Cephalometrics for orthodontics

CEPHALOMETRICS
www.indiandentalacademy.com

INTRODUCTION
• A Scientific approach to the scrutiny of human
craniofacial patterns was first initiated by
anthropologists and anatomists who recorded
the various dimensions of ancient dry skulls.
• The measurement of the dry skull from
osteological landmarks, called CRANIOMETRY,
was then applied to living subjects as a tool for
‘longitudinal growth studies’

• The measurement of the head of a living subject
from the bony landmarks located by palpation or
pressing through the supra-adjacent tissues is
called-CEPHALOMETRY.
• The discovery of X-rays by Roentgen in 1895
revolutionized the dental profession. A
radiographic head image could be measured in
two dimensions, thereby making possible the
accurate study of craniofacial growth and
development.

• Roentegenographic cephalometry- The
measurement of head from the shadows of bony
and soft tissue landmarks on the radiographic
image.(Krogman & Sassouni,1957).
• Von loon was probably the first to introduce
cephalometrics to orthodontics.For analyzing
facial growth he made plaster casts of face in
which he inserted oriented casts of dentition.

• Hellman used cephalometric techniques
and described their value beginning with
1920’s.
• A teleroentegenographic technique for
producing the lateral head film was
introduced by Paccini in 1922.He
identified the following landmarks on the
roentegenogram:
Gonion,Pogonion,Nasion and ANS.

• In 1922 Paul Simon gave the idea of
diagnosing dental deformities by means of
planes and the angles.
• In 1931 Broadbant in USA and Hofrath in
Germany simultaneously presented a
standardized cephalometrics technique
using the high powered X-ray machine
and a head holder called a Cephalostat or
the Cephalometer.

THE CEPHALOSTAT
• It is based on the same principles that described
by the Broadbent.
• The patients head is fixed by the two ear rods
that are inserted into the ear holes so that the
upper borders of the ear holes rest on the upper
border of the 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
• 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,to eliminate rotation
around the ear rods in the sagittal plane and for future
references in subsequent exposures.

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.

• 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.

X-Ray Source position
• It is positioned 5 feet(152.4cm) from the
subject’s midsagittal plane.
• The projection is taken when the teeth are
in centric occlusion &the lips in the repose,
unless other specifications have been
recommended ( e.g. with the mouth open
or with a specific interocclusal registration
used as orientation.

Film position
• Magnification factors are affected by the
distance from the film cassette to the midsagittal
plane of the patient.
• 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.
• However, to place the film cassette as close to
the patient head as possible is also in practice.

Development of Cephalometric
analysis
• Cephalometric analysis is carried out not
on the radiograph itself, but on a tracing or
digital model that emphasizes the
relationship of selected points.
• Tracing or the model is used to reduce the
amount of information to a manageable
level.

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.

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.

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.

• Place the matte acetate film over the
radiographand 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. www.indiandentalacademy.com

Stepwise tracing technique
• Tracing the soft tissue profile, external
cranium and the vertebrae,
• Tracing the cranial base, internal border of
the cranium, frontal sinus and the ear
rods,
• Maxilla and related structures including
the nasal bone and pterygomaxillary
fissure,
• 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 vectors of growth of
specific areas.
• Landmark should permit valid quantitative
measurement of lines and angles.

• Measure points and the 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 cephalograms
HARD TISSUE
LANDMARKS
• A-
point(pt.A,subspinale)
:The most posterior
midline point in the
concavity between
the ANS and the
Prosthion

• Anterior nasal
spine(ANS):The
anteriortip of the sharp
bony process of the
maxilla at the lower
margin of the anterior
nasal opening.
• Articulare(Ar):A point at
the junction of the
posterior border of the
ramus and the inferior
border of the posterior
cranial base(occipital
bone).

• B-
point(Pt.B,Supramentale
): The most posterior
midline point in the
concavity of the
mandible between
infradentale and
Pogonion
• Basion – The most
anterior inferior point on
the anterior margin of
Foramen magnum.

• Bolton point(Bo): The
intersection of the outline
of the occipital condyle
and the Foramen
Magnum at the highest
point on the notch
posterior to the occipital
condyle.
• Condylion(Co): The most
superior point on the
head of mandibular
condyle.

• Glabella(G): The most
prominent point of the
anterior contour of the
frontal bone.
• Gnathion(Gn): The
point taken between
the
anterior(Pogonion)
and inferior
point(Menton) on the
bony chin.

• Gonion(Go): A point
on the curvature of
angle of the mandible
located by bisecting
the angle formed by
lines tangent to the
posterior ramus and
inferior border of the
mandible.
• Incision
inferius(Ii):The incisal
tip of the most labialy
placed mandibular
incisor

• Incision superius(Is):The
incisal tip of the most
labialy placed maxillary
incisor.
• Infradentale(Id,Inferior
Prosthion): The most
superior anterior point on
mandibular alveolar
process between the
central incisors.
• Menton(Me): The most
inferior point of the
mandibular symphysis in
the midsagittal plane

• Nasion(Na):
Intersection of the
frontonasal and
internasal sutures in
the midsagittal plane.
• Orbitale(O): The
lowest point on the
inferior orbital margin.

• Pogonion(P,Pg,Pog): The
most anterior point on the
contour of bony chin in
the midsagittal plane.
• Porion(Po): The most
superior point of the
outline of the external
auditory meatus
(anatomic porion). When
the anatomic porion
cannot be readily
located,the superiormost
point of the image of the
ear rods (machine porion)
is used www.indiandentalacademy.com

• Posterior Nasal
Spine(PNS): The
most posterior point
on the bony hard
palate in the
midsagittal plane.
• Prosthion (Pr,
Superior Prosthion,
Supradentale): The
most inferior anterior
point on the maxillary
alveolar process
between the central
incisors.

• Pterygomaxillary Fissure
(Ptm): A bilateral inverted
teardrop shaped
radiolucency whose
anterior border
represents the posterior
surface of maxillary
tuberosities.
• Ptm landmark is taken at
the most inferior point of
the fissure, where the
anterior and the posterior
outlines of the inverted
teardrop merge with each
other

• Sella (S): The
geometric centre of
the pituitary fossa
(sella turcica),
determined by
inspection.

Cephalometric planes
Are derived from at least 2 or 3
landmarks and 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:

• Frankfurt Horizontal
plane: This plane is
drawn from Po to Or.
The name is given in
the conference of
anthropology held at
Frankfurt in1985.

• Sella-Nasion plane: It
represents the
anterior cranial base.
Can be accurately
located on the
radiographs. Cranial
base undergoes little
change after the age
of 6-7 years but the
N-point can drift either
forwards or vertically
giving rise to an error.

• Basion-Nasion plane:
This plane is used in
the Rickett’s analysis.
• Palatal plane: plane
passing through the
ANS and the PNS.
• Occlusion plane: It is
the plane passing
through the cusp tips
of the upper and
lower first molars and
a point bisecting the
overbite. www.indiandentalacademy.com

• Mandibular plane:
Different definitions are
given in different analysis,
1. Downs analysis – it
extends from Go to Me.
2. Steiner’s anlysis – it
extends from Go to Gn.
3. Tweed took lower border
of the mandible as the
mandibular plane.

HORIZONTAL PLANES

Vertical planes
• Facial plane : It
extends from nasion
to pogonion.
• Y-axis : It is the line
joining sella to
gnathion.
• Ramal plane : It is
drawn tangent to the
posterior border of the
ramus and the
condyles.

Vertical planes

MEASUREMENT ANALYSIS
1. DOWN’S ANALYSIS
In this analysis 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.

Facial angle

Angle of convexity

A-B plane angle

FMA angle

Y-(growth axis)

Dental patterns

Mean values of Down’s analysis
Skeletal Mean Value
1. Facial angle (N.Pog
-FHP)
87.8°
2. Angle of convexity
(N.A - A.Pog)
0°
3. A – B plane angle -4.6°
4. Mandibular plane
angle
(FHP – MP)
21.9°
5. Y axis (S.Gn-FHP) 59.4°

Dentition to skeletal pattern
1. Cant of occlusal
plane
9.3°
2. Inter incisal angle 135.4°
3. Lower incisor to
occlusal plane
14.5°
4. Lower incisor to
mandibular plane
91.4°
5. Upper incisor to 2.7mmwww.indiandentalacademy.com

TWEED’ 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

The values of the angles according to
Tweed’s finding are as follows:
1. FMA- Frankfurt Mandibular plane angle
= 25°
2. FMIA- Frankfurt Mandibular incisor plane
angle = 65°
3. IMPA- Incisor Mandibular angle = 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.

Angle SNA

Angle SNB

Angle ANB

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°

Errors of the cephalometric
measurements
These are grossly divided into three
heads :
1. Radiographic projection errors
2. Errors within the measuring system
3. Errors in landmark identification.

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

Limitation of cephalometrics
• It gives two dimensional view of a three
dimensional object.
• It gives a static picture which does not
takes time into consideration.
• The reliability of cephalometrics is not
always accurate.
• Standardization of analytical procedures
are difficult.

Cephalometrics for orthodontics

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