Down's,ricket's & cephalometric superimposition /certified fixed orthodontic courses by Indian dental academy

DOWN’S ANALYSIS
RICKETT’S ANALYSIS
&
CEPHALOMETRIC SUPERIMPOSITION

www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


DOWNS ANALYSIS
DOWNS ANALYSIS WAS INTRODUCED BY W.B. DOWNS IN 1948.
This analysis was one of the first to be introduced

DOWNS SAMPLE


The control material studied by downs was derived form 20 white
subjects, who ranged in age from 12 to 17 years.



All individuals possessed clinically excellent occlusions.


VARIOUS LANDMARKS USED IN DOWNS ANALYSIS

Nasion
Sella
Porion
Point A (Subspinale)
Point B (Supramentale)
Gnathion
Pogonion
Orbitale
Bolton point - The highest point on the concavity behind
the
occipital condyles

VARIOUS PLANES USED IN THIS ANALYSIS

Most important reference plane (FRANK FORT HORIZONTAL
PLANE)

OCCLUSAL PLANE

N

MANDIBULAR PLANE
FACIAL PLANE
Pog


Downs anaylsis describes the
skeletal pattern and dental pattern
Skeletal pattern
 Facial angle
 Angle of convexity
 A-B plane
 Mandibular plane angle
 Y (Growth) Axis

Dental pattern
 Cant of occlusal plane
 Inter incisal angle
 Incisor occlusal plane
angle
 Incisor mandibular plane
angle
 Protrusion of maxillary
incisors.


Downs Facial Types
WB downs noted the position of
the mandible could be used in
determining the facial types.
Downs four basic facial types
Retrognathic facial type

Orthognathic facial type

Prognathic facial type

True prognathism

FACIAL ANGLE
This is the inferior inside angle in which
the facial line (nasion-pogonion)
intersects Frankfort horizontal plane.
The mean reading for this angle is 87.8
degrees (SD, 3.6) range varies from 82
to 95 degrees.
The facial angle is used to measure the
degree of retrusion or protrusion of the
lower jaw.

N
FH Plane

Pog

ANGLE OF CONVEXITY
 The angle of convexity is formed by the
intersection of line N-point A and point
A-pogonion.
 This angle measures the degree of the
maxillary basal arch at its anterior limit
(point A) relative to the total facial
profile (nasion-pogonion)
 This angle measures the convexity or
concavity of skeletal profiles.
 The range extends from a minimal of –
8.5 degrees to a maximal of +10 degrees,
with a mean reading of 0 degree.

A-B PLANE
 This angle is formed between a line
connecting point A and point B and line
Joining nasion to pogonion (facial
plane) .
 The A-B plane is a measure of the
relation of the anterior limit of the apical
bases to each other relative to the facial
plane.
 The readings extend from a maximal of
0 degree to a minimal of –9 degrees with
a mean reading of –4.6 degrees.

MANDIBULAR PLANE PLANE
 Mandibular plane according to
downs, is tangent to the gonial
angle and the lowest point of the
symphysis.
 The mandibular plane angle is
established by relating the MP
to the Frank fort horizontal
plane.
 The range of readings extends
from a minimal of 17 degrees to
a maximal of 28 degrees with
mean reading of 21.9 degrees.

Y – (GROWTH) AXIS
 The y-axis is measured as the acute
angle formed by the intersection of a
line from the sella turcica to
gnathion with the Frankfort
horizontal plane
 The y-axis indicates the degree of
the downward, rearward, or forward
position of the chin in relation to the
upper face.
 The range extends from a minimal
of 53 degrees to a maximal of 66
degrees with a mean reading of 59.4
degrees.

CANT OF OCCLUSAL PLANE
 Downs
occlusal

originally
plane

defined
as

that

the
line

bisecting the overlapping cusps of
the first molars and the incisal
overbite
 The cant of the occlusal plane is a
measure of the slope of the
occlusal plane to the Frankfort
horizontal .
 The minimal angular measurement
is +1.5 degrees; the maximal +14
degrees;

and

the

mean

+9.3


INTERINCISAL ANGLE
 The interincisal angle is established
by passing a line through the incisal
edge and the apex of the root of the
maxillary and mandibular central
incisors.
 The minimal angular reading is 130
degrees; the maximal 150 degrees;
and the mean 135.4 degrees.
 This angle is decreased in class I
bimaxillary protrusion and Class II
div1 cases. Increased in Class II div 2
cases.


INCISOR – OCCLUSAL
PLANE ANGLE
 The incisor – occlusal plane angle
relates the lower incisors to their
functioning surface at the occlusal
plane .
 The inferior inside angle is read as a
positive or negative deviation from a
right angle. The positive angle
increases as the teeth incline forward.
 The minimal angle is +3.5 degrees;
the maximal +20 degrees; and the
mean 14.5 degrees (SD, 3.5)

INCISOR – MANDIBULAR PLANE
ANGLE
 The incisor mandibular plane angle
is formed by the intersection of the
mandibular plane with a line
passing through the incisal edge
and the apex of the root of the
mandibular central incisor
 The minimal angular reading is –
8.5 degrees; the maximal, +7
degrees; and the mean 1.4 degrees.

PROTRUSION OF MAXILLARY
INCISORS
 The protrusion of the maxillary
incisors is measured as the distance
between the incisal edge of the
maxillary central incisor to the line
from point A-pogonion
 The distance is positive if the incisal
edge is ahead of the point Apogonion line and indicates the
amount
of
maxillary
dental
protrusion.
 The minimal reading is –1.0 mm; the
maximal +5 mm, and the mean +2.7
mm

Parameter

Minimal
(degrees)

Maximal
(degrees)

Mean
(degrees)

SD

Skeletal pattern
Facial angle

82

95

87.8

3.6

Angle of
convexity

-8.5

+10

0

5.1

A-B plane angle

-9

0

-4.6

3.7

Mandibular plane 17
angle

28

21.9

3.2

Y- axis

66

59.4

3.8

53

Dental pattern
Cant of occlusal
plane

+1.5

+14

+9.3

3.8

⊥to 1

130

150.5

135.4

5.8

+20

+14.5

3.5

+7

+1.43

3.8

+2.7 mm

1.8

+3.5
⊥ To occlusal
plane
1 To mandibular -8.5
plane
⊥ To A-P plane

-1.0 mm

+5 mm

Vorhies and Adams, 1951
Polygonic interpretation of
Downs analysis


RICKETT’S ANALYSIS
This analysis was introduced by Robert Murray Ricketts
in the year 1960
Material for this study was collected form 1000 white
subjects in the age group of 3-44 yrs

Various land marks in this analysis
 A6 - point on the occlusal plane located
perpendicular to the distal surface of the
crown of the upper first molar.
 B6 - Point on the occlusal plane located

PT
CC

perpendicular to distal surface of the crown
of the lower first molar.
 C1 - Point on the condyle head in contact
with and tangent to ramus plane.
 DT - Point on the anterior curve of the soft tissue chin tangent to the
esthetic plane or E-line.
 CC - Point of intersection of the basion – nasion plane and the faical

Other land marks
 DC - Point in the center of the condyle
neck along the Ba-N plane
 PT -Point

at

junction

of

the

pterygomaxillary fissure and the foramen
rotundum

PT
CC

 En - Point on the soft tissue nose tangent
to the esthetic plane or E-line.
 Gn - Point at the intersection of the facial
and the mandibular planes


Go - Point at the intersection of the ramus and the mandibular planes.



TI - Point of intersection of the occlusal and the facial planes


PM - Point at which the shape of the symphysis
mentalis changes from convex to concave- also
known as protuberance menti.
Pog - Point on the bony symphysis tangent to the

facial plane.
PO - Intersection of the facial plane and the corpus
axis.


LOCATION OF Xi POINT
Xi - Point located at the centre of the ramus.
 Locate FH and draw PtV plane
perpendicular to the FH plane
 Construct four planes tangent to
points R-1, R-2, R-3 and R-4 on the
borders of the ramus.
 The constructed planes form a
rectangle enclosing the ramus
 Xi point is located in the center of
the rectangle at the intersection of
the diagonals.


REFERENCE PLANES USED

Facial plane
Mandibular plane
Frank fort horizontal plane
Basion - Nasion plane
Ptv plane
Denture plane
Esthetic plane

LOCATION OF AXIS

DC

Facial axis
Condylar axis
Corpus axis


Various measurements used in this analysis
To locate the position of chin
Facial axis
Facial angle
Mandibular plane angle
Convexity of the face
Convexity at point A
Position of upper & lower teeth
Lower incisor to APog line
Upper molar to Ptv plane
Lower incisor to Apog plane
Evaluate the facial profile
Lower lip to E-plane


Facial
Angle

Facial axis
FACIAL ANGLE (Depth)
The angle formed between the facial plane (N-pog) and the frank fort
horizontal plane.
Mean values for 9 year old is 87o ± 3 and increases 1o every 3 years

FACIAL AXIS
The angle formed between the Basion -Nasion plane and the plane
from foramen rotandum (PT) to gnathion.
On the a average this angle is 90o ± 3.5 degrees and there is no age
changes.

Go

MANDIBULAR PLANE ANGLE
Measures an angle formed by the mandibular plane
(Gonion – Gnathion) with Frankfort horizontal plane
On the average this angle is 26o at 9 yrs of age and
decreases 1o every 3 years

Facial contour indicator
Convexity at point A
The convexity of the middle face is measured form (point A –
N- pog).
Normal value on the average is 2 mm at 9 years of age and
decreases approximately 1mm every 3 years
According to AJO 1960
Faces displaying 2mm convexity or concavity  straight
faces.
Faces with 5 to 6 mm of convexity or concavity
moderately convex or concave.
If it is more than 10 mm or more  severely convex or
concave.

INDICATOR OF LOWER DENTURE
POSITION
Lower incisor to A-pog

Dentureplane (A-Pog) plane

The incisal tips of lower incisors are
measured to A- Pog plane and position
of lower anterior teeth determined.
 Indicates protrusion of lower anteriors
Ideally the lower incisor is 1 mm
ahead of A-Pog line.
Lower incisor Inclinations
The angle between the long axis of the lower
incisor and the A- pog plane (1 to A-Po) is
measured
On the average this angle is 28 degrees
Mean values for 9 years old is 22o±4 and there
is no changes with age. www.indiandentalacademy.com

Upper molar to PtV Plane
This measurement is the distance from the
ptery goid vertical plane to the distal of
upper molar.
Mean value in a 9 year old patient is (age
+3 mm) and 1 mm is added per year.
Evaluation of the profile
The distance between the lower lip and
esthetic plane is an indication of soft tissue
balance between the lips and profile.

CEPHALOMETRIC SUPER IMPOSITION


A

CEPHALOMETRIC

SUPERIMPOSITION

IS

AN

ANALYSIS OF LATERAL CEPHALOGRAMS OF THE
SAME PATIENT TAKEN AT DIFFERENT TIMES
CEPHALOMETRIC SUPER IMPOSITIONS INVOLVE
THE EVALUATION OF:
♦ 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

TO PERFORM ACCURATE SUPER
IMPOSITION
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.

SUPERIMPOSITION OF THE
Evaluates

MAXILLA

1. Movement of maxillary teeth
2. Rotation of maxilla
 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

Progress treatment
tracing

Super imposition of
pre & progress treatment
tracing

On each cephologram 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

MANDIBULAR SUPERIMPOSITIONS
Evaluates
Movement of the mandibular teeth
Mandibular rotation
Amount & direction of condylar growth
Stable structures for superimposition on the mandible:According to Bjork and Skieller (1983).
 The anterior contour of the chin (area 1)
 The inner contour of the cortical plates at the inferior border of
the symphysis. (area 2)
 Posteriorly, the contours of the mandibular canal (area 3)
 Lower contour of a mineralized molar germ. (area 4) before root
formation.

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.

Evaluation of the overall changes in the face
Nelson’s (1960) and Melsen (1974)
identified certain stable
structures for superimposition.
1. The anterior wall of sella turcica;
2. The contour of the cribiform plate of the ethmoid
bone (lamina cribrosa);
3. Details in the trabecular system in the ethmoid
cells;
4. The median border of the orbital roof; and
5. The plane of the sphenoid bone (planum
sphenoidale)

What can we learn from cranial base
superimpositions ?
1. Cranial base superimpositions provide an over all assessment
of the growth and treatment changes of the facial structures.
2. Amount and direction of maxillary and mandibular growth or
displacement
3. Changes in maxillary – mandibular relationships
4. Relative changes in the soft tissue (specifically the nose, lips,
and chin)
5. Information on the overall displacement of the teeth.


RICKETTS SUPER IMPOSITION
TECHNIQUE
It is one of the most important superimposition technique used.
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
1. The chin
2. The maxilla
3. The teeth in the mandible
4. The teeth in the maxilla
5. The facial profile

Superimposition area 1 (Basion – Nasion at CC point
(Evaluation area 1)

Evaluates:- growth of the chin
Position of upper molar

In normal growth chin grows
down the facial axis at 2.8mm per year
Mean change = 0o SD± 3.3o/year


Super imposition area 2 (Basion – Nasion at Nasion)
Evaluation area 2
Skeletal behaviour of maxilla

Evaluates:- Any change in position
Maxilla

In normal growth:- Basion Nasion
point A angle does not change
Maxilla drops in a parallel fashion with
point A straight down Nasion A line.
Mean change = 0o SD± 2o/year


Super imposition area 3 (Corpus axis at PM)
Evaluation area 3 & 4
Relation of mandibular teeth to
mandible

Evaluates:- Position of lower central
incisors & lower molar

Super imposition area 4 (Palate at ANS)
Evaluation area 5 & 6
Relation of maxillary teeth to
maxilla

Evaluates:- Any changes in the upper
central incisors and upper molars

Super imposition area 5
(Esthetic plane at the crossing of the occlusal plane)
Evaluation area 7

Evaluate the soft tissue
profile

Other Super Imposition Methods to Evaluate
over all changes in the face
The broadbent triangle (Na-S-Bo)
and its registration point R were
among the first structures used for
superimpositions to determine overall
changes
Sella – nasion line
Broadbent triangle
(Na-S-Bo)
In this method two tracings on the Sella
– nasion line with registration at sella

CONCLUSION
Rickett’s, Down’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.


BIBLIOGRAPHY
Orthodontic cephalometry
-

By E. Athanasiou

Radiographic cephalometry
-

By Alexander Jacobson

Contemporary orthodontics
-

By R. Proffitt

American journal of orthodontics, 1960 May (Ricketts)


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