INDIAN DENTAL ACADEMY
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Lateral cephalometric radiographs have
become indispensable to orthodontists in
treatment of patients ..
They are important in orthodontic growth
analysis, diagnosis,treatment planning,
monitoring of therapy and evaluation of final
treatment outcome.After the introduction of
a standardized radiographic technique using
the cephalometer by Broadbent in 1931,
different methods to evaluate the lateral
cephalometric radiograph was put forward.
A.M.SCHWARZ proposed his analysis for
orthodontic diagnosis in the year 1961 to
evaluate the lateral cephalometric radiograph
making use of standard landmarks on the
He divided his analysis into two
parts.CRANIOMETRY and GNATHOMETRY
making use of the spinapalate plane
(SpP),which is the plane that separates the
dentition from skull and also serves as the
base plane of the maxilla.
Craniometry deals with the evaluation of
the skeletal base and the profile,while
Gnathometry deals with the evaluation of the
The craniometric reference lines
used are NSe,H,SpP,
NA, and Pn.
Line NSe-is the anterior
cranial base,where Se
is the entrance of
Line NA-is the line drawn
from nasion to point A,
point A is the anterior end of
The H plane -is the Frankfort horizontal
of Simon,is determined by the skin
landmarks of the eye and ear points and
runs parallel to the NSe plane.
The Pn plane is the nasion perpendicular
of Dreyfus .This is a line drawn from soft
tissue nasion perpendicular to the H plane.
The angle formed between the SpP plane
and the Pn plane is called the inclination
angle or the “J”angle.This is similar to the
facial angle of Downs.
The average value is 85 degrees and this
is seen in cases of straight faces.5
degrees variation is accepted as normal.
If the value decreases below the
normal,in cases where the jaws slant
backwards,then it is considered as
If the angle is increased as in cases of
the jaws slanting forward it is termed as
The SpP plane forms an angle of 5
degrees with the NSe plane
The angle formed between the NA plane
and the NSe plane is called the “F “ angle
or the facial angle , the normal value is
85 degrees.If the value is larger than
normal as in case of forward displacement
of the jaw,it is considered as anteface.If
the value is lesser than normal as in case
of backward displacement of jaws,it is
considered as retroface.
Assessment of Temporomandibular joint
position is done using the angle formed
between the H plane and the Pn plane .the
normal value should be 90 degrees.
If the angle is larger
than 90 degrees then it
indicates that the
is inferiorly positioned.
If the angle is decreased
it indicates supraposition of
The landmarks and lines used by Schwarz
for analyzing the profile are
O-eye point or orbitale.
H- Frankfort horizontal plane
connecting the orbitale and the
porion(Simons eye-ear plane)
n-is the soft tissue nasion.
sn-is the subnasale
pg-is the soft tissue pogonion
gn-is the soft tissue gnathion
tr-n -is the forehead third of the face
n-sn -is the nasal third of the face
sn-gn -is the jaw third of the face
For an average profile the forehead,nasal
and jaw thirds are approximately equal in
size,the jaw third can be slightly
longer(upto 10 percent).
The jaw third is divided into two parts,one
third belonging to maxilla and the other two
thirds belonging to mandible.
The line T( mouth tangent ) drawn from
subnasale to pogonion forms and angle of
10 degrees with the Pn plane,this is called
the “T” angle.
In an ideal profile the T line should
touch the edge of the lower lip and bisect
the upper lip.
Helps to ascertain the important
morphological details of various
Deals with the evaluation of the dentition
which is contained between the two base
planes SpP and the MP(mandibular plane
go-gn) .Therefore it is independent of the
The ANGULAR MEASUREMENTS are
The Base plane angle(“B”angle) which is
the angle formed between the SpP plane
and mandibular plane,the average should
be 20 + or – 5 degrees,if the angle is less
than normal it indicates a well developed
masticatory system, if the angle is larger
it indicates underdevelopment of height in
the molar region,it plays an important role
in differentiation between the gnathic and
the alveolar open bites.gnathic openbite is
characterized by severe increase in both
the “B” angle and the gonial angle.
The gonial angle is the angle formed
between the tangent drawn to the body
of mandible(MT1 )and the tangent drawn
to the ramus of mandible( MT2),the
average should be 123 degrees plus or
minus 10 degrees.
The AB angle which is the angle formed
between the line connecting point A and
point B and the SpP plane,the average
should be 90 degrees.
The maxillomandibular angle is the angle
formed between the line connecting the
point A and pgo(pogonion osseous) and the
SpP plane ,the average being 90 degrees.
If the angle is increased
in relation to maxilla
whereas the mandibular
length may be normal or
indicates the supraposition
of the TM Joint and an
If the angle is decreased it indicates a
forwardly placed mandible in relation to
the maxilla.and also indicates
of the TM Joint and decreased
“B”angle.Every 10 degrees change in the
“B”angle corresponds to 7 degrees change
in the maxillomandibular angle.
Axial inclinations of the teeth-is the
angle formed between the long axis of
the teeth and their respective base
The average angles formed by long axes
upper central incisors,canines and first
premolars to SpP plane should be 70,80
and 90 degrees. The average angles for
lower incisors and canines to the
mandibular plane is 90 degrees.5 degrees
variation for all the angles is considered
Inter incisal angle which is the
projection of long axes of the upper and
lower central incisors till the point of
intersection should be 140 degrees plus
or minus 5 degrees.
The interincisal angle is reduced in cases
where there is an enlarged B angle in
spite of the inclinations of the teeth
being normal .
Distance between Nasion and Se(sella
entrance) is considered the length of
anterior cranial base ,average value ranging
Length of body of mandible measured along
the mandibular tangent MT1,average value
should be anterior cranial base + 3 mm.
Length of ramus-measured from gonion
upwards to the point where it intersects the
The length of the maxilla is measured
along the SpP plane from the projected
point A to to the outline of pterygomaxillary
fissure as it crosses the spina palate
plane.The average value is 47.5mm.
The average length of the jaws is
calculated in comparison with the anterior
cranial base,the average length ratio of
anterior cranial base to upper jaw should be
The average length ratio of upper jaw
to the mandibular corpus should be 2:3 .
The average length of NSe and
pogonion-gonion line is 20:21 or 60:63.
The length ratio of mandibular body
to that of mandibular ramus is 7:5.
The average length ratio between the
upper incisors and upper molars to
SpP=lower incisors and the lower first
molars to the mandibular plane which is
The average length ratio of upper
incisor (oi) to lower incisor (ui ) and
upper first molar (om1)lower first
molar (um1) which is equal to 2:3.
For all sagittal malocclusions a
variation of 5 degrees or 5mm is
acceptable because the distance
between the two buccal cusps of the
maxillary first molar is equal to 5
mm,so a 5mm shift is a must to shift
the occlusion from normal to a class II
or class III
Soft tissue thickness in the jaw region
is also considered in linear
measurements of profile.
The average horizontal
distance from subnasale
to NA line is 12mm in
children and 14-16mm
Horizontal distance of upper lip to
upper central incisor= 12 mm.
The distance of lower lip to the labial
surface of the lower incisors = 12 mm.
The average chin cushion = 10mm and
soft tissue thickness at gnathion = 6
Various cranial reference planes have
been used as baselines from which to
determine the degree of jaw
dysplasia..these reference planes deal
with cranial architecture and as such are
useful in relating the jaws to the
Measurements from the cranial base,
however do not always provide a reliable
expression of anteroposterior jaw
relationships in the dentoalveolar
The ANB angle (difference between SNA
and SNB angles is the most commonly used
measurement for appraising the
anteroposterior disharmony of the jaws.the
average ANB angle is 2 degrees.angles
greater than the mean indicate class II
skeletal disharmony and smaller angles are
indicative of class III skeletal base.
Although the ANB angle is a reliable
indication of anteroposterior jaw
relationship,there are many situations in
which this reading cannot be relied on . As
in cases with rotation of jaws.
The Wits appraisal was developed in an
effort to reduce inconsistencies found
within angle ANB when both the rotational
effect of the jaws relative to cranial
reference planes and the anteroposterior
spatial relationship of nasion relative to the
jaws are considered.
The wits appraisal is a measure of the
extent to which the jaws are related to
each other. This appraisal relates point A
and point B to the occlusal plane, providing
a measurement of the anteroposterior
relationship of the jaws nearer the teeth
than is provided by the angle ANB.
The Wits appraisal uses a constructed
occlusal plane, which is the plane of
maximum intercuspation of posteriors.
Perpendicular lines are drawn from points
A and B to this occlusal plane.
The points on the occlusal plane is named
AO and BO. From these points on the
occlusal plane, a measurement is made in
Positive values occur when point A is anterior
to point B, and negative values occur when
point B is anterior to point A.
The average jaw relationship according
to wits reading is –1.0mm for men and
0mm for women.in cases of skeletal
class II point BO would be located well
behind point AO(positive
reading)whereas in skeletal class III
the wits reading would be negative(point
BO is ahead of point AO).
The severity of anteroposterior
disharmony depends on the amount of
deviation of wits reading from the
Since the introduction of wits
appraisal,various papers addressing the
subject have been published.
Roth and Martina et al recognized the
ANB angle as an invalid measure of
sagittal skeletal disharmony because of
it being affected by rotations and
variations in the sagittal and vertical jaw
dimensions relative to the cranial base.
According to Roth two factors affect
the wits reading,they are occlusal plane
angle and vertical alveolar dimensions.
If the distance between point A and
point B is increased then the wits
reading also increases…so Roth gave an
alternate procedure whereby a
standard distance of 50 mm is used
along the A-B line .
According to him the anteroposterior
effect of wits appraisal of changes in
occlusal plane could be used for
determining changes in the molar
relationship relative to the occlusal
This technique is possible only if the first
molars move on arcs with centers at A and
Since Jacobson defined the functional
occlusal plane only as "the line drawn
through the region of maximum cuspal
inter digitation," the diagnosis of "anteroposterior jaw discrepancy" by means of
the Wits appraisal may incorporate a large
inherent error arising from the
subjectivity of the method.
Various attempts have therefore been
described to reproduce the occlusal plane
in a more satisfactory manner .
Wits appraisal is a linear measurement
and not an analysis itself.It is simply
adjunctive diagnostic aid that may prove
useful in assessing the extent of
anteroposterior skeletal dysplasia and
determining the reliability of the ANB
Identification of landmarks and
interpretation of findings of a three
dimensional object on a two-dimensional
image cannot be regarded as truly
No single parameter in cephalometry
should be relied on entirely and
interpreted as an absolute
value,Correlation between the linear and
angular measurements is a must for
Textbook of radiographic cephalometry
by Alexander Jacobson.
A practical evaluation of the X-ray
headplate by A.Martin Schwarz (original
article )(AJO-Aug 1961)
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