Examination with bitewing X-rays
Two small X-rays show decay between the back teeth and under old fillings long before it is visible or painful, and let us measure how deep it goes.
About this treatmentDental condition · Wimpole Street, Marylebone
Cavities: how holes form in teeth and how small we can keep the repair
A cavity is the end point of a process that has usually been running quietly for months or years. Bacteria in plaque turn sugar into acid, the acid leaches minerals out of enamel, and saliva puts some of them back between meals. When the balance tips towards loss for long enough, the surface finally collapses into a hole. By the time a cavity hurts, the damage has often reached the softer dentine underneath and the repair is bigger than it needed to be. That is the case for regular examinations: most of the cavities we fill at Wimpole Street are found on X-rays or with careful probing, not because a patient came in with pain.
Recognising it
How it usually feels
A brown, grey or black mark that does not brush away
Staining in a groove is not always decay, but a dark shadow under enamel usually is.
A twinge with sugary food or drink
Sugar reaching exposed dentine is a very specific sign of a cavity.
Sensitivity to cold that passes in seconds
Short, sharp and quickly gone suggests the nerve is irritated but healthy.
Food or floss catching between two teeth
Cavities between teeth often first show up as a shredding floss.
A rough spot or small hole felt with the tongue
By the time you can feel it, the cavity has broken the surface.
No symptoms at all
Most early cavities are silent, which is why they are found at check-ups.
Behind the symptoms
What's going on
- 01
Frequency of sugar, more than quantity
Each time sugar enters the mouth, plaque bacteria produce acid for around twenty to thirty minutes. Six small snacks or sips of a sweet drink through the day mean six acid attacks, whereas the same sugar taken with one meal means one. Grazing and sipping are the habits behind most adult cavities.
- 02
Plaque left in the same place day after day
Decay develops where plaque is not disturbed: between teeth, along the gum edge and in the deep grooves of molars. Brushing well but never flossing protects the surfaces you can see and leaves the ones you cannot.
- 03
Too little saliva
Saliva neutralises acid and carries the calcium and phosphate that repair early enamel damage. Medicines that dry the mouth, dehydration, mouth breathing and some medical conditions tip the balance towards decay, sometimes dramatically.
- 04
Deep fissures and tooth anatomy
The chewing surfaces of back teeth have grooves narrower than a toothbrush bristle. Bacteria at the bottom are undisturbed and sheltered, which is why these surfaces are the commonest site for a first filling.
- 05
Gaps around existing fillings and crowns
Restorations age. A margin that has opened slightly lets plaque in where nothing can clean it, and decay recurs underneath. Checking old work is a large part of every examination.
- 06
Not enough fluoride
Fluoride makes enamel more resistant to acid and speeds up repair between attacks. Skipping fluoride toothpaste, rinsing it away immediately after brushing, or living with very low-fluoride water all remove that protection.
Before your appointment
What you can do today
- Brush twice a day with a fluoride toothpaste, spit but do not rinse afterwards, and clean between the teeth daily.
- Keep sugar to mealtimes and drink only water or unsweetened tea and coffee between meals; a sweet drink sipped over an hour is worse than one finished quickly.
- If a hole is sensitive, avoid very cold or sweet food on that side until it is filled.
- Chew sugar-free gum after meals to stimulate saliva, particularly if your mouth tends to feel dry.
- Note which tooth is bothering you and what sets it off; this helps us confirm the culprit quickly.
These are holding measures, not a substitute for an examination. Use any pain relief exactly as directed on the pack and check with a pharmacist if you take other medicines.
In the chair
How we treat it at Wimpole Street
Remineralisation for early lesions
Where enamel has softened but not yet broken, high-fluoride varnish, improved cleaning and dietary changes can arrest the lesion and avoid a filling altogether.
About this treatmentWhite composite filling
Decay is removed under local anaesthetic, the cavity is kept as small as the decay allows, and it is rebuilt in layered composite bonded to the tooth. Usually one visit of 30 to 45 minutes.
About this treatmentOnlay or crown for larger cavities
When a cavity has undermined a cusp, a laboratory-made ceramic onlay or crown restores strength more reliably than a very large filling.
About this treatmentRoot canal treatment if the nerve is involved
Deep decay that has reached the pulp requires the nerve space to be cleaned and sealed before the tooth is restored.
About this treatmentFees
Costs to expect
An examination at Wimpole Street is expected to be £95, with bitewing X-rays included where clinically needed. White fillings are indicative from £185 per tooth, varying with size and the number of surfaces involved. Fluoride varnish for early lesions is a modest additional fee.
Larger cavities may need an onlay or crown, from £995, and where the nerve has been reached root canal treatment is around £695 for a front tooth or £895 for a molar, quoted in addition. Every cavity found is listed with its proposed treatment and fee so you can see the whole picture before starting.
Figures are indicative prices for Wimpole Street and are confirmed in a written plan once a dentist has examined you. Fees match our South Kensington and St Paul's clinics.
Don't wait if
When to see a dentist
- You can see a dark spot or hole, or feel one with your tongue.
- A tooth reacts to sweet, hot or cold and the sensation lingers or is getting worse.
- Floss shreds or food consistently packs between two particular teeth.
- You have a dull ache in a tooth, especially one that disturbs sleep.
- An existing filling feels rough, has a gap at the edge or has chipped.
- It has been more than a year since your last examination and X-rays.
FAQ
Common questions
Enamel that has been weakened but not yet cavitated can remineralise with fluoride and a reduction in sugar frequency; we watch these areas rather than fill them. Once the surface has actually broken and a hole exists, the tooth cannot regrow that tissue and a filling is needed.
The surfaces between back teeth are hidden from view and from the probe. Bitewing X-rays reveal decay there, and under existing fillings, while it is still small. Finding a cavity on an X-ray typically means a smaller filling than finding it once it hurts.
A well-placed composite filling commonly lasts ten years or more, and many last far longer. Failure is usually because decay has recurred at the edge or the tooth has chipped, both of which are linked to diet and cleaning rather than to the material wearing out.
Removing decay and bonding the filling irritates the nerve slightly, and some sensitivity to cold for a week or two is normal. If it lasts longer, worsens, or the tooth is tender on biting, the filling may need a small adjustment or the nerve may have been more inflamed than expected.
Often, yes, but for different reasons. Gum recession exposes root surfaces, which decay more easily than enamel; saliva tends to reduce; medicines dry the mouth; and old fillings develop gaps. The same prevention applies, with extra emphasis on fluoride and moisture.
For small and medium cavities, bonded composite performs comparably and has the advantage of being glued to the tooth, which supports the remaining walls. For very large cavities on heavily loaded molars we may recommend a ceramic onlay rather than either material.
Marylebone, W1
Wimpole Street opens 1 October 2026
Leave your details and we will be in touch when the Marylebone diary opens. If the problem cannot wait, the same clinicians are already seeing patients in South Kensington and at St Paul's.
Related conditions
Opening 1 October 2026
Wimpole Street is not yet seeing patients. Until then, please book or call our South Kensington clinic on 020 7183 2362 or our St Paul's clinic on 020 7183 3709. Questions about the new clinic: wimpolestreet@md.co.uk.
Until we open
Need an appointment before 1 October 2026?
The same clinical team already works from two other Medical & Dental clinics. Book at either one now and, if you prefer, move your ongoing care to Wimpole Street once the doors open.
South Kensington
- 20 Old Brompton Road, London SW7 3DL
- Open seven days a week
- 020 7183 2362
St Paul's, City of London
- 5 Ave Maria Lane, London EC4M 7AQ
- Open Monday to Friday
- 020 7183 3709
