member) / £185 | From £497.50 (member) / £995 |
| Longevity | 5–10 years with proper care | 10–15 years or more with proper care |
| Suitability | Small cavities, minor decay, chip repairs | Larger cavities, cusp damage, failing large fillings |
Type of Restoration
Filling
Direct — placed and shaped in the mouth in one visit
Onlay
Indirect — custom-made in a dental laboratory
Size of Damage Treated
Filling
Small to moderate cavities and decay
Onlay
Moderate to large damage — too extensive for a filling
Strength and Durability
Filling
Good for small restorations — may weaken over time in larger cavities
Onlay
Very strong — custom-made for a precise, durable fit
Tooth Preservation
Filling
Minimal preparation — preserves natural tooth structure
Onlay
Conservative — covers damaged area including cusps without full crown
Treatment Time
Filling
Single appointment (30–60 minutes)
Onlay
Two appointments (impression + fitting)
Cost (at Our Practice)
Filling
From £92.50 (member) / £185
Onlay
From £497.50 (member) / £995
Longevity
Filling
5–10 years with proper care
Onlay
10–15 years or more with proper care
Suitability
Filling
Small cavities, minor decay, chip repairs
Onlay
Larger cavities, cusp damage, failing large fillings
A dental filling is a direct restoration used to repair small to moderate areas of tooth decay or damage. The decayed portion of the tooth is removed, and a composite resin material is placed directly into the cavity, shaped to match the natural contours of the tooth, and hardened with a curing light — all in a single appointment.
Modern composite fillings are tooth-coloured, providing a natural appearance that blends with the surrounding tooth. They are one of the most common and well-established treatments in general dentistry, suitable for restoring teeth affected by minor to moderate decay.
Dental fillings are suitable for patients with small to moderate cavities, minor chips, or early-stage decay. They work best when the damage is limited and the surrounding tooth structure is strong enough to support the filling. For larger cavities or damage to the cusps, a more substantial restoration such as an onlay may be recommended.
A dental onlay is an indirect restoration that is custom-made in a dental laboratory and bonded to the tooth. Unlike a filling, which is placed directly, an onlay is designed to cover and protect a larger area of damage — including one or more of the cusps (the raised points on the biting surface of the tooth).
Onlays are sometimes referred to as partial crowns because they provide more coverage than a filling but less than a full crown. They are made from porcelain, composite, or gold and are part of restorative dentistry treatments designed to preserve as much natural tooth structure as possible while providing the strength needed for long-term function.
Onlays are suitable for patients with moderate to large cavities, cracked or weakened cusps, or large failing fillings that need replacing with a stronger restoration. They are ideal when the damage is too extensive for a filling but the tooth does not require the full coverage of a crown. Candidacy is determined through a clinical assessment.
Fillings are designed for small to moderate cavities within the tooth. Onlays cover larger areas of damage, including the cusps. An onlay is used when a filling would be too large to provide reliable long-term support.
Onlays are fabricated in a laboratory from stronger materials and custom-fitted to the tooth, making them more durable than composite fillings — particularly for larger restorations. Fillings are effective for small cavities but can weaken or crack when used in bigger areas.
Both fillings and onlays are conservative compared to crowns. Fillings require only the removal of decayed material. Onlays require slightly more preparation but preserve significantly more tooth structure than a full crown would.
Fillings are placed directly in a single appointment. Onlays require two visits — one for preparation and impressions, and a second for fitting the custom-made restoration. A temporary filling is placed between appointments.
Composite fillings typically last 5–10 years, while onlays can last 10–15 years or more. The longer lifespan of onlays reflects the stronger materials and laboratory precision involved in their fabrication.
Fillings are more affordable — from £92.50 (member) / £185. Onlays cost more due to laboratory work — from £497.50 (member) / £995. However, onlays may be more cost-effective over time due to their greater durability and reduced need for replacement.
Fillings are more affordable as a direct, single-visit treatment. Onlays cost more due to laboratory fabrication and the precision fitting involved. The final cost depends on the material, complexity, and the tooth being treated.
| Treatment | Member Price | Standard Price | Notes |
|---|---|---|---|
| Composite Filling | From £92.50 | From £185 | Direct — single appointment |
| Dental Onlay | From £497.50 | From £995 | Lab-made — two appointments |
Composite Filling
Dental Onlay
The cost difference reflects the laboratory work and stronger materials used for onlays. When considering long-term value, an onlay's greater durability may reduce the need for future replacements. Membership patients receive 50% off all treatments.
If the decay is small to moderate and the tooth structure is sound, a composite filling is an effective, affordable, and quick solution — completed in a single appointment with minimal preparation.
Dental FillingIf the cavity is large, the cusps are damaged, or a previous filling has failed, an onlay provides the strength and coverage needed. It protects the weakened areas without requiring a full crown.
Dental OnlayBoth fillings and onlays are conservative options. Fillings preserve the most structure for small repairs. Onlays preserve more structure than a crown while providing greater protection than a large filling.
Both OptionsIf you want the longest-lasting restoration for moderate to large damage, an onlay typically outlasts a filling — 10–15 years compared to 5–10 years — reducing the need for future replacement.
Dental OnlayThe best way to determine which restoration is right for your tooth is with a personalised clinical assessment. Our dental team will examine the extent of damage and recommend the most appropriate treatment — book a consultation with a dentist in London to discuss your options.
This page 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 depend on individual clinical factors and cannot be guaranteed. The suitability of a filling or onlay is determined during a clinical assessment. South Kensington Medical & Dental is registered with the Care Quality Commission (CQC) and all practitioners are registered with the General Dental Council (GDC).
Our experienced dental team is fully qualified and registered with the GDC, delivering safe, high-quality care in line with the highest professional standards.
Because our patients deserve nothing less.
At South Kensington Medical & Dental, we are fully registered with the Care Quality Commission (CQC) and our clinicians are registered with the relevant UK regulatory bodies, including the GDC and GMC. Our dentists, dental nurses and medical professionals deliver care that meets the highest clinical, safety and ethical standards, because our patients deserve nothing less.
