Abstract:

To display the anatomic markers of the mandibular posterior area in digital orthopantomography and to study the approach and depth of extraction of impacted teeth, orthognathic surgery and dental implantation. MethodsStandardized digital orthopantomographys were taken for 100 subjects (38 males and 62 females) with an average age of 38.2 years. All Xray images were taken with sirona orthophos plus DC ceph and were dealt by a digital computer. Anatomic markers of the mandibular posterior area were observed and measured by the computer. ResultsPosition of the mental and foramen height of the mandibular body at the mental foramen area was similar between the two sides; The mandibular canal of 42 patients could be found out in the orthopantomographys. Distance between the mandibular canal and the root point at the mandibular molar area was gradually decreased from front to back.There was no obvious difference between the diameter of the left mandibular canal and that of the right mandibular canal. Both the height of the mandibular body and the distance between the superior margin of the mandibular foraman and the alveolar ridge crest at the molar area were decreased from front to back. No obvious difference was found between the angle of the left mandible and that of the right. The average mesioangulation of the third molars in the impacted group was 48.80 and that in the erupted group was 6.84. The retromolar space of the impacted groups was significantly smaller than that of the erupted groups(P＜0.05). The average ratio of space／crown width in the erupted and impacted groups was 1.17 and 0.62(P＜0.05). No statistical significance was found in the mesiodistal diameter of the tooth crown between the impacted and erupted groups. There was an obvious positive relationship between frequency of the third molar impaction and angulation degree (P＜0.05),　but the former was inversely associated with the retromolar space (P＜0.05). The maxillary sinus was 90％ displayed and reached the maxillary canine area to the front and the maxillary tuberosity to the back. ConclusionDigital orthopantomography can provide enough information of siagon features for orthognathic surgery,extraction of impacted teeth and dental implantation. 

Key words:  Radiography, dental, digital； Mental foramen； Mandibular canal； Molar， third； Maxillary sinus