Not brushing your teeth allows some bacterias to build up in the body that can have a damaging effect, some studies are finding scary mouth bacteria in damaged human hearts. Ancient people were not eating the same foods as us, some foods stick to the teeth more than others. Ancient people had much shorter life spans so you cant conclusively blame all degenerative diseases on modern society it could equally reflect a natural degeneration due to age in susceptible individuals that would previously not have lived long enough to show obvious symptoms. A healthy body should be able to deal with minor doses of un-natural products. I wont risk my chances with a nuclear reactor but im not going to wrap myself in cotton wool to avoid toxins. You do more damage to your imunity avoiding exposure to most everyday bacteria and substances. This doesnt mean exposure to serious diseases such as HIV wont harm you but you will be in a much worse state with the flu if your immune system hasnt been exposed to foreign substances before. I brush and floss my teeth and use mouth wash, a whole cart load of chemicals and dont spend a moment worrying about the minute traces of chemicals I ingest. Sanitation is one of the major breakthroughs that helped extend the human life span. For me its just mouth sanitation, and on par with washing your hands, you make be using chemicals but in terms of the whole picture and its benefits soap is better than walking around with god knows what continuously in contact with your skin. It also smells nicer :)