306 Australian Dental Journal, October, 1974

Extraora I radiographic technique for third molars

Dan Fisher, D.M.D.

Faculty of Dental Medicine. Hebrew University, Jerttsalem

ABSTRACT-A technique using an occlusal film extraorally for obtaining roentgenograms of the third molar regions is described. A case report shows its value in disclosing a dentigerous cyst in the upper third molar region.

(Rcccivcd for pitblicatiori Novcwiber, 1973)

Radiographic examination of impacted upper third molars is usually made in most offices with the standard periapical technique or with a modi- fied intraoral technique in which the entry of the central ray is much higher and passes under the zygomatic arch (Fig. 1).

Method Position of head 1. The sagittal plane should be perpendicular and

the maxillary occlusal plane parallel to the floor.

2. The head is tilted approximately 30" laterally toward the side being radiographed.

3. The head is tilted so that the chin is extended forward as far as possible, thus helping to prevent superimposition of the vertebral column on the mandibular body and enabling easier access to the central beam.

4. The mandible should be in the rest position. 5. The film is positioned against the side of the

face and with its longer dimension oriented supero-inferiorly and its lower border parallel to the lower mandibular border (Fig. 2A).

6. The central ray enters the other side of the face about 1 cm distal to the mandibular angle and on the level with the lower border of the mandible (Fig. 2B). It is directed to exit at the level of the occlusal plane of the side being radiographed in the third molar region (Fig. 2C, D).

7. When a region is of specific interest, the film can be moved and the direction and exit of the central ray can be respectively changed.

Exposures at 15 milliamps were: KVP 90 0.5 sec KVP 65 1.0 sec Film Kodak 8F.45

Australian Dental Journal, October, 1974 307

Fig. 1.-Roentgenogram produced by modified intraoral technique with central ray passing

under zygomatic arch.

Fig. 3.-Unerupted third revealed in

molar and dentigerous extraoral film.

cyst

Fig. 2.-Position of patient’s head and film A , C, D. Direction of central ray B, C, D.

The area usually recorded in this technique is shown in Fig. 3.

Case report A 22-year-old woman was referred to the

Department of Oral Diagnosis with an unaccount- able swelling in the region of the vestibulum above the upper right second molar that she had noticed a month ago. Clinical examination con- firmed the findings of the referring dentist: The upper third molar was not present in the arch, and 16 showed no abnormalities and 17 had a Class 1 amalgam filling and recurrent caries but was vital. Intraoral radiographic examination revealed a radiolucent tuberosity. A roentgeno- gram made by the extraoral technique revealed an impacted third molar high above 17 with a big radiolucent area suspected as a dentigerous cyst (Fig. 3). Removal of the second third molars and the enucleation of the cyst was performed. Histological examination confirmed the diagnosis of a dentigerous cyst.

Department of Oral Diagnosis and Roentgenology,

Faculty of Dental Medicine, Hebrew University - Hadassah

Jerusalem, Israel