Study models

This topic include the various types of study regarding the model cast

1. Model
Analysis
Dr. SURESH KUMAR.K
Dept of Orthodontics and Dentofacial
Orthopedics
S.B.Patil institute for dental sciences and
Research

2. Introduction
•Success in orthodontic treatment –Diagnosis.
•Many diagnostic aids are available today but
study models are oldest.
•Model analysis is an adjunct in diagnosis and
treatment planning. It should hence be
correlated with the other data in the diagnosis
before formulating any treatment plan.

3. •Orthodontic study models are
plaster reproductions of the
teeth and their surrounding soft
tissues.
•They provide three dimensional
view of the dentition.

4. Parts of a study model
Anatomic portion:-It is
the actual impression of
dental arches and
surrounding soft tissue
structures.
Artistic portion:-plaster
base that supports the
anatomical portion.

5. IDEAL ORTHODONTIC STUDY
MODELS
•Models accurately reproduce the teeth and
their surrounding soft tissues.
•Models are to be trimmed so that they are
symmetrical which helps in identifying arch
asymmetry.
•Models should trimmed so to meet the
proposed ideal measurement.

6. Steps in construction of study models
1.Impression making.
2.Disinfection of the impression.
3.Casting the impression.
4.Basing and trimming of the cast.
5.Finishing and polishing of study
models.

7. 1.Impression making
Patient should be asked to rinse the mouth before and
after impression.
Should record hard and soft tissues completely.
The impression should have no voids, borders of
impression should be rolled with good extension into the
vestibule with the frenal attachment recorded.
Maxillary impression should not extend to the soft palate
which can cause gag .
Use high flange orthodontic trays and it should include
last erupted molars and 3mm distal to it.
Irreversible hydrocollids are widely used for impression
making.(alginate)

8. 2. Impression disinfection
Impressions rinsed thoroughly in water
to wash away blood , saliva & debris .
Disinfection is done by soaking in a 2%
gluteraldehyde, iodophors or sodium
hypochlorite .

9. 3. Casting the impression
Through rinsing of impressions after disinfection is
necessary to avoid possible adverse effects on study
model .(Molinari et ai.,1991)
Stone is mixed in vacuum mixer to avoid air
incorporation.
The stone is poured into the tooth portion first with
the impression held over the vibrator ,then rest of the
anatomical part are filled
impressions are poured using white orthodontic
stone.
The mix is vibrated to eliminate air bubbles.
After 30-60 minutes of set the separation is done
carefully to avoid breakage of cast or teeth

10. 4. Basing and trimming of the cast
After the set of stone in the impression, stone is
poured into base former and anatomical part is
seated into the stone in base former considering
following factors .
1.Occlusal surface parallel to the base.
2.Mid line coinciding with anterior vertex.
3.Mid line perpendicular to the posterior base.
4.There should be about 5mm of stone distal to the last
erupted tooth.
4.Thickness of base should be 13mm to 15mm.
(13mm as per ABO STANDARD)
5.Total height should be 7 to 7.5cm or each cast
measuring 3.5 to 4cm.
6. The posterior plane of upper & lower cast should be
on same plane.
7.Borders are kept 5-6mm around .

12. Study Model Fabrication

13. Base former angular
measurements
66deg
22 deg
66deg
79deg

14. 5. Finishing and polishing
Artistic portion of study model should be
polished using fine grained sand paper.
Care should be taken not to round off
the edges of model.
Final polishing done by placing in soap
solution , then dried followed by buffing
to acquire a smooth and shiny surface.

15. Study models are used for
•Space analysis.
•assess and record the dental anatomy.
•assess and record the intercuspation.
•assess and record arch form.
•assess and record curves of occlusion.
•evaluate occlusion, with aid of articulator.
•To detect abnormalities ( distorted arch form).
•Teeth /tooth migrations
•To provide a record before, immediately after,
and several years following treatment for the
purpose of studying treatment procedures.

16. Sagital occlusal
relationship
Cross bites anterior
,posterior

17. Number &
morphology of teeth
are noted
Type of arch form

18. Overjet & Over bite

19. Vertical position of teeth

20. Curve of Spee

21. Asymmetry of dental arches
Symmetrograph according Bernklau

22. Permanent & mixed dentition model
analysis
Permanent Dentition:
1.Pont’s index.
2.Korkhaus analysis.
3.Linder harth index.
4.Arch perimeter
analysis.
5.Bolton tooth size ratio.
6.Ashley Howe’s
analysis.
7.Peck and Peck index.
Mixed dentition :
1.Moyers mixed dentition
analysis.
2.Huckaba’s analysis.
3.Hixon & old father
method.
4.Nance carey’s analysis.
5.Total space analysis.

23. TOOTH SIZE-ARCH WIDTH
DISCREPANCY
•PONT’S ANALYSIS.
•LINDERHARTH ANALYSIS
•KORKHAUS ANALYSIS
•ASLEY–HOWE ANALYSIS

24. TOOTH SIZE-ARCH LENGTH
DISCREPENCY
•ARCH-PERIMETER ANALYSIS
•NANCE-CAREY’S ANALYSIS
•IRREGULAR INDEX
•DIAGNOSTIC SET UP
•TOTAL SPACE ANALYSIS

25. UPPER/LOWER TOOTH SIZE
DISHARMONY
BOLTON’S TOOTH RATIO ANALYSIS

26. TOOTH-SHAPE DISHARMONY
PECK & PECK INDEX.

27. Armamentarium
a) Ruler
b) Digital Caliper
c) Brass Wire
d) Cast

28. Mixed dentition space analysis
•Diagnosis.
•Space management strategies such as
space maintainers ,space regaining
appliance therapy ,serial extraction
decision .

29. Mixed dentition space analysis
Three factors are
considered mainly
Sizes of all
permanent teeth
Expected changes
in the arch perimeter

30. There are three basic approaches for
space analysis in mixed dentition
1.Measurement of teeth on radiographs
2.Estimation from proportionality tables
3.Combination of radiographic and prediction
table method

31. Measurement of teeth on radiograph
Nance analysis
Estimation from proportionality tables
Moyer’s analysis
Tanaka Johnston analysis
Combination of radiographic and prediction
table
Satley and Kerber analysis

32. Huckaba Analysis
•Recommended by HUCKABA. G. W in 1964.
•Radiographic measurement of unerupted tooth
periapical film.
•It is based on the assumption that degree of
magnification for a primary tooth will be the
same as that of its underlying permanent
successor on the same film.

34. Measurement of teeth on radiographs
•Requires undistorted radiographic image
•It is necessary to compensate for
enlargement of the radiographic image
True width of E = True width of unerupted
PM
Apparent width E Apparent width of unerupted
PM

35. Nance analysis
•Helps in diagnosing tooth size arch perimeter discrepancy.
•M-D width of the erupted permanent central & lateral incisor
teeth from the cast measured with digital caliper.
•(3,4,5) from radiographs are measured.
•The total M-D width of all the teeth in each quadrant will indicate
space required to accommodate the permanent.
•The arch perimeter measurement.
A piece of .026 inch brass ligature wire is placed on the
lower cast extending from the mesial contact point of the first
permanent molar on one side of arch through contact points of
primary molars ,incisal edges & similarly upto the first the first
permanent molar on the opposite side in a smooth curve.
•The space required & space available are compared to arrive at
the arch perimeter discrepancy

36. Moyer’s analysis
Moyers (1969)
The mesiodistal width of the lower incisors is used to
predict the size of both the lower and upper
unerupted canines and premolars.
•Ballard,Wylie & Greivereported strong correlation
between mesiodistal widths of lower permanent
incisors & that of upper & lower premolars’ &
canine.
•Estimation (3,4,5) of upper and lower arches done
using proportionality tables.

37. Advantages:
•It has minimal error and the range of
possible error is precisely known if used
from the same population.
•Radiographs are not required.
•It is not time consuming.
•Does not require special instruments.
•Can be used for both the arches.

38. Procedure:
•The sum of mesiodistal width of lower mandibular
incisors measured.
•The space left behind for 345 on either side
measured.
•By using Moyer’s probability chart the M-D width of
upper and lower 3,4,5 obtained.
•The space available and space required in all the four
quadrants compared.
•The Moyers analysis recommended its use
at 75% probability level, which clinically, is
thought to give protection on the crowded
side.

39. Moyers prediction values

40. Tanaka Johnston method:
They developed another way to use the width
of lower incisors to predict the size of
unerupted canines and premolars.

41. Hixon and Oldfather (1958)
•Combination of radiographic and prediction
table methodgiven by Hixon and Oldfather
(1958)
•He added the maximum mesio-distal diameters
of the permanent mandibular central and lateral
incisors with those of the unerupted premolars
measured on the intraoral periapical film. The
summation is called the "measured value,"
which is used to determine the "estimated
value" from prediction charts.
•The prediction charts compensate for
magnification inherent in radiography and are
valid only for measurements taken from
radiographs from a long-cone (16 inch) x-ray
unit.

42. •The modifications to the original Hixon and
Oldfather (1958) improved its predictive value
(Staley and Kerber, 1980; Staley et al., 1979;
1983; Bishara and Staley, 1984),
•particularly when separate equations were
used for males and females from the same
Iowa Facial growth study subjects (Staley et
al., 1979).
•The revised equations resulted in a lower
standard error of estimate as compared to the
original equation (Staley and Kerber, 1980).

43. Combination of radiographic and
prediction table
Staley and Kerber
method
This method is used
only for
mandibular arch
Requires
periapical
radiograph.
It is quite accurate
method

44. All three methods are based on data from
white school children of northern European
descent.
If patient fits this population group ,the Staley
Kerber will give the best result followed by
Tanaka Johnston and Moyer’s.

45. Permanent dentition
analysis

46. Permanent dentition analysis:
•Carey’s Analysis
•Pont’s Analysis
•Ashley Howe’s Analysis
•Korkhaus Analysis
•Bolton’s Analysis
•Peck and Peck analysis
•Little’s irregularity index

47. Carey’s analysis & Arch perimeter
analysis
Carey’s analysishelps in
determining the extent of tooth
size arch perimeter
discrepancy
Similar analysis on upper cast
is called Archperimeter
analysis

48. It is used to evaluate
-tooth material (space required)
-arch perimeter (space available)
Determination of tooth
material
M-D width of teeth anterior to first molars
is measured and summed

49. Inference
If discrepancy is
0-2.5 mm : minimal tooth material
excess,proximal reduction can be
carried out
2.5 –5 mm: need to extract second PM
> 5 mm :need to extract the first PM

50. Cephalometric correction
N-A Line reference
to upper central
incisor.
4mm/22 deg
Part of Steiner
analysis

51. Cephalometric correction
N-B REFERENCE
LINE TO LOWER
INCISAL EDGE .
4mm/25deg

52. Cephalometric correction
N-Pog reference line
is used.
Normal range
Distance of upper
incisal edge to N-
Pog line +2 to +4
Distance of lower
incisal edge to N-
Pog line +2 to -2

53. Pont’s analysis
Introduced this analysis in (1909)
This analysis indicates contracted or expanded
arches.
Measurement of M-D of 4 maxillary incisors
determines the ideal arch width in PM and
molar area before the eruption of canines.
In case there is missing or abnormal variation in
size of upper incisor, then Tonn’s formula is
used to calculate the normal size of upper
incisors for the patient based on the size of
lower incisor.
Tonn’s formula size of upper incisors=(size of
lower incisors*4/3)+0.5

54. Pont’s Index
•In 1909 Pont presented to the profession a system of
analysis whereby ,mere measurement of the four
maxillary incisors automatically establish the widths of
the arches in the premolar & molar region .
•Pont’s index can give an approximate indication of
degree of narrowness & also the amount of expansion
required in order that the arches be of sufficient size to
accommodate the teeth in perfect alignment.
•His method helps to predetermine the arch widths before
eruption of canine.

55. •Pont stated: “I must warn you that my research
has been made exclusively on the jaws of
French race and I would be much pleased if at
later date others of my colleagues could verify
the correctness of this on other race”
•He in his article did not indicate the sample size
except to say that he used normal complete
dental arches.

56. combined mesiodistal
width of the maxillary (
2 1/ 1 2 )=X
The ideal arch width in
premolar region is
calculated by
(X/80)×100
The ideal arch width in
molar region is
calculated
by,(X/64)×100

57. Measurement of premolar & molar
arch width.
The points used in this
analysis are lowest
most point on
transverse fissure of
upper 1
st
premolar.
Central pit of upper first
molar
Facial contact point of
1
st
& 2
nd
lower
premolars.
Tip of distobuccal cusp
of lower 1
st
permanent
molar

59. If measuredvalue< calculated value
need for expansion
Inference

60. Review of literature
•Hotzsuggested that deviation from Pont’s
index may be related to narrowly shaped
dental arches. He concluded that due
consideration must be given to the shape of
skull in assessment of arch form & width.
•Grevefound low correlation between the
sum of upper incisor width & arch width at
premolar & molar .
•Korkhausproposed index formula of 84 &65
instead of 80 &64 as in Pont’s index
estimation. His study was of Rhineland
population

61. Drawbacks
•Analysis is based on study of French
population and hence, its universal validity is
questionable.
•Maxillary laterals are the most commonly
missing and malformed teeth (i,e Peg
shaped).
•Does not consider skeletal mal-relationships
and relationship of teeth to the supporting
bone.

62. •Did not indicate the sample size
•Relationships between the form of the skulls and
form of dental arch
•Reliability of index should be tested in other
populations.
•Mandibular arch form and mandibular intercanine
diameter have been repeatedly found to be more
reasonable treatment guides for both maxillary and
mandibular ultimate arch widths than the pont’s
index.
Disadvantages of Ponts analysis

63. Linder Harth analysis
•Similar toPont’s analysis.
A variation has been proposed to determine
the calculated premolar value and calculated
molar value.
Calculated premolar value : S.I X 100
85
Calculated molar value : S.I X 100
65
Where S.I is sum of mesio distal widths of incisors.

64. Korkhaus analysis
He proposed two index
1.Anterior arch length index
2.Palatal height index

65. 1. Anterior arch length index
Introduced in (1938)

66. For a particular width of incisors there is a
specific value of distance from the incision to
the inter premolar line according to Korkhaus.
Inference :
a) This analysis tells about the arch width.
b) If the perpendicular distance is more
than ideal, then anterior teeth are
proclined.
c) If the perpendicular distance is less than
the ideal, then the anterior teeth are
retroclined.

67. For the values noted
the mandibular
value (Ll) should be
equal to the
maxillary value (Lu)
in millimeters minus
2mm.

68. Formula for calculating
the standard value of
upper anterior arch
length
Sum of upper incisors x
100
160

69. Palatal height index
This index was introduced in (1939). Purpose
of this index was to evaluate the palatal
shape.
Posterior arch width= mesial pits on occlusal
surface of upper first molar
Palatal height= perpendicular distance from
the connecting line between the reference
points for posterior arch width to the surface
of the palate

70. Palatal height analysis
Palatal
height
index
=
Palatal height ×100
posterior arch width
Palatal height is measured in the
midsagittal plane in the region of
the upper 1
st
molars on the level
of the occlusal plane using
korkhaus three dimensional
orthodontic divider.
The average index value is 42%
Inference:-
-If >42%high palate.
-If <42%shallow palate.,

71. Howe’s Analysis(1954)
•Howe developed analysis on the premise
that in normal dention, the width of maxilla
in the first premolar area must be at least
43% of it’s total tooth material.
The study was done on 14 normal dentition
& subsequently on 200 case

72. •Howes analysis is useful in planning treatment
of problems with suspected apical base
deficiency & decide whether to
1.Extract
2.Widen the dental arch
3.Rapid palatal expansion

73. Method
Total tooth material (T.T.M.)
The tooth material refers to combined mesiodistal
measurement of all teeth in the arch from right
permanent first molar to left first permanent molar.
Arch width in first premolar (premolar diameter-
PMD) region was measured just inside the summit
of the buccal cusps of first premolar.
The width of apical basal bone is measured from
right canine fossa to left canine fossa ,just above
the first premolar root apice distal to canine
eminence (PREMOLAR BASAL ARCH WIDTH ).

74. Ratios were derived separately for maxilla and
mandible
PM ratio= PM distance x 100
TTM
Basal arch width ratio= Basal arch width x 100
TTM
Basal arch length ratio= Basal arch length x 100
TTM

75. Inference
The P.M.B.A.W.and P.M.D. are compared.
If P.M.B.A.W is < P.M.D. arch expansion is
not possible.
If P.M.B.A.W is > P.M.D arch expansion can
be undertaken safely.
P.M.B.A.W Ratio:
The ratio between the apical base width at
the premolar region and the total tooth
material is called the P.M.B.A.W
percentage.

76. Inference
P.M.B.A.W % = P.M.B.A.W. x 100
T.T.M.
IF P.M.B.A.W.% is 37% or less. Need for extraction
If P.M.B.A.W.% is 44% or more. Treatment by non
extraction
If P.M.B.A.W.% is 37-44%. Borderline case

77. Conclusion on Howes analysis
•According to moyer, Howes analysis is
superior to Ponts.
•Mandibular apical base is more critical
than maxillary in treatment decision

78. Bolton Analysis
•Introduction
In order for the maxillary teeth to fit well with
mandibular teeth ,there must be a definite
proportion.
Disproportion can exist which can be recognized
by observation but may also remain undetected
by inspection alone, this discrepancy become
evident during treatment specially during
finishing stage.
Bolton analysis detects such interarch tooth size
disproportions

79. •Bolton in 1958
introduced Bolton
analysis.
he studied 55 cases
with excellent
occlusion.
METHOD:
Mesiodistal
dimensions of teeth
were measured.

80. Method continued:
1. Sum of mandibular 12
teeth
2. Sum of maxillary 12
teeth
3. Sum of mandibular 6
teeth
4. Sum of maxillary 6 teeth
Percentage relationship of M-D width of
mandibular anteriors to maxillary anteriors.
Anterior ratio = Sum of mandibular 6 x100
Sum of maxillary 6
Anterior ratio was given as 77.2% and standard
deviation 1.65

81. Overall ratio:
Percentage relationship of mandibular
arch length to maxillary arch length.
Overall ratio = Sum of mandibular 12 x100
Sum of maxillary 12
Overall ratio was given as 91.3% and
standard deviation 1.91

82. If ratio exceeds the normal ratio, it indicates
the discrepancy in the mandibular tooth
material excess.
If value is less, then the discrepancy in
maxillary tooth material tooth excess.

83. The following ratio’s were established by
Bolton:
Overall ratio:
Percentage relationship of mandibular arch
length to maxillary arch length.
Overall ratio = Sum of mandibular 12 x100
Sum of maxillary 12
Overall ratio was given as 91.3% and
standard deviation 1.91

84. Table of average values for the overall and
anterior ratio’s of maxillary and mandibular
tooth width according to Boltan

85. •Quick check for anterior tooth size discrepancy
can be done by comparing the size of upper &
lower lateral incisors. The upper is expected to
be wider than lower lateral other wise there is a
Bolton discrepancy
•Similarly the M-D width difference of lower
second premolar & upper second premolar
should not be greater than 1.5mm

86. Drawbacks of Bolton’s analysis
Bolton(1958, 1962)
Results tabulated were derived from the use of mean
figures. So one must consider each patient as an
individual.
Larry White(1982)
Coefficient of correlation b/w the anterior and overall
ratios was very low.
WCraig(1995)
significant measurement error occurs in cast with
more that 3mm crowding advocated bolton analysis
be used as screening tool

87. D.J.Rudolph, (1998)
Geometry of arch form was not considered.
Labio-lingual thickness of teeth is not taken
into account.
Axial inclination of teeth was not considered.
Sexual dimorphism in maxillary cuspids was
not considered.
overjet , overbite influence

88. Digital Models
•Computers have become a mainstay in almost
every workplace.
In the 1990s, digital radiographs, photographs
& electronic charts were introduced
•Recently, computer models have been
developed. OrthoCAD (Cadent
www.orthocad.com),
•e-models (Geodigm Cor-technology in
orthodontic )

89. 3-dimensional imaging methods of the dentition,
which can generally be classified as:
1.Destructive and non-destructive scanning.
2.Direct and indirect methods
These includes:
1.Holography
2.Structured light principle.(Direct dental imaging using
a recently developed, light-based 3D-intraoral
scanner (OraScanner™ from www.OraMetrix.com).
3.Various types of lasers.
4.CT scanning

90. Intraoral 3D Camera (Image
courtesy of OraMetrix, Int)
A defined pattern is projected onto the dental
crowns and its distortion is recorded by a small
video camera. The stamp-sized images are
streamed to a computer, processed and stitched
together to create a complete dental arch. A
dental arch can be imaged in approximately one
minute.

91. HOLOGRAPHY
•A method of three dimensional morphometry in which
contour maps are produced from overlapping
interference fringes created when an object is illuminated
by beams of coherent light issuing from different point
source.
•Materials
Holography camera
•Disadvantages
Expensive
Difficult to produce
Cannot be manipulated as a set of study models can
Poor quality of recording

92. Laser scanning of Stone Model
(Image courtesy of Geodigm, Corp).
OrthoCAD™ software has been developed by
CADENT,(Laser based system multiaxis
robot to obtain several perspectives of the
plaster model)
Alginate impressions of the maxillary
and mandibular dentitions, together with a
bite registration are required for the
construction of 3D digital study models.
downloaded manually from the worldwide
website using a utilitycalled OrthoCAD
Downloader. The average file size for each
3D model is 3 Mb.

93. Computed tomography
•Images plaster model or impressions
directly (HYTEC Inc ,Los Alamos ,New
Mexico)

95. Digital study models
Advantages
Virtual casts can be kept in
digital format & hence
eliminating storage problems.
Immediate data transmission.
Measurements on digital casts
is easy, accurate & automatic.
Digital images can be made
bigger and hence localizing
anatomic points easily.
Digital study casts can be
used for patient motivation.
Stores original malocclusion
in 3D formate.
Disadvantages
If the plaster dental
casts are poor, than the
obtained digitalized
images will be altered
during digitization .
Dental images in mixed
dentition are difficult to
recognize and measure.
Digitalizing dental casts
is a laborious process
that has always to be
made under the same
conditions.

96. •Joshua:Digital orthodontic study models (e-
models) are a valid alternative to traditional
plaster study models .
•Bell & AyoubThe average difference between
measurements of dental casts and 3D images
was 0.27 mm. This difference was within the
range of operator errors (0.10–0.48 mm) and
was not statistically significant (P< 0.05)

97. conclusion
The technological advances helps clinician
to discharge health care more efficiently
provided one understands the advantages
& disadvantages or limitations thoroughly
since skill & knowledge can not be
replaced.

98. References
ORTHODONTICS PRINCIPLES AND PRACTICE ,
-GRABER T.M.
Handbook of orthodontics.
-ROBERT E. MOYERS.
Contemporary orthodontics.
-WILLIAM R. PROFFIT.
Orthodontics Current Principles and Techniques.
-THOMAS M. GRABER & Vanarsdall
Orthodontic Diagnosis
-Thomas Rakosi
Textbook of Orthodontics
-Bishara S.E
A Study Of Pont's, Howes', Rees', Neff's And Bolton's Analyses On Class I
Adult Dentitions*
JohnStifter B.S., D.D.S. Angle orthodontist 1958,vol28 ;no4: 215–225.

99. References
D.J.Rudolph, P.D.Dominguez, K.Ahn, and
T.Thinh.1998: The use of tooth thickness in
predicting intermaxillary tooth-size
discrepancies.The Angle Orthodontist: Vol. 68, No.
2, pp. 133–140.
W. Craig Shellhart, D. William Lange, G. Thomas Kluemper, E.
Preston Hicks, and Alan L. Kaplan: Reliability of the Bolton
tooth-size analysis when applied to crowded dentitions. The
Angle Orthodontist: Vol. 65, No. 5, pp. 327–334.
Assessment of the accuracy of a three-dimensional imaging
system for archiving dental study models
Journal of Orthodontics, Vol. 30, No. 3, 219-223, September 2003