Experts say various things about oral sex and flossing, but agree flossing is not recommended before engaging in oral sex. The advice varies anywhere from 30 minutes to 4 hours, regarding how long to wait. It takes 4 hours for membranes around your gums to heal.
The risk of contracting HIV from oral sex is relatively low, but other STIs can be transmitted through mouth to genital contact. If you have sores or cuts in your mouth or gums or an inflammation from an infection in your throat or mouth, you are at greater risk for contracting an infection or HIV.
Oral sex is a common sexual behavior. People enjoy various combinations of positions and techniques when engaging in cunnilingus and fellatio, but it is the mouth and tongue that provide the pleasure in all cases.