A diastema is considered normal in the mixed dentition as part of normal dental development. This period is known as the "ugly duckling" stage of development.

(Photo: the "ugly duckling" stage)

A diastema, or space, between primary or permanent central incisors is often associated with, though not necessarily caused by, a prominent superior labial frenum.

(Diastema: frenum in an 8-month-old)

[The diastema can also be caused by an unerupted supernumerary, or extra, tooth. A diastema in excess of 3 mm persisting after eruption of the permanent canines (age 10-13) should be evaluated for treatment options such as a frenectomy and/or orthodontic treatment.]