Crowns, Onlays and Veneers: The Conservative Choice You Probably Weren’t Offered

In the last piece in this series I made the case that teeth are the only structure in your body that don’t heal, and that this single fact ought to change how we approach every decision about treatment. Translation: when work is needed, we should be removing the absolute minimum tooth we can.

This piece is the practical follow-on. When a tooth really does need a restoration, there are usually choices — and in my experience, most patients have only ever been told about the most aggressive option. So let me walk you through how I think about three of the most common restorations: crowns, onlays, and veneers. Two of them are often necessary. One of them I refuse to do far more often than I agree to.

Picture a tooth as a small pillar

Before we get to the techniques, it helps to picture a back tooth. Imagine a small upright pillar — flat-ish on top where it does its chewing, with four walls running down to the gum. The flat top is the chewing surface. The walls are what hold the structure up. Both matter.

When a tooth has been damaged badly enough that an ordinary filling won’t do the job — for example, when it’s had a root canal, or when there’s a large old filling that’s failing and weakening the walls — we need to put something over it to hold it together. The two main options for doing that are a crown and an onlay. They sound similar. They are not.

Crowns: the full cap

A crown — patients often call them caps, which is exactly what they are — covers the entire tooth. The top, all four walls, all the way down close to the gum. To fit a crown, the original tooth has to be cut down to a small pillar, sometimes just a stump, so that the crown can slip over the top and surround what’s left. When the work is finished, you don’t see any of the original tooth at all. The crown is the tooth, visually speaking.

Crowns have their place. There are situations where a tooth has been so badly damaged that there isn’t enough structure left to do anything else, and a crown really is the right answer. I fit them when I need to.

But — and this is the part most patients have never been told — there’s a significant cost to a crown, and it’s the amount of healthy tooth you have to remove to make room for it. Every millimetre of the walls of that tooth that gets ground away to fit the crown is a millimetre of your foundation gone forever. As I explained in the last article, no restoration sitting on top of a tooth is stronger than the tooth underneath it. If we’ve stripped the foundation down to a stump in order to fit the cap, we’ve weakened the structure that holds everything else up.

In the chair, I see this play out as: a beautifully made crown that comes loose because the underlying tooth fractures. The crown is fine. The foundation isn’t. And once the root has split, the tooth is usually finished — out it comes, and we’re into implants or bridges.

Onlays: the lid that keeps the walls

An onlay does a similar job to a crown — it covers and protects the tooth — but with a very different starting point. Instead of reducing the entire tooth to a stump, we only prepare the biting surface and a small portion of the walls. Typically we remove around two millimetres of the top, plus a thin shoulder around the edges. The onlay then sits over that prepared surface like a lid, bonded firmly in place.

The key word is lid. A crown is a cap that wraps the whole tooth. An onlay is a lid that covers the top while leaving the walls of the tooth largely intact.

The result is that you get the best of both worlds. The chewing surface is protected, the tooth is held together against the forces of biting, the appearance is excellent — and you’ve kept much more of your natural tooth than you would have with a crown. Which means the foundation underneath the restoration is stronger, and is more likely to keep that restoration in place for the long run.

Onlays are, broadly speaking, a technique for back teeth — they’re particularly useful when a tooth has had a root canal, because root-canal-treated teeth are inevitably weaker and need protecting from the forces of biting. The old answer to that problem was a crown. The conservative answer, where the tooth still has enough structure left to work with, is an onlay. We do a lot of them at BDS, and I’d argue we should be doing more of them across UK dentistry as a whole.

If you are about to have a back tooth crowned and you’re not entirely sure why, it’s a fair question to ask: would an onlay work here instead? If the answer is genuinely no — because there’s not enough tooth left, or because the situation calls for a crown for other reasons — that’s fine. But the question is worth asking.

Veneers: porcelain fingernails on the front of your teeth

Now I want to turn to veneers, because this is where I find myself having the most difficult conversations.

Veneers are essentially thin shells of porcelain bonded to the front surface of your teeth. The way I sometimes describe them to patients is porcelain fingernails — small pieces of artificial material glued onto what’s underneath. Veneers are mostly cosmetic. They’re used to change the appearance of front teeth: colour, shape, alignment, the impression of evenness.

They have their place. Where teeth are genuinely chipped, badly discoloured, or have other real problems on the front surface, veneers can be a perfectly reasonable solution — and they remove less tooth than crowns do. But the conversations I find difficult are the ones where the teeth aren’t really damaged at all. Where a young patient walks in with healthy, natural front teeth and asks for eight veneers because of a look they’ve seen on social media.

Here’s what I try to explain in those conversations.

To make veneers look good, the dentist has to create space for the porcelain. If we don’t reduce the tooth at all, the veneer either ends up too bulky — making your teeth look chunky and unnatural — or has visible thick edges. So we shave a layer off the front of each tooth to make room for the porcelain to sit flush. That layer is enamel, and enamel does not grow back. Once it’s gone, it’s gone.

If you look online you can find images of what teeth look like underneath after the enamel has been prepared for veneers. It is, frankly, a sobering picture. It’s not subtle. And it’s permanent.

The slippery slope, in slow motion

The other thing I try to walk young patients through is the maths over a lifetime. Let me run it for you here.

You’re twenty. Your front teeth are perfectly healthy. You decide you want veneers on the front six. We prepare the teeth and fit the veneers. They look great.

Veneers don’t last forever. With good ones, well looked after, you might get ten to fifteen years before they need redoing. So at thirty-five, more or less, those veneers are at the end of their life. We have to remove them and start again. In doing so, we always end up taking off a little more tooth than we did the first time.

Round two of veneers takes you to roughly fifty. Now the original tooth structure is even thinner, and we’re working with very little enamel left. Sometimes by this point the veneers have become crowns, because there isn’t enough surface left to bond a veneer to. By sixty or seventy, those teeth have often been through root canal treatment, and some of them may have failed altogether — meaning implants.

This is the slippery slope I mentioned in the last article. It isn’t a horror story I’m inventing to scare people. It’s the documented natural history of cosmetic veneer work started young on healthy teeth. If you have dentistry done, you are more likely to need more dentistry. And the place that’s most true is the place where dentistry was started for purely cosmetic reasons on a tooth that didn’t need any.

I have on occasion refused to do veneer work on young patients who weren’t going to be talked out of it through ordinary conversation. They can go elsewhere, and sometimes they do. But my job, as I see it, is to explain what the next forty years actually look like with this decision, and let them make it with their eyes open. Many of them, hearing it laid out, decide against. Some go for whitening instead, perhaps with a little careful bonding to refine shapes — much more conservative options that achieve a lot of what they were really after.

What to ask, and when to slow down

If you remember nothing else from this article, take these:

When a back tooth needs significant restoration, ask whether an onlay would work instead of a crown. Often it will, and you’ll keep more of your natural tooth.

When you’re considering veneers for cosmetic reasons on healthy teeth — particularly if you’re young — ask the dentist to show you how much tooth structure is removed, and ask what the realistic plan is twenty, thirty, forty years from now. If those answers aren’t being given to you clearly, slow down.

If a practice is enthusiastic about cosmetic work on healthy teeth without any of those conversations happening, that’s information about the practice.

In the next piece in this series, I’ll move from the restorative side to the side I’d actually rather spend more of my time on — prevention. I have a small framework I once came up with for a radio interview, the five Fs of dentistry, which is the best summary I’ve ever managed of what patients can do at home to need as little of my work as possible. That’s part four.

Dr Ian Davis is a partner at BDS Dental. To book a consultation or a second opinion on restorative or cosmetic treatment you’ve been offered elsewhere, contact the practice here.