Impacted mandibular third molar area (retromolar space ) has been a topic of interest for a long time, and one of the most investigated parameters for two reasons:1- the lower third molars are the second most frequently impacted teeth 2- the lack of space is considered to be the major cause of this.so the radiographic diagnosis for this area is an important issue for orthodontists because of it's important role in mandibular third molar eruption wich play an impact on lower arch crowding and stability of orthodontic treatment.O