radio last lec
TRANSCRIPT
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Dr. Louie Hammad
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Extra-Oral Radiographs
*Panoramic Radiography
-Panoramic radiograph is an extra-oral radiograph. Its also called(Orthopantomograms). that is used to examine the upper and lower
jaws on a single film.
-When taking a panoramic radiograph the patient may stand up or sit
down depending on the type of machine. The head, chin & the occlusal
plane must be in correct position.
PANORAMIC X-RAY MACHINE
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-The source of radiation always moves
behind the patient and the film in front of
the patient.
-Panoramic radiograph is called 2Dmodality however it is highly used, it
shows the mandible, maxillary sinuses
&TMJ all in 1 radiograph.
-Nowadays we have other 3D modalities
(like cone beam CT) & we use these
modalities to generate panoramic
radiograph. (We can also generate
panoramic radiograph from 3D images.)We also have normal panoramic
radiographs.
-I am sure many of you took a panoramic radiograph when you went to
your dentist to check your dental status, old teeth, and sinuses. It is also
the 1st step to see abnormalities in TMJ & is commonly used to see the
status & position of 3rd molars.
-Radiation dose is equal to 4-5 times more than intra-oral films which are
not a lot.
-Around 50 landmarks can be seen in the radiograph. Doctor said weshould search about them.
-Panoramic radiograph can also show us pathology, but its resolution is
not as good as intraoral radiograph so we cant depend on panorama to
show us caries or periodontal problems.
-Most common anatomy landmarks are in this pic.
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-We are expected to memorize all of them Why? To differentiate thenormal from abnormal anatomy.
*Now we are going to talk about soft tissues that can be seen on the
panoramic radiograph
1-tongue
2-soft palate
3-ear lobe
-soft tissues appear radiopaque in comparison with air.
*We have 3 air spaces:
1- Between the tongue and palate. Its called (palatoglossus /
glossopalatine air space)
2- Between the nose and pharynx. Its called (nasopharygeal air space)
3 Between the oral cavity and pharynx. Its called (glossopharyngeal /
oropharyngeal air)
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*In extra- oral radiography the tube head and the film is connected to
each other within the same x-ray machine, while in intra- oral
radiography the film is not a part of the x-ray machine. As a result, in
extra-oral radiography when the tube head rotates, automatically the film
will rotate. Since the two jaws are going to be radio graphed from left to
right, then it is a must that the tube head and the image receptors (film)
will rotate all around the skull.
-Now the area closest to cassette will be exposed by x-ray photons and
printed on a defined part of the film, afterwards the tube head will rotate
and at same time the cassette is rotating in the opposite direction,
eventually exposing another part to x-ray photons and printing it on
another defined area on the film.This is the principle of
tomography
**EXPLANATION OF TOMOGRAPHY TECHNIQUE:
-we have a tube head, cassette carrier, and an axis of rotation. Now the
cassette and the tube head will rotate around the axis of rotation so the
patient must be positioned in the center.
-The tube head and the cassette carrier will rotate in the same direction
(NOT the cassette or the film), while the film and the cassette will
move in the opposite direction. In the cassette itself there is a little
window or slit that exposes the film, and this little part of the film is
going to be exposed by the x-ray photons...This technique is called
Tomography.
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-where the x-ray photons can reach the film, there is a continuous
movement of the film, thus each part of the film will be accommodated
for anatomical structure, and once this anatomical structure exposed this
part of the film will be covered by metal shield, as a result it will be cut asslices (1st slice, 2nd slice, 3rd sliceetc), then at the end we will get
sectional images as a one section (one image).
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*Tomography:
-Tomography means sections, panoramic will not be taken as a single
shot the machine rotates at least 180 degrees & then forms the image.
*Tomography: it is a radiographic technique that allows the imaging of
one layer or section of the body while blurring images for structures inother planes.
***ROTATION CENTERS
-In panoramic radiograph the film or cassette carrier and X-ray tube head
are connected and rotate simultaneously around a patient during
exposure.
-The pivotal point or axis around which the cassette carrier and X-ray
tube head rotate is termed a rotation center.
-Some panoramic machines have 2 or 3 rotational points depending on
the manufacturer.
-The function of rotation centers is to facilitate getting the real dimension
of the jaws and to get a clear final image.
-In order to improve the image quality of the skull radiogram in the
panorama film we should increase the number of rotation centers, so in
order to make the image quality comparable to the intra-oral films .we
should increase the number of rotation centers as much as possible
*Note: the number of rotation centers starts from two so we will have:
1. Double-center rotation2. Triple-center rotation
3. Moving or sliding center rotation
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Double-Center rotation
*Let suppose that the x-ray photon will enter the right cheek , it will
continue to left cheek and it will go to the film through the window offilm(through the slit on the cassette)..The x-ray photon passes from the
right side to the left side so which of them will be on the final
image???
-Its the part that is closer...That means once the photon travels from right
side to the left side...The final image will be forthe left side.
-And the rotation will be continued...molars left side, premolars left side,
left laterals and left centrals.
And the position of tube head will be in the opposite side, so the image
will reveal right anteriors, premolars, and finally right molars.
-The x-ray photon enters to the center of rotation, and it will give us the
image that related to the opposite side, and it will continue to the anterior
teeth, premolars, and molars.
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Triple-center
rotation
lateral
rotation
center
anterior
rotation
center
path of
sliding
rotation
center
Moving or sliding center rotation
Here we have one for the right side (posterior)one forleft side (posterior)
and one forthe anteriors both left and right.
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-The quality when we use sliding or moving center rotation is much better
than when we use 3 centers of rotation or 2 centers of rotation.This is
out of our business, its related to manufacturer of x-ray machine
itselfThats why we have x-ray machine costs 10000 JD and some
might reach up to 40000 JD So increasing in the quality of the film it
will cost more.
*FOCAL TROUGH
-Focal trough: its a three dimensional curved zone in which the
structures are clearly demonstrated on panoramic radiograph.
Three-dimensional curved zone or
image layer in which structures are
reasonably well defined
Focal Trough
minimal visibility*
less sharp
sharpest
* The images of objects with minimal tissue density
are blurred and are not easily seen on film. Dense
objects, such as a bullet fragment, will still be seen.
-Structures out of the focal trough will not appear clear on theradiograph, this is imaginary, and some machines will allow you to
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choose the shape of the focal trough, so by choosing a narrow focal
trough that suits the patients jaw this is going to give you a clear
radiograph.
-If I increase the width of the focal trough the final panoramic radiographwill not be clear.*EQUIPMENT:
-The doctor started to view images about the machine that we use in our
clinic we have ways to make you see the lines.
-We have 2 lines & there are buttons to
adjust the lines like the midsagittal linewhich has to be perpendicular to thefloor. And Frankfurt line, which is comingfrom the upper border of the external
auditory meatus to the lower border or the
orbital rim, parallel to the floor.
*what you have to do when you have apatient in your clinic and you want to do a
panoramic radiograph??
1. The patient comes to you, you must
make him stand straight as tall as possible.
2. The patient should not slump
or bend since this will result in a shadow in
the middle of the radiograph.
3. The patient bites on the bite block andmake sure the teeth are edge to edge &
tongue is on the palate.
4. The tongue must be on the palate, by
asking the patient to put his tongue on the
palate or ask him to swallow. If it is not onthe palate this will obscure the clearance of
the maxillary teeth.
-The plastic side of the cassette must be
facing the tube head.
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* What is the difference between panoramic radiograph machine & intra-
oral radiographic machine?
1. itsthe collimator, the collimator in panoramic machine is a verticalnarrow slit it's not rectangular or round like normal intra-oral machines,
the collimator is in the tube head and there is also vertical slits in the
cassette.
2. The vertical angulation of the tube head in not varied. The tube head
is fixed in position so that the x-ray beam is directed slightly upward.
rotation center
filmtubehead angledupward
-Panoramic radiograph is a kind of tomography which deals with section.
You are building sections until the cycle is finished. Sometimes if the
patient is huge the tube head will stop suddenly from rotating (whichprevents some sections to appear in your final image) & other times it
will continue.
-Number of tomography images taken depends on the machine & its type.
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*HEAD POSITION
-The head position consists of:
1- A chin rest for the patients chin.
2-Notched Bite blockis there for the patient to bite on
3-Forehead rest and lateral head support. Sometimes the shadow of the
head support may appear on the radiograph.
-If you put Frankfurt line parallel with the floorand the patients forehead
on the forehead rest, then you can notice that the occlusal plane is slightlydownward inclined and the beam is slightly come downward.
-You can choose with the controllers of the machine, the control time,
voltage and mille ampere to make the radiograph. However, the machineusually comes with a fixed time.
-The extra oral film must be inside of the cassette. We have several types
of cassettes: green light cassette and blue lights cassettes and it depends
on the type of phosphor used in the extra-oral films.
-Screen spectrum must match the phosphor spectrum of the film. There
are different types of cassettes such as rigid, flexible, curved and
straight depending on the panoramic x-ray unit.
*PURPOSE & USE of OPG
1. We use it to see all the teeth in the both jaws in the same image.
2. To evaluate impacted teeth
3. To evaluate eruption patterns, growth, and Development.
4. Assessing wisdom teeth this is a very important although as I told
you nowadays due to cone-beam computed tomography (CBCT), 3D
imaging is considered the golden standard
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-In assessing the relationship between the third molar and the canal.
Using panoramic radiography you can sometimes see a shadow of the
canal superimposed on the third molars (due to loss of bone, loss of
cortical bone at that area) but this doesnt happen with CBCT.
5. To examine fractures of the mandible.
6. To Detect Diseases (periodontal diseases if there is loss of bone and
vertical healing), lesions, and conditions of the jaws.
-Its inadequate to use panorama to detect lesions, the much better is
intra-oral radiograph.
7. Assessment of locations of the objects in the jaw and permanent teethimpacted by using panoramaUsually lingually impacted looks high and
magnified
8. To examine the extent of Large lesions
9. To Evaluate Trauma. & fractures of the mandible and the
bilateral/contra-lateral condyle fracture
10. Examination of the sinuses, nasal cavity and the orbit
11. Before and after implants: usually when the patient comes to you and
he wants to do an implant, you can start by taking a panoramic radiographor periapical radiograph However, panorama is not enough because
panorama tells you if there is bone but you have to do another test by
cone beam CT to make sure.
- If panorama shows you that there is no bone then you have to stop and
ask the patient to go home.
*Advantages:1) Comfortable for the patient because there is no film inside the mouth
2) Easy to use for the incooperative patient like edentulous patients,children, old people.
3) Less exposure if you want to compare it with CMS (complete mouth
survey)
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4) Wide coverage for mandible and maxilla
5) Reduce superimposition in anatomical structures
*Disadvantages
1) Equipment cost: Initial cost of the machine is relatively high.
2) Image quality: The images of the radiograph are not sharp compared to
intra-oral images, the resolution of the panoramic image is 4 lines per
millimeter but the intra oral is 5 times sharper than panorama.
3) Objects outside the focal trough may not be evident.
4) Age limitation: Not suitable for children under 5 years of age because
of the relatively long exposure time.
5) Dark room processing (like students in the center because there is no
safe light they have to change the film in the dark each time).
6) Changing of the bite block because of hygienic purposes. It has to be
sterilized and covered.
7) Minimal bone changes cannot be detected in the panoramic radiograph
due to super imposition.
*Patient preparation
1. Explain the radiographic procedures to be performed.
2. Place lead apron, without thyroid collar in order not to block the x-
ray beam and also double sided lead apron is recommended (one thatprotect the patient from the front and the back.
3. Remove all objects from the head and neck area like earrings,
necklaces, eyeglasses, complete and partial dentures
4. Instruct the patient to Stand or sit (as tall as possible) with straight
back, the vertebral column must be straight to prevent white shadow to
appear over the middle of the radiograph (superimposition).
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5. Patient must bite a plastic bite block, the front teeth should be placed in
end to end position in the notch found on the bite block, and this groove
will align the teeth and the jaw in the focal trough area.*COMMON ERRORS
1-Ghost image: it is a radiopaque artifact seen on panoramic film thatis produced when a radiodense object penetrated twice by the X-ray
beam.
-This object is located between the source of x-ray and the rotational
center appears on the radiograph as an object indistinct, higher and
magnified
Ghost Image:
Opposite side
Same shape
Larger
Projected higher on film
Less distinct
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*Ghost Images summary:1. Image from other side of patients jaw that is seen as a blurred shadow
2. Results from radiodense objects left on patient during exposure
3. Resembles its real counterpart in shape
4. Found on opposite side of film as blurred, enlarged and higher than
actual object
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2) Wearing thyroid collar might block the x-ray beam
-Usually we let the patients wear a lead apron. This prevents photons
from interacting with any area that we dont want it to appear on the
radiograph.
-The lead apron should not be extended upward also thyroid collar should
be avoided because It will be imaged on the film and making it useless
Lead apron shadow
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3) Patient positioning errors
-The most crucial factor in getting a
correct image is patient position.
-The patient should be in correct
antero-posterior position. The patient
should not be too far forward or too far
backward. The patient should be in the
natural head position.
-The patient should also be correctly
positioned on the midsagittal plane. His
head should not be tilted or twisted...
Why?
-Because tilting or twisting the head
will cause one side to be closer to the
film while the other is farther away
from the film, this will cause magnification of the image( One side of the
image will have small teeth while the other will have larger teeth).
- To prevent this, some x-ray machines have a light which indicates the
midsagittal plane. This light will divide the nose into two equal parts and
this will help keep the midsagittal plane respected.
-Usually there is a chin rest on the x-ray machines. If the chin is down,
the upper teeth are closer to the source of x-ray. This will cause
magnification. Again there is a line on the machine that represents the
Frankfort plane or the occlusal plane. This plane should be parallel to thefloor.
*If the head is turned to the left or to the right side
-If the head turned to the right side: the right side will be smaller in
size than the left side
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-If we look at the pic we notice that the width of the ramus in the right
side is smaller
Structures smaller on the side to which head is
turned; larger on opposite side.
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*Note: When you see that there is deference in the width between the
right ramus and the left one, you must know that the patient's head was
tilted.
-Always the side next to image receptor is smaller and the opposite side is
larger.
*In both tilted and twisted we will have deference in the ramus
width, so how can we differentiate between them?
I f twistedthe 2 ramus at the same level( one ramus is larger thanthe other and the angles at the same level so it is twisted )
I f tiltedone is higher than the other ( so if one ramus higherthan the other and one is larger than the other it is tilted )
-So the deference between twisted and tilted is the level of angles!!!!!!!!
*If the patient is too far forward
So the anterior teeth will be closer to image receptor so we will have
minimum magnification decreasing of the size of ant teeth. plus the
cervical spine will be super imposed on the ramus.
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*If the patient is too far backward
So the distance between the teeth and the image receptor will increase,
the ant teeth will be larger than the normal size.
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*If the back is not erect this will produce a ghost image of the spine on
the film. This will be pyramid shaped, opaque, and in the middle. This
will often be a technical mistake. The image will be radio opaque and the
radiograph will be useless.
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Shadow of vertebral column, usually
from patient not standing straight
*If the chin is down
So the anterior teeth will be close to image receptor and the lower border
of the mandible will give us acute angle (slightly curved), anterior teeth
smaller, the spine is superimposed on the ramus
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Mandibular incisors shortened, V-shaped mandible
HEAD TIPPED DOWN
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If the chin is up:
Then the lower border of the mandible will look flat or Reverse smile, the
anterior teeth away so they will be magnified.
-If the chin is up then the hard palate will be superimposed on the apexesof the anterior teeth ((usually the hard palate appear above the apexes of
the anterior teeth))
HEAD TIPPED UP
Squared-off mandible, palate superimposed over maxillary teeth
-Exaggerated smile line of the mandible due to chin tilted down
so the incisor will appear smaller
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-We also instruct the patient to swallow and hold the tongue on the palate.
If there is a gap between the palate and the tongue, then there is going to
be an air space. This air space will not interact with the photons passing
and these photons will interact and expose the crystals on the film and
will cause radiolucency on the film
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Palatoglossal Air Space
-If the patient moves during exposure then the result will be unclear
image
-If the radiograph is not clear it's either thepatient move or the tube head
move.
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*Why the patients move?
-Usually all the patients think that the panoramic radiograph needs few
seconds like in peripical radiograph
-We must instruct the patient that the panorama will take from 1825
sec
Static electricity; caused by removing film from box
or cassette too quickly, creating static discharge
Tongue ring