If my teeth are infected, is it possible that it will spread?

Absolutely: Untreated dental infections will destroy bone and can spread to other parts of your body causing serious complications, and can even be life threatening. People have died from untreated infections. See a dentist asap!

Possibly: If your teeth are decayed, it cannot jump from one tooth to the other. However, if the infection is in the bone and gum tissue around the tooth (and this can happen with a badly decayed tooth) the infection gets in your blood stream and is carried to all parts of your body. So, decay -- no, infection -- yes. Good idea to see your dentist to be checked for seriousness of infection. Good luck.

Yes: It is very possible that it will spread into the adjacent tissues causing swelling in the mouth and the face. After this, it will spread into the blood stream. See a dentist asap as infections can spread very rapidly. The infection can be life threatening in as little as 2 days.

Probably, as can gum disease. Bactria spread through circulatory system to other organ systems. Infected teeth/gums do not self heal. And the longer you put off treatment the more extensive/expensive the treatment.