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L9 Cephs and Other EO Views

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titleL9 Cephs and Other EO Views
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9 min read

Cephalograms and Other 2D Extraoral Views1

Dr Dayea Oh OMF Radiologist

Learning Objectives2

  • What are intensifying screens?
  • Understanding the purpose of using intensifying screens in extraoral radiography
  • Understanding differences between Cephalograms and Skull Views
  • What are the clinical indications for:
    • Lateral cephalogram (Lat Ceph)
    • Frontal Views
    • Submentovertex (SMV) Projection
    • Water’s View
    • Reverse Towne View
    • Lateral Oblique (or Oblique Lateral) Radiograph

Introduction to Extraoral Radiography

Extraoral radiography involves placing the X-ray source and image receptor outside the mouth.

General Indications3

  • Patient is unable to open mouth
  • Severe gag reflex
  • Trauma
  • Impacted third molars
  • Extensive jaw pathology
  • TM joint assessment
  • Orthodontic & orthognathic treatment planning

Technical Background and Equipment

X-Ray Cassette Components4

The cassette consists of the following layers (from front to back):

  • Cassette front
  • Front padding
  • Intensifying screen
    • Support layer
    • Phosphor layer
  • Emulsion layer (double-coated film)
  • Support layer (film base)
  • Emulsion layer
  • Intensifying screen
    • Phosphor layer
    • Support layer
  • Lead foil
  • Back padding
  • Cassette back

Intensifying Screen Mechanics5

  • Used to reduce radiation exposure
  • Film (AgBr) is sensitive to UV and blue light
  • Intensifying screen makes the film 10-60 times more sensitive to x-rays
  • Screens are placed on each side of the film (double coated film) to help increase image sharpness.

Phosphor Layer Composition

  • Composed of phosphor crystals
    • Inorganic salts
      • calcium tungstate (CaWO): blue light
      • lanthanum oxybromide (LaOBr): blue light
      • gadolinium oxysulfide (GdOS): green light
    • Rare earth elements
      • Have better light conversion efficacy
      • Lanthanum, gadolinium and yttrium

Base and Reflective Layers6

  • Base = Polyester plastic that ~0.25 mm thick (mechanical support)
  • Reflective layer reflects light emitted from the phosphor layer back toward the x-ray film
  • This reflective base increases the light emission of the intensifying screen but also results in image fogging “unsharpness” because of the divergence of light rays reflected back to the film.

Fig. 2-10 Screen parts identified (cross section).

Protective Layer7

  • Polymer coat (≤15 µm thick) is placed over the phosphor layer to protect the phosphor and to provide a surface that can be cleaned

Fig. 2-10 Screen parts identified (cross section).

Screen-Film Speed and Sensitivity8

Fig. 2-9a Resulting image patterns of mandible exposed on film directly.

Screen-Film Speed9

  • Fast screen-films are used in dentistry (speed of 400 or more)
  • They contain large phosphor crystals
    • Thick
    • Reduced radiation exposure
    • Rapidly conversion of x-ray photons into visible light at the expense of decreased image sharpness
ManufacturerScreenFilmSpeed
KodakLanex FineTMG, TML100
TMH250
Medium600
Regular800
Fast1200
3MTrimax 2XD/A, XL/A100
4200
8XM800
121200
Du PontQuanta Detail10T, 10TL100
Fast Detail200
Rapid400

TMG, XD/A, 10T: Medium detail, medium speed, high contrast TML, XL/A, 10TL: Medium detail, medium speed, wide latitude TMH, XM: Low detail, high speed, high contrast

The descriptions of these films should be used only to compare the films with others by the same manufacturer.

Fig. 2-9b: On film/screen combination.

TABLE 5-3. Speed class of various screen-film combinations*

Clinical Projections and Techniques1011

Common Extra-oral Views

Patient placementLateral CephSMVWatersPA CephReverse TowneOblique Lateral
Film parallel to midsagittal planeCanthomeatal line parallel to filmCanthomeatal line at 37° with filmCanthomeatal line at 10° with filmCanthomeatal line at –30° with filmFilm in contact with cheek at molar areaBeam in contact with cheek at ramus area
Central beamBeam perpendicular to filmBeam perpendicular to filmBeam perpendicular to filmBeam perpendicular to filmBeam aims at the molar-premolar areaBeam aims at the ramus area
Diagram of patient placement
Illustration of patient placement
Skull view
Resultant image

Lateral Cephalogram12

Overview13

  • Cephalogram = standardised view
  • Reproducible
  • True Lateral Skull projection
  • Midsagittal line parallel to film
  • X-ray beam perpendicular to film
  • Soft tissue definition achieved by aluminium wedge filter

FIG. 11-4. Patient positioning for a lateral cephalometric projection of the facial bones.

Indications

  • Orthodontic and orthognathic assessment (pre, peri and post)
    • Anteroposterior (AP) relationships between the maxilla, mandible, and cranial base
    • Skeletal, dental and soft tissue relationships
  • Other (less common)
    • Skull bone disorder (Paget’s, Multiple myeloma, hyperparathyroidism etc.)
    • Paranasal sinus diseases
    • Trauma
      • Cranial base and Midface

Cephalostat

CEPHALOSTAT

Lateral Cephalogram Positioning14

  • Patient placed in cephalostat
  • Midsagittal line parallel to receptor
  • Frankfort plane horizontal to floor
  • Markers – forehead / infraorbital rests, and ear rods
  • Teeth in maximum intercuspation (MIP) OR mandible in most retruded position with posterior teeth occluding
  • Lips fully rested (closed or open)

Lateral Cephalogram Anatomy and Landmarks15

Lat Ceph Landmarks

  • Orbital Roof
  • Greater Sphenoid Wing
  • Sella Turcica
  • Condyles
  • Ramus
  • Frontal Sinus
  • Frontal Sinus
  • Nasal Bone
  • Maxillary Sinus
  • Maxilla
  • Mandible
  • Cervical spine
  • Soft palate
  • tongue

Anatomy and Landmarks Labelled

  • Pterygoid plates
  • Clivus
  • Pterygoid spine
  • Pterygomaxillary fissure
  • Posterior clinoid processes
  • Sella turcica
  • Anterior clinoid processes
  • Sphenoid sinus
  • Planum sphenoidale
  • Posterior maxillary sinus
  • Roof of orbit
  • Pterygoid maxilla
  • Ethmoid air cells
  • Nasion
  • Nasal bone
  • Lens of eye
  • Lower eyelid
  • Frontal process of zygoma
  • Inferior rim of orbit
  • Floor of orbit
  • Zygomatic process of maxilla
  • Anterior nasal spine
  • Point A
  • Hard palate
  • Tooth bud
  • Point B
  • Base of middle cranial fossa
  • External auditory meatus
  • Mastoid air cells
  • Mastoid process
  • Occipital condyle
  • Posterior arch of atlas
  • Anterior arch of atlas
  • Dens axis
  • Posterior pharyngeal wall
  • Earlobe
  • Salpingopharyngeal fold
  • Superior border of inferior turbinate
  • Soft palate
  • Inferior border of zygomatic arch
  • Dorsum of tongue
  • Hyoid bone

Anatomy Practice Lat Ceph

Postero-Anterior and Frontal Projections1617181920

  • Frontal / PA Ceph, PA Skull, PA Mandible, Rotated PA
PA SkullAB
PA CephalogramPA SkullPA Jaw / MD

Indications21

  • PA Ceph: Facial asymmetry (developmental or traumatic)
  • PA Skull
    • Trauma
    • Paranasal sinuses
    • Skull bone disorders (Paget’s disease, Multiple myeloma, and Hyperparathyroidism)
  • PA Mandible
    • Fractures (post 1/3 body, angles, rami, and low condylar necks)

FIG. 11-2. Patient positioning for a posteroanterior cephalometric projection of the skull.

Patient positioning

  • Canthomeatal line 0 to +10°
    • 0° for PA skull, PA mandible
    • +10° for PA CEPH
  • Chin and forehead touch film
  • Beam perpendicular to film horizontal

Submentovertex Projection2223

SMV (Submentover)

"Jug Handle View"
Right zygomatic arch fracture

Axial plane24

AB
FIG. 11-10. Patient positioning for a submentoverex projection of the skull.
Positioning
  • Chin up
  • Canthomeatal line parallel to film.
  • X-ray beam perpendicular to film (or up to -5°)
Indications
  • Zygomatic arch fractures
  • Thickness of body of mandible
  • Skull base

Contraindicated in patients with suspected neck injuries, especially suspected fracture of the odontoid peg.

  • Mandibular Symphysis
  • Zygomatic Bone
  • Zygomatic Arch
  • Temporal Bone

Waters View2526

Standard Waters View

Positioning27

  • Canthomeatal line at 37° to 45° to film
  • X-ray beam perpendicular to film (standard)
  • Modified Water’s view aka ‘30° Occipitomeatal’
  • X-ray beam at +30° to horizontal / floor
Water's radiographic view of skullFIG. 11-6. Patient positioning for a Waters projection of the skull.

Indications

  • Paranasal sinuses (maxillary, frontal, and ethmoid).
    • If assessing the sphenoid sinus, image needs to be taken with mouth open.
  • Midface fractures (Le Fort I/II/III, zygomatic complex, naso-ethmoidal complex, and orbital blow-out).
    • If midface fracture is suspected. Both standard and modified views are required for traditional imaging.

45° Orbitomeatal line Radiographic plate ← Direction of X-ray beam

Water’s radiographic view of skull

FIG. 11-6. Patient positioning for a Waters projection of the skull.

Occipitomental Variations

30° Occipitomental View (30° OM)28

A

B

AB
30° Waters View - Alternative Technique29

30° Waters View - Alternative Technique

Reverse Towne View3031

Reverse Towne Anatomy

Patient Positioning32

  • Canthomeatal line -30° & x-ray beam horizontal; OR
  • Canthomeatal line horizontal & x-ray beam -30°
  • Jaws always open!
FIG. 11-b. Patient positioning for a reverse-Towne projection of the skull.

Indications

  • Condylar neck fractures
  • TM Joint disorder

Oblique Lateral Radiography33

BA
AB

Mandibular Body34

FIG. 12-7 Anatomic landmarks identified in the oblique lateral projection of the mandibular body.

  • Hard palate
  • Inferior border of orbit
  • Posterior wall of sinus
  • Posterior wall of zygomatic process of maxilla
  • Inferior border of zygomatic arch
  • Dorsum of tongue
  • Tube side, inferior border of mandible
  • Inferior border of mandible
  • Area of osteosclerosis
  • Hyoid bone
FIG. 12-7 Anatomic landmarks identified in the oblique lateral projection of the mandibular body.FIG. 12-8 Anatomic landmarks identified in the oblique lateral projection of the mandibular ramus.

Mandibular Ramus

FIG. 12-8 Anatomic landmarks identified in the oblique lateral projection of the mandibular ramus.

  • Articular eminence
  • Dorsum of soft palate
  • Posterior wall of maxillary sinus
  • Hard palate
  • Zygomatic process of maxilla
  • Anterior wall of zygomatic process of maxilla
  • Coronoid process of mandible
  • Inferior border of maxilla
  • Zygomatic arch
  • External oblique ridge of mandible
  • Mandible canal
  • Hyoid bone
  • Mandibular foramen
  • Dorsum of tongue
  • Condyle of mandible
  • Lateral border of mandibular fossa
  • Medial border of mandibular fossa

References35

Footnotes

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  33. Original PDF page 37: L9 Cephs and Other EO Views, p.37 ↩

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