Brushing teeth does not keep them from rotting when consuming large quantities (and for some, small quantities, based on their heritage, etc.) of sugar, because sugar needs minerals to be digested, and if the minerals are not in the food itself, then it searches for it in the teeth, bones and eventually organs. And it steals it away from them. It esp likes the calcium, phosphorus and other minerals that the teeth are mainly made up of. So, while brushing your teeth after eating sugar might help an itty bit, it won't help much, since the damage is being done internally.
Which is why I use unrefined sugars such as honey, maple syrup and rapadura with their minerals in tact, the way God intended.
For that matter, any refined foods, salt, flour, etc, with the minerals stripped away, do the same thing. Not only do we need to consume these minerals for overall health, but we need to consume them for proper digestion as well.
Merry Christmas, and enjoy the celebration of our Savior's birth. I might even indulge in a bit of sugar, with it's minerals intact.