A gap between the teeth can result from a mismatch between the size of the teeth and the jaw bone; spaces result when the teeth are too small for the jaw, according to Colgate. Teeth may also be undersized or missing, which causes a space to develop in the jawline.
Another cause of a space between the teeth, which is clinically known as a diastema, is an oversized labial frenum, states Colgate. The labial frenum is the piece of tissue that ordinarily extends to above the two upper front teeth from the inside of the upper lip. If this tissue grows to the point that it passes between the two front teeth, the natural closing of the teeth cannot occur.
Another cause of spaces between teeth are habits, such as sucking the thumb, which creates gaps by pulling the teeth forward. An inappropriate swallowing reflex can cause spaces to develop too. This occurs when people develop a tongue thrust where pressure exerted by the tongue onto the back of the front teeth causes the teeth to shift forward and spaces to develop over time.
Finally, a cause of space between the teeth is periodontal disease. In advanced cases of gum disease where bone loss has occurred, the teeth can move and gaps can be revealed.