The ABC guide to the OPG
Presented by:
Dr Anshul Aggarwal (B.Sc., B.D.S, M.D.S (OMR))
Consultant oral diagnostician & oral & maxillofacial radiologist
ORTHOPANTOMOGRAM
ORTHO - Orthodontics refers to correct or straight
PAN - Refers to the panoramic display of the teeth produced by the technique
TOMOGRAM - X-ray image that is focused in a single plane of the patient which shows a sharp image; layers above and below it, being unsharp or blurred
Learning objectives
To demonstrate the principles of image formation in OPG
To demonstarate the errors in OPG
The ABC guide to OPG.
Use in dental implant
Special focus on importance of detailed reporting of OPG.
Background
Radiographic interpretation of the OPG is dependent
On the recognition of normal anatomy.
An understanding of the technique involved.
An awareness of the tomographic artifacts that may arise from this technique.
TECHNIQUE
OPG is more common- a dental panoramic tomogram (DPT)
technique - conventional tomography & slit beam scanning
curved mandible is displayed as a flattened two-dimensional image, hence the term „panoramic‟.
Principals
It involves the following principals:
The patient remains stationary as the x ray tube and film both rotate around the patient
There is a continuous vertical beam of x rays during an exposure cycle, which is directed at a slight upward angulation of 8 degrees.
The patient has to be “positioned” correctly in the focal trough to allow the required dental features to be in focus.
The typical radiation dose is 0.016Sv (the equivalent to one chest x ray).
7 X-ray
tube head
Slit collimator
Slit collimator Image
receptor
8
9
10
11
MOVEMENT PATTERN OF X-RAY BEAM
13
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Beam first rotates around a laterally positioned rotation center which serves as a functional focus while major part of the opposite is exposed
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14
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The anterior region is now exposed with this second rotational center as the functional focus
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15
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Rotation center is once more shifted so that the projection of the jaws is symmetric on both sides
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ERRORS IN POSITIONING THE PATIENT
Position too forward
Position too far back
Patient is twisted/tilted on machine
Chin is tip too low
Chin is tipped too high
Patient is slumped
Lip are open and tongue is not on palate
16
POSITIONED
TOO FORWARD
18
POSITIONED
TOO FAR BACK
19
Patient is twisted /tilted on machine
Twisted
Tilted
20
CHIN IS TIPPED
TOO LOW
21
CHIN IS TIPPED
TOO HIGH
22
PATIENT IS
SLUMPED
LIP ARE OPEN
& TONGUE IS
NOT ON PALATE
Both the condyle should be at same level The width of both
side of ramus of mandible should be
equal
The anterior region should be clear.
Both upper and lower anteriors is should be clearly visible
Tooth should not Overlap with adjacent teeth/
But should be in close contact with each other The contrast of the
bone between teeth should be clear
The lips should be closed while shooting opg . No radiolucency is visible on upper and
lower anterior teeth
The Occlusal line is Just like a smile line 1
2
3
4 5
6
7
T H E A B C GU IDE
The following systematic approach to assessment is suggested:
A Anatomy, air shadows and artifacts
B Bony structures
C Check areas and calcification
D Dentition
A - ANATOMY
The soft tissue structures.
Air shadows that may be seen on an OPG.
The concept of ‘ghost’ shadows.
AIR SHADOWS & SOFT TISSUES
GHOST SHADOWS
Ghost images
BONY LANDMARKS IN MANDIBLE
1
1. Condylar head 2. Sigmoid notch 3. Coronoid 4. External oblique ridge
5. Mandibular canal
2
3
4 5
6. Post. Border of Ramus 7. Gonial Angle 8. Lower border
6
7
9. Mental ridge 10. Genial tubercle 11. Mental foramen 13. Lingula
12. Internal Oblique Ridge 14. Hyoid bone
8
9 10
11
12 13
BONY LANDMARKS IN MAXILLA
15
15. Glenoid fossa
19. Floor of Max.Sinus
17. Zygomatic Arch
16. Articular eminence 18.Post. wall max. sinus 20. Zygomatic process of max. forming inominate line
21. Hard palate 22. Floor of the orbit 23. Nasal septum 24. Incisive foramen 25. Inferior choncha 26. Meatus 27. Frontal process of Z.bone
16 1 7
18
19
20 21
22 23
25 29
24 26
28.Pterygo max. fissure 30. Maxillary tuberosity
29.Spine of the sphenoid bone 31. Lateral pterygoid plate
31 15
28 27
OTHER STRUCTURES
32
32. External acoustic meatus 33. Styloid process 34. Shadow of ear lobe 35. nose 36. Shadow of Cervical spine
33 34 35
36 36
36. Cervical vertebrae
37
37. Nasopharyngeal space 38. Shadow of uvula
39
38
39. Submandibular fossa
Use in dental implant
evaluation of the remaining bone height available for implant insertion
Vertical magnification is 10% while
horizontal is 20% and also variable
Determination of bone height for implants in various regions.
A,B- from alveolar crest to nasal fossa in the maxillary anteriors.
C,D- from alveolar crest to maxillary sinus floor in maxillary posteriors.
E- from alveolar crest to inferior alveolar canal in mandibular posteriors.
F- from alveolar crest to lower border of the mandible in mandibular anteriors
G- from alveolar crest to mental foramen in mandibular premolar region.
Metal balls attached to mandibular cast with cardling wax
Radiographic stent made with self-polymerizing acrylic resin
OPG with metal balls
ADB ABH
(Actual diameter of metal ball ) ( Actual bone height available )
== (vertical distance between alveolar crest & opposing landmark).
--- --- RDB RBH
(Radiographic Diameter of metal ball) (Radiographic bone height)
OPG after implant surgery
Advantage
Opposing landmarks are easily identified
Vertical bone height can be assessed
Procedure performed with great ease and speed
Gross anatomy and related pathology can be
assessed
Disadvantages:
Does not demonstrate bone quality
Misleading due to magnification
Little use in depicting the spatial relation
Least useful in deciding angulation.
Overlapping in maxillary anterior region.
Interpretation of the orthopantomogram requires an understanding of the radiographic technique involved and a fundamental knowledge of the normal anatomical structures seen on the radiograph.
Normal variants and common tomographic artifacts should not be confused with pathology.
Lesions that arise in the mandible may be odontogenic or non- odontogenic in origin, and they have a range of appearances varying from radiolucent to radio-opaque.
