The short answer
A toothbrush cleans three of the five surfaces of every tooth. The two surfaces where neighbouring teeth touch are, for the bristles, unreachable — and that is precisely where decay in careful brushers usually begins. The second thing brushing cannot influence is timing: how often your teeth meet acid over a day matters more than how much sugar you eat in total. Six sweetened coffees spread across a working day are harder on enamel than one large dessert. Add saliva, which varies enormously between people and is quietly reduced by dozens of common medications, and you have the honest answer. A cavity found at a check-up is rarely a verdict on your discipline; it is information about where and when your mouth is under attack.
What brushing does — and what it cannot reach
Brushing has one job and does it well: it breaks up the soft bacterial film (Plaque) on the outer, inner and chewing surfaces. That film is where the whole process starts, so removing it twice a day is genuinely the most valuable habit you have.
Look at a molar from above, though, and the limits become obvious. Five surfaces: cheek side, tongue side, chewing surface, and two flanks pressed tightly against the neighbours. Bristles are too thick to enter that contact zone, so whatever collects there stays until something thinner goes in — floss, an interdental brush (Interdentalbürste) or a water flosser.
Three sites account for most cavities in people who brush conscientiously:
- Between the teeth. Nothing visible from outside, nothing painful, and the lesion is often found only on an X-ray.
- The deep grooves of the back molars. A fissure can be narrower than a single bristle. Some people have shallow, self-cleaning grooves; others have deep ones that trap plaque however well they brush.
- The margin of an existing filling or crown. Every restoration has a join with the tooth, and where that join is no longer sealed, bacteria have a sheltered address — the subject of Decay under an old filling.
The acid clock: why frequency beats quantity
This is the part most people have never been told, and it changes behaviour more than any lecture about sugar.
Every time you eat or drink something containing fermentable carbohydrate, plaque bacteria produce acid within a couple of minutes, and enamel loses minerals while that acid persists. Saliva then buffers the acid and returns minerals to the surface — but repair takes considerably longer than damage, so the mouth needs an uninterrupted stretch of time to recover before the next assault.
Compare two days with identical sugar. On the first, a slice of cake after lunch and nothing between meals: two or three acid episodes, long recovery windows. On the second, a sweetened latte sipped through the morning, a biscuit at three, juice on the train home — the clock is reset again and again and the windows never open. The second day produces the cavities, and office coffee or an energy drink before a deadline count just as much as sweets.
The practical rule. Eat something sweet with a meal rather than on its own an hour later, and keep to water or unsweetened tea in between. “Sugar-free” is not “acid-free” either: sparkling water, citrus and vinegar dressings soften enamel chemically, with no bacteria involved.
Saliva: the variable nobody thinks about
Saliva is your repair system. It rinses, buffers acid and delivers the calcium and phosphate that rebuild softened enamel. Two people with identical habits can have very different decay rates simply because one produces markedly more of it.
Flow drops for reasons that have nothing to do with dental care: medication (antidepressants, antihistamines, blood pressure tablets and many others list dry mouth as a side effect), mouth breathing and snoring, which dry the teeth for hours at a stretch, dehydration, stress, and radiotherapy to the head and neck.
If your mouth is regularly dry, say so at your appointment. There are practical countermeasures — from sugar-free gum after meals to a higher-fluoride toothpaste — but they only get recommended if the problem is known.
Technique, timing and toothpaste
Assuming the blind spots are covered, small details still separate an effective routine from a busy one.
Pressure, not force. Scrubbing wears the enamel and pushes the gum back, exposing the softer root surface, which decays more readily than the crown of the tooth. After orange juice or wine, wait about half an hour before brushing — enamel is briefly softened, and brushing scrubs that layer away.
Spit, do not rinse. The fluoride left on the tooth surface is the part that works overnight, and washing it away undoes half the point of the toothpaste. The relevant figure is the concentration in ppm printed on the tube; people at higher risk can be prescribed a higher one. German dental associations regard fluoride toothpaste as the best-evidenced everyday measure against caries there is.
One point specific to Germany: tap water here is not fluoridated, as it is in parts of the US, the UK, Ireland and Australia. Fluoridated table salt (Fluoridsalz) is sold in every supermarket and is the usual dietary route instead. If you moved here from a country with fluoridated water and your decay rate has quietly risen since, that is one plausible piece of the puzzle — and among the easiest to change.
Risk you did not choose
Some of what decides your decay rate was settled long before you owned a toothbrush, and it is worth saying plainly so nobody carries unnecessary guilt. Deep, narrow fissures in the molars, teeth standing so tightly that floss barely passes, enamel that developed with defects, gum recession that exposes root dentine — none of that is a habit. Every filling and crown adds another margin, and margins are the natural weak point of any repaired tooth. Sealing deep fissures (Fissurenversiegelung) is covered for children and adolescents at the relevant ages, and is one of the few items on this list you can act on directly.
What actually changes the odds
In order of impact:
1. Clean between the teeth once a day — floss or interdental brushes, whichever you will genuinely use. This single habit addresses the surfaces where careful brushers get their cavities. 2. Cut the number of eating occasions, not necessarily the amount. Three or four defined episodes a day, water in between. 3. Use fluoride properly. Twice daily, spit rather than rinse, and ask whether a higher concentration suits your risk. 4. Keep the check-up rhythm. Statutory insurance covers a check-up twice a year for adults, and there is a second reason to go: each year’s stamp in the bonus booklet (Bonusheft) raises the fixed subsidy (Festzuschuss) your fund pays if you ever need a crown or denture — from 60 % of standard care to 70 % after five unbroken years and 75 % after ten. The appointment you skip this year costs you money in a decade. 5. Consider professional cleaning (professionelle Zahnreinigung, PZR), which removes hardened deposits a brush cannot. For adults it is generally a private service, though many funds contribute part of the cost — ask yours, because the policies differ.
What's normal — and when to book an appointment
Contact us the same day if a tooth aches spontaneously without any trigger, the pain wakes you at night, or the face or gum is swollen. What those signals mean is set out in Does tooth decay hurt?.
Special situations
You are new to Germany. Two habits are worth adopting quickly: book a check-up even without symptoms, and pick up a bonus booklet at that first appointment. If phoning a practice in German is the obstacle, English-Speaking Dentist in NRW explains how appointments, insurance and treatment plans work when your German is still limited. We are in Wuppertal-Elberfeld and see patients from across the Bergisches Land, including Solingen and Remscheid.
Pregnancy. Hormonal changes make gums more reactive and morning sickness exposes teeth to stomach acid. Do not brush straight after vomiting — rinse with water first. Check-ups during pregnancy are covered and specifically recommended.
Children. Milk teeth have thinner enamel, so decay progresses faster than in adults. The funds cover a defined programme of preventive appointments, fluoride varnish and fissure sealing at specific ages — ask which items apply to your child’s age.
Dry mouth from medication. Tell us what you take. We do not change your prescription; we change the prevention plan around it.
Usually not. In people who brush twice a day, cavities typically appear where a brush cannot go — between the teeth, in deep fissures and at the margins of old fillings. The most common genuine errors are brushing too hard, rinsing the toothpaste away, and skipping interdental cleaning altogether.
No. A rinse reaches the surfaces its liquid touches but cannot disrupt the sticky film in a tight contact point, which requires mechanical removal. A fluoride rinse is a useful addition for people with braces or a high decay risk — an addition, not a substitute.
Several things usually change at once: a different diet and coffee culture, more frequent snacking under work stress, no fluoridated tap water here, a gap in check-ups during the move, and sometimes new medication. Any one of them shifts the balance slightly; together they can shift it a lot.
Only the earliest stage. While the damage is confined to the enamel and shows as a chalky white patch rather than a hole, fluoride and better cleaning can arrest and partly repair it. Once the surface has broken and bacteria are in the dentine, the tooth cannot rebuild itself. How fast does tooth decay spread? sets out how long that window usually stays open.
Cavities in people who brush properly are not a moral failing; they are a mapping problem. The brush covers three surfaces out of five, the acid clock is set by how often you eat rather than how much, and saliva — the part you notice least — quietly does half the work. Fix the blind spots between the teeth, reduce the number of eating occasions, use fluoride the way it is meant to be used, and keep the twice-yearly check-up. Everything else is detail.
Zahnarztpraxis Tsypin · Wuppertal. This article was medically reviewed and is provided for information; it does not replace an examination. Updated August 2026.
