<unk> is the loss of tooth structure by mechanical forces from a foreign element.  If this force begins at the cementoenamel junction, then progression of tooth loss can be rapid since enamel is very thin in this region of the tooth.  Once past the enamel,<unk> quickly destroys the softer dentin and cementum structures.
Possible sources of this wearing of tooth are toothbrushes, toothpicks, floss, and any dental appliance frequently set in and removed from the mouth.  The appearance is commonly described as V-shaped when caused by excessive pressure during tooth brushing.
The teeth most commonly affected are premolars and canines.
Abrasion 
Frostbite
Crossbite
Pinguecula
Freckle
Pinna
Supernumerary nipple
Bandage