I especially like this quote directly from the article Torrie is citing!
The theory of focal infection is kept alive today by the American legal tort system (lawyers using junk Science to turn a profit), by some self serving groups within the holistic health movement, and even by a few dentists trying to increase their productivity. In most cases, there is a heartfelt belief that the patient's ills would be cured if only the teeth were extracted, or if their fillings were all replaced. This belief is, however based on ignorance and hearsay, and not on scientific evidence.