Many adults seem to forget that sugar is bad for teeth. The amount of time the sugar is left on teeth is also important. Your teeth will be healthier if, for example, you eat ten sugar cookies in ten minutes and then floss and brush than if you nibble on three sugar cookies for three hours and constantly bathe your teeth in sugar. The same goes for sugared sodas and fruit juices. The delicious sugary taste in your mouth should make you aware that cavities could be forming.
Many people believe that they cannot get cavities after their teeth are capped (crowned). They are wrong. While you cannot get a cavity through a cap you can easily get a new cavity at the junction, or margin, where the cap ends on the outer tooth structure near the gum.
Most of the bacteria that causes cavities and gum disease collect in the spaces between teeth. If you have to choose, you will always be better off if you only floss and never brush.