If you have an ear infection can it spread to a bad tooth causing an abscess?

No: Infections from a broken down tooth come from bacteria that has infected your tooth from within your mouth... The bacteria cannot spread from your ear and infect a tooth.

No: Abscess is caused by the tooth being infected, an untreated cavity. Ears don't infect teeth. Different problems, different treatments. You need to see both a physician and a dentist, and don't put the appointments off because this can really go south very quickly.

Location matters: These are both in your head, but that does not mean what happens with one has anything to do with the other. They are separated by tissues & distance and have no direct way for the germs in one to travel to and be involved with the other.