most important time to brush your teeth
At night, your mouth is much less active, which allows bacteria more time to grow without being mechanicalyl sloughed off. Many years ago my orthodontist told me that it was most important to brush your teeth before going to sleep (I guess either for the night, or for a nap). Saliva production is down, and if you happen to sleep with your mouth gaping open, your teeth dry out and don't have that protective layer of saliva.