One of my top teeth fell out, and I neglected to have the roots removed for a few years. It had started hurting again, but I don't know as there was any swelling. There was infection at the tip of the roots (is periapical the correct term?). And a bottom molar had a chunk break off and later developed a huge cavity. I had it pulled and the upper roots, too. The dentist said something about the amount of infection correlating with the amount of decay in the tooth, and said it was pretty much infected to the bone (the bottom tooth). It hurt, also, but I'm not sure about swelling. The left side of my face was a bit warmer than the right though. Just my experience. My tinnitus worsened on the left. My left ear felt full and ached a little, and the left side of my neck ached, too. I can't remember if the ear and neck aching started before or after they were pulled though. Dumb, I know. ha.
That's interesting that there can be pulpal infection without trauma or cavities.