The basic shape of the tooth is narrow end towards the gums and the wider end towards the chewing surface. That makes the contact of the tooth with its neighbour only at a point.This is the point of contact of that tooth. Underneath the contact point a gap exists between all the teeth. This is an area that is inaccessible to the best brushes in the world!! The gap is a potential area for plaque accumulation. Using interdental cleaning aids like a floss or interdental brushes is essential to clean this space. Any unremoved plaque or debris in this area causes decay and gum problems.