Extra-oral Radiographic Techniques

Extra-oral Radiographic Techniques

1. EX T RA O R AL RADIOGRA P HY Dr. ARUN PANWAR MDS II 28/07/2020

2. Contents Introduction Technique Lateral Skull Projection Submentovertex Projection Waters projection Postero anterior Skull Projection Reverse-Towne Projection Mandibular Oblique Lateral Projections TMJ Imaging Conclusions References

3. History of Extra-oral radiographic techniques

4. EXTRA-ORAL SOURCE Discovered by Dr. Hisatugu Numata of Japan, 1933

5. History The first attempts to image the whole jaw in one exposure were started at the beginning of 19 th century . In 1922, A . F. ZULAUF (USA ) described a method where a narrow beam scanned the upper or lower jaw . He called his device “the panoramic x-ray apparatus”. In 1933, H . NUMATA (Japan) constructed a device which was suitable for clinical examinations, calling the method “parabolic radiography ”. E arly 1950s witnessed a major event in the development of extraoral rotating panoramic radiography in Finland. PAATERO introduced the terms “ pantomography ” and , later, “ orthopantomography ” ( orthoradial panoramic tomography ).

6. T he first experimental device had a stationary tube but the patient’s chair rotated . This equipment was constructed by T. NIEMINEN. In 1957, an orthopantomograph with 3 rotation centres was constructed and installed at the Dental Clinic of the University of Helsinki.

7. Based on Area of Interest Skull views- PA Skull, Submentovertex view (base of the skull), Lateral skull, Lateral cephalogram Maxillary sinus-– Water’s view/PNS, Modifications- Granger’s view, Caldwell’s projection Mandible - Lateral oblique views: Body and Ramus TMJ views – Transcranial , Transpharyngeal , Transorbital , Reverse Towne’s view

8. Film Size

9. INTRODUCTION Extraoral radiographs are taken when large areas of the skull or jaw must be examined or W hen patients are unable to open their mouths for film placement . In extraoral radiographic examinations both the x-ray source and image receptor are placed outside the patient’s mouth. Extraoral radiographs do not show the details as good as intraoral films do. Extraoral radiographs are very useful for evaluating large areas of the skull and jaws . B ut are not adequate for detection of subtle changes such as the early stages of dental caries or periodontal disease.

10. The main anatomic landmark used in patient positioning during extraoral radiography is the canthomeatal line. This line joins the central point of the external auditory canal to the outercanthus of the eye. The canthomeatal line forms approximately a 10-degree angle with the Frankfort plane. This line that connects the superior border of the external auditory canal with the infraorbital rim.

11. Techniqu e The first step in obtaining a radiograph is the selection of the appropriate projection for the diagnostic task. Extraoral radiographs are produced with conventional dental x-ray machines, or certain models of panoramic machines . It is critical to correctly and clearly label the right and left sides of the image . This usually is done by placing a metal marker (an R or an L) on the outside of the cassette in a corner in which the marker does not obstruct diagnostic information. The proper exposure parameters depend on the patient’s size, anatomy, and head orientation ; image receptor speed; x-ray sourceto-receptor distance; and whether grids are used.

12. EXTRAORAL RADIOGRAPHIC TECHNIQUES

13. Lateral cephalometric projection Film Placement Film is placed perpendicular to the floor Patient Position MSP is vertical and parallel to the cassette. Patient should be instructed to close the mouth and teeth should be in occlusion. Central Ray Horizontal beam should be centered on the external acoustic meatus , perpendicular to the cassette Indications To evaluate relationship between soft and hard tissues of the face. To assess the skeleton pattern, facial growth and developmental anomalies. To assess the position of teeth. The lateral cephalometric projection is most commonly used in dentistry. All cephalometric radiographs, including the lateral view, are made with a cephalostat that helps maintain a constant relationship among the skull, the fi lm , and the x-ray beam..

14. Exposure parameters : KVp= 84 mA= 13 Seconds =1.6 At the beginning of treatment, these measurements are often compared with an established standard; during treatment, the measurements are usually compared with those from previous cephalometric radiographs of the same patient to monitor growth and development as well as treatment.

15. Anatomic Landmarks identified in lateral cephalometric projection

16. Submentovertex ( base) projection Film Placement Film is placed perpendicular to the floor Patient Position Patient’s neck should be hyper-extended to bring the vertex of the skull in contact with the cassette. MSP should be perpendicular to the cassette. Canthomeatal line should be parallel to cassette Central Ray Directed perpendicular to the film and through the MSP Indications To evaluate # of zygomatic arches For visualization of base of the skull To evaluate the lesions of the palate and sphenoid sinuses. Exposure parameters KVp= 50 mAs= 20 Seconds = .4

17. A, Anatomic landmarks identified in the submentovertex projection . B , An underexposed submentovertex view reveals the zygomatic arches

18. Jug handle view Modification of SMV The exposure time for the zygomatic arch is reduced to approximately one- third the normal exposure time for a submentovertex projection.

19. P ostero - A nterior skull projection (Granger Projection) Film Placement Film is placed perpendicular to the floor Patient Position MSP is vertical and perpendicular to the plane of cassette. Canthomeatal line should be 10 o to film Nose and forehead should touch the cassette Central Ray Directed perpendicularly from backward Indications Fractures of the skull vault Investigation of the frontal sinuses Fracture, cyst, tumour of the body, angle or ramus of mandible Le fort 1 # of middle third of face Displacement of teeth in alveolar fractures.

20. Anatomic landmarks identified in the PA cephalometric projection.

21. Modifications of PA skull Caldwell projection It is to see orbits and ethmoidal sinuses Central beam is directed at angle of 15 o to the Canthomeatal line. Puffed cheek PA View It is to visualize parotid duct stones Ask patient to blow cheeks, making the parotid duct prominent. Rotatated PA View It is to visualize parotid gland pathologies/stones. Ask patient to turn face 10 o to opposite side of gland of interest.

22. Reverse Towne’s Projection Film Placement Film is placed perpendicular to the floor Patient Position MSP is vertical and perpendicular to the film. Canthomeatal line should be 25-30 o to the image receptor Patient’s head should touch the film. Pateint’s mouth should be open. Central Ray Directed through MSP at the level of mandible and perpendicular to the film Indications To view condylar head and neck To evaluate high condylar fractures, intracapsular fractures of TMJ. To assess the condylar hypoplasia or hypertrophy. Exposure p a r a met e rs KVp = 65 mAs = 10 Seconds = 2-3

23. Anatomic landmarks identified in the open-mouth reverse-Towne projection

24. PROJECTIONS FOR MANDIBLE

25. Lateral oblique The x-ray beam is aimed perpendicular to the film, but is oblique to the saggital plane of the patient. Indications: Assessment of the presence or position of unerupted teeth. Evaluation of lesions or conditions affecting jaws including cysts, tumours , giant cell lesions and osteodystrophies . In patients with severe gagging. As specific views of te salivary gland or TMJ Types: Mandibular body projection Mandibular ramus projection Exposure parameters: KVp= 65-70, mAs= 10, seconds= 0.8

26. Mandibular body projection Area of interest Premolar-molar region and the iferior border of the mandible Fil m placement Cassette is placed against patient’s cheek and centred over the first molar. Extending 2 cm below the border of mandible Patient should hold the cassette Hea d position Head is tilted towards the side being examined and mandible is protruded.

27. Anatomic landmarks identified in the oblique lateral projection of the mandibular body.

28. Mandibular ramus projection Area of interest Ramus from the angle of the mandible to condyle . In examining 3 rd molar regions of maxilla and mandible. Fil m placement Cassette is placed over the ramus and as far as enough to include to the condyle . Lower border of the cassette should be parallel with inferior border of the mandible and should extend 2 cm below it. Hea d position Head is tilted towards the side being examined and mandible is protruded.

29. Anatomic landmarks identified in the oblique lateral projection of the mandibular ramus

30. PROJECTIONS FOR MAXILLARY SINUS-

31. Water’s V iew (PNS) Film Placement Film is placed perpendicular to the floor Patient Position MSP is vertical and perpendicular to the plane of the film. Patient’s head is extended so that only the chin touches the cassette. Canthomeatal line forms an angle of 37 o from the plane of cassette Central Ray Directed perpendicular and to the midpoint of the film. Indications To demonstrate maxillary sinus, ethmoidal sinus and frontal sinus. For evlauation of nasal cavity, coronoid process of mandible and zygomatic arch. In open mouth water’s view : sphenoidal sinuses can be seen. Exposure parameters • KVp = 65 • mAs = 10 • Seconds =2-3 sec

32. Anatomical Landmarks in Waters Position

33. T e m p o r o- m a n d i b ul a r Joint Views

34. A combination of transcranial , transpharyngeal , transorbital , and submentovertex (basal) projections allow visualization of the TMJs in various planes. Transcranial and transpharyngeal projections provide lateral views. The transcranial view is taken in both closed and open mouth positions and depicts the lateral aspect of the TMJ. Whereas the transpharyngeal projection is taken in the mouth open position only and depicts the medial aspect of the condyle . The transorbital projection is taken in the open or protruded position and depicts the entire medial-lateral aspect of the condyle in the frontal plane and is very useful in detecting condylar neck fractures. Transorbital view is rarely being used now due to unwanted radiation exposure to the eyes.

35. TMJ- transcranial projection Film Placement The cassette is placed flat against the patient’s ear and centered over the TM- joint of interest parallel to the sagittal plane. Patient Position The patient's head is adjusted so that the sagittal plane is vertical. A la-tragus line is parallel to the floor. This view is taken with both open and closed position Central Ray Directed downward from the opposite side, through the cranium and above the petrous ridge of the temporal bone at an angle of 20- 25 o Structures seen: Lateral aspect of condyle and temporal component. Indications: To evaluate the joint’s bony relationship Detecting arthritic changes on the articular surface. To investigate the range of movement in the joints.

36. Exposure parameters KVp = 70 mAs = .7 Seconds =1.5

37. Post auricular or Lindblom techni que : Point of entry of central ray is ½ inch behind and 2 inches above external auditory meatus.

38. Grewcock techni que : (1953), central ray ent ers through point 2 inches above external auditory meatus perpendicular to occlusal plane .

39. Gill ‘s approach (1939), central ray entry point is 1/2 inch in front and 2 inches above external auditory meatus parallel and perpendicular to occlusal plane.

40. Transpharyngeal Projection Film Placement The cassette is placed flat against the patient’s ear and centered to a point ½ inch anterior to the external auditory meatus over the TMJ of interest parallel to the sagittal plane. Patient Position Sagittal plane is vertical and parallel to the film Patient should open his mouth Central Ray Vertical direction: Directed at an angle of -5 to -10 from the sigmoid notch of contralateral side. Horizontal direction: 10 posterior to TMJ of interest The point of entry may be taken at: Pupil of the same eye, asking the patient to look straight ahead. Medial canthus of the same eye Medial canthus of the opposite eye Structures seen: Medial surface of the condylar head and neck Indications: To assess the developmental anomalies of the condylar neck. To detect grossly displaced fractures of the condyalr neck. (Macqueen Dell Technique/ Infracranial / Parma Projection)

41. It is a lateral projection showing medial aspect of condylar head and neck. Exposure parameters: KVp= 70 mAs= 7 Seconds = 1.5

42. Transorbital (Zimmer Projection) Film Placement The film cassette is placed behind the patient’s head, perpendicular to the x-ray beam. Patient Position Patient’s head is tilted downward 10 so that the canthomeatal line is horizontal. Mouth should be wide open or protruded to avoid superimposition Central Ray Vertical direction: Downward 10 to the canthomeatal line. Horizontal direction: CR perpendicular to the film The point of entry may be taken at: Pupil of the same eye, asking the patient to look straight ahead. Medial canthus of the same eye Medial canthus of the opposite eye Structures seen: The entire mediolateral dimension (anterior view of TMJ) of the condyle . Indications: To evaluate the abterior view of TMJ Medial displacement of fractured condyle and neck of condyle .

43. Exposure p a ram e ters: KVp = 70 mAs = 7 Seconds =.8

44. Different R/G appearances Multiple Myeloma

45. Sickle Cell Anaemia

46. Rheumatoid Arthritis

47. Summary

48. Limitations Magnification occurs due to the greater object to film distance used. Details are not well defined. Contrast is reduced as the secondary radiation produced by the soft tissues is more. It is a 2- D image of 3- D structure.

49. Conclusion Thorough knowledge of the indications of various extra oral techniques allows accurate and timely diagnosis of various maxillofacial pathologies. Also, helps arrive at a diagnosis with minimum number of x-rays there by reducing patient exposure to radiation.

50. References White and Pharoah Oral Radiology Principles And Interpretations 6 th edition Langland and Langlais , Principles Of Dental Imaging.7 th edition Freny R,Karjodkar , Textbook Of Dental And Maxillofacial Radiology.6 th edition

51. Relative usefulness of extraoral radiographic projections to display various anatomic structures.