A diastema most commonly refers to an open space between a person's upper incisors, or two front teeth. Diastemas are more common in children but can occur in adults as well. Various conditions can cause a diastema, but most commonly they are caused by an unequal relationship between the jaw and size of a person's teeth.

Dental Development

Diastemas occur naturally in children as part of dental development. Around age 8, the unerupted lateral incisors push against the roots of the already-erupted incisors, creating a space that usually closes naturally. If a child has small lateral incisors or an overbite, the teeth can jut out creating a space that will not close.

Hormonal Imbalance

If there is a hormonal imbalance in the endocrine gland, the jaw can become abnormally large while the teeth remain normal in size. This can cause a space to form between the front teeth.

Poor Angulation

Excessive side-to-side angulation of the teeth, called excessive distal crown angulation in dentistry, occurs when the teeth angle too much to the side. This angulation creates a space between the front incisors.

Muscular Imbalance

Sometimes the tongue is excessively large due to a genetic condition called macroglossia. If the tongue (a muscle) is excessively large, it can push the front teeth forward and create a jutting effect that causes a gap.

Habits

Harmful oral habits can also contribute to the formation of a diastema. These habits include lower lip biting or flaccid (weak) lips, both of which can create a protrusion of the teeth. Pushing the tongue against the back of the front teeth can also affect the position of the incisors.

Source:

DentalSource.org