Again, a gentle reminder from Australian Federation of AIDS Organization
2 Hours before and after sex no later than 2 hours before : Do not brush your teeth or even floss your teeth to prevent any abrasion or tear to your gums -- Hence, reducing the risk of STDs.
Before or after or immediately / sex - You can gargle or rinse your mouth with mouthwash / salt water as the better option instead of brushing your teeth.
The time asides from the 2 hours window of sexual activity --- You can brush and floss your teeth, clean your tongue as many times as you want to maintain good oral hygiene so that you will not have bad breath for impending wild, passionate kisses and also to wash away the cum residues that you had drank earlier!!