Bisecting angle vs paralleling technique /orthodontic courses by Indian dental academy 

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1. Seminar
Bisecting angle versus Paralleling Bisecting angle versus Paralleling
techniquetechnique
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
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2. Learning ObjectivesLearning Objectives
At the end of the session the learners should
be able to-
Enumerate the basic principles of projection
geometry.
Describe the bisecting angle and paralleling
technique.
Describe advantages and disadvantages of
bisecting angle and paralleling technique.
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3. Contents
Ideal positioning requirements
Principles of projection geometry
Comparison between paralleling and
bisecting angle technique
Conclusion
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4. Ideal positioning requirement
The tooth under the investigation and the film packet
should be in contact or, if not feasible, as close together as
possible.
The tooth and film packet should be parallel to one another
The film should be positioned with its long axis vetically for
incisors and canines, and horizontally for premolars and
molars with sufficent film beyond the apices to record the
apical tissues.
The X-ray tubehead should be positioned so that the beam
meets the tooth and film at right angles in both horizontal
and vertical planes.
The positioning should be reproducible.
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5. Radiographic techniques
The anatomy of the oral cavity does not always
allows these ideal positioning requirements to be
satisfied.
In an attempt to overcome the problems, two
techniques for periapical radiography have been
developed.
- The paralleling technique
- The bisected angle technique
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6. PRINCIPLES OF PROJECTION GEOMETRY
(SHADOW CASTING)
BASIC PRINCIPLES:-
The focal spot (Source of radiation) should
be as small as possible.
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7. PRINCIPLES OF PROJECTION GEOMETRY
(SHADOW CASTING)
The focal spot – Object distance should
be as long as possible.
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8. PRINCIPLES OF PROJECTION GEOMETRY
(SHADOW CASTING)
The Object – Film distance should be as
small as possible.
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9. PRINCIPLES OF PROJECTION GEOMETRY
(SHADOW CASTING)
The long axis of the object & the film planes
should be parallel.
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10. PRINCIPLES OF PROJECTION GEOMETRY
(SHADOW CASTING)
The X-Ray beam should strike the object &
the film planes at right angles.
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11. There should be no movement of the
tube, film or patient during exposure.
(Given by Mason & Lincoln)
PRINCIPLE OF PROJECTION GEOMETRY
(SHADOW CASTING)
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12. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Synonyms -
Short cone
technique
 Finger holding
technique
Synonyms -
Long cone
technique.
Right angle
technique.
Extension
paralleling
technique
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13. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Based on geometric
principle CIESZYNSKI’S
Rule of isometry - Two
triangles are equal if
they have two equal
angles and share a
common side.
Based on the fact that
x-ray film is supported
parallel to the long axis
of the tooth being
radiographed.
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14. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Central ray is
perpendicular to
imaginary bisector of
angle formed by film &
long axis of tooth.
Central ray of the x-ray
beam is directed at right
angles to both the tooth
and the film.
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15. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Satisfies Rule 1 &
3 of shadow
casting.
Size 2 film
preferred.
Satisfies Rule 1, 2, 4
& 5 of shadow
casting.
Size 1 film preferred
anteriors and size 2
film for posteriors.
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16. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Target -Film
Distance is 6” – 8”
Target – Film
Distance is 16” – 18”
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17. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Use of film holder
is not mandatory
Rinn BAI
Stable bite block
Snap-A-Ray
Use of film holder
is mandatory
Rinn XCP
Precision film
holders
Grip film holder
Hemostat with bite
block
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18. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Film touches tooth at
crown portion. Thus,
the crown film
distance is less than
apex film distance.
Film is parallel &
away from tooth.
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19. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Requires less
exposure
Hence kvP is
reduced
Divergent rays
used for image
formation.
Requires more
exposure
Hence kvP is
increased
Parallel rays used
for image
formation.
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20. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Film placement
easier.
Film placement
difficult, so
discomfort to the
patient.
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21. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Patient can hold
the film.
Patient cannot hold
the film. Film
holder mandatory.
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22. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Film holders not
routinely used so
vertical and
horizontal
angulations have
to be adjusted.
Use of film holder
with a beam
alignment device
eliminates the
need to device
vertical and
horizontal
angulations so
distortions
eliminated.
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23. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Film holders not
used routinely. So
chances are less
for impingement
and causing
discomfort.
Film holders used
may impinge on
oral tissue causing
discomfort &
gagging to the
patient.
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24. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Distortion of the
image.
Image is more or
less anatomically
accurate.
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25. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Increased
elongation or
foreshortening of
image.
Image has same
size & shape as
that of object.
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26. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Distortion of image
due to oblique
exposure & bending
of film due to
incorrect digital
pressure.
Film holders
prevent such
errors producing
anatomically
accurate image.
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27. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Incorrect horizontal
angulations may lead
to overlapping of the
crowns and roots.
Less chances of
incorrect horizontal
angulations.
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28. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
More vertical
angulation.
Less vertical
angulation.So
maximum chances
of overlapping of
buccal and lingual
cusps.
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29. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Less tooth area
underneath the
restoration is
relevant due to
more vertical
angulation.
More tooth area
underneath the
restoration is
relevant due to
less vertical
angulation.
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30. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Difficult to visualize
the imaginary
bisector and
determine the
vertical angulation
and direct the
central ray.
Central rays
perpendicular to
both film and long
axis of tooth.
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31. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Superimposition of
the shadow of the
zygomatic arch on
the teeth
Less vertical
angulation causes
minimum
superimposition of
zygomatic buttress
of maxilla over the
upper roots. Teeth
apices & maxillary
sinus better seen.
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33. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Cone cut results
particularly if
rectangular
collimation used.
PID aims the X-ray
beam accurately so
there is no coning
off or cone cutting.
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34. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Shadows of the
alveolar bone tend to
fill the interproximal
spaces. The loss of
bone or pathology is
misinterpreted.
Alveolar crest seen in
true relationship to
the teeth.
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35. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
More effective
when palatal vault
is deep or shallow,
bony overgrowth
or children with
underdeveloped
jaws.
Difficult in shallow
palatal vault, small
mouth, children,
handicapped
patients.
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36. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Film holders not
used making it
comparatively
easier to carry
Endodontic work.
Use of film holder
with a beam
alignment device
makes it difficult to
carry Endodontic
work.
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37. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Sterilization of
holders not
required as they
are not used
usually.
Unnecessary
exposure because
patient touches
film.
Sterilization must.
Holders need to be
autoclaved or
disposable holders
(Styrofoam bite
blocks) to be used.
Film holders are
used - so no
unnecessary
exposure.
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38. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Vertical
angulations may
expose vital organs
such as thyroid
gland and the lens
of the eye.
Lack of extreme
vertical angulations
cause less
exposure to critical
organs.
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39. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Shifting may lead to
improper centering
of the film- cone
cutting and/or
blurring.

Position indicating
device used, so
shifting of patients
head may not affect
much.
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40. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Duplication of
technique is
difficult.
Hence, comparison
in serial
radiographs not
possible.

Technique is easy
to standardize &
can be accurately
duplicated.
Hence serial
radiography is
possible.
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42. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Positioning of the
film in third molar
region
comparatively easy
Positioning the film
in the third molar
region very
difficult.
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43. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Economic
Requires less time
Comparatively
expensive because
of need of higher
KVP machine and
film holders.
Requires more
time
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44. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Requires less
space.
Adjustments can
be made easily.
Does not have any
anatomical
constraints.
Requires more
space.
Adjustments
cannot be made so
easily.
Have anatomical
constraints.
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45. BISECTING ANGLE PARALLELING
TECHNIQUE TECHNIQUE
Can be used when
tooth is longer
than film.
More factors to be
standardized.
Is difficult to use
when the patient is
in supine position.
Cannot be used
when tooth is
longer than film.
Less factors to be
standardized.
Not difficult as
PID’s are used.
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46. Conclusion
 The diagnostic advantages of the accurate,
reproducible images produced by paralleling
technique using film holders and beam-
aiming device should be regarded technique
of choice for periapical radiography.
Periapical radiography is not always as
straightforward in practice as it appears in
theory.
Although paralleling technique should be
regarded as the technique of choice, it is not
always possible.
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47. However, a knowledge of the theoretical
requirements of imaging enables the
clinician to modify the available techniques
to suit individual needs of patients.
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48. ReferencesReferences
Oral Radiology – White & Pharoah
Dental Radiography- Haring Jansen
Textbook of Dental & Maxillofacial Radiology
– Freny R.Karjodkar
Essentials of Dental Radiography & Radiology
third edition – Eric Whaites,
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