A brief overview on Orthodontic Study Model Analysis

1. MODEL ANALYSIS
MODEL ANALYSIS
Submitted By :-
Dibya Falgoon Sarkar
North Bengal Dental College & Hospital

2. INTRODUCTION
• Model analysis is one of the
essential diagnostic aids in
orthodontics.
• The study model provides a three
dimensional view of the
maxillary and mandibular dental
arches in all three planes of
space, i.e., sagittal, vertical and
transverse planes.
• Model analysis allows us to
carefully examine several
parameters such as dentition, jaw
relationships and make objective
measurements for detailed
evaluation and treatment
planning.
• Helps in detecting midline
discrepancies

3. REQUSITES OF STUDY MODELS
• Should accurately reproduce all the teeth
and soft tissues without any distortion.
• Should be trimmed symmetrical on either
side.
• Posterior surface should be trimmed, such
that when placed on their back they should
reproduce the occlusal plane.
• Should reproduce the alveolar process as
much as possible.

4. PARTS OF A STUDY MODEL
• Anatomic PortionAnatomic Portion - Consists
of the actual impressions of
the dental arch & its
surrounding structures.
• Artistic PortionArtistic Portion - Consists
of the plaster base that
supports the anatomic
portion and helps in
analysing the occlusion &
orientation of the study
models.
• The ratio of the anatomic
portion to the artistic portion
should be 3:1.

5. According to ABO (1990) Guidelines
Lateral view of the study model
1.Base of the maxillary
cast is trimmed parallel
to the occlusal plane.
2. Upper & lower cast
base should be parallel.

6. Maxillary occlusal view of study model

7. Mandibular occlusal view of
study model

8. REQUIREMENTS TO DO MODEL
ANALYSIS
• Well prepared study models
• Vernier calipers
• Divider
• Ruler
• 0.033” Soft Brass wire

9. CLASSIFICATION
PERMANENT DENTITION
MODEL ANALYSIS
MIXED DENTITION MODEL
ANALYSIS
Arch perimeter analysis Moyer’s Mixed dentition analysis
Carey’s analysis Tanaka and johnston analysis
Ashley Howe’s analysis Nance mixed dentition analysis
Pont’s analysis Huckaba’s mixed dentition analysis
(Radiographic method)
Linder Harth analysis
Korkhaus analysis
Bolton’s analysis

10. PONT’S ANALYSIS
• Pont in 1909, proposed a method of determining the ideal
dental arch width in premolar and first molar area based
on the sum total of mesio-distal widths of maxillary
incisors
Pont suggested that :
• The ratio of the combined upper incisor width to
transverse arch width was ideally 0.80 in the premolar
area and 0.64 in the molar area.
• He also suggested that the maxillary dental arch should
be expanded 1-2 millimeters more during treatment than
that found in normal occlusion to allow for relapse.

11. PONT’S ANALYSIS HELPS
IN
• Determining whether the dental arch is
narrow or is normal in the premolar and
molar region for a given sum of widths of
incisors.
• Determining the need for lateral arch
expansion.
• Determining how much expansion is
possible at the premolar and molar regions.

12. ANALYSIS
• DETERMINATION OF SUM OF INCISORS (SI)
• DETERMINATION OF MEASURED
PREMOLAR VALUE (MPV)
• DETERMINATION OF MEASURED
MOLAR VALUE (MMV):

13. • CALCULATED PREMOLAR VALUE (CPV): or the
expected arch width in the premolar region is determined
by:
CPV = SI X 100
80
• CALCULATED MOLAR VALUE (CMV): or expected
arch width in the molar region is determined by:
CMV = SI X 100
64

14. INFERENCE
•If the measured value is less than the
calculated value, then the arch is narrow for
the given sum of incisors width and
expansion can be done.
•If the measured value is greater than the
calculated value, the arch is wider and there
is no scope for expansion.

15. DRAWBACKS
• Maxillary laterals are the teeth most
commonly missing from the oral cavity.
• Peg-shaped laterals can be seen.
• The analysis was done from the casts of
French population
• It does not take skeletal mal-relationships
into consideration.

16. LINDER HARTH ANALYSIS
• Linder Harth proposed an index very similar to
that of Pont’s analysis.
• He made variation in the formula to determine
the calculated premolar and molar values
• The calculated premolar value (CPV):
CPV = SI X 100
85
• The calculated molar value (CMV):
CMV = SI X 100
64

17. KORKHAUS ANALYSIS
• This analysis is similar
to Pont’s analysis.
• Only difference is that it make
use of Linder Harth’s formula
to determine the ideal width
in the premolar & molar
regions.

18. • According to Korkhaus for a given width
of the upper incisors a specific value of the
perpendicular distance between the mid
point of the inter premolar line to the point
between the two maxillary central incisors
should exist.
• An increase in this measurement denotes
proclination of the upper anterior teeth,
while a decrease in this value denotes
retroclined upper anteriors.

19. Korkhaus’ Measurements

20. ARCH PERIMETER
ANALYSIS
• Many malocclusions occur due to discrepancy
between arch length & tooth material.
• It is done in the upper arch.
• Two measurements are required for intra-
maxillary analysis of space requirement:
1. Calculation of space required
2. Calculation of space available.
• Arch perimeter is the geometrical dental arc
formed by teeth at their incisal / cuspal edges.

21. PROCEDURE
• DETERMINATION OF SPACE REQUIRED:
• measure the mesiodistal dimension of all the teeth mesial to the
first molar (54321│12345)
• DETERMINATION OF SPACE AVAILABLE:
1. measure the arch perimeter using brass wire. From
mesiobuccal line angle of maxillary right first molar , pass the
wire along the buccal cusp and incisal edges in the anterior
region, ‘pass the wire on the left quadrant like a mirror image
till the mesiobuccal line angle of the left maxillary first molar.
2. Mark the wire and measure the wire, which gives the space
available.

22. • In case of proclined incisors, pass the brass
wire in the cingulum region, and if the
anterior teeth are retroclined, pass the wire
labial to them like a smooth curve.

23. DETERMINATION OF THE DISCREPANCY
•The difference between the space required
and space available gives the arch
discrepancy or excess.
•If the tooth material is more than the arch
length, the space available for alignment is
not sufficient results in crowding.
•If the tooth material is less than the space
then there can be spacing.

24. INTERPRETATION OF ARCH
PERIMETER ANALYSIS
ARCH LENGTH DISCREPANCY INFERENCE
0 to 2.5 mm
Proximal stripping can be carried out
to reduce the minimal tooth material
excess
2.5 to 5 mm
Extraction of second premolar is
indicated
Greater than 5mm
Extraction of first premolar is usually
required

25. CAREY’S ANALYSIS
• The arch length-tooth material discrepancy
is the main cause for most malocclusions.
• This discrepancy can be calculated with
the help of Carey’s analysis.
• The analysis is carried out in the lower
arch.

26. INTERPRETATION OF
CAREY’S ANALYSIS
ARCH LENGTH DISCREPANCY INFERENCE
0 to 2.5 mm
Proximal stripping can be carried out
to reduce the minimal tooth material
excess
2.5 to 5 mm
Extraction of second premolar is
indicated
Greater than 5mm
Extraction of first premolar is usually
required

27. ASHLEY HOWE ANALYSIS
• Ashley Howe considered the crowding of
teeth to be the result of deficiency in arch
width rather than arch length.
• He found the relationship between the
twelve teeth anterior to the permanent
second molars and the width of the dental
arch in first premolar region.
• This is usually done in the upper arch.

29. ANALYSIS
• DETERMINATION OF TOOTH MATERIAL (TTM): mesodistal
width of all the teeth anterior to the permanent second molars are
measured with the help of callipers and all the values are summed
up.
• DETERMINATION OF PREMOLAR DIAMETER (PMD): it
refers to the distance or arch width from the tip of the buccal cusp
of one fiirst premolar to the tip of the buccal cusp of opposite first
premolar.
• DETERMINATION OF PREMOLAR BASAL ARCH WIDTH
(PMBAW): measurement of width from canine fossa of one side to
another gives us the width of the dental arch at the apical base or
junction between the basal bone and the alveolar process.

30. INFERENCE I
• The PMBAW and PMD are compared.
• If the PMBAW is greater than the PWD,
then it is indicated that arch expansion is
possible.
• If on the other hand, the PMBAW is less
than PMD, then arch expansion is not
possible.

31. INFERENCE II
• According to Howe, to achieve a normal
occlusion with a full complement of teeth,
the basal arch width at the premolar region
(PMBAW) should be 44% of the sum of
the mesiodistal widths of all the teeth
mesial to the second molar (TTM)

32. INFERENCE
PMBAW % CONCLUSION
37% or less It indicates a need for extraction
37-44% Borderline case
44% or more
Possibly non extraction if other
factors are favorable

33. BOLTON’S ANALYSIS
• Wayne Bolton considered the ratio of the tooth material
of the maxillary arch to the mandibular arch i.e M-D
widths of upper & lower teeth by nature have
predetermined proportions to maintain normal occlusal
relaionship.
• An alteration in this balance will lead to improper
intercuspation, overjet or spacing
• Bolton said that extraction of one/several tooth should
be done acc. to the ratio of tooth material b/w upper &
lower arch to get ideal overjet & overbite .

34. Measurements
• Sum of maxillary 12
• Sum of mandibular 12
• Sum of maxillary 6
• Sum of mandibular 6
• Overall ratio
• Anterior ratio

35. • Overall Ratio = Sum of mandibular 12 *100
Sum of maxillary 12
• For establishing ideal overjet & overbite overall ratio should be
91.3%
• If the overall ratio is less than 91.3%, it indicates maxillary tooth
material excess.
• The amount of maxillary tooth material excess is determined by
using the formula
• The amount of mandibular tooth excess is determined by:
Determining Overall Ratio

36. • The sum of M-D widths of the mandibular
anteriors to the M-D width of the max.
anteriors should be 77.2%
• The anterior ratio is determined using the
following formula:
• If < 77.2 , maxillary anterior excess
• If >77.2 , mandibular anterior excess
Determination of Anterior Ratio :

37. Disadvanatages of Bolton’s Analysis
• Does not take into account the sexual
dimorphism in the maxillary canine
widths.
• Study done on specific population.

38. MIXED DENTITION
ANALYSIS

39. AIM
• The purpose of mixed dentition analysis is to
evaluate the amount of space available in the
arch for succeeding permanent teeth and
necessary occlusal adjustments.
• Methods of analysis of archlength during mixed dentition
i. Those in which the sizes of unerupted cuspids and
premolars are estimated from radiographic images
ii. Those in which the sizes of cuspids & premolars are
derived from the knowledge of already erupted
permanent tooth in the mouth.(Probability Tables)
iii.Combination of the above two method

40. HUCKABA’S MIXED DENTITION
ANALYSIS (RADIOGRAPHIC METHOD)
• This analysis makes use of a radiograph
and study cast to determine the width of
unerupted teeth.
• Advantages: Easy, practical & relatively
accurate.
• Disadvantage: Chances of distortion of
radiographic image.
• IOPAR are preferred over Panoramic
Images as they are more accurate.

41. PRINCIPLE
• It is based on the principle that if we measure an object,
which can be seen both in radiograph as well as on a cast,
then we can compensate for the enlargement of the
radiographic image
• A simple proportional relationship can be established as
follows:

42. • SPACE AVAILABLE:
the arch is divided into
segments which are
approximately straight
lines. The dimensions in
each of the segments is
measured and added up.
• SPACE REQUIRED: for
the un-erupted teeth is
calculated from the
radiographs. The
discrepancy is calculated
segment wise

43. • It is based on the premise that there is a reasonably good
correlation b/w the size of erupted permanent incisors and
the unerupted canines & premolars
• This is because a person with large teeth in one part of
the mouth will have large teeth elsewhere also, as their
development is controlled by the same genetic
mechanism.
• Here the lower permanent incisors are measured and the
mesio-distal widths of unerupted permanent upper and
lower canines and premolars is derived from the
probability chart.
• The mandibular incisors are chosen for measuring as they
are the first teeth to erupt in the mixed dentition period.
MOYER’S MIXED DENTITION
ANALYSIS

44. PROCEDURE
• STEP I: SPACE REQUIRED- measure the mesio-distal
dimension of all four lower incisors and sum it up.
Using the Moyer’s probability chart find the total
mesio-distal width of upper and lower canine and
premolars from the upper and lower charts at 75%
probability for the given lower incisor dimension.
• STEP II: SPACE AVAILABLE- measure the distance
between the distal surface of permanent lateral incisors
and mesial surface of permanent first molar. Determine
the amount of space required for the proper alignment
of mandibular incisors. The amount of space left
behind gives the space available.

45. Moyer’s Probability Tables

46. TANAKA AND JOHNSTON
ANALYSIS (1974)
• They developed a method to predict the width of un-erupted canine
and premolar using the width of lower incisors.
• This methods has good accuracy despite a small bias towards over-
estimating the un-erupted tooth size.
• They have simplified Moyer’s 75% prediction table into a formulas
• Predicted width of maxillary canine & premolars =
Sum Of Mandibular Incisors + 11
2
• Predicted width of mandibular canine & premolars =
Sum of Mandibular Incisors + 10.5
2

47. CONCLUSION
Mixed dentition analysis forms an integral
aspect of orthodontic diagnosis to determine
whether the treatment plan is going to
involve serial extraction, space maintenance,
space gaining or simply periodic observation
of the patient.

48. RECENT ADVANCES IN
MODEL ANALYSIS

49. Cast analysis by E Models/ 3D Digital Models

50. ADVANTAGES OF
COMPUTERIZED ANALYSIS
• More Accurate
• Easy
• More information:
– Arch form
– Determine asymmetric Arch
– Space analysis
– Rotation
– Prediction

51. REFRENCES:
William R. Proffit 5th
edition.
OP Kharbanda 2nd
edition.
S.M Bhalajhi 5th
edition.