Limitations of cephalometrics of ceph

SEMINAR
ON
LIMITATIONS OF
CEPHALOMETRICS
www.indiandentalacademy.com

CONTENTS
1.INTRODUCTION
2.REVIEW OF LITRETURE
3.CLASSIFICATION OF CEPHALOMETRIC
ERRORS
4.PROJECTION ERRORS
5.LANDMARK IDENTIFICATION ERRORS
6.LIMITATIONS IN SUPERIMPOSITION
7.LIMITATIONS OF CEPHALOMETRIC
ANALYSIS

CONTENTS
8) LIMITATIONS OF VERIOUS REFERENCE
PLANES USED IN CEPHALOMETRICS
9) CONCEPTS OF NATURAL HEAD POSITION
AND NATURAL HEAD POSTURE
10) LIMITATIONS OF VARIOUS CEPHALOMETRIC
ANALYSIS COMMONLY USED
11) ADVANTAGES & LIMITATIONS OF DIGITAL
CEPHALOMETRY
12) CONCLUSION AND BIBLOGRPHY

• Cephalometry, or the measurement of the head, was
developed as an anthropological technique to quantify shape
and size of skull. The discovery of x-rays by Roentgen in
1895 revolutionized medicine and dentistry. About 36 year
later i.e; 1931, traditional cephalometry in two dimensions,
known as roentgenographic cephalometry, was introduced to
the dental profession by Broadbent and has since remained
relatively unchanged.
• Since these early years, cephalograms have been used
widely as a clinical and research tool for the study of
craniofacial growth, development, and treatment.
• However, because of the traditional 2-dimensional
cephalometry, use of this method for deriving clinical
information as a basis for determining treatment plans has
been questioned.
INTRODUCTION

• The following issues question the validity of 2-
dimenstional cephalometry to derive clinical
information used in treatment planning.
1) A conventional head film is a 2-dimentional
representation of a 3-dimentional object. When 3-
dimentional object is represented in 2-
dimentions,the imaged structures are displaced
vertically and horizontally. The amount of
structural displacement is proportional to the
distance of the structures from the film or
recording plane.

2) Cephalometric analysis are based on
the right assumption of perfect superim -
position of the right and left sides about
the midsagittal plane.
• Perfect superimposition is observed
infrequently because facial symmetry is
rare and because of the relative image
displacement of the right and left sides.
• These inherent technical limitations do
not produce an accurate assessment of
craniofacial anomalies and facial
asymmetries. www.indiandentalacademy.com

3) The projection geometry prevent the
ability to acquire accurate dimensional
information aligned in the direction of the
x-ray beam.
4) A significant amount of external errors,
known as radiographic projection error, is
associated with image acquisition. These
errors include size magnification, errors in
patient positioning, and projective
distortion inherent to the film-patient-focus
geometric relationships.

5) Manual data collection and processing in
cephalometric analysis have been shown to have low
accuracy and precision.
6) Significant error is associated with ambiguity in
locating anatomic landmarks because of the lack of
well-defined anatomic features, outlines, hard edges
and shadows, and variation in patient position. Such
landmark identification errors are considered
major source of cephalometric errors. Despite
these limitations of cephalometry, many
cephalometric analyses have been developed to help
diagnose skeletal malocclusions and Dentofacial
deformities. However, several investigations have
questioned the scientific validity of such analyses.www.indiandentalacademy.com

• Pacini in 1922 – described a rather primitive
method for the standardization of radiograph
imaging of the head. He recommended the
positioning of a subject at a fixed distance of 2
mtr from the x-ray source with a film cassette
fixed to the head with a wrapping of gauze
bandages.
• Hofrath of Germany and Broadbent of the
United states in 1931- published their own
method of obtaining standardized head
radiographs.
REVIEW OF LITRATURE

• Bjork in 1947 –described errors arising from
differences in projection between two films of the same
individual. He also noted that the difficulties involved in
locating different landmarks varied depending on the
nature of the landmark examined. This was confirmed
by Richardson 1966- who noted that some landmarks
were more reproducible vertically than horizontally and
vice versa.
• In a study by Van Aken in 1963- projection errors
were found to be small but might be of significance in
cephalographs of asymmetrical skulls or in the case of
anatomical landmarks that do not lie in the midsagittal
plane.
REVIEW OF LITRATURE

• Baumrind and Frantz in 1971- found that repeated
identification of the same landmark on the same
cephalometric image resulted in errors and they also
studied the side effects of uncertain landmark
identification and found these errors were significant
when transmitted to angular & linear measurements.
• Rossmann & Wiley in1970- claimed that
interpretation of radiographic image is dependent on
radiological knowledge, pattern recognition , physical
image quality.
• Bergersen in 1980- studied magnification and
distortion in cephalometric radiography and found
discrepancies between distance measured on the film
and true distances in the object.www.indiandentalacademy.com

CLASSIFICATION OF
CEPHALOMETRIC ERRORS

Some limitations of cephalometrics According
to Moyers
1) Assumptions
a) Symmetry
b) Occlusal position
c) Orientation on the transmeatal Axis
d) Adequacy of one or two planar projections
2) Fallacies
a) The fallacy of false precision
b) The Fallacy of ignoring the patient
c) The fallacy of superpositioning
d) The fallacy of Using Chronological Age
e) The fallacy of the “ideal”
3) Misuses of cephalometric analyses

Geometric methods
I) Basic elements : A tracing has some actual
biological information, namely, location of curves
and landmarks. It also contains some non
biological information-artifacts-such as non-
curves and non-points.
A) Curves:
The curved images in the cephalogram are of three
different biological types (i) edge regression (ii)
curves in space (iii) transversals of surfaces.
i) Edges of regression surfaces –the edges of
surfaces are sometime properly shown. The
anterior border of the coronoied process, for
instance, really is a fairly sharp edge.www.indiandentalacademy.com

• But sometime that which we perceive as an
edge of a surface is neither an edge nor a
horizon. For e.g., the line we call the “alveolar
crest” line represents a col, a saddle-shaped
depression in the crest of a mountain ridge.

ii) Curves in space
In a cephalogram curves are
seen but are foreshortened and
simplified by flattening; for e.g.
the image of the mandibular
canal in cephalogram and the
resulting image in not realistic.

iii) Transversals of surfaces:
• Transversals of surfaces are neither
edges nor true anatomic loci but places
where a bone of irregular shape is viewed
most parallel to the central ray. Some
surfaces are nearly parallel to the central
ray and hence appear as a line, a problem
inherent in reducing 3-dimensions in to
two.

• For e.g. , the radiographic shadow of the
bony orbit in cephalograms and real bony
orbit on a dry skull.

B) Points& landmarks classified
A landmark is a point serving as a guide
for measurement. Cephalometric
landmarks are of the following kinds;
a) True anatomic point- anatomic points
are really small regions which might be
located on the solid skull even better than
in the cephalogram.
e.g.- ANS, infradentale, cusp tips/ incisal
edges, nasion,

b) Implants- implants are artificially
inserted radiopaque markers, usually
made of an inert metal. They are not
landmark in the usual sense . They are
private points their position from subject
to subject is not homologous. They may
be located more precisely than
traditional point and provide precise
superpositioning, but they cannot be
used to measure accurately any aspect
of the single form.www.indiandentalacademy.com

c) External points - Are points
characterized by their properties
relative to the entire outline: a) points
which are extrema of curvature, for e.g.
incision superius (Is) (b) points whose
coordinates are largest or smallest of
all points on a specific outline ,for eg
point A, point B, gnathion, condylion.
These points are less precision of
location than true anatomic points.

d) Intersection of edges of regression as points –
points defined as the intersection of images are
really lines looked at down their length. For e.g.,
articulare (Ar) and PTM are not points at all and
are in no way part of the solid skull. Such points
exist only in projections and are dependent on
subject positioning.
e) Intersection of constructed lines –intersections
of constructed lines are used as points for e.g. :
“gonion” some times is defined as the
intersection of the ramal and mandibular lines.

C) Lines / planes:
• In reality many of the so called cephalometric
planes are not flat. For e.g., the occlusal plane
drawn in the cephalogram as a straight line
represents a very complicated 3-dimensional
relationship of cusp contacts. Cephalometric lines
usually of the following types:
i) Line joining true anatomic points, for e.g. ,the
palatal line joins the ANS-PNS .

ii) Anatomic tangent lines:
• Lines through an anatomic point and tangent
to an outline elsewhere. For e.g., the facial line
is defined as joining nasion to pogonion; but
the Pog is just the point of tangency of this line
at the chin.
• Lines formed by double tangents, that is,
lines tangent to a structure, or structures, at
two points. For e.g. , the ramal line usually
touches the mandible both at the posterior
border of the ramus and along the condyle; the
mandiular line touches both near menton and
near gonion. www.indiandentalacademy.com

I) Assumptions
In any method some things must be taken
for granted as a basis for action.
a) Symmetry
• Analysis, particularly in the lateral
projection, is based on presumed skeletal
symmetry.
• All faces have minor asymmetries which
are clinically unimportant, but more serious
imbalances may be obscured by the
method or neglected by the dentist.
• Routine study of the PA projection is a
good antidote. www.indiandentalacademy.com

b) Occlusal position
• Cephalograms must be taken in some occlusal
position. It is conventional to position the
mandible in the usual occlusal position when
taking the cephalograms since this is where the
patient “bites”.
• In malocclusions with an important functional
element this convention may be misleading. One
should study carefully the patient’s mandibular
functional movements prior to recording the
cephalogram. Suspicions noted visually may be
confirmed quantitatively in the cephalogram by
two procedures;

• Use wax bites of both the usual
occlusal position ( centric occlusion)
and the detruded contact position
(centric relation) to record two lateral
cephalograms. In extreme cases the
patient may wear a diagnostic splint
for several days before the
cephalogram is obtained.
• Use the postural position as well as
an occlusal position for both the
lateral and PA projections.www.indiandentalacademy.com

c) Orientation on the transmeatal Axis
• It is convenient to use ear rods to orient the
patient’s head. The central ray is supposed to
pass along the transmeatal axis. But of course the
external auditory meati are just asymmetric as
any other cephalic structures.
• Special cephalometric procedures have been
designed without ear rods so the central
ray is 90 degrees to the midsagittal plane, but they
are not in common use.

d) Adequacy of one or two planar
projections:
Almost all routine cephalometric
analysis is done using only the lateral
projection. Much can be learned from
PA , oblique, and basilar views. The
future may bring a practical true 3-
dimensional cephalometric method.

2) FALLACIES
Any method may involve specific miscalculation,
omissions, blunders, oversights, errors, or
inaccuracies which are not the fault of the method
itself. We speak hear not about such mistakes but
about fallacies: misrepresentations intrinsic to the
method.
a) The fallacy of false precision
If one makes a series of separate cephalograms of
the same head, traces each cephalogram, locate
“A” point , nasion, and “B” point , and measures
the ANB angles, it will be discovered that the
standard error of that measure is greater than
1.5 degrees.

• Therefore, any decision, such as a
choice of treatment procedure, based on
the value of ANB angle, alone or in
combination with other measurements,
must have a gray area of approximately
+/- 1.5 degrees where the treatment
prescription is ambiguous.
• This problem is compounded when a
clinician compares a case he or she has
traced to standards developed, and
therefore filmed and traced, by another.

b) The Fallacy of ignoring the patient
• Means are population averages
which have nothing to do with the
specific characteristics of particular
patient. A patient’s measure need not
to be increased by , for e.g., 4mm just
because it differs by 4mm from the
mean.

•There are many beautiful faces in good
occlusion which have measures far from
the norms. It is not necessary to treat
malocclusion with relation to a fixed
cephalometric goal.
•Rather, cephalomerics should provide a
range of satisfactory treatment goals
which, combined with other information
from dental casts ,case history, and
observation of the patient, make possible
an individualized treatment plan.

c) The fallacy of superpositioning:
Super positioning , registering of two or
more tracing of an individual on particular
structures ,occasionally helps one to
visualize growth or treatment changes.
• Localized remodeling can be shown by
superposition's nearby. As one moves
away from the registration site the
changes observed are a combination of
summated growth in several regions,
effect of treatment, enhancement of errors
in positioning.

• For e.g., where registration is in the cranial
base region, the chin seems to have “grown”
downward & forward, but one may as well say
that the condyle has been growing upward & the
chin has been translated away from the articular
fossae. Little growth occurs at the chin itself.
The many changes b/w chin & sella are
summated & directed downward & forward not
by growth but by the artifact of super-
positioning.
• If one superposed on the symphysis, it would
be misleading to speak of upward & backward
growth of the cranial base.

d) The fallacy of Using Chronological Age
Although it is conventional to use
chronological age (birth age) for
comparisons and reference,
developmental age is a better criterion: it
reduces the variance of sizes, angles and
proportions within age classes. Some
orthodontists take routine radiographs of
the wrist of patients to assign their “
carpal age” an index of bone maturation.

e) The fallacy of the “ideal”
Practical problems arise when “ ideals”
for skeletal relationships are
oversimplified into numbers inflexibly
and arbitrarily imposed on every patient.
The use of contrived “ideals” as
standards sometimes produces a set of
ipso facto findings by setting up artificial
criteria for abnormality and then
uncovering the incidence and prevalence
of these variations.

• By definition, abnormal must always
refer to the normal, which can only be
determined from an appropriate
population.
• One cannot discover “abnormality” by
comparison with subjective ideals based
on personal perceptions of facial
esthetics, nor can one label such ideals as
normal.

3) Misuses of cephalometric analyses
• Even when we protect ourselves from misleading
assumptions or fallacious misconceptions we may err
simply by misuse of any analysis.
a) An analysis is misused if too rigid an application of mean
values is made. The total range and variance are more
practical than the mean itself. Because means are
population averages, they usually are very poor treatment
goals.
• Occasionally means of tooth positions are useful, but only
when the array of skeletal values is close to the means for
sex and age. When skeletal values deviate from the mean,
dentitions must adapt. The clever clinician does not apply
the same mean value to all faces but determines those
adaptation compromises to be made in treatment which
are most suitable to be pleasing and stable.www.indiandentalacademy.com

b) An analysis is misused when it is applied
inappropriately.
• Values derived from 12-year old North American
white boys who sought orthodontic treatment in a
dental school, for e.g. are obviously of little use in
assessing the specific clinical needs of a 6-year
old black girl in practice: there are too many
differences resulting from age, sex, race, etc
• The samples from which many of our most
popular cephalometric analyses were derived
have not been adequately described in the
literature, making it very difficult for the clinician
to know whether or not the analysis is
appropriately useful.www.indiandentalacademy.com

c) An analysis is misused when it is applied in a
way for which it was not intended. Analyses
contrived to visualize treatment goals (e.g. those
of Tweed or Steiner, both designed to depict
goals of treatment )are used improperly when
used for growth studies.
d) Standards derived from cross-sectional
samples, in most instances, cannot properly be
used in lieu of longitudinal data to access
expected growth. For establishing growth
standards, a small serial sample is much better
than cross-sectional sample having the same
number of radiographs.www.indiandentalacademy.com

e) The substitution of a subjectively
derived “ideal” for a statistically
developed population norm
misinforms and misleads.
•“Ideals” represent artificial
constructs of faces one clinician
likes; norms present real values of a
particular group. They cannot be
used interchangeably.

According to Baumrind and Frantz;
AJO -1971, Head film measurements
like all measurements involve error
which falls into two categories.
• Errors of Projection
• Errors of Identification

Hatcher recently has reviewed and categorized
source of errors include those caused by
internal and external orientation and those
related to geometry and association.
1) INTERNAL ORIENTATION ERROR :
• This error refers to the 3-dimentional
relationship of the patient relative to the
central x-ray beam or imaging device and
assumes that a minimal error of this type
occurs with a specific and consistent head
position. Because this is not always true, an
internal orientation error is introduced.www.indiandentalacademy.com

2) EXTERNAL ORIENTATION ERROR :
• This error refers to the 3 dimensional spatial
relationship or alignment of the imaging device,
patient stabilizing device, and image recording
device.
• Minimal error is assumed when the x-ray source is
60 inches from the midcephalostat as the central ray
passes through the ear rods and the beam is
horizontal to the horizon and perpendicular to the
film plane.
• The distance from the midcephalostat plane to the
film plane should be known and be consistent
between images. Any deviations from these
assumptions will introduce errors into the final
image. www.indiandentalacademy.com

3) GEOMETRIC ERROR:
•This error primarily refers to the
differential magnification created by
projection distance between the imaging
device, recording device, and a 3-
dimensional object.
For e.g. ; structures farthest from the film
will be magnified more than objects closer
to the film. The error is related to the
divergence of the x-ray beam on its path
from the x-ray source to the recording
device.

4) Association error:
• This error refers to the difficulty in
identifying a point in two or more
projections acquired from different
points of view. The difficulty in
identifying the identical point on two or
more images is proportional to the
magnitude of change in the angle of
divergence between the projections.

PROJECTION ERRORS

Errors of projection
• Results because headfilm is a two
dimensional depiction of a three dimensional
object.
• Since the rays that produce the image are
not parallel and originate from a small
source , headfilms are subject to distortion;
the side nearer the x-ray source is enlarged
more than the side closer to the film.

• The degree of magnification is determined
by the ratio of the x-ray source-to-object
distance and source to film distance. The
larger the distance from the source being
imaged to the film plane, the greater the
magnification.
• To minimize this effect, the distance from
the x-ray source to the midsagittal plane
of the patient’s head in cephalometric unit
is 60 inches. This ensures that the x-ray
photons are traveling toward the
object/film more parallel to each other,
thus reducing magnification.www.indiandentalacademy.com

• However, there is still magnification of
most of the oral and craniofacial structures
ranging from near zero for objects close to
the film and in the exact center of the x-ray
beam to 24% at regions 60 mm from the ear
rods and beyond. This magnification is not
constant for all of the possible sagittal
radiographic planes of the patient.

• Those structures located closest to the
film will be magnified less than those located
in the sagittal plane, and those nearest to the
x-ray source will be magnified to the
greatest extent.
• Magnification factors are further affected
by the distance from the film cassette to the
midsagittal plane of the patient, with
magnification increasing as the film is
moved away.

• To minimize variation in magnification from
patient to patient and to obtain consistent
measurements on the same patient over time,
many orthodontists choose to keep that distance
constant.
• A distance of 15 cm from the midsagittal plane of
the cephalostat to the film cassette is often used.
This fixed distance produces magnification that is
somewhat consistent, with in tolerable limits.
• However many practitioners choose to place the
film cassette as close to the patients head as
possible to achieve maximum sharpness and
reduce magnification of the dental structures.www.indiandentalacademy.com

• Note that because the x-ray beam is diverging, the image
magnification will be less when placing the film at position
(A) than will be the case at position (B).www.indiandentalacademy.com

For eg : if the x-ray beam
enters the patients head
from the right side ,the
image of the right side of
the mandible will be larger
than that of the left side.
Also, a given anatomic
structure, such as the
angle of the right
mandible, will appear
further from objects in the
center of the orofacial
image than will be the
angle of the left mandible.www.indiandentalacademy.com

• Errors due to the projection of the 3-dimensional
object on to a 2-dimensional film have been
studied less extensively.
• Similarly, there has been little analysis of errors
arising from misalignment b/w the different
components of the cephalometric equipments or
misalignment of the patient in the cephalogrpic
system.
• In a study by Van Aken(1963) projection errors
were found to be small but might be of
significance in cephs of asymmetrical skulls or in
the case of anatomical landmarks that do not lie in
the mid-sagittal plane.www.indiandentalacademy.com

• Bergersen-1980- studied magnification and distortion
in cephalometric radiography and found discrepancies
b/w distance measured on the film and true distance in
the object.
• According to Ahlqvist the relations b/w the different
components of the cephalographic system are
affected by a number of factors.
1.The focal spot, the cephalostat, and the film may be
linearly displaced in relation to each other.
2.The cephalostat and the film may be rotated with
respect to each other.
3.The patient may be linearly displaced and /or
rotated in relation to the cephalographic system.

Fig-A- direction of possible misalignments of the patientwww.indiandentalacademy.com

Fig-B : the projection length of an object will vary with its
inclination toward the focal spot or toward the film.www.indiandentalacademy.com

ERROR IN
CEPHALOMETRIC
LANDMARK
IDENTIFICATION

Error of identification
• Involves the process of identifying
specific landmarks on headfilms.
• To test landmark identification reliability ,
4 instructors and 3 orthodontic residents
were requested to select and plot four high
quality radiographs.
• They were provided with a list of
landmarks and definitions of each and were
asked to identify them using a pencil point
on a clean sheet of acetate paper on the
radiograph. www.indiandentalacademy.com

• The porion, condylion , orbitale and
basion were less readily identified than
some of the other landmarks.
• Condylion was less readily identified
and Gnathion more accurately identified.
• Baumrind and Frantz demonstrated
marked differences in magnitude and
configuration of envelope of error found
among different landmarks. Other factors
that can influence landmark identification
are film density and sharpness.

•Identification of landmark by seven individuals.
Each circle is the smallest possible circle that would
encompass the landmarks.www.indiandentalacademy.com

Point A revisited – Jacobson- AJO 1980
• Subspinale or point A is a midline point whose
relationship to the anterior teeth in lateral ceph may be
influenced by head position. It is located somewhere b/w
the root apex and the coronal third of the root of the tooth.
• Subspinale is defined anthropologically as “ the deepest
midline point on the premxilla b/w ANS & prosthon.
• Bjork defined it as the “ deepest point on the contour of
the alveolar projection b/w the spinal point and prosthion.
• Because of the difficulty in locating point A, alternate point
have been suggested by Van der Linden i. e point L, which
is located on the anterior surface of the image of the labial
lamella at the region of the apex of the maxillary incisors.
• Jarabak & Fizzel defined a point 2 mm ahead of the root
apex as a redefinition of point A.www.indiandentalacademy.com

Point A revisited – Jacobson- AJO 1980
• Jacobson concluded that Point A cannot be
accurately identified in all cephalometric
radiographs. In instances where this landmark is
not clearly discernible, an alternative means of
estimating the anterior extremity of the maxillary
base is shown.
• A point plotted 3.0 mm. labial to a point between
the upper third and lower two thirds of the long
axis of the root of the maxillary central incisor
was found to be a suitable point (estimated point
A) through which to draw the NAE line and one
which most closely approximates the true NA
plane. www.indiandentalacademy.com

The precision with which any landmark
may be identified depends on a number
of factors.
1. Landmarks lying on a sharp curve or at
the intersection of two curves are
generally easier to identify than points
located on flat or broad curves.
2. Points located in areas of high contrast
are easier to identify than points located
in areas of low contrast .
3. Superimposition of other structures,
including soft tissue over the area of
landmark in question, reduce the ease of
identification.

4) Precise written definitions of
describing the landmark reduces
the chance of interpretation error.
5) Operator experience is an
important factor since increased
knowledge of anatomy and
familiarity with the radiographic
appearance of the subject reduces
interpretive errors.

LIMITATIONS OF
SUPERIMPOSITION

LIMITATIONS OF SUPERIMPOSITION
• Serial radiographic cephalometry has been
used, almost from its inception, to measure
craniofacial growth and treatment changes.
• This gives rise to the question, just how
accurate are cephalometric measurements?
Radiographic cephalometry is only scientific if it
can be measured.
• The validity of cephalometric measurement
therefore is directly dependent on the accuracy of
the method of measurement, which in turn is
limited by the following problems.

A) Lateral or frontal headfilms taken at
different times, and possibly by different
people, are difficult to reproduce with any
degree of accuracy, whether the head is
steadied in a cephalostat or in the natural
head position.
B) The double images of the bilateral
structures often are not consistently
equally spaced in serial headfilms
because of even minor faulty head
positioning.

C) Film contrast and density differences
often encountered are the result of lack of
strict quality control.
D) Anatomic or structural landmarks are not
consistently identifiable.
E) Most important limitation of traditional
cephalometric radiographic
measurements is that 3-dimensional
changes are measured in only two
dimensions.

Limitations of traditional superimposition
methods
• No points or planes in the craniofacial
complex are stable and all move relative
to each other during growth. Orthodontic
analyses, in effect , relates relatively
stable areas as depicted by arbitrarily
selected points or planes to more remote
but less stable landmarks.

• While the primary errors are biologically
induced , the secondary errors are entirely
mathematically defined, since they are related to
the primary errors.
• Errors in tracing superimposition can be
compounded by the method of superimposition
used in interpreting the findings.
• A study conducted by Ghafari et al
demonstrated differences in interpretation of
facial changes by comparing four traditional
cephalometric methods of superimposition on
the cranial base: best fit on anterior cranial base
anatomy, sella-nasion, registration of point R
with Bolton-nasion planes parallel, and basion-
nasion plane.

• The results of their study showed differences
among all paired methods to be statistically
significant.
• Growth behavior of an individual as recorded
on a sequential set of roentgenograms has been
shown to differ greatly when studied using
different superimposition methods. Nothing is
known of the growth behavior of the individual
parts in the continuum of the discrete points
studied.
• Because of the inability of conventional
cephalometry to understand curved forms, it is
limited to landmark indices.

LIMITATIONS OF
CEPHALOMETRIC
ANALYSIS

1) Most individuals with Dentofacial deformities have
anatomic variations in the location of the cephalometric
landmarks used as a baseline in many analyses, such
as sella, nasion, and orbitale. This often results in
incorrect conclusions from the analysis.
2) The clinician must not base interpretations on
single cephalometric measurements.
3) The clinician must recognize the limitations, as well
as the advantages, of cephalometry and be sure to
integrate measurements with clinical findings.
Limitations of cephalometric analysis

4) The art of cephalometric interpretation
lies in understanding abnormal findings
and identifying the etiologic factors
behind these cephalometric abnormalities
in patients with dentoskeletal deformities.
5) Although cephalometric analysis forms
an important part of the database for
diagnosis and treatment planning, it
should not take precedence over the
clinical evaluation of the patient.

Reliability of cephalometric analyses:
• Fundamental to orthodontics is the need
to determine the relationship of the
various skeletal components, particularly
those of the jaws to each other and to the
rest of the cranium in the cranio facial
complex.
• The interpretation of the measurements
continues to be the subject of much
debate. www.indiandentalacademy.com

• Wylie et al compared five analyses in ten
individuals who underwent various surgical
corrections.
• Pre treatment cephalometric radiographs of the
ten patients were selected to illustrate different
Dentofacial deformities , each of which was
corrected with a different surgical procedure.
• The pretreatment cephalometric radiographs
were blindly assessed by one investigator who
used the criteria for each of five popular
analyses.
• The results of the analyses ( diagnoses ) were
then compared to one another and to the actual
surgery performed.

• The outcome of the study revealed that
performance of the analysis in relation to actual
surgery was generally poor.
• In the case with mandibular advancement there
was 35 % agreement with the surgery performed.
• For maxillary advancement - 20 %
• For maxillary superior positioning 100%
• For maxillary advancement and mandibular
reduction- 20%
• For bimaxillary protrusion – all analyses agreed
that the teeth were protrusive and that the lower
third of the face was too long.
• This illustrates the unreliability of
cephalometric analyses.www.indiandentalacademy.com

For e.g.;
1) In class III malocclusion, 2 analyses
suggested mandibular protrusion, 2
determined that the maxilla was retrognathic,
and one identified the problem as a “short”
maxilla and “forward mandible”.
• In class II, div 2 malocclusion, one analyses
claimed that the skeletal pattern was class I,
3- analyses indicated that class II tendency
was due to maxillary protrusion, and one
noted a short mandible. Only one analyses
would support the decision to surgically
advance the mandible.www.indiandentalacademy.com

LIMITATIONS OF
VERIOUS
REFERENCE PLANES
USED IN
CEPHALOMETRICS

Reference planes
•A cephalometric evaluation of the craniofacial
complex requires a plane of reference from
which to asses the location of various anatomic
structures. Traditionally two planes have been
used, namely the sella tucica-nasion(SN) plane
and the Frankfort horizontal(FH).
• The SN plane is more suitable for assessment
of changes induced by growth and/or treatment
within the same individual over time. Low
variability in identifying sell turcica and nasion
is an advantage of using this plane , as is the
fact that sell turcica and nasion represent
midsagittal structures.

• If the goal is to compare a particular individual
to a certain population group (ie; established
norms), use of the SN plane may provide
erroneous information if the inclination of this
plane is either too high or too low.
• A sella turcica positioned to a great extent
superiorly or inferiorly would account for a low or
high inclination of the SN plane, respectively.
• Frankfort horizontal (FH) has also been used
extensively in cephalometry. Despite the difficulty
in locating porion reproducibly, FH has been
advocated to more accurately represent the
clinical impression of jaw position.

• As an alternative, Legan and Burstone
suggested using a constructed horizontal
(cHP). This is line drawn through nasion
at an angle of 7 degrees to the SN line.
• This constructed horizontal tends to be
parallel to true horizontal. However, in
those cases in which SN is excessively
angulated, even the constructed
horizontal would not approximate true
horizontal, in which case an alternative
reference line must be sought.www.indiandentalacademy.com

• Another approach involves obtaining the
cephalogram with head in the natural head
position. “True horizontal” is drawn perpendicular
to a plumb line on the radiograph. Finally, a
vertical reference line cane be traced passing
through subnasale (SnV) or glabella.
• This approach offers the advantage that natural
head position approximates the position in which
clinical judgments are made.
• Its drawbacks include strict adherence to
technique and difficulty in conducting studies
where cephalograms have been obtained from
various facilities.www.indiandentalacademy.com

Variability between the optic plane and
Frankfort horizontal:Tremont-AJO-DO;1980
• Frankfort horizontal is commonly
constructed on a lateral cephalogram from
the top of the ear rod to orbitale. Ear rod
positioning and identification of orbitale
present obvious variables with such a
reference plane. The optic plane has been
proposed as a more accurate
representation of Frankfort horizontal.

• The optic plane was constructed,
as defined by Sassouni, by drawing
the supraorbital plane (a line
tangent to anterior clinoid and the
roof of the orbit), drawing the
infraorbital plane (line tangent to
the inferior of sella turcica and the
floor of the orbit), and then
bisecting the angle formed by their
intersection to obtain the optic
plane. www.indiandentalacademy.com

• The optic plane, was significantly different
from anthropologic Frankfort horizontal.
Also, the optic plane did not vary
significantly less from anthropologic
Frankfort horizontal than from ear rod to
orbitale Frankfort horizontal.
• According to the parameters of this study,
the optic plane is not a more accurate or
reliable method of representing
anthropological Frakfort horizontal on lateral
cephalograms. www.indiandentalacademy.com

• Traditionally, intracranial reference lines have
been used for clinical cephalometric analysis of
malocclusion cases. Several authors have,
however, questioned the validity of intracranial
reference because of their variability to the
horizontal plane, related to the head in natural head
position (NHP).
• The study was undertaken to determine the
reliability of the FH as a cephalometric reference
line. The main alternative to intracranial reference
lines is the nonvariable extracranial horizontal line
(HOR) related to the head in natural head position.
Frankfort horizontal basis for cephalometric
analysis Lundström and Lundström- AJO 1995

fig shows- extreme difference with regard
to inclination of frankfort horizontal in
natural head position.

• They concluded that no difference was found
between the variability of the Frankfort horizontal
and the sella-nasion line with regard to the
horizontal plane. The large variation of both
intracranial reference lines, related to NHP, as well
as to NHO, confirms their relative unsuitability as
cephalometric references for clinical purposes.
• Findings indicate that a horizontal line, related to
natural head position, adjusted to natural head
orientation when indicated, presents the most
reliable basis for cephalometric analysis.

Fig showing- angles b/w horizontal plane and
frankfort horizontal (FH/HOR, negative) and S-N
line (S-N/HOR, positive)www.indiandentalacademy.com

CONCEPTS OF
NATURAL HEAD POSITION
AND NATURAL HEAD POSTURE

NATURAL HEAD POSITION
• Natural head position is a standardized
and reproducible orientation of the head
in space when one is focusing at a
distant point at eye level.
• German Anthropological society in 1884
– Frankfort Agreement ie, The plane
which passes through the left and right
porion landmarks and the left orbitale, to
achieved uniformity in craniometric
research. www.indiandentalacademy.com

• The Frankfort horizontal is a useful
compromise for studying skulls but not for
orienting natural head position in the living
because the F-H plane located in the living
is normally distributed around a true
extracranial horizontal.
• Nonetheless, orthodontist dealing with
living subjects, rather than inert crania, have
used this Frankfort horizontal faithfully in
cephalometry.

Downs had shown that discrepancies b/w
cephalometric facial typing and
photographic facial typing disappear when
the Frankfort plane is not horizontal, but
tilted up or down.

• Bjerin and Thurow pointed out that intracranial
landmarks are not stable points in the cranium,
their vertical relationship to each other is therefore
also subjected to biological variation.
fig shows-Two ceph tracings
with similarity in their facial
profiles exhibit marked
difference in the slope of their
skull base( SN line) and in the
FH.
Conventional ceph analyses
utilizing these intracranial
reference lines would show
markedly divergent facial
configuration, rather than the
similarity observed clinically.www.indiandentalacademy.com

• Bjorks studies of facial prognathism also
illustrates the unreliability of intra cranial
reference lines on cephalograms.
• Two adult Bantu men were selected to represent
maximum and minimum facial prognathism
relative to the S-N plane.

• This fig- shows the same two Bantu men tracing aligned in
natural head position illustrate nearly identical profile outline
and a low and high inclination of the S-N line, rather than
difference in prognathism.
• When various methods of cephalometric analyses are
applied to the study of the same cephalogram, results may
differ dramatically depending on the choice of reference
lines.

•The simplest procedure to obtain facial
photographs and head radiographs is to instruct
patients to sit upright and look straight ahead to
a point at eye level on the wall in front of them.
• The conventional use of two ear rods to
stabilize the head in radiographic cephalometry
is based on the assumption that the transmeatal
axis of humans is perpendicular to the mid
sagittal plane.
• The relationship of the left and right ears in their
vertical and horizontal relation is frequently
asymmetric. www.indiandentalacademy.com

Fig-A Fig-B Fig-C
Fig-A : Facial symmetry of eyes, ears, contour of the lips,
and mandible.
Fig-B : Asymmetry of eyebrows and lips, but transmeatal
axis perpendicular to the facial midline.
Fig-C : Marked asymmetry of eyes, eyebrows, and ear but
symmetry of lips. www.indiandentalacademy.com

• The insertion of ear rods will obviously
result in vertical and/or horizontal rotation
of the head, which introduces a deficient
and misleading image.
• There by, the attempt to determine facial
asymmetry of a patient generally results in
a compromise rather than as an exact
definition.
• Only the left ear rod should be used in
radiographic cephalometry both for the
lateral and frontal projection.
• The right ear rod should merely be
inserted against any part of the ear.www.indiandentalacademy.com

CONCEPTS OF NATURAL HEAD POSTURE
• In the later part of the 19th century, many
anthropologists believed that the study of cranial
morphology necessitated the orientation of skulls to a
position that approximates the natural head posture of
living beings.
• The concept of natural head posture (NHP) on the
living subject was introduced into the orthodontic
literature in the 1950s by Broca, an anatomist,
described NHP as the position of the head attained
when an individual stands with the visual axis in the
horizontal plane.
• Cooke and Wei defined NHP as the natural,
physiologic position of the head that is assumed when
a relaxed subject looks at a distant reference point.www.indiandentalacademy.com

• Various methods have been devised to obtain
NHP
• MIRROR METHOD by Moorees and Kean.
• SELF BALANCE METHOD by Solow and
Tallgren.
• The term natural head position and head
posture are not interchangeable, one being a
standardized procedure applied to all individuals
for analysis of Dentofacial morphology and the
other i.e.; head posture is an individually
characteristic physiologic posture of the head to
study the relation b/w posture and morphologic
features.

• Note that only a small mirror should be
used to record natural head position to
force subject to look straight ahead into
the image of their eyes rather than a long
mirror that prevent standardization of head
position.
• A long mirror is needed to accommodate
subjects when recording their postural
position, which is an individual,
nonstandardized head position.

• The various reference lines still compete
with each other. One system is more or less
as good or poor as any other and none is
completely reliable because each is subject to
large individual variability.
• What can be done to diminish this problem?
The answer is to choose measurements that
are based on different reference planes, in
this way it is hoped to compensate for
pronounced variations in one or the other
reference lines.

LIMITATIONS OF
VARIOUS
CEPHALOMETRIC
ANALYSIS
COMMONLY USED

ANB angle as a measure of jaw Dysplasia
• According to Steiner, the SNA reading indicates
whether face protrudes or retrudes bellow the skull.
Although the ANB is a reliable indication of A-P jaw
relationship in most instances, there are many
situations in which this reading cannot be relied on.
• The ANB angle in normal occlusions is generally 2
degrees. Angle greater than this mean value indicate
tendency toward class II jaw disharmonies; smaller
angles (negative readings) reflect class III jaw
discrepancies. While this is an acceptable
generalization, numerous instances exist in which this
does not apply.

For eg – in fig A lateral ceph tracing of a class II
malocclusion. The ANB angle is 7 degrees, which high and
it is typical for class II type malocclusion.
fig –B; lateral ceph tracing of a normal occlusion in which
the ANB angle also measures 7 degrees.www.indiandentalacademy.com

Cephalometrics for you and me – Steiner –
1953 ;AJO
• Porion and Orbitale are not accurate for our
use as we are not dealing with dry skulls.
• Points S and N are clearly visible in the X- ray
pictures and can be located easily and
accurately.
• Emphasizes that points S and N are located in
the mid sagittal plane of the head and therefore
they are moved a minimum amount whenever
the head deviates from the true profile position
and that the points are located on hard non
yielding tissue. www.indiandentalacademy.com

• The same holds true for a rotation
of the occlusal plane: backward
(counterclockwise) rotation of the
occlusal plane has a decreasing
effect on the ANB angle, though
sagittal basal relationships remain
constant.

Fig A- normal occlusion with an ANB angle of 2 degrees.
Fig B- denture base are retro- positioned in the
craniofacial complex. This has the effect of reducing the
ANB from 2 degrees to -2 degrees. The relationship of the
jaws to each other remains unchanged.
Fig C- same relationship of the jaws only now both jaws
are positioned forward relative to nasion. This has
increased the ANB angle from 2 degrees to 5 degrees.

• In fig B- the relation of the jaws to each other is
unchanged, but the jaws are rotated in counterclockwise
direction relative to the S-N plane as compared to fig A.
The rotation had the effect of producing a class III type
jaw relationship. The ANB angle has been reduced from
2 degrees to -5 degrees.
• Fig C- A clockwise rotation of the jaws produce the
opposite effect.( i.e., class II-tape jaw relationship)

Fig shows effect on
ANB angle of change of
0.5 inch in position of
nasion with points A &
B held constant.
Fig 1- horizontal
positioning of nasion
results in different ANB
angles
1=2degrees,2=8degrees
, 3= - 4. 5degrees
Fig 2- vertical
positioning of nasion
results in different ANB
angles. 1=2degrees,
2=1degree, 3=0degreeswww.indiandentalacademy.com

Shortcomings of ANB angle
• Taylor in 1969 pointed out that ANB angle did not
always indicate true apical base relationship. Varied
horizontal discrepancies of points A and B could
give the same ANB measurement because variation
in the vertical distance from nasion could
compensate for other variation.
• Beatty in 1975 reported that ANB angle is not
always an accurate method of establishing the
actual amount of apical base divergence.

• As an alternative to ANB angle for measuring apical
base discrepancy , he devised the AXD angle, where
point- x is located by projecting point A on to a
perpendicular to SN line. Point D is located in the bony
sympyhsis as described by Steiner. The two variables,
nasion and point B, were eliminated. He also introduced a
linear measurement AD, to describe the A-P relationship
of the jaws.

• Cross evaluation with different reference
planes is important and can be demonstrated
with the ANB angle.
• If one takes only the ANB angle to measure
the relative position of maxilla and mandible to
each other ,one must realize that any different
horizontal or vertical position of point N and
the location of the points A and B in the
vertical plane will have an influence on the size
of this angle and not on the actual sagittal
relation of the two jaws. (Hussals and Nanda-
1984)

STEINERS ANALYSES
Acceptable compromises:
• Steiner clearly recognized that cephalometric
standards are merely gauges by which to
determine more favorable compromises as a
treatment goal. He developed a chart that reflects
a number of average measurements of normal
Dentofacial relationships.
• Steiner recognized variations in antero
-posterior jaw relations to each other.
• The compromise describes the anticipated axial
inclinations of the maxillary and mandibular
incisors to the NA and NB lines at various ANB
relationships. www.indiandentalacademy.com

•The Steiner compromises are geometric
resultants of morphogenetic variations and
their resulting treatment possibilities.

Method of appraisal of jaw disharmony-
Wits
• The Wits appraisal is the extent to which the
jaws are related to each other.
• The occlusal plane is drawn through the
region of the overlapping cusps of the first
premolars and first molars.
• The wits appraisal is done by drawing
perpendicular lines from points A and B to the
functional occlusal plane.
• The distance b/w the points of intersection
AO & BO is measured & it is describes the
maxillary and mandibular relationships.

• The average jaw
relationship according to
Wits is – minus 1 mm for
men and 0 mm for women.

Shortcomings of Wits appraisal
However, the wits appraisal relates point A & B to
the functional occlusal plane; this generates 2
major problems.
1) Accurate identification of the occlusal plane is not
always easy or accurately reproducible, especially
in in mixed dention patients or patients with open
bite, sever cant of the occlusal plane, multiple
impactions, missing teeth, skeletal asymmetries, or
steep curve of spee.
2) Any change in the angulation of the functional
occlusal plane, caused by either normal
development of the dentition or orthodontic
intervention, can profoundly influence the Wits
appraisal. www.indiandentalacademy.com

WITS APPRACIAL APPLIED TO CLASS I
AND CLASS II SKELETAL JAW BASES

A new approach of assessing sagittal
discrepancies; The Beta angle – Chong Baik
and Maria Ververidou –AJO-DO;2004
• Because of lot of limitations in assessing A-P
jaw relation by various analysis like ANB, wits
appraisal. To overcome these limitations they
established new cephalometric measurements
i.e. Beta angle.
•This angle does not depend on any cranial
landmarks or dental occlusion.
•The Beta angle uses 3 skeletal land marks( 1) A
point( 2) B point( 3) the center of the condyle,
found by tracing the head of the condyle and
approximating its centre (point- C).www.indiandentalacademy.com

• Next it require 3-lines; (1)line connecting the
centre of the condyle C with B point ( C-B line).
(2) line connecting A and B points .(3) line from
point A perpendicular to the C-B line.
• Finally, measuring the Beta angle, which is the
angle b/w the last perpendicular line and the A-B
line.

• It uses 3 points located on the jaws ( 1) A
point( 2) B point( 3) the center of the condyle
(point- C).
• So changes in this angle reflect only changes
with in the jaws. In contrast to ANB angle, the
configuration of the Beta angle gives it the
advantage to remain relatively stable even when
the jaws are rotated, for e.g.; when B point is
rotated backward & downward, then C-B line is
also rotated in the same direction, carrying the
perpendicular from point A with in it. Because A-
B line is also rotating in a same direction, the
Beta angle remains relatively stable.

B
e
t
a
a
n
g
l
e
Fig shows: Beta angle remains relatively stable
even when jaws are rotated

• Another advantage of Beta angle is that it can be
used in consecutive comparisons throughout
orthodontic treatment because it reflects true
change of the sagittal relationship of the jaws,
which might be due to growth or orthodontic or
orthognathic intervention.
SHORTCOMING OF BETA ANGLE:
1) Precisely tracing the condyle and locating its
center is not always easy. For that reason, some
clinicians might hesitate to use the Beta angle.
2) To accurately use this angle, the cephalometric
x-rays must be high quality.www.indiandentalacademy.com

•The advantage of locating the center of the head of
the condyle versus the condylion point, as used by
McNamara, is that very precise tracing of the
contour of the condyle is not really necessary. The
clinician can visualize and approximate the centre
with a minimum error in the Beta angle as long as
that point is with in 2 mm of its actual location.

they concluded that:
1) Previously established measurements for
assessing the sagittal jaw relationship can often
be inaccurate.
2) A new angle, the Beta angle, was developed as
a diagnostic aid to evaluate the sagittal jaw
relationship more consistently.
3)White subjects with a Beta angle b/w 27 degrees
& 35degrees have a class I skeletal pattern; a
Beta angle less than 27 degrees indicates a class
II skeletal pattern, and a Beta angle greater than
34 degrees indicate a class III skeletal pattern.
4) There is no statistically significant difference
b/w mean Beta angle values of males and
females. www.indiandentalacademy.com

A-Po line and cephalometric correction-
Ricketts
• The A-Po line is another method used in
cephalometric analyses to assess the
position of mandibular incisor tooth.
• A range of –2mm to +3mm is considered
a satisfactory incisor position, with + 0.5
mm lower incisor tip to A-Po line being an
idealized position.
• Downs credits Ricketts for suggesting
relating the lower incisor to the profile,
specifically the lower face using A-Po.

• Cephalometric correction describes a
method to determine mandibular dental
arch crowding or spacing by assessing
mandibular incisor position on a
cephalometric radiograph in concert with
mesiodistal dimensions of mandibular
teeth and mandibular arch circumference.
• The rationale is that by advancing or
retracting the mandibular incisor 1mm will
result in a 2mm gain or a 2 mm reduction
in the available space for mandibular
arch, respectively.

• Calculations have indicated that tipping the
lower incisor tooth forward by 3 degrees results
in total dental arch length increase of 2.5mm.
• Conversely, retracting the mandibular incisor 3
degrees will encroach on the lower arch length
by 2.5mm.
• Use of the linear measurement lower incisor to
A-Po line alone must be used with caution. This
linear measurement does not take into account
lower incisor angulation, which emphasizes the
risks inherent in using single measurements in
cephalometric diagnosis and treatment planning.

In fig (a), (b), and (c), the mandibular incisor tip lies on the
A-Po plane. The incisor mandibular plane angle (dotted line
to MP) varies from near ideal (a), to obtuse (b), and acute
(c).
Accepting linear lower incisor position to the A-Po line
alone is inadvisable. The profile, as judged by the S-line, is
optimal in (a).

•Ricketts stresses the significance
of utilizing linear as well as angular
measurements in these
assessment.
• All cephalometric measurements
must be evaluated in concert with
other measurements and must
include clinical and diagnostic
judgment.

Mc Namara analyses:
• For determining the anteroposterior
relationship to maxilla and mandible , mid
facial length is measured from condylion to
point A. The effective length of the mandible
is measured from condylion to gnathion.
• Birte Melsen suggests that there are
displacements of condyle,pogonion,menton
and point B relative to superimposition on
implants at a study done on annual intervals
between 8.5 yrs and 15.5 yrs of age.

Soft tissue analyses- Holdaway
• NASO LABIAL ANGLE – formed by two lines
namely the columella tangent and an upper lip
tangent. Arbitrary value is 90 to 110 degrees.
• Legan and Burstone report a mean value of 102
+/- 4 degrees.

• Scheidman et al drew a postural horizontal
line through subnasale and further divided the
nasolabial angle into columella tangent to
postural horizontal ( 25 degrees) and upper lip
tangent to postural horizontal ( 85 degrees).
• They argue that each of these angles should
be assessed individually in as much as they
vary independently.
• An apparently normal nasolabial angle may
be oriented in an abnormal fashion, a fact that
would be disclosed if the component angles
were measured individually.

• E line: (Esthetic plane) Drawn from tip
of nose to soft tissue pogonion.
Normally the upper lip is about 4 mm
behind this reference line while the lower
lip lies about 2 mm behind it.
• Ricketts admits that considerable
variation exists in terms of age and sex.
He therefore advises that adult lips
should be contained with nose – chin lip
line.

E- LINE ( ESTHETIC PLANE)

S line:- Steiner line is a line drawn from soft
tissue pogonion to the mid point of the S shaped
curve between sub nasale and nasal tip.

H line: The harmony line is tangent to the chin
point and the upper lip. The H line angle formed
between this line and the soft tissue nasion –
pogonion line.
The H line angle measures either the degree of
upper lip prominence or the amount of
retrognathism of the soft tissue chin.

ADVANTAGES
AND
LIMITATION OF
DIGITAL
CEPHALOMETRYwww.indiandentalacademy.com

Introduction
• Digital radiography has been widely accepted
for medicine; however, it was not until the1980s
that first intra- oral sensors were developed for
use in dentistry.
• The introduction of extra- oral digital
radiography was initially delayed due to the high
cost of extra -oral systems. Recently, the
development of cost-effective extra -oral digital
technology, coupled with an increased utilization
of computers in orthodontic practice, has made
direct digital cephalometric imaging valid option.

• As a result, an increasing number of
conventional film based radiographic units are
being replaced by direct digital machines. Direct
digital images can be acquired through the use
of photostimulable phosphor plates, or charge
coupled device receptors, both of which offer a
number of advantages over film.
• These advantages include instantaneous image
acquisition, reduction of radiation dose,
facilitated image enhancement and archiving,
elimination of technique sensitive developing
process and its associated costs, and facilitated
image sharing.

Digital imaging
A digital image is a matrix of square
pieces, or picture elements (pixels),
that form a mosaic pattern from which
the original image can be
reconstructed for visual display. An
analog image, such as a radiographic
film, has virtually an infinite number of
elements, with each element
represented by a continuous gray
scale. www.indiandentalacademy.com

• The pixels in a digital image are arranged in a matrix
for e.g., a 512 x 512 pixel matrix will contain 262,144
pixels. If large number of pixels are used to represent an
image, their discrete nature becomes less apparent, i.e.
the spatial resolution of the image improves as the
number of pixels increases.
• Each pixel has a digital value that represents the
intensity of the information recorded by the detector at
the point. Each digital value is represented as binary
number; information is recorded in terms of a series of
ones or zeros. Each one or zero is called a “bit”. In 6-bit
image each pixel will have 64 possible values, ranging
from 0, which represent a black area on the image, to
63, which represents a white area; an 8-bit image each
pixel will have 256 possible values. The quality of an
image depends on both the number of pixels and
number of gray levels which make up the image.www.indiandentalacademy.com

IMAGE ACQUISITION
There are 2 ways to acquire a digital image.
1)Indirect acquisition:
A digital image can be produced by scanning
conventional radiographs using a flatbed scanner
and a transparency adaptor, or by using a
charged coupled device camera instead of the
flatbed scanner. This image can be manipulated
using software packages or be passed on to a
second party via a modem.

2) Direct digital imaging
There are two systems available, one
produces the image immediately on
the monitor post-exposure and is
therefore called Direct Imaging.
The second has an intermediate
phase, whereby the image is produced
on the monitor following scanning by
laser. This is known as semi-direct
imaging.

a) Semi-direct image plate systems
• The image plate method involves the use of phosphor
storage plate (psp). This plate stores energy after
exposure to radiation and emits light when scanned by
a laser. The scanner stimulates the phosphor plate and
stores a record of the number of light photons detected.
• Loading of the scanner generally only requires
subdued lighting as the plates are slightly sensitive to
visible light. However, some products are more light
sensitive than others. The lasers used are centered
around the 600-nm band and are usually of the helium-
neon variety.
• Scanners, the size of a bread- maker, can
accommodate multiple image plates at any one time.
The exact numbers varies between manufacturers.
There is a delay while the image is ‘developed’ before it
appears on the monitor.

• Up to eight bitewing radiographs take about 90
secs and a panoramic image can take
approximately 3 minutes to be scanned. Again,
the scan times do vary between manufacturers.
• Although the plate can store energy for a
number of days, information starts to be lost
within minutes after exposure and it is advised to
scan the plates quite quickly to optimize the
image recovered. To fully remove the latent
image the plate should be exposed to high
intensity light.

• Image plates are available in
exactly the same sizes as
conventional film and come with
disposable plastic barriers. They
have no wires attached and are
reusable for thousands of
exposures, but do need careful
handling to avoid surface damage.

b) Direct sensor systems
• The sensor for the radiation image is
usually a Charged Coupled Device [CCD].
It consists of silicon crystals arranged in a
lattice and converts light energy into an
electrical signal.
• This technology is widely used in video
cameras. The sensor cannot store
information and must be connected via fiber
optic wires to the monitor, which can make
the sensor bulky and awkward to use.

• The greatest advantage of the direct
sensor system is the gain in time. The
image is directly projected onto the
computer screen.
• Originally, the active areas of the
sensors were smaller than conventional
film, which increased the incidence of
‘coning off’ and required repeat
exposures to capture all the desired
information. Recent innovations have
produced sensors approaching or equal
to standard film sizes.www.indiandentalacademy.com

Advantages of digital imaging
1) Image archiving
2) Teleradiology
3) Reduction in radiation exposure to the
patient
4) Image enhancement
5) Automated cephalometric analysis
6) Surgical planning
7) Environmentally friendly

1) Image archiving
• The storage of cephalometric radiographs is
expensive and requires space and staff-time
that, in theory, could be reduced with the
archiving of digital images.
• In addition, viewing digital images on
display monitors could be more convenient
for the operator than retrieving the original
radiograph.
• Archiving cephalometric radiographs would
be of particular benefit in studying
craniofacial growth or assessing the effect of
treatment, where large number of
radiographs are analyzed.www.indiandentalacademy.com

Several methods can be used to store digital
images, including
i) magnetic storage media- it comes in the form
of magnetic disks or magnetic tape.
ii) Laser or optical disks -have become the
most practical method of storing digital
images.
iii) Optical tape- is a recent development which
uses technology similar to that of optical disks
and has a high capacity and low cost.

2) Teleradiology
• Teleradiology is the transmission of
radiographic images to distant sites.
It would provide easy access to
radiology facilities in rural or isolated
areas and would also permit the
transfer of images b/w centers which
may improve patient care and aid
research.

3) Reduction in radiation exposure to the patient
• High quality radiographs are essential for
cephalometry. The aim of high quality
radiographs should not compromise the need for
minimal radiation exposure to the patient.
• Although the radiographic exposure and
potential risk is minimal in dentistry, any
reduction in radiographic exposure to the patient
from cephalometric radiographs would be of
obvious benefit.
• With digital imaging, it may be possible to
reduce patient exposure using recently
introduced techniques in image capture or by
enhancing digital images.www.indiandentalacademy.com

• The most important technological advance to date in
image capture is the introduction of a reusable
photostimulable phosphor plate to replace the
conventional radiographic film.
• A system using this type of plate was first reported by
Sonada et al. and has been gradually introduced into
clinical situations in the last 10 years.
• Using photostimulable phosphorus plates, a digital
image is produced directly from the detected x-ray
without the intermediate step of producing a
conventional radiographic film.
• Kogutt et al. showed that an 85 % reduction in
radiation dose, the diagnostic quality of images was
comparable to conventional radiographs.www.indiandentalacademy.com

4) Image enhancement
• There is potential for improving the diagnostic
quality of digital images by enhancing the images
using various algorithms. Digital images can be
enhanced using algorithms that mathematically
manipulate the gray-level values of the pixels
• Using enhancement algorithms it may be possible
to extract information from radiographs that
previously required further additional radiographic
exposure to the patient.
• However image enhancement is actually the
suppression of information that the operator deems
unnecessary for a particular task, rather than the
addition of further information.www.indiandentalacademy.com

• Images that are of poor quality due to
factors such as incorrect exposure or
blurring could be manipulated and
reformatted thereby avoiding further
exposure.
• So it may be possible to use a faster
film/screen combination, reducing
radiation exposure to the patient, then
enhance the images without
compromising diagnostic quality.

5) Automated cephalometric analysis
• With the introduction of digital imaging,
automated and semi-automated landmark
identification directly from the digital image has
been investigated.
• This would avoid the need for manual tracing of
cephalometric radiographs and remove operator
subjectivity.
• With regard to cephalometric analysis, several
systems have shown varying degrees of success
in identifying different landmarks.
• The system developed by Parthasarathy et al.
demonstrated a success rate of 83% in
identifying nine cephalometric landmarks on five
cephalometric images.www.indiandentalacademy.com

Landmark identification on digital cephalometric
radiograph:
• When carrying out landmark identification on a
digital image of a cephalometric radiograph,
identified landmarks can be shown on the
displayed image.
• Corresponding angular and linear measure-
ments can also be displayed and then stored
with the image.
• This enables the operator to edit landmarks
that may have been incorrectly placed. It also
permits the operator to review identified
landmarks at a later date and again edit their
positions.

6) Surgical planning:
• With displayed digital images, cut-and-paste
facilities can be used to move areas of either a
photograph or a cephalometric radiograph
which has been captured as a digital image.
• A system outlined by Sarver et al. produced
profiles on pre -surgical photographs of the
expected result after orthognathic surgery.
• The system was able to move soft tissue, with
the planned hard tissue movement, and to
simultaneously superimpose the cephalometric
radiograph on the photograph.

7) Environmentally friendly:
• No processing chemicals are used
or disposed of. Both CCD sensors
and the PSP plates are capable of
being reused for many thousands of
exposures.
• They can, however, become
scratched and damaged if not
handled carefully.

LIMITATIONS OF
DIGITAL
CEPHALOMETRY

• Digital imaging to truly offer
significant advantages in cephalo-
metry, the image must yield as much
information as is currently available
on radiographic films.
• The properties of conventional film
radiography are difficult to match for
high spatial resolution, wide dynamic
range.

• The quality of digital image is strongly
dependent on the spatial resolution, the
relationship of the gray level values of the
pixels to the optical density of the
radiograph and image display.
• The number of pixels and gray levels
that are required to produce an image of
acceptable quality will vary depending on
the image itself. Image which contain a
large amount of detail depend more on
the number of pixels rather than number
of gray levels. www.indiandentalacademy.com

Spatial resolution
• Spatial resolution is the ability to record
separate images of small objects that are placed
closely together ; it is measured in line pairs per
mm (lp/mm). The smaller the pixel size, the more
detail in the image and therefore the greater the
resolution. The smallest detail detectable by
human eye is 0.1 by 0.1mm.
• To provide digital images of radiographs with at
least as much information as is available in the
original conventional radiograph, pixels no larger
than 0.1mm are required, giving a spatial
resolution of 5 line-pairs per mm (lp/mm)

• Several studies have been carried
out to assess the spatial resolution
required for different clinical
applications.
• Spatial resolution of 8 lp/mm is
necessary for skeletal images , for
chest and GIT images a spatial
resolution of 4 lp/mm is adequate.
For musculoskeletal radiography is
10-12 lp/mm. is required.

Optical density
• Film blackness is measured by optical
density, which is calculated from the
logarithm of the ratio: light incident to
light transmitted by a film. The quality of
digital images is related to the number of
gray levels.
• Fraser et al. suggested that a 12-
bit(4,096 gray levels) images is required
to adequately reproduce the wide
dynamic range present on the radiograph.

Image display
• With improving technology ,the limitations of
pixel size and the number of gray levels can be
overcome and the limiting factor in the quality
of digital images will be the spatial resolution of
the display monitor, which can be dictated by
the number of raster lines.
• Monitors displaying up to 625 lines are
routinely used for viewing of digital images.
Where image quality is particularly important, a
2,048 – line monitor should be used to give
comparable resolution to a radiographic film.www.indiandentalacademy.com

Forsyth D.B et al. (AO-1996;66;43-50) studied
to compare conventional cephalometric
radiographs with their digital counterparts with
regard to the validity and reproducibility of
angular and linear measurements.
They concluded that:
1) Calibration of the digital image produces a
small but significant error.
2) The spatial resolution of the digital image is
less than that of the conventional radiograph.
3) The digital image is unable to match the
conventional radiograph in dynamic range and
sensitivity to small changes in optical density.

4) The random error associated with
angular/linear measurements and landmark
identification tend to be greater with the
digital images than the conventional
radiographs.
5) With the majority of angular and linear
measurements there is a systematic error
b/w the digital images and the conventional
radiographs. Landmarks on poorly defined
edges such as nasion and point A appear
to have the greater error.

MEDICOLEGAL
• Concerns have been raised in the past
about the ability to manipulate the
images for fraudulent purposes.
Manufacturers of software
programmers have installed ‘audit
trails’ which can track down and
recover the original image.

Conclusion
• Although innumerable limitations exist in the
field of cephalometrics. This is not to suggest
that cephalometry is not a useful measurement
tool for use by clinical orthodontist, it is still a
very significant & effective diagnostic tool.
• A combination of various cephalometric norms
and variables should be compiled to arrive at a
proper diagnosis.

• The technology is now available to run a practice
almost paper free. It is theoretically possible to
store clinical notes, photographs, radiographs, &
study models on disc, refer or consult on line. The
future of digital imaging could include the testing
& upgrade of X-ray equipments & software online.
• Research is also continuing in to the
development of a credit card sized ‘smart card’,
which could carry a patient’s medical & dental
notes along with their radiographic images.
• It is important that advances in technology are
accepted & the benefits that they produce utilized
in order that clinical practice & patient care
continue to improve.www.indiandentalacademy.com

BIBILOGRAPHY
1) Text book of Radiographic Cephalometry by Alexander
Jacobson.
2) Text book of Orthodontic current principals & tech; 4th
edn, by T.M.Graber & Robert .L. Vanarsadall.
3) Baumrind et al- The reliability of head film measurement
1.landmark identification –AJO;1971;60;2
4) Steiner.C; Cephalometrics for you & me;AJO-1953,39;10
5) Salzmann.J.A ; Limitations of roentgenographic ceph’s;
AJO;1964;50;3
6) Miller.A – Analysis of errors in ceph measurement of 3-
dimensional distance of the maxilla- Ang Ortho-1966;36;2

7) Richardson .A ; An investigation in to the reproducibility
of some points, planes & lines used in ceph analysis –
AJO;1966;52;9
8) Ahlqvist et al; The effect of projection errors on
cephalometric length measurements-EJO;1986;8;141-148
9) Midtgard. J- et al; Reproducibility of cephalometric
landmark errors of measurements of cephalometric
cranial distances- Ang Ortho;1974;44;56-61
10) McWilliam.J. et al –The effect of image quality on the
identification of ceph landmarks –Ang. Ortho-1978;48;1
11) Jacobson R.;Point A revisited;AJO-DO; 1980;JAN;94-96
12) Tremont T.J. ;An investigation of the variability b/w the
optic plane & frank fort horizontal –AJO-DO ;
1980;Aug;192-200 www.indiandentalacademy.com

13) Houston W.J.- the analysis of errors in orthodontic
measurements- AJO;1983;83;5
14) Hussels.W & Ram Nanda- Analysis of factors affecting
angle ANB –AJO-DO;1984;MAY;411-423
15) Lundstrom A et al- The frankfort horizontal as a basis for
cephalometric analysis-AJO-DO;1995;May;537-540
16)Trpkova B. et al-Cephalometric landmarks identification &
reproducibility ;A meta analysis –AJO-DO ;1997;112;165-70
17) Major. P et al- landmark identification error in P-A ceph
-Ang.Ortho ;1994;64;6
18) Baik & Ververidou – A new approach of assessing sagittal
discrepancies : The Beta angle- AJO-DO;2004;126;100-5www.indiandentalacademy.com

19) Handbook of Orthodontics- 4th
edn; by
Robert E Moyers.
20) Forsyth.D.B et al.– digital imaging of
cephalometric radiography. Part 1:
advantages and limitations of digital
imaging -AO-1996;66;1
21) Forsyth.D.B et al- digital imaging of
cephalometric radiography-part 2: image
quality- AO-1996;66;1
22) Brennan.J –An introduction to digital
radiography in dentistry- Jurnl of Ortho-
2002;29;66-69 www.indiandentalacademy.com

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Limitations of cephalometrics of ceph

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