supernumerary• Mesiodens which presence between the upper centrals cause mid line displacement..
Alveolar size• alveolar size is the primary factors that determine the status of the permanent dental arch. If it too large spacing.
Physiological spacing (ugly duckling stage )• The maxillary central incisors can also be quite distally inclined when they first erupt, which produces a midline diastema between them.• the maxillary incisor apices being initially quite close together when lateral pressure from the erupting maxillary lateral incisors & canines .
Reverence• mccdonalds pediatric dentistry text book