Modalities

The most common imaging modalities in dentistry are panoramic and intraoral radiography. Panoramic radiography (Figs. 1, 2) is frequently used to supplement other radiographic examinations. It yields a view of the dentition and surrounding bone, and of adjacent facial structures and cranial base. Intraoral radiographs can either be periapical and bitewing radiographs or occlusal radiographs. The latter are placed in the occlusal plane. Occlusal radiographs are used for increased coverage and for localization of objects, such as impacted teeth and foreign bodies (Fig. 14).

A complete intraoral survey of the permanent dentition consists of 14-16 periapical films and four bitewing films of the posterior teeth. A bitewing radiograph displays the crowns of the maxillary, as well as the mandibular teeth and the marginal alveolar bone. In most cases a panoramic radiograph (Fig. 2) and two bitewing films are adequate for examination of the primary dentition. Periapical radiographs are taken as needed. Although several systems for dental digital radiography are available, conventional radiography is still predominant.

Other classical projections commonly used in the diagnosis of pathological processes within the jaws are projections such as cephalometric, Waters, Towne, Caldwell, and submentovertex. Tomography has to a

	Figure 1. Panoramic radiograph of an adult patient. Left maxillary third molar is impacted (arrow). 1. Zygomatic arch. 2. Pterygomaxillary fissure. 3. Maxillary zygomatic process. 4. lnfraorbital margin. 5. Maxillary sinus. 6. Hard palate. 7. Soft palate. 8. Ghost image of opposite mandibular ram us. 9. lnferior coneha. 10. Nasal septum. 11. Tongue. 12. Styloid process. 13. Submandibular fossa.
	Figure 2. Panoramic radiograph of a 5-year-old child. 1. Cervical spine. 2. Adenoid hyperplasia. 3. Pharyngeal space. 4. Prevertebral soft tissues. 5. Maxillary sinus. 6. Mandibular foramen. 7. Mandibular canal. 8. Cranial base.

large extent been replaced by computed tomography (CT) and magnetic resonance imaging (MRI). Both CT and MRI, as applied to the jaws, have a limitation, however, since dental materials may cause disturbing artefacts. It should be emphasized that tomography is still valuable in some areas of oral and maxillofacial radiology by virtue of its comparable diagnostic yield, lower radiation doses, and significantly lower costs

Figure 3. Left mandibular molars showing normal anatomy. The root development of the third molar is incomplete. The enamel capping the crowns is more radiopaque than the dentin due to its higher mineral content. The pulp chambers, as well as the root pulps are fully discernible. The roots are separated from the lamina dura (arrow) of the tooth socket by the periodontal ligament (double arrows), which appears as a radiolucent line.

than CT and MRI.

Isotope scans are employed to examine the jaw bones in a number of disease processes. For instance, in metastatic disease and osteomyelitis, they disclose affected areas earlier than plain radiography. Ultrasound is being used increasingly to examine soft tissues adjacent to the jaws. It is also applied to depict changes in the outer contour or the jaw bones.

In lesions within the jaws it is common to combine panoramic or other extraoral radiographs with intraoral radiographs, to achieve the necessary three-dimensional information about extent, borders and relationships to other structures or lesions. The intraoral radiographs are more likely to depict finer structures than extraoral radiographs, tomograms, and CT or MR images. Sometimes the detailed information of an intraoral radiograph is crucial for the differential diagnosis of a jaw lesion.

Lars Hollender and Karl-Åke Omnell