The common habit of grinding the teeth - bruxism - while asleep can have wide-ranging health consequences.
"The teeth are worn down, and the relief patterns on the crowns of the teeth go," says Thomas Wolf of the Free Association of German Dentists based in Bonn.
This exposes the dentine, which contains nerve endings. As a result the teeth become increasingly sensitive.
"The more you grind or bite hard, the closer you get to the nerve," he says.
In extreme cases, the jaw bones are affected, and the teeth can become loose and even fall out or crumble.