2 extra-oral radiography

05/19/1605/19/16 Ossama El-ShallOssama El-Shall
Extra-oral Radiography
Dr. Ossama EL-ShallDr. Ossama EL-Shall
Professor and Chairman, Oral Medicine,Professor and Chairman, Oral Medicine,
Periodontology, Diagnosis and RadiologyPeriodontology, Diagnosis and Radiology
Dept., Faculty of Dental Medicine Al-AzharDept., Faculty of Dental Medicine Al-Azhar
University , Cairo Egypt.University , Cairo Egypt.
E.mail address: oelshall@hotmail.comE.mail address: oelshall@hotmail.com

Extra oral films
Extra-oral films are the films placed extra-
orally during exposure in order to exam the
mandible, the maxilla, the TMJ and all the
facial bones.
Extra-oral films usually supplied in special
light tight boxes in quantities of 50 or 100
films and loaded in a special light protected
holder (cassette) inside the dark room.

General indications of use of extra-oral
films
1- Patients who cannot open their mouths sufficiently for
insertion of intra-oral films due to any causes such as trauma
of truisms.
2- Unco-operative patient such as mentally retarded and children.
3- Examination of large pathologic involvement, such as large
cyst.
4- Obtaining a large generalized view of jaws, sinuses and bones.
5- Examination of fracture lines and extension of fracture in skull
bone.
6- Localization of foreign bodies.
7- Examination and diagnosis of TMJ disorder.
8- Obtaining of generalized view of unerupted, impacted or
supernumerary teeth.

Types of extra-oral films.Types of extra-oral films.
Screen filmsScreen films
Non screen filmsNon screen films

Screen filmScreen film
Is used in combination with intensifyingIs used in combination with intensifying
screens.screens.
These films are different from other dentalThese films are different from other dental
films in that they are designed to befilms in that they are designed to be
particularly sensitive toparticularly sensitive to visible lightvisible light ratherrather
than to X-radiation.than to X-radiation.
This is because they are used by being placedThis is because they are used by being placed
between two intensifying screens.between two intensifying screens.
The intensifying screens absorb X rays andThe intensifying screens absorb X rays and
emit visible light that exposes the screen film.emit visible light that exposes the screen film.

Non screen filmsNon screen films
Or direct exposure films;Or direct exposure films;
they are more sensitive to x rays than to light.they are more sensitive to x rays than to light.
It requires a longer exposure time as itIt requires a longer exposure time as it
depends on thedepends on the x rays onlyx rays only to affect the filmto affect the film
not on any emitted light.not on any emitted light.
It may be used for thin bones only such asIt may be used for thin bones only such as
long bone and mandible.long bone and mandible.
However its use in dental radiography is notHowever its use in dental radiography is not
recommended.recommended.

Extra-oral film equipmentsExtra-oral film equipments
Intensifying screenIntensifying screen
CassetteCassette

Intensifying screenIntensifying screen
It is a device used to intensifies theIt is a device used to intensifies the
photographic effect of X-rays and thusphotographic effect of X-rays and thus
shortens the exposure time that otherwiseshortens the exposure time that otherwise
would be long to suit the thickness andwould be long to suit the thickness and
density of tissues in case of extra-oraldensity of tissues in case of extra-oral
radiography.radiography.

The use of intensifying screen is based
on three main principles:
X radiation have a biological damaging
effect that should be protected through
decrease the exposure time.
Certain substances can cause
fluorescence if it absorb X radiation.
Photographic film is sensitive to both X
radiation and visible light.

When x-rays strike intensifying screen, they
immediately activate it so it emits light
which is going together with the x-rays to
expose the film.
Thus the light produced by the screen
intensifies the effect of the x-rays on the
film and helps reduction of exposure time.
The intensity of this fluorescence is directly
proportional to the intensity of the exiting
x-ray.

= phosphor crystal
film
Mechanism of action of the screen

Composition of intensifying screen:
Plastic or cardboard base.
Reflecting layer: It is a layer of titanium oxide that covers
the base of the screen and lies beneath the phosphor layer.
Its function is to reflect any light emitted from the
phosphor layer back to the film and thus increase the
effect of the screen.
The phosphor layer: It is the light sensitive crystals layer,
it formed from Calcium tungestate or Barium lead
sulphate (conventional type that emit a blue light) or
formed from a rare earth phosphors as Gadolinium or
Lanthanium (rare earth type that emit green light).
Protective layer: made up of a plastic layer with smooth
surface.

Intensifying Screen Composition
-Base (thick white line) = plastic for support
-Reflecting layer (red line) = reflects light
back
toward film
-Phosphor layer (green line) = rare earth
(10
)
(this side toward film)

Types of intensifying screens:
I- According to the phosphor layers:
Conventional screens: the phosphor layer made of
Calcium tungestate or Barium lead sulphate and it
emit a blue light. For example: Kodak X-Omatic
screens.
Rare earth screens: the phosphor layer made of
rare earth phosphors, Gadolinium or Lanthanium
and it emit a green light. For example: Kodak
Lanex screens.

II- According to speed: (phosphor crystal
size)
Slow: has the smallest crystals and give the
best image details.
Intermediate: Have larger crystals and less
detail.
Fast: The largest crystals and least details.

= phosphor crystal
film
Light Emission from the screen

Loaded Screen film
film

Cassettes
Cassette holder is another equipment
necessary for the extra-oral films.
The extra-oral film is sandwiched between 2
intensifying screens of matching size and
type and secured in a cassette holder.

Cassette and its contents
1. Cassette front: made of plastic, aluminum
or carbon fibers to allows more rays to
pass and thus reducing patient exposure.
2. Two intensifying screens.
3. The screen film
4. Felt padding: to assure intimate and even
contact between film & screens
5. Cassette back: made of lead

Cross section of loaded cassette
Cassette front
Screen
Film
Screen
Felt padding
Cassette back

Cassette/Film

Cassettes
Hold intensifying
screens (2) in
tight contact with
film
Rigid (metal) or
soft (vinyl)
Rigid metal cassette
Flexible vinyl cassette

Extra-Oral radiographic projections.Extra-Oral radiographic projections.
(Plain radiographs).(Plain radiographs).
Lateral skull projectionLateral skull projection
Posteroanterior projection:Posteroanterior projection:
(PA).(PA).
Mandibular Lateral obliqueMandibular Lateral oblique
projections.projections.
Water’s view:Water’s view:
(occiptomental projection).(occiptomental projection).
Reverse-Towne projection.Reverse-Towne projection.

Plain radiographs.Plain radiographs.
Frankfort plane:Frankfort plane: It extendedIt extended
from the anterior border of the externalfrom the anterior border of the external
auditory meatus to the infra-orbital rim.auditory meatus to the infra-orbital rim.
The canthomeatal line:The canthomeatal line: It isIt is
the line between the central points of thethe line between the central points of the
external auditory meatus to the outerexternal auditory meatus to the outer
canthus of the eye. It makes 10 degree withcanthus of the eye. It makes 10 degree with
the frankfort plane. (radiographic base line)the frankfort plane. (radiographic base line)

Frankfort planeFrankfort plane
Canthomeatal lineCanthomeatal line

Concerning the nomenclature of theConcerning the nomenclature of the
film projection, thefilm projection, the firstfirst word of theword of the
description isdescription is where the tube is;where the tube is; thethe
secondsecond word isword is where the film iswhere the film is i.e. PAi.e. PA
film has the tube at the back of thefilm has the tube at the back of the
head (P) and the film is placed by thehead (P) and the film is placed by the
face (anterior).face (anterior).

Lateral cephalometric, True lateral, Dead lateralLateral cephalometric, True lateral, Dead lateral
It used to survey the skull and facial bones for
evidence of trauma, disease, or developmental
abnormality.
This view reveals the nasopharyngeal soft
tissues, paranasal sinuses, and hard palate.
Orthodontists use it to assess facial growth,
and in oral surgery and prosthetics it
establishes pretreatment and post-treatment
records.

Film placement: the film is positioned vertically in a
cassette-holding device.
Head position: the head should be positioned with
the side of the face near the cassette, the
interpupillary line perpendicular to the film, and
the midsagittal plane parallel to the plane of the
film.
Projection of the central ray: It directed toward the
external auditory meatus and perpendicular to the
plane of the film and midsagittal plane. Therefore,
superimposition of both sides of the skull, facial
bones and mandible.

Lateral Cephalometric
Identify trauma, abnormalities
Assess facial growth; treatment record
film at set distance from MSP
film horizontal
extraoral x-ray
unit
MSP
floor
MSP

Patient and film position during lateral
projection

Cephalometric MachineCephalometric Machine

Position of the patient in the cephalometric machine
for lateral cephalometric film

Posteroanterior projection: (PA)Posteroanterior projection: (PA)
It is so named because the X-ray beam passes in a
posterior-to-anterior direction through the skull.
It used to examine the skull for disease, trauma or
developmental abnormalities.
It provides a good record to detect progressive
changes in the mediolateral dimensions of the skull.
It also offers a good visualization of facial
structures, including the frontal and ethmoid
sinuses, nasal fossae, and orbits.

PAPA

Film placement: the cassette is
positioned vertically in a hold in
device in front to patient.
Head position: the head is centered
in the front of the cassette with
the canthomeatal line parallel to
the floor and the tip of the nose
and forehad are in contact with
the cassette.
Projection of the central ray: the
central ray is directed
perpendicular to the plane of the
film and coincident with the
midsagittal plane of the head at
the level of the bridge of the
nose.

Patient head position in relation to the
cassette during P.A projection

Posteroanterior (PA) Skull
Identify trauma, pathology, or
developmental abnormalities
FP
floor
MSP
extraoral x-ray unit

Position of the patient for posteroanterior projection
produced by cepalometric machine

It is a variant of the postero-anterior view.
It particularly used for evaluation of
maxillary sinuses, in addition to frontal and
ethmoid sinuses, the orbit, nasal cavity and
the coronoid process of the mandible.
Water’s viewWater’s view
(Occiptomental projection)(Occiptomental projection)

Film placement: the cassette is positioned
vertically.
Head position: the sagittal plane of the head is
perpendicular to the plane of the film. The
chin is raised to elevate the canthomeatal line
37 degrees above horizontal plane. A bite block
is used to secure max. jaw opening.
Projection of the central ray: the central ray
should be perpendicular to the film, through
the midsagittal plane, at the level of the
maxillary sinus.

Water’s view
(Occiptomental projection)

Waters
Evaluate the maxillary sinus
MSP
floor
extraoral x-ray
unit
(Sinus view)
tip of nose 1” from
cassette
CR
FP

Position of the patient for Water’s view using
cephalometric machine

Mandibular posterio-anterior viewMandibular posterio-anterior view
(Reverse-Towne projection)(Reverse-Towne projection)
It used to examine a patient with aIt used to examine a patient with a
suspected fracture of the condylarsuspected fracture of the condylar
neck,neck, especially in cases of mediallyespecially in cases of medially
displaced condyle.displaced condyle.

Film placement: the cassette is positioned in a
holding device in front to the patient.
Head position: the head is centered in front of
the cassette with the canthomeatal line
oriented downward 25 degree. The patient
instructed to open his mouth as wide as
possible to help visualize the condyles.
Projection of the central ray: the central ray is
directed to the film in the sagittal plane
through the occipital bone.

CM lineCM line RaysRays

Mandibular posterioanterior view
(Reverse-Towne projection)

Position of the patient for Reverse-TowneReverse-Towne
projectionprojection using cephalometric machine

Submentovertx projectionSubmentovertx projection
(base view)(base view)
This view used to exam the base of the
skull, condyles, sphenoid sinus, curvature of
the mandible, fractured zygomatic arch,
and foramina of the base of the skull.

Film placement: the cassette is placed vertically
in a holding device.
Head position: patient’s head is fully extended
backward as far as possible with the vertex of
the skull touches the center of the cassette.
Projection of central ray: the central ray is
directed from below the mandible upward
toward the vertex of the skull.

Submentovertx projectionSubmentovertx projection
(base view)(base view)
(Reverse-Towne projection)Occiptomental projection
PA
Water’s view Mandibular
Posterioanterior view

Specialized radiography

Specialized radiography.Specialized radiography.
Panoramic radiography.
Computed Tomography.
Sialography.
Magnetic resonance image.
Digital imaging.

Panoramic radiography
rotational radiography, or curved surface
tomography
It is a radiographic technique for
producing a single image of the facial
structures that includes both maxillary and
mandibular arches and their supporting
structures.

PanoramaPanorama
Panoramic radiography is an extraoralPanoramic radiography is an extraoral
radiographic technique that is used toradiographic technique that is used to
examine the upper and lower jaws on a singleexamine the upper and lower jaws on a single
filmfilm ..
The film and the tubehead rotate aroundThe film and the tubehead rotate around
the patient, producing a series of individualthe patient, producing a series of individual
imagesimages ..

As Tomographic principles, the x-ray
tube and film cassette rotate in opposite
directions around the patient’s head to
produce a specific curved image of the
maxilla and mandible on the film.

Panoramic principles are combination
of Scanography and Tomography
principles.
In order to understand the principle of
panoramic radiography, we have to
explain the meaning and principles of
both Tomography and Scanography

Tomography
Conventional film-based tomography is a special
radiographic technique designed to image more
clearly objects lying in a plane of interest.
This is accomplished by focusing on the plane of
interest and blurring the image of structures
lying superficial and deep to this plane.
Word Tome in Greek = Section

Conventional tomography is applied
primarily to high contrast anatomy, such
as encountered in dental implant
diagnostics.
In the other word, we can define the
tomography as a radiographic
presentation of a layer within the body
while body structures above and below
that layer are blurred out of focus.

Tomographic methods are divided into 2
major categories:
I- Conventional tomography.
II- Computerized tomography (C.T).

Scanography
Scanography is a process by which an x-ray
tube and a dental film are linked together
through a mechanical linkage and rotate
around a fixed object (patient’s head).

In panoramic technique, during exposure,
the x-ray source moves in one direction
while the film moves in the opposite
direction
The area of the object in the center of this
movement will appears in focus and very
sharp on the resultant radiograph as its
shadow.
All other structures will appears blurred or
out of focus

Advantage of panoramic radiography
1. Give a complete image for both jaws as well as
cervicofacial bones to exam any abnormality
such as, fractures, tumors, cysts, impaction
anomalous of teeth , etc……..
2. Simple technique, as it requires less co-
operation of the patient especially handicapped,
children, and jaw-fractured patients.
3. Low patient radiation dose; it is about 3 times
less than the amount received via full mouth
Periapical survey (14 films).

4. Quick procedure, the time required to
complete a panoramic radiographic
examination is quite short, usually in the
range of 3-4 minutes; this includes the
time necessary for positioning and the
actual exposure cycle (about22 sec.)
5. Panoramic films are readily accepted by
patients as a visual aid in case
presentation and for patient education.

Disadvantages:
The resultant Image does not resolve the fine
anatomical details that may be seen on intra-oral
Periapical radiographs.
Interproximal caries and changes of lamina dura
can not be diagnosed in most cases due to lack of
fine details and sharpness.
Magnification, geometric distortion and
overlapped images of teeth, especially in the
premolar region.

4. Due to superimposition of the spine, specially in
short-necked patients, there is always lack of
clarity in the central portion of the film (Ghost
shadow appearance of the spine)
5. Soft tissues and air shadows can overlie the
required hard tissue
6. High coast, 2-4 times that of an intra-oral X-ray
machine.

Indications:
1. Overall view of the teeth and facial bones.
2. Evaluations of trauma, extensive disease, tumor
extension, fracture, and gross swelling.
3. It reveals fractures of the mandible from the
midline to the neck of the condyle.
4. Cases of truisms, to locate or exam impaction,
pathology or fracture.
5. It reveals the maxillary sinuses floor of the orbits
and nasal bone.

6. Uncooperative patient, such as children, or
handicapped.
7. Full mouth survey instead of full mouth X-ray, 14
film.
8. Bilateral comparison of any pathology.
9. Orthodontic treatment
10. Evaluation of tooth development (especially in the
mixed dentition), retained teeth or root tips (in
edentulous patients), and developmental
anomalies.

Contra-indications:
Panoramic films are not suitable for
diagnostic examinations requiring high
image resolution, such as detection of early
bone loss, dental caries, periodontal
diseases, or analysis of trabecular bone
changes associated with early Periapical
lesions.

Computerized Tomography
C.T.

C.T.
1. Simply the computed tomographic scanner consists
of a multiple radiographic tubes with narrow
beams that are mounted in a circular gantry
opposite an array of scintillation receptors designed
to accept these beams.
2. The patient is placed in the center of the gantry and
the gantry rotates, allowing the x-ray beams to
irradiate patient from various angles.
3. The receptors record the radiation passing through
each small section of the patient and convert it into
electric impulses, which are sent to a computer for
storage and manipulation.

4. It provides excellent imaging of TMJ, salivary
gland, facial fractures and lesions, and tumor
extension and assists in the positioning of implants.
5. It completely eliminates the superimposition of
images of structures superficial or deep to the area
of interest within the patient.
6. It give a good differentiation between tissues due to
its high contrast resolution
7. The main disadvantages of it that, anything denser
than enamel produces serious artifacts. This causes
some problems when examining the jaws of patients
with metal restorations or implants.

Magnetic Resonance Imaging.
(MRI)
Magnetic resonance imaging is a
technique, which uses a combination of
magnetic fields and radio-frequency
waves to generate images of the body.

Able to image soft tissue without
contrast agents
Magnetic Resonance
1. Magnetic field aligns atoms (Hydrogen)
2. Radiowaves alter alignment
3. Atoms realign, releasing energy
4. Computer produces image
NO IONIZING RADIATION

Instead of detecting tissues by the x-ray, magnetic
resonance detects the presence of hydrogen nuclei
through their resonance in a magnetic filed.
Human tissues consist of molecules containing
hydrogen nuclei (protons). Each proton has an axial
spin and, because of its charge, behaves as a small
magnet, have both north and south poles.
Normally the protons are randomly arranged;
however, when the patient is placed in a strong
magnetic field, the direction of the spine of the
protons aligns with that of the filed.

The application of a pulsed resonant radio-
frequency waves, causes the protons to tilt
away from the magnetic filed. Once radio-
frequency waves are turned off, the protons
return to their preferred alignment with the
magnetic filed, and gives off the acquired
radio wave signals.
Magnetic Resonance Imaging is the process
of locating these individual protons radio-
signals in a three dimensional visual image.

To produce a MR image. The patient is placed
inside a large magnet, which induce a relatively
strong static magnetic field. This cause the nuclei
of many atoms in the body, including hydrogen to
align them with the magnetic filed.
Magnetic resonance imaging specifically image the
presence of H2 nuclei, water, lipids and the degree
of H2 are bound with molecules. So the tightly
bound hydrogen atoms as in bone appears black as
that of cortical plate, and loosely bound or mobile
H2 atoms such that of salivary glands and liquids
appears gray.

Magnetic Resonance
radiofrequency
coils
Magnet
(0.5 – 2.0 tesla = 5,000 – 20,000 gauss)
sliding table

Advantages:
Excellent soft tissues imaging especially T.M.J and
salivary glands without radiation exposure or
contrast media injection.
Disadvantages:
1. Long scan time.
2. Some patients can not stay motionless for long
times.
3. Noisy MR scanner
4. Any vascular clips can move due to magnetic filed.
5. High coast.

Thank you all for listening
Dr. Ossama El-Shall
Professor of Oral Medicine & Periodontology,
Faculty of Dental Medicine, Al-Azhar
University, Cairo, Egypt.
E-mail address: oelshall@hotmail.com

2 extra-oral radiography

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