Brief discussion on dental panoramic tomography, various types, views and interpretation, errors

1. Dr. Tania Arshad Siddiqui
Assistant Professor-Orthodontics
Date: 26th December 2019
Panoramic Radiography (Dental
Panoramic Tomography-DPT) and
Periapical (PA) X-Ray

2. Reasons for DPT
 All teeth and supporting structures are shown on
one film
 Simple technique
 Low radiation dose
 Rare earth intensifying screens
 Digital image receptors

3. Selection Criteria
 Bony lesion or unerupted tooth is of a size or
position that cannot be seen on intra oral film
 Grossly neglected mouth
 Periodontal assessment especially when there is
pocket depth greater than 6 mm
 Assessment of wisdom teeth before extraction
 Orthodontic assessment for:
 Dental age
 State of dentition
 Presence/Absence of teeth

4. Other:
 Mandibular fracture
 Antral disease
 Destructive diseases of the articular surfaces of
the TMJ
 Vertical alveolar bone height as part of preimplant
planning
2004 Selection criteria in Dental Radiography (UK)-
panoramic radiography should be taken in

5. Types of Tomography
 Linear tomography using a wide or broad X-ray
beam
 Linear tomography using a narrow or slit X-ray
beam
 Rotational tomography using a slit X-ray beam

6. Broad-beam linear tomography

7.  Synchronized movement of tubehead and film in
the vertical plane
 Straight linear tomography
 Exposes entire film throughout exposure

8. Slit or Narrow Beam linear
tomography

9. Narrow Beam Rotational
Tomography

10. Focal Trough
It is a 3D curved zone where structures lying within
this layer are reasonably well defined on final
panoramic image

11. Vertical wall of the focal trough in incisor region and relative
positions of the teeth with different underlying dental or
skeletal abnormalities

12. Normal Anatomy
 Real or Actual Shadows of structures in , or close to,
the focal trough
 Ghost or artefactual shadows created by tomographic
movement and cast by structures on the opposite side
or a long way from the focal trough
 Cervical vertebrae
 Body, angle and ramus of C/L
side of Md
 Palate

13. Advantages Disadvantages
Large area imaged , including
anterior teeth when patient is unable
to open mouth
Represents only a section of the
patient, structures or abnormalities
not in focal trough may not be
evident
Image is easy for patients to
understand , useful teaching aid
Soft tissue and air shadows can
overlie the required hard tissue hard
tissue structures
Vertical patient movement distorts
only that part of the image being
produced
Artefacts overlie structures in the
focal trough
Simple patient positioning, minimal
expertise
Distortion and magnification of the
final image X1.3
Overall view allows rapid
assessment of underlying
unsuspected disease
Indirect action film and intensifying
screens result in some loss of quality
image, improved by digital image
receptors
View of both sides of the mandible
on one film is useful when assessing
Not suitable for patients under 5
years old or some disabled patients

14. Advantages Disadvantages
Useful for evaluation of periodontal
status
Some patients do not conform
to the focal trough and some
structures will be out of focus
Simus floor, medial and posterior
walls are visible
Movement of patient during
exposure can create difficulties
in image interpretation
Both condylar heads are shown on
one film, allowing easy comparison
Radiation does (effective dose) is
about 1/5th dose from a full mouth
survey of intraoral films
Development of field limitation
techniques with resultant dose
reduction

15. Assessment of rejected films and
determination of errors
Patient
Preparati
on errors
Failure to remove jewellery
Failure to remove dentures, removable orthodontic appliances
Failure to remove spectacles
Inappropriate use of lead apron
Patient
positionin
g errors
Ghost Shadow Error- Failure to ensure spine is straight
Antero-Posterior error- incisors are not biting edge to edge on the bite peg
Horizontal error- failure to use light beam marker to ensure mid sagittal plane is vertical and head is
not rotated
Vertical error- failure to use light beam marker to ensure Frankfort plane is horizontal
Air shadow error- Failure to instruct patient to press the tongue against the roof of the mouth
Movement error- Failure to instruct patient to remain still during exposure
Equipme
nt
positionin
g error
Failure to set height adjustment correctly
Failure to select correct exposure setting
Failure to use cassette correctly

16. Periapical X-ray

17. Periapical Xray
Bisecting Angle
Technique Paralleling Technique

18. Main Localization Methods for
Impacted Canine
Parallax-Apparent displacement of the object
because of different positions of the observer
 Parallax in horizontal plane
 Parallax in vertical plane
 OPG
 CBCT

19. Interpretation
If canine is palatally positioned, it will move in
the same direction as the X-ray tubehead
If the canine is buccally positioned, it will
appear to move in the opposite direction to the
x-ray tubehead
If the unerupted canine is in the same plane as
the incisors i.e. in line of arch, it will appear not
to have moved at all
• SLOB- Same Lingual Opposite Buccal
• Tube shift technique OR Clarks Rule OR Buccal Object
Rule

20. Parallax in Horizontal Plane
Norm
al
Distal
Angle
 2 periapicals- one centered on the upper central
incisor and the other centered on the canine
region
Two periapicals showing the relative positions of the unerupted 13 to
the incisors — M in the midline and R from the right. The X-ray
tubehead (white arrow) and the canine (black arrow) appear to have
moved in the same direction. The canine is thus palatally positioned.

21. Parallax in Horizontal Plane
 An upper standard occlusal, centered in the
midline plus a periapical or an upper oblique
occlusal, centered on the canine region
An upper standard occlusal (the mid-line view) and two periapicals centred on the unerupted canines on
either side. The teeth can be localized as follows:
1. Examine the midline view radiograph (M), centred on the upper central incisors. The tip of the RIGHT canine
appears opposite the root canal of 11 ; the tip of the LEFT canine appears opposite the mesial aspect 22.
2. Examine radiograph (R), the periapical centred on the RIGHT canine region (i.e. the X-ray tubehead has been
moved distally
in the direction of the white arrow). The tip of the canine appears opposite the mesial aspect of 12 . Therefore, it
appears to have moved distally in the direction of the black arrow, i.e. in the same direction as the X-ray
tubehead was moved.
3. Examine radiograph (L), the periapical centred on the LEFT canine region. The tip of the canine appears
opposite the root canal of 22. Again both the X-ray tubehead (white arrow) and the canine (black arrow) appear

22. Parallax in Horizontal Plane
Two periapicals showing an unerupted mesiodens. It can be localized as follows:
1. Examine the mid-line radiograph (M). The tip of the mesiodens’ crown appears opposite the mesial aspect of
21, while its apex appears opposite the root canal of 11 .
2. Examine the periapical centred on the RIGHT canine region (R). The tip of the mesiodens crown appears
opposite the root canal of 21, while its apex appears opposite the mesial aspect of 12 .
3. The X-ray tubehead was moved distally in the direction of the large white solid arrow.
4. The crown of the mesiodens appears to have moved mesially (black open arrow), i.e. in the opposite direction
to the tubehead. It is thus buccally placed.
5. The apex appears to have moved in the same direction (white open arrow) as the tubehead and is thus palatally
placed.
The mesiodens thus lies across the arch, between the central incisors, with its crown buccally positioned and its

23. Parallax in Vertical Plane
 X-ray tubehead moves in vertical plane
 A dental panoramic radiograph — the X-ray beam is
aimed upwards at 8° to the horizontal
 An upper standard occlusal — the X-ray beam is aimed
downwards at 65°–70° to the horizontal

24. Parallax in Vertical Plane
Part of a dental panoramic radiograph and an upper standard occlusal showing an unerupted mesiodens. It can
be localized as follows:
1. Examine the panoramic radiograph (P) taken with the tubehead aimed upwards at 8° to the horizontal. The
tip of
mesiodens’ crown appears opposite the neck of the lateral incisor, while its apex appears opposite the root of
11.
2. Examine the occlusal radiograph (O) taken with the tubehead aimed downwards at 65° to the horizontal. The
tip of the mesiodens’ crown now appears beyond the apex of 12 , while its apex appears opposite the crown of
21.
3. The X-ray tubehead has moved vertically upwards from view (P) to view (O) in the direction of the solid white
arrow.