Decayed Teeth: The Stages of Tooth Decay and the Fix for Each

Almost everybody who goes looking for this has one particular tooth in mind, and one particular dark patch on it they've been quietly not looking at for a while. Here's the reassuring part: decay moves through five recognisable stages, each stage has its own fix, and most of those fixes are far smaller than the one currently playing in your head.

What Tooth Decay Actually Is, in Plain English

Let's translate the word first, because "decay" sounds like rot, and what's happening is far more ordinary.

The outer shell of a tooth, the enamel, is a wall of tightly packed minerals, and it lives in a permanent tug of war. The bacteria in the soft film on your teeth, the plaque, feed on sugar and starch from whatever you've just eaten, and give off acid while they do it. That acid pulls minerals out of the wall. Then your saliva arrives, washes the acid away, and puts minerals back in.

So every day your enamel loses a bit and gains a bit back. Picture a bank account with money going out and money going in, all day long. Decay is what happens when the outgoings beat the deposits, week after week, until the wall gets thin enough to give way.

Which explains what surprises people most. How often the chocolate bar turns up does far more damage than how big it is, because each time something sweet goes in the acid runs for a good while until saliva catches up. Six little snacks across a day keep that account overdrawn nearly all day.

And it starts in predictable places, because decay begins wherever plaque gets to sit undisturbed: the deep grooves along your back teeth, which hold plaque the way the tread of a boot holds grit; the tight point where two teeth touch, where a brush bristle is too fat to reach; and the little ledge where the tooth meets the gum. Look at where your brush actually goes, and you're looking at where decay doesn't start.

Stage One: The Chalky White Spot (Early Tooth Decay)

The first sign of decay is white, which throws absolutely everybody, because we all expect it to be brown. Enamel that has lost minerals stops reflecting light the way the rest of the tooth does, so it turns dull and chalky, rather like the difference between a glazed tile and an unglazed one. It shows up best on a dry tooth, often as a small crescent hugging the gum line, and you'll feel nothing, because enamel has no nerve in it.

This is the good stage, and worth being pleased about. The surface is still whole, and this is the only point in the whole story where a tooth can go backwards to healthy. You can put minerals back into a wall that's still standing. You can't rebuild one that's already fallen.

The usual fix here involves no drill at all. A dentist will normally record it, keep an eye on it at each visit to see whether it's spreading or holding steady, and strengthen the surface, which is what fluoride does, since it helps the mineral crystals rebuild in a tougher form than they were before. If the spot sits inside a deep groove, sealing that groove stops plaque settling back into it. And they'll talk through what's feeding it, because a white spot is a message about habits.

Stage Two: The Surface Gives Way

Keep the acid coming and the weakened patch eventually caves in, the way a thin patch of plaster finally goes when you lean on it. Now there's a real hole, a cavity, though at this stage it's often smaller than a pinhead.

Here's the frustrating part, and it's the entire reason check-ups exist. You still feel nothing, because enamel has no nerve supply, so a hole in it is silent. On a chewing surface you might notice a dark speck or a grey shadow. Between two teeth, where a great many of them hide, the only thing that ever notices is floss catching and shredding on the sharp edge. An X-ray sees straight through the tooth and shows that decay as a dark notch, which is why the first look after years away includes X-rays where they're needed.

The usual fix is a filling, which at UrgentCare Dental runs £149 to £349 depending on the size of the hole and how many surfaces of the tooth it touches. The decay is cleaned out under local anaesthetic, the space filled with tooth-coloured composite set hard with a blue light, then shaped and polished until your bite lands where it did before. One visit, and that tooth is finished with. It's the smallest and quickest repair a tooth can have, which is the whole argument for catching decay here rather than three stages later. Our guide to white fillings and what they cost covers the materials, and how long fillings last covers what happens afterwards.

Stage Three: Into the Dentine, Where You Start to Feel It

Under the enamel sits dentine, and dentine changes the whole story. Picture a mug. The hard, shiny glaze on the outside is your enamel, and the clay body underneath is the dentine. Dentine is softer, so once decay breaks through it spreads faster and wider, hollowing out underneath while the surface still looks nearly fine. That's why a tiny dark speck on a molar sometimes turns out to be a far bigger space than anybody expected.

Dentine is also threaded with thousands of microscopic tubes running inwards towards the nerve, like a bundle of drinking straws all pointing the same way. Which is exactly why this is the stage where you start to feel things. Cold water gives a sharp zing, something sweet makes the tooth twinge, cold air catches it when you breathe in. And here's the detail worth holding onto: it stops the moment the cold or the sugar goes away. A twinge that comes and goes with whatever set it off is dentine talking, and the nerve itself is still perfectly healthy. If that's all you're feeling, our guide to sensitive teeth and what settles them is worth a read.

The usual fix is still a filling most of the time, just a larger one, and still £149 to £349. When the hole has taken out so much of the tooth that there's more filling than tooth left, a filling stops being the right answer, because the walls left behind are thin, and thin walls crack under chewing. That's where a crown comes in at £650 to £895, capping what's left and taking the bite force off it so the tooth can go on working for years. Between the two sits a tooth reconstruction at £500, rebuilding a badly broken-down tooth. For the comparison, we've written about when a crown beats a filling.

Stage Four: The Nerve Gets Involved

At the centre of every tooth is the pulp: a soft core of nerve and blood vessels in a narrow chamber running down into the roots. It's the living part of the tooth, and the part that gives you toothache.

When decay gets close enough, the pulp becomes inflamed. Inflammation anywhere else has somewhere to swell into, and that's precisely the problem here, because the pulp is sealed inside hard walls that won't give an inch. Think of a ring a size too small on a swollen finger. The pressure has nowhere to go, so it presses on the nerve instead, which is why toothache feels so out of proportion to the size of the thing causing it.

The pain changes character here, and the change is the useful signal. The twinge that used to vanish when the cold water left now hangs around for minutes. Then it starts arriving on its own, and heat can set it off where cold used to. And it gets worse when you lie down, because lying flat raises the blood pressure in your head a little, and more pressure in a chamber that already has too much is the last thing that tooth needs. That's the classic two-in-the-morning toothache.

The usual fix is root canal treatment, from £399 and up to £950 per canal, since a front tooth has one canal and a back molar can have three or four. It clears the inflamed tissue out of the chamber and canals, disinfects them and seals them, which ends the pain because there's nothing left in there that can hurt. A crown is usually the sensible finish, since a tooth that's had that much taken out needs its bite force spread across a cap. And root canal has a reputation it stopped deserving years ago: with the tooth numbed the whole way through, it tends to feel much like a big filling. There's a full guide to root canal treatment and what it costs if that's where yours has got to.

Stage Five: The Nerve Dies and the Infection Moves Out

Here's the strangest part of the whole process. If the pulp is left inflamed long enough, it dies, and when it dies the pain stops.

Plenty of people take that as the problem solving itself. It doesn't, and the reason is simple: the bacteria are still in there, and now they have an empty chamber to live in with nothing pushing back. They work their way down the canal and out through the tip of the root into the bone, and your body walls the area off with a pocket of infection, which is what an abscess is.

So the pain comes back, days or months later, and it feels different. The throb has gone. What replaces it is a tooth that's tender to bite on and sore to press, sometimes feeling slightly taller than its neighbours, because the inflamed tissue at the root tip pushes it up a fraction. There may be a small bump on the gum beside it, and the tooth often goes grey or dark as the dead tissue inside shows through the enamel. That's one of several reasons a tooth turns dark, and what dark teeth and stains actually mean walks through the others.

The usual fix is either root canal treatment from £399, which clears the infection out and keeps your own tooth, or taking the tooth out at £149 for a straightforward extraction and £399 when it's more involved. Which one is right depends on how much solid tooth is left to build on, and the X-ray answers that rather than the eye. Our post on whether rotten teeth can be fixed goes through the decision tooth by tooth.

If a sore tooth comes with swelling in your face or under your jaw, come in that same day rather than waiting, because an infection is far easier to deal with early.

Tooth Decay Stages and Treatment, at a Glance

Here's the whole story in one place, so you can find the row that sounds like your tooth.

The Speed of It, and What Slows It Down

Decay is slow, which is good news for anybody reading this with a knot in their stomach. The gap between "something is starting here" and "this needs a root canal" is usually long enough for a check-up to land in the middle and catch it while it's still a £149 job. That's the entire logic behind going every six months, and it's why regular visits work out kinder on the wallet than waiting does, since a filling costs a fraction of a root canal and a crown together. It also means the teeth in one mouth are rarely all at the same stage, so a long gap gives you a spread, never a single verdict.

As for slowing it down, how often sugar turns up matters more than how much, for the reason we covered earlier: each visit starts a fresh acid attack and the account never gets a chance to rebalance. Brushing last thing at night with a fluoride toothpaste does the heavy lifting, because saliva flow drops while you sleep and enamel needs all the help it can get overnight. Spit the toothpaste out and skip the rinse, since rinsing washes away the fluoride you just brushed on. And clean between your teeth somehow, because that contact point is where the brush never reaches.

There's one honest limit to it. Home care decides whether new decay starts, and it can turn an early white spot back around. It can do nothing about a hole already through the surface, because a tooth cannot grow enamel back. So a dark spot you've been brushing at for a year was never going to fade, and that's no reflection on you.

Finding Out Which Stage Your Tooth Is At

The answer to "which stage is mine?" is that you can't tell from the outside, because the two things that settle it are how deep the hole goes and how the nerve is behaving. Both come from an X-ray and a few simple tests on the tooth, and both take minutes.

At UrgentCare Dental that first appointment is £20: a dentist goes over the whole mouth, takes digital X-rays where the tooth needs them, and hands you a plan with every price on it in writing before a thing is touched. If you're seen after 11pm it's £50 for the same appointment. Treatment only goes ahead that day if you decide it should, the check-ups after any treatment cost nothing, and any treatment over £500 is eligible for 0% finance over 12 months. Every figure we've used here sits on our price list.

If it's been a long time, what actually happens at a check-up walks you through the appointment, and going back to the dentist after years away covers the rest, including the lecture that doesn't happen.

Common Questions About Decayed Teeth

Can tooth decay be reversed?

Only at the very first stage, before the surface breaks. A chalky white spot is enamel that has lost minerals while the wall is still standing, and minerals can be put back into a standing wall with fluoride, better cleaning and less frequent sugar. Once the surface has caved in, reversing it is off the table, because a tooth cannot grow new enamel the way skin grows back, so from there the hole gets filled rather than healed.

What are the first symptoms of tooth decay?

Nothing, for quite a long while, which is the slightly annoying answer. Enamel has no nerve in it, so early decay and even a small cavity are silent. The first thing most people notice is a twinge with something cold or sweet that disappears the second the cold or sweet does, which is decay having reached the dentine underneath. Before then the clues are visual: a chalky patch near the gum, a dark speck in a groove, or floss that shreds in the same gap.

How long does it take for tooth decay to reach the nerve?

Usually years rather than months, though it speeds up as it goes. Working through enamel is the slow part, because it's the hardest material your body makes and saliva keeps repairing it. Once decay is into the softer dentine it spreads faster, and the last stretch to the nerve can go in weeks. That's why six-monthly check-ups work so well: they land in the middle of the slow part.

Does a decayed tooth always have to come out?

No, and since this is the fear that keeps most people at home, it's worth saying plainly. Most decayed teeth are repaired and kept, with a filling at the earlier stages and a crown or root canal treatment further along. A tooth only really comes out when there isn't enough solid structure left to build anything onto, or when it's broken below the gum. That call comes from the X-ray, and you'll be told which yours is before anything is agreed.

How much does tooth decay treatment cost?

At UrgentCare Dental a filling is £149 to £349 depending on its size, a crown is £650 to £895, root canal treatment runs from £399 up to £950 per canal, and a simple extraction is £149. The appointment that tells you which of those you need is £20 with X-rays included. Those are guideline prices for a straightforward case, and your own written quote is agreed before anything starts, so the figure never moves afterwards.

Does having a decayed tooth filled hurt?

The tooth is fully numbed with local anaesthetic first, so what you feel is pressure and vibration rather than pain. The bit people remember is the injection, and even that is a few seconds of sting. If the thought of it turns your stomach, say so when you book, because there's a whole ladder of help: a light oral tablet to take the edge off, inhalation sedation, or IV sedation with a dedicated sedation nurse from £249 an hour, where you're awake and deeply relaxed and tend to remember none of it.

The Part Worth Taking Away

Decay is one slow process with five stops along the way, and the difference between an easy fix and a hard one is simply which stop your tooth is at right now. There's no moral in it and no verdict in it.

So if there's a tooth you've been avoiding, the useful move is simply to find out where it sits on that list. It's very likely further back than you think, because the stages that hurt are the late ones. One look and an X-ray will settle a question you've been carrying for months, and that on its own is usually the best part of the appointment.