Inlays and Onlays Explained: The Middle Ground Between a Filling and a Crown

If you’ve gone to the dentist for a cracked tooth or a cavity too big for a standard filling, your dentist might suggest an inlay or onlay. Inlays and onlays are custom-made repairs, tougher than a filling and far less drastic than a crown, designed to fix only the part of the tooth that’s actually damaged.

But when do dentists actually recommend an inlay or onlay instead of a crown or a filling? Let’s walk you through that, along with what the procedure looks like, and what it might cost you.

Filling, Inlay/Onlay, or Crown: The Quick Comparison

Here’s how the three stack up side by side, before we get into the details.

What Exactly Is an Inlay, and What’s an Onlay?

The two terms get used almost as if they mean the same thing, but the difference comes down to how much of the tooth actually gets covered.

An inlay fits neatly within the bumps that make up the tooth’s biting surface, in the same space a filling would normally sit in. It’s essentially a filling made outside the mouth instead of packed in directly, then cemented into place once it’s ready.

An onlay does more. It extends over one or more of those bumps, strengthening a part of the tooth that’s become too weak or damaged to trust with just a filling. Some dentists call it a partial crown, which is a fair description. It covers more than an inlay but stops well short of wrapping the whole tooth the way a full crown does.

Why Not Just a Filling, or Just a Crown?

A filling works by packing material directly into a cavity while it’s still soft, then hardening it in place. That’s brilliant for small to medium cavities. But once the damage gets too large, a direct filling simply doesn’t have enough healthy tooth structure left to bond to securely, and it can flex and crack under normal biting pressure.

A crown solves that by covering the entire tooth, but getting there means shaving down healthy structure all the way round, even the parts that were never actually damaged, which is a lot to remove for a problem that might only affect one side of the tooth.

An inlay or onlay sits between the two. It’s not a full cap or a small patch either. Rather, it’s something that can handle the exact damage that’s there, using a tough enough material and a precise fit rather than packed in by hand. It leaves the rest of your natural tooth exactly where it’s always been.

It only replaces the part of the tooth that’s actually damaged, leaving the healthy structure around it completely untouched.

What Inlays and Onlays Are Made Of

Three materials cover almost every inlay and onlay fitted in the UK.

Composite resin is the cheapest option and blends in well with your natural tooth colour, though it doesn’t hold up quite as long as the alternatives under heavy biting pressure.

Ceramic, sometimes called porcelain, is the most commonly recommended material today. It’s tooth-coloured, resists staining, and with reasonable care a ceramic inlay can hold up for well beyond a decade.

Gold is the oldest option and, in fairness, the most durable of the three. It simply isn’t tooth-coloured, which is why most people now choose it only for back molars that never show when you smile, if they choose it at all.

What the Inlay or Onlay Procedure Actually Involves

Getting an inlay or onlay fitted the traditional way takes two visits, usually a week or two apart.

At the first, the dentist removes the decayed or damaged part of the tooth and takes an impression or digital scan of what’s left. A temporary filling goes in to protect the tooth while the permanent piece is made in a lab. At the second the temporary comes out, the finished inlay or onlay gets checked for fit and bite. Once everything lines up, it’s bonded permanently into place.

Some practices, including ones that can make the piece in-house on the same day, can scan, design, and fit the whole thing in a single visit, cutting out the wait and the temporary altogether.

Not sure whether your tooth needs an inlay, a filling, or something else entirely? Call us on 020 7580 4200. 

How Long Do Inlays and Onlays Actually Last

Materially, considerably longer than a standard filling.

A composite inlay typically holds up for around 10 to 15 years. Ceramic tends to go further, often 15 to 20 years or more with proper care. Gold, if you’re willing to live with the colour, can genuinely outlast both.

That longevity is a big part of why dentists reach for an inlay or onlay in the first place. Replacing a large filling every five or six years is expensive and, each time, removes a little more of your natural tooth structure. An inlay or onlay is built to only need doing once.

What Do Inlays and Onlays Cost?

On the NHS in England, inlays and onlays fall under NHS Band 3, currently £332.10. That’s the exact same charge as a full crown, which means there’s no NHS saving in choosing the option that keeps more of your own tooth. The clinical benefit is real, but the price tag isn’t any lower for it.

Privately, inlays and onlays can cost upwards of £1000, with consultations starting at £325. 

Either way, it’s usually less than a private dental crown, which tends to start higher given the extra material and lab work a full crown involves.

Do You Actually Need an Inlay or Onlay?

Not every damaged tooth needs an inlay or onlay, and it’s worth knowing where the line actually sits.

If the cavity is small enough that a dental filling can bond to plenty of healthy tooth around it, a straightforward filling remains the simpler, cheaper choice. If the damage is so extensive that barely any original tooth structure survives, a full crown is usually the safer long-term option regardless of cost. Inlays and onlays earn their place in the gap between those two: real damage, but real tooth left to work with.

Your own dentist is the one who can actually see which category your tooth falls into. That’s exactly the kind of thing worth getting a proper assessment for rather than guessing from a search result.

Where That Leaves You

Inlays and onlays exist because teeth don’t only come in “small cavity” or “barely holding together.” Plenty land somewhere in between, and that’s precisely the gap these were designed to fill.

If you’ve been told you need one, or you’re simply trying to work out why your dentist didn’t just recommend a filling, here’s the honest answer. It’s very likely the tooth had real damage but real structure worth protecting too. We’re happy to talk you through your own case rather than leave you guessing.

At Specialist Dental Services, we offer an assessment at a fixed price of £325, whatever your case turns out to be, so you leave with a proper look and a straight quote for your own tooth.

Call 020 7580 4200

Book Online

Or see every price on one page