Cephalometry

Question 1

What uses can lateral cephs have?

Answer 1

• Diagnosis + tmt plan
• Monitoring treatment changes
• Monitor growth
• Research

Question 2

What is the distance from mid saggital plane to x-ray source?

Answer 2

150cm

Question 3

What is the formula for magnification?

Answer 3

(source x-ray to film)
(———————————————- - 1 ) x100
(source x-ray to mid sagittal plane)

Question 4

What is the usual degree of magnification used?

Answer 4

8. 8% (at mid sagittal plane–> one side closer to the film will be enlarged more)–>may see double outlines
   - Centre also enlarged less than peripheral structures

Question 5

How much kV should be used for lat cephs?

Answer 5

65-90

Question 6

Where were the pins placed during the Bjork experiment?

Answer 6

• Anterior aspect of symphysis
• RHS + LHS first and second premolar root apex at base of mandible
• External aspect of RHS ramus

Question 7

What are the stable points used to re-align x-rays and monitor growth?

Answer 7

Cranial base:

• Anterior border of pituitary fossa
• Greater wings of sphenoid
• Plane of the sphenoid
• Ethmoid air spaces
• Cribriform plate
• Medial border of orbital roof

Maxilla
-Line drawn tangent to anterior contour of zygomatic process

Mandible:

• Inferior alveolar nerve canal
• Inner cortex of the symphysis
• External countour of chin just above maximum convexity
• 3rd molar crypt

Question 8

What is the mA usually used in lateral ceph?

Answer 8

12mA

Question 9

How long is film exposed for?

Answer 9

0.4-0.64 seconds

Question 10

What is the distance of the mid sagittal plane to the film?

Answer 10

30cm

Question 11

What is an umbra and how can you reduce it?

Answer 11

• Shadow produced by divergence of x-ray beams

- Reduce by reducing anode size

Question 12

What is the Tweed Analysis?

Answer 12

(Gonion-Gnathion)
Frankfurt horizontal (Porion to orbitale)
Lower incisor apex (incision inferius to lower incisor apex)

Incisor mandibular plane= 90 +/- 5 degrees
Frankfurt mandibular angle = 25 +/- 4 degrees
Frankfurt mandibular incisal angle 65+/- 3 degrees

Question 13

What are advantages /disadvantages to Tweed’s analysis?

Answer 13

-Simple and quick

• No distinction between gender and ethnic groups
• Limited to lower incisors (doesn’t aim treatment at anything else)
• Mandibular plane angle not sole indicator of profile

Question 14

What is the Down’s Analysis?

Answer 14

Frankfurt horizontal
Nasion to pogonion

(should have 90 degrees in between lines)

Mandibular plane (gonion to menton)-->22 degrees to frankfurt
Occlusal plane (bisect anterior/posterior bite)-->9 degrees to frankfurt
Sella-gnathion 59 degrees to frankfurt
Nasion A point pogonion angle zero-->Class II will increase Class III will decrease

A point/B point to (Nasion-Point A, Pogonion)–> -4.5 degrees

Intercisal angle: 135 degrees

Lower incisal apex to occlusal plane: 14.5 degrees

Lower incisor apex to mandibular plane: 91 degrees

A point to pogonion: how far does upper incisor stick out (3mm)

Question 15

What are the advantages/disadvantages of Down’s Analysis?

Answer 15

• Growth direction
• Standard value for other groups
• Small sample size
• Variability in Frankfurt horizontal
• No soft tissue consideration
• mainly in A-P

Question 16

How do you know when patient stops growing?

Answer 16

-Overlap, no change in film after 12 months