When you brush your teeth, you’re only able to reach about 60% of your teeth. So, imagine if you left 40% of your body unwashed for weeks upon weeks, you’d be pretty dirty. So, why would you do that to your teeth?
http://www.examiner.com/x-15633-Health-101-Examiner~y2009m6d29-Dental-care-101-Why-should-I-floss