Do you say "wash one's teeth" to mean "brush one's teeth" or "floss"?
I have heard it from a very small number of people insted of "brush your teeth". I don't think I've ever heard in the context of flossing.
The vast majority say either "brush your teeth" or "clean your teeth".
Many people rinse their mouths with 'mouthwash' after brushing their teeth, but in spite of the name of the liquid this is not called 'washing'. There is also the metaphorical 'Wash your mouth out [with soap and water]', still used today idiomatically (when someone has used foul language) - but referring to an actual Victorian disciplinary practice.