It is an ugly arrangement of anterior teeth , which is merely a temporary phase during the process of normal development . Here the developing upper permanent canines, causes mesial displacement of roots of permanent incisors around the age of 8 to 9 years. This causes a distal divergence of crowns of these incisors . This usually corrects itself when the canines erupts and the pressure is transferred from the roots to the crowns of the incisors. This position of teeth at this stage is compared to that of an ugly look of the duckling and hence the name ugly duckling stage.
Space for 21[12 i s provided by existing incisor spacing, by intercanine width growth, and by their greater proclination than ba ab.
111 are usually distally inclined initially; median diastema reduces with 212 eruption. As 3 3 migrate and press on the roots of 212, their crowns, and to a lesser extent those of 111, are frequently flared distally with a median diastema -’ugly duckling’ stage (Fig. 3). This usually corrects as 3s erupt.