Cast Analysis
Introduction

Model analysis is the study of dental casts, which helps to study the
occlusion and dentition from all three dimension to derive the diagnosis &
plan for treatment. Model analysis is an essential diagnostic record that
helps to study the occlusion and the dentition from a three dimensional
aspect. The study ranges from the metric analysis of the arch form to the
prediction of the sizes of the unerupted permanent teeth during the mixed
dentition.

They have been the “gold standard” in orthodontic diagnosis with the
advantages ranging from being a routine dental techniques, ease of
production, inexpensiveness and ease in measurement to plaster casts
being able to be mounted on an articulator for study in three dimension.
Arch Perimeter Analysis
•
Many Malocclusions occur due to DISCREPANCY BETWEEN ARCH LENGTH AND TOOTH
MATERIAL
•
Arch Perimeter Analysis will help you assess wether the available space in the arch is
enough to accommodate the dentition, specially if they are maligned
•
Effective in the Permanent Dentition
•
Two measurements are required for intra-maxillary analysis of space requirement
1.
Calculation of Space Required
2.
Calculation of Space Available
Arch Perimeter Analysis : Space
Available
1. Using a wire, measure from mesiobuccal line angle of the right molar, pass the wire
along the buccal cusps and incisal edges then mirror on the other side to reach the
mesiobuccal line angle of the left first molar
2. Mark the wire and measure the wire, this is the Space Available
•
In case of proclined incisors, pass the wire on the cingulum region
•
If the anterior teeth are retroclined, pass the wire labial to teeth like a smooth curve
Arch Perimeter Analysis : Space
Required
•
Measure all the individual mesiodistal width of all teeth ANTERIOR TO THE
FIRST MOLARS
Arch Perimeter Analysis : Inferences
ARCH LENGTH DISCREPANCY
INTERPRETATION
Less than 0
Spaces are observed
0 to 4 mm
Minimal tooth width excess which can be
remedied through interproximal stripping
4 to 8 mm
Moderate tooth width excess needing extraction
of first premolar OR stripping to accommodate
space
Greater than 8 mm
Excessive space discrepancy needing extraction
of first premolar and probably stripping of anterior
interproximals
Mixed Dentition Analysis
Mixed Dentition Analysis

After completion of the dental cast review, depending upon the age of the pt, a mixed
dentition analysis can be completed, an early assesment of available space may
permit intervention or minimise development of malocclusions

Basis for Mixed Dentition Analysis (Fields and Profit):

First Permanent Molar and Permanent Incisors are erupted

The succedaneous Permanent Teeth are forming

Size relationship between unerupted Permanent Teeth and Primary Teeth

There is size difference in primary canines and molars, and the succedaneous teeth

M-D width of primary canines and molars are greater than permanent successors
(Nance’s Leeway Space)
Mixed
Dentition
Analysis

Mixed Dentition Analysis is based on three categories, either
Tooth Size Analysis, Relationship of Tooth Size to Supporting
Structures and Space Analysis, the later being the most used
catergory for being simple yet reliable.

Tooth Size Analyses



Bolton’s Tooth Ratio Analysis

Sanin Savara Analysis
Tooth Size to Supporting Structures

Ashley Howe’s Analysis

Pont’s Analysis

Linder Hearth’s Analysis

Korkhaus’ Analysis
Space Analyses

Moyer’s Analysis

Tanaka Johnston Analysis

Hixon-Oldfather Analysis

Nance’s Mixed Dentition Analysis
Space
Analysis
Space analysis, using the study cast is valuable
in evaluating the likely degree of crowding for a
child in the mixed dentition; and in that case, it
must include the prediction of the size of the
unerupted permanent teeth.
Space Analysis - Moyer’s

The high correlation among groups of teeth is the
rationale for this analysis where in measuring the
M-D width of one group of teeth may closely
approximate the size of the other group of teeth.
The analysis usually requires a dental cast, Boley’s
gauge and a Probability Chart
Space Analysis – Moyer’s

Produre

Measure widths of each of four
permanent incisors of the upper jaw
(maxillary centeral incisors and
maxillary lateral incisors) and lower
jaw (mandibular central incisors and
mandibular lateral incisors).

The total Mesio-Distal width of the
incisors is calculated

A prediction chart is used for space
available in each arch, and the
value that matches closest to the
sum of incisors is picked.

Advantages and Disadvantages

Some of the advantages of this analysis are that
it has minimum systemic errors, easy to perform
by both beginners and expert dentists, it can be
used for both the arches, can be performed on
both casts or in mouth, and does not require any
radiographs. Limitations of this analysis are that
this is a probability analysis, does not account for
tipping of incisors lingual or buccal and that
maxillary tooth sizes are predicted by the
mandibular tooth sizes. Other limitations of this
analysis is that Moyer's never clarified which
population this analysis was done on initially.
Therefore, this analysis cannot be truly applied to
different populations.
Space Analysis – Tanaka Johnston


The prediction of the size of the unerupted
canines and the premolars in contemporary
orthodontic population can also be done with
this method, they believed that equations and
size of the confidence intervals used by Moyer’s
MDA have never been validated by any other
studies.
Advantages and Disadvantages

The technique involves simple, easily
repeatable procedures with minimum
material requirement and a Prediction chart
and radiograph is unnecessary. However, the
values were tested to be quite accurate on
caucasians, while having some noticable
inaccuracies with other races.
To predict the size of undererupted premolars and
canines:
1/2 of Mesio-Distal width of four lower incisors + 10.5 =
Estimated width of mandibular premolars + canine in
one quadrant
1/2 of Mesio-Distal width of four lower incisors + 11.0 =
Estimated width of maxillary premolars + canine in
one quadrant
This analysis takes 3 measurements into account:
• The Mesiodistal widths of the mandibular incisors
• Predicted size of permanent canines and
premolars and
• The space available after the incisors are correctly
aligned.
Tooth Size Analysis – Bolton’s

Wayne Bolton pointed out that
the extraction of one tooth or
several teeth should be done
according to the ratio of tooth
material between the maxillary
and mandibular arch to be able
to achieve the ideal occlusion,
overjet, overbite and alignment of
teeth.

Procedure

Overall Ratio: Get the sum of the mesiodistal
diameter of the 12 maxillary teeth and divide that
with the sum of the mesiodistal diameter of the 12
mandibular teeh and multiply by 100

Anterior Ratio: In the same manner, the sum of the
6 maxillary anterior teeth and divide that with the
sum of the 6 mandibular anterior teeth and
multiply by 100

Overall Ratio’s mean value is 91.3

Anterior Ratio’s mean value is 77.2

Inference

If the ratio is more than the mean value, then
the mandibular tooth material is in excess

If the ratio is less than the mean value, then
the maxillary tooth material is in excess
Tooth Size Analysis Bolton’s

Bolton preferred to do trimming of tooth
material through interproximal stripping
on the arch in excess when the value in
excess is minimal. And tooth extraction
would be done to equalize the
occlusion in cases with great
discrepancies

Quiz. Solve for the Bolton’s Tooth Size Analysis and give the Inference for this case

Maybe handwritten or typed (should have solving formula). Pass through “2nd Prelim
Quiz 3” tab for this week together with the quiz.