Cephalometric Superimposition
superimposition errors: individual film method Errors of projective displacement (2D of 3D)
- in the same plane - between different planes
global superimposition structures that grow and remodel (cannot be used to superimpose on)
-posterior cranial base due to the growth that occurs throughout childhood and adolescence due to the sphenoid-occipital synchondrosis -the remodeling that occurs on the occipital and posterior sphenoid bones including the posterior wall of sella
sphenoid-occipital synchondrosis initial osseous connection forms when?
12-13 yr (girls) and 14-15 yr (boys)
regional superimposition
= Mx or Md
global superimposition image
Black: initial lateral ceph Blue: progress lateral ceph Red: final lateral ceph
superimposition errors: individual film method
Errors of projective displacement (2D of 3D) Errors in landmark identification, tracing errors Modeling at the reference line
the modeling process of the nasal cavity
Floor of nasal cavity undergoes resorption and models downward.
systematic error example
Geometric magnification and distortion due to differential magnification in different planes
In order to superimpose lateral cephalograms, you need to be able to identify certain structures on the lateral cephalogram that do not change overtime.
It is these structures that you will use to overlay the progress or final lateral cephalogram over the initial lateral cephalogram.
the modeling process of the key ridge
Key ridge undergoes apposition (downward and backward)
general concept of mandibular growth
Mandible grows in AP direction via resorption at the anterior border of the ramus and apposition at the posterior border of the ramus. Mandible grows in vertical direction as well.
maxillary superimposition secondary reference structure
Maxillo-zygomatico-temporal sulci
superimposition errors
Modeling in the area of registration Poor film quality Observer error Individual film method superimpositional method
the modeling process of the orbit
Orbital floor undergoes apposition (upward and forward)
superimposition errors: superimpositional method
The above three errors: -Errors of projective displacement (2D of 3D) -Errors in landmark identification, tracing errors -Modeling at the reference line PLUS inaccuracy of the act of superimposition (reproducibility)
superimpose the anterior border of the zygomatic process, then adjust the superimposition vertically to reflect apposition at the floor of the orbit and resorption at the nasal floor. -superimposition at the orbital floor
The red line (final ceph) should be higher than the black line (initial ceph) at the orbital floor to reflect apposition at the orbital floor. more apposition at orbital floor than nasal floor (ratio 3:2)
superimpose the anterior border of the zygomatic process, then adjust the superimposition vertically to reflect apposition at the floor of the orbit and resorption at the nasal floor. -superimposition at the nasal floor
The red line (final ceph) should be lower than the black line (initial ceph) at the nasal floor to reflect resorption of the nasal floor more apposition at orbital floor than nasal floor (ratio 3:2)
regional superimposition looks at
Tooth movement only at the periodontium Growth and treatment changes External modeling changes of the bone surface
maxillary superimposition primary reference structure
anterior surface of zygomatic process (most stable area of mx during growth)
mandibular superimposition primary reference structures
anterior-inferior border of the chin below pogonion, inferior border of the internal symphysis, and the inferior alveolar canal
anterior margin or foramen magnum apposition or resorption?
apposition up until around 16 yr
systematic error
bias in the recording and measuring system
pretreatment color code
black
progress color code
blue
In order to superimpose lateral cephalograms, you need to be able to identify
certain structures on the lateral cephalogram that do not change overtime.
superimposition: tx changes can be assessed in 2 ways
comparing head films taken at 2 or more time points-individual film method superimpositional method
the problem arises when superimposition is used to demonstrate the
directional expression of growth of the entire face
mandibular growth and remodeling
due to modeling that occurs, md growth and tx effects cannot be evaluated by superimposing on the mandibular line why superimpositions on lower border cannot be relied upon true for all areas except for the periosteal contour of the chin just below the pogonion during growth and tx the teeth move within the md along with the md to determine displacement of the md the ortho must subtract the tooth movements that occur within the mandible (mandibular superimposition) from the total changes that occur (cranial superimposition)
global superimposition cranial base anatomy
easily identifiable on lateral cephalograms start by identifying radiopaque surface of anterior wall of sella turcica, move along wall until anterior wall intersects with anterior crinoid process (walker point) as you continue anteriorly along sphenoid bone you hit the plane sphenoidale continuing anteriorly you should see 2 radiopaque lines that diverge inferiorly (cribriform plate) and superiorly (ethmoidal crest)
retention color code
green
superimposition helps to assess
growth changes ortho treatment effect
global superimposition: structures that show little or no growth
in anterior and middle cranial base there are structures that show little or no growth after 7 years of age -spheno-ethmoidal synchondrosis after that time a number of structures (esp those associated with neural tissues) remain stable and can be relied upon for superimposition
mandibular superimposition secondary reference structures
inferior border of the third molar tooth bud before root formation of the third molar starts
primary cranial base landmarks: walker point
intersection of the anterior wall of sella and anterior clinoid processes
random error: lack of resolution contrast
kV, scattered radiation
superimposition errors Modeling in the area of registration
less when using ACB
Maxillo-zygomatico-temporal sulci location
located behind the lateral contour and extends below the orbit, starts just below the cribriform plate and goes down to nasal floor at level of maxillary first molars
individual film method
make same set of measurement (SNAa, SNAb) measured value subtracted (SNAa - SNAb) differences are measures of between-time point changes
superimposition types
maxillary mandibular global (aka cranial base)
in growing skulls various bones _______
move apart from each other at different rates
random error: lack of resolution sharpness
movement, object sharpness
Differentiating dentofacial changes caused by orthodontic treatment from those induced by growth (in a growing pt) is
nearly impossible
why is the Maxillo-zygomatico-temporal sulci a secondary reference structure
overtime the sulci remodels in a posterior direction isn't very stable
how the cranial base grows further at sites of apposition and resorption
posterior part of the sella turcica sphenoid-occipital synchondrosis anterior margin of the foramen magnum spheno-ethmoidal synchondrosis
systematic error produces
predictable difference from true value
ABO sequential tracing color code
pretreatment progress end of treatment retention
primary vs secondary structures
primary structures are used first if they cannot be easily seen, secondary/support structures are used
There is no problem with superimposing stable portions to _____
quantify relative changes within the face.
end of treatment color code
red
superimpostional method
regional mx or global superimposition ie: noticing a point when downward and forward, increasing by 2 degrees
planum sphenoidale
relatively flat and extends to the greater wing of the sphenoid which demarcates the separation between the sphenoid and ethmoid bones
superimposition is a valuable tool for
research & clinical evaluation
posterior part of sella turcica apposition or resorption?
resorption until later teens
random error: lack of resolution
sharpness contrast
walker point
stable after 5-6 yrs and serves as important landmark to superimpose on
sphenoid-ethmoidal synchondrosis
stable after about 7 yr
in order to accurately superimpose you need
structures that do not change over time
to determine the effects of growth, the orthodontist does what?
subtracts the tooth movement found in mx and md superimpositions from total change found in cranial base superimpositions
how to do maxillary superimposition
superimpose the anterior border of the zygomatic process, then adjust the superimposition vertically to reflect apposition at the floor of the orbit and resorption at the nasal floor.
cephalometric errors
systematic error random error
superimposition represents
the algebraic sum of changes at all of the potential intervening growth sites.
global superimposition represents
the algebraic sum of changes at all of the potential intervening growth sites. growth and treatment changes together hard and soft tissue changes
to verify if mandibular superimposition is correct always check
the anterior border of the rams (usually moves posteriorly indicating resorption of bone, never moves anteriorly in a growing pt)
primary cranial base landmarks
the anterior wall of sella greater wings of the sphenoid walker point cribriform plate
what happens to the distance between the orbital and nasal floor during growth?
the distance increases
in order to superimpose the maxilla accurately it is important to know
the modeling process of the orbit, the nasal cavity, and the key ridge.
global superimposition growth sites
the most important structures for cranial base superimposition are -anterior wall of sella turcica below the anterior clinoid process (stable after 5-6 yrs) -cribriform plate (stable around 4-5 yrs)
use cephalograms made from _____
the same machine (to avoid errors like magnification)
we need to superimpose what kind of landmarks?
those least affected by growth
superimposition error Observer error:
tracing, measuring, superimposing
superimpositions definition
tracings of lateral cephalograms from different timepoints that are superimposed on one another on natural cranial and cranial base reference structures to describe effects of tx and (in a growing pt) the effects of growth
random error
uncertainty in the visual identification Lack of resolution
in order to have accurate superimpositions
you have to ensure your lateral cephalograms are traced as accurately as possible