Sensitive teeth: when is decay behind it?

Most sensitive teeth are not decay — but some are, and the two feel different enough to tell apart. The strongest clue is not cold. It is sweet: a jolt from chocolate, juice or a spoonful of honey in one particular tooth points at a cavity far more reliably than a reaction to cold water does. Cold sensitivity spread across several teeth on both sides, ending the moment the drink is swallowed, is usually exposed dentine. Decay-related sensitivity is local, traceable to one tooth, provoked by sweet things and by food packing between the teeth, and unmoved by sensitive toothpaste. The awkward part of the subject: a cavity at its earliest and most treatable stage usually causes no symptoms at all.

Ask a dentist which single question separates a cavity from ordinary sensitivity, and most will ask what happens with sweet things.

The reason is physical. Dentine, the layer under the enamel, is threaded with microscopic fluid-filled channels running inwards towards the nerve. Anything that moves that fluid sharply registers as a short, stabbing pain. Cold does it by contraction; sugar does it osmotically, drawing fluid outwards through the channels.

Here is why that matters for diagnosis. Intact enamel is a closed lid: sugar sits on it and nothing happens. For a sweet stimulus to reach open dentine channels, something must have breached the surface — and the commonest thing that breaches enamel is decay. Gum recession can expose dentine at the root too, so sweet sensitivity is not exclusively a decay signal. But if one tooth reacts to sweet and its neighbours do not, that tooth deserves an examination.

Cold sensitivity is the symptom everyone reports and the one that discriminates worst, because nearly everything causes it: receding gums, hard brushing, acid erosion, grinding, a recent cleaning, a new filling, whitening — and decay as well. What makes cold useful is not whether it hurts but how it hurts.

If your pattern sits in the left-hand column, the causes and the remedies are covered in depth in Sensitive teeth but no cavities: why healthy teeth still hurt. This article stays with the right-hand column.

This is the single most counter-intuitive fact about tooth decay, and it explains why symptoms are a late warning system rather than an early one.

Read down that table and the logic becomes clear. The stage at which decay can still be stopped with fluoride and better habits, and the stage at which a small filling does the job, are both stages with no symptoms. By the time a tooth announces itself, the repair needed is bigger. German dental associations frame the six-monthly check-up in exactly these terms: it exists to find the problem during the silent phase, not to confirm one you already know about.

None of this makes a twinge an emergency. It makes a twinge information, and information ages badly.

People reasonably conclude that if they cannot see a hole, there is no hole. Decay’s three favourite locations all defeat a bathroom mirror.

Between two teeth. The contact point where neighbours touch is invisible, unbrushable without floss or interdental brushes, and the most common decay site in adults. A cavity can be well into the dentine there while both teeth look flawless from the front. This is what the small bitewing X-ray is for.

Under an existing filling. Fillings do not decay, but the seal at their edge can fail over the years and bacteria travel into the gap. From above the filling looks intact, while the tooth reacts to sweet with no visible explanation — Decay underneath an old filling covers that situation properly.

On an exposed root. Where gums have receded, the root surface has no enamel at all. Root decay (Wurzelkaries) develops more quickly, sits at the gum line where it is easy to overlook, and is often soft and yellow-brown rather than the black spot people expect.

None replaces an examination. All of them make the appointment more useful, because “one of my teeth hurts sometimes” is a far weaker starting point than a precise description.

1. The sweet test. Hold something sugary against the suspect tooth deliberately. A clear reaction in one tooth while its neighbours stay silent is worth reporting. 2. The pointing test. Can you name the tooth? Pain you can localise behaves differently from a vague ache across a quadrant — and nerve pain is often the hardest to place, sometimes seeming to come from the opposite jaw. 3. The floss and food test. Floss that shreds or catches at the same spot every time suggests a rough edge — a broken filling margin or a cavity wall. Food packing repeatedly into one gap points the same way.

Note what you observe and when. A week of notes beats any single sensation recalled from memory in the chair.

The examination is systematic rather than dramatic. We reproduce the symptom under controlled conditions — a defined cold stimulus on each tooth in turn, a gentle stream of air, tapping to check for inflammation around the root, and biting on a small wedge cusp by cusp where a crack is suspected. Small bitewing X-rays cover the two places the eye cannot reach. Working under a microscope makes hairline cracks and leaking filling margins visible that would otherwise be guesswork, and digital scans can be reviewed with AI support alongside our own assessment, never instead of it. Where a 3D X-ray (DVT) is genuinely warranted — a suspected root fracture rather than a routine cavity — it costs 178 € with us and we say so beforehand.

All of it serves one purpose: separating three different problems that produce a single symptom. A cavity needs a filling, exposed dentine needs sealing and better habits, and an inflamed nerve needs something else again.

Your gums have receded. Exposed roots are simultaneously the classic cause of harmless sensitivity and a high-risk site for decay. That combination is exactly why “it’s only sensitivity” is worth confirming rather than assuming.

You are anxious about dental appointments. Sensitivity is a common reason for postponing, and postponing is what turns a small filling into a large one. We work slowly, explain each step first, and offer sedation or laughing gas (Lachgas) where it helps.

You are new to Germany. Describing a twinge precisely in a second language is genuinely hard, and the diagnosis rests on those nuances. You can describe it in English here. English-Speaking Dentist in NRW explains how examinations, insurance and appointments work if you have recently arrived in Wuppertal or the surrounding area.