Role of cephalometry in orthdodontics /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
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INTRODUCTION
The discovery of X-rays led to the measurement of the head
from shadows of bony and soft tissue landmarks on the roentgenographic
image that came to be known as the Roentgenographic Cephalometry.
For many years since the 1930’s spawned by the classic work of
Broadbent and Hofrath in the United States and Germany respectively,
cephalometrics has enjoyed wide acceptance as an essential component
of the diagnostic phase for the more traditional forms of orthodontic
treatment. Innumerable research works and papers have been published
in this field.
In more recent times, the importance of sophisticated
cephalometric methods, often computerized, has become clearly
established as an indispensable diagnostic tool for the analysis and
correction of a wide range of craniofacial orthopedic problems.

DEFINITION
Origin: ‘Cephalo’ means head and ‘Metric’ is measurement.

In oral surgery and orthodontics:
1. “The scientific measurement of the bones of the cranium and
face, utilizing a fixed, reproducible position for lateral radiographic
exposure of skull and facial bones”.
2. “ A scientific study of the measurements of the head with
relation to specific reference points; used for evaluation of facial
growth and development, including soft tissue profile”.


HISTORY OF CEPHALOMETRICS

In

1780, Petrus Camper, probably the first to employ angles in
measuring the face, oriented the skull on a horizontal from the
middle of porus acusticus to a point below the nose. Craniostats
were designed to hold the skull in an oriented position to give
greater reliability to the measurements, and they were the
forerunners of the cephalostat or headholder. The dry skull
measurements, craniometry, was done from countless aspects. But
these static and nonvital studies did not interest the
orthodontists. With the application of these measurements to
living subjects, their use in orthodontics was deemed important.


At

the 1882 meeting of the International Congress of Anthropology
in Frankfort, Germany, Von Ihering’s line (drawn from the upper
margin of the external acoustic meatus to the lowest point of the
infraorbital margin) was accepted as a standard plane of orientation.
This line is the forerunner of the Frankfurt Horizontal plane, which is
the basis of the roentgenographic cephalometric orientation.
In

1895 Wilhelm Conrad Roentgen discovered X-rays. In the same
time period Milo Hellman adopted techniques of physical anthropology
to orthodontic research followed by which skull radiographs came into
use.
1921, A.J. Pacini, presented the paper “Roentgen Ray
Anthropometry of the Skull” which stated that the accuracy of
roentgen ray anthropometry far surpassed ordinary anthropometry.
He aligned the subjects head so that the mid-sagittal plane was
parallel the film. A constant target-film distance of 2½ feet was
employed and the central ray was directed one inch above and in front
of the EAM.
In


In

the 1920’s, B. Holly Broadbent of the USA worked with the anatomist
T. Wingate Todd, after his orthodontic training in the Angle school. His
previous experience with profile roentgenography helped Broadbent design
his roentgenographic craniostat. His success with this led him to the
development of the cephalostat or head holder. In Feb 1931, Broadbent
presented his paper under the title “A new X-ray technique and its
applications to orthdodontics”, describing roentgenographic cephalometry at
the mid winter meeting of the Chicago Dental Society. Further work
produced the roentgenographic cephalometer. It is a head positioning device
similar to a craniostat.
Further

more in 1931, Herbert Hofrath published in the German
literature an article entitiled “Importance of teleroentgenograms for the
diagnosis of Jaw Abnormalities”. A 2M target distance was used. The X-ray
tube was placed at one end of a long tube and at the other end was a device
carrying two pairs of crossed wires for the purpose of orienting the axis ray.
Hofrath’s method differed from that of Broadbent’s in that there was
littkle mention of a frontal view, the path of the central ray was not fixed in
relation to the head, there was no plane for superimposition and
considerable stress was laid on the recording of the soft tissue. His
procedures had less refinement and precision than Broadbent.

The

University of Illinois and the University of Colorado were a
few early centers for cephalometric research. After the invention
of cephalometric radiograph, Lucien de Costar of Belgium was the
first to publish an analysis based on the proportional relationships
of face.

Korkhaus

(Germany) developed a systematic diagnostic evaluation
of cephalometric films, which resembles our present analytical
tracing.

After

the advent of Cephalometrics in 1931 (Broadbent &
Hofrath), aspects of these standardized methods were propagated
into general clinical use during 1940-1950 [Brodie, 1941; Downs,
1948; Ricketts, 1950; Krogman & Sassouni, 1952; Wylie, 1952;
Steiner, 1953; Schwartz, 1961]. By 1960’s it had become a
routine component of treatment planning.

TECHNICAL ASPECTS
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 machines housing.

Image

receptor system:
An image receptor system records the final product of X-rays after
they pass through the subject. It consists of an extra oral film,
intensifying screens, cassette, grid, and a soft tissue shield.


Cephalostat:

The use of a cephalostat, also called a head-holder or
cephalometer, is based on the same principle as that described by
Broadbent. The patient’s head is fixed by the two ear rods. The head
which is centered in the cephalostat, is oriented with the Frankfort
plane parallel to the floor and the midsagittal plane vertical and
parallel to the cassette.


CHOICE OF A HORIZONTAL REFERENCE LINE
At the International Congress of Anatomists and Physical
Anthropologists held in Frankfort, Germany in 1882, the Frankfort
plane [extending from the upper rim of the external auditory meatus
(porion) to the inferior border of the orbital rim (orbitale) ], was
adopted as the best representation of the natural orientation of the
skull. For living patients, however, it is possible to use a “ true
horizontal” line, established physiologically rather than anatomically, as
the horizontal reference plane. This approach requires that the
cephalometric radiographs be taken in Natural Head Position.

FH Plane

The inclination of SN to the true horizontal plane (or FH plane if
THP is not known) should always be noted, and if the inclination of
SN differs significantly from 6 degrees, any measurement based on
SN should be corrected

NHP-Natural

Head Position:

Broca defined it in 1861 as “when a man is standing
and when his visual axis is horizontal, his head is in the
natural horizontal position”. The simplest procedure to
obtain head radiographs in the NHP is to instruct the
patient to sit upright and look straight ahead to a point at
eye level so that the head level is determined by the
internal physiological mechanism.
Other devices such as fluid level device,
inclinometer and the plumb line have been used to measure
the head posture.

ANALYSIS
Cephalometric analysis is used to assess, express
and predict the spatial relations of soft tissues,
craniofacial and dentofacial complexes at one point or over
time. The analysis is either objective or subjective.
Objective evaluation involves quantification of spatial
relationships by angular or linear measurements.
Subjective evaluation involves the visualization of changes
in spatial relationships of areas or anatomical landmarks
within the same face and relating to a common point or
plane over time.


CLASSIFICATION OF ANALYSES
ANALYSES
Methodological

Normative

Acc. To Area of
Analyses

1. Methodological:

Angular: Dimensional Analysis, Proportional Analysis, Analysis to
determine position.
Linear : Orthogonal Analysis, Dimensional Linear Analysis,
Proportional Linear Analysis.

2. Normative:

Mononormative Analyses: Arithmetical or Geometrical.
Multinormative Analyses.
Correlative Analyses.

3. Acc. to Area of Analysis:

Dentoskeletal Analyses: Facial Skeleton, Maxillary and
Mandibular Base.
Dentoalveolar Analyses: Position and Angulation of Upper &
Lower Incisors.
Soft Tissues Analyses.

APPLICATIONS IN ORTHODONTICS
Cephalometrics is used in three major areas:
Morphological

Analysis; by evaluating the sagittal and
vertical relations of dentition, facial skeleton and soft
tissue profile.
Growth Analysis; by taking two or more cephalograms at
different time intervals and comparing the changes.
Treatment

Analysis; by evaluating alterations during and
after therapy.

VARIOUS ANALYSES
STEINER

ANALYSIS: [AJO-1960] was developed and promoted
by Cecil Steiner in the 1950s. It can be considered the first of the
modern cephalometric analyses for two reasons: it displayed
measurements in a way that emphasized not just the individual
measurements but their interrelationship into a pattern, and it
offered specific guides for the use of cephalometric measurements in
treatment planning.


SASSOUNI

ANALYSIS: [AJO-1969] was the first cephalometric
method to emphasize vertical as well as horizontal relationships and
the interactions between vertical and horizontal proportions.
Sassouni pointed out that the horizontal anatomic planes-the
inclination of the anterior cranial base, Frankfort plane, Palatal plane,
Occlusal plane and Mandibular plane-tend to converge toward a single
point in a well-proportioned face. The inclination of these planes to
each other reflects the vertical proportionality of the face. If the
planes intersect relatively close to the face and diverge quickly as
they pass anteriorly, the facial proportions are long anteriorly and
short posteriorly which predisposes the individual to an openbite
malocclusion. Sassouni coined the term Skeletal Open Bite for this
anatomic relationship, the opposite of which is Skeletal Deep Bite.


RICKETTS

ANALYSIS: is a 11 factor summary analysis that
employs specific measurements to
(1) locate the chin in space,
(2) locate the maxilla trough the convexity of the face,
(3) locate the denture in the face, and
(4) evaluate the profile. The Ricketts approach emphasizes not only an
analysis of the patients initial condition, but the prediction of
future growth and treatment effects in a VTO.


HARVOLD

ANALYSIS, WITS ANALYSIS: both analyses were
aimed solely at describing the severity or degree of jaw disharmony.
Harvold [1974] using data derived from the Burlington growth study,
developed standards for the ‘unit length’ of the maxilla and mandible.
The difference between these provides an indication of the size
discrepancy between the jaws.

The Wits analysis [AJO-1975] was conceived primarily as a way to
overcome the limitations of ANB as an indicator of jaw discrepancy.
The Wits in contrast to the Harvold analysis, is influenced by the
teeth both horizontally and vertically.

McNAMARA

ANALYSIS: [AJO-1984] was originally published in
1983, and still represents the state of the art in cephalometric
measurement analysis reasonably well. It combines elements of
previous approaches (Ricketts and Harvold) with original
measurements to attempt a more precise definition of tooth and jaw
positions.
This analysis has two major strengths: (1) it relates the jaws via the
nasion perpendicular, in essence projecting the difference in
anteroposterior position of the jaws to an approximation of the true
vertical line, (2) the normative data are based on well defined Bolton
sample, which is also available in template form, meaning that the
McNamara measurements are highly compatible with preliminary
analysis by comparison with Bolton templates.


ENLOWS

COUNTERPART ANALYSIS: [AJO-1969] The basic
idea of interrelated dimensions leading to an ultimately balanced or
unbalanced facial pattern was expressed well by Enlow in the 1960s, in
his “counterpart analysis”. As Enlow et al pointed out, both the
dimensions and alignment of craniofacial components are important in
determining the overall facial balance.

TWEED ANALYSIS: [AO-1954] originally included only three
measurements. It is centered around two highly critical parameters:
the position of the mandibular incisors (over the basal bone), and the
angle FMA, which represents the (anterior) vertical dimension of the
maxilla and the mandible. www.indiandentalacademy.com

DOWNS’

ANALYSIS: [AO-1956] when observing facial profiles,
W B Downs noted that generally the position of the mandible could be
used in determining whether or not faces were balanced. Downs
reduced his observations to the following four basic facial types:

Retrognathic, Mesognathic, Prognathic and
True Prognathism (a pronounced protrusion of the lower face)


WYLIE

ANALYSIS: [AO-1947] The terms “orthognathism” and
“prognathism” were selected to categorize facial types, in preference
to “Class II faces” and “Class III faces”.
“Prognathism” and “orthognathism”, when used by others, may apply
either to the maxilla or the mandible or both. As it is used here it
applies mainly to the mandible in relation to the maxilla. A method is
presented whereby discrepancies in size of facial bones occurring in
the anteroposterior plane of space may be assessed quantitatively in
terms of millimeters. The method of assessment presented makes
possible a net score of anteroposterior dysplasia which is
approximately zero where such dysplasia is either non-existent or
compensated for by variation in different parts, and which is negative
in the type of face where relative mandibular insufficiency exists, and
positive in cases of mandibular prognathism.


BJORKS

ANALYSIS: [1954] the mechanism for the
control and modification of craniofacial growth had been
discussed earlier by Bjork, who noted after a survey of
cephalometric X-ray analyses that compensation was
dominant during adolescence, while dysplastic changes
appeared mainly at an early stage of development.


DI

PAOLO’S QUADRILATERAL ANALYSIS: [AJO-1983] The
quadrilateral analysis offers an individualized cephalometric diagnosis on
patients with or without skeletal dysplasias. It includes Skeletal
assessment, Dental assessment and Assessment of Facial Types
(normodivergent, hypodivergent and hyperdivergent). It is a reliable and
accurate method of assessing whether orthodontic treatment, surgical
treatment, or a combination of both is required to achieve a
satisfactory result.

RIEDEL ANALYSIS: [AO-1952] was established on the basis of a
study undertaken by Richard A Riedel to determine the constancy or
variation in the relation of maxilla to cranium and the mandible.

Other Analyses are:
SCHWARZ

ANALYSIS: [AJO-1961]
JARABAK ANALYSIS:[1972]
WORMS AND COWORKERS ANALYSIS: [AO-1976]
HASUND ANALYSIS: [1977]
FARKAS AN COWORKERS ANALYSIS: [1985]
COBEN CRANIOFACIAL AND DENTITION
ANALYSES: [1986]


SOFT TISSUE CEPHALOMETRIC ANALYSIS
A good mechanical relationship between maxillary and
mandibular dentures was formerly regarded as the sole aim of
orthodontic treatment. In the course of time, however, orthodontists
have become increasingly aware that facia esthetics must also be
considered in planning. According to Wuerpel, a face is beautiful and
shows harmonious featuresif the proportions of its individual
components are right, ie, no individual structure is over emphasized in
relation to the others - what he refers to as ‘balance’.
For soft tissue analysis, distinction is made between:
Profile Analysis.
Lip Analysis.
Tongue Analysis.


PROFILE ANALYSIS:
Further divided into Proportional Analysis and Angular Profile Analysis.
Proportional Analysis: were in the profile may be divided into three approximately
equal parts,
Frontal Third (tr-n),
Nasal Third (n-sn), and
Gnathic Third (sn-gn).
Angular Profile Analysis: were in Subtelny makes the distinction between the
convexity of,
the skeletal profile,
the soft tissue profile, and
the full soft tissue profile (including the
nose).
Skeletal Convexity is represented by N-A-Pog
mean=175°
Soft Tissue convexity is determined as n-sn-pog mean=161°
Full Soft Tissue Convexity is based on n-n-pog
mean=137°M/133°F


Profile

Analysis by A M Schwarz: were in three reference lines are
constructed for profile analysis:

to

1. The H line, corresponding to the FH plane,
2. The Pn line, and
3. The Po line (orbital perpendicular), a perpendicular from the orbital
the H line.

The Gnathic Profile Field (GPF) permits assessment of the profile.
Depending on the position of the subnasale relative to the nasion perpendicular
three types of faces are seen,
1. Average Face – sn on nasion perpendicular,
2. Retroface
– sn behind the nasion perpendicular, and
3. Anteface
– sn in front of the nasion perpendicular.


LIP

ANALYSIS:
Analysis of the lip plays a significant role in treatment planning.

Ricketts: uses the E line drawn from the tip of the nose to skin pogonion.
Steiners: uses the S line drawn from the centre of the S shaped curve
between the tip of the nose and sn, to the pog.

Holdaways Lip Analysis: this is a quantitative analysis to assess lip
configuration. Holdaway determines the angle between a tangent
to the
upper lip and NB line, called the H angle.
Holdaway defines the perfect profile as follows:
-ANB angle 2°, H angle 7-8°.
-Lower lip touching the soft tissue line, and with
-The relative proportions of nose and upper lip well balanced.


TONGUE ANALYSIS:
Contains two parameters
1) assessing tongue position, and
2) assessing tongue motility
Tongue Position: in relation to the

Root: a space is formed between the root of the tongue and soft palate
in cases of mouth breathing (nasal obstruction) & Cl II
malocclusion.
Dorsum: of the tongue is high in Cl II malocclusion and in deepbite cases.
In all others it is low.
Tip: is retracted in Cl III and in Cl II with nasal breathing and in
deepbite cases. In openbite, tip is forward.


Tongue Motility: the changes in the position of the tip relate closely to
the different types of malocclusion.
With Cl II the tip is back at rest position, and with Cl III the
tip lies further forward. It may be assumed that the changes in position
of the tip of the tongue relate to the tendency to mandibular
malformation.


ARNETT

& BERGMAN ANALYSIS:

The analysis is a radiographic instrument that was developed
directly from the philosophy expressed in Arnett and Bergman’s Facial
keys to orthodontic diagnosis and treatment planning [AJO April /
May 1993]. Many authors have suggested utilizing soft tissue
analysis as a reliable guide for occlusal treatment and attendant soft
tissue changes. Arnett and Bergman presented the Facial Keys to
Orthodontic Diagnosis and Treatment Planning as a three-dimensional
clinical blueprint for soft tissue analysis and treatment planning.
In preparation for the cephalometric radiograph, metallic
markers were placed on the right side of the face to mark key
midface structures. These included the orbital rim marker,
cheekbone marker, alar base marker, subpupil marker and neck-throat
marker. The True Vertical Line (TVL) was then established. The line
was placed through subnasale and was perpendicular to the natural
horizontal head position.

...........contd.

CLINICAL IMPLICATIONS:
Soft Tissue Cephalometric
Analysis (STCA) provides dental
and facial diagnosis. Data provided
by the STCA can then be used for
Cephalometric Treatment Planning
(CTP). The STCA can be used to
diagnose the patient in five
different but interrelated areas;
dentoskeletal factors, soft tissue
components, facial lengths, TVL
projections, and harmony of parts.


................contd.

CEPHALOMETRIC TREATMENT PLANNING (CTP):
Diagnosis generated by STCA is used to guide cephalometric
treatment planning. Seven steps are involved in CTP to optimize
occlusal and facial results:
1.
2.
3.
4.
5.
6.
7.

Proper angulation of lower incisor teeth,
Proper angulation of upper incisors,
Maxillary incisor positioning,
Autorotation of mandible to 3mm of overbite,
Mandible is moved anteriorly or posteriorly to correct the overjet
with the maxillary arch,
Maxillary occlusal plane is defined, and lastly
Chin projection and height assessment.


...........contd.

Cephalometric Treatment Planning:

There are a number of other soft tissue analysis such as Powell’s, Farka’s, Lehman’s,
Burstone’s, Wolford’s, Bolton’s, Spradley’s, Bowker and Meredith’s and Holdaway’s
soft tissue analysis. The Reed Holdaway’s analysis has 11 measurements including
facial angle, upperlip curvature, skeletal convexity, upper and lower depth,
thickness and strain, harmony line angle etc.

FUNCTIONAL ANALYSIS OF THE RADIOGRAPH
Cephalometric radiography will also demonstrate the
relationship between rest and occlusal positions. Relative to
its occlusal position, the mandible may be further back or
further forward than in rest position. If a radiograph is
taken in rest position and another in occlusion, mutual
relations between these two may be established. In every
movement of the mandible we can differentiate between a
rotatory and gliding component. The principle of
comparative assessment consists in the determination of
one angle for the rotational component and another for the
gliding component.


ASSESSING HORIZONTAL RELATIONS ORTHO/RETRO/PROGNATHIC:
Cephalometrics helps in finding out whether the
fault is in the maxilla or mandible in the cases of Cl II or
Cl III. Also in the maxilla whether the malocclusion is due
to fault in the basal bone or dento-alveolar or purely
dental proclination. The treatment for each differs, from
a bodily movement required in the basal bone fault, to just
an incisor tipping in case of pure dental proclination. For
assessing this the angles SNA, SNB, upper incisor
angulation and position relative to N-Pog line are
important.


ASSESSING VERTICAL RELATIONS:
If growth in the posterior face (condylar growth) is greater
than that in the anterior face (growth in facial sutures and alveolar
growth), it causes forward rotation; while growth of anterior face
greater than posterior face causes backward rotation. Equal growth
produces no rotation but only parallel displacement.
Mandibular rotation not only produces retro/prognathism but
also deep/open bite. Therefore by determining this rotation, it is
helpful in treatment planning. With forward rotation, treatment of Cl
III and deep bite are difficult. With backward rotation, treatment
of Cl II and openbite are difficult.
Maxillary rotation occurs in midface which is partly due to
growth and rest due to occlusal forces and gravity. Rotation also
develops during headgear therapy and specially developed activators.
Therapeutic parallel displacements of the maxilla enforced by
translation are less liable to relapse.
Measuring the centre of such rotation is possible by
superimposing cephalometric radiographs taken before and after
treatment.

AIMS OF INTERPRETATION OF THE
MEASUREMENTS
 To determine the skeletal structure and facial type.
 To establish relationship between max. and man. base and
determine type of growth.
 To assess dental relationships.
 To analyse the soft tissues regarding aetiology and prognosis.
 To establish location of malocclusion and in the facial skull and
determine, the extent to which it is skeletal /
dentoalveolar.
 Treatment planning, and also to determine how far, the
treatment can be causal and how far merely compensatory
(for skeletal abnormalities).


GROWTH PREDICTION
The site, direction, growth potential, growth timing and
growth pattern have to be determined. Generally
horizontal growth changes are easily predictable than
vertical changes.


Forecast Grid: L E Johnston has produced a diagram on
the assumption of regular annual changes and an average
direction of growth. He feels accurate prediction can be
made in 65% of the cases. In this forecast grid each
point was advanced one grid per year.



Rickett's short term prediction makes distinction between
vertical and horizontal growth. Rickett's Computer Analysis
considers individual growth curves for separate regions. The
computer diagnosis requires the patient to be of a certain age.
During growth noticeable increase in linear dimensions of N-Me,
S-Gn, Ar-Gn occurs. There is an average increase in SN line. This
is used for prediction of sagittal and vertical growth changes.
Growth rate of different regional growth centres is different.
Also age and function change the form of growth. In order to
determine the stability of the results and length of retention
period, growth following conclusion of treatment is determined .



Holdaway's Growth prediction: it is based on the average increase
in SN line. We can assess the different possibilities of treatment,
thus visualize certain treatment objectives. It has some 12 stages
of superimposition and was found that horizontal growth was
better predictable.


SUPERIMPOSITION
Serial superimposition of cephalograms reveals the
rate, amount and relative directions of the growth and
treatment changes of facial structures, including the
changes in maxillary mandibular relationships, and the
relative changes in the soft tissue integument. It however
does not reveal either the sites or mode of growth of
bone. 2D information was interpreted of a 3D process. It
demonstrates the sum total of apposition and resorption
at that particular time without detailed intervening
changes.


Maxillary

Superimposition:

A comparison of three methods for cephalometric evaluation of
growth and treatment change was made by Neilson [AJO 1989 May].
Previous cephalometric studies have indicated an apparent stability of
the growth patterns of both the maxilla and mandible. There is a
parallel descent of the maxilla, in relation to the anterior cranial base,
in which the nasal floor appeared to remain unchanged during growth.
The technique most commonly used for evaluating growth and
treatment changes has been to superimpose serial head films along
the palatal plane from ANS to PNS with the films registered at ANS.
Broadbent found that when superimposition was made on the palatal
plane at ANS, the anterior surface of the maxilla and point A moved
posteriorly. Brodie and Downs recommended the superimposition of
the nasal floors and films registered at the anterior surface of the
maxilla.

The superior and inferior surfaces of the hard palate have been
recommended for maxillary superimposition to eliminate possible
appositional growth at ANS. Moore suggested the superimposition
along the palatal plane but registered at the pterygomaxillary fissure.
Riedel coincided the infratemporal fossa and the posterior portion of
the hard palate. Luder made superimposition on the anterior contour of
the zygomatic process registered at the most inferior point of the
process at key ridge.
Studies of maxillary growth with metallic implants by Bjork and
Skieller have demonstrated that the maxilla undergoes extensive
differential remodeling- a resorptive lowering of the nasal floor,
greater anteriorly than posteriorly. It showed that the zygomatic
process of the maxilla does not undergo the same remodeling changes.
In fact the anterior surface remains unchanged during growth with the
exception of the most inferior part at key ridge and the most superior
part at the orbital floor. There is appositional growth at the orbital
foor.


On the basis of these findings, Bjork and Skieller
have suggested a “structural method” for evaluating
maxillary growth and treatment changes. The head films
are superimposed on the anterior surface of the
zygomatic processof the maxilla with the second head film
oriented so that the resorptive lowering of the nasal floor
is equal to the apposition at the orbital floor. In general
the results of the comparitive study between the
different methods of superimposition showed that the
displacement of the dental landmarks was greater with
the implant superimposition than with best fit.
Comparison between the implant and the structural
methods, showed no significant difference in the vertical
plane. In the horizontal plane, overall less displacement
was observed with the structural method.

Mandibular superimposition:
In the workshop on cephalometry conducted in 1960 superimposition
of radiographs along the lower border of the mandible was adopted.
Superimposition of the inferior border, however, proved difficult
because of the curving path of the radiographic outline; to overcome
this problem, Downs suggested a single straight line from the lowest
point on the external contour of the symphysis to the midpoint at the
gonian angle.
Bjork’s studies have shown, however, that the inferior border of the
mandible undergoes extensive differential remodeling during growth.
The anterosuperior border of the chin, inner cortical structure of the
inferior border of the symphysis, lower contour of the developing
molar tooth germ and mandibular canal could be used to analyze
mandibular growth. This was Bjork's structural method of
superimposition.
Ricketts developed a four-position analysis to study growth and
treatment changes in the craniofacial complex. Position four uses the
reference line, the corpus axis, which is used for analysis of
mandibular changes.



Cranial Base superimposition:

1) Superimposition on the best fit of anterior cranial base anatomy:
Based on de Coster's observation of a stable basocranial line
from inner contour of frontal bone to the anterior aspect of sella
turcica Bjork advocated superimposing the anterior wall of sella
turcica, the anterior contours of middle cranial fossa, the contours
of cribriform plate and fronto ethmoidal crests and cerebral
surfaces of the orbital roof and cortical layers of the frontal bone.
The cribriform plate stops growing in length antero posteriorly
after 2 yrs of age.


2) Superimposition on sella nasion:
It is found to be relatively stable. Steiner used SN plane with
registration at S to evaluate mandibular positions. And registration
at N to evaluate position of maxilla (SNA changes). Bjork used sella as
the registration point to assess changes in both jaws. It is especially
suitable during adoloscence because of constancy in relation SN and
the deepest median contour of the anterior cranial fossa. But SN
plane can't be used for facial contour estimation because of
displacement of Nasion with growth of fronto nasal suture. Stramrud
used sella ethmoidale (SE) because of variations of nasion SE and SN
plane vary little after 3 yrs of age. Rickett's used the FHplane.
3) Superimposition at registration point R with Bolton-Nasion planes
parallel:
This method was introducedby Broadbent. A perpendicular to
sella from
Bo- N plane is erected. The mid point of this line is registration point
R. Superimposition is done with registration at R keeping Bo- N plane
parallel over each film.

4) Superimposition over basion nasion plane:
Advocated by Ricketts. A point called pterygoid point is
selected at the lower rim of foramen rotundurn as the highest and
most posterior point of the pterygopalatine fossa. A line from Pt to
Gnathion constitutes the central axis.
Atr, the inter section of Ba- N and central axis is located at a point
CC which is used as a reference centre. The angle between Ba-N and
central axis indicates the position of the mandible relative to cranial
base. The direction of mandibular growth is evaluated by changes in
the direction of the central axis. Registration at nasion depicts
changes in position of maxilla through movement of Pt.

The best fit method of anterior cranial base is better than others
because it takes into consideration the detailed individual anatomy of
the cranial base, rather than simplifying this anatomy into lines and
points.


FINITE ELEMENT ANALYSIS
It was first used to analyse cephalograms by Moss et al and
Bookstein et al in 1985. It is an engineering principle that uses partial
differential equations to interpolate loading values for intermediate
points in irregular structures by dividing the structure into sets of
regular geometric shapes (usually into a triangle).
A finite element is a small block that is a part of the whole object
under consideration. For example if you consider mandible, as a whole it is
difficult to predict the growth pattern of the mandible. However should
the mandible be visualised as "broken into small regular geometric
shapes" like a triangle the problem of mandibular growth has now broken
into the problem of growth of the individual triangles. The exact growth
can now be reproduced by reassembling the individual blocks.
Recent advances in finite element allow irregular patterns for
objects that are even non-homogeneous to be assessed (earlier only
homogeneous materials were assessed by this method), and this allows
for accurate reproduction of mandibular growth.

DISTINGUISHING BETWEEN NATURAL GROWTH
FROM ORTHODONTIC CHANGES
A

Four-Step method to distinguish orthodontic changes from
natural growth: (ROBERT MURRAY RICKETTS) [JCO 1975]
Ricketts suggested a method of superimposition to accomplish this.
Method of Superpositioning:
The objective of the four position analysis is very simple- two skeletal
and two dental. First, it attempts to analyze the skeleton in terms of
the chin, and secondly the maxilla. This comes from Position One and
Position Two, respectively. Position Three is for the maxillary teeth.
Position Four is for the mandibular teeth.

Pitchfork

Analysis:

To evaluate growth and displacement of the maxilla and mandible and
to register the movements of the upper and lower molars and incisors,
Johnston developed his Pitchfork Analysis. Growth or displacement
of maxilla and mandible are measured relative to the cranial base (SE
registration). The changes in the upper and lower incisors are
measured relative to basal bone. The dental and skeletal
measurements were executed parallel to the mean functional occlusal
plane (MFOP) and each was given a sign appropriate to its impact on
molar or overjet correction.
Positive- if it improved the relationship (as with forward growth of
the mandible/distal movement of maxillary molars and incisors).
Negative- if it made them worse (eg. forward growth of the maxilla
or mesial movement of the maxillary dentition.)


Using the Bjork's method of superimposition the following were found:
Mandibular

symphyseal movement relative to maxilla,

The

displacement (as a result of growth, orthopedic changes, or
functional shift) of maxillary and mandibular basal bone
relative
to cranial base.
The

movement of the first molars (measured at the mesial contact
point and at a point midway between the apices) and central incisors
(at the incisal edge) relative to basal bone.


CEPHALOMETRICS IN TREATMENT PLANNING:
Effective treatment planning in depends on accurate diagnosis.
*In cases of malocclusion due to muscular dysfunction some times inhibition therapy is
suggested. Cephalometeric radiography makes its possible to judge whether after
elimination of the dysfunction the growth trend is likely-to be normal .
*Similarly the indication of activator therapy can be determined using
cephalometrics:
Three conditions are essential
1)SNB small -suggesting a small mandible
2)Growth pattern is horizontal
3)SNA normal - maxilla in normal position
*Cervical headgear therapy is indicated when SNA is large with anteinclination of
maxilla (large J angle.)
*Discrepancy calculation is made to determine the amount of space available and that
required. It is done models and radiographs. On radiographs, the distance from the
lower incisor to N-Pog line is determined. This is the sagittal discrepancy.(SD). Total
discrepancy (TD) is calculated from SD & DD (Dental Discrepancy which is
calculated from a model.
TD = SD + ½ DD
Treatment is planned so that the lower incisors are not more than 4mm anterior to the
N-Pog line.

*Planning Anchorage -three degrees of anchorage are
found.

Minimal Anchorage is needed when lower incisors are very
upright and behind N-Pog line.
Moderate Anchorage is needed when lower incisors after
treatment will be 2-4mm anterior to N-Pog line.
Maximum Anchorage is needed when lower incisors after
treatment will be 4mm anterior to N-Pog line.

P-A View
Frontal view is particularly important in cases of dentoalveolar & facial
asymmetry, crossbites and functional mandibular displacements.
There are different methods of analysis 1)Rickett ‘s- measures the nasal cavity width, maxillary, mandibular,
intermolar & intercuspid widths by connecting bilateral identical points and
measuring the distance between them. Symmetry is measured from the
mid-sagittal plane and relating the points pogonion and ANS to it.

2)Svanholt and Solow analysis- it measures the relationships between the
midlines of the jaws and dental arches. It measures the transverse
maxillary and mandibular positions, transverse jaw relationship, position of
upper and lower incisors and the compensation of upper and lower incisors.
It incorporates variables that will be zero in symmetrical subjects.
3)Grayson analysis- it uses multiple planes at selected depths to analyse facial
asymmetry.
4)Hewitt analysis- it is performed by dividing the craniofacial complex into
constructed triangles-triangulation of face
5)Chierici analysis- focuses on asymmetry of upper face.
6)Grummon 's analysis


COGS (CEPHALOMETRIES FOR ORTHOGNATHIC SURGERY)
It was developed by Burstone and Legan. Normally during orthodontic
treatment, the alveolar base is stable. But during orthognathic
surgery, the alveolar base also changes position. The COGS system
describes the horizontal and vertical position of facial bones by use
of a constant coordinate system.
1. The chosen landmarks and measurements can be altered by various
surgical procedures.
2. The comprehensive appraisal includes all of the facial bones and a
cranial base reference.
3. Rectilinear measurements can be readily transferred to a study
cast for mock surgery.
4. Critical facial skeletal components are examined.
5. Standards and static's are available for variations in age and sex.
6. Systematised approach to measurements that can be computerised.
7. COGS appraisal describes dental, skeletal and soft tissue
variations.


PHOTOCEPHALOMETRY
It is an attempt to obtain a more accurate and detailed information of the
soft tissues in head views by superimposing co-ordinated head films with
photographs. !t was developed for patients requiring orthognathic surgery.
The assumption behind this technique is that the photographic images can be
enlarged so that metal markers placed on the patient's skin are accurately
superimposed on the corresponding radio opaque images on the cephalogram.
The benefits are
~ A more detailed visualisation of the soft tissues in the frontal and lateral
views.
~ A more accurate analysis of soft and hard tissue relationships,
particularly of soft tissue thickness.
There are 2 errors inherent in this method
~ Magnification distortion errors in superimposition of photographic
cephalometric image.
~ Landmark identification
The photocephalometric apparatus is simply-.an adaptation of the standard
cephalometric set-up

DIGIGRAPH
A software product Digigraph enables clinicians to
perform non-invasive and non-radiographic cephalometric
analysis. This device uses sonic digitizing electronics to
record cephalometric landmarks by lightly touching the
sonic digitising probe to the patient and pressing the
probe button. The probe emits a sound and the
corresponding landmark is recorded sonically by the
microphone array. Using this cephalometric analysis and
monitoring of the patient's treatment progress is
performed as often as desired without radiation exposure.
Also data collection is non-invasive and efficient. It is
very useful in quatifying facial asymmetries.

DIGITAL COMPUTED RADIOGRAPHY SYSTEM (CR)
CR system operates with a punctiform X-ray beam which
stimulates a 2-D memory sensor, in the space of only
1/100 th of a second. This memorised data is converted
into electrical signal and then to a numerical 2-D image
consisting pixels. The image is then enhanced by
multiplying the value of each pixel and modifying the
relationships between values of the pixels making up a
certain area. This helps in varying the type of response
that can be obtained from the detector.
The imaging plate (analogous to a film), temporarily stores
the X-ray energy and then emits it when scanned with a
He-Ne laser. The blue light emitted is converted to an
electrical signal which is read by the image reader. These
signals are amplified and logarithmically converted before
being transmitted through an analogical-digital converter
which converts them to digital signals.

.........contd.

Advantages
>- Surpass conventional analogical radiology.
>- Reduces radiation exposure by 28.6% for PA view and 58.4% for
lateral Cephalometry.
>- Converts information to digital signals (digital imaging) and
enhanced information.
>- Provide more sensitive, higher definition images.
>- Optimisation of processing of images in terms of contrast,
gradation, sharpness and granulosity, enhancing the diagnostic
significance of the information.
>- Process images to enable establishment of databases.
>- Remote image transmission
>- Increased reliability and accuracy
>- Wide latitude.
>- Modulation of the images (enlarging/reducing/changing contrast) is
possible.


COMPUTERISED CEPHALOMETRICS
This has two components- data acquisition and data management.
X-ray beam attenuation is recorded directly and converted to a
digital image. Sonic technology is also used nowadays. A variety of
soft ware programmes are available ( like Por Dios, Dentofacial
planner, etc. ) which use one of the pre-programmed analysis. They
also allow superimposition, estimation of growth, simulation of
orthodontic tooth movement, etc.
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.

Thank you
For more details please visit


Role of cephalometry in orthdodontics /certified fixed orthodontic courses by Indian dental academy

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