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