Superimposition techniques

SUPERIMPOSITION
TECHNIQUES
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Contents
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Introduction
Methods of assessing dentofacial changes
Method of superimposing radiographs
Maxillary super-impositions
Mandibular superimpositions
Ricketts superimposition for treatment design
Ricketts four-step method

Definition
Superimposition is the placement of an image on
top of an already existing image usually to add to
overall image effect and to conceal something eg.
Such as a different figure is superimposed over an
original figure.
 The transformation of one or more figures to
achieve the geometric relationship to another
figure
Wikipedia
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Introduction
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In 1931 Broadbent (USA) and Hofrath (Germany)
- cephalometric technique using a cephalostat.
Treatment planning.
Evaluation of treatment results by quantifying the
changes brought about by treatment
Predicting growth related changes


What is cephalometric
superimposition ?
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“A cephalometric superimposition is an
analysis of lateral cephalograms of the same
patient taken at different times”.


TO PERFORM ACCURATE SUPER
IMPOSITION

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Consecutive cepholograms should be taken under
identical condition of magnification head position,
and radiological exposure
The tracing of the superimpositions must be accurate
It is of great importance that exactly the same
structures and their corresponding radiographic
shadows be traced in the consecutive cepholograms
One should have the thorough knowledge of anatomy
of dentofacial & cranial structures as well as
radiographic interpretation
They have to be registered on stable reference areas in
the face.

CEPHALOMETRIC SUPER IMPOSITIONS
INVOLVE THE EVALUATION OF:

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Changes in the overall face
Changes in the maxilla and its dentition
Changes in the mandible and its dentition
Amount and direction of condylar growth
Mandibular rotation


Method of superimposing
radiographs

Superimposing on a stable plane
or structure

Registration on a stable
landmark


Validity and reproducibility
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Validity: It is the extent to which the value
obtained represents the object of interest.
 Planes and landmarks should be anatomically
valid and should agree with the anatomic
structures they represent
Reproducibility: It is the closeness of successive
measurements of the same object.


Methods of assessing
Dentofacial changes
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Brodie and Broadbent AJODO 1987-Dentofacial
growth patterns are established at a very early age
and thereafter are subject to proportional changes.
Downs and Ricketts AJO 1960 -several angles and
dimensions change with age but in an orderly and
progressive manner
Hellman -suggested that the infant face is
transformed into that of an adult face by increase
in size by changes in proportion and by
adjustment in position.

Methods of assessing
Dentofacial changes
Color coding suggested by ABO:
 Pretreatment – Black
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Progress – Blue

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End of treatment – Red

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Retention - Green

Evaluation of overall changes
in the face
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Superimposition methods:
 Broadbent triangle
 Sella nasion line
 Basion horizontal
 Basion nasion plane
 De Costers anterior cranial base reference line
 Viazis cranial base triangle
 Frankl’s occipital reference base

in the face
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Objectives
 Overall assessment of growth and treatment
changes of the facial structures
 Amount of change in direction of displacement
and growth of maxilla and mandible.
 Changes in soft tissue
 Changes in maxillo mandibular relationship
 Overall displacement of teeth.

in the face
Superimposition at registration point
R with Bolton-nasion planes parallel

Broadbent triangle

Among the first structures
used for superimposition
 On observations of dried
skulls and a comparative
study of cranial base planes
(Bolton-nasion, porionnasion, sella-nasion) in
persons 3 to 18 years of age.
 Bolton point maybe obscured
by Mastoid
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in the face
Sella nasion plane:
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SN is a frequently used
reference line that has been
reported to be relatively
stable.
Both points S and N are
located in the mid sagittal
plane and are displaced a
minimal degree by
movement of the head.


Steiner -SN with registration
point
 At sella to evaluate sagittal
changes in mandibular
positions and
 At nasion to evaluate the
position of the maxilla
through changes in the
angle SNA


in the face
Sella nasion plane:
 Unlike Steiner, Björk
used sella as
registration point to
assess changes in
position of both jaws.


in the face

Basion horizontal
 Basion is used as the
registration point.
 The SN planes are made
parallel by the help of the
Basion horizontal line and it’s
constant relationship with SN.
 A coordinate grid system is
used to superimpose the
radiographs.


in the face
Basion - Nasion plane:
 Suggested by Ricketts as
Facial Axis
 He considered Ba-N plane as
a line of separation of the
face from the skull and hence
a basic cranial axis for
growth and structural
reference.


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Based on studies of
laminograph sections,
Ricketts suggested that
the cranial base angle,
while constant on
average, exhibits a
change of 5° in either
direction over a 3-year
period


in the face
De Coster lineAjodo1952
The line represents the axis of skull base.
 He advocated tracing the inner contour of the frontal
bone through the cerebral aspect of the ethmoid , the
planumsphenoidale and the anterior aspect of the
sella turcica.


in the face
Viazis cranial base
triangleJco;25
 The anterior wall of
sella turcica and the
cribriform plate
(laminar cribrosa)
remain unchanged
after age of 5 years.


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Superimposition on the
anterior wall of sella turcica
and the stable TC (cranial
base) line, with registration
on T point, provides a
practical and reliable
formation in both the
anteroposterior and vertical
planes.


in the face
Viazis cranial base triangle
 First priority - to
registering on T point,
followed by
superimposing on the
inner structure of the
triangle, and finally
superimposing on the TC
line. This "best-fit"
approach meets the
realistic expectations of
any superimposition
technique.

Frankel’s occipital reference
base

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Among the basal structures of the neurocranium,
the occipital bone around the foramen magnum is
the first to ossify (between the third and fourth
year of life).
Minimalpostnatal growth of this structure and
surrounding tissues is seen.

Frankel’s occipital reference
base
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Reference plane –
based on natural head
posture and parallel to
the ground


in the face
Reliability of the various cranial base reference
planes used.
For meaningful interpretations of
superimpositions they have to be registered on
stable reference landmarks.
 Cranial base superimpositions are subject to error
due to the continued growth of the sphenoccipital
synchondrosis (Knott).
 Bone remodelling at sella and Nasion are also
responsible for further errors.

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Nasion position can change in a vertical direction
(Nelson and Knott).
Melsen’s study’s on human autopsy material has
shown that the position of sella may change in a
downward or a downward and backward direction.
She also showed that the position of Basion
changed due to remodelling of the clivus.
The Bolton point could be difficult to locate in
children due to the shadow of the mastoid process

Growth changes in position of Nasion and sella


Reference structures for
overall face superimpositions.
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Nelson’s and Melsen’s - stable structures in the
anterior cranial base.
 Anterior wall of sella turcica
 The contour of the cribriform plate of the
ethmoid
 Trabecular system of the ethmoid air cells
 The median border of the orbital roof
 Planum sphenoidale

SUPERIMPOSITION OF THE
MAXILLA
Evaluates
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Movement of maxillary teeth
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Rotation of maxilla
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Two method for superimposing the maxillary
structutres are recommended- the structural
method and a modified best fit method.
Structural Method : - Suggested by Bjork & Skieller
in 1976. is recommended if the details of the
zygomatic process of the maxilla are clearly
identified in both cephalograms.
Modified best fit method : - If the details of
zygomatic process of maxilla are not identified in
both cephalograms.

Structural method of superimposition of maxilla

Pre treatment
Tracing

Post treatment
Tracing

Super imposition of
pre & post treatment tracing

On each cephologram, trace the contours of palate, maxillary 1st
molar, central incisors, zygomatic process of maxilla, floor of the
orbit N-S line and the construction line.

Modified best fit method

Pre treatment
Tracing

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Post treatment
Tracing

Super imposition of
pre & post treatment tracing

On each cephalogram trace the outline of the palate 1st
permanent molars and central incisors.
Following structures are in a best fit alignment.
 Contour of the oral part of the palate
 Contour of the nasal floor

Evaluation of changes in maxilla
and its dentition in relation to the
maxilla
Superimposition along the
palatal plane registered at
ANS
Broadbent, Moore, Salzman,
Ricketts, McNamara
 Compromised by
remodelling of the palatal
shelves and ANS
Bjork and Skeiler
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maxilla
Superimposition on
the nasal floors with
films registered at the
anterior surface of the
maxilla
Downs and Brodie.
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maxilla
Superimposition
along the palatal plane
registered at the
pterygomaxillary
fissure
Moore
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maxilla
Superimposition on
the outline of the
infratemporal fossa
and the posterior
margin of the hard
palate.
Reidel
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maxilla
Superimpostion
registered at the
common Ptm
coordinate
maintaining the basion
horizontal
relationship.
Coben
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maxilla
superimposition on the
best fit of the internal
palatal structures.
McNamara
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maxilla
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The structural
superimposition on the
anterior surface of the
zygomatic process of
the maxilla
Bjork and Skeiler


maxilla
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Neilsen on a study of various maxillary
superimposition techniques concluded that:
 The best fit method significantly under estimates the
vertical displacement of skeletal and dental
landmarks
 With the structural method ANS showed twice as
much vertical displacement as PNS


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Structural method did not show any significant
differences
The structural method is a valid method of
assessing maxillary growth and treatment
changes


Mandibular superimposition
Evaluates
 Movement of the mandibular teeth
 Mandibular rotation
 Amount & direction of condylar growth


Stable areas according to
Bjork and Skieller (1983)
 Anterior contour of the chin
 The inner contour of the
cortical plates at the inferior
border of the symphysis
 Contours of the mandibular
canal
 Lower contour of the
mineralized molar tooth germ


Step – by – step approach for
mandibular superimpositions

Pre treatment
Tracing

Progress treatment
tracing

Super imposition of
pre & progress treatment
tracing

On each cephologram trace the following
 The symphysis with inner cortical bone
 The inferior and posterior contour of the mandible
 The anterior contour of the ramus
 The most labially positioned lower incisor, and
 The first molar.

Methods to assess growth Vs
treatment changes
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Differentiate between changes produced due to
growth and changes produced due to treatment.
Assess treatment changes against the background of
natural growth of the individual


RICKETTS SUPER
IMPOSITION TECHNIQUE
It is one of the most important superimposition
technique used.
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Ricketts super imposition is used to differentiate the
changes in normal growth and those due to treatment
mechanics.
This techniques involves five super imposition areas to
evaluate
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The chin
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The maxilla
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The teeth in the mandible
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The teeth in the maxilla
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The facial profile www.indiandentalacademy.com
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Rickett ’s Eleven factor
summary analysis
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Eleven factors of the basic facial and skeletal
structures are recorded from the cephalometric
tracing to describe the chin, maxilla, teeth and soft
tissue profile.
Five areas of superimposition within which are a
total of seven areas of evaluation are used to
evaluate in amount and direction, change in
normal growth and change due to treatment.

Rickett’s Eleven factor
summary analysis


summary analysis
MEAN

CHANGE

FACIAL AXIS

90+/-3

No change

FACIAL DEPTH

87+/-3

+10 for 3 yrs

MAND PLANE

26+/-4

-1o for 3 yrs

FACIAL TAPER

68+/-3

No change

LFH

47+/-4

No change

MAND ARC

26=/-4

Mand arc
closes1/2yr
Angle inc 1/2yr

CON AT A

2mm+/-2mm

-1mm / 3 yrs

L1 TO APO

1+/-2

No change

L1 INCL

22+/-4

No change

U6 TO PTV

Age+3+2

1mm / year

L LIP TO E LINE

-2+/-2

Less with age


summary analysis
SUPERIMPOSITION AREA 1 – EVALUATION
AREA 1
• FACIAL AXIS OPENS 1o FOR
DOLICOFACIAL PATTERN
•FACIAL AXIS CLOSES 1O FOR
BRACHYFACIAL PATTERNS
•FACIAL AXIS OPENS 1O FOR 5mm
CONVEXITY REDUCTION
•FACIAL AXIS OPENS 1O FOR 3mm
MOLAR CORRECTION
•FACIAL AXIS OPENS 1O OR 4mm
OVERBITE CORRECTION
•FACIAL AXIS OPENS 1 TO 1.5O FOR
CROSS BITE CORRECTION AND
RECOVERS ONE HALF

BASION-NASION PLANE at CC

summary analysis
SUPERIMPOSITION AREA 2 – EVALUATION
AREA 2
• THE BASION-NASION-POINT A
ANGLE OF 66O DOES NOT CHANGE
WITH GROWTH
•SO ANY CHANGES PRODUCED
MUST BE DUE TO TREATMENT
•HEADGEAR - -8mm
•CLASS II ELASTICS - -3mm
•ACTIVATOR - -2mm
•TORQUE- - 1 TO 2mm
•CLASS III ELASTICS 2 TO 3mm
•FACIAL MASK - 2 TO 4mm
BASION NASION PLANE AT
NASION

summary analysis
SUPERIMPOSITION AREA 3 – EVALUATION AREAS 3
AND 4
• LOWER DENTURE REMAINS
CONSTANT WITH THE A Pog LINE
•Without treatment, the lower molar will erupt
directly upward to the new occlusal plane.
•The LOWER INCISAL angle is 22° at +1mm
to the APo plane and + 1 mm to occlusal
plane, but the angle increases 2° with each mm
of forward compromise.

CORPUS AXIS AT PM

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OCCLUSAL PLANE TO
CORPUS AXIS DOES NOT
CHANGE
LOWER MOLAR ERUPTS IN A
DIRECTION PERPENDICULAR
TO THE FH PLANE
OCCLUSAL PLANE ERUPTS
0.8mm UPWARDS FROM THE
CORPUS AXIS.


summary analysis
SUPERIMPOSITION AREA 4 – EVALUATION AREAS 5
AND 6
• THE UPPER MOLAR AND INCISOR
FOLLOW THEIR POLAR AXIS WITH
GROWTH
•CHANGES IN POSITION OF THE
MOLAR OR INCISOR IS DUETO
TREATMENT.
•UPPER DENTAL ARCH ERUPTS
DOWNWARD AND FORWARD 0.2 TO
0.3mm PER YEAR

PALATE AT ANS

summary analysis
SUPERIMPOSITION AREA 5 – EVALUATION AREA 7
•

ESTHETIC PLANE AT INTERSECTION
OF OCCLUSAL PLANES


Rickett’s four position analysis
Takes into consideration two superimposition areas
to evaluate skeletal change and two
superimposition areas to evaluate dental change
against growth.


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Position 1
Mandible or chin
Central axis 90+/-3


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Position 2
Maxilla
Backward moment
of .A of 3 help
reduce convexity


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Position 3
Upper teeth
Tracing are
superimposed on
palatal plane and
registered at ans
1 intrusion&
retrusion 7mm
Molar 2mm forward

Position 4
Lower teeth
Tracings are
superimposed on
corpus axis and
registered at pm
Incisor crown
7mm,root 3mm
molar2mm

Pitchfork analysis
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Johnston in 1985
Used to evaluate
growth/displacement of
the max and mand
To register moments of
max and mand
Data recorded in the
form of a pitch fork


Pitchfork analysis
Growth and displacement of
max and mand are
measured relation to cranial
base(registration at sella)
The changes of max and mand
molars and incisors are
measured relative to basal
bone
All measurement are executed
parallel to MFOP and are
given signs appropriate to
the nature of their
contribution to the molar and
overjet corrections or
changes.

Pitchfork analysis
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Superimposition on
D
Measurement of
molar and incisal
changes


Pitchfork analysis
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Measurement of
amount of molar
correction


Pitchfork analysis
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Measurement of
overjet correction


CONCLUSION

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Rickett’s Cephalometric superimposition are a
valuable tool in treatment planning.
These analysis help in orthodontic diagnosis by
enabling the study of skeletal, dental and soft tissue
structures of the cranio facial region.
These analysis also classify the skeletal and dental
abnormalities and establish the facial type.


References:
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Orthodontic cephalometry Text book-Athanasios
E Athanasiou
Radiographic cephalometry second ed.,-Alexander
Jacobson(Text book)
Bioprogressive therapy-Robert M.Ricketts(Text
book)
A Four- step method to distinguish orthodontic
changes from natural growth:J.C.O,Vol 9,1975
pgs208-228

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Superimposition techniques

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