Cephalometric Analysis Flashcards
Basics of Cephalometry
Invented simultaneously in 1931 US and Germany
Taken using standard method
Results in constant magnification
Skeletal pattern
Clinically assess in all 3 planes
Cephs used to assess AP and vertical
Class I
Nasium just behind upper lip, mandible behind
Class II
Nasium in line with upper lip, mandible far behind
Class III
Nasium between upper lip and mandible
Vertical (Frankfort Mandibular Planes Angle)
Average FMPA: lines converge at back of head
If way out back: reduced lower anterior face height (deep overbite)
If in front: increased lower face height (anterior open bite)
Uses
Diagnosis
Treatment planning
Measure (predict?) growth
Assess treatment
Limits of cephalometry
Slightly magnified, 2D representation of 3D object
Not a science
Use as guide not prescription
Many sources of error
Errors affecting validity
Positioning o head in cephalostat (random)
Magnification and distortion
3D object projected to 2D image (projection errors)
Landmarks defined for convenience rather than anatomical validity
Remodelling (upper incisors)
Errors affecting reproducibility
Blurring of image due to movement during exposure
Variation in film contrast
Thickness of pencil
Perceptive limits of human eye
Inconsistency in identification of landmarks
Growth prediction
Add average amounts Not accurate Skeletal pattern remains same in 60% of individuals, improves in 30% and gets worse in 10% Stable reference point? Serial radiographs show past growth
Sella (S)
Midpoint of pituitary fossa
Nasion (N)
Most anterior point on frontnasal suture
A point (A)
Deepest point on anterior surface of maxilla
B point (B)
Deepest concavity on anterior surface of mandible
SNA
81 +/- 2
Indicates position of maxilla relative to cranial base
SNB
78 -/+ 2
Indicates position of mandible relative to cranial base
ANB
2-4 degrees
Indicates relationship of maxilla and mandible to each other (skeletal relationship)
ANS (anterior nasal spine)
Tip of bony anterior nasal spine
PNS
Tip of the posterior nasal spine
Menton (Me)
Lowermost point on mandibular symphysis
Gonion (Go)
Constructed point, intersection of lines tangent to posterior margin of ascending ramus and mandibular symphysis
MMPA
27 +/- 3
>30 more difficult to treat
U1
Upper incisor
Apex and tip
U1/ MaxP
109 +/-2
Indicates degree of proclination/ retroclination
L1
Apex and tip of lower incisor
L1/ MandPlane
92 +/-2
L1/ MandP + MMPA should = 120
Indicates degree of proclination/ retroclination
