When tooth decay is left untreated, bacteria can reach the exposed soft tissues in the pulp chamber. This leads to infection, which causes unbearable toothaches and can even be life-threatening. If the tooth needs a root canal, the pulp of the tooth is exposed or will likely be exposed as the current decay progresses. This exposed dental pulp can easily be infected with bacteria, which can travel to the bloodstream and increase the chance of dangerous blood clots that can cause a stroke or heart attack.
It can even cause a potentially fatal systemic bacterial infection called sepsis. Cavities are a gateway to infection, which can spread quickly the longer it's not treated. As soon as an infection reaches the bloodstream, it can travel throughout the rest of the body, with fatal consequences. Cavities won't go away on their own and will only continue to grow and cause more decay in the tooth if left untreated.
Another danger of untreated tooth decay is the development of gum disease. Plaque bacteria can spread to the gums and cause inflammation if dental care is not sought. Once your gums turn red and inflamed, you may experience bleeding, especially when you brush your teeth. It's important to seek dental care as soon as possible if you have a decayed tooth. Ignoring a decayed tooth can have dramatic results that can be so severe that they can even cause death.
A dentist will be able to assess your situation and provide you with the best treatment options.