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
For orthodontic diagnosis, maximum displacement
of soft tissues, created by

Maximum extension of the impression, is
desired.
The inclination of the teeth, not just the location of
the crown, is important.
The angles shown for the casts are
suggested values;
Symmetry is more important than the
precise angulation to detect
asymmetries

Digital casts, produced from laser scans of
impressions or inter – mediate casts
Displayed with symmetric bases
 Emphasize that they are equivalent to physical casts
 Symmetric base helps the observer detect asymmetries
within the dental arches
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Discrepancy between CR and habitual occlusin
Record the lateral and excursive paths
Display the orientation of the occlusal plane to the
face
In adults with symptoms of TM
dysfunction(clicking,limitation of motion,pain)
Preadolescent and early adolescent orthodontic
patients
No need

Symmetry

Alignment (Crowding) / Space Analysis
◦ Space analysis requires a comparison between the
amount of space available for the alignment of the teeth
and the amount of space required to align them properly.
Tooth size Analysis(Bolton analysis)
Anterior:77.2
Posterior:91.3
Archform
Tapered
Square
Ovoid
Curve of Spee (sagittal )
Related to space analysis

An asymmetric position of entire arch should have
been detected already in the facial examination.

An asymmetry of arch form also may be present
even if the face looks symmetric.
A transparent ruled grid
placed over the upper
dental
arch
and
oriented to the mid
palatal raphe can make
it easier to see a
distortion of arch form
in either virtual or
digital casts.
Asymmetry within the dental arch, but with
symmetric arch form, also can occur.
This usually results either from lateral drift of incisors
or from drift of posterior teeth on one side…
The ruled grid also helps in seeing where drift of teeth
has occurred.
Lateral drift of incisors occurs with severe crowding,
particularly if a primary canine was lost prematurely
on one side. This often results in one permanent
canine being blocked out of the arch while the other
canine is nearly in its normal position, with all the
incisors shifted laterally.
Drift of posterior teeth is usually caused by early loss
of a primary molar, but sometimes develops even
when primary teeth were exfoliated on abnormal
schedule.
It is important to quantify the amount of crowding
within the arches, because treatment varies depending
on the severity of the crowding.
Space analysis, using the dental casts, is required for
this purpose.
Such an analysis is particularly valuable in evaluating
the likely degree of crowding for a child in the mixed
dentition.
Principles of Space Analysis

Space available = from the mesial of one first molar to
the other, over the contact points of posterior teeth and
incisal edge of anteriors.

Space required = the sum of the mesiodistal
widths of all individual teeth, measured from
contact point to contact point.
Three important assumptions:
( l) the anteroposterior position of the incisors is
correct (i.e., the incisors are neither excessively
protrusive nor retrusive)
(2) the space available will not change because of
growth
(3) all the teeth are present and reasonably normal in
size
There is an interaction between crowding of the teeth
and protrusion or retrusion.
Crowding and protrusion are really different
aspects of the same phenomenon. If there is not
enough room to properly align the teeth, the result
can be crowding, protrusion, or (most likely) some
combination of the two.
 Information about how much the incisors protrude:
from clinical examination and cephalometric
analysis
The second assumption, that space available will not
change during growth, is valid for most but not all
children.
In a child with a well-proportioned face, there is little
or no tendency for the dentition to be displaced
relativet o the jaw during growth, but the teeth
often shift anteriorly or posteriorly in a child with a
jaw discrepancy.
Important Note:
The position of the permanent molars changes when
primary molars are replaced by the premolars(arch
length decreases).
If space analysisis done in the mixed dentition, it is
necessary to adjust the space available measurement
to reflect the shift in molar position.
1. either directly on the dental casts :
2. or by a computer algorithm after appropriate
digitization of the arch and tooth dimensions.

space available =from the mesial of one first molar
to the other, over the contact points of posterior
teeth and incisal edge of anteriors.

There are two basic ways to accomplish space
available manually:

(1) by dividing the dental arch
into segments that can be
measured as straight line
approximations
(2) by contouring a piece of wire
to the line of occlusion and then
straightening it out for
measurement.
The first method is preferred for
manual calculation because of its
greater reliability.
In the posterior region it crosses the
contact points and anteriorly it
follows the incisal edges.

This is done by measuring the mesiodistal width of
each erupted tooth from contact point to contact
point, estimating the size of unerupted permanent
teeth, and then summing the widths of the
individual teeth .
Divider
Boley gauge
1
2
3
• Measurement of the teeth on radiographs.
• Estimation from proportionality tables.
• Combination of radiographic and prediction table methods.

Panoramic radiographs are distorted.
It is often difficult to obtain an undistorted view
of the canine
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The technique can be used in maxillary and
mandibular arches for all ethnic groups
.
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Upper lateral incisors are extremely variable teeth.

Despite a tendency to overestimate the size of
unerupted teeth, accuracy with this method is fairly
good for the northern European white children on
whose data it is based.

No radiographs are required, and it can be used for
the upper or lower arch.
no radiographs no reference tables
For children from a European population group,
the method has good accuracy despite a small bias
toward overestimating the unerupted tooth sizes.

NOTE:
Space analysis based on correlations of tooth sizes,
should be used with caution if the radiographs show
anything unusual(anomalies in tooth size or form)
3) Combination of radiographic and
prediction table methods
Staley & Kerber
Since the major problem with using radiographic
images comes in evaluating the canine teeth,
it would seem reasonable to use :
1. the size of permanent incisors measured from
the dental casts
2. and the size of unerupted premolars measured
from the radiographs
to predict
the size of unerupted canines.
Canine+ Premolar
Incisor +
Premolar
This method can be used only for the
mandibular arch and, of course.
It requires periapical radiographs.
For children of European ancestry, it is quite
accurate.
Staley-Kerber method
Tanaka- Johnston
Moyers

The prediction tables work surprisingly well when
applied to the population group from which they were
developed. These methods are superior to
measurement from radiographs.

On balance, the Tanaka- Johnston method probably is
most practical for manual calculation because:
◦
◦
no radiographs
no reference tables

On the other hand, if the patient does not fit the
population group, as an African or Asian child
would not, direct measurement from the
radiographs is the most accurate approach.
11
10
20.5
6 E D C 2 1 1 2 C D E 6
1=5.5mm
2=6mm
C= 6.5mm D=7.5mm E=9mm
6= 10.5mm
19
For good occlusion, the teeth must be proportional in size.
Although the natural teeth match very well in
most individuals, approximately 5% of the
population have some degree of disproportion
among the sizes of individual teeth.
This is defined as tooth size discrepancy.
upper lateral incisors
premolars
all the upper teeth
Bolton analysis
A quick check for anterior tooth size discrepancy
comparing the size of upper and lower lateral incisors.
Upper wider
A quick check for posterior tooth size
discrepancy
comparing the size of upper and lower 2nd
premolars
equal
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A tooth size discrepancy of less than 1.5mm
is rarely significant, but larger discrepancies create
treatment problems and must be included in the
orthodontic problem list.