Gum recession is usually not caused by disease but is a special category of gum problems. Exposed roots are subject to sensitivity, tooth decay, and abrasive action from tooth brushing. There are several reasons a person may have gum recession:
The jaw bone may be narrow from front to back meaning bone next to the lip may not extend all the way up near the crowns of teeth.
Crowded teeth may leave certain teeth too far out with less bone and gum available for that tooth.
The gums may be thin and fragile and easily damaged by the toothbrush.
A person could be brushing too hard, too long, and or with a too hard toothbrush.
Muscle attachments may cause movement of the gum in some sites.