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

1. CEPHALOMETRIC
SUPERIMPOSITION
DR NIVYA KRISHNA
POST GRADUATE STUDENT
DEPT OF ORTHODONTICS
MAR BASELIOS DENTAL COLLEGE ,KOTHAMANGALAM

2. CONTENTS
•INTRODUCTION
•METHODS OF SUPERIMPOSING
RADIOGRAPH
•REFERENCE PLANES FOR
SUPERIMPOSITION
•MAXILLARY SUPERIMPOSITION
•MANDIBULAR
SUPERIMPOSITION
•RICKETS 12 FACTOR ANALYSIS
•RICKETS 5 POSITION ANALYSIS
•PITCHFORK ANALYSIS
•PANCHERZ ANALYSIS
•I POINT & I CURVE
SUPERIMPOSITION
•ABO SUPERIMPOSITION
•AUTOMATIC
SUPERIMPOSITION
•3D SUPERIMPOSITION
•CONCLUSION

3. INTRODUCTION
A cephalometric superimposition is an analysis of
lateral cephalograms of the same patient taken at
different times.
Uses:
◦ Evaluate a patients growth pattern at different ages
◦ To evaluate changes in basal and dentoalveolar
relationships after treatment
◦ To quantify growth and treatment changes in
dentoalveolar and basal relationships.

4. Method of superimposing radiographs
Superimposing on a stable plane or structure

5. Registration on a stable landmark

6. Validity and reproducibility
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.

7. Methods of assessing
Dentofacial changes
Study of changes in dentofacial dimensions using
cephalometric superimposition have shown varying results
Brodie and broadbent have shown that dentofacial growth
patterns are established at a very early age and thereafter
are subject to proportional changes.
Downs and Rickkets pointed out that 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.

8. Areas studied to assess changes due to growth or
treatment or both include:
◦ Changes in the overall face
◦ Changes in the maxilla and it’s dentition
◦ Changes in the mandible and its dentition
◦ Amount and direction of condylar growth
◦ Mandibular rotation

9. Color coding of consecutive cephalograms
suggested by ABO:
◦ Pretreatment – black
◦ Progress – blue
◦ End of treatment – red
◦ Retention - green

10. 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.

11. Reference planes for superimposition-
a review
Bolton-nasion plane Broadbent
Basion nasion plane Ricketts
Anterior cranial base De coster
Sella nasion line ABO 1990
Basion horizontal Coben

12. a)Bolton nasion plane
Superimposition at registration point R with Bolton-nasion planes parallel

13. Reference plane : Bolton –Nasion plane
Registration point: midpoint of perpendicular
drawn from ‘S’ to the bolton nasion plane.

14. Among the first structures used for superimposition,
Broadbent based this method on observations of
dried skulls and a comparative study of cranial base
planes (Bolton-nasion, porion-nasion, sella-nasion)
in persons 3 to 18 years of age.
Bolton point may be obscured by Mastoid
Shows the downward and forward growth of the
face from beneath the cranium.

15. b)Sella nasion plane:
x

16. SN is a frequently used reference line that has been reported
to be relatively stable.
Reference plane- SN line
Registration point-sella

17. Both points S and N are located in the midsagittal
plane and are displaced a minimal degree by
movement of the head.
Steiner used 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 SNA angle

18. Unlike Steiner, Björk used sella as
registration point to assess changes in
position of both jaws.
He stated that an upward or
downward displacement of nasion may occur
with growth at the frontonasal suture.
Likewise, a posterior displacement of sella
may be induced by the remodeling of
dorsum sellae connected with the increased
size of the pituitary gland.

19. Sella nasion line- ABO 1990
-Shows the amount of growth change between two
serial radiographs.
-Accurate as long as the growth at the nasion is a
linear extension of the sella nasion line.

20. c) Basion horizontal
Coben presented the Basion horizontal concept.

21. Reference plane-
Plane constructed at the basion parallel
to the foramen magnum.
Registration point- basion
.

22. 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.

23. d) Basion - Nasion plane:
Suggested by Ricketts

24. Reference plane-basion nasion plane
Reference point- ‘cc’ - point of intersection
between the basion nasion plane and the
Rickett’s facial axis

25. 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.
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

26. One may doubt the
reliability of this axis because
growth at nasion is subjected to
individual variations.
Moreover, the position of
basion is influenced by
remodeling processes on the
clivus surface and on the anterior
border of the foramen magnum
associated with growth in the SOS.

27. e) De Coster line
It is the sella tursica – ethmoid line.

28. 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 sos (Knott).
Bone remodelling at sella and nasion are also responsible
for further errors.
Nasion position can change in a vertical direction
(Nelson and Knott).

29. Melsen’s study on human autopsy material has
shown that the position of sella may change in a downward
or a downward and backward direction.
He 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

30. Nelson’s cephalometric study and Melsen’s
histological study on human autopsy materials
have reveled a few stable structures in the anterior
cranial base for use in superimposition.
◦ Anterior wall of sella tursica
◦ 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

31. Superimposition methods to study
growth

32. Maxillary superimposition
Broadbent
Palatal plane registered at ANS
anterior surface of maxilla and
point A moved posteriorly.

33. Downs and Brodie
Superimposition
on the nasal floors with
films registered at the
anterior surface of the
maxilla
(Eliminate appositional
changes at ANS.)

34. Moore
Superimposition
along the palatal plane
registered at the
pterygomaxillary
fissure

35. Reidel
Superimposed the
infra-temporal fossa at
the posterior portion of
the hard palate.

36. Coben
Superimpostion
registered at the common
Ptm cordinate maintaining
the basion horizontal
relationship.

37. McNamara
Superimposition on the
best fit of the internal
palatal structures.

38. Bjork and skeiller
Superimposition on
metallic implants
TANTALUM PINS-
1.5 X 0.5

41. The structural
superimposition on the
anterior surface of the
zygomatic process of the
maxilla
(Bjork and Skeiler)

42. According to Bjork and Skieller
Remodelling involves resorptive lowering of the
nasal floor which is greater anteriorly than
posteriorly.
Zygomatic process underwent remodelling in the
superior part of the orbital floor and the most
inferior part of the key ridge.

43. Hard palate undergoes continuous resorption on its
nasal floor and apposition on the oral side.-
superimpositions are unsatisfactory
ANS and PNS undergo significant remodelling.
The best fit method provides a higher degree of
validity compared to ANS -PNS.

44. Two methods of maxillary superimposition
1.Structural method
2.Best fit method.

45. Structural method
BJORK & SKEILLER 1977
Superimposition on the anterior contour of the
zygomatic process of maxilla.
This area is relatively stable after 8 yrs.

46. •On both the pretreatment
and post-treatment
cephalogram
•1.Trace anterior contour of
the zygomatic process
•2.Draw a line tangent to it –
construction line
•3.Trace the orbit, palate,
N-S line

47. Assessing maxillary rotation
•The pretreatment and post-treatment cephalograms
are superimposed on the construction line.
•
The amount of apposition at the orbital floor is
obtained.
•
The superimposition is moved so that the amount of
resorption is equal to the amount of apposition at
the nasal floor.

48. The two tracing are stabilised.
The angle formed by the two S-N line gives the
amount of maxillary rotation.

49. superimposition

50. Best fit method
MCNAMARA 1981
If the zygomatic
process of maxilla is
not clearly defined
then the best fit
method is used.
The superimpositions
are made on the nasal
and palatal surfaces of
the hard palate that is
not influenced by tooth
movement.

51. •On the pretreatment and post-treatment cephalogram
maxillary structures are traced.
•The 2nd tracing is placed over the 1st tracing for best fit
alignment of
-the contour of the oral part of the palate
-the contour of the nasal floor.
-the entrance of the incisal canal.
The best fit method has low degree of validity and
minimum degree of reproducibility

52. 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 implant method and the structural method ANS
showed twice as much vertical displacement as PNS
◦ Structural method and implant method did not show any
significant differences
◦ The structural method is a valid method of assessing
maxillary growth and treatment changes

53. Mandibular superimposition
Bjork’s reference planes
:Stable areas for
superimposition:
1.Anterior contour of the chin
2.The inner contour of the
cortical plates at the inferior
border of the symphysis
3.Contours of the mandibular
canal
4.Lower contour of the
mineralized molar tooth germ

54. Reference plane for mandibular superimposition –
Salzmann1972
 The mandibular plane between menton and
gonion.
Tangent to the lower border.
The Mandibular outline

55. Bjork’s four stable
landmarks are marked
on the pretreatment
and post-treatment
cephalogram.
The two cephalograms
are superimposed .

56. •This method gives a
medium to high
degree of validity and
reproducibility
•Mandibular rotations
are evaluated by
changes in N-S lines.
•The angle between
the two line gives the
amount of mandibular
rotation.

57. The mandibular superimposition method
advocated by the ABO is to register on the internal
cortical outline of the symphysis with the best fit
on the mandibular canal to assess mandibular
tooth movement and incremental growth of the
mandible

58. Methods to assess growth vs treatment
changes
Though the techniques described till now will assess
the amount of growth changes in a given duration of time or
the overall changes of treatment and growth during a given
treatment period they do not however differentiate between
changes produced due to growth and changes produced due
to treatment.
The following cephalometric analyses help us to assess
treatment changes against the background of natural growth
of the individual

59. Superimposition methods to study
treatment changes

60. Rickett’s twelve factor summary
analysis
Ricketts’ approach to selection of landmarks and
parameters was primarily based on the pattern of facial
growth.
Two types of landmarks were used by him .
The first types were skeletal landmarks and second dental
landmarks.
His 11 factor analysis of skeleton and dental relationship
later had the addition of 12th factor which encompasses
evaluation of soft tissue profile.

61. Rickett’s 12 factor summary analysis

76. Rickett’s five position analysis
The analysis is based on Rickkets short
term growth forecasting data which was obtained
on patients – both male and female of different
ages and growth patterns undergoing orthodontic
treatment.
Takes into consideration two superimposition
areas to evaluate orthopedic change and two
superimposition areas to evaluate orthodontic
change against growth.

77. Five areas of superimposition within which are a
total of seven areas of evaluation are used to
evaluate amount and direction,
change in normal growth and
change due to treatment.

78. Rickett’s five position analysis
Position 1

79. Position 2

80. Position 3

81. Position 4

82. Position 5

83. Pitchfork analysis
The pitchfork analysis was developed by Johnston in
1985

84. Used to describe the
treatment effects of
different treatment
strategies used to correct
Class II patients
Data recorded in the form
of a pitch fork

85. Superimposition
The pitchfork analysis requires that one measures
skeletal changes as actual physical displacement, rather
than apparent change in the position of a landmark due
to surface remodeling.
The pitchfork analysis employs three general
superimpositions – cranial base, maxilla and mandible.

86. Cranial Base
The reference structures employed are: the anterior
wall of sella turcica, the greater wings of sphenoid,
the cribriform plate, the orbital roof and the inner
surface of frontal bone.

87. Maxilla
Registration is based on the zygomatic process of the maxilla
(‘key ridge’) and the curvature of the palate.
Orientation is based on the superior and inferior surfaces of
the posterior hard palate.

88. W – maxillary advancement
relative to cranial base (MAX).
D – mandibular displacement
relative to maxilla (ABCH).
Both the measurements are
made parallel to MFOP

89. Mandible
Registration is achieved by aligning the bony architecture of the
facial half of the symphysis.
Orientation is by aligning the mandibular canal or the molar tooth
germs. However, these details are often absent, difficult to see, or
distorted in the cephalogram.
In these cases, the mandibular plane can be used as a substitute
orientation line.

90. Mandibular regional superimposition

91. Measurement of change
Although the face undergoes widespread change during
orthodontic treatment, only effects that are felt at the level of
occlusion can have direct impact on the molar and incisor
relationships.
For this reason, the Pitchfork analysis measures change
projected onto the plane of occlusion (i.e. parallel to the occlusal
plane).

92. The Pitchfork analysis uses a ‘functional’ occlusal plane (FOP)
which is defined as: “the average occlusal plane of the buccal
teeth, including canine and the first permanent molar”.
The FOP is a best-fit line passing through the occlusal overlap in
the region of the first molars, premolars and canines.
It is insensitive to incisor movement, it is representative of the
bulk of the buccal occlusion, and it is relatively stable over time.

93. When a two-film series is to be analyzed, the maxillae are
superimposed, and the two FOP are averaged by inspection to
yield a mean functional occlusal plane (MFOP).
When more than two films need to be analyzed, the MFOP is
obtained by averaging the initial and final functional occlusal
planes.
After establishing the MFOP, regional superimposition within
cranial base, maxilla and mandible is used to measure the various
components of antero-posterior change.

94. In the anterior cranial base, ‘wing point’
(W, the point at which the averaged outline of the
greater wings of the sphenoid crosses the jugum
sphenoidale) serves as the registration point, and is
used here as the cranial base reference point from
which maxillary and mandibular displacement are
measured.
Jaw growth/displacement relative
to cranial base

95. To measure displacement of the maxilla relative to
cranial base (MAX), the maxillary fiducial lines are
superimposed and the separation of the W points is
measured parallel to MFOP.
The separation of the D points is measured parallel
to MFOP.
This measurement represents apical base change
(ABCH), the growth/displacement of the mandible
relative to the maxillary basal bone

96. Thus, the mandibular displacement relative to cranial
base (MAND) can be estimated by:
MAND = ABCH – MAX
These three measurements abstract the sagittal growth
of the jaws and, together with tooth movement, account
for change in molar relationship and overjet.

97. Tooth movement relative to basal bone.
Tooth movement is measured parallel to MFOP.
Molar crown movement is measured at the mesial contact
point.
Root movement is measured from the point at which the long
axis is crossed by a line drawn between the apices of the
buccal roots.
Crown(total) movement is the algebraic sum of root (bodily)
movement and a component of tipping. Thus, tipping
component can be estimated by subtracting root movement
from crown movement.

98. Incisal movement is estimated by the displacement of the incisal edges of the
upper and lower central incisors.

99. Molar relationship and overjet change.
The change in molar relationship is measured by registration on
the mesial contact point of one molar (upper or lower) and
then measuring the separation of the contact point on the
other.
The change in overjet is measured by registering on the
averaged incisal edge of the upper or lower incisors and then
measuring the displacement of the averaged incisal edge in the
other arch.

100. Mandibular tooth movement is measured with reference to an orientation on
MFOP and a registration on a perpendicular from MFOP erected through D.

101. Over-jet change

102. Pancherz analysis
For all the linear measurements on the before- and after-
treatment tracings,
the occlusal line (OL) and the occlusal line perpendicular
(Olp) from the first head film were used as a reference grid.
The grid was transferred from the first tracing to the second
tracing by superimposition of the tracings on the nasion-
sella line (NSL) with sella (s) as registration point.
All measurements were done parallel to OL

104. 1. is/OLp minus
ii/OLp— Overjet.
2. ms/OLp minus
mi/OLp— Molar
relation (a positive
value indicates a distal
relation; a negative
value indicates a
normal relation).

105. Skeletal measuring points
3.sp/OLp— Position of
the maxillary base.
4.pg/OLp— Position of
the mandibular base.
5.ar/OLp— Position of
the condylar head.
6.pg/OLp + ar/OLp—
Mandibular length.

106. 7.is/OLp— Position of the
maxillary central incisor.
8.ii/OLp— Position of the
mandibular central incisor.
9.ms/OLp— Position of the
maxillary permanent first
molar.
10.mi/OLp— Position of the
mandibular permanent first
molar

107. Changes in the different measuring points in relation to OL,
occurring during the examination period were registered by
calculating the difference (d) in landmark position.
Changes in variables 3 to 6 represent skeletal changes,
while changes in variables 7 to 10 represent a composite
picture of skeletal and dental changes.
Variables for dental changes within the maxilla and
mandible were obtained by the following calculations
(variables 11 to 14)

108. •11. is/OLp (d) minus sp/OLp (d)—
Change in position of the maxillary
central incisor within the maxilla.
•12. ii/OLp (d) minus pg/OLp (d)—
Change in position of the mandibular
central incisor within the mandible.
•13. ms/OLp (d) minus sp/OLp (d)—
Change in position of the maxillary
permanent first molar within the maxilla.
•14. mi/OLp(d) minus pg/OLp(d)—
Change in position of the mandibular
permanent first molar within the
mandible.

109. The OL/OLp reference system was chosen for
the following reasons
(1) The system is close to the problem area.
(2) The system is consistent.
The main reference point sella (s) is relatively stable
(3) All registrations are performed to only one reference line
(OLp) .
This makes it possible to relate alterations in the occlusion to
skeletal and/or dental changes and to assess the
interrelationship between these changes in and between the
two jaws.

110. I-point and I-curve superimposition
Standerwick et al. proposed a new orientation
plane for the purpose of cephalometric
superimposition.
The ACB is oriented parallel and referenced at
I-point/I-curve on the occipital condyles (OCs),
from which the other landmarks are measured

112. Landmarks for the use of the OC as a posterior cranial base
reference are I-point, U-point, and I-curve (Ic).
Occipital point O′ is the intersection of the ventrocaudal
contour and the anterior outlines of the OCs.

113. Advantages
1. It was found that I-point registered superimpositions
consistently displayed a facial growth pattern that was
more consistent with the classic necropsy specimens of
children and the cephalometric studies superimposing on
implant markers.
2. By superimposition at I-point, the physiologic movement
of sella turcica, development of the airway and proportional
craniofacial development is better displayed than with
traditional ACB superimposition

114. Superimposition requirements of
American Board of Orthodontics
ABO guide lines recommend use of the same template to
trace the maxillary and mandibular incisor and molars so as
to maintain consistency in shape and size of teeth.
The soft tissue outline of the facial profile is required for
each tracing.
The FH line is drawn on all tracings.
Craniofacial tracings are superimposed on the anterior
cranial base (ACB).

116. Automatic superimpositions
The process is conducted in three stages.
Stage I: To digitise and calibrate the cephalogram through the
CCD camera, in case images are not digital.
Stage II: To extract the feature curves for the cranial base using
the best orient edge detector and Hough transform, and for the
mandible using the Laplacian of Gaussian and grouping.
Stage III: To automate the superimposition based on the clinically
available procedure and finally to display the associated results.
This procedure should typically take 5–6 min of computation.
Chen et al. reported a high precision with this method which for
the cranial base superimposition was about 0.312 cm, and the
mandible was about 0.005 cm

117. (A) The feature curve obtained using the grouping method.
(B) (B) The final result for mandible cephalometric superimposition.

118. 3D superimposition
The superimposition of 3D CBCT images is used for
evaluation of growth related changes and evaluation of
treatment effects.
3D CBCT images from two different time points can be
superimposed using landmark based method or
mathematical algorithm methods.
In landmark based method, three are more landmarks on
two or more CBCT images are used for superimposition.
Once the initial superimposition is made, the software
program allows operator to move the CBCT images
manually for further fine tuning

120. The mathematical methods include:
1) voxel based superimposition,
2) software based technique using information
therapy,
3) ICP method,
4) triple voxel based superimposition.

121. Voxel based superimposition method is an automated
computerised superimposition method, which eliminates
observer dependent landmark plotting.
In this method the stable anatomical structures, ACB, grey
values of each voxels between two CBCT images are
compared by the software program
In this way the software computes the rotation and
translation required in three dimensions to align the post
treatment CBCT images according to pre-treatment CBCT
image.
It does not depend on the precision of the 3D surface
models.

123. CONCLUSION
Cephalometric superimposition has been extensively
used to assess growth and treatment changes since its
introduction and has been a major research tool in the
hands of orthodontists.
Serial cephalograms have been superimposed on
stable cranial points to study changes in the face, jaws and
dentition.
The 3D visualisation and volume rendering images
obtained through CBCT have opened up new vistas of
studies in craniofacial morphology and studies on growth.