"RADIOGRAPHIC SKULL SERIES"

OVERVIEW

* INTRODUCTION * MID-FACE SERIES

* INDICATIONS * LOWER FACE SERIES

* EQUIPMENT * OTHER MEDICAL PROJECTIONS

* DEFINITIONS * OTHER DENTAL PROJECTIONS

* FRACTURES * HELPFUL HINTS

1. INTRODUCTION

1. Extraoral radiographic examinations include all views of the orofacial region with films positioned extraorally.
2. Importance to the Comprehensive Dentist:

- Federal Service Boards

- Maxillofacial trauma

- diagnosis

- communication

1. INDICATIONS FOR EXTRAORAL RADIOGRAPHS

1. Facial trauma

-Extraoral radiographs are used to confirm the suspected clinical diagnosis.

-High resolution CT is the imaging procedure of choice.

Lateral view, and Submentovertex view.

B. Pathology

-Tumors, cysts, etc.

C. Orthodontics

-To assess skeletal growth.

1. DEFINITIONS

Cephalometric radiography - head measurement x-ray; taken using a cephalostat [head-holding

device] in a precise manner so it can be repeated at a later date for comparison

The first word of the description of the x-ray is where the tube is; the second word is where the

film is, i.e. a PA film has the tube at the back of the head [posterior] and the film is placed by the face [anterior]

Tube side is always superimposed

Exposure factors - kVp, exposure time, mA and source-to-film distance

kVp - the potential difference between the cathode and anode of an x-ray tube; the energy of the beam x-rays lower than 65 kVp are seldom used in dentistry

mA - 1/1000 of an ampere; refers to the current flow from the cathode to the anode, which, in turn, regulates the intensity of radiation emitted by the x-ray tube and, hence, directly influences the radiographic density

exposure time - length of time the x-rays are actually produced

"Rule of 15" - for every 15% increase in kVp, the density on the x-ray will double. If the kVp is

increased by 15 then the time must be reduced by ½ to maintain the same density

2. FRACTURES

¶ Simple - break in bone ONLY and one that does not involve the skin externally or the

mucous membrane internally

Ë Compound - does involve the skin or the mucous membrane, which enhances risk of

infection

Ì Comminuted - number of small fractures at fracture site

Í Greenstick - splintered like a twig

• LeFort I [horizontal] - 15%

• Alveolar Ridge is separated from the maxilla
• the width of the maxilla and the pterygoid plates

• Le Fort II [pyramidal] – 10%

• Medial orbital areas and nasal bone
• involves the suture lines between the maxilla and the frontal and lacrimal [to include the nasal bones], perisuturally the zygomaticomaxillary interfaces and the infraorbital rim and floor of the orbit; CSF LEAK

Ì Le Fort III [craniofacial disjunction] – 10%

• Midface separation:

Fracture extends through the medial and lateral orbital walls and the zygoma

• fracture through the frontomaxillary and nasal sutures, the frontozygomatic sutures, the

zygomatic arch, the floor of the orbits, the ethmoids and the lacrimals; CSF LEAK

Í Fracture of the Orbital Floor [blow-out fracture]

• fracture of the inferior orbital floor into the maxillary antrum
• RIM STAYS INTACT

V. EQUIPMENT

A. X-ray units

-Conventional dental x-ray machines

-Some types of panoramic machines.

-Large x-ray units designed specifically for extraoral radiographs.

B. Film and intensifying screens

-Basic process:

photons**Film**Intensifying screen(fluoresce)+Photon(x-ray)à exposes the x-ray film

-Medium or high speed screen film

-Intensifying screens in combination with film result in an image receptor system 10 to 60 times

more sensitive to x-rays than film alone. Bottom line is less exposure of radiation to the patient.

-Film size: Skull films are 8x10 inches. Lateral oblique views of mandible are 5x7 inches.

-Process either in conventional wet tank or an automatic processor.

C. Patient positioning

-Cephalostat (head positioning device)

-Skeletal landmarks (canthomeatal line) central point of the external auditory meatus to the

outer canthus of the eye. Easily visualized by the technician and is used as a reference

line for positioning the central ray to the film.

VI. TRAUMA TO THE MAXILLA: MID-FACE SERIES

1. Waters: (Occipitomental projection)

-variation of the posterior anterior projection.

-Best view for evaluating facial fractures.

-Zygomatic arches, orbital rims and floors, nasal spine and septum, coronoid processes.

-Can also be used for evaluating the frontal, maxillary, and sphenoid sinuses.

-Trace the lines of Dolan and the elephants of Rogers

-cassette held by a holding device vertically

-example: sagittal plane is perpendicular to the plane of the film; chin is raised 37° so that

canthomeatal line is 37° to the deck; beam is directed at the level of the maxillary sinus;

75-80 kVp

2. Posterior-anterior:

-examines skull for disease, trauma, developmental abnormalities or provides a good

record to detect progressive changes in mediolateral dimensions of skull

-can be used to evaluate orbital rim, frontal and ethmoid sinuses, nasal septum, nasal fossa

and orbits; invaluable in detecting a fracture-dislocation

-cassette held by a holding device vertically

3. Submentovertex:

-view used to evaluate fractures and displacement of a fractured zygomatic arch

-contraindicated with patients who have a suspected spinal injury

-reveals the position and orientation of the condyles, the sphenoid sinus, the curvature

of the mandible, the lateral wall of the maxillary sinuses

-good visualization of the base of the skull with foramina and the medial and lateral

pterygoid plates

- cassette held by a holding device vertically

-example: hyperextend neck backwards as far as possible until the vertex of the head is

centered on the film; the canthomeatal line is projected 10° past vertical so the Frankfurt

plane is parallel to the film; beam is directed from below the mandible upward to the vertex;

4. Lateral Skull (Cephalometric):

-Used to survey the skull and facial bones for evidence of disease, trauma, developmental

abnormalities, in ortho. used for assessing head growth

-Proper patient positioning is essential: when truly lateral, the lack of superimposition of the

normally superimposed structures suggests a fracture with displacement of fractured

segments.

-Anterior/posterior walls of the frontal and maxillary sinuses, nasopharyngeal soft tissues,

paranasal sinuses and hard palate; are also delineated in this view

-cassette held by a holding device vertically

-example: head is positioned with left side of face near the cassette and the midsagittal plane

parallel to the plane of the film; source of beam [the tube] is 60" from the midsagittal plane of

the patient; to reveal the soft tissue outline

-use either a wedge filter to reduce the radiation intensity in the anterior region or a cassette

with intensifying screens which provide reduced fluorescence in the area; 75-80 kVp

VII. TRAUMA TO THE MANDIBLE: LOWER FACE SERIES

1. Panorex: Best single view short of a CT for viewing the mandible.

-View of choice for viewing condyles.

2. Lateral Oblique: Excellent for viewing the mandibular body and ramus

- film-5x7 screen film usually hand held horizontally by patient

-views premolar, molar and inferior border of the mandible; broader than PA’s

-example: Body Of Left Mandible [right to left]

x-ray tube [aimed under right side of mandible] Þ head tilted to left

Þ cassette held against side of face by patient parallel to border of mandible and extending

2 cm below it [centered on 1^st molar]; 65 kVp, 10 mA

-views ramus from the angle of the mandible to the condyle; useful for ­ / ¯ 3rds

-example: Ramus of Left mandible [right to left]

x-ray tube [aimed under right side of mandible] Þ head tilted to left until a line from the right

angle of the mandible to the left condyle is parallel to the deck

Þ protrude the mandible...keeps the spine out of the view

Þ cassette held against side of face [ramus] by patient and extending 2 cm below the

inferior border of the mandible; 65 kVp, 10 mA

3. Towne's: (anterior-posterior projection)

. -AP view w/ 30° tilt of the tube caudally

-view can be used to observe condyles, necks, rami and mandibular symphysis

-also visualized: occipital bone, foramen magnum, dorsum sellae and petrous ridges

-cassette held by a holding device vertically

4. Reverse Towne's: (Modified Towne’s)

-Posterior-Anterior view, mouth open

-View can be used to observe fractures involving the condylar neck, and also when

displacement of the condyle is suspected

-good visualization of the posterolateral wall of the maxillary antrum

-cassette held by a holding device vertically

-example: head is centered in front of film with the canthomeatal line projected 25° -30° downward; beam goes through the occipital bone; 75-80 kVp

5. Posterior-Anterior: View used to observe the mandibular angle and body.

VIII. OTHER RADIOGRAPHS CONSIDERED BY MEDICAL

1. BONES OF THE CALVARIUM

Caldwell’s Projection

- PA view w/ 15° tilt of the tube caudally

- advantage over straight PA - view of orbits unobstructed by petrous ridges

Straight PA

- bones are undistorted in frontal projection

Towne’s Position

- AP view w/ 30° tilt of the tube caudally

- good for occipital bone, foramen magnum, dorsum sellae and petrous ridges; also status

of condyles, necks and rami because superimposition of mastoid and zygoma over

neck in the straight PA makes interpretation difficult

Lateral Projections [Left & Right] (CEPHS)

-best for sella turcica

Vertico-submental [Axial view]

-base of skull and foramina

2. FACIAL BONES APART FROM THE NOSE

Water’s Projection - PA view w/ the nose raised 2-3 cm and the chin on the film

best view for maxilla, zygoma, orbits and nasal cavity

Submento-vertical [Axial view]

-lighter exposure; allows better view of maxilla and zygoma than vertico-submental

Lateral Projection - includes the whole face

3. MANDIBLE

Straight PA

Lateral Oblique

Special views of the TMJ [open and closed mouth]-discussed next section

Occlusal view – Occlusal film placed between teeth, beam from under mandible

Panorex-discussed next section

¶ Transpharygeal Projection

- film-5x7 screen film [usually held vertically] hand held by patient

- provides an excellent "scout" view of gross changes on the condylar surfaces

- example for left TMJ

patient’s midsagittal plane perpendicular to deck

Þ rotate head 7° -10° away from the cassette [moves opposite condyle out of the way]

Þ cassette held against ear and cheekbone on left side of face by patient

mouth can be opened or closed

Þ x-ray tube directed -5° , beneath the zygomatic arch on right

Ë Transorbital Projection

- cassette held by a holding device vertically [cephalostat]

- frontal radiograph

- medial and lateral aspect of condyle, the neck, the eminence and sometimes the zygomatic arch

- example for left TMJ

patient is seated with midsagittal plane perpendicular to deck and Frankfort plane

parallel to the deck

Þ cassette is placed behind the left TMJ Þ turn head 20° to the left

Þ x-ray tube directed +35° , from the front through the floor of the left orbit and left TMJ

Ì Transcranial Projection

- film-5x7 screen film [usually held vertically] and is hand held by patient

- provides a view down the long axis of the condyle and the relationship of the condyle

to the fossa

- example for left TMJ - patient’s midsagittal plane perpendicular to deck

Þ cassette held against ear and cheekbone on left side of face by patient

Þ x-ray tube [directed +25,1/2" behind and 2" above the right external auditory meatus

2. PANOREX

- Correctly called a pantomograph or a panoramic radiograph; Panorex the brand name of the first

panoramic machine introduced to North America by the S.S. White Co. in 1959

- The area where the images are sharp is a 3D horseshoe shaped zone called the focal trough,

image layer, zone of sharpness, central image layer; therefore, correct patient positioning is

critical

- Frankfort plane parallel to the deck, the midsagittal plane, perpendicular to the deck, and the

teeth in the focal trough

- Real image - object lies between the center of rotation and the film

X. Helpful Hints for Reading Extraoral Films - Facial fractures

Radiographic examination should document fractures from two different angles.

Know the most common patterns of facial fractures

In an operational environment, the comprehensive dentist should be familiar with the four basic medical views: Waters, Posterior-Anterior, Lateral, and the Submentovertex for evaluating facial trauma.

References:

Dolan, Jacoby and Smoker; Radiology of Facial Injury, Field and Wood, Inc., 1988

Goaz and White, Oral Radiology- Principles and Interpretation, C. V. Mosby Co., 1987

Langlais and Kasle, Exercises in Oral Radiographic Interpretation, W. B. Saunders Company, 1985

Langland, Langlais and Morris, Principles and Practice of Panoramic Radiology, W. B. Saunders

Company, 1982

Meschan, Normal Radiographic Anatomy, W. B. Saunders Co., 1959

Miles, Van Dis, Jensen and Ferretti; Radiographic Imaging for Dental Auxiliaries, W. B. Saunders