Could you explain why do we brush our teeth at night and the morning?

To clean them: Brushing your teeth removes bacteria that can cause cavities and gum disease. The times you mentioned are the most convenient for a vast majority of people.. Difficult to carry around toothpaste an a brush while you are out and about, and impossible to do while you are sleeping. The times are also spaced about 12 hours apart. Other times are fine if they work for you.