Opg

OPG

1. Orthopantomogram

2. INTRODUCTION Panoramic imaging also called pantomography is a technique for producing a single tomographic image of facial structures that includes both the maxillary and mandibular dental arches and their supporting structures .

3. INDICATION To evaluate impacted teeth To evaluate eruption patterns, growth and development To detect diseases ,lesions and conditions of the jaw To examine extent of large lesions To evaluate trauma and fractures. To evaluate periodontal   bone  loss and periapical involvement.

4. Finding the source of dental  pain Assessment for the placement of dental  implants Orthodontic  assessment. pre and post operative Caries detection especially in the inter-dental region. Diagnosis of developmental anomalies such as  Cherubism ,  Cleido cranial dysplasia Carcinoma  in relation to the jaws Tempero mandibular joint dysfunctions and  ankylosis

5. ADVANTAGES Broad coverage of facial bones and teeth Low patient radiation dose Convenience of the examination of the patient Use in patients unable to open their mouth Short time required In patient education and case presentation

6. DISADVANTAGES Image quality are not sharp Focal trough limitations Distortion Expensive equipment cost

7. PRINCIPLES OF PANORAMIC IMAGE FORMATION Numata and Paatero - describe the principles of panoramic radiography B ased on the principle of reciprocal movement of x-ray source and an image receptor around a central point or plane called the image layer, in which the object of image is located. Object in front or behind this image are not clearly captured because of their movement relative to the centre of rotation of the receptor and the x-ray source.

8. Two adjacent disks rotate at the same speed in opposite directions as an xray beam passes through their centers of rotation . Lead collimators in the shape of a slit are located at the x-ray source and at the image receptor to limit the central ray to a narrow vertical beam. O bjects A, B, C, and D present on disk 1 and rotate past the slit. Their images are recorded on the receptor, which also moves past the slit at the same time. 9

9. The objects are displayed sharply on the receptor because they are moving past the slit at the same rate and in the same direction as the receptor. This causes their moving shadows to appear stationary in relation to the moving receptor. Other objects between the letters and the center of rotation of disk 1 rotate with a slower velocity and are blurred on the receptor. Any objects between the x-ray source and the center of rotation of disk 1 move in the opposite direction of the receptor, and their shadows are also blurred on the receptor. 10

10. The same relationship of moving film to image is achieved if disk I is held stationary and the x-ray source is rotated so that the central ray constantly passes through the center of rotation of disk 1 and, simultaneously, both disk 2 and the lead collimator ( Pb ) rotate around the center of disk 1. In this situation, as before, the objects A through D move through the x-ray beam in the same direction and at the same rate as the receptor. 11

11. Replace disk 1 with the patient, and objects A through D representing teeth and surrounding bone. Structures on the opposite side of the patient (near the x-ray tube) are distorted and appear out of focus because the x-ray beam sweeps through them in the direction opposite that in which the image receptor is moving. 12

12. In addition, structures near the x-ray source are so magnified (and their borders so blurred) that they are not seen as discrete images on the resultant image. These structures appear only as diffuse phantom or ghost images. Therefore, only structures near the receptor are usefully captured on the resultant image. Structures located more centrally in the body relative to the jaws, such as the hyoid bone and epiglottis, appear on the right, left, and sometimes central areas of the final image. 13

13. The x-ray tube head and the film holder move around the patient in same direction and the film within its holder moves in the opposite direction

14. IMAGE LAYER   Also known as focal trough It is a three dimensional curved zone where the structures lying within this layer are reasonably well defined on final panoramic image. The structures seen on a panoramic image are primarily those located within image layer. Objects outside the image layer are blurred magnified are reduced in size. Even distorted to the extent of not being recognizable. This shape of image layer varies with the brand of equipment used.

15. FOCAL TROUGH

16. ROTATION CENTER The pivotal point or axis around which the cassette carrier and tube head rotate is termed rotation center Three basic rotation center used in panoramic radiography Double centre rotation Triple centre rotation moving centre rotation The location and number of rotational centers influence size and shape of focal trough

17. PARTS OF PANORAMIC UNITS a. x-ray tube head b. head positioner : chin rest notched bite block forehead rest lateral head support c. exposure controls

18. X-RAY TUBE HEAD: Similar to intraoral x-ray tube head Each has a filament to produce electrons and a target to produce x-rays Collimator is a lead plate with narrow vertical slit Narrow x-ray beam emerges from collimator minimize patient exposure to radiation

19. Tube head is fixed in position and rotates behind the patient head Film positioner is used to align the patients teeth accurately in focal trough

20. PATIENT POSITIONING AND HEAD ALIGNMENT Dental appliance earrings ,necklace , hairpins, and any other metallic objects should be removed Instruct the patient to stand as tall as possible with back straight and stand erect . Vertical column must be straight Instruct the patient to bite on the plastic bite block tooth must be positioned in edge to edge position in the groove present in the bite block it is used to align the teeth in the focal trough

21. Midsagittal plane perpendicular to floor Frankfort horizontal plane parallel to the floor Tongue must be positioned on the roof of the mouth Instruct the patient to remain still while machine is rotating

22. Common errors in panoramic radiography Due to faults in technique:- Errors in patient positionening , Errors in film exposures and processing errors. Errors in handling the film .

23. Errors in patient positioning Anterior teeth positioning errors Midsagittal plane positioning errors Occlusal plane positioning errors Spinal column positioning errror Patient’s shoulder touching the cassette holder during the movement Distortion due patient movement

24. Anterior positioning For anterior teeth positioning, insert a bite block between incisal edges of maxillary and mandibular teeth Advantages of using bite block : Places the teeth in image layer Prevents overlapping vertically Prevents undue unsharpness,widenening or narrowing of anterior teeth

25. Patient positioned too far forward : Features:- Narrow blurred anterior teeth, superimposition of spine over the ramus. Correction :- Use bite block. Line up the incisal edge of the teeth with notch, Ask edentulous patients to bite about 5mm behind the groove on the block

26. Patient positioned too far back Feature:-Wide blurred anterior teeth Correction ;- Use bite block. Line up the incisal edge of the teeth with notch

27. Occlusal plane positioning :- The patients head should be tilted downwards so that the ala tragus line is about 5 degree downwards,this will position occlusal plane slightly downwards towards the floor. In this plane patients franfurt’s horizontal plane , the plane intersecting the lower orbit of the eyes and ear opening ,is alighned horizontally with floor level.

28. Chin positioning too low Feature :- Excessive curving of the occlusal plane:loss of image of roots of lower anterior teeth Narrowing of intercondylar distance and loss of head of condyle at top of film. Correction;- Tip chin down , but ala-tragus line should not exceed 5-7  downwards. Use chin rest

29. Chin positioned too high Features Flattening or reverse curvature of occlusal plane. Loss of image of the roots of upper anterior teeth Lenghtening of intercondylar distance and loss of head of condyles at the edge of the film hard palate shadow superimposed on apices of maxillary teeth. Correction Tip chin down 5-7degrees Use chin rest

30. Midsagittal plane positioning error When the midline of the head is not in center of the unit, the rami and posterior teeth are unequally magnified . The image of the structures farthest from the film are magnified ,whereas,on the oppposite,the image of the structures closest to the film are decreased in size.

31. Patient twisted Features Unequal right –left magnification Severe overlap of contact points and blurring Correction Line up the patient’s midline with middle of incisal bite guide. Close side guides

32. Slumped position Features :- Ghost image of cervical spine superimposed on midline of the film Correction :- Stand up machine –have patient step forward ,or place feet on markers.

33. Spinal column positioning errors Incorrect vertebral column positioning results in underexposed area in middle portion of film . This happens because if spine is not kept erect,the radiation is excessively absorbed by the spinal column and surrounding soft tissue sof the neck, resulting in low density area around the lower center of the film.

34. spine-shadow ghost

35. Chin not on the chin rest Features :- Sinus not visible on the film Top of condyle is cut off Excessive distance between inferior border of mandible and lower edge of the film. Correction :- Position chin on chin rest

36. Tongue not on palate Features :- Relative radiolucency obscuring the apices of maxillary teeth Palatoglossal air space Correction :- Ask the patient to swallow or suck on the tongue and cheek during exposure

37. Lips open Features Relative radiolucency on coronal portion of upper and lower teeth. Correction Ask the patient to swallow or suck on the tongue and cheek during exposure.

38. Patient movement Features :- Wavy outline of the cortex of inferior border of the mandible Blurring of image above the wavy cortical outline Correction :- Ask the patient to hold still and explain the function of the machine to avoid startling the patient

39. Ghost image

40. Ghost image: 1) Opposite side 2)Higher up in position 3)Larger in size 4)Blurred-more in horizontal dimension

41. Double image Double real images are formed in the central diamond area as the beam will pass through here twice. -One image is the mirror image of the other -Both images are real -Each image has similar proportions -Each image has the same location on the opposite side -Only occurs with midline objects e.g Hard and soft palate, palatal tori, body of the hyoid, epiglottis, cervical spine

42. Errors in handling the film

43. Static electricity Features Lightning like radiolucency. Dot like radiolucencies. Other patterns are herring bone, star burst or smudge. Correction :- Dry air in darkroom can be humidified with humidifier or large bowl of water. Avoid rapid pulling of film from envelope type cassette. Use antistatic carpet.

44. INTERPRETING PANORAMIC IMAGE

45. THE MANDIBLE

46. Condylar process and TMJ : a bony rounded radioopaque projection extending from ramus of mandible Coronoid process : triangular radio opacity posterior to tuberosity region Ramus : shadow of other structure may superimposed over the ramus such as Pharyngeal airway shadow Posterior wall of pharynx Cervical vertebra Ear lobe Nasal cartilage Soft palate and uvula Dorsum of tongue Ghost shadow

47. Body and angle : radiopaque bony structure where the ramus join the body of the mandible mandibular dentition and alveolus

48. MIDFACIAL REGION       Individual bones: Temporal zygoma mandible frontal Maxilla Sphenoid Ethmoid Vomer   Nasal Palate

49. Cortical boundary of maxilla including posterior border and alveolar ridge Pterygomaxillary fissure : radiolucent area between the lateral pterygoid plate and maxilla Maxillary sinuses : paired radiolucencies located above the apices of premolars and molars

50. Zygomatic complex or buttresses of midface : includes lateral and inferior orbital rims zygomatic process of maxilla zygomatic arch Nasal cavity and conchae : radiolucent area above the maxillary incissors TMJ Maxillary dentition and alveolus

51. SOFT TISSUES

52. Tongue under the hard pala te : radiopaque area superimposed over the maxillary posterior teeth Lip line : seen in the region of anterior teeth Soft palate : extending posteriorly from hard palate Posterior wall of pharynx Nasal septum Ear lobes Nose and nasolabial fold

53. DENTITION Teeth and supporting alveolar bone are evaluated Teeth examined for Gross anomalies of number ,position, and anatomy Impacted third molars Endodontic obturations , crowns, fixed restoration

54. THANK YOU