Cavities: how they start, and how they're treated.

A cavity is permanent damage to the hard surface of a tooth that has developed into a tiny hole. It starts when the enamel is repeatedly softened by acid and loses minerals faster than saliva can replace them. At the very earliest stage — a chalky white spot — the process can sometimes still be reversed with fluoride. Once a hole forms, though, the tooth cannot repair itself, and the decay will slowly spread inward unless it is cleaned out and filled.

The bacteria that naturally live in everyone's mouth feed on sugars and refined carbohydrates and produce acid as a by-product. That acid attacks the enamel. It is not the amount of sugar so much as how often teeth are exposed — frequent snacking and sipping sugary or fizzy drinks keep the mouth acidic all day, giving enamel no time to recover. Decay starts fastest where plaque sits undisturbed: between teeth, in the grooves of back teeth, and along the gum line. A dry mouth, exposed roots and existing worn fillings all raise the risk.

Early decay is usually silent — which is exactly why regular check-ups and X-rays matter, since they catch it before you feel anything. As it deepens you may notice sensitivity to sweet, hot or cold things, a dull ache after eating, a visible white, brown or black spot, a hole you can feel with your tongue, or food that keeps catching in one place. By the time there is constant or throbbing pain, the decay is usually close to the nerve — so earlier signs are worth acting on.

Treatment depends on how far the decay has gone. A very early white-spot lesion may be remineralised with fluoride and better cleaning. A genuine cavity is cleaned out and restored with a filling. Larger decay that has weakened the tooth may need an inlay, onlay or crown to rebuild it. If it has reached and infected the nerve, a root canal saves the tooth, and only where a tooth is too far gone is removal the answer. The earlier it is caught, the smaller and cheaper the fix.

Decay is largely preventable: brush twice a day with a fluoride toothpaste, clean between the teeth daily, and — most importantly — keep sugary and acidic food and drink to mealtimes rather than grazing through the day. Don't rinse with water straight after brushing, so the fluoride stays on longer. Regular check-ups catch the early, painless cavities that are cheapest to treat. None of this is dramatic, but consistency is what keeps teeth out of the chair.