Absesses can be pretty common and don't necessarily hurt but can be "fixed" with antibiotics. The dentists did x-rays and gave you antibiotics and did what they could with what was showing; if they can't see anything they can't see anything. Dentistry is a bit harder than regular medicine as there are only so many tests and things one can do to see what's wrong. My dentist was trying to decide whether a problem I had was one tooth or the other (which to replace the crown on) and I suggested he just replace both and it turned out both had decay underneath and both needed replacing. Sometimes you have to tell dentists to pull teeth or drill/do root canals, etc. as they're often not going to want to make you spend that kind of money only to find there was nothing wrong.

My husband had a couple of the bad absesses and one's whole face swells up; it still turns out fine if you start the antibiotic right away. If they didn't see anything and there wasn't any swelling, just pain, it could have just been an exposed nerve from the cracked tooth/little bit of decay. That's where you get really bad pain. Sometimes though those cracks are tiny or between teeth, etc. and can't show on the xrays because of their location. They need to invent an MRI or CT scan for teeth, LOL.

I've had 5-6 root canals now; they get more common the older you get and cavities will get less (mostly because of all the root canals and crowns; you can't very well get a cavity in a fake tooth :-) They've got such good materials nowadays though that I think some of my crowns are now older than the tooth they were put on was when they were put there :-)