Model analysis final

Model Analysis
www.indiandentalacademy.com

Contents
 Introduction
 Definition
 Model analysis
1) Permanent Dentition 2) Mixed Dentition
- Pont’s Index - Moyer’s
- Linder Harth’s - Hixon & Old Fathther’s
- Korkhaus - Nance carey’s
- Arch Perimeter - Huckaba’s
- Bolton’s - Total Space analysis etc.
- Ashley Howe’s etc.
 Recent Advances
 Conclusion

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.

Comprehensive diagnosis
Clinical
Examination
Functional
Analysis
Roentgeno-
Cephalo-
MetricAna-
lysis
Photographic
AnalysisRadiographic
Examination
Study Cast
Analysis
Case History

Definition
 Model analysis is the study
of maxillary and mandibular
dental arches in all the
three planes of spaces
using study models and
radiographs which is a
valuable tool in orthodontic
diagnosis and treatment
planning.

Study Model Fabrication

OBJECTIVES OF IDEAL
ORTHODONTIC STUDY MODELS
 Models accurately reproduce the teeth and their
surrounding soft tissues.
 Models are to be trimmed so that they are
symmetrical and also the asymmetrical arch
form can be readily recognized.
 Models should trimmed so to meet the
proposed ideal measurement.

 Models are to be trimmed in such a way that the
occlusion shows by setting the models on their
backs.
 Models are to have clean, smooth, bubble free
surfaces with sharp angles where the cuts meet.
 The finished models will be treated with a soap
solution to give a glassy mar-proof finish.

USES OF STUDY MODELS
 They enable the study of occlusion from all
aspects.
 They enable accurate measurements to be
made in a dental arch.
 They help in assessment of the treatment
progress.
 They help in motivation of the patient and to
explain the treatment plan.

 It makes possible to simulate treatment
procedures on the cast such as mock surgery.
 Study models are useful to transfer records in
case the patient is to be treated by another
clinician.
 Study models helps to determine the midline
discrepancy.
 It also helps in assessment of surrounding
tissue.

PARTS OF THE STUDY MODELS
 Study models can be divided into two
parts:
 The anatomic portion.
 The artistic portion.

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

TOOTH SIZE-ARCH LENGTH
DISCREPENCY
 ARCH-PERIMETER ANALYSIS
 NANCE-CAREY’S ANALYSIS
 IRREGULAR INDEX
 REE’S ANALYSIS.
 DIAGNOSTIC SET UP
 LAARRY WHITE ANALYSIS
 SANIN & SAVARA ANALYSIS
 TOTAL SPACE ANALYSIS
 TWEED METHOD

MIXED- DENTION ANALYSIS
(Estimating the size of unerupted teeth)
 MOYER’S ANALYSIS.
 TANAKA-JOHNSTON ANALYSIS.
 HIXON-OLD FATHER METHOD.
 HUCKABA ANALYSIS.

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

TOOTH-SHAPE DISHARMONY
 PECK & PECK INDEX.

PHOTOGRAPHIC ANALYSIS
OF STUDY MODEL
 STEROPHOTOGRAMETRY
 OCCLUSOGRAMS
 HOLOGRAPHIC IMAGE ANALYSIS

COMPUTERIZED ANALYSIS
 OSCOPO
 REFLEX METROGRAPHY

Armamentarium
 a) Divider
 b) Ruler
 c) Wedge Ruler
 d) Vernier Caliper
 e) Brass Wire

Measurements Required
 Tooth Measurements
a) Centrals
b) Laterals
c) Canines
d) First Premolars
e) Second Premolars
f) First Molar
 Other measurements
a) Sum of 2 to 2
b) Tooth material
( Sum of 5 to 5 )
c) Total Tooth Material
( Sum of 6 to 6 )
d) Arch Width
e) Arch Perimeter
f) PMD
g) PMBAW etc.

Pont’s Analysis
 In 1909, Pont devised a method of predetermining
an “ideal” arch width based on the mesio-distal
widths of the crowns of the maxillary incisors.
 Pont suggested that the ratio of combined incisor to
arch width ( as measured from the center of the
occlusal surface of the teeth) was ideally 0.8 in the
bicuspid area and 0.64 in the first molar area.
A clinical evaluation. Angle, Orthod ; 1970.

 Pont also suggested that the maxillary arch be
expanded 1 to 2mm more during treatment
than his ideal to allow for relapse.
 Pont’s analysis helps in,
a) Determining whether dental arch is narrow or is
normal.
b) Determining the need for lateral arch
expansion.
c) Determining how much expansion is possible
at the premolar and molar regions.

 Determination of sum of
incisors (S.I)
 Determination of
measured premolar value
(M.P.V)
measured molar value
(M.M.V)

calculated premolar
value (C.P.V)
calculated molar value
(C.M.V)

Inference
 If measured value is less than the calculated value,
then arch is narrow for the sum incisors width and
needs expansion.
 If measured value is greater than the calculated
value, then the arch is wider and there is no scope
for the expansion.

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.

 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.
 Pont’s index is naive in concept and of little use in
rational treatment planning.

Linder Harth analysis
 Similar to Pont’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
64
Where S.I is sum of mesio distal widths of incisors.

Korkhaus Analysis
 This analysis is similar to Pont’s analysis.
 Korkhaus uses Linder Harth’s measurements.
 An orthometer was devised by Korkhaus and
from that ideal arch width in premolar region and
molar region can be determined.
 The perpendicular distance from the inter-
premolar line to the incision for a given S.I can
be determined.

 Introduces a third measurement from the
midpoint of inter- premolar line of upper arch to
a point in between the two maxillary incisors.
Measurements.
a) Arch width in premolar
region & b) in molar Region.
c) Perpendicular distance from
the midpoint of inter premolar
line to incision.

 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.

Korkhaus Measurements.www.indiandentalacademy.com

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

Arch perimeter Analysis
 Many malocclusions are as a result of discrepancy
between arch length and tooth material.
 This analysis helps us to find the difference between
the basal bone and the tooth material i,e in
determining the extent of Discrepancy.
 The same analysis is called “Carey’s Analysis” in
the lower cast.

 Determination of arch
length.
Arch length anterior to
the first permanent
molar is measured
using a 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 the premolars and along
the anteriors and is continued on the opposite side
in the same way upto the mesial surface of the
opposite first permanent molar.

 In case of proclined anteriors, the wire is
passed along the cingulum of anterior teeth.
 If the anterior teeth are retroclined, the brass
wire is passed labial to the teeth.
 If the anterior teeth are well aligned, the wire
is passed over the incisal edges of the
anterior teeth.

 Determination of tooth
material.
The mesio-distal width
of the teeth anterior to
the first molars
(second premolars to
second premolars) is
measured and
summed up.

 Determination of the Discrepancy.
The discrepancy refers to the difference between
the arch length and tooth material.
 Inference.

Drawbacks
 This procedure of accessing arch length does not
appear to be clear-cut in border line cases.
 The visualized form will vary with the individual who
is contouring the wire.

Peck and Peck Index
 Tooth shape (mesio distal and faciolingual) is
determining factor in the presence and absence of
lower incisor crowding.
 Harvey peck and Sheldon Peck present a new
method of detecting and evaluating tooth shape
deviations of the mandibular incisors.
Index for assessing tooth shape deviations.
Am. J. Orthod April 1972

 Orthodontic Odontometry.
 Crown dimensions more frequently reported are
the mesio distal diameter.
 No curently used clinical analysis employs or
even takes into consideration the facio lingual
tooth dimension.
 Both MD and FL dimensions appear to be related
to incisor alignment.
 This index incorporates both dimensions for
orthodontic tooth size analysis.

 According to Peck and Peck, persons with ideal
incisal arrangement had smaller mesiodistal width
and comparatively larger faciolingual width than in
persons with incisal crowding.
 On the basis of this observation, Peck and Peck
suggested certain clinical guidelines.

 Index = M.D X 100
F.L/L.L
 MD/FL index as a
numerical expression
of crown shape as
viewed incisally is
confined to the
mandibular incisors.

 Mean value for lower central incisor should be
88% to 92%.
 Mean value for lower lateral incisor should be
90% to 95%.
 Inference :
a) Lower incisors within or below these
ranges are considered favorably
shaped.
b) Lower incisors with MD/FL index above
these ranges considered to have crown
shape deviations contributing to
crowding phenomenon.

 The reference table provides the computed value
of the MD/FL index, given the MD and FL crown
dimensions.
 Example: Mandibular right lateral incisor having
MD=6.0 and FL=6.3, will have MD/FL index of
95.
 In a given case if the value is more, then authors
recommend Proximal stripping or Tooth
Reproximation.

 Reproximation: Tooth reproximation is a clinical
procedure involving the reduction, anatomic
recontouring, and protection of the mesial and/or
distal enamel surfaces of a permanent tooth.
 A consideration of tooth shape and the MD/FL
index appears essential for the successful
orthodontic management of the incisor
irregularities.

Sanin and Savara Analysis
 Mesio distal crown-size relationships are decisive
variables in the search for,
a) Factors associated with the development of
occlusal and facial irregularities.
b) The possible effects of discrepancies upon
interdigitation during after orthodontic treatment,
c) The isolation of discrepant teeth of minor tooth
malocclusions that may be treated in part by
selective mesio distal grinding and minor tooth
movement.
An analysis of permanent mesio distal crown size.
Am.J.Orthod (59) 1971.

 There is a direct relationship between the
magnitude of the crown-size
differences( regardless of the number of teeth
involved) and the presence of occlusal
irregularities.
 There is also a direct relationship between
number of discrepant teeth( regardless of the
magnitude of the crown size differences) and the
presence of occlusal irregularities.

 The purpose of their study was to examine the
possibility of using a norm of mesio distal size of
the permanent teeth for locating and analyzing
crown-size discrepancies.
 The analysis proposed would contribute to a
more complete evaluation of intra-oral etiologic
factors and a more precise diagnosis and
prognosis of the dental problem.

Mesio distal crown sizes of 51 boys and 50 girls of north west European
ancestry selected from the university of Oregon dental school.www.indiandentalacademy.com

 Some of the characteristics that may be studied
with the assistance of the tables are,
a) The size of the maxillary teeth as a whole relative
to the size of the mandibular teeth as a whole,
b) The size of the individual teeth or groups of teeth
relative to individual teeth or groups of antagonist
teeth, and
c) Discrepancies between right and left sides and, in
all cases, the direction of the discrepancy if
present( small, average or large) and their
magnitude.

 This analysis presents an effective way of
locating and analyzing crown-size discrepancies.
 Crown size patterns differ greatly, even among
good occlusions.
 The complexity of interdigitation in orthodontic
treatment is emphasized.

Ashley Howe’s Analysis
 Ashley Howe considered tooth crowding to be
due to deficiency in arch width rather than arch
length.
 He found a relationship between total width of 12
teeth anterior to the second molars and the
width of the dental arch in the first premolar
region.
A Polygon Portrayal of coronal and basal arch dimensions
in the horizontal plane. Am. J. Orthod. Nov,1954.

Howe’s analysis measurements.

 Determination of total
tooth material.
The mesio distal width
of all the teeth mesial to
the second permanent
molars is measured
with the help of dividers
and the values are
summed up. This value
is called Total Tooth
material (TTM).

 Determination of first
bicuspid coronal arch
width.( BIC.W)
This measurement is
the distance between
the summits of the
buccal cusps of the first
bicuspids.

 Determination of basal
arch width( B.A.W)
above the maxillary first
bicuspids and below of
mandibular first
bicuspids.
 Basal arch width will be
greater than the
coronal arch.

 The canine fossa is found diatal to the canine
eminence. The measurement of the width from
canine fossa of one side to the canine fossa of
other gives the premolar basal arch width
( P.M.B.A.W).
 If the canine fossa is not clearly distinguishable
then the measurement is made from a point
8mm below the crest of inter dental papilla distal
to the canine.

 The percentage
relationship of first
bicuspid width to tooth
material.
BIC.W = %
TTM
 The percentage
relationship of first
bicuspid basal arch
width to tooth material.
B.A.W = %
TTM

 Determination of Basal
arch length.( B.A.L)
In the maxilla the
median line
measurement from
Downs A point
perpendicular to the
occlusal plane , then to
the median point on a
line connecting the
distal surface of the first
molar.

 In the mandibular arch
the measurement is
made from downs B
point to a mark on the
lingual surface of cast
as was incase of the
maxilla.

 Determination of the percentage of arch length
to the tooth material.
B.A.L = %
TTM
 The percentage relationship is more important
than the actual measurement.

Inference
 Howe’s believed that the premolar basal arch
width ( B.A.W) which he called as the canine
fossa diameter should equal approximately
44% of the mesio distal widths of the 12 teeth in
the maxilla, if it is to be sufficiently large enough
to accommodate all the teeth.
 When the ratio is less than 37%, he considered
this to be a basal arch deficiency necessitating
extraction of premolars.

 If the premolar basal
arch width is greater
than the premolar
coronal arch width
(B.A.W>BIC.W),
expansion of the
premolars may be
undertaken safely.

Advantages
 Howe’s analysis is useful in treatment planning
of problems with suspected apical base
deficiencies and deciding to whether to,
1) Extract teeth,
2) Widen the dental arch, or
3) Expand rapidly the palate.
 Howe’s analysis is applicable to each arch.

Wayne A. Bolton Analysis
 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 get ideal
interdigitation, overjet, overbite and alignment of
teeth.
 Bolton’s analysis helps to determine the
disproportion between the sizes of the maxillary
and the mandibular teeth.
Disharmony in tooth size and its relation to the analysis and
treatment of malocclusion. Angle orthod (28) 1958.

 To attain an optimum inter- arch dental
relationship, the maxillary tooth material should
approximate desirable ratios, as compared to
the mandibular tooth material.
 Average proportion between upper and lower
teeth in overall and anterior region helps to
create a normal overjet and overbite.

Measurements
 Sum of mandibular 12.
 Sum of maxillary 12.
 Sum of mandibular 6.
 Sum of maxillary 6.
 Overall Ratio.
 Anterior Ratio.

 Determination of overall Ratio.
According to Bolton, the sum of mesio distal
widths of the mandibular teeth anterior to the
second permanent molar is 91.3% the mesio
distal widths of the maxillary teeth mesial to the
second molars.
Overall Ratio = Sum of mandibular 12 X 100
Sum of maxillary 12
1) If ratio is less than 91.3%, maxillary tooth
material excess.
2) If ratio is more than 91.3%, Mandibular tooth
material excess.

 Determination of anterior ratio.
The sum of mesio distal width of the
mandibular anteriors to the mesio distal width
of the maxillary anteriors should be 77.2%.
Anterior Ratio = Sum of mandibular 6 X 100
Sum of maxillary 6
1) If ratio is less than 77.2%, maxillary anterior
excess.
2) If ratio is more than 77.2%, Mandibular anterior
excess.

Advantage & Disadvantages
 When contemplating the extraction of four
premolars, it is useful, before selecting the teeth
for extraction, to ascertain the effects of various
extraction combinations on these ratios.
 Study done on specific population.
 Does not take into account the sexual
dimorphism in the maxillary canine widths.

Irregular Index
 Given by Robert M. Little.
 Anterior dental crowding is perhaps the most
frequently occurring characteristics of
malocclusion.
 Adjectives such as mild, moderate and severe
etc. are descriptively helpful but still allow a wide
range of interpretation.
The irregularity index ; A quantitative score of mandibular
anterior alignment. AJO, Vol. 68 : 1975.

Method
 The proposed scoring method involves
measuring the linear displacement of anatomic
contact points, of each mandibular incisors from
the adjacent tooth anatomic points.
 The sum of these five displacements represent
the degree of anterior irregularity.

 Each of five
measurements
represents, in horizontal
linear distance between
the vertical projection of
the anatomic contact
points of adjacent teeth.

Calculations/ Inference
 The results of the irregularity index can be
correlated with the scale ranging from 0 to 10
formed by the subjective ranking.
 0 – Perfect Alignment.
 1,2,3 - Minimum irregularity.
 4,5,6 - Moderate irregularity.
 7,8,9 – Severe irregularity.
 10 to 20 – Very severe irregularity.

Rees Analysis
 Given by Denton J. Rees.
 All the measurements are made on study
models which should be essentially accurate.
 Special attention given to the extension into the
mucobuccal fold in order to approximate basal
bone to at least the distal of first permanent
molar.
A method of assessing the proportional relation of apical bases &
contact diameters of teeth. AJO, VOL: 39: 1953.

Method
 A ruler is placed against the
side of the cast, at right
angles to the occlusal surface,
and a line is drawn at the
mesial contact point of each
first permanent molar.
 The third line is drawn through
the midline contact of upper
and lower central incisor.
 This line is extended to a point
8-10mm from the gingival
margin in the apical direction.

 A piece of scotch tape 5 inches long is cut into strips
approximately 1/8th
inch wide and a thin strip of tape is then
placed so that one end is superimposed on the molar mark.
 The tape is pressed firmly to the cast to pass through the
incisor point, and then trough the opposite molar point.
 The teeth on each cast from second premolar to second
premolar are recorded at their greatest mesio distal
diameter.

Calculations
 Following chart permits a quick analysis on any
sets of casts.
UB to UT =1.5 to 5 - mean 3.5 - range 3.5
LB to LT =2 to 7 - mean 4.5 - range 5
UB to LB =3 to 9.5 - mean 6.5 - range 6.5
UT to LT =5 to 10 - mean 7.5 - range 5
Where U = MAXILLA; L= MANDIBLE;
B= APICAL BASE; T= TOOTH CROWN

Inference
 By comparing the average normals to the
measurements taken on the set up casts,
following points of diagnostic importance can
be derived.
1) UB to UT or LB to LT.
If discrepancy exists, in borderline cases,
internal and external muscular forces, facial
esthetics, and other factors will determine the
treatment plan.

2) UB to LB.
If discrepancy exists, reduction of teeth and
base may be necessary in one arch, or if not
indicated, expansion of other arch is the only
alternative.
3) UT to LT.
If discrepancy beyond normal range are
present, tooth mass is reduced in one arch or
increased in the other by judicious placement
of crown or inlays.

Diagnostic Set up
 HD Kesling introduced the diagnostic set up
which is made from an extra set of trimmed
study models.
 Also called as Prognostic Set Up, as it helps to
ascertain precisely the amount and direction of
each tooth to be moved.
 For visualizing space problems in three
dimensions in the permanent dentition, the teeth
are cut off from the cast and reset in a more
desirable position.
The Diagnostic Set-up with consideration of third dimension
Am. J. Orhtod, 42 ; 740-748, 1956

Steps
 Obtain an accurate
wax bite. Trim
posterior portion of
the bases of the casts
with the wax bite
interposed so that the
bases are flush.
 Drill a whole trough
the alveolar portion of
the cast well below
the gingival margin of
the teeth.

 Insert a fine saw blade
through the hole and cut
up to the crest of the
gingival margin between
two of the teeth.
 Cut along the line of the
arch, well beneath the
gingival margin of the
teeth, and come up again
at the point of the gingival
crest below the contact
point on the opposite side
of the tooth.

 Repeat this for all the
teeth to be cut off the
cast. Do not cut
through the contact
points. Cutting up to
the gingival crest will
permit gentle
breaking of plaster
without damage.
 Align the teeth and
wax them into the
desired positions.

 It is best not to cut off all the teeth so that the
bite relationship can be kept.
 A more accurate method involves taking a wax
bite in the retruded contact position, mounting
the casts on the adjustable articulator, and
finishing the diagnostic set up within the limits of
the jaw relationships thus imposed.
 One may combine the cephalometric analysis
and prediction of incisal positioning and
angulations with the prognostic set up.

Uses
 Aids in treatment planning as it helps to visualize
tooth size arch length discrepancies and
determine whether extraction is required or not.
 The effect of extraction and tooth movement
following it on occlusion can be visualized.
 It also acts as a motivational tool as the
improvements in tooth positions can be shown
to the patient.

Space Analysis
 To quantify the amount of crowding within the
arches.
 Because treatment varies depending on the
severity of the crowding.
 Principle : Since malaligned and crowded
teeth usually result from lack of space, this
analysis is primarily of space within the
arches.

 It requires a comparison between the amount
of space available for the alignment of
crowded teeth and amount of space required
to align them properly.
 Analysis can be done either directly on the
dental casts or computer after appropriate
digitization of the arch and tooth dimensions.

Method
 Space available
 Accomplished by
measuring arch perimeter
from first molar to the other,
over the contact points of
posterior teeth and incisal
edges of anteriors.
 There are two basic ways:
1. By dividing the dental arch
into segments that can be
measured as straight line
approximations of the arch.

2. By contouring piece
of wire to the line of
occlusion and then
straightening it out for
measurement.
 The first method is
preferred for manual
calculation because of
its greatest reliabilty.

 Space Required
 Done by measuring the
mesiodistal width of
each tooth from contact
point to point, and then
summing the widths of
individual teeth.

Inference
 If the sum of widths of the permanent teeth is
greater than the amount of available space,
there is an arch perimeter space deficiency and
crowding would occur.
 If space available is larger than the space
required (excess space), gaps between some
teeth would be expected.

 Space analysis carried out in this way is based
on two important assumptions:
1. The anteroposterior position of the incisors is
correct ( i,e the incisors are neither excessively
protrusive nor retrusive), and
2. The space available will not change because of
growth.
 Neither assumptions can be taken for granted.

References
 ORTHODONTICS
PRINCIPLES AND PRACTICE,
- GRABER T.M.
 Handbook of orthodontics.
- ROBERT E. MOYERS.
 Contemporary orthodontics.
- WILLIAM R. PROFFIT.
 Orthodontics
current principles and concepts.
- THOMAS M. GRABER & Vanarsdall

 Index for assessing toothe shape deviations.
Am. J. Orthod April 1972.
 A method of assessing the proportional relation
of apical bases & contact diameters of teeth.
AJO, VOL: 39: 1953.
 Accurate arch – Discrepancy measurements.
AJO, Vol. 72: 1977.
 The irregularity index ; A quantitative score of
mandibular anterior alignment. AJO, Vol. 68 :
1975.

 Disharmony in tooth size and its relation to the
analysis and treatment of malocclusion. Angle
orthod (28) 1958.
 A Polygon Portrayal of coronal and basal arch
dimension
in the horizontal plane. Am. J. Orthod.
Nov,1954.
 An analysis of permanent mesio distal crown
size. Am.J.Orthod (59) 1971.

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