Impacted third mandibular molar seems as a common and easy case but actually a difficult one when the odontectomy proceeds. besides, another unpredicted problems ofte appear such as fractured lip, traumatized and damaged of the mandibular canal. To decide the odontectomy procedure, a dentist has to do the examination systematically. In this case, radiographic examination is very important to perceive the location as well as shape of the third molar, especially its position to the adjacent anatomic structure that has to be considered during operation. This whole view will help dentist to decide appropriate approach.A special radiographic examination enables dentist to predict the treatment result more accurately, since the location and shape of the tooth correctly perceived. With this more complete diagnostic information, an appropriate treatment plan could be arranged and unfavorable risk could be limited, therefore complication and failure could be avoided.