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2. INTRODUCTION
Cephalometric radiography is a standardized method of production
of skull radiographs which are useful in making measurements of the cranium
and the orofacial complex. The radiograph thus obtained is called a
cephalogram.
Cephalometrics had its beginning in craniometry. For many
years, anatomists anthropologists were confined to measuring the craniofacial
dimensions of skull of long dead individuals. This, however was not possible
in case of living, individuals where the varying thickness of soft tissues
interfered with the accuracy of these measurements. With the advent of
radiography, an alternative, method was provided indirectly but with
sufficient accuracy, reproducibility and convenience.
Eventhough the science of cephalometrics can be a useful
diagnostic and evaluative tool for the pedodontists, the prosthodontists, the
oral surgeons and the general practitioners of dentistry, it is seen that it has
primarily remained with in the province of the orthodontic profession.
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3. HISTORY OF CEPHALOMETRICS
The concept of standardized radiographic head images
was reported by Pacini, who in 1922 demonstrated the
basic procedure of cephalometrics where by the subjects
were positioned to the cassette with gauze bandages at a
distance of 2mm from the x-ray tube. In 1931, Hofrath in
Germany and Broadbent (U.S.A.) published articles in
which they had refined the technique and applied these
principles to orthodontics.
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4. It is mandatory to use cephalometrics as a tool in the
growing child to have an idea of the growth
contributions and to cope successfully with the
problem of jaw mal-relationship.
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5. USES OF CEPHALOMETRICS
The major uses of cephalometrics are
To predict the various growth patterns.
To establish standard norms against which other
cephalograms can be compared.
Prediction of future growth.
Predicting the consequences of particular treatment plan.
Differentiation between skeletal and dental mal-
relationship by identifying and locating the nature of the
problem
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6. By diagnosing and evaluating the craniofacial morphology,
cephalometrics help in a clear treatment plan
Evaluation of treated cases serial cephalograms permit the
orthodontist to evaluate and assess the progress of treatment and
also help in guiding any desired change.
Cephalometrics had also helped in revealing much concerning
the nature of orthodontic relapse and stability of treated
malocclusions
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7. Disadvantages of
cephalometrics
Two dimentional representation of a three
dimentional object
Highly operator dependent
Anatomy or structural land marks are not constantly
identifiable
Soft Tissue and air shadow can overlie the required
hard tissue structures.
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8. BJORK’S ANALYSIS
Bjork has been an outstanding researcher in the field
of cephalometrics and its research was based on the
study of growth related changes
In 1947 he coined the term articulare (Ar), which is a
point of intersection of the posterior margin of the
ascending ramus and outer margin of the cranial base.
Feature of this analysis is to assist anterior and
posterior height relationship and to predict the
direction of growth in the lower face.
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9. BJORK ANALYSIS
Bjork conducted extensive studies on 322 Swedish boys,
12 years of age and 281 young adults 21 to 23 years of age and
included almost 90 different measurements.
This analysis was done by Bjork to investigate the effects of
variations of jaw growth and the relationship between facial form
and occlusion.The profile analysis, is similar to Steiner analysis in
that it uses the SN as the reference and SNA, SNB along with Go-
Gn.
This was published in his book “The face in profile”.
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10. Bjork used the angle N-S-Ar (saddle angle),
S-Ar-Go (Articular Angle) and Ar-go-Gn (gonial
angle) to predict the growth change in face.
Bjork felt that at the age of 11years the length of
anterior cranial base (S-N) should be equal to
mandibular body length (go-me)
He stated that the ideal ratio of posterior cranial
base length to ramus height is 3:4.
This gives the basic skeletal evaluation and
the incisor axis to A-Pog relates the denture to the
skeletal base.
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11. 1. S-NA 7. S-gn
2. S-Ar 8. Na-Go
3. Ar-Go 9. Na-A
4. Go-Gn 10. Na-B
5. Na-Pog 11. A-Po
6. Occlusal Plane 12 long axis of the incisors
The lines that are used are as follows.
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12. THE CRITERIA USED
CRITERIA NORMAL VALUES
1. SADDLE ANGLE 123o
+ 5o
2. ARTICULARE ANGLE 143o
+ 6o
3. GONIAL ANGLE 130o
+ 7o
4. SUM OF ABOVE 3 396o
5. ANT. CRANIAL BASE LENGTH 71 + 3 mm
6. POST. CRANIAL BASE LENGTH 32 + 3 mm
7. RAMUS HEIGHT 44 + 5 mm
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13. 8. BODY LENGTH 71 + 5 mm
9. MANDIBULAR BODY:
ANTERIOR CRANIAL BASE 1 : 1
10. SNA 80o
11. SNB 78o
12. ANB 2o
13. ANTERIOR FACIAL HEIGHT 62 - 62%
POSTERIOR FACIAL HEIGHT
14. LOWER INCISOR TO MANDIBULAR PLANE 90 + 3
15. UPPER INCISOR TO FACIAL PLANE 5 mm + 2 mm
16. LOWER INCISOR TO FACIAL PLANE 2 mm + 2 mm
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14. BJORK’S POLYGON
In this analysis a polygon is used to assess the anterior and
posterior facial height relationships and also to predict the
direction of growth change in the lower face. The basis of this
is the relationship of the 3 angles.
Saddle angle (N.S Ar), Articulare angle (S-Ar-Go), Gonial
Angle (Ar-Go_me) and the length of the sides of the polygon.
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15. It says, Anterior cranial base (S-N) should be
equal to the mandibular body length (Go-Me).
The ideal ratio of the posterior cranial base
length (S-Ar) to the ramus height is 3:4
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16. If the sum total of the 3 angles, Saddle angle, Articular
angle, Gonial angle exceeds 396, there would be tendency
towards “clockwise” growth change in mandible. In case
with the total less than 396 there would be a tendency
of“counter clock-wise” growth change in the mandible.
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17. Clockwise Change:
Indicates that the anterior facial height is increasing more
rapidly than posterior facial height and it could be associated
with backward growth at the symphysis leading to anterior
openbite tendency.
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18. Counter Clockwise Change:
Indicate that the posterior face height is increasing more rapidly
giving rise to forward growth of chin and anterior deep bite tendency
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19. Bjork along with the Skieller (1977) in order to study growth,
applied implants studies in animals and human beings.
It involves the implanting of small bits of inert alloy into the bone as
radiographic reference points.
The areas where the implants were placed :
Maxilla : Hard palate behind the deciduous canines.
Below the anterior nasal spines.
Two on each side of the zygomatic process
Mandilble : One in the mid line of the symphysis
Two under the first and the second pre molar
One under the external aspect of the ramus.
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21. Their study revealed
Maxilla :They stated that maxilla undergoes extensive
remodeling during the growth period
Resorption occurs in the lower part of the lower part of
the nasal floor more anteriorly than posteriorly.
Mandible :Mandibular growth occurs essentially at the condyle and
the direction of the growth generally forward
Thickening of the symphysis was found to be attributable to
growth on posterior surface and on the lower border. The apposition
and resorptive processes result in individual shaping of the lower
border of the mandible, characterizing its growth
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22. Their results showed that the maxilla grows downward from
the cranial base at the rate of about 0.7 mm per year.
Maxillary tooth eruption increases dentoalveolar height about
0.9 mm per year. Mandibular eruption is about 0.75 mm
annually. The nasomaxillary complex descends around 1.5 to
2 mm per year of the eruption of the mandibular teeth is
added to this. These is a total vertical development between
2 & 3 mm per year.
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24. Jarabak Skeleto Dental
Cephalometric Analysis
Jarabak introduced a new measurement by adopting
and modifying the Bjork’s analysis
The following is a description of the linear and
angular measurements of the Jarabak Skeleto-Dental
Analysis.
The means of these angles is based on an average for
Caucasian boys and girls at age 11 years
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25. SKELETAL ANALYSIS
SADDLE ANGLE:
This angle is formed by the junction of the N.S.
line meeting with the a-S line at the center of the
sella. The small “a” is the articulare.
The mean of the saddle angle is 123o
+ 5o
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26. ARTICULARE ANGLE:
This is referred to as the joint angle and is an
angle that can be changed by orthodontic
treatment. It is the angle formed by the line from
the S to “a” and the line from “a” to Go
The mean value for this angle is 143o
+ 6o
.
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27. GONIAL ANGLE:
This angle is formed by the body of the
mandible and the ascending ramus meeting at
extended Go point.
The mean value of this angle is 130o
+ 7o
.
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28. Saddle angle (S), articular angle (ar) and gonial angle (go)
and upper and lower gonial angles (Go1 & Go2)www.indiandentalacademy.com
29. SUMTOTAL
This total is obtained by adding the saddle, articular and
gonial angles.
The mean total of this skeletal angles is 396o
. Any
skeletal angle with the total of 403o
– 405o
or greater is a
clockwise (posterior) grower. Any skeletal angle below
394o
is a counterclockwise (anterior) growing face.
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30. ANTERIORCRANIAL BASE:
This is the S-N line measured linearly. According to
Bjork the linear measurement for twelve year olds is
68.75 mm with a standard deviation of 2.97
The mean for this measurement established by Jarabak, is
71 mm – 3mm.
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31. POSTERIORCRANIAL BASE:
This is the linear measurement from point S to
point “a”.
The mean for this line is 32 mm. This line is
related to ramal height (a-Go) in a 3 : 4 ratio.
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32. GONIAL ANGLE ANDITS PARTS:
In order to estimate growth direction more accurately,
we must go beyond accepting the gonial angle as a
single factor of mandibular morphology.
If the upper angle is large 58o
to 65o
the remaining
growth increment will be sagittal.
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33. In the facial structures if the upper half of the gonial
angle is small (43o
to 48o
) the remaining mandibular
growth increment will be downward and backward.
Growth in the ramus will make the lower face more
prognathic.
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35. RAMUS HEIGHT:
This linear measurement is from the articulare to extended gonion
angle. The Bjork sample height is 43.48 mm + 0.26mm.. In the
Jarabak sample the mean length is 44 mm. This measurement
(44 mm) is related to the posterior Cranial Base Length (32
mm) in a 3 : 4 ratio. The ramus height increased in length with
growth.
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36. MANDIBULARBODY LENGTH
(CORPUS):
The mandibular body length mean is 77mm. It
is in a 1:1 ratio with anterior cranial base. This
value is the same as the Bjork sample
(73.58 mm + 0.31 mm).
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37. SNA ANGLE:
The maxilla can be related to the cranium
in one of three ways:
Normal relation
Maxilla posterior to normal
Maxilla anterior to normal.
The criteria which is used to determine which one of the three
possibilities is present in the angle is described by two planes.
Sella to nasion (SN) and
Nasion to point A(NA).
The Jarabak mean for the SNA angle is 78o
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38. SNBANGLE:
The mandibular apical base is also
related to the cranium in of the three ways;
Normal raltion
Mandible posteriorly related to cranium.
Mandible anteriorly related to cranium.
The mandibular apical base is identified by the letter B. the
angle between mandibular base and cranium is SNB. The
Jarabak mean is 76o
to 78o
.
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39. SN-gome ANGLE
(ANTERIORCRANIAL BASE AND
MANDIBULARBODY LENGTH)
The mean of this angle is formed by the extended junction of the
SN line with GoMe line is 32o
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40. FACIAL DEPTH– N.Go:
This is a line measured from the nasion (N) to the
extended gonion and is listed in millimetres.
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41. FACIAL LENGTHON ‘ Y AXIS:
This is a line measured from the sella to a
point at the lowest portion of the most
prominent part of the pogonion.
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42. Y AXIS TO SN:
This angle is formed by the junction of the
facial length with anterior cranial base line
(N-S).
The mean range for this angle is 64o
to 68o
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43. POSTERIORFACE HEIGHT
(S-Go):
This is also known as the Jarabak axis and
contributes along with anterior face height in
forming the Face Height Ratio.
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45. POSTERIORANDANTERIORFACE
HEIGHT RATIO:
This ratio is indicated by percentage is determined by
dividing the anterior face height (mm) into the
posterior face height (mm). This will then give the
direction the face will grow, either clockwise or
counterclockwise.
In this both the anterior and posterior facial heights are
expressed in the form of a ratio as follows
Anterior facial height
x 100
Posterior facial height
The mean range for clockwise growers is 54 to 58% or
less. In the counterclockwise grower the mean range is
64 – 80%. www.indiandentalacademy.com
47. DENTAL ANALYSIS:
OCCLUSAL PLANE TOBODY OF
MANDIBLE (OCC. PL. TOGoMe):
This is measured at the junction of the occlusal plane
line where it meets the Go-Me line to form an angle.
The mean of this angle is 12o
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48. DENTAL CONVERGENCE OF
MAXILLARY ANDMANDIBULAR
INCISORS (DENT. CONV. 1.1):
This angle is the junction of a line drawn through the
long axis of the maxillary and mandibular incisors.
The mean of this angle is 133o
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49. MANDIBULARINCISORTO
BODY OF MANDIBLE ( 1 to GO-Mr):
A line is drawn through the long axis of the
mandibular incisor tooth which meets the line of the
body of mandible gives the angle of the forward or
backward position of the incisors.
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50. MAXILLARY INCISORRELATED
TOSN LINE (1 TOSN):
The mean angle of the junction of the long axis
of the maxillary incisor where it meets the SN
line is 102o
+ 2o
.
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51. MAXILLARY AND
MANDUBULARINCISORS TOFACIAL
PLANE (N-Po):
The mean for the maxillary incisors to facial
plane is 5 mm + 2 mm.
The mean for the mandibular incisors to the facial
plane is –2 mm to + 2mm.
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52. FACIAL ESTHETIC LINE
(RICKETTS):
The Rickett’s facial esthetic line is used by Jarabak because of
its simplicity, reliability and because it can be used at the
chairside without depending on the cephalogram.
Method : - Placing a straight edge on the tip of the nose and the tip
of the chin in the midline, assuming the lips are not too forward,
the relationship of the lips to the straight edge can be determined
readily.
The mean range, taken from a cephalogram, is –1 to 0.4 for the
upper lip and 0 to +2 for the lower lip.
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