The dentists would absolutely prefer we clean the teeth before bed for this reason, but they would also prefer that we clean the teeth first thing in the morning, of the bad stuff that accumulates at night. The fact is, the ADA recommends brushing twice a day. It is not an option for me and it would interfere with my ability to go to bed on time, because you are not supposed to brush for 30 minutes after eating, 60 minutes if you eat acidic foods and I often eat tomatoes, and that means waiting after dinner and I eat a later dinner. So, apart from the fact that I am simply tired in the evening to do the laborious task of flossing, I cannot fit in brushing given my late dinner. In the morning, flossing is very first thing I do after, of course, going to the bathroom, and I have the energy and attention span to do it right. If you can brush twice a day, including right before bed, of course it is better than what I do. If it is just once a day, there is an argument for the evening and an argument for the morning, but making sure acid is not acting on your enamel right before you subject the enamel to brushing is an important factor.