If a person is cleaning their teeth effectively (see "Finding Hidden Bacteria in Your Mouth" and "Why Are You Flossing?") then the teeth and gums are safe until the bacteria return, organize their bio-environment and begin causing damage.
Studies indicate it takes 24 hours or a little longer depending on mouth chemistry and diet.
So effectively cleaned teeth are safe for one full day. Most people will brush more than once per day because they are concerned about food particles showing in their smile and about food particles on teeth creating bad breath.
So most people will brush a couple times daily after meals. For "healthy" teeth, however, one "effective tooth cleaning" each day is enough for excellent oral health.
Scott Thompson,DDS
530-878-2357