Model analysis 1 /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Model analysis
Introduction:
Model analysis is a three dimensional
assessment of the maxillary and mandibular
dental arches and occlusal relationships for
orthodontic diagnosis and treatment planning
It is a diagnostic aid, one can analyze the arch
form, arch symmetry, alignment of the teeth,
palate shape, tooth size, tooth shape, rotations
of teeth and other information.

The plaster models for study cast analysis
are oriented to the following planes
Mid sagittal plane – for assessment of
transverse discrepancies
Tuberosity plane – for assessment of
antero-posterior dental malposition
Occlusal plane – for assessment of
vertical dental malpositions


Analysis of tooth development :
Eruption – predicting emergence
Use of tables of development
Sequence of eruption
Number of teeth
Position of teeth
Anomalies
Size of teeth

Analysis of arch form
Sum of upper incisors
Anterior arch width
Posterior arch width
Anterior arch length
Palatal height
Dental arch width……

PONTS ANALYSIS - indicates ideal value for anterior arch width
and helps in
(a) determining whether the dental arch is narrow
(b) determining the need for lateral arch expansion
(c) determining how much expansion is possible
at premolar and molar regions


Determination of sum of incisors (S.I.)
The mesio-distal width of the 4 maxillary incisors
is measured and the values summed up. This
value is called sum of incisors (S.I.)
Determination of measured premolar value
(M.P.V.)
The width of the arch in the premolar region from
the distal pit of one upper first premolar to the
distal pit of the opposite first premolar is
measured it is called the measured premolar
value

Determination of calculated
molar value (M.M.V.)
The width of arch in molar region from the mesial pit of one upper first molar
to the mesial pit of the opposite first molar is measured. This value is called
the measured molar value.
Determination of calculated premolar value (C.P.V.)
Calculated premolar value or the expected arch width in the molar region is
determined by the formula: S.I.x100/80
Determination of calculated molar value (C.M.V.)
Calculated molar value or the expected arch width in molar region is
determined by the formula: S.I.x100/64
Inference -:
If measured value is less than calculated value, it indicates the need for
expansion. Thus it is possible to determine how much expansion is needed
in molar region and the premolar regions.

Drawbacks of Pont's Analysis:
Pont being French, carried out his study over
French population. So the standards can't be
taken for granted or other population
Sum of upper incisors can be variable eg.Peg
laterals, so the inference can be misleading
Pont hasn't considered the width of basal bone ,
which led to the illogical and irrational expansion
of the dental arches in the past.


Linder Harth index:
This analysis is very similar to Pont’s analysis
except that a new formula has been proposed to
determine the calculated premolar and molar
value
The calculated premolar value is determined
using the formula: S.I.x100/ 85
The calculated molar value is determined using
the formula: S.I.x100/ 64

Chadda index:
The dental arch width in premolar and molar
region is carried out in Indian population by
new formula.
Its similar to Pont’s index its values are more
reliable
Anterior arch width = S.I.x100/ 82.7
Posterior arch width = S.I.x100/ 63.7

Dental arch length….
Korkhaus analysis:
This analysis is also similar to Pont’s analysis. In
addition, this analysis utilizes a measurement made from
the midpoint of the inter-premolar line to a point in
between the two maxillary incisors.
Determination of arch length
The arch length is the distance perpendicular to the line
connecting the reference points of anterior arch width in
the mid-sagittal plane.
The formula for calculating the standard value of the
upper anterior arch length according to Korkhaus is as
follow -:
Maxillary arch length (Lu) = SuI x100/ 160
SuI=Sum of upper incisors

Correlation between maxillary and mandibular arch
length -:
The anterior arch length of the mandible (Ll) is
shorter than the maxillary arch length (Lu) by
labiolingual width of the incisal edge of the upper
central incisor
Standard value Ll= standard value of Lu-2mm
Inference -:
The measurement permits a crude analysis of the
anteroposterior position of incisors.
An increase in this measurement denotes
proclined upper anterior teeth while a decrease in
this value denotes retroclined upper anteriors.

Intra maxillary symmetry
Transverse symmetry
Anteroposterior symmetry
Korbitz estimate the right-left differences in transverse and
anteroposterior tooth positions
To perform these measurements, precisely defined reference
Planes are necessary
Construction of the reference planes
Midpalatal raphe:
The mid-palatal raphe is constructed with help of two anatomic
reference points on the palatine raphe.
Anterior point ; (X) cross section of the second palatine rugae with the
palatine raphe.
Posterior point ; (^) the border of hard and soft palate on the raphe
respectively the midpoint between the paired foveolae, next to the
raphe in this segment. www.indiandentalacademy.com

Marking of the reference planes:
Construction of midpalatal raphe (MRP) through
anatomically defined midpoints on the palatine
raphe of the maxilla. The MRP is the maxillary
midline and reference plane for assessing
transverse symmetry
The anteroposterior symmetry assessment is
made using the relationship to the tuberosity
plane which is perpendicular to the MRP and
extends through the most distally positioned
maxillary tuberosity.

Analysis of transverse symmetry
The transverse distance of the pont reference points to the
arch midline is determined and the actual measured value is
compared with the half value of standard width of dental arch.
According to Schmuth –measurements should not to be
taken from these reference points but rather from the
linguogingival margin of the teeth, since erroneous
measurements can occur in case of tooth rotation
From a diagnostic point of view assessment of the transverse
symmetry is clinically relevant, particularly in cases of
transverse malocclusions
Inference -:
Symmetry/asymmetric width development between right and
left sides of the arch (malposition, symmetric, asymmetric,
unilateral)

Midline shift:
Midline is shifted in maxillary arch when the
contact point of the mesial approximal surfaces of
the upper central incisors don't coincide with the
midsagittal plane of the upper arch.
Differentiation between dental and skeletal midline
shift in mandible arch
The anterior skeletal midpoint of the mandible is
either determined with the help of the mental spine
view or by assessing the point of insertion of the
lingual frenum. But the radiographic method is
most reliable.

Analysis of anteroposterior
symmetry
The analysis serves to diagnose first and foremost any
mesial tooth drift.
Asymmetric mesio-distal tooth position of corresponding
teeth in the right and left side of the dental arches.
In practice this involves drawing a line parallel to the
Tuberosity plane, which runs through the posterior
surface of distal-most first molar, and comparing the
sagittal distances of the individual posterior teeth
Inference -:
If there is no right-left asymmetry, the teeth are correctly
positioned or there has been symmetric mesial
migration.
Asymmetry of a transverse arch form may result in a
relative mesial position of the more buccaly placed teeth

Palatal height index (P.H.I.)
According to Korkhaus palatal height is defined as a vertical line
perpendicular to the mid palatal raphe, which runs from the surface
of the palate to the level of the occlusal plane.
This is measured between the reference point of the Ponts index for
the posterior width.
P.H.I. = palatal height x 100/posterior arch width
Measurement of palatal height -: using Korkhaus 3-dimensional
orthodontic divider, the palatal height can be measured as well as
posterior arch width.
Palatal height is measured in the midsagittal plane in the region of
the upper first molar on the level of occlusal plane

Inference-:
Average value is 42%
Value is increased when the palatal vault relative to the transverse
arch development is high and decreased when palate is shallow.

Analysis in vertical plane
Supraversion – over eruption of teeth in relation to the
occlusal plane
Infraversion – under or insufficient eruption of teeth in
relation to occlusal plane
Occlusal plane is a constructed plane which does not
actually exist, as the occlusal surfaces of teeth do not lie
on one plane. Therefore precise measurements cannot be
made. Occlusal plane is defined as the tangent which
runs through the tips of the mesio-buccal cusps of first
molars and the buccal cusps of the premolars.
Curve of spee – the depth of the curve of spee is defined
as the distance from the vertex of the curvature to the
side of a plastic template placed over the lower arch. The
template touches anteriorly the incisal edges and
posteriorly the distal-most molar cusps

To determine the amount required
to the curve of spee of space
Balridge formula
space required to level the arch =
(Rt. Side depth + Lt. side depth / 2)+0.5


Bolton’s analysis
Determines the tooth size discrepancy between maxillary and
mandibular teeth
Sum of mandibular 12 – the mesio-distal width of all the teeth
mesial to the mandibular second permanent molars is measured
and summed up.
Sum of maxillary 12 – the mesio-distal width of all the teeth
mesial to the maxillary second permanent molars is measured
and summed up.
Sum of mandibular 6 - the mesio-distal width of all the teeth
mesial to the mandibular first premolars is measured and
summed up.
Sum of maxillary 6 – the mesio-distal width of all the teeth mesial
to the maxillary first premolars is measured and summed up.
Overall ratio = sum of mandibular 12 x100 / sum of maxillary 12
Anterior ratio = sum of mandibular 6 x100 / sum of maxillary 6

Inference-:
If overall ratio is less than 91.3%, it indicates
maxillary tooth material excess
If overall ratio is more than 91.3%, it indicates
mandibular tooth material excess
If anterior ratio is less than 77.2%, it indicates
maxillary anterior tooth material excess
If anterior ratio is more than 77.2%, it indicates
mandibular anterior tooth material excess


Analysis of apical base
Ashley howe’s analysis
Determines whether the deficiency in arch width or arch length
Determination of total tooth material (T.T.M.) –the mesio-distal width
of all the teeth mesial to the second permanent molars is measured
with help of dividers and all the values are summed up. This is called
as total tooth material
Determination of premolar diameter (P.M.D.) –the premolar diameter
refers to the arch width from the tip of the buccal cusp of opposite first
premolar
Determination of premolar basal arch width (P.M.B.A.W.) the canine
fossa is found distal to canine eminence. The measurement of the
width from canine fossa of one side to the other gives us the width of
dental arch at apical base. If canine fossa is not clearly
distinguishable the measurement is made from a point that 8mm
below the crest of interdental papilla distal to the canine

Inference -:
P.M.B.A.W.% = P.M.B.A.W. x100 / T.T.M
If P.M.B.A.W% is 37% or less, it indicates
extraction case
If P.M.B.A.W% is 44% or more, it indicates
non-extraction case
If P.M.B.A.W% is 37-44%, borderline case


Space analysis in permanent
dentition
Determine the difference between space available and
space required for alignment of teeth
Nance and Carey’s analysis
Determination of tooth material -:
measure the mesio-distal width of each tooth mesial to
the first permanent molar . The sum total of the width
corresponds to the necessary space required i.e. ideal
arch length.

Determination of arch length -:
measure the actual arch length using soft brass wire.
The wire is placed contacting the mesial surface of the
first permanent molar of one side and is passed over
the buccal cusps of premolar and along the anteriors
and is continued on the opposite side in same way
upto the mesial surface of the opposite first molar
If proclined anteriors, the wire is passed along the
cingulum of anterior teeth
If retroclined anteriors, the wire is passed over the
incisal edge of anteriors
Determination the arch length discrepancy -:
The discrepancy refers to the difference between the
arch length and tooth material

Inference -:
If ideal arch length is more than actual
then negative value and space deficiency,
extraction is required in that case
If space available is more than ideal arch
length then positive value and space
excess, no extraction is required in that
case

The Lundstorm segmental analysis
Segmental analysis involves an indirect assesment of
the dental arch perimeter which can be carried out in
following manner-:
Division of the dental arch into six straight line
segments of two teeth per segment, including the first
permanent molars.
Measure the mesio-distal width of twelve teeth
Summing the individual tooth width of each segment.
Measure the available mesio-distal space on the study
cast separately for each segment
The sum of the difference between ideal and actual
length of each segment express the space relationship

Peck and Peck index
Peck and peck determined the presence or absence of
lower incisor crowding and related to the shape of lower
anterior teeth.
It is based on the finding that individuals with ideal incisal
arrangement had smaller mesio-distal width and larger
labio-lingual width than in persons with incisal crowding
Method -:
1. Measure the mesio-distal width of lower incisors
2. Measure the labio-lingual width of lower incisor individually
3. Calculate the ratio of mesio-distal width and labio-lingual
width separately for lower centrals and laterals
4. Compare the value with ideal mean value
Ideal mean values -:
For lower centrals -: 88-92%
For lower laterals -: 90-95%

Inference -:
If calculated value is greater than mean
value then mesio-distal width is more than
labio-lingual width.
Hence proximal stripping can be done to
relieve the crowding


Mixed dentition analysis
The purpose is to evaluate the amount of space
available in the arch for succeeding permanent
teeth and necessary occlusal adjustments.
Many methods of mixed dentitions analysis have
been suggested; however, all fall into two
strategic categories:
1. Those in which the sizes of unerupted cuspids
and bicuspids are estimated from measurements
of the radiographic image , and
2.Those in which the sizes of the cuspids and
premolars are derived from knowledge of the
sizes of permanent teeth already erupted in the
mouth.

The correlation between the sizes of
mandibular incisors and the combined
sizes of cuspids and bicuspids in either
arch is high enough to predict the amount
of space required for the unerupted teeth
during space management procedures.
The mandibular incisors have been
chosen for measuring, since they are
erupted into the mouth early in the mixed
dentition, the mandibular incisors are not
used in any of predictive procedures,
since they show too much variability in
size, and their correlations with other
groups of teeth are of lower predictive
value.

Moyer’s mixed dentition Analysis
Procedure - :
1. Measure with the tooth-measuring gauge or a pointed
Boley’s gauge, the greatest mesio-distal width of the
four mandibular incisors.
2. Determine the amount of space needed for alignment
of the incisors. Set the Boley’s gauge to the left central
incisor and left lateral incisor. Place one point of the
gauge at the midline of the alveolar crest between the
central incisors and let the other part lie along the line of
the dental arch on the left side. mark on the tooth or the
cast the precise point where the distal surface of the
lateral incisor will be when it has aligned. Repeat this
process for the right side of the arch.

3. Compute the amount of space available after incisor
alignment. To do this, measure the distance from a point
marked in the line of the arch to the mesial surface of
first permanent molar. This distance is the space
available for cuspid and two bicuspids and for any
necessary molar adjustment after the incisor have been
aligned. Record the data for both sides on the mixed
dentition analysis form.
4. Predict the size of the combined widths of mandibular
cuspids and bicuspids. Prediction of the combined
widths of cuspid, first and second bicuspids is done by
use of probability charts. Locate in the left column of the
mandibular chart value that most nearly corresponds to
the sum of the widths of the four mandibular incisors. To
the right is a row of figures indicating the range of values
for all the cuspid and bicuspids sizes that will be found
for incisors of the indicated size. The value at the 75
percent level of probability is chosen as the estimate ,
since it has been found to be the most practical from
clinical standpoint. www.indiandentalacademy.com

Tanaka and Johnson analysis
Prediction of the size of unerupted canines
and premolars can be done
They simplified Moyers 75 percent level of
the prediction table into a formula
Predicted width of maxillary canine and
premolar = sum of mandibular incisors +
11 divided by 2
Predicted width of mandibular canine and
premolar = sum of mandibular incisors +
10.5 divided by 2

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Model analysis 1 /certified fixed orthodontic courses by Indian dental academy

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