2. Extra oral Radiography:
• All extra oral radiographic projections should
be performed using screen film.
• Medium or high speed (rare-earth) screenfilm combination are recommended to reduce
pt’s exposure.
• Metallic letters (L) &(R) are used to determine
left & right sides of pt as well as grids to
reduce the fog.
4. Intensifying Screen Function
One of the properties of x-rays is that
they cause certain materials to
fluoresce (emit light); the phosphor
crystals found in intensifying screens
are one of these materials.
The light emission is usually green or
blue, depending on the type of
phosphor crystal used.
5. Intensifying Screen Function
The composition of the films used
with these screens is adjusted by
the manufacturer to be sensitive to
either blue light or green light.
correct film should be used with
corresponding screen type. (Bluesensitive film with blue lightemitting screen, etc.)
6. Screen Film
• Screen film is sensitive to the effects of light
from an intensifying screen. When these
screens, on either side of the film in a cassette,
are exposed to x-rays, they emit light which in
turn exposes the film.
• Using the screen-film combination allows a
very large reduction in the amount of radiation
needed to expose the film (30-60 times less
radiation than that required by direct exposure
film).
7. Intensifying Screen Composition
(this side toward film)
The base of the screen (yellow line above) is made of
above
plastic and provides support. A reflecting layer
(silver line) reflects light emitted by the phosphor
line
back toward the film. The phosphor layer (green line)
line
contains the phosphor crystals that emit the light.
The surface of the phosphor layer is covered with a
protecting coat (white line) , which is a thin layer of
plastic that protects the phosphor layer from
damage when the screens are handled.
8. Rare Earth Phosphor
The most common type of phosphors being used
are the rare earth phosphors, which emit blue or
green light depending on the type of rare earth
material being used.
film
= phosphor crystal
9. Intensifying Screen Speed
The speed of the screen depends on crystal size and
the thickness of the phosphor layer (larger crystals
and thicker layer increase speed). Image quality
decreases as the screen speed increases. The three
speeds are:
• Fast (Rapid): requires the least exposure but the
images are less sharp
• Medium (Par): medium speed, medium sharpness
• Detail (Slow): produces the sharpest images but
requires the most exposure
10. Screen Film
The two types of screen film used with rare earth
screens are T-Mat and Ektavision. These films are
available in three styles: G, which is used to
provide the best contrast; L, which has the widest
latitude (long-scale contrast) and is good for soft
tissue visualization and H, which is used to provide
an extra film for referral purposes (two films are
placed in the cassette at the same time).
The advantage of Ektavision film over T-Mat film is
that it has anti-crossover layers incorporated into
the film. This prevents light from one screen
affecting both emulsion layers; this produces a
sharper image on the film.
11. T-Mat (crossover)
Light produced by the phosphor crystal spreads out
as it goes toward the film and with T-Mat film it
affects the emulsion on both sides. Since it has
spread out more when it reaches the emulsion on
the opposite side of the film (crossover), the
crossover
sharpness (edge detail) of the image is decreased.
film
12. Ektavision (anti-crossover)
Ektavision film has a crossover control layer on each
side of the film base. These layers allow the light from a
phosphor crystal to reach the emulsion on the same
side as the crystal but prevent the light from reaching
the emulsion on the opposite side of the film. X-rays
easily pass through this anticrossover layer.
film
14. 1] Lateral oblique projection:
• 2 views for mandibular projection;
• a) body projection:
• For demonstration premolar-molar region
and inferior border of the body of the
mandible.
• Head position: Head tilted to the side to
be examined with the mandible
protruded.
15. Lateral oblique projection body
(cont.):
• Film placement:
• Film is placed against the patient’s
cheek and centered over the first
molar .
• The lower border of the cassette
should be parallel to the inferior
border of the mandible and at least
2cm below it.
• Point of entry:
• 2cm below angle of the mandible
directed toward the 1st molar region
of cassette side.
17. B) Mandibular Ramus projection:
• To view the ramus from the mandibular
angle to the condyle for examining the 3rd
molar region of both the maxilla and
mandible.
• Head position: head tilted towards the
projected mandible where the mandibular
angle of tube side and condyle of cassette
side parallel to the floor.
18. Mandibular ramus projection (cont.):
• Film placement :
• film is placed over the ramus of
the mandible to the far
posterior to include the
condyle. Lower border of the
cassette 2cm below the inferior
border of the mandible.
• Point of entry:
• 2cm below the inferior border
of the first molar region on the
tube side toward the center of
the ramus of the cassette side.
20. 2- True Lateral (Cephalometric):
Cephalo=Head
• Metric=Measurement.
Cephalometrics
introduced for use by
orthodontists by Dr.
Broadbent in 1931 for
studying dento -facial
growth.
21. True Lateral (Cephalometric) (cont.):
• Uses:
•
•
•
•
•
•
Evaluation of facial growth & development.
Le Fort I & II fractures.
Posterior wall of antera.
Perforation of hard palate.
A foreign body in the air way.
The film: is positioned parallel to the sagittal plane of
the film.
• The central ray :is ┴ the film in both horizontal &
vertical plane.
22. True Lateral (Cephalometric) (cont.):
• Reproducibility:
• Cephalometric has the
unique property of
presenting a
reproducible image,
unlike any other
radiographic technique
used for dental films
23. True Lateral (Cephalometric) (cont.):
• Reproducibility:
• The patients head is
oriented in the same
position relative to the xray beam every time a film
is taken, with the use of
positioning ear posts
24. True Lateral (Cephalometric) (cont.):
The distance from the x-ray source to the
patient’s midsagittal plane is always the same
60 inches to reduce the magnification.
25. • Soft tissue profile
can be added by
using reducing the
exposure to 50% or
put aluminum filter
in the front of
cassette.
26. Uses in orthodontics:
• Evaluate skeletal patterns
(bone-to-bone relations)
• Does the patient have a
Class I, Class II or Class III
skeletal pattern?
• Is the problem due to a
prognathic maxilla, a
retrognathic maxilla, a
prognathic mandible, a
retrognathic mandible or a
combination of these?
27. Cephalometric Landmarks
• Landmarks are
locations which
represent biological
homology between
image locations
• Example: The tip of
the chin in one
cephalometric image
corresponds to the tip
of the chin in another
cephalometric image
28. Cephalometric Landmarks
• Landmarks need to have 3 properties:
1.Landmarks should not remodel over time
(neither be created nor destroyed)
2.Landmarks need to capture biological form,
including the shape, size and position of the
tissue component of which it represents
3.Landmarks have to be reliably located on
cephalometric radiographs
29. Common landmarks
• Sella Turcica (S):
• midpoint of the
pituitary fossa.
• Orbitale (O):
lowest point on
lower margin
of orbit
30. Orthodontic tracing
• To the fixed anatomical points is applied to assess the
nature and extent of any malocclusion which may be
present.
• Tracing of anatomical landmarks should be drown
with sharp , hard (6H) pencil on good quality tracing
paper or acetate drafting sheet not on the film and
done on film viewer.
31. Main areas of concern:
- Skeletal relationships.
- Dento-skeletal
relationships.
- The facial profile.
Radiographs can be digitized
and measured in personal
computer with special
software or cephalometric
tracer attached to
computer can be used.
32. 4-Submentovertex (SMV) view:
• The projection shows the
base of the skull,
Sphenoidal sinuses and
facial skeleton from
below(radiographic
baseline is vertical).
• The pt’s head tipped
backwards and x-ray beam
is aimed upwards at 5° to
the horizontal.
34. 4-Submentovertex (SMV) view:
• Film placement: cassette
± floor and placed
vertically.
• Head position: tipped
backward & touch the
cassette .Frankfort plane
± floor.
• Beam alignment:
• center to the head and ±
cassette.
