Cavities will not heal independently, and the decay will worsen when left untreated, leading to further problems. They can spread to other teeth and the surrounding gum tissue, leading to gum disease and tooth loss. In more severe cases, the decay can spread to the supporting bone structure of the teeth, leading to pain, infection, and even abscesses, which require more extensive treatment like root canals. Untreated cavities can cause bad breath, toothaches, and sensitivity to hot and cold temperatures.