Crowding occurs when there is insufficient space for all of the teeth in the upper arch, lower arch or both. The teeth may look slanted, twisted, uneven or pushed in front of, or behind, adjacent teeth. In addition to looking unsightly, crowded teeth are more difficult to clean and raise the risk of tooth decay and gum disease. Crowded teeth can also lead to chronic tooth grinding and clenching since the teeth do not have a proper position in which to rest. Orthodontics gently and gradually shift the teeth into an ideal position; appliances such as an expander can also be used to modify the shape and width of the arch to accommodate all of the teeth.