I've had a lot of dental work done in the last 2 years, including 2 root canals, an extraction, and 15 fillings. Here are my general findings:
- Root canals are better than extractions: You keep the tooth, your chance of dry socket is low/none, and you don't have to gag on gauze for hours. The expense is worth it.
- Malocclusion plays a pretty big role in tooth pain.
- Abscesses aren't something to mess around with. If you feel pain when biting down, the tooth feels wiggly, or your nearby lymph nodes are swollen, call the dentist and try to see him again. I had an abscess producing puss that filled a sac in half of the roof of my mouth. Disgusting.
- Pain from biting down: Abscess, malocclusion, or referred pain from a different tooth (I sometimes had pain in the tooth beside or below the one that was actually causing the problem)
- Pain after root canal: Didn't get all the pulp, you have an untreated abscess (this is my guess, since you said it feels loose and hurts when you bite down), or you developed an infection after the procedure.
- Take better care of your teeth. See the dentist for checkups and as soon as you think something is wrong. Mouth pain is the worst. You can't really push it to the back of your mind. It will keep you awake at night.
Keep in mind that I am not a dental professional, so this could be entirely wrong.