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4. INTRODUCTION
Radiographic cephalometry is a two dimensional
representation of three dimensional object.
Conventional roentographic cephalometry
have not been useful for accurate assessment
of craniofacial anomalies and facial
asymmetries.
The validity of many cephalometric analysis
have not been documented.
Other limitations of radiographs
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5. Classification of errors of lateral
cephalometric radiographs.
Errors in cephalometric measurements
a)Radiographic projection error
Magnification
Distortion
b)Errors within measuring system
c)Errors in landmark identification
Quality of radiographic image
Precision of landmark definition
Reproducibility of landmark location
The operator and registration procedure
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6. Classification of errors of lateral
cephalometric radiographs.
2)Errors in growth prediction and superimposition techniques
3)Limitations of cephalometric analysis
Sagittal basal relationship
Vertical basal relationship
Dentoalveolar relationship
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7. Radiographic projection errors
Magnification:
It occurs because x ray beams are not parallel with all
points on the object to be examined .
The use of long focus object and short object film
distance have been recommended in order to minimize
such projection errors (Franklin 1952)
Focus film distance > 280 cms doesn’t alter magnitude
of projection error (Ahlquvist et al 1986)
Enlargement compensation for lateral ceph. Radiograph
is 4.6 to 7.2 % & for frontal film 0.3 to 9.2 % at 60”
anode to midsaggital plane distance (Bergersen O E
1980)
Use of angular than linear measurement
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8.
Distortion:
Misalignment of patient head and X-ray apparatus
(Ahlquvist et al 1983 , 1986)
Different magnification between different planes
Bilateral landmarks – “dual image” on the radiograph
Mild asymmetry- difficult to differentiate between
geometric distortion and true subject asymmetry
(Cook 1980)
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9. Factors to Control Radiographic
Projection Errors
Standardization of radiographic cephalometry
stabilization of patient head
Special research applications: stereo- head
films and osseous implants (Rune et al 1977)
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11. Errors in landmark identification
Many factors are involved
Quality of radiographic image
Precision in landmark definition and
reproducibility of land mark location
Operator and registration procedures
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12. Quality of radiographic image
It is expressed in terms of sharpness/ blurr ,
contrast & noise
SHARPNESS
Related to blurr and contrast
3 types of unsharpness
Geometric
Motion
Receptor
BLURR
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13.
CONTRAST
Magnitude of optical density difference between
structure and its surroundings
Increased contrast: increases subjective
perception but leads to loss of details owing to
blackening of regions
Deteremined by
Tissue being examined
Receptor
Level of kV used
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14.
NOISE:
it refers to all factors that disturb signal in a
radiograph
Noise of pattern, structure or anatomy
Receptor mottle or quantum noise
In recent years the application of digital
technology to conventional radiography has
enhanced image sharpness , contrast and reduce
noise.
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15. Precision in landmark definition and reproducibility
of land mark location
Geometrically constructed landmarks and
landmarks identified as points of change between
convexity and concavity often prove to be very
unreliable
Rad. Complexity of the region makes it difficult to
locate landmarks
Baumrind and Frantz pointed out: errors in
landmark location is a function of 3 variables
1.
2.
3.
Absolute magnitude of error
Relative magnitude or linear distance between the landmarks
Direction from which the line connecting the landmarks
intercept their envelope of errors.
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16.
Errors in landmark identification can be
reduced by:
Replication of measurements
Localization of landmarks is more exact 2nd time than at
first judgement
Specific landmark location – radiologic registration can
minimize error
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17. Operator and registration procedures
Experience and calibration
TEST: Land mark identification reliability
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18. Systemic errors depending on design of study
Inter observer variability
Intra observer variability
Bias due to subconcious expectation of the
operator while assessing the outcome of scientific
research- double blind expt. Design.
Method to reduce error- calibration and periodical
recalibration test to establish specific confidence
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19. Errors in growth prediction
Various methods have been proposed most of
which are based on mathematical models of
growth process
Prediction method used in industry and science
Theoretical method
Regression method
Experimental method
Time series method
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20.
Growth prediction is difficult for number
of reasons
•
•
•
•
Wide range of marphological difference
Varying rates and direction of growth
Varying in timing of different area of active growth
Lack of correlation b/w size of facial structure at an
early age and ultimate adult size
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21.
Rakosi (1982)-source of eror in growth
prediction
•Variable growth rate in regional growth sites
•Growth pattern not being fully taken into account
•The relationship of form and function
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22. Limitations of growth predictions
These are derived from means of large
samples,there is no reason to suggest that growth
pattern under investigation behaves as a mean
Past growth does not predict future growth
There is no evidence to suggest that appareance
of single part such as mandible is clue to future
growth of face
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23. Can jaw rotation be predicted?
Skeiller and Bjork-growth rotation of mandible based on
morphological criteria using implants
Baumrind et al-experiment to determine ability of clinician in
distinguishing forward rotation from backward rotation based
on head film information
232 treated classII patients-14 groups
Each group contain 2 or 3 forward/backward rotation
5 senior board certified orthodontists
Result showed none of experts performed at a that was
Statistically better than chance.
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24. Errors in superimposition
Reference points are used for
superimposition(cranial base,maxilla, mandible)
Various technique for superimposition(best fit
technique,tracing,punching pin holes,blink
method/substraction technique)none of these
methods are more accurate than others(Houston
and Lee 1985)
Study by Ghafari et al showed statistical
differences in interpretation of facial changes by
different superimposition methods
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25. Reliability of cephalometric analysis
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.
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26.
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 The pretreatment cephalometric radiographs
assessed by one
investigator who used the criteria for each of five
popular analyses.
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27. Limitations of horizontal reference planes
used in various analysis
FH plane
SN plane
Functional occlusal plane
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28. Downs – timely warning. It was he who had shown
that discrepancies between cephalometric facial
typing and photographic facial typing disappear
when the Frankfort plane is not horizontal but
tilted up or down.
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31. 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.Bjork illustrates the greatest variation in
the inclination of the cranial base rather than the
greatest differences in prognathism.
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33. 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. The plane which passes through the left and
right porion landmarks and the left orbitale achieved
uniformity in craniometric research.
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34. 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.
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35. The insertion of ear rods will obviously result in
vertical and/or horizontal rotation of the head ,which
introduces a deficient and misleading image.
Thereby,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.
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37. Point A revisited – Jacobson- AJO 1980
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.
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38. Vertical basal relationship
Different cephalometric parameters are used
Different reference lines used
Duterloo et al(1985)-distinction between skulls
with small and large divergency
DiagramGraphical representation-vorhies and adams
1981-overall vertical index
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40.
various cephalometric analyses used in
routine orthodontic practice
1) stieners analyses
2) witts
3)Mcnamara
4)Burstones-hard and soft tissue analyse
5)Schwartz analyses
6)Rakosi jaraback
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41. 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 annaual
intervals between 8.5 yrs and 15.5 yrs of age.
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42. Limitations of cephalometric radiographic
analyses
1)Growth pattern not taken into consideration
2)Mean values are based on different population
3)Two dimensional representation of three
dimensional object
4)Form and functions not taken into consideration
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43. Conclusion:
A combination of various cephalometric norms
and variables should be compiled to arrive at a
proper diagnosis.Although innumerable
controversies exist in the field of
cephalometrics, it is still a very significant &
effective diagnostic tool.
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44. References
cephalometric radiography-Thomas Rakosi
cephalometric radiography-Athenosis
radiographic cephalometry-Jacobson
Broadbent BH. A new X-ray technique and its application to Orthodontia. Angle Orhod
1931;1:45-66.
Adams JW. Correction of error in cephalometric roentgenograms. Angle Orthod 1940;10:313.
Hixon EH. The norm concept and cephlometrics. Am J Orthod 1956;42: 898-919.
Salzmann JA. Cephalometrics : Resume of the workshop and limitations of the technique.
Am J Orthod 1958;44:901-5.
Ricketts RM. Variations of the temporomandibular joint as revealed by Cephalometric
laminography. Am J Orthod 1959;36: 877-98.
Harvold E (1963) Some biological aspects of orthodontic treatment in the transitional
dentition. Am J Orthod 49: 1-14.
Salzmann AJ. Limitation of roentographic cephalometry Am J Orthod 1964;64:204-10.
Miller AP, Savaras B, Singh JI. Analysis errors in cephalometric measurements of 3dimensional distances on the maxilla. Am J Orthod. 1966;36(2):169-75.
Richardson A. An investigation into the reproducibility of some points, planes and lines
used in cephlometric analysis. Am J Orthod 1966;52: 637-51.
Bjork A. The use of metallic implants in the study of facial growth in children: method
and application. Am J Phys Anthropol 1968;29:243www.indiandentalacademy.com
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Frantz RC. The reliability of head film measurements 2. conventional angular and linear
measurements. Am J Orthod 1971;60(5):505-17.
Hixon EH. Cephalometrics: a perspective. Angle Orthod 1972;42:200-11.
Kvam E, Krogstad O. Correspondence of Cephalometric values. A methodological study using
duplicating films of lateral head plates. Angle Orthod 1972;42:123-8.
Sekiguchi T, Savara BS. Variability of Cephalometric landmarks used for face growth studies.
Am J Orthod 1972;61: 603-18.
Gravely JF, Benzies PM. The clinical significance of tracing error in cephalometry, Br J Orthod
1974;1: 95-101.
Midtgard J, Bjork G, Lander-Aronson S. Reproducibility of cephalometric landmarks and errors
of measurement of cephalometric cranial distances. Am J Orthod 1974;44(1):57-6.
Greenberg LZ, Johnston LE. Computerized prediction: The accuracy of a contemporary longrange forecast. Am J Orthod 1975; 67: 243-52.
Baumrind S, Miller DM, Molthen R. The reliability of head film measuments. 3. Tracing and
superimposition. Am J Orthood 1976; 70:617-44.
Popovich F, Thompson GW. Craniofacial templates for orthodontic case analysis. Am J Orthod
1977;71:406-20.
McWilliam J, Welander U. the effect of image quality on the identification of cephalometric
landmarks. Am J Orthod 1978;48(1):49-56.
Hurst RVV, Schwaninger B, Shaye R. Interobserver reliability in xeroradiographic
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