Tooth Decay: How Cavities Form and What Actually Prevents Them
Tooth decay is the most common chronic disease in the world and one of the most preventable. The prevention that works is not what most people think it is.
How a cavity forms
Bacteria in dental plaque ferment sugars and produce acid. That acid dissolves mineral out of the tooth surface, which is demineralisation. Saliva then buffers the acid and redeposits minerals, which is remineralisation.
Decay happens when demineralisation consistently outpaces remineralisation. Each time you eat something sugary or starchy, the mouth stays acidic for roughly 20 to 30 minutes.
This is why frequency matters more than quantity. A whole chocolate bar eaten in one sitting causes one acid attack. The same bar eaten one square at a time across the afternoon causes eight. Sipping sweet tea through the day is worse for teeth than a single dessert.
The same applies to sweetened drinks sipped slowly, hard sweets and toffees that stick, and frequent snacking on biscuits or crackers.
Stages of decay
- White spot lesion — early demineralisation. Reversible with fluoride and better habits. No drilling needed
- Enamel cavity — a hole in the outer layer, often painless
- Dentine cavity — sensitivity to sweet, cold or hot. Needs a filling
- Pulp involvement — severe, often spontaneous pain, especially at night. Needs root canal treatment
- Abscess — swelling, throbbing pain, fever, sometimes facial swelling. Needs urgent treatment
Pain arrives late. A tooth can be substantially decayed and feel completely normal, which is the argument for regular check-ups rather than symptom-driven visits.
How fluoride works
Fluoride does three things: it makes enamel more acid-resistant by forming fluorapatite, it promotes remineralisation of early lesions, and it inhibits bacterial acid production.
Practical points:
- Use a fluoride toothpaste, 1000 to 1500 ppm for adults. Check the box
- Spit, do not rinse. Rinsing with water immediately after brushing washes away the fluoride before it can act. This single change measurably reduces decay and almost nobody does it
- Brush twice daily, with the last brushing right before bed, since saliva flow falls during sleep and that is when teeth are most vulnerable
- Children: a smear for under-threes, a pea-sized amount for three to six years, supervised so it is spat out rather than swallowed
- High-fluoride prescription toothpaste and professional varnish are available for people at high risk
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Excess fluoride during tooth development causes fluorosis, white or brown mottling. This is relevant in parts of India with naturally high fluoride in groundwater, where additional supplements should be avoided and water source matters.
Brushing properly
- Two minutes, twice daily. Most people brush for under 45 seconds
- Soft bristles. Hard brushing causes gum recession and abrasion without cleaning better
- Angle the brush at 45 degrees to the gumline, small circular or short strokes
- Cover every surface: outer, inner and chewing
- Replace the brush every three months or when splayed
- An electric brush, particularly oscillating-rotating, removes more plaque for most people
- Clean between the teeth daily with floss or interdental brushes. Brushing misses about 40 percent of tooth surface, and that is exactly where cavities between teeth start
- Do not brush immediately after acidic food or vomiting; wait 30 minutes, since enamel is temporarily softened
Other real protections
- Fissure sealants on children’s permanent molars, which prevent decay in the deep grooves where it most often starts
- Sugar-free chewing gum after meals, particularly with xylitol, which stimulates saliva
- Cheese or plain milk at the end of a meal, which raises mouth pH
- Drinking water after sweet food
- Treating dry mouth, which is a major and under-recognised decay risk from medications, diabetes, Sjögren’s syndrome and radiotherapy
- Regular dental check-ups, typically every six to twelve months
Things that do not work
Oil pulling does not prevent cavities. Charcoal toothpaste is abrasive, usually lacks fluoride, and has no decay-prevention evidence. “Natural” fluoride-free toothpastes remove plaque but lose the single most effective ingredient. Neem and salt have mild antibacterial properties but do not replace fluoride. No diet or supplement regrows a cavity once it has broken through enamel.
Children’s teeth
Baby teeth matter: they guide permanent teeth into position, and infection in them affects the developing teeth beneath. Never put a baby to sleep with a bottle of milk or juice, which causes early childhood caries. Start cleaning as soon as the first tooth appears. First dental visit by the first birthday.
See a dentist promptly for
Pain that keeps you awake, swelling of the face or gum, a tooth that feels loose or has changed position, sensitivity lasting more than a few seconds after cold, visible holes or dark spots, bleeding gums persisting beyond two weeks, a broken tooth, or any mouth ulcer or patch that has not healed in three weeks.
This is general information. Decay is far cheaper and simpler to treat early, so routine check-ups are worth more than any product on this list.