1. Chapter 42 Extraoral and Digital Radiography
Copyright 2003, Elsevier Science (USA).
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2. Introduction
Extraoral radiographs (outside the mouth) are taken when large areas of the skull or jaw must be examined or when patients are unable to open their mouths for film placement.
Extraoral radiographs do not show the details as well as intraoral films.
Extraoral radiographs are very useful for evaluating large areas of the skull and jaws but are not adequate for detection of subtle changes such as the early stages of dental caries or periodontal disease.
There are many type of extraoral radiographs. Some types are used to view the entire skull, whereas other types focus on the maxilla and mandible.

3. Panoramic Radiography
Panoramic radiographs show the entire dentition and related structures on a single film.
Some types of panoramic units operate with the patient in a seated position, and other types require the patient to be in a standing position.
Regardless of the type of machine, you must follow the manufacturer’s instructions carefully.
Because the images on a panoramic film are not as clear or as well defined as the images on intraoral films, bite-wing films are used to supplement a panoramic film to detect dental caries or periapical lesions.

4. Basic Concepts
In panoramic radiography the film and tubehead rotate around the patient, and it produces a series of individual images.
The term panorama means “an unobstructed view of a region in any direction.” When the series of images are combined onto a single film, an overall view (panorama) of the maxilla and mandible is created.

5. Fig The film and x-ray tubehead move around the patient in opposite directions in panoramic radiography.
Fig. 42-2

6. Focal Trough
An imaginary, three-dimensional curved area that is horseshoe shaped.
This is a very important concept because many technique errors are caused by improper positioning of the patient’s jaws within the focal trough.
When the jaws are positioned within this area, the radiograph will be clear.
When the jaws are positioned outside of this area, the images on the radiograph will appear blurred or indistinct.

7. Fig. 42-3 An example of an image layer, or “focal trough.”

8. Components of the Panoramic Unit
Panoramic x-ray tubehead
Head positioner
Exposure controls

9. Fig. 42-4 The main components of a panoramic unit.

10. The Head Positioner
Each panoramic unit has a head positioner used to align the patient’s teeth as accurately as possible.
Each head positioner consists of a chin rest, notched bite-block, forehead rest, and lateral head supports or guides.
Each panoramic unit is different, and the operator must follow the manufacturer’s instructions on how to position the patient in the focal trough.

11. Fig. 42-5 The head positioner is used to align the patient’s teeth in the focal trough.

12. Common Errors Patient preparation errors
Ghost images: A ghost image looks like the real object except that it appears on the opposite side of the film.
Lead apron artifact: If the lead apron is placed too high, or if a lead apron with a thyroid collar is used, a cone-shaped radiopaque artifact results.
Patient seating errors
Chin too high
Chin too low

13. Fig. 42-13 Large hoop earrings (A) and ghost images (B)
Fig Large hoop earrings (A) and ghost images (B). The ghost image of the earring appears on the opposite side of the film.
Fig

14. Fig On a panoramic radiograph, a lead apron artifact appears as a large cone-shaped radiopacity obscuring the mandible.
Fig

15. Fig. 42-16 The patient’s head is tipped too far upward.

16. Fig. 42-18 The patient’s head is incorrectly positioned; the chin is tipped downward.

17. Positioning of the Teeth
Posterior to focal trough
If the patient’s anterior teeth are not positioned in the groove on the bite-block and are either too far back on the bite-block or posterior to the focal trough, the anterior teeth appear “fat” and out of focus on the radiograph.
Anterior to focal trough
If the patient’s anterior teeth are not positioned in the groove on the bite-block and are either too far forward or anterior to the focal trough, the teeth will appear “skinny” and out of focus.

18. Fig. 42-21 The patient is biting too far back on the bite-block.

19. Fig The anterior teeth appear widened and blurred on a panoramic film when the patient is positioned too far back on the bite-block.
Fig

20. Fig The anterior teeth appear narrowed and blurred on a panoramic film when the patient is positioned too far forward on the bite-block.
Fig

21. Fig If the patient is not standing erect, superimposition of the cervical spine (arrows) may be seen on the center of the panoramic film.
Fig

22. Positioning of the Spine
If the patient’s spine is not straight, the cervical spine will appear as a radiopaque artifact in the center of the film and obscure diagnostic information.

23. Extraoral Radiography
Extraoral radiographs provide images of larger areas such as the skull and jaws.
In some instances, an extraoral film may be necessary for handicapped patients who cannot open their mouths for film placement, or because a patient has swelling or severe pain and is unable to tolerate the placement of intraoral films.
Extraoral films are also very useful for patients who are uncooperative and may refuse to open their mouths.
Images seen on an extraoral film are not as clear or as well defined as the images seen on an intraoral radiograph.

24. Equipment
Extraoral radiographs may be taken with a standard intraoral x-ray machine.
To aid in patient positioning, special head positioning and beam alignment devices can be added to the standard x-ray unit.
In addition, panoramic x-ray units may also be fitted with a special device known as a cephalostat.
The cephalostat includes a film holder and head positioner that allow the operator to easily position the patient.

25. Grid
A device used to decrease film fog and increase the contrast of the radiographic image.
It does this by reducing the amount of scatter radiation that reaches an extraoral film during exposure.
Scatter radiation causes film fog and reduces film contrast.

26. Fig. 42-27 A grid decreases the amount of scatter radiation that reaches the extraoral film.

27. Lateral Jaw Projection
Used to view the posterior region of the mandible. This type of projection is very useful for patients with a limited jaw opening and in patients who cannot or will not tolerate intraoral film placement.
A lateral jaw projection does not provide as much diagnostic information as a panoramic radiograph.
The advantage is that the lateral jaw projection can be taken with a standard x-ray unit.

28. Lateral Jaw Projection Techniques
Body of mandible projection
Ramus of mandible projection

29. Fig A, The body of the mandible; proper patient and film positioning is shown as viewed from the front and side of the patient. B, The body of the mandible.
Fig

30. Ramus of the Mandible
This film is used to evaluate impacted third molars, large lesions, and fractures that extend into the ramus of the mandible.
The ramus from the angle of the mandible to the condyle is visible in this projection.

31. Fig A, Ramus of the mandible; proper patient and film positioning is shown as viewed from the front and side of the patient. B, An example of a lateral jaw radiograph; the ramus of the mandible.
Fig

32. Skull Radiography Lateral cephalometric projection
Posteroanterior projection
Water’s projection
Submentovertex projection
Reverse Towne’s projection

33. Fig. 42-30 B, An example of a lateral cephalometric radiograph.

34. Fig. 42-31 B, An example of a posteroanterior skull radiograph.

35. Fig. 42-33 B, An example of a submentovertex radiograph.

36. Fig. 42-34 B, An example of a reverse Towne’s radiograph.

37. Temporomandibular Joint Radiography
Radiographs of the temporomandibular joint (TMJ) can be very difficult to examine because of the multiple adjacent bony structures.
The articular disc and other soft tissues of the TMJ cannot be examined by radiographs.
Special imaging techniques (e.g., arthrography, magnetic resonance imaging) must be used.
Radiographic projections of the TMJ can be used to show the bone and the relationship of the jaw joint.

38. Fig. 42-36 Patient positioned for a transcranial radiograph of the temporomandibular joint.

39. Digital Radiography
Advances in digital technology have led to a unique “filmless” imaging system known as digital radiography.
Introduced in 1987, digital radiography has influenced both how dental disease is recognized and how it is diagnosed.
In the last 2 years, the use of digital radiography is rapidly increasing in both general and specialty dental practices.
Numerous companies are producing digital radiography systems.

40. The Basics of Digital Radiography
Digital radiography uses a sensor to capture a radiographic image, breaking it into electronic pieces and storing the image in a computer.
The patient is exposed to less x-radiation than with conventional radiography.
The image is displayed on a computer screen rather than on film.
The term image (not radiograph) is used to describe the pictures that are produced.

41. The Basics of Digital Radiography- cont’d
The x-ray beam strikes the sensor.
An electronic charge is produced on the surface of the sensor, and this electronic signal is digitized.
The digital sensor in turn transmits this information to the computer.
Software in the computer is used to store the image electronically.

42. Fig The size of the electronic sensor is compared with sizes 0, 1, and 2 of traditional intraoral film.
Fig

43. Fig. 42-39 All types of radiographs may be produced in digital format.

44. Radiation Exposure
Digital radiography requires much less x-radiation than conventional radiography because the sensor is more sensitive to x-rays than to conventional film.
Exposure times for digital radiography are 50% to 80% less than that required for radiography using conventional film.
With less radiation, the absorbed dose to the patient is significantly lower.

45. Equipment
For digital radiography, special equipment is required. The essential components include:
Dental x-ray unit
Intraoral sensor
Computer

46. Types of Digital Imaging
Direct digital imaging
Indirect digital imaging
Storage phosphor imaging
The difference between each method is in how the image is obtained and in what size the receptor plates are available (e.g., panoramic).

47. Fig. 42-40 Computer with modified image.

48. Fig : If the tongue is not placed on the roof of the mouth, a radiolucent shadow will be superimposed over the apices of the maxillary teeth.
Fig