Caries develops from the interplay of plaque, sugar and time. The bacteria in the plaque metabolise dietary sugar and produce acid, which dissolves minerals out of the tooth (demineralisation). At first this shows as a whitish spot (initial caries) that is still reversible. If left untreated, the decay penetrates through the enamel into the softer dentine and finally reaches the tooth nerve (pulp).
The tricky part is that early-stage caries causes no symptoms. Only later does sensitivity to sweet, cold or hot appear, then pain and a visible hole. The dentist detects caries at a check-up visually, with a probe and – especially between the teeth – on the X-ray, before it becomes visible.
Treatment depends on the stage. Beginning caries can still be stopped with fluoride and better oral hygiene. If a defect has already formed, the decay is removed and the tooth restored with a filling (usually tooth-coloured composite). Large defects need an inlay or crown; if the decay has reached the nerve, a root canal becomes necessary.
Caries can be prevented effectively: brush twice a day with fluoride toothpaste, clean between the teeth with floss or interdental brushes, cut down on sugary snacks and drinks, and go regularly for check-ups and dental hygiene.
As a guide (no guarantee), a simple composite filling in Switzerland costs roughly CHF 150 to 250, and a larger multi-surface filling around CHF 250 to 450. The cost depends on the size, location and effort involved.