A diastema (pl.: diastemata, from Greek διάστημα, 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to as gap teeth or tooth gap.

In humans, the term is most commonly applied to an open space between the upper incisors (front teeth). It happens when there is an unequal relationship between the size of the teeth and the jaw. Diastemata are common for children and can exist in adult teeth as well.

1. Oversized Labial Frenulum: Diastema is sometimes caused or exacerbated by the action of a labial frenulum (the tissue connecting the lip to the gum), causing high mucosal attachment and less attached keratinized tissue. This is more prone to recession or by tongue thrusting, which can push the teeth apart.

2. Periodontal Disease: Periodontal disease, also known as gum disease, can result in bone loss that supports the teeth. If a person loses enough bone, the teeth can become loose and cause gaps to form.

3. Mesiodens: Mesiodens is an extra tooth that grows behind the front teeth. A mesiodens may push the front teeth apart to make room for itself thus creating a gap between the front teeth.

4. Skeletal discrepancy: Dental skeletal discrepancy can be a cause behind gap teeth. If the upper jaw grows more than the lower jaw, teeth on the upper jaw will have more space to cover thus leaving gaps between them.

5. Proclination: If the front teeth are angled forward, a small gap between them may appear large. This is called proclination; it may be a result of aggressive tongue thrusting.

A diastema is not a pathology and doesn't require treatment. Any interventions to modify a diastema are purely cosmetic.