**3.2. Mixed dentition**

In the mixed dentition phase, the diastemas continue to appear as a physiological characteristic, mainly the diastema between the permanent maxillary incisors. The germs of these teeth remain separated within the maxilla, respecting the intermaxillary suture interposed between them [16].

Broadbent [12] published a study of 5000 individuals observed over 12 years. The author called the "ugly duckling stage" the period that ranges from the eruption of the upper incisors, around the age of 7 years, until approximately 10 years of age, when the upper canines erupt. At this stage, the lateral incisors remain with the converging roots until the maxilla size is sufficient to assume a more vertical position. With sufficient increase in the size of the subnasal area, and in the presence of normal growth, the canines move down, forward, and laterally to the lateral incisor roots. Correction of the ugly duckling stage will occur in the period between 8 and 12 years of age.

Burstone [13], observing the normal changes during development, identified that during the "ugly duckling phase" of Broadbent [12], protrusion of the crowns, overjet, and anterosuperior spaces occurs. He also reported that the upper central interincisive diastema would be closed with the eruption of the other permanent teeth, especially the canines, and that the overjet of the incisors would be corrected by the pressure of the labial musculature and the irruption of the other permanent teeth.
