Understanding tooth decay: from early signs to treatment

The single most useful thing to know about tooth decay is this: it is painless until it is serious. By the time a tooth hurts, the cheap and simple option has usually passed.

That is why decay is found at check-ups rather than felt at home — and why the early stages, which are the ones you can still reverse, produce no symptoms at all.

How decay actually happens

Bacteria in plaque feed on sugars and carbohydrates in what you eat and produce acid. That acid dissolves minerals out of the enamel. Your saliva then neutralises the acid and puts minerals back.

Decay is what happens when that balance tips — when demineralisation outpaces repair, day after day.

Frequency matters more than quantity. This is the part that surprises people. Every time you eat or drink something sugary, your mouth stays acidic for roughly 20–40 minutes. One chocolate bar eaten at once means one acid attack. The same chocolate bar nibbled across an afternoon means an all-afternoon acid attack. Sipping a soft drink or a sweet coffee slowly at your desk is considerably worse for your teeth than drinking it quickly.

Four things have to line up for a cavity: a susceptible tooth surface, the bacteria, fermentable carbohydrate, and time. Remove any one and decay does not progress — which is why fluoride (the tooth), cleaning (the bacteria), diet timing (the carbohydrate) and check-ups (the time) each work, and why doing all four works best.

The stages

1. Early demineralisation. A chalky white spot, often at the gumline. No pain, no hole. This stage is reversible — with fluoride, better plaque control and cutting sugar frequency, the enamel can remineralise. Nothing needs drilling. This is what we are looking for at check-ups.

2. Enamel decay. The surface breaks down and a cavity forms. Still usually painless. Now needs a filling, but a small one.

3. Dentine decay. Past the enamel into the softer layer beneath, where decay spreads faster. Sensitivity to sweet, hot or cold may start. A larger filling.

4. Pulp involvement. The nerve is affected. This is where real pain arrives — often throbbing, often worse at night. Now it is root canal treatment or extraction. A filling is no longer an option.

5. Abscess. Infection spreads beyond the root tip. Severe pain, swelling, sometimes fever. Needs urgent treatment.

The distance between stage 1 and stage 4 is measured in years, and almost all of it is silent.

Stage	What you feel	What it takes to fix
1. Demineralisation	Nothing	Fluoride, cleaning, diet change. No drilling
2. Enamel cavity	Usually nothing	A small filling
3. Into dentine	Sweet, cold or hot sensitivity	A larger filling, sometimes an onlay
4. Pulp involved	Throbbing pain, worse lying down	Root canal and a crown, or extraction
5. Abscess	Severe pain, swelling, sometimes fever	Urgent treatment; possibly hospital

Read the right-hand column top to bottom. Every row costs several times the one above it, and each one is only available for a limited time.

What you might notice

White, brown or black marks on a tooth
Sensitivity to sweet things, or lingering sensitivity to hot or cold
A visible hole, or catching floss consistently in one spot
Food packing between the same two teeth every time
Toothache, particularly waking you at night
Bad breath or a bad taste from one area
A filling that feels rough, or a corner that has broken away
A tooth that has changed colour, or looks greyer than its neighbours

Decay between teeth is invisible to you. It is one of the most common sites, and it is found on X-rays, not by looking in a mirror.

Where decay starts, in order of how common it is

Site	Who it affects most	Why
Grooves of back teeth	Children and teenagers	Deeper and narrower than a bristle. Sealants address this
Between teeth	Everyone	A brush cannot reach; only floss or an interdental brush can
At the gumline	Adults, especially with dry mouth	Plaque accumulates where tooth meets gum
Root surfaces	Older adults with recession	Root is softer than enamel and decays faster
Around existing fillings	Anyone with restorations	The margin is a joint, and joints collect plaque
Around braces brackets	Teenagers in orthodontics	Cleaning is harder at exactly the wrong age

What decay is not

Two things that look like decay and are not, because the treatment differs entirely.

Erosion is acid dissolving enamel directly — from citrus, soft drink, wine, vinegar or reflux — with no bacteria involved. It looks like thinning, yellowing, and cupped hollows on biting surfaces rather than a hole. Cleaning more does not fix it; changing the acid exposure does.

Abrasion and wear — notches at the gumline from hard brushing, or flattened edges from grinding. Again, not decay, and the answer is a softer brush or a splint rather than a filling.

All three can be present at once, which is why a diagnosis is worth more than a self-assessment.

A warning about "the pain stopped"

If a tooth was hurting badly and then the pain went away on its own, that is not recovery. It usually means the nerve has died. The infection is still there and will eventually cause an abscess. Get it seen.

How decay is found

Worth knowing, because "I can't see anything" and "nothing hurts" are both poor tests.

Visual examination with good light and drying — finds surface cavities and white spots
Bitewing X-rays — the standard way of finding decay between teeth, which is otherwise invisible
Transillumination — light through the tooth, showing decay as a shadow, without radiation
Intraoral photographs — magnified, and useful for showing you what we are describing
Comparing over time — an image from two years ago is often the most useful thing in the file, because it shows whether something is moving or stable

This is also why "watch and review" is a legitimate plan. A lesion confined to enamel that has not changed in two years is being managed correctly.

Treatment

Early stage — high-fluoride toothpaste or professional fluoride application, better cleaning, reduced sugar frequency, and monitoring. No drilling.

Small cavity — a tooth-coloured composite filling. We are amalgam-free, and for some small cavities we can use air abrasion rather than a drill, which often means no needle.

Larger cavity — a larger filling, an inlay/onlay, or a crown where too little tooth remains to support a filling.

Nerve involved — root canal treatment to remove the infected pulp, usually followed by a crown, or extraction if the tooth cannot be saved.

Each step up costs considerably more than the one before. That gap is the entire economic argument for regular check-ups.

If a filling is recommended and you are not sure

Reasonable questions, and any practitioner should answer them plainly:

Can I see it? On the X-ray or the camera image
How deep is it? Enamel only, or into dentine
What happens if we watch it instead? And when would we review
Is this new decay, or decay under an existing filling?
What will it cost, and what is the item number?

If the answers do not satisfy you, a second opinion from another appropriately qualified practitioner is a sensible step, not an insult.

Decay in children

Baby teeth decay faster than adult teeth, because the enamel is thinner and the nerve is closer to the surface. What looks like a small mark can reach the nerve in months rather than years.

Early childhood caries — a pattern affecting the upper front teeth, strongly associated with a bottle in bed, or a sipper cup of milk or juice used through the day
Baby teeth matter even though they fall out: they hold space, they hurt when they decay, and infection can affect the adult tooth forming underneath
Sealants on the six-year molars address the most common site
Fluoride varnish at check-ups is quick, painless and effective for children at higher risk

See family and children's dentistry.

Prevention

Brush twice daily with fluoride toothpaste. Spit, do not rinse — rinsing washes the fluoride away
Clean between your teeth daily
Reduce how often, not just how much. Confine sweet things to mealtimes; water between meals
Avoid sipping sugary or acidic drinks slowly
Nothing but water in a bottle at bedtime, for children and adults
Regular check-ups, with X-rays at intervals matched to your risk
Fissure sealants for children's back teeth — the grooves are where most childhood decay starts
Sugar-free gum after meals, which raises saliva flow and helps clear acid

Higher risk

Dry mouth is a big one — hundreds of common medications reduce saliva, and less saliva means less natural repair. Also: existing large fillings and crowns, gum recession exposing softer root surfaces, orthodontic appliances, frequent snacking, reflux, eating disorders, and a history of decay.

If you take regular medication and your mouth feels dry, tell us. It changes what we recommend.

If you are at high risk, there is more that can be done

Beyond the standard advice:

High-fluoride toothpaste (5000 ppm), which is available on prescription
Professional fluoride varnish at shorter intervals
A shorter recall interval, often three or four months
Saliva substitutes and stimulants for dry mouth
Tooth mousse and similar remineralising products, where indicated
A structured diet review, which is more useful than general advice because it looks at your actual pattern

Ask for this if decay keeps recurring. Repeated fillings without addressing why is treating the symptom.

Questions we are asked

Can a cavity heal itself? Early demineralisation — a white spot with the surface intact — can remineralise. Once there is a hole, no.

Why do I get decay when I brush twice a day? Usually because brushing does not reach between the teeth, or because of frequency of eating, or dry mouth. It is rarely about effort.

Does sugar-free mean safe? For decay, largely. For erosion, no — most sugar-free soft drinks are still acidic.

How fast does decay spread? Highly variable: months in a child or a dry mouth, years in a low-risk adult. That variability is why the recall interval is individual.

Is it better to fill early or wait? Neither, universally. Enamel-only lesions are usually monitored; lesions into dentine are usually restored. The judgement should be explained to you.

Do I need to replace all my old fillings? No. A sound filling is left alone. Replacement removes more tooth every time.

Who provides this here

Victorian Dental Group is a general dental practice in Malvern East and holds no specialist registration. Examinations, fillings and root canal treatment are provided by our dentists. Where a case needs specialist care — complex root canal treatment, surgery — we refer to a registered specialist.

Victorian Dental Group — 291 Wattletree Road, Malvern East VIC 3145 · (03) 9088 5808 · Monday to Friday, 8:00am–5:00pm · book online

General information only, not personal dental advice. See our disclaimer.

How does decay start?

Bacteria in plaque produce acid after you eat, and that acid dissolves minerals out of the enamel. The first visible sign is a chalky white spot along the gum line or between the teeth — decalcification, not yet a hole. It is painless, and it is the stage at which the process can still be turned around.

Can early decay be reversed?

Yes, at the white-spot stage. Enamel can take minerals back up from saliva and fluoride, so a white spot lesion can remineralise and arrest with better cleaning at the gum line, fluoride toothpaste used properly, professionally applied fluoride varnish, and fewer sugar episodes through the day. That is why early detection matters — it is the one stage where a filling can be avoided altogether.

Does every early spot need a filling?

No, and this is worth knowing. Early lesions that have not broken through the surface are often better monitored and remineralised than drilled, because once a tooth is filled it enters a cycle of repair and replacement that takes more tooth each time. Where a decision is finely balanced you should be told that, shown the X-ray, and given the option of reviewing it rather than treating immediately.

What happens if it progresses through the enamel?

The surface breaks down and a cavity forms. At this point the tooth cannot repair itself and a filling is needed. It still usually does not hurt — which is exactly why decay between teeth is found on X-rays rather than by symptoms, and why waiting for pain is a poor strategy.

What happens when decay reaches the dentine?

Dentine is softer and more porous than enamel, so decay spreads faster once it gets there, undermining the enamel above it. Sensitivity to cold and sweet things is common at this stage, and a tooth can look almost intact from the outside while being substantially hollowed out underneath.

What if it reaches the nerve?

The pulp — the nerve and blood vessels inside the tooth — becomes inflamed and then infected, which is the point at which people typically get severe, lingering or throbbing pain that can wake them at night. Once the pulp is irreversibly inflamed, a filling is no longer enough: the options are root canal treatment or extraction. Root canal treatment is a procedure carried out under local anaesthetic, not surgery.

What is an abscess?

A collection of pus where the infection has spread out of the tooth into the surrounding bone. There may be swelling, tenderness to bite on, and a bad taste. Sometimes the pain stops at this stage because the nerve has died — that is not recovery. Spreading facial swelling, fever, or difficulty breathing or swallowing means a hospital emergency department or 000, not a dental appointment.

How is decay found before it hurts?

By examination and X-rays — decay between teeth is largely invisible to the eye until it is well advanced. That, plus keeping sugar to mealtimes, cleaning between the teeth daily, and brushing twice a day with fluoride toothpaste and not rinsing afterwards, is how most fillings are avoided. Victorian Dental Group, 291 Wattletree Road, Malvern East VIC 3145 — (03) 9088 5808, Monday to Friday 8:00am to 5:00pm.