Cavities are sneaky, and there is no sneakier cavity than the one between your teeth, the one called proximal or inter-proximal.
Toothbrush bristles do not reach in there too well, and even regular flossing clears out most but not all of the food debris and hardened plaque. Natural bacteria in plague that forms on teeth feed on the sugar in food, and the byproducts of this are acids that disintegrate a tooth’s protective enamel surface. Underneath hardened plaque and out of sight, a tiny yellowish or black dot may be hiding.
That dot is likely the top of a cavity getting started, and that can quickly enlarge underneath. If it is not close to a nerve, pain may not be an early warning, and that means that cavity can get bigger and deeper. By that time, for many people, the first real symptom is a sudden “shock” when drinking something cold, or a stab of pain when chewing. Brush as often as you want, but the problem is not going away.
Cavities between the teeth are treated much as any other, starting with an x-ray to help assess the extent and depth of the damage. Depending on the diagnosis, drilling and filling may be the course of action.
But if the cavity has gotten through the enamel, through the middle layer of dentin, and into the pulp that contains nerves and blood vessels, a root canal may be the solution.
Regular brushing and flossing are good but incomplete defenses. Add regular teeth cleanings by a dental hygienist coupled with checkups by the dentist. After the cleaning, the dentist can get a better look at the tooth surfaces. Updates of X-rays are widely recommended once a year.