If you have a chronic infection, consider getting your teeth checked. Teeth in poor health can serve as a kind of reservoir for pathogens, letting them lie dormant before they reactivate and wreak havoc on your health. 

What does this look like? Chronic low-grade infections that flare up periodically, usually after the immune system is stressed (stress, insomnia, other illnesses, cold or wetness etc.), your teeth deteriorate, the pathogens enter new areas or grow.

How do they survive? Either in necrotized tissue, form biofilms in cavities, root canals, periodontal pockets or stick around in dental abscesses. Some of these are quite visually obvious, others aren't. Biofilms are a sort of slimy extracellular matrix with bacteria embedded within them, and are much more resistant to antibiotics. 

How long do they last? If left untreated, months to years, though the affected teeth may not be painful for all, or even most, of the infections' duration. 

Which teeth are affected? Any tooth, but teeth in poor health are likely to be affected. Severe cavities, broken teeth, gum disease and other injuries to the mouth, e.g. failed dental work or partially erupted wisdom teeth, can all cause openings for bacteria to enter. The damage need not be visible. 

How are they treated? Typically through extraction or root canals. The bacteria may not clear out on their own, as the damaged tooth provides them a safe haven.