Cephalometric Radiography

Question 1

Purpose of Cephalometric Radiography and its analysis

Answer 1

1. Uses
   - Help PLAN certain tx
   - To EVALUATE growth or tx changes (taken at standard conditions so comparisons can be made)
2. Analysis
   - Help assess facial form
   - Aid to tx planning
   - Evaluate the extent to which any changes occur are due to growth or tx

Question 2

Pt positioning in cephalostat

Answer 2

• Ear posts are not deflected and within ear canals
• Pt’s Frankfort plane is viewed as being horizontal
• Teeth are generally held in ICP
• Lips relaxed and in habitual position

Question 3

What does cephalometric landmarks S, N, ANS, PNS, A, B, Me, Go and FOP mean

Answer 3

• Stella turcica (midpoint of pituitary fossa)
• Nasion (antero-inferior point on the frontal bone
• Anterior Nasal Spine
• Posterior Nasal Spine
• A point (sub-spinale)
• B point (supra-mentale)
• Menton (most inferior point on mandibular symphysis
• Gonion (lowest point on curvature of angle of mandible)
• Functional Occlusal Plane (line passing through occlusion of premolars)

Question 4

How do you determine AP dental base relationship using Eastman analysis? What values categorise pts into Skeletal class I, II or III?

Answer 4

• Measuring ANB angle
  ANB > 4º Skeletal II
  ANB = 2-4º Skeletal I
  ANB < 2º Skeletal III

SNA and SNB measures the relationship between both the maxilla and mandible in relation to the cranial base (S-N line). Therefore, the difference between the two angles indicates the jaw relationship

Question 5

What is the Eastman correction? Why is it needed?

Answer 5

• ANB can vary with vertical or horizontal positioning of S or N, therefore, the further the SNA angles varies from 81º (± 3º) the more inaccurate ANB angle is
• For every degree that SNA is above 81º, subtract ½º from the angle ANB. For every degree below 81º add ½º to ANB
• Only works if S is in normal position (checked by measuring the angle SN to maxillary plane – should be 8º (± 3º))

Question 6

Interpretation of the Eastman analysis: what are the normal values for:
SNA, SNB, ANB, MMPA, LFc Ht %, 1/ Mx PL, 1/MPL and 1/1?

Answer 6

• SNA 81º (± 3º)
• SNB 78º (± 3º)
• ANB 2-4º
• MMPA 27º ( ± 4º)
• L Fc Ht % 55%
• 1/ Mx Pl 109º (± 6º)
• 1/MPL 93º (± 6º)
  (NB: this is inversely related to MMPA (i.e. 93º if MMPA is 27º))
• 1 / 1 133 -135º

Question 7

What does Ballard’s Conversion Tracing consist of

Answer 7

• Uses the max and Mand planes and the shadows of the most prominent upper and lower central incisors
• On a superimposed second tracing the upper incisor is then tipped to ideal inclination (109º) by moving it about a point on its long axis 1/3 of its length from the root apex
• The long axis of the lower incisor is adjusted depending on the MMPA (NB: this is inversely related to MMPA (i.e. 93º if MMPA is 27º))

Question 8

What does Wits analysis consist of

Answer 8

• Uses FOP and perpendiculars from A and B point
• if AO and BO within 1mm the Skeletal class I
• Skeletal class II if AO more than 1mm ahead of BO
• Skeletal class III if BO more than 1mm ahead of AO