Download File - Dentistry Notes

Contents
Introduction
History
Indications
Advantages
Disadvantages
Principles of panoramic image formation
Rotation center
Focal trough
Equipment
Step by step procedures
Common errors
Normal anatomic landmarks of maxilla
Normal anatomic landmarks of mandible
Air space images seen on panoramic radiographs
Soft tissue images seen on panoramic radiographs
Introduction
Panoramic radiography is an extraoral radiographic technique that is used to examine the
upper and lower jaws on a single film. This is a curvilinear variant of conventional
tomography and is also based on the principle of reciprocal movement of an x-ray source and
an image receptor around a central plane, called the image layer, in which the object of
interest is located.
The movement of the film and tubehead produces an image through the process known as
tomography. The term tomo means section; tomography is a radiographic technique that
allows the imaging of one layer or section of the body while blurring images from structures
in other planes.
History
•
Dr H Numata of Japan in 1933 and later, Dr YV Paatero of Finland in 1948 first gave
the techniques of rotational panoramic radiography.
•
In 1985, Kashima et al reported the implementation of computed panoramic
radiography.
•
Later, McDavid et al introduced direct digital panoramic imaging using a linear array
of silicon photodiodes.
Indications
1. To evaluate impacted teeth.
2. To evaluate eruption patterns, growth and development.
3. To detect diseases, lesions and conditions of jaws.
4. To determine the extent of large lesions.
5. To evaluate trauma
Advantages
1. Broad coverage of facial bones and teeth.
2. Low patient radiation dose.
3. Convenience of examination for the patient.
4. Ability to be used in patients unable to open their mouth.
5. Short time required to make a panoramic image, usually in the range of 3 to 4
minutes.
6. Patient’s ready understandability of panoramic films, making them a useful
visual aid in patient education and case presentation.
Disadvantages
1. Does not display fine anatomic detail available on intraoral periapical
radiographs. So not useful in detecting small carious lesions, fine structure of
marginal periodontium, or periapical disease.
2. Unequal magnification and geometric distortion across the image.
3. Occasionally the presence of overlapping structures, such as cervical spine,
can hide the odontogenic lesions, particularly in the incisor region.
4. Clinically important objects may be situated outside the plane of focus and
may appear distorted or not present at all.
Principles of panoramic image formation
In panoramic radiography the film and x-ray tubehead move around the patient. The
x-ray tube rotates around the patient’s head in one direction while the film rotates in
the opposite direction. The patient may stand or sit in a stationary position, depending
on the type of panoramic x-ray machine that is used.
During exposure cycle, the machine automatically shifts to one or more additional
centers of rotation. The rate of movement of receptor behind the lead collimator slit is
regulated to be the same as that of the central ray sweeping through the dental
structures on the side of the patient nearest the receptor. Structures on the opposite
side of the patient (near the x-ray tube) are distorted and appear out of focus because
x-ray beam sweeps through them in the direction opposite that in which the image
receptor is moving. In addition, structures near the x-ray source are so magnified (and
their borders so blurred) that they are not seen as discrete images on the resultant
image. These structures only appear as diffuse phantom or ghost images. Because of
both these circumstances, only structures near the receptor are usefully captured on
the resultant image. Structures located more centrally in the body relative to the jaws,
such as hyoid bone and epiglottis, appear on the right, left and sometimes central
areas of final image.
Rotation center
In panoramic radiography, the film or cassette carrier and x-ray tubehead are
connected and rotate simultaneously around a patient during exposure. The pivotal
point, or axis, around which the cassette carrier and x-ray tubehead rotate is termed a
rotation center.
Depending on the manufacturer, the number and location of rotational canters differ.
Three rotation centers used in the panoramic x-ray machines are as follows:
1. Double center rotation
2. Triple center location
3. Moving center rotation
Double center rotation: there are two centers of rotation. One is for the right and one for the
left side of the jaws.
Triple center rotation: there are three center of rotation and create an uninterrupted
radiographic image of the jaws.
Moving center rotation: machine rotate around a continuously moving center that is similar
to the arches, creating an uninterrupted image of the jaws.
Focal trough (image layer)
In panoramic radiography, the focal trough is a theoretical concept used to determine where
the dental arches must be positioned to achieve the clearest image.
The focal trough can be defined as a three-dimensional curved zone in which structures are
clearly demonstrated on a panoramic radiograph. The structures located within the focal
trough appear reasonably well defined on the resulting panoramic radiograph. The structures
located inside or outside of the focal trough appear blurred or indistinct and are not readily
visible on the panoramic film.
The shape of the image layer varies with the brand of equipment used. The factors that affect
its size are variables that influence image definition: arc path, velocity of the receptor and xray tubehead, alignment of the x-ray beam, and collimator width.
The closer the rotation center is to the teeth, the narrower the focal trough. In most panoramic
x-ray machines, the focal trough is narrow in the anterior region and wide in the posterior
region.
Equipment
Equipment includes:
1. Panoramic x-ray unit
2. Screen films
3. Intensifying screens
4. Cassette
Panoramic x-ray unit:
The main components of the panoramic unit include the following:
1. X-ray tubehead
2. Head positioner
3. Exposure controls
X-ray tubehead: similar to an intraoral x-ray tubehead. Each has a filament used to
produce electrons and a target used to produce x-rays.
Collimator: the collimator used in the panoramic x-ray machine is a lead plate with an
opening in the shape of a narrow vertical slit. The function of collimator is to restrict the
size and shape of the x-ray beam. The narrow x-ray beam that emerges from the
collimator minimizes patient exposure to x-radiation.
Head positioner: it consists of a chin rest, notched bite-block, forehead rest, and lateral
head supports or guides.
Exposure factors: the milliamperage and kilovoltage settings are adjustable and can be
varied to accommodate patients of different sizes. The exposure time, however, is fixed
and cannot be changed.
Screen film:
Screen film is used in panoramic radiography. This film is sensitive to the light emitted
from intensifying screens. A screen film is placed between two intensifying screens in a
cassette holder. When the cassette holder is exposed to x-rays, the screens convert the xray energy into light, which in turn exposes the screen film. Some screen films are
sensitive to green light whereas others are sensitive to blue light.
The film used in panoramic radiography is available in two sizes: 5x12 inch and 6x12
inch.
Intensifying screens:
Two basic types of intensifying screens: calcium tungstate and rare earth.
Calcium tungstate screens emit blue light, and rare earth screens emit green light. Rare
earth screens require less x-ray exposure than calcium tungstate screens and are
considered ‘faster.’
Cassette:
It is the device that is used to hold the extraoral film and intensifying screens. The
cassette may be rigid or flexible, curved or straight, depending on the panoramic x-ray
unit. All cassettes must be ‘light-tight’ to protect the film from exposure.
The cassette must be marked to orient the finished the radiograph. Before exposure, a
metal letter “R” can be attached to the front of cassette to indicate the patient’s right side;
the letter “L” is used to identify the patient’s left side.
Step by step procedures
Equipment preparation:
1. Load the panoramic cassette in the darkroom under the safelight condition.
2. Cover the bite-block with a disposable plastic coverslip.
3. Set the exposure factors (kilovoltage, milliamperage) according to the manufacturer’s
recommendations.
Patient preparation:
1. Place a lead apron, without a thyroid collar, on the patient and secure it. A doublesided apron is recommended.
2. Remove all objects from the head and neck area that may interfere with film
exposure. The patient must remove eyeglasses, earrings, necklaces, napkin chains,
hearing aids, hairpins, and complete and partial dentures.
Patient positioning:
1. Instruct the patient to stand or sit with the back straight and erect.
2. Instruct the patient to bite on the bite-block. The upper and lower front teeth must be
placed in an end to end position in the groove (notch) that is found on the bite-block.
This groove is used to align the teeth in focal trough.
3. Position the midsagittal plane perpendicular to the floor. The patient’s head must not
be tipped or tilted.
4. Position the Frankfort plane parallel with the floor.
5. Instruct the patient to position the tongue on the roof of the mouth.
6. After the patient has been positioned, instruct the patient to remain still while the
machine is rotating during exposure.
7. Expose the film and proceed with film processing.
Common errors
Patient preparation errors:
Ghost images
Ghost images: ghost image is a radiopaque artifact seen on a panoramic film that is produced
when a radiodense object is penetrated twice by the x-ray beam. A ghost image resembles its
real counterpart and is found on the opposite side of the film; it appears indistinct, larger, and
higher than its actual counterpart.
It occurs when metallic or radiodense objects (eyeglasses, earrings, necklaces, hairpins,
removable partial dentures, complete dentures, orthodontic retainers, hearing aids) are not
removed before the exposure is made.
Solution: instruct the patient to remove all radiodense objects in the head and neck region
before positioning the patient.
Lead apron artifact: if the lead apron is incorrectly placed, or if a lead apron with a thyroid
collar is used during the exposure, a radiopaque cone-shaped artifact results.
Solution: always use a lead apron without a thyroid collar. The lead apron must be placed low
around the neck of the patient so that it does not block the x-ray beam.
Patient positioning errors:
Teeth placed too posterior on bite-block
Positioning of Frankfort plane upward: if the patient’s chin is positioned too high or tipped
up, the Frankfort plane is angled upward, and the following results1. The hard palate and floor of the nasal cavity appear superimposed over the roots of
the maxillary teeth.
2. There is a loss of detail in the maxillary incisor region.
3. The maxillary incisors appear blurred and magnified.
4. A “reverse smile line” (curved downward) is apparent on the radiograph.
Solution: carefully position the patient so that the Frankfort plane is parallel with the floor.
Positioning the Frankfort plane downward: if the patient’s chin is positioned too low or is
tipped down, the Frankfort plane is angled downward and following results1. The mandibular incisors appear blurred.
2. There is a loss of detail in the anterior apical regions.
3. The mandibular condyles may not be visible.
4. An “exaggerated smile line” (curved upward) is apparent on the radiograph.
Solution: carefully position the patient so that the Frankfort plane is parallel with the floor.
Positioning of teeth anterior to focal trough: If the patient’s anterior teeth are positioned
too far forward on the bite-block or anterior to the focal trough, the anterior teeth appear
“skinny” and out of focus on the radiograph.
Solution: position the patient so that the anterior teeth are placed in an end to end position in
groove on the bite-block.
Positioning of teeth posterior to focal trough: if the patient’s teeth are positioned too far
back on the bite-block or posterior to the focal trough, the anterior teeth appear “fat” and out
of focus on the radiograph.
Solution: position the patient so that anterior teeth are placed in an end to end position in the
groove on the bite-block.
Positioning of midsagittal plane: if the patient’s head is not centered, the ramus and
posterior teeth appear unequally magnified on the panoramic radiograph. The side farthest
from the film appears magnified, and the side closest to the film appears smaller.
Solution: position the patient’s head so that the midsagittal plane is perpendicular to the floor
while the midline is centered on the bite-stick.
Positioning of spine: if patient is not standing or sitting with a straight spine, the cervical
spine, the cervical spine appears as a radiopacity in the center of the film and obscures
diagnostic information.
Solution: instruct the patient to stand or sit “as tall as possible” with a straight back.
Miscellaneous problems:
Static electricity: Static electricity appears as black lines or dots on the film, often having a
tree-branch appearance. It is caused by removing the film from the box or cassette too
quickly, creating static discharge.
Failure to remove appliances: Failure to remove complete upper denture before exposure.
Failure to remove glasses
Slight movement of the patient
Double exposure
Normal anatomic landmarks of maxilla
Normal anatomic landmarks of maxilla and surrounding structures: 1. mastoid process, 2. styloid process, 3.
external auditory meatus,4. glenoid fossa, 5. articular eminence, 6. lateral pterygoid plate, 7. pterygomaxillary
fissure, 8. maxillary tuberosity, 9. infraorbital foramen, 10. orbit, 11. incisive canal, 12. incisive foramen, 13.
anterior nasal spine, 14. nasal cavity, 15. nasal septum, 16. hard palate, 17. maxillary sinus, 18. floor of
maxillary sinus, 19. zygomatic process of maxilla, 20. zygomatic arch, 21. hamulus
Mastoid process: it is a marked prominence of bone located posterior and inferior to the
temporomandibular joint(TMJ).
Radiographic appearance: it appears as a rounded radiopacity located posterior and inferior
to tha TMJ area. It is not seen on periapical radiograph.
External auditory meatus: it is a hole or opening in the temporal bone located superior and
anterior to the mastoid process.
Radiographic appearance: it appears as a round to ovoid radiolucency anterior and superior
to the mastoid process. The external auditory meatus is not seen on the periapical
radiographs.
Styloid process: it is a long, pointed, and sharp projection of bone that extends downward
from the inferior surface of the temporal bone anterior to the mastoid process.
Radiographic appearance: on a panoramic radiograph, it appears as a long radiopaque spine
that extends from the temporal bone anterior to the mastoid process. It is not seen on
periapical radiograph.
Glenoid fossa: also known as mandibular fossa. It is a concave, depressed area of the
temporal bone. The mandibular condyle rests in the glenoid fossa. The glenoid fossa is
located anterior to the mastoid process and external auditory meatus.
Radiographic appearance: it appears as a concave radiopacity superior to the the mandibular
condyle. The glenoid fossa is not seen on periapical radiographs.
Articular eminence: also known as articular tubercle. It is a rounded projection of the
temporal bone located anterior to the glenoid fossa.
Radiographic appearance: it appears as a rounded radiopaque projection of the bone located
anterior to the glenoid fossa. It is not seen on the periapical radiographs.
Lateral pterygoid plate: it is a wing shaped bony projection of the sphenoid bone located
distal to the maxillary tuberosity region.
Radiographic appearance: it appears as a radiopaque projection of bone distal to the
maxillary tuberosity region. It is not seen on periapical radiographs.
Pterygomaxillary fissure: it is a narrow space or cleft that separates the lateral pterygoid
plate and the maxilla.
Radiographic appearance: it appears as a radiolucent area between the lateral pterygoid plate
and the maxilla. The zygoma is often superimposed on this region and obscures the
pterygomaxillary fissure. This is not seen on periapical radiographs.
Maxillary tuberosity: it is a rounded prominence of bone that extends posterior to the third
molar region.
Radiographic appearance: it appears as a radiopaque bulge distal to the third molar region.
Infraorbital foramen: it is a hole or opening in bone found inferior to the border of the orbit.
Radiographic appearance: the infraorbital foramen appears as a round or ovoid radiolucency
inferior to the orbit. It may be superimposed over the maxillary sinus. It is not seen on the
peripaical radiograph.
Orbit: it is the bony cavity that contains the eyeball.
Radiographic appearance: it appears as a round radiolucent compartment with radiopaque
borders located superior to the maxillary sinuses. On most panoramic radiographs, only the
inferior border of the orbit is visible, where it appears as a radiopaque line.
Incisive canal: also known as nasopalatine canal. It is a passageway through bone that
extends from the superior foramina of incisive canal to the incisive foramen.
Radiographic appearance: the incisive canal appears as a tube like radiolucent area with
radiopaque borders. It is located between the maxillary central incisors.
Incisive foramen: also known as nasopalatine foramen. It is an opening or hole in bone that
is located at the midline of the anterior of the hard palate directly posterior to the maxillary
central incisors.
Radiographic appearance: it appears as a small, ovoid or round radiolucency located
between the roots of the maxillary central incisors.
Anterior nasal spine: it is a sharp bony projection of the maxilla located at the anterior and
inferior portion of the nasal cavity.
Radiographic appearance: it appears as a V-shaped radiopaque area located at the
intersection of the floor of the nasal cavity and the nasal septum.
Nasal cavity: also known as nasal fossa. It is a pear shaped compartment of bone located
superior to the maxilla.
Radiographic appearance: it appears as a large radiolucent area above the maxillary incisors.
Nasal septum: it is a vertical bony wall or partition that divided the nasal cavity into the right
and left nasal fossae.
Radiographic appearance: it appears as a vertical radiopaque partition that divides the nasal
cavity.
Hard palate: it is the bony wall that separates the nasal cavity from the oral cavity.
Radiographic appearance: it appears as a horizontal radiopaque band superior to the apices
of the maxillary teeth.
Maxillary sinus and floor of maxillary sinus: the maxillary sinuses are paired cavities or
compartments of bone located within the maxilla and are located above the maxillary
premolar and molar teeth.
Radiographic appearance: the maxillary sinuses appear as paired radiolucent areas located
above the apices of the maxillary premolars and molars. The floor of the maxillary sinus is
composed of dense cortical bone and appears as a radiopaque line.
Zygomatic process of maxilla: it is a bony projection of the maxilla that articulates with the
zygoma, or malar bone.
Radiographic appearance: it appears as a J- or U-shaped radiopacity located superior to the
maxillary first molar region.
Zygoma: also known as malar process. It is the cheek bone and articulates with the
zygomatic process of the maxilla.
Radiographic appearance: it appears as a radiopaque band that extends posteriorly from the
zygomatic process of the maxilla.
Hamulus: also known as hamular process. It is a small, hook like projection of bone that
extends from the pterygoid plate of the sphenoid bone.
Radiographic appearance: it appears as a radiopaque hook like projection posterior to the
maxillary tuberosity area.
Normal anatomic landmarks of mandible
Normal anatomic landmarks of mandible and surrounding structures: 1. condyle, 2. coronoid notch 3. coronoid
process, 4. mandibular foramen, 5. lingula, 6. mandibular canal, 7. mental foramen, 8. hyoid bone, 9. mental
ridge, 10. mental fossa, 11. lingual foramen, 12. genial tubercle, 13. inferior border of mandible, 14. mylohyoid
ridge, 15. internal oblique ridge, 16. external oblique ridge
Mandibular condyle: it is a rounded projection of bone extending from the posterior
superior border of the ramus of the mandible. The mamndibular condyle articulates with the
glenoid fossa of the temporal bone.
Radiographic appearance: it appears as a bony, rounded radiopaque projection extending
from the posterior border of the ramus of the mandible. It is not seen on the periapical
radiographs.
Coronoid notch: it is a scooped-out concavity of bone located distal to the coronoid process
of the mandible.
Radiographic appearance: it appears as a radiopaque concavity located distal to the coronoid
process of the mandible. It is not seen on periapical radiographs.
Coronoid process: it is a marked prominence of bone found on the anterior superior ramus
of the mandible.
Radiographic appearance: it appears as a triangular radiopacity posterior to the maxillary
tuberosity region.
Mandibular foramen: it is a round or ovoid hole in bone on the lingual aspect of the ramus
of the mandible.
Radiographic appearance: it appears as a round or ovoid radiolucency centered within the
ramus of the mandible. It is not seen on periapical radiographs.
Lingula: it is a small, tongue-shaped projection of bone seen adjacent to the mandibular
foramen.
Radiographic appearance: it appears as an indistinct radiopacity anterior to mandibular
foramen. It is not seen on the periapical radiographs.
Mandibular canal: it is a tube lioke passageway through bone that travels the length of the
mandible. It extends from the mandibular foramen to the mental foramen.
Radiographic appearance: it appears as a radiolucent band outlined by two thin radiopaque
lines representing the cortical walls of the canal.
Mental foramen: it is an opening or hole in bone located on the external surface of the
mandible in the region of mandibular premolars.
Radiographic appearance: it appears as a small, ovoid or round radiolucency located in the
apical region of the mandibular premolars.
Mental ridge: it is a linear prominence of cortical bone located on the external surface of the
anterior portion of the mandible that extends from the premolar region to the midline.
Radiographic appearance: it appears as a thick radiopaque band that extends from
mandibular premolar region to the incisor region.
Mental fossa: it is a scooped-out depressed area of bone located on the external surface of
the anterior mandible above the mental ridge in the mandibular incisor region.
Radiographic appearance: it appears as a radiolucent area above the mental ridge.
Lingual foramen: it is a tiny opening or hole in bone located on the internal surface of the
mandible near the midline.
Radiographic appearance: it appears as a small radiolucent dot located inferior to the apices
of the mandibular incisors.
Genial tubercles: these are the tiny bumps of bone located on the lingual aspect of the
mandible.
Radiographic appearances: they appear as a ring-shaped radiopacity surrounding the lingual
foramen.
Inferior border of mandible: it is a linear prominence of cortical bone that defines the lower
border of the mandible.
Radiographic appearance: it appears as a dense radiopaque band that outlines the lower
border of the mandible.
Mylohyoid ridge: it is a linear prominence of bone located on the internal surface of the
mandible that extends from the molar region downward and forward toward the lower border
of the mandibular symphysis.
Radiographic appearance: it appears as a dense radiopaque band that extends downward and
forward from the molar region.
Internal oblique ridge: it is a linear prominence of bone located on the internal surface of
the mandible that extends downward and forward from the ramus.
Radiographic appearance: it appears as a dense radiopaque band that extends downward and
forward from the ramus.
External oblique ridge: it is a linear prominence of bone located on the external surface of
the body of the mandible.
Radiographic appearance: it appears as a dense radiopaque band that extends downward and
forward from the anterior border of the ramus of the mandible.
Angle of mandible: it is the area of the mandible where the body meets the ramus.
Radiographic appearance: it appears as a radiopaque bony structure where the ramus joins
the body of the mandible.
Air space images seen on panoramic radiographs
Palatoglossal air space: it refers to the space found between the palate (palato) and tongue
(glossal).
Radiographic appearance: it appears as a horizontal radiolucent band located above the
apices of the maxillary teeth.
Nasopharyngeal air space: it refers to the portion of the pharynx (pharyngeal) located
posterior to the nasal cavity (naso).
Radiographic appearance: it appears as a diagonal radiolucency located superior to the
radiopaque shadow of the soft palate and uvula.
Glossopharyngeal air space: it refers to the portion of the pharynx (pharyngeal) located
posterior to the tongue (glosso) and oral cavity.
Radiographic appearance: it appears as a vertical radiolucent band superimposed over the
ramus of the mandible. It is continuous with the nasopharyngeal air space superiorly and the
palatoglossal air space inferiorly.
Soft tissue images seen on panoramic radiographs
Soft tissue images seen on panoramic films: 1. tongue, 2. soft palate and uvula, 3. lipline, 4. ear
Tongue: it is a movable muscular organ located to the floor of the mouth.
Radiographic appearance: it appears as a radiopaque area superimposed over the maxillary
posterior teeth.
Soft palate and uvula: they form a muscular curtain that separates the oral cavity from the
nasal cavity.
Radiographic appearance: it appears radiopaque extending posteriorly from hard palate over
each ramus.
References
•
White and Pharoah 6th edition
•
Haring and Howerton 3rd edition
•
www.harpercollege.edu
•
www.monroecc.edu
•
www.dent.ohio-state.edu