Hygeine is an interesting thing. Scientists had figured out something I believe they called the hygeine effect. As people showered daily, washed hands more, etc. we have become "too clean" and certain good microorganisms that come from places like the soil are not benefiting the microbiomes in our bodies as they should. We have gotten rid of many diseases this way, but have increased other immune system illnesses. People that work with getting their hands in the soil have been proven to live longer lives.
About brushing teeth...I have heard eating softens the enamel so it is a bad idea to brush teeth within an hour or eating as it ia thought to brush the enamel away. However, looking at studies like from Weston A. Price, brushing teeth has squat to do with dental health and that it is actually our diet. A lot of interesting reads and studies there, too.