Yeah, staining of teeth is common and of course smoking and drinking coffee doesn't help but I don't think that's the bottom line cause.
Mouth ulcers, sores, etc. can be caused antibiotics, just happens to be a side effect. I think taking lots of probiotics would help as well as kefir, yogurt, changing one's diet to a high protein diet and avoiding bad carbs (they turn into sugar, not good for teeth or lyme). Establishing good flora in one's body is important.
I read that taking lots of Vitamin C may help as well as avoiding acidic foods:
http://www.atlantadentist.com/mouth_ulcers.html
Also found this:
2. Tetracyclines (bacteriostatic)
Tetracycline, minocycline and doxycycline
a. Mode of action
The tetracyclines reversibly bind to the 30S ribosome and inhibit binding of aminoacyl-t-RNA to the acceptor site on the 70S ribosome.
b. Spectrum of activity -
These are broad spectrum antibiotics and are useful against intracellular bacteria
c. Resistance
Resistance to these antibiotics is common
d. Adverse effects
Destruction of normal intestinal flora often occurs, resulting in increased secondary infections. There can also be staining and impairment of the structure of bone and teeth
http://pathmicro.med.sc.edu/mayer/antibiot.htm
Hope this helps,
Denise