orthodontic cast analysis

1. MODEL ANALYSIS

2. INTRODUCTION
 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.

3. Advantages
1. They are three dimensional records of the patients
dentition.
2. Occlusion can be visualized from lingual aspect.
3. They provide a permanent record of the
intermaxillary relationship.
4. Helps to motivate the patients as they can visualize
the treatment progress.
5. They are needed for comparison purposes at the
end of the treatment and act as a reference for post
treatment changes.
6. They serve as a reminder for the parent and the
patient of the condition present at the start of the
treatment.
7. In case the patient has to be transferred to another
clinician study model are an important record.

4. PARTS OF A STUDY MODEL
 Anatomic Portion - Consists of the actual impressions of
the dental arch & its surrounding structures.
 Artistic 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.

6. 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.

7. 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.

8. Maxillary occlusal view of study
model

9. Mandibular occlusal view of study
model

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

11. CAST ANALYSIS
• CAST APART
• CAST IN OCCLUSION

12. CAST APART
 Arch form
 Arch symmetry
 Teeth present
 Teeth absent
 Crowding
 Spacing
 Buccoversion / linguoversion
 Supraversion / infraversion
 Torsiversion
 Transposition
 Proclined
 Retroclined

13. DEFINITIONS
 Buccoversion when the tooth is displaced bodily in a labial or
buccal direction
 Linguoversion when entire tooth is displaced in a lingual or
palatal direction
 Infraversion tooth that has not erupted enough in comparison
to adjacent teeth
 Supraversion tooth that has over-erupted
 Torsiversion rotated tooth or tooth movements around its long
axis
 Transposition when two teeth have exchanged their positions

14. TORSIVERSION
LINGUOVERSION

15. BUCCOVERSION
SUPRAVERSION

16. TRANSPOSITION

17. CAST IN OCCLUSION
 Incisor relationship
 Canine relation
 Molar relation
 Overjet
 Positive – Class II
 Negative – Class III
 Overbite
 Positive – Deepbite
 Negative - Openbite
 Crossbite
 Palatal Crossbite
 Buccal Crossbite – Scissors bite
 Dental midline

19. Molar and canine
relationships

20. MIDLINES

21. 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

22. ARCH PERIMETER ANALYSIS
Tooth Material and Arch Length Discrepancy
(ALD)
 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

23. 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.

24.  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.

25. SPACE REQUIRED
SPACE AVAILABLE

26. 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.

27. 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.

28. INTERPRETATION OF ARCH
PERIMETER ANALYSIS
ARCH LENGTH DISCREPANCY
ALD INFERENCE
0 to 4 mm
Proximal stripping can be carried out
to reduce the minimal tooth material
excess
Avoid extractions
4 to 8 mm
Patient can be treated with or without
extractions depending on lip
procumbency and other factors
Greater than 8mm
Extraction of teeth usually first
premolar might be required

29. PONT’S ANALYSIS FOR ARCH
WIDTH
 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.

30. 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.

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

32. 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.

33.  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
Patient A:
SI = 40mm
CPV = 50 Measured Inter-premolar width = 42mm
CMV = 62.5 Measured Intermolar width = 50mm
Patient B:
SI = 30mm
CPV = 37.5 Measured Inter-premolar width = 40mm
CMV = 46.8 Measured Intermolar width = 48mm

34. 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.

35. 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

36. 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 relationship.
 An alteration in this balance will lead to improper
intercuspation, overjet or spacing

38. Measurements
 Sum of maxillary 12
 Sum of mandibular 12
 Sum of maxillary 6
 Sum of mandibular 6
 Overall ratio
 Anterior ratio

39.  Overall Ratio = Sum of mandibular 12 x 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

40.  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 :

41. Disadvantages of Bolton’s
Analysis
 Does not take into account the sexual dimorphism in the
maxillary canine widths.
 Study done on specific population.

42. BOLTONS ANALYSIS
 Ideal Value for Overall Ratio = 91.3%
 Ideal Value for Anterior Ratio = 77.2%
 Patient A
 Overall Ratio = 94%
 Patient B
 Anterior Ratio = 81%
 Patient C
 Overall Ratio = 88%
 Patient D
 Anterior Ratio = Sum of Mand 6/ Sum of Max 6 = 38/45 =

43. MIXED DENTITION
ANALYSIS

44. AIM
 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

45. 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.

46. 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:

47.  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

48. MOYER’S MIXED DENTITION
ANALYSIS
 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.

49. PROCEDURE
 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.

51. 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 / quadrant=
Sum Of Mandibular Incisors/2 +11
 Predicted width of mandibular canine & premolars / Quadrant
Sum of Mandibular Incisors + 10.5
2

52.  Predicted width of maxillary canine & premolars / quadrant=
Sum Of Mandibular Incisors/2 +11
 Predicted width of mandibular canine & premolars / Quadrant
Sum of Mandibular Incisors + 10.5
2
 Patient A
 Sum of Mandibular Incisors = 24mm
 Predicted width of maxillary canine & premolars?
 Predicted width of maxillary canine & premolars?
 Patient B
 Sum of Mandibular Incisors = 19mm
 Predicted width of maxillary canine & premolars?
 Predicted width of maxillary canine & premolars?

53. RECENT ADVANCES IN
MODEL ANALYSIS

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

55. ADVANTAGES OF
COMPUTERIZED ANALYSIS
 More Accurate
 Easy
 More information:
 Arch form
 Determine asymmetric Arch
 Space analysis
 Rotation
 Prediction

56. QUESTIONS?

57. Group A
Define Anchorage Burn.
Give methods to reinforce anchorage in
Class III cases.
What is Becker’s method of reinforcing
anchorage?
Group C
Define Anchorage Loss.
Give methods to reinforce anchorage in
Class II cases.
What is Begg’s method of preserving
anchorage?
Group B
Define Critical Anchorage.
What are different anchorage types?
What is Tweed’s method of reinforcing anchorage?