Cephalometrics

CEPHALOMETRICS
www.indiandentalacademy.com

CONTENTS
• HISTORY
• TECHNICAL ASPECTS
• TRACING TECHNIQUE
• CEPHALOMETRIC LANDMARKS
• CEPHALOMETRIC ANALYSIS
• APPLICATION OF CEPHALOMETRICS

• ERRORS OF CEPHALOMETRIC
MEASUREMENTS
• METHODS OF CONTROLLING ERRORS
• STANDARDIZATION OF IMAGE
GEOMETRY
• LIMITATIONS OF CEPHALOMETRICS
• DIGITAL CEPHALOMETRY
• CONCLUSION

HISTORY
History prior to the advent of radiography begins
with the attempts of the scientists to classify the
human physiques.
Basically it stems from the history of Anthropometry.
Human forms have been measured for many reasons
1.To aid self portrayal in
- sculpture
- drawing
- painting
2. To test the relation of physique to health,
temperament and behavioral traits.
Radiographic cephalometry- Alexander Jacobson

Vitruvivous pollio www.indiandentalacademy.com

History of
Cephalometric
Radiography
• In 1895, Prof. Wilhelm Conrad Roentgen made
a remarkable contribution to science with the
discovery of x-rays.
• On December 28, 1895 he submitted a paper “On A
New Kind of Rays, A Preliminary
Communication” to the Wurzburg Physical Medical
Society.

• Prof. Wilhem Koening & Dr. Otto Walkhoff
simultaneously made the first dental radiograph in
1896.
• Van Loon;
- First to introduce Cephalometrics to orthodontics.
- He applied anthropometric procedures in analyzing
facial growth by making plaster casts of face in to
which he inserted oriented casts of the dentition.

• Hellman in 1920s used cephalometric techniques
and described their value.
• The first x- ray pictures of skull in the standard lateral
view were taken by A.J.Pacini & Carrera in 1922.
• Pacini received a research award from the American
Roentgen Ray Society for a thesis entitled
“Roentgen Ray Anthropometry of the Skull”.

• Pacini;
Introduced a teleroentgenographic
technique for standardized lateral head radiography
which proved to be of tremendous use in
cephalometry, as well as in measuring growth and
dev of face.
• Atkinson in 1922 advocated the use of
roentgenograms in locating the ‘key ridge’ and the
soft tissue relations to the face and the jaws.

• In 1923 Mc Cowen used profile roentgenograms for
orthodontic purposes to visualize the relationship
between the hard and soft tissues and to note
changes in profile which occur during treatment.
• In 1931 cephalometric radiography came to full
function when B. Holly Broadbent in USA
published methods to obtain standardized head
radiographs in the Angle Orthodontist (A new X ray
tech & its application to orthodontia).

• H. Hofrath simultaneously published the same in
Fortschritte der Orthodontie in Germany.
• The interesting fact is that Broadbent was an
Orthodontist, whereas Hofrath was a
Prosthodontist.
• This development enabled orthodontists to capture
the field of cephalometry from the anatomists and
anthropologists.

Broadbent’s
contribution
1. Broadbent’s interest in craniofacial growth began
with his orthodontic education under E.H. Angle in
1920.
2. He continued to pursue that interest along with his
orthodontic practice, working with a leading
anatomist J.Wingate Todd
3. During 1920’s he refined the craniostat in to
craniometer.
4. That proved to be the first step in the evolution of
craniostat in to a radiographic cephalostat.

• The diagnosing dental deformities by means of planes
& angles was first proposed in 1922 by Paul Simon
in his book, “Fundamental Principles of a
Systematic Diagnosis of Dental Anomalies”.
• Although his “Law of the Canines” was later
disproved by Broadbent, his theories stimulated
Broadbent to apply the principles of craniometry to
living subjects.

• Hofrath’s technique differed from
Broadbent’s in that the path of the central
ray was not fixed in relation to the head.
• In 1937, using serial records of twins;
Broadbent showed how growth – or its lack –
was the greatest limiting factor in clinical
success.
• In 1943 he stipulated that eruption of the
third molars had no ill effect on the denture,
particularly the lower incisors.

• Brodie, in a landmark study, corroborated
Broadbent’s contention that the growth pattern of the
normal child’s face develops in an orderly downward
and forward fashion and that the pattern, once
attained at an early age, did not change.

Thompson and Brodie in a report on the rest
position of the mandible, concluded that:
• The morphogenetic pattern of the head was
established at a very early age and did not
change.
• The presence or absence of teeth has little bearing
on the form or the rest position of the mandible.
• Vertical facial proportions are constant throughout
life.

• Margolis (1943) wrote on the relationship between
the inclination of the lower incisor and the incisor-
mandibular plane angle.
• In 1947 Margolis contributed his maxillo-facial triangle.

THE TECHNICAL
ASPECTS

The basic components of the equipment for
producing the lateral cephalogram are:
1. An X-ray apparatus
2. An image receptor system
3. A cephalostat
Oral Radiology, Principles and interpretation- White and Pharoah (5th edition)

THE X- RAY APPARATUS
The three basic elements that generate that
X-ray are:
A. Cathode
B. Anode
C. The electrical power supply.

CATHODE
• Tungsten filament
surrounded by a
molybednum focusing cup.
• Connected to a low voltage &
high voltage circuit.
• A step down transformer
supplies the low voltage
circuit with 10V and a high
current to heat the filament
un till the electrons are
emitted.

STEP UP TRANSFORMERSTEP UP TRANSFORMER
• Supplies the high voltage
circuit with 65-90kV.
• Differential potential
accelerates the electrons.
• The electron beam is
directed by the focusing
cup to strike a small target
in the anode called focal
spot.

ANODE
• Small tungsten block embedded in the copper stem, which
stops the accelerated electrons whose kinetic energy causes
the production of photons.
• Less then 1% is converted to photons, rest is converted to
heat.
• Although tungsten is a high molecular substance, its thermal
resistance is unable to withstand the heat.

THE IMAGE RECEPTOR
SYSTEM
It records the final product of X-Rays after they
pass through the subject. The extraoral projection
like the lateral cephalometric technique, requires a
complex image receptor system that consists of :
1. Extraoral film
2. Intensifying screen
3. A cassette
4. A grid & a soft tissue shield

THE CEPHALOSTAT
Ear rod
forehead clamp
1.Ear rod
2.Forehead clamp
3.Infra orbital pointer
4.Cassette holder
Cassette
holder

X-Ray Source position
• It is positioned 5 feet(152.4cm) from the
subject’s midsagittal plane.
Film position
To minimize variations in magnification from patient to
patient& to obtain consistent measurements on the
patient over time, a distance of 15cm is often used.

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
152.4 cms

PATIENT
POSITIONING;
• It is based on the same principles that described by
the Broadbent.
• The patients head is fixed by the two ear rods.
• The head which is centered in the cephalostat, is
oriented with the Frankfurt plane parallel to the
floor & the midsagittal plane vertical & parallel to
the cassette.
Ear rod
LATERAL CEPHALOGRAM

• The standardized Frankfurt plane is achieved by
placing the infraorbital pointer at the patients orbit
and then adjusting the head vertically until the
infraorbital pointer & the two ear rods are at the same
levels.
• The upper part of the face is supported by the
forehead clamp, positioned at the nasion.
Ear rod
forehead clamp
cassette

• Identical to that of lateral ceph except that the Patient
is facing the film.
• Patient mid saggital plane is perpendicular to the film
plane.
• FH plane is horizontal.
• Canthomeatal line directed upward by 100
.
PATIENT
POSITIONING;
PA
CEPHALOMETRIC
RADIOGRAPH

Shortcomings of
the Frankfurt
horizontal plane
• Some individuals show a variation of their FH plane
to the true horizontal to an extent of 10°.
• The landmarks to locate the FH plane on a
cephalogram, orbitale & porion, are difficult to
locate accurately on the radiographs.
Am J Phys. Anthropol. 16: 1956

• An alternative to overcome this was to use a
functionally derived NHP.According to Morrees &
Kean.
• It was obtained by the patient standing up & looking
directly into the reflection of his/her eyes in a mirror
directly ahead in the middle of the cephalostat.
• To record the NHP,the ear rods are not used for
locking the patient head into a fixed position but
serve to place the midsagittal plane at a fixed
distance from the film plane.
Am J Phys. Anthropol. 16: 1956

TRACING TECHNIQUE

Tracing supplies
and equipments
• A lateral cephalogram
• Acetate matte tracing paper(.003 inches thick,
8×10 inches)
• A sharp 3H drawing pencil or a very fine
tipped pen
• Masking tape
• A few sheets of cardboard (preferably black)
and a hollow cardboard tube.

• A protractor and tooth symbol tracing
template for drawing the teeth. Also templates
for tracing the outlines of ear rods.
• Dental casts trimmed to maximum
intercuspation of the teeth in occlusion.
• Viewbox (variable rheostat desirable but not
essential).
• Pencil sharpener and a eraser.

Tracing of a
Cephalogram
• Thorough familiarity with the gross anatomy is
required before the tracing.
• By convention the bilateral structures (eg, the
rami and inferior borders of the mandible) are
first traced independently. An average is then
drawn by visual approximation, which is
represented by a broken line.

General considerations
for the tracing
• Start by placing the cephalogram on the viewbox
with the patient’s image facing towards the right.
• Tape the four corners of the radiograph to the
viewbox.
• Draw three crosses on the radiographs, two
within the cranium and one over the area of the
cervical vertebrae (registration crosses).

• Place the matte acetate film over the radiograph and
tape it securely.
• After firmly affixing the acetate film, trace the three
registration crosses.
• Print the pt name, record number, age in years and
months, the date on which the cephalogram was
taken and your name on the bottom left corner of the
acetate film.
• Begin tracing using smooth continuous pressure.

Stepwise tracing
technique
1. Tracing the soft tissue profile, external cranium
and the vertebrae,
2. Tracing the cranial base, internal border of the
cranium, frontal sinus and the ear rods,
3. Maxilla and related structures including the
nasal bone and pterygomaxillary fissure,
4. The mandible.

CEPHALOMETRIC
LANDMARKS

A landmark is a point which serves as a
guide for measurement or construction of
planes. They are divided into two types:
1. Anatomic: These represent actual anatomic
structure of the skull.
2. Constructed: These have been constructed
or obtained secondarily from anatomic
structures in the cephalogram.

Requisites for a
landmark
• Landmark should be easily seen on the
roentegenogram, be uniform in outline, and
easily reproducible.
• Lines and planes should have significant
relationship to the growth vectors of specific
areas.
• Landmark should permit valid quantitative
measurement of lines and angles.

• Measurement should have significant relation to
the information sought.
• Measurements should be amenable to statistical
analysis but should preferably not require
extensive specialized training in statistical
methods.
• Following is the list of most commonly used
Cephalometric landmarks.

LATERAL CEPHALOGRAM

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.
Procedure;
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

3mm

Cephalometric
planes
1. Are derived from at least 2 or 3 landmarks
2. Are used for;
- measurements,
- separation of anatomic divisions,
- definition of anatomic structures of relating parts
of the face to one another.

The various cephalometric planes used
are:
1. Horizontal planes
2. Vertical planes

Sella-
Nasion
plane:
Frankfurt
Horizontal
plane: (The
name is given in the
conference of
anthropology,held at
Frankfurt in1985)

Basion-
Nasion
plane
Palatal plane
Occlusal
plane

Mandibular
plane:
1.Salzmann took lower
border of the mand.
2. Go – Me
- Mc Namara
- Rakosi
- COGS
3. Go – Gn
- Steiners’s

Vertical
planes;
• Facial plane
• Ramal plane
• Y- Axis
• NA
• NB

CEPHALOMETRIC
ANALYSIS

Principle of
Cephalometric analysis
• The goal is to compare the patient with a
normal reference group, so that
differences between the patient’s actual
dentofacial relationships and those
expected for his/her racial or ethnic
groups are revealed.
• First popularized after world war-II in the
form of Down’s analysis.

• The standards developed for the Down’s
analysis are still useful but have been
largely replaced by newer standards,
based on less rigidly selected groups.

Two basic ways to
approach this goals
are:
• Use of selected linear and angular
measurements to establish the
appropriate comparisons.
eg; Down’s analysis.
• Template method: Express the
normative data graphically and to compare
the patient’s dentofacial form directly.

MEASUREMENT ANALYSIS
HARD TISSUE
ANALYSIS
• DOWN’S
• TWEED’S
• WITS APPRAISAL
• STEINER’S
• Mc NAMARA’S
• RAKOSI’S
• SCHWARZ
• COGS
SOFT
TISSUE
ANALYSIS
• HOLDAWAY’S
• ARNETT

- FH plane is used as the reference plane.
- It was based on the study of 25 white
subjects who had good occlusion and
proportional facial skeleton.
- This analysis indicates whether the
dysplasia is in the facial skeleton or in
the dentition or both.
DOWN’S ANALYSIS

TWEED’S ANALYSIS
Tweed used three planes to establish a
diagnostic triangle, the three planes used
in this analysis are:
1. Frankfurt horizontal plane
2. Mandibular plane
3. Long axis of lower incisor

TWEED’S
TRIANGLE

The values of the angles according to
Tweed’s finding are as follows:
1. FMA = 25°
2. FMIA = 65°
3. IMPA = 90°

STEINER’S ANALYSIS
Developed by Cecil.C.Steiner in the 1950’s
can be considered the first of the modern
cephalometric analysis for two reasons:
1. It displayed measurements in a way that
emphasized not just the individual
measurements but their interrelationship into a
pattern.
2. Specific guide for use of cephalometric
measurements in treatment planning.
AJO DO-1959

Steiner analysis
• Skeletal analysis
• Dental analysis
• Soft tissue analysis
AJO DO-1959

SNA: 820
SKELETAL
AJO DO-1959

SNB: 800
SKELETAL
AJO DO-1959

ANB: 20
SKELETAL
AJO DO-1959

OP-SN: 140
SKELETAL
AJO DO-1959

MP-SN: 320
SKELETAL
AJO DO-1959

UI-NA= 220
UI-NA= 4mm
DENTAL
NA
AJO DO-1959

LI-NB = 250
LI-NB = 4mm
DENTAL
NB
AJO DO-1959

INTERINCISA
L
ANGLE: 1300
DENTAL
AJO DO-1959

SOFT TISSUE
ANALYSIS
STEINER’S
S-LINE
AJO DO-1959

The mean values for Steiner’s analysis
are as follows:
SNA 82°
SNB 80°
ANB 2°
SND 76°
Upper incisor to NA 22°
Upper incisor to NA 4mm
Lower incisor to NB 25°
Lower incisor to NB 4mm
interincisal angle 130°
MP to SN 32°

McNAMARA ANALYSIS
Divided craniofacial skeletal complex into
5 major sections;
1. Maxilla to cranial base.
2. Maxilla to mandible.
3. Mandible to cranial base.
4. Dentition.
5. Airway.

NASOLABIAL
ANGLE: 1020
MAX TO CRANIAL BASESOFT TISSUE
EVALUATION

Pt A-N
Perpendicular:
1.mixed
dentition= 0mm
2.adult= 1mm
MAX TO CRANIAL BASEHARD TISSUE
EVALUATION

1. EFF MAX
LENGTH
MAX TO MANDIBLE
91
117
ANTEROPOSTERIOR
2.EFF MAND
LENGTH

Ans-Me
VERTICAL MAX TO MANDIBLE

Mand plane
angle
MP-FH: 220
SKELETAL
AJO DO-1959

Facial axis
angle= 900
SKELETAL
AJO DO-1959
900
- obtained

Pog-N Perpen
1. mixed dent
(6-8mm)
2.female=(-4-
0)
3.males =(+/-
2)
MANDIBLE TO CRANIAL BASE

MAX INCISOR
POSITION
DENTITION
4-6mm

MAND
INCISOR
POSITION
DENTITION
1-3mm

Upper pharynx=15-
20mm
Lower pharynx=11-
14mm
AIRWAY

WITS APPRAISAL
• Indicates antero-posterior disharmonies of the
jaws.
• It’s a linear measurement, not an analysis
• Was developed as a shortcoming to ANB.

Shortcomings
of ANB

AO-
BO
1. Sk Cl-I ; BO 1mm front of AO
2. Sk Cl-II; BO is behind AO
3. Sk Cl-III; BO is ahead of AO

DRAWBACKS;
1.Value varies with occ plane.
2.Value varies with dist betw points A and B
3.OP is not the actual plane and the left and
the right side do not always coinside in a
lateral ceph

RAKOSI JARABAK’S
ANALYSIS
1. Cephalometric radiography; Thomas Rakosi.

Saddle Angle
1230
+/-5

ARTICULAR ANGLE
1430
+/- 6

GONIAL ANGLE
Gonial
angle
=1280
+/-7
U=52-55
l=72-75

SUM OF POST ANGLES
396+/-60

MAND PLANE ANGLE
MP-SN=320

ANGLE OF INCLINATION
850

Pn-OP
750

Pn-MP
650

BASAL PLANE ANGLE
250

Ant-Post face Ht
62-65%

Inter-Incisal
1350

UI-SN
1020
+/-2

UI-PP
700
+/-5

LI-MP
900
+/-3

CEPHALOMETRICS FOR
ORTHOGNATHIC SURGERY
1. Cephalometric analysis specially
designed for the patient who requires
maxillofacial surgery.
2. Landmarks and measurements were
made which could be altered by
common surgical process.
J Oral Surgery:vol-36, April 1978

3.The comprehensive appraisal includes all of the
facial bones and a cranial base reference.
4. Rectilinear measurements can be readily
transferred to a study cast for mock surgery.
5. Critical facial skeletal components are examined.
6. Standards and static's are available for variations
in age and sex.
7. Systematised approach to measurements that can
be computerised.
8. COGS appraisal describes dental, skeletal and
soft tissue variations.
J Oral Surgery:vol-36, April 1978

1.Ar-Ptm
2.Ptm-N
J Oral Surgery:vol-36,April 1978
CRANIAL BASE
Ar-
Ptm
Ar-N
Ptm-
N
HP

1.N-A-Pg(ANGLE)
2.N-A (ll-HP)
3.N-B (ll-HP)
4.N-Pg(ll-HP)
HORIZONTAL(SKELETAL)
HP

1.N-ANS(PER-HP)
2.ANS-Gn(PER-HP)
3.PNS-N(PER-HP)
4.MP-HP(ANGLE)
5.UI-NF(PER-NF)
6.U6-NF(PER-NF)
7.LI-NF(PER-NF)
8.L6-NF(PER-NF)
VERTICAL(SKELETAL,DENTAL)
HP
N-ANS
ANS-Gn
PNS-N

1.N-ANS(PER-HP)
2.ANS-Gn(PER-HP)
3.PNS-N(PER-HP)
4.MP-HP(ANGLE)
5.UI-NF(PER-NF)
6.U6-NF(PER-NF)
7.LI-NF(PER-NF)
8.L6-NF(PER-NF)
VERTICAL(SKELETAL,DENTAL)
HP

1.PNS-ANS(II-HP)
2.Ar-Go (LINEAR)
3.Go-Pg (LINEAR)
4.B-Pg (II-MP)
5.Ar-Go-Gn(ANGLE)
MAX & MAND
HP

1.PNS-ANS(II-
HP)
2.Ar-Go
(LINEAR)
3.Go-Pg
(LINEAR)
4.B-Pg (II-MP)
5.Ar-Go-
Gn(ANGLE)
HP
MAX & MAND

1.U OP-
HP(ANGLE)
2.L OP-
HP(ANGLE)
3.A-B (II-
OP)
4.UI-NF(ANGLE)
5.LI-MP(ANGLE)
DENTAL
HP

1.U OP-
HP(ANGLE)
2.L OP-
HP(ANGLE)
3.A-B (II-
OP)
4.UI-NF(ANGLE)
5.LI-MP(ANGLE)
HP
DENTAL

THE HOLDAWAY SOFT-
TISSUE ANALYSIS
• The analysis outlines the parameters of
soft tissue balance.
• Consists of 11 measurements.

Facial angle
(900
)

Upper lip
curvature;2.5
mm

Skeletal
convexity at
point A;+/-
2mm

H-angle; 7-150

Nose tip to
H-line; 12mm
max

Upper sulcus
depth;5mm
Lower sulcus
depth;15mm
Lower lip to H-
line; 5mm

Upper lip
thickness; 15mm
Upper lip stain;
within 1mm
Soft tissue chin
thickness; 10-
12mm

TEMPLATE ANALYSIS
• In the early years of cephalometric analysis, it
was recognized that representing the norm in
graphical form might make it easier to recognize
a pattern of relationship.
• In recent years, direct comparisons of patients
with templates derived from the various growth
studies has become a reliable method of
analysis.

- One of the objectives of any analytic approach is
to reduce the practically infinite set of possible
cephalometric measurement to a manageably
small group that can be compared to the norms
and thereby provide useful information.
- From the beginning it was recognized that the
measurements for comparison with the norms
should have several characteristics.

The following were specifically desired:
1. The measurements should be useful clinically
in differentiating patients with skeletal and
dental characteristics of malocclusion.
2. The measurement should not be affected by
the size of patient:.
3. The measurement should be affected
minimally by the age of the patient.

What is a template?
Any individual cephalometric tracing can be
represented as a series of coordinate points
(x,y) on an grid. Similarly the cephalometric data
from any group also could be represented
graphically by calculating the average
coordinates of each landmark point, and then
connecting the points. The resultant average or
composite tracing often is referred to as a
“template”.

Male and Female diagnostic templates

At present two forms of
the templates are
currently available:
• Schematic template (Michigan,
Burlington): These show the changing
position of selected landmarks with age on
a single template.
• Anatomically complete
template (Broadbent-Bolton, Alabama):
These are a different ones for each age.

Selecting of a template
for analysis
The first step in template analysis is to
pick the correct template from the set of
age different ones that represent the
reference data. Two things that have to be
kept in mind are:
• The patient’s physical size
• Developmental age.

The best thing to do is to select the
reference template considering the length
of the anterior cranial base, which
should be same for the patient and the
template.
After this we move forward or
backwards in the template age if the
patient is developmentally quite advanced
or retarded.

Doing analysis using a
template
It is based on a series of
superimpositions of the template over a
tracing of the patient being analyzed. The
sequence of superimpositions follows:
1. Cranial base superimpositions:
- This allows the relationship of the maxilla
and mandible to the cranium to be
calculated.

- Superimposition being done on SN-plane,
registering the patient’s tracing at nasion rather
than sella if there is a difference in the anterior
cranial base length.
- With the cranial base registered, the
anteroposterior and vertical position of the
maxilla and mandible can be observed.
- ANS, ptA for the anterior maxilla, PNS for the
posterior maxilla.
- PtB, Pog and Gn for the anterior mandible and
Go for the posterior mandible are looked for.
Eg; 11yr old pat with mand showing age of 6yrs.

2. Regional superimposition:
- The (second) superimposition is on the maxilla
to evaluate the relationship of the maxillary
dentition to the maxilla. Template makes the
vertical evaluation of the teeth possible which
is not possible with the measurement
approach.
- The (third) superimposition is on the mandible
same as that of maxilla

Advantages of the
template analysis
• It allows the easy use of the age related
samples,
• It quickly provides an overall appraisal of
the way in which the patient’s dentofacial
structures are related unlike the
measurement approach in which the focus
sometimes shifts to acquiring the numbers
themselves.

APPLICATIONS OF
CEPHALOMETRICS

Application of
cephalometrics
• For gross inspection
• To describe morphology and growth
• To diagnose anomalies
• To forecast future relationships
• To plan treatment
• To evaluate treatment results

ERRORS OF CEPHALOMETRIC
MEASUREMENTS

ERRORS OF CEPHALOMETRIC
MEASUREMENTS
These are grossly divided into three
heads :
1. Radiographic projection errors
2. Errors within the measuring
system
3. Errors in landmark identification.

A.RADIOGRAPHIC PROJECTION
ERRORS;
Occurs during the recording procedure, the
object as imaged on a conventional
radiographic film is subject to magnification
and distortion.

1.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

EFFECT OF FOCUS FILM DISTANCE ON
RADIOGRAPHIC MAGNIFICATION

EFFECT ON OBJECT FILM DISTANCE ON
RADIOGRAPHIC MAGNIFICATION AND SHARPNESS

2.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.

3. DIRECTIONS OF POSSIBLE
MISALIGNMENTS OF THE HEAD
Z-Vertical axis
X-Transverse axis
Y-PA axis

a.Furthermore landmarks and planes not located in the
midsagittal plane are usually bilateral giving a dual
image on the radiograph.
b.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
4.BILATERAL
STRUCTURES

- 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.

B.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.
- An accuracy of .1mm is desirable without any distortion over
the surface of the digitizer.www.indiandentalacademy.com

Erickson 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.

C.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.

1.THE QUALITY OF THE RADIOGRAPHIC
IMAGE
a. Expressed in terms of sharpness/blur and contrast and
noise.
b. Sharpness is related to blur and contrast
c. Blur is the distance of optical density change between
the boundaries of a structure and its surroundings.
3 types of unsharpness
1. Geometric unsharpness
2. Motion unsharpness
3. 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
Eg; Combinations of fast films and rare earth intensifying
screen have reduced the exposure required, but produces
images with poorer definition.

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 movements,
- Blur from scattered radiation can be reduced by using a
grid at the image receptor end.

2.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 quitewww.indiandentalacademy.com

•The radiographic complexity of the region also lays an
important role making some landmarks more difficult to
identify.
The most reliably identified landmarks are; (According to
Miethke)
1.Incision superior incisal and
2.incision inferior incisal.
Landmarks difficult to identify are;
1.Anatomical porion and
2.Landmarks on the condyle.
3.The cusps of the posterior teeth or the lower incisor apex.

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:
1. The absolute magnitude of the
error in landmark location.
2. The relative magnitude or the
linear distance between the
landmarks considered for that
angular or linear
measurement.
3. 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.

3. THE OPERATOR AND REGISTRATION
PROCEDURE
The operator’s alertness , 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.www.indiandentalacademy.com

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.

METHODS OF CONTROLLING
ERRORS
A.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.2. Every effort must be made to
obtain films of high quality as
described in the standard texts.
3. Use of an aluminum wedge to
improve the definition of the soft
tissues and anterior bony
structures

4. Fast films and rare-earth intensifying screens reduce the exposure
greatly but give poorer definition than slower films and high-
definition screens.
5. Nevertheless, exposure reduction is of primary importance and
attention should be directed to obtaining the best screen/film
combination.
6. 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.

B. Landmark identification;
1. Tracings should be made on good-quality drafting paper which
does not obscure any details.
2. The most important contributions to improvement in landmark
identification are experience and calibration.
3. Before any major study is undertaken, particularly if more than
one measurer is involved, calibration is of the greatest importance.

C. 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

5. The procedure is much less tedious if radiographs are digitized
directly.
6. Baumrind and Millersuggested that tracings should be repeated
four times, which will halve the random error, but this is too
arduous for all but gives the most exacting investigations.
7. 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

STANDARDIZATION OF IMAGE
GEOMETRY
The early cephalometrists recognized the importance of standardized
head position if cephalograms were to be measures consistently.
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.

LIMITATIONS OF
RADIOGRAPHIC
CEPHALOMETRY
1. It gives two dimensional view of a three
dimensional object.
2. The reliability of cephalometrics is not always
accurate.
3. Standardization of analytical procedures are
difficult.
4. Growth pattern not taken into consideration
5. Mean values are based on different population
6. Form and functions not taken into consideration

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.
COMPUTERISED
CEPHALOMETRIC SYSTEMS:

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

Three possible approaches may be used to perform a cephalometric
analysis.
1. 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.
2. 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.
3. The third approach is completely automated. The cephalometric
radiograph is scanned into the computer. The computer
automatically locates landmarks and performs the
cephalometric analysis.
(Rudolph, Sinclair,AJO 1998)

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.

Automatic 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

Digitized cephalometry
– Dentofacial planner
– Quick ceph image
– Por dios
– Digigraph
– Rocky mountain orthodontics – JIFFY
orthodontic evaluation
– Prescription planner.

DIGITAL RADIOGRAPHY
• A digital image is a matrix of square pieces or picture elements (pixels), that
form a mosaic pattern from wherein original image can be reconstructed for
visual display.
Analog Image Digital Image
• 1) Conventional radiographic 1) a) Light sensitive
Image elements to record
the image.
b) Shades of gray to
display the Image
• 2) Silver halide grain 2) Light sensitive
elements
• 3) Randomly dispersed 3) Regular grid of rows
and Columns
• 4) Continuous Spectrum 4) Numeric and Discrete.

PIXELS AND VOXELS
• Pixel
2-D Digital Images – Composed of Picture elements.
• Voxel
3-D Digital Images – Composed of volume elements.
PRODUCTION OF DIGITAL IMAGE
Analog to Digital conversion (ADC).
• Sampling - Small range of voltage values grouped
together.
• Quantization - Every sampled signal is assigned a value.
Pixels are arranged in proper locations and given a
shade of gray corresponding to quantization

Advantages;
• It is very fast.
• It is only necessary to digitise the points
directly on the cephalogram and calculations
are done in seconds.
• It removes human error
• Facilitates use of double digitisation of
landmarks, thus increasing reliability.
• Easy storage and retrieval of values.
• Simultaneous demonstration of anatomical
structures of different thickness--i.e., bone and
soft tissues--and its lower exposure dose make
digital radiography the diagnostic procedure of
choice in cephalometrics.
• Filmless imaging.
• Patient education.
• Better treatment planning.

CONCLUSION
• Roentgenographic cephalometrics although a
major one-is one of many approaches and
considerations in the diagnosis and treatment of
an orthodontic patient.
• A roentgenographic cephalometric analysis is
essentially a technique to be used as a guide in
the diagnosis of a case of malocclusion.
• Although innumerable controversies exist in the
field of cephalometrics, it is still a very significant
& effective diagnostic tool.

A knowledge of what we have done and not done &,
particularly, what we have not done, moulds and
crystallizes our treatment philosophy & conditions it
for better service for those who come to us. Thus
making cephalometrics indispensable in clinical
practice.

1. Radiographic cephalometry- Alexander
Jacobson
2. Oral Radiology, Principles and interpretation-
White and Pharoah (5th edition)
3. Orthodontic cephalometry; Athanasios.
5. Moores and Kean; NHP; Am J Phys.
Anthropol. 16: 1956
6. Point A revisited – Jacobson- AJO 1980
7. Cecile Steiner-AO-1959, vol;29, no;1
8. Cecile Steiner- cephalometrics for you and
me;AJO DO-1953, vol 39.
9. Soft tissue cephalometric analysis: AJODO-
1999: 116.
10. Cephalometrics for orthognathic surgery:
REFERENCE

11. A frontal asymmetric analysis: JCO/July 1987
12. A cephalometric analysis based on NHP: JCO
1998; vol 1991, March.
13. Downs. W . F :analysis of dentofacial profile,
angle orthod. Vol 26; 1956
14. McNamara;’ a method of cephalometric
evaluation; AJODO. 86; 1984
15. Orthodontics in 3 millennia. Chapter 8;AJODO
2006; 129.

Cephalometrics

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