Mars, I used to smoke. I hated that taste in my mouth so when I could, I brushed my teeth after smoking a cigarette. That was a lot of brushing. LOL One time I went to the dentist after years with no dental work and the tech told me my dental hygiene was great for not being at the dentist for so long. I still brush often, but not as often as I did when I smoked. Also, I have to brush my teeth before I have my coffee in the morning. I have heard that coffee puts a lot of acid on your teeth and softens the enamel. If you brush after having that acid on your teeth, you could wear away the enamel. So I brush BEFORE so I don't have to brush afterwards.
One time when I was in the hospital I got up early, and would brush my teeth first thing. I was in the bathroom brushing, and I was wearing a heart monitor. Two nurses came rushing into the room and opened the bathroom door then said "Oh, she's brushing her teeth." That up and down motion was really throwing off the reading on my monitor! LOL