Extra oral views: lateral cephalometric radiography

Question 1

What are the principles of extra-oral radiography?

Answer 1

Xray source outside the patient
Image receptor outside the patient
Digital CCD/CMOS and storage phosphor options
Previously indirect x-ray film used with intensifying screens
Patient positioning critical
X-ray beam and image receptor related to patient.

Question 2

What is the radiographic baseline?

Answer 2

Outer corner of eye to external auditory meatus.

Question 3

How many degrees of a difference is it between RBL and FP?

Answer 3

10 degrees.

Question 4

What is the Frankfort plane?

Answer 4

Superior border of EAM to the lowest point of infra-orbital rim.

Question 5

What is true lateral radiography?

Answer 5

Film and MSL are parallel and x-ray and beam is perpendicular to both.

Question 6

What is oblique lateral radiography?

Answer 6

Film and MSP (mid saggital plane) are not parallel

X-ray beam is not perpendicular to either but oblique to both.

Question 7

What are some examples of lateral view radiographs?

Answer 7

Lateral ceph
Lateral oblique
Bimolar (both sides on one receptor).

Question 8

What is cephalometric radiography?

Answer 8

Standardised and reproducible form of skull/facial bones radiography
Used extensively in ortho
Orthognathic surgery
Implants but this has recently been replaced by CBCT
Lateral or postero-anterior (PA) projections.

Question 9

What is lateral cephalometric?

Answer 9

True lateral view of facial bones, base of skull and upper cervical spine. Also shows paranasal sinuses and nasopharyngeal soft tissues.

Question 10

What can you see on a lateral ceph?

Answer 10

Can see soft tissue of the nose and lips

• can see soft tissue around chin if adjust contrast
• need to look at how patient looks and not just skeletal
• upper cervical spine and sinuses can be seen
• nasopharyngeal soft tissues can be seen e.g. tongue and soft palate.

Question 11

In orthodontics, when would you take a cephalogram?

Answer 11

Patients with skeletal vertical or antero-posterior discrepancy
Requiring fixed or functional appliance therapy, for labio-lingual movement on incisors
Requiring orthognathic surgery in addition to orthodontics.

Question 12

What are the indications for a lateral ceph?

Answer 12

Orthognathic surgery- pre-op assessment and post review
Implant planning- anterior mandible
BOTH OF THESE OFTEN SUPERSEEDED IF CBCT AVAILABLE.

Question 13

What equipment do you need for a ceph?

Answer 13

Cephalostat
CCD/CMOS
Anti-scatter grid
Source to patients MSP (5 feet in traditional equipment)
Image receptor to MSP
Nasion marker
Magnification scale
Automatic facial contour in direct digital machines
OR aluminium wedge filter ideally at tube head
OR
triangular lead collimator in older machines.

Question 14

What is the effect of increasing anode-object distance on magnification?

Answer 14

Increase the distance, reduced magnification and have less difference between right and left sides.

Question 15

What is the effective dose with and without a collimator?

Answer 15

1. 6 with

3. 0 without.

Question 16

What is the positioning for a lateral ceph?

Answer 16

Select for lateral ceph and press button to line up X-ray tube head and cephalostat with receptor
Hinge nasion rest and sideways
Thyroid collar on
Frankfort plane horizontal (use light)
MSP vertical and parallel to cassette
MSP correct distance from cassette if adjustable
Teeth together- in centric occlusion or as requested
Ear rods in EAM move symmetrically
Nasion support in place.

Question 17

What is the distance usually used between the patient and the image receptor?

Answer 17

25cm.

Question 18

Why must you use a fixed distance for an individual?

Answer 18

So subsequent images will always be able to be directly comparable.

Question 19

What are the indications for oblique lateral radiography?

Answer 19

Generally the same for panoramic radiography but particularly when:
panoramic not available or possible eg. handicapped patient. No longer done at GDH&S.

Question 20

What is the indications for oblique lateral radiography?

Answer 20

Film and MSP not parallel
X-ray beam not perpendicular to either MSP or film
Extra oral view of jaws- right and left sides taken separately
Uses dental or E/O x-ray set
Limited use now due to panoramic radiography.

Question 21

In cm, what is the anterio-posterior dimensions for a lateral ceph?

Answer 21

17cm.

Question 22

How do you work the collimator on a lateral ceph?

Answer 22

Height and depth of field of view or triangular adjustable by programme or visual.