extra oral radiograph
TRANSCRIPT
Skull Radiography
• Lateral cephalometric projection
• Posteroanterior projection
• Water’s projection
• Submentovertex projection
• Reverse Towne’s projection
Main indications
• Fractures of the maxillofacial skeleton
• Fractures of the skull
• Investigation of the antra
• Diseases affecting the skull base and vault
• TMJ disorders.
Main maxillofacial/skull projections
Standard occipitomental (0° OM) • 30° occipitomental (30° OM) • Postero-anterior of the skull (PA skull) sometimes referred to as occipitofrontal (OF) • Postero-anterior of the jaws (PA jaws) • Reverse Towne's • Rotated postero-anterior (rotated PA) • True lateral skull • Submento-vertex (SMV) • Transcranial • Transpharyngeal.
Standard occipitomental (0° OM)
• This projection shows the facial skeleton and
• maxillary antra., and avoids superimposition of the
• dense bones of the base of the skull.
The main clinical indications include: Investigation of the maxillary antra Detecting the following middle third facial fractures: — LeFortI — Le Fort II — Le Fort III — Zygomatic complex — Naso-ethmoidal complex — Orbital blow-out Coronoid process fractures • Investigation of the frontal and ethmoidal sinuses • Investigation of the sphenoidal sinus (projection needs to be taken with the patient's mouth open).
Technique and positioning
1. The patient is positioned facing the film with
the head tipped back so the radiographic baseline
is at 45° to the film, the so-called nose-chin position. This positioning drops the dense bones of the base of the skull downwards and raises the facial bones so they can be seen.
2. The X-ray tube head is positioned with the
central ray horizontal (0°) centered through the
occiput
30° occipitomental (30° OM)
• This projection also shows the facial skeleton, but
• from a different angle from the 0° OM, enabling
• certain bony displacements to be detected.
Main indications
• Detecting the following middle third facial
fractures:
— LeFortI
— Le Fort II
— Le Fort III
• Coronoid process fractures.
Technique and positioning
1. The patient is in exactly the same position as
for the 0° OM, i.e. the head tipped back, radiographic baseline at 45° to the film, in the nose-chin position.
2. The X-ray tube head is aimed downwards
from above the head, with the central ray at 30° to
the horizontal, centered through the lower border
of the orbit
Postero-anterior of the skull (PA skull)
This projection shows the skull vault, primarily
the frontal bones and the jaws.
Main indications
• Fractures of the skull vault
• Investigation of the frontal sinuses
• Conditions affecting the cranium, particularly:
— Paget's disease
— multiple myeloma
— hyperparathyroidism
• Intracranial calcification.
Technique and positioning
1. The patient is positioned facing the film with the head tipped forwards so that the forehead and tip of the nose touch the film — the so-called forehead-nose position. The radiographic baseline is horizontal and at right angles to the film. This positioning levels off the base of the skull and allows the vault of the skull to be seen without superimposition. 2. The X-ray tube head is positioned with the central ray horizontal (0°) centered through the occiput .
Postero-anterior of the jaws (PA jaws/PA mandible)
• This projection shows the posterior parts of the
• mandible. It is not suitable for showing the facial
• skeleton because of superimposition of the base of
• the skull and the nasal bones.
Main indications
• Fractures of the mandible involving the following sites: — Posterior third of the body — Angles — Rami — Low condylar necks • Lesions such as cysts or tumors in the posterior third of the body or rami to note any medio-lateral expansion • Mandibular hypoplasia or hyperplasia • Maxillofacial deformities.
Technique and positioning
1. The patient is in exactly the same position as
for the PA skull, i.e. the head tipped forward, the
radiographic baseline horizontal and perpendicular
to the film in the forehead-nose position.
2. The X-ray tube head is again horizontal (0°),
but now the central ray is centered through the cervical spine at the level of the rami of the mandible.
Reverse Towne's
This projection shows the condylar heads and necks. The original Towne's view (an AP projection) was designed to show the occipital region, but also showed the condyles. However, since all skull views used in dentistry are taken conventionally in the PA direction, the reverse Towne's (a PA projection) is used.
Main indications
• High fractures of the condylar necks
• Intra capsular fractures of the TMJ
• Investigation of the quality of the articular
surfaces of the condylar heads in TMJ disorders
• Condylar hypoplasia or hyperplasia.
Technique and positioning
1. The patient is in the PA position, i.e. the head tipped forwards in the forehead-nose position, but in addition the mouth is open. The radiographic baseline is horizontal and at right angles to the film. Opening the mouth takes the condylar heads out of the glenoid fossae so they can be seen. 2. The X-ray tube head is aimed upwards from below the occiput, with the central ray at 30° to the horizontal, centered through the condyles.
True lateral skull
This projection shows the skull vault and facial skeleton from the lateral aspect. The main difference between the true lateral skull and the true cephalometric lateral skull taken on the cephalostat is that the true lateral skull is not standardized or reproducible. This view is used when a single lateral view of the skull is required but not in orthodontics or growth studies.
Main indications
• Fractures of the cranium and the cranial base • Middle third facial fractures, to show possible downward and backward displacement of the maxillae • Investigation of the frontal, sphenoidal and maxillary sinuses • Conditions affecting the skull vault, particularly: — Paget's disease — multiple myeloma — hyperparathyroidism • Conditions affecting the sella turcica, such as: — tumor of the pituitary gland in acromegaly.
Technique and positioning
1. The patient is positioned with the head
turned through 90°, so the side of the face touches
the film. In this position, the sagittal plane of the
head is parallel to the film.
2. The X-ray tube head is positioned with the
central ray horizontal (0°) and perpendicular to
the sagittal plane and the film, centered through
the external auditory meatus .
Submento-vertex (SMV)
• This projection shows the base of the skull, sphenoidal
• sinuses and facial skeleton from below.
Main indications
• Destructive/expansive lesions affecting the palate, pterygoid region or base of skull • Investigation of the sphenoidal sinus • Assessment of the thickness (medio-lateral) of the posterior part of the mandible before osteotomy • Fracture of the Zygomatic arches — to show these thin bones the SMV is taken with reduced exposure factors.
Technique and positioning
1. The patient is positioned facing away from the film. The head is tipped backwards as far as is possible, so the vertex of the skull touches the film. In this position, the radiographic baseline, is vertical and parallel to the film. 2. The X-ray tube head is aimed upwards from below the chin, with the central ray at 5° to the horizontal, centered on an imaginary line joining the lower first molars . Note: The head positioning required for this projection means it is contraindicated in patients with suspected neck injuries, especially suspected fracture of the odontoid peg.
Temporomandibular Joint Radiography
Radiographs of the temporomandibular joint (TMJ) can be very difficult to examine because of the multiple adjacent bony structures. The articular disc and other soft tissues of the TMJ cannot be examined by radiographs. Special imaging techniques (e.g., arthrography, magnetic resonance imaging) must be used. Radiographic projections of the TMJ can be used to show the bone and the relationship of the jaw joint.
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