Limitations of cephalometric radiographs

CEPHALOMETRICLIMITATIONS
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15"15"60"60"
Source PlaneSource Plane
X-ray SourceX-ray Source
Patient in Head Positioning
Device
Patient in Head Positioning
Device
Mid-Sagittal PlaneMid-Sagittal Plane
Film PlaneFilm Plane
X-ray Film in
Cassette
X-ray Film in
Cassette
CephalostatCephalostat

CEPHALOMETRY:
The measurement of
the head from the shadows of
the bony and soft tissue
landmark on the radiographic
image is known as
roentgenographic
cephalometry
According to Moyer in 1988, cephalometrics is a radiographic
technique for abstracting the human head into a geometric shape:
The original Broadbent apparatus.

Cephalometry had been and still is to a very large extent
the only available method that permits the investigation
of the spatial relationships between cranial structures and
between dental and surface structures.
Study casts give more complete information on dental
structures and photographs give better information on
surface structures but only cephalometric images can
yield accurate information on the spatial relationships
between the superficial and deep structures.
ADVANTAGES OF CEPHALOMETRY:

CEPHALOMETRICLIMITATIONS •Computer tomograms, magnetic resonance imaging and
ultrasound also permit simultaneous mapping of surface and
internal details but these modern modalities still involve to some
extent a higher economic and/or physiologic cost and they yield
information of a lower spatial resolution in the sagittal and
frontal projections which are the main areas of interest.
•Therefore cephalograms are relatively non destructive and
non invasive producing a high yield of information at
relatively low physiologic cost.
•Cephalometrics has also rendered possible the serial
assessments of growth

•Cephalograms are tangible records that are relatively
permanent unlike other diagnostic measurements like
caliper readings, palpation. probing etc.
•the same set of cephalograms can be used for testing
different hypothesis and theories.
•Since cephalograms area two-dimensional they are easy to
store transport and reproduce

CEPHALOMETRICLIMITATIONS LIMITATIONS OF CEPHALOMETRY IN RESEARCH
The limitations derive from the fact that the advantages listed
above are more relative than absolute.
The most important limitation is that though the diagnostic
yield is very high compared to the physiologic cost , the
biologic cost in the form of radiation exposure are real and
must be taken into account each time a cephalogram is
generated.
Therefore in contemporary clinical usage it is unacceptable to
generate cephalograms unless it is diagnostically and
therapeutically desirable in the interests of the patient being
examined. www.indiandentalacademy.com

•The absence of anatomical references which remain
constant with time is a serious disadvantage when
clinicians wish to compare cephalograms taken at different
time points.
•The lack of standardization in image acquisition as well
as measurement procedures further complicates the issues.
•The inherent ambiguity of locating landmarks and
surfaces on the x-ray image as the image lacks hard edges
shadows and well defined outlines.

CEPHALOMETRICLIMITATIONS•The structures being imaged unlike the two dimensional
image is three dimensional.
• this contradiction leads to differential projective
displacement of anatomical structures lying at different
planes within the head.
•The fact that all structures lying along the given ray
between the x ray source and film are imaged at the same
point on the film makes it physically impossible to locate
the positions of structures accurately even in two
dimensions with the absence of information in the third
dimension.

The basic components for producing a lateral
cephalogram are:
•X ray apparatus
It comprises of an x-ray tube, transformers, filters,
collimators, and a coolant system all encased in the
machine’s housing.
•Image receptor system
It requires a complex image receptor system that consists
of an extraoral film,intensifying screens, cassette,grid,and
a soft tissue shield.
•Cephalostat

CEPHALOMETRICLIMITATIONS Two ear rods that are inserted into the ear holes so that the
upper border of the ear holes rest on the upper part of the ear
rods fix the patient head.
The head is centered on the cephalostat is oriented with the
Frankfort plane parallel to the floor and the mid sagittal plane
parallel and vertical to the cassette.
The system can be moved to accommodate sitting or standing
patients.
Placing the infraorbital pointer at the patients orbit and then
adjusting the head till the ear rods and the pointer are at the
same level achieve the standardized Frankfort plane.
The upper part of the face is supported by the forehead clamp
positioned at the nasion.

If it is necessary for the cephalogram to be produced in the natural
head position which represents the true horizontal plane, the
patient should be standing up and look directly into the reflection
of his or her own eyes in the mirror directly ahead in the middle of
the cephalostat. (Solow and Talgren 1971)
To record the natural head position the ear rods are not used for
locking the patients head into a fixed position but to serve to place
the median sagittal plane of the patient at a fixed distance from
the film plane and to assist the patient in keeping the his or her
head in a constant position during exposure. However ear rods
should allow for small adjustment of the head to correct
undesirable lateral tilt or rotation.

CEPHALOMETRICLIMITATIONS The projection is taken when the teeth are in centric
occlusion and the lips are in repose unless other
specifications have been recommended( eg with mouth open)
The focus film distance is usually 5 feet but different
distances have also been reported.
It is usual for the left side to face the cassette.

QUALITY OF THE CEPHALOMETRIC
RADIOGRAPHIC IMAGE;
Image quality is a major factor influencing the accuracy of
the cephalometric analysis.
An acceptable diagnostic radiograph is considered in light of
the following characteristics:
•Visual characteristics
•Geometric characteristics

VISUAL CHARACTERISTICS:
They include density and contrast
They relate to the ability of the image to demonstrate optimum detail
within anatomical structures and to differentiate between them by
means of relative transparency.
DENSITY
It is the degree of blackness of the image when viewed in front of a
view box
Density= log( intensity of light beam striking the image/ intensity of
light transmitted through the film )

CEPHALOMETRICLIMITATIONSThe factors which control density are:
1)Exposure technique
Exposure factors which are related to image density are:
•Tube voltage ( kVp)kilovoltage peak
•Tube current (millimpere, mA)
•Exposure time (seconds) S
•Focus film distance (D)
Density= (kVp X mA X S) / D

The factors which control density are:
2) Processing factors:
Image density is directly proportional to
•The developing solution temperature
•Developing time.
•A film with larger grain size ( high speed film) will
produce greater density then a film with smaller grain
size.

CEPHALOMETRICLIMITATIONSCONTRAST:
Contrast is the difference in densities between adjacent areas on
the radiographic film.
Factors controlling contrast are:
•Tube voltage:
When the kilo voltage peak is low the contrast of the
film is high and the film has short scale contrast
When the kilovoltage peak is high the contrast of the
film is low and the film has long scale contrast
•Secondary radiation or scatter radiation:
Decreases the amount of contrast by increasing fog
of the film. Several devices like aluminum filter
grids and lead diaphragm have been added to reduce
scatter.

•Subject contrast
Refers to the nature and properties of the subject
like thickness density and atomic number.
•Processing procedure:
The higher the developing temperature, the greater
the contrast.
Factors controlling contrast are:

GEOMETRIC CHARACTERISTICS:
•Image unsharpness
classified into three types depending on etiology:
1. Material unsharpness
2.Motion unsharpness
3.Geometric unsharpness
•Image magnification
•Shape distortion

CEPHALOMETRICLIMITATIONSGeometric unsharpness
It is the fuzzy outline caused by the penumbra
Factors that influence the geometric unsharpness are:
•Focus film distance
•Size of the focal spot
•Object film distance
In order to reduce the penumbra the focal spot size and the object film
distance should be reduced and the focus film distance increased.
Geometric unsharpness=
(Size of the focal spot X Object film distance)/Focus film distance

RADIOGRAPHIC IMAGE
PRODUCED BY A
DIVERGENT BEAM

Motion unsharpness
Caused by movement of the patients head or movement of the
tube and film.
Material unsharpness
It is related to two factors
•It is directly proportional to the silver halide
crystals in the emulsion
•It is related to the intensifying screens which
although can minimize x ray dose also increase film
unsharpness.

Image magnification:
It is the enlargement of the actual
size of the object
Factors affecting image
magnification are the same
affecting image unsharpness
Magnification % = ( focus film distance/ (focus film
distance- object film distance))-1 X100

IMAGE MAGNIFICATION

Shape distortion:
This results in an image that does not correspond
proportionally to the subject.
This occurs due to improper orientation of the head in
the cephalostat or improper alignment of the film and
central ray.

FACTORS AFFECTING THE QUALITY OF THE IMAGE:
Quality of the image is controlled by the manufacturer of
the equipment as well as the operator.
The manufacturer provides pre programmed exposure factors such
as milliamperage, kilovoltage peak and exposure time
The operator can adjust the exposure factors such as type of X ray
machine, target film distance, screen film combination, and the grid
chosen.
The exposure time is the commonest factor to change.

PROTECTION FROM RADIATION:
Although the amount of radiation in clinical diagnosis is very small
protective measures are obligatory for both the doctor and the
patient.
XRAYS are a form of electromagnetic
radiation that can cause biologic
changes to a living organism by
ionizing the atoms in the tissue they
irradiate.

RISK BENEFIT CONSIDERATIONS IN
CEPHALOMETRY:
In brief the radiation risk from cephalometry is real but very
small.
The fact is that the use of intensifying screen in cephalometry
reduces the exposure dramatically as compared to non screen
techniques.
The cephalometric dose of 25-40 mrems ( millirems) per film is
very low in the spectrum of medical diagnostic procedures.

ALARA
The most recent recommendations involving the establishment
of permissible doses and dose limits to occupational and
nonoccupational groups can be summarized in the principle of
ALARA (As low as reasonably achievable).
This means that every available method for reducing exposure
to ionizing radiation will be implemented to minimize
potential risks and adverse consequences

Protective measures that aim to minimize the radiation exposure to
the patient are:
•Utilization a high sped film and intensifying screens to reduce
the dose of radiation and the exposure time.
•Filtration of secondary radiation or scatter radiation produced
by low energy x-ray photons by an aluminum filter.
•Collimation by a diaphragm made of lead in order to achieve
optimal beam size

•Proper exposure technique and processing in order to avoid
unnecessary repetition of the procedure.
•The patient ‘s wearing a lead apron in order to absorb scatter
radiation
•In order to avid scatter radiation he operator must stand at
least 6 feet behind the tube head or should stand behind a lead
protective barrier while making the x-ray exposure.

Margolis pointed out that the radiation officer of the
Massachusetts Institute of Technology had measured the
skin dose for typical cephalometry and recorded an
average of 0.1 r per film.
On the basis of this observation, about fifty cephalograms
a year would still be a safe dosage, with respect to the
probability of exposure producing any clinically
detectable biologic effect at a future time in the patient's
life.

White and Graber employed ionization chambers to check
radiation exposure of various parts of the body during a typical
cephalometric examination.
•Maximum radiation in the film area was even less than reported
by Margolis— 0.075 to 0.090.
•In the cervical area the radiation dropped to 0.015 r; in the
thoracic region it dropped to 0.005 r.
•No exposure was recorded at all in the comparatively critical
gonadal region. Radiation hazard is thus practically nil.
•Lead-impregnated Fiberglas or rubber aprons are available but
not necessary. www.indiandentalacademy.com

Even with the faster emulsion film that has been introduced, x-
radiation alone is not adequate to sensitize the emulsion.
The dosage and exposure time would be prohibitive.
Intensifying screens of calcium-tungstate-impregnated Bristol board
should be placed in the film-holding cassette in close contact with
each side of the film.

When the cassettes are subjected to radiation, the short rays pass
through the bakelite front, screens, and film.
As this happens, the calcium tungstate crystals fluoresce, creating
light. This together, with the x-ray energy, activates the silver
salts of the emulsion, reducing the exposure time to as much as
one-fifth of what it would be without the intensifying Screens.
Unfortunately, intensifying screens also reduce the sharpness of
the image, as does secondary radiation or "scatter."
The image can be improved somewhat by the use of a stationary
type of grid, a movable grid, or a Buckey diaphragm, with no
appreciable increase in exposure time.

This study was undertaken to evaluate the reliability of locating
cephalometric landmarks on films taken with "rare earth" methods
compared to those taken with standard intensifying screens
In the majority of the studies it is a common finding that the rare
earth systems generally show less contrast, which may not affect
diagnostic information, and less image sharpness.
Stathopoulos, Poulton. Angle Orthodontist 1990

•Density was comparable while radiation exposure was
dramatically reduced.
• Therefore, there is agreement in the usefulness of rare earth
screens in clinical practice, though most studies used a phantom
head.
• These findings showed no landmark accuracy preference of
one screen system over the other, the 96 percent reduction in
patient radiation with the rare earth system would mandate this
be used in cephalometric radiography
Stathopoulos, Poulton. Angle Orthodontist 1990

SOURCES OF ERROR IN LATERAL CEPHALOMETRY
VALIDITY
Validity or accuracy is the extent to which in the absence
of measurement error the value obtained represents the object of
interest. Both what is being measured and the method of
measurement have to be taken into account. Some reference
landmarks and planes do not agree with the anatomical
landmarks they represent because they have been chosen for
convenience of identification rather than on grounds of
anatomical accuracy. www.indiandentalacademy.com

REPRODUCIBILITY
Reproducibility or precision is the closeness of successive
measurements of the same object
If a certain measurement is persistently over or underestimated a
systematic error or bias is introduced. If no systematic error is
present the cluster of observations will be randomly distributed
around the true value to express the random error.
The word reliability is used in a broader sense to represent both
validity and reproducibility.

CEPHALOMETRICLIMITATIONSTo ignore the errors is to deny the clinician full use and the
advantages of the system of cephalometrics.
•Symmetry is taken for granted in cephalometric analysis
•Occlusal position:
It is convention to take the cephalogram in the position
of maximum intercuspation,
Thus an important functional component of the malocclusion
will be missed out. Two cephalograms may be recorded with
the help of a wax bite one with the patient in centric occlusion
and the other in retruded contact position
•Orientation on the transmeatal axis
It is conventional to orient the patient’s head so that the
central ray of the xray passes through the transmeatal axis. This
assumes that the external auditory meatuses are symmetrical.

•Means are population averages which have nothing to do with
the specific characteristics of the patient itself.
•Beautiful faces in good occlusion with measures far from the
norm exist.
•Cephalometrics should not be used to treat “to the norm” but
instead should be used to provide satisfactory treatment goals
which along with other data recorded from the patient should
be used to come up with a customized treatment plan.

Some of the errors in cephalometrics is more due to the user than
the method itself:
•Rigid application of mean values lead to poor treatment
goals. The total range and variance is more practical than
the means itself.
•The clever clinician does not apply the same values to all
the faces but determines those adaptational compromises to
be made which is most apt to be stable and pleasing

•Inappropriate application of norms: when samples from which
“norms” are derived are not specified it is difficult for the
physician to know whether the norms are applicable to the race
and gender of the patient he is treating
•An analysis should not be used for a purpose for which it was
not intended: for e.g.: an analysis for visualizing treatment
goals should not be used for growth studies
•Ideals represent the artificial constructs of faces one clinician
likes. Norms represent real values of a particular group. They
cannot be used interchangeably.

ERRORS OF CEPHALOMETRIC MEASUREMENTS:
Cephalometric measurements in radiographs are subject to errors
that may be caused by:
1. radiographic projection errors
2. errors within the measuring system
3. errors in landmark identification
RADIOGRAPHIC PROJECTION ERRORS
During the recording procedure the object as imaged on a
conventional radiographic film is subject to magnification
and distortion.

MAGNIFICATION:
Magnification occurs because the X ray beams are not
parallel with all points of the object to be examined.
The magnitude of the enlargement is related to the distances
between the focus, the object, and the film.
The use of the long focus-object and the short object-film
distances has been recommended in order to minimize such
projection errors.
Although long focus objects distances are preferable, a focus-
film distance of more than 280 cms does not significantly alter
the magnitude of the projection error.www.indiandentalacademy.com

The use of angular
rather than linear
measurements is a
consistent way to
eliminate the
impact of
magnification since
angular
measurements
remain the same
regardless of the
magnification
EFFECT OF FOCUS FILM
DISTANCE ON RADIOGRAPHIC
MAGNIFICATION

EFFECT ON OBJECT FILM DISTANCE ON
RADIOGRAPHIC MAGNIFICATION AND SHARPNESS

DISTORTION:
Distortion occurs because of different magnifications
between different planes.
Although most of the landmarks used in cephalometric analyses
are located within the mid Sagittal plane, some landmarks and
many structures that are useful for superimposition are affected by
distortion, owing to their location in a different field of depth.
In this instance both linear and angular measurements will be
affected.
Linear distances will be foreshortened, an effect that can be
compensated for if the relative lateral displacement of the
landmarks and their distance from the midsagittal plane are
known.
A combination of information from both PA and lateral
projections has been suggested, but only a few landmarks can be
identified in both projections.

DIRECTIONS OF POSSIBLE
MISALIGNMENTS OF THE EHAD

Furthermore landmarks and planes not located in the midsagittal
plane are usually bilateral giving a dual image on the radiograph.
The problem of locating bilateral structures can somewhat be
compensated by recording the midpoints between these structures.
Bilateral structures in the symmetric head position do not
superimpose in a lateral cephalogram !!
The fan shaped X-ray beam expands as it passes thus causing a
divergence between the images of all bilateral structures except those
along the central beam
For convenience therefore it is averaged and traced those structures
whose images are doubled and exhibit an apparent asymmetry.
However this is inadequate to describe a head that is truly
asymmetrical.
BILATERAL STRUCTURES

CEPHALOMETRICLIMITATIONSTherefore if proper care is taken during obtaining a radiograph the
errors introduced during this phase can be regarded as negligible
for routine clinical purposes.
In order to control errors during radiographic projection, the
relationship between the X ray target, the head holder and the film
must be fixed.
The metal markers in the ear rods must be aligned and its good
practice to include a metal scale of known length to provide
permanent evidence of the enlargement of each film.
For special research purposes, projection errors can be reduced by
a combination of stereo head films and the use of osseous implants.

ERRORS WITHIN THE MEASURING SYSTEM:
The development of computerized equipment for electronic
sampling of landmarks has greatly speeded up data collection
and processing and has reduced the potential for human
measuring errors.
The errors with a digitizer has two components:
• The error of the digitizing system
• The precision with which a marked point on the film or tracing
can be identified by the cross hair of the recording device.
An accuracy of .1mm is desirable without any distortion over the
surface of the digitizer.www.indiandentalacademy.com

CEPHALOMETRICLIMITATIONSErickson and Solow (1981) have described specific procedures for
testing and correcting the digitizers before any routine use in
cephalometric research.
Errors of scaling can be corrected by setting switches in the control
unit of the digitizer or by scaling the incoming x-y coordinates by
a software programme. Non-linearlities can be corrected by
including certain matrices in the software programme .
If these requirements are met , the measurements are more reliable
than those obtained by any manual device owing to the superior
accuracy of the digitizer.
Moreover the digitizer allows direct registration of the landmarks
on the cephalogram thus eliminating the need for tracing
procedures.

•Richardson (1981) AND Cohen (1984) claimed that direct
observation on untraced radiographs resulted in an increased
reliability in landmark location.
•Therefore electronic plotting devices make repetitive
measurements faster and less tedious and has facilities like
error checking routines can greatly reduce random
cephalometric errors.

ERRORS IN LANDMARK IDENTIFICATION:
The major source of error in cephalometric has been
landmark identification
The factors involved are:
• The quality of the radiographic image
• The precision of the landmark definition and the
reproducibility of landmark location
• The operator and registration procedure

THE QUALITY OF THE RADIOGRAPHIC IMAGE
The quality of a radiograph is expressed in terms of sharpness-
blur and contrast and noise.
Sharpness is the subjective perception of the distinctiveness of
the boundaries of a structure and it is related to blur and
contrast
Blur is the distance of optical density change between the
boundaries of a structure and its surroundings.
It results from three factors:
Geometric unsharpness
Motion unsharpness
Receptor unsharpness

Geometric unsharpness
Is directly related to the size of the focal spot
and the focus film distance.
Receptor unsharpness
• Depends on the physical properties of the film
and the intensifying screen
•Combinations of fast films and rare earth intensifying screen
have reduced the exposure required but produces images with
poorer definition.
•It is a matter of controversy whether this results in significant
differences in accuracy of landmark identification.

Motion unsharpness
Movement of the tube, object or the film during exposure results
in image blur. by increasing the current it is possible to reduce
the exposure time and thus reduce the effect of movement .blur
from scattered radiation can be reduced by using a grid at the
image receptor end.
In clinical orthodontics the major parameters that influence the
sharpness of the film are
Focus to film distance (geometric unsharpness)
Voltage capacity (kV) of the cephalometric equipment
(motion unsharpness)

•Contrast is the magnitude of the optical density differences
between a structure and its surroundings.
•It plays an important role in radiographic image quality.
•Increased contrast increases the subjective awareness of the
image sharpness but excessive contrast leas to loss of details due
to blackening out of regions of low absorption and reverbering
of regions of high absorption.

The contrast is determined by:
The tissue being examined
The receptor
The level of kV being used
Clinically the most important parameters influencing the
contrast are film cassette system and the kV level used.
High kV levels tend to level out any differences in
radiation absorption thus reducing the difference in gray
levels between various tissues.

Noise refers to all factors that tend to disturb the signal in a
radiograph
It may be related to:
The radiographic complexity of the region
( ie the radiographic superimposition of anatomical
structures located in different depth planes)
This is know as noise of pattern, structure or anatomy

Receptor mottle:
This is known as quantum noise. it depends on the
sensitivity and the number of radio sensitive grains present in the
film.
In principle structured noise can be reduced by cephalometric
laminography (Rickkets)
But in conventional radiography this is unavoidable.
These types of films can be addressed by films of high quality.

In recent years the application of digital technology to conventional
radiography has changed the parameters of image quality by making
it possible to process the image in order to enhance the sharpness
and contrast ands to reduce the noise.
It has also been said that the main advantage of digital processing
may be a reduction in radiation dose due to lower exposure times.
Furthermore the contrast and density of a single unexposed image
can be adjusted for several diagnostic tasks thus reducing the
number of examinations.
In digital images resolution and discrimination of anatomical
structures can be improved after digital filtering. This is especially
applicable to underexposed films.www.indiandentalacademy.com

PRECISION OF THE LANDMARK DEFINITION AND THE
REPRODUCIBILITY OF LANDMARK LOCATION
A clear unambiguous definition of cephalometric landmarks chosen
is of utmost importance for cephalometric reliability.
•The reference plane to which they are related should accompany
definitions of landmarks.
•Conditions required to record some landmarks should not be
unspecified or ambiguous.
•(EG: lips in repose/ centric occlusion/ head posture)
•Some landmarks can be more reliably located than others.
•Geometrically constructed landmarks and landmarks identified as
points of change between concavity and convexity are quite
unreliable. www.indiandentalacademy.com

•The radiographic complexity of the region also lays an important
role making some landmarks more difficult to identify.
•According to Miethke the most reliably identified landmarks are
incision superior incisal and incision inferior incisal. Anatomical
porion and landmarks on the condyle are difficult to identify on the
closed mouth radiographs. ( Adenwalla 1998)
•Landmarks that lie within the confines of the skull have a greater
likelihood of being confounded by noise from adjacent structures or
superimposed structures .this may cause difficulty in locating the
cusps of the posterior teeth or the lower incisor apex.

•The distribution of errors for many landmarks is
systematic and follows a typical pattern, some landmarks
being more reliable in the vertical and some in the
horizontal plane depending on the topographic orientation
of the structures along with which their identification is
assessed.
•The validity of certain landmarks will also vary
depending on whether they are used for angular or linear
measurements.

Baumrind and Franz (1971) pointed out that the impact that
errors in landmark location have on angular and linear
measurements is a function of three variables:
The absolute magnitude of the
error in landmark location
The relative magnitude or the
linear distance between the
landmarks considered for that
angular or linear measurement
The direction from which the
line connecting the landmarks
intercepts the envelops of the
error www.indiandentalacademy.com

The envelope is the pattern of total error distribution.
Since cephalometric landmarks have a non-circular
envelope of error, the average error introduced in
linear measurements will be greater if the line segment
connecting them to another point intersects the wider
part of the envelope.

•Errors in landmark identification can be reduced if
measurements are replicated and their values averaged.
•Consecutive evaluation of one cephalogram at random showed
that the localization of a landmark is more exact the second time
that at the first judgment. (Miethke 1989)
•The more the replications the smaller the impact of random error
on the total error becomes. There is however a practical limit for
the repeated assessment .
•Even for the purpose of scientific research if cross sectional or
serial measurements from two groups must be compared,
duplicate measurements are sufficient.

THE OPERATOR AND REGISTRATION PROCEDURE
The operator’s alertness and training and his or her working
conditions affect the magnitude of the cephalometric error. In
cephalometric studies therefore the error level specific to the
operator must be established if any meaningful conclusions can
be drawn from the data.
The most important contribution to improvement in landmark
identification are experiences and calibration. In studies that
compare two groups of radiographs ,the operator can introduce
different types of error or bias.

One type of operators bias is the operators variability which
involves both
inter observer variability (disagreement between observers
for the identification of a particular landmark)
and intra observer variability ( the disagreement within the
same observer over time due to changes in his or her
identification procedure)
A good method to reduce this error consists of calibration and
periodic recalibration tests to establish confidence limits of
reproducibility for each observer

Another kind of error can be introduced because of
unconscious expectations of the operator when
assessing the outcome of the scientific research (that is
the outcome of different treatment results)
Randomization of record measurements or double blind
experimental designs can be used for reducing such
bias

When serial records are being analyzed it has been suggested that all
the records of one patient should be traced on the same occasion.
This minimizes the error variance within individual observers
although it increases the risk of bias.
Since serial tracing must maintain precise common landmarks in
regions without change during treatment or growth, landmark
location in such regions can be identified in one of the cephalograms
and then transferred to the other cephalogram by use of templates of
the corresponding structures.
After collection cephalometric values should be examined for wild
values, which can be expressions of normal variations, but
sometimes attributed to incorrect identification of a landmark or
misreading of an instrument.www.indiandentalacademy.com

CEPHALOMETRICLIMITATIONS STANDARDIZATION OF IMAGE GEOMETRY
The early cephalometrists recognized the importance of
standardized head position if cephalograms were to be measures
consistently.
Most modern users of the cephalostat take the equipment for
granted however these instruments provide a precision in head
positioning that surpasses that of any other standard diagnostic
radiographic procedure in dentistry or medicine.
All conventional cephalometric analyses are based on the
assumptions of standardized and fixed distances between the
anode object and film. If they are met valid comparison can be
made between images generated on different cephalostats. If they
are not maintained comparisons cannot be made even if they are
two radiographs from the same machine.

Another gap in the conventions is the direction in which the
patient is facing.
In the USA the left side of the face is positioned closer to the
film while in Europe the right side of the face is closer to the
film.
Obviously either convention is acceptable but care should be
taken not to mix conventions in the same subject.
It should be kept in mind that the side closer to the film will
appear larger.
Any image acquired with the ear rods disengaged will be
subject to increased measurement errors because the central
beam will inevitably deviate from the porion-porion axis.

CEPHALOMETRICLIMITATIONSMETHODS OF CONTROLLING ERRORS
Taking the radiographs
The relationships of x-ray target, head holder, and film must be fixed.
The metal markers in the ear rods must be aligned, and it is good
practice to include a metal scale of known length at the midsagittal
plane to provide permanent evidence of the enlargement of each
radiograph.
Every effort must be made to obtain
films of high quality as described in
the standard texts. Use of an
aluminum wedge to improve the
definition of the soft tissues and
anterior bony structures may be a
considerable advantage www.indiandentalacademy.com

There is a conflict between radiation control and film quality in the
choice of films and screens.
Fast films and rare-earth intensifying screens reduce the exposure
greatly but give poorer definition than slower films and high-
definition screens.
It has been claimed that the poorer quality of image makes little
difference to the accuracy with which landmarks can be identified,
although further research on this topic is needed.
Nevertheless, exposure reduction is of primary importance and
attention should be directed to obtaining the best screen/film
combination.
Minor distortions can arise if the film is not flat, because the cassette
does not support it adequately. This can be checked by exposing a
test grid which will reveal any serious lack of flatness of the film.

Landmark identification
There is little point in having radiographs of high quality if
they are measured in bright ambient lighting or if tracings are
made on poor-quality drafting paper which obscures detail.
The most important contributions to improvement in
landmark identification are experience and calibration.
Before any major study is undertaken, particularly if more
than one measurer is involved, calibration is of the greatest
importance.

Experimental design
As they are collected, measurements should be checked for "wild"
values.
This can be done against previously published standards as the
study progresses or against the measurements of the study itself
after it has been completed.
Measurements more than 3 standard deviations away from the
mean may, indeed, be expressions of normal variation, but often
they will be the result of incorrect identification of a point or
misreading of an instrument.
Random errors are reduced if measurements are replicated and
averaged. If this is to be done, it is the tracings which should be
replicated, not the measurements of tracings, because the greatest
errors may arise in point identification rather than in measurement.www.indiandentalacademy.com

The procedure is much less tedious if radiographs are digitized
directly.
Baumrind and Millersuggested that tracings should be repeated four
times, which will halve the random error, but this is too arduous for
all but the most exacting investigations.
An important way of controlling systematic errors is to randomize
the order in which the records are measured.
Thus, for example, if two groups of cases are being compared, they
should be traced in random order and, if possible, in a way that
prevents the measurer from knowing to which group any record
belongs. www.indiandentalacademy.com

Ahlqvist et al. reported that the error
introduced by head rotations of 5° or
less results in an insignificant amount
of error (less than 1%) in lateral
cephalometric distance
measurements.
They stated that head rotations of
greater than 5° should not occur with
careful patient positioning.
Paul W. Major
Angle Orthodontist 1996
Effect of head orientation on posterior anterior cephalometric
landmark identification

Ishiguro et al. stated that head rotation of 10° or less,
either up-down or left-right, was a negligible factor in
width measurements but did, however, affect height
measurements to a greater extent.
It is apparent that patient positioning can introduce
errors in cephalometric radiography and that the
magnitude of the error depends not only on the amount
of malpositioning but also on the type of measurement
and the relative positions of the structures being
measured.

Rotation about the transverse axis will affect the relationship of
landmarks vertically but not horizontally, as landmarks on both
sides of the skull move the same amount. The relationship of
landmarks to the best vertical midline is not affected, as no change
in horizontal relationships take place. The true vertical distance
between landmarks will change, depending on each landmark’s
distance from the rotational axis, but the vertical assessment of
symmetry will not be affected.

Rotation about the vertical axis has the opposite effect, with
horizontal relationships being affected while vertical relationships
remain unchanged. This creates a potential problem because
assessment of symmetry for bilateral landmarks involves relating
them to a midline reference plane. If the midline reference plane is
constructed from landmarks not located at the same antero-
posterior position within the skull, any rotation about a vertical
axis (left and right) will change the relationship between the
bilateral landmarks and the midline reference line. Ideally, to
eliminate the effects of rotation about a vertical axis, each pair of
bilateral landmarks should be measured with respect to a midline
reference located at the same anteroposterior position within the
skull.

Rotation about the anterior-posterior axis will not
distort the image.
This is because rotation is parallel to the central ray
and will alter only the overall image position on the
film, not the relationship between landmarks.

COMPUTERISED CEPHALOMETRIC SYSTEMS:
The manual technique of tracing a cephalogram is time
consuming and tedious.
In comparison computerized cephalometry is very fast and takes
just 10% of the time a manual tracing requires.
Due to direct digitization of the landmarks the process removes
human errors except those of landmark identification.
In addition to speed computerized cephalometry also facilitates
the use of double digitization of landmarks thus significantly
increasing the reliability of the analysis.

CEPHALOMETRICLIMITATIONSOther benefits of this method include:
•Easy storage and retrieval of cephalometric values and tracings
•Intergration of the cephalometric reghistrations within an office
management computerized sytem.
•Combinationof the cephalometric data with patients files photos and
dental casts.

CEPHALOMETRICLIMITATIONSThree possible approaches may be used to perform a cephalometric
analysis. (Rudolph, Sinclair,AJO 1998)
•The most common method is by manually placing a sheet of
acetate over the cephalometric radiograph, tracing salient
features, identifying landmarks, and measuring distances and
angles between landmark locations.
•Another approach is computer aided. Landmarks are located
manually while these locations are digitized into a computer
system. The computer then completes the cephalometric
analysis.
•The third approach is completely automated. The
cephalometric radiograph is scanned into the computer. The
computer automatically locates landmarks and performs the
cephalometric analysis.

Currently, several commercially available systems can perform
basic cephalometric analysis tasks.
The user locates landmarks manually with a mouse cursor on
the display monitor on some systems. Other systems digitize
landmark locations on a digitizing pad. In either case a
computer algorithm performs a cephalometric analysis by
calculating distances and angles between landmark locations.
In addition, the algorithm connects these landmarks with line
segments to produce a tracing. Some systems are capable of
moving the tissues to simulate treatment effects, growth
effects, and surgical prediction. Finally, some of these systems
also are able to produce a time series of images using landmark
locations, not superimposition contours, to register images.www.indiandentalacademy.com

Generally, these systems do not save time, are expensive,
and require technical training. The accuracy of these
computer-aided programs has been demonstrated to be
similar to that of manual digitization, and because manual
landmark identification programs require subjective user
point identification, they are limited in scope.
In addition, the number of landmarks required are high; this
tends to negate any time saved using this method. Although
the analysis uses a computer, the process of manual point
digitization can be time-consuming and error-prone.

CEPHALOMETRICLIMITATIONSAutomatic Landmark Identification
A third approach to cephalometric
analysis is completely automated. The
cephalometric image is scanned into a
computer and both landmark
identification and cephalometric
analysis are automated.
The process has the potential to
increase accuracy, provide more
efficient use of clinicians' time, and
improve our ability to correctly
diagnose orthodontic problems.
Additionally, this process may provide mathematical descriptions
of landmark locations that could be applied to new ways of
evaluating cephalometric radiographs to derive clinically
important information. www.indiandentalacademy.com

CONCLUSION:
A roentgenographic cephalometric analysis is essentially a
technique to be used as a guide in the clinical interpretation
of a case of malocclusion.
This is its ultimate, and should be its fundamental, purpose.
It is not an end; it is a means to an end.
The only answer is the whole approach to the whole child.
Roentgenographic cephalometrics although a major one
-is only one of many approaches and considerations in the
diagnosis and treatment of an orthodontic patient.

Limitations of cephalometric radiographs

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Limitations of cephalometric radiographs