I almost always read in the news/press that dentists recommend to brush teeth two times a day for 2-3 minutes.
This drives me crazy, because it does not make sense; The point for dental health is to systematical clean every surface of your teeth twice a day (and use inter-dental brushes/floss once a day). For me, brushing my teeth takes around 6 minutes, if I hurry up. For someone faster it might be possible in 1 minute.
So, why do dentists always give the 2-3 minutes recommendation?
From someone with a science background: There are a lot of expenses with that type of clinical trial.
In particular, if you're going to assign someone to a group that is known to be unhealthy (brushing once a month) you need to pay for any dental or medical problems that arise from them not brushing.
For sure, and they should def stop if there were any serious long-term affects, like any medical trial.