Model Analysis
Model analysis
Model analysis is the
study of maxillary &
mandibular dental arches
in all three planes of
space(sagittal, vertical,
transverse planes ) using
study models &
radiographs which is a
valuable tool in
orthodontic diagnosis &
treatment planning
• DIFFERENT IMPORTANT ANALYSIS ARE AS
FOLLOWS
• CAREY’S ANALYSIS
• BOLTON’S ANALYSIS
• ASLEY–HOWE ANALYSIS
CAREY’S ANALYSIS
• The arch-length-tooth material discrepancy--calculated with the help of Carey’s analysis.
• It is performed on lower cast.
( same analysis on upper cast is called Arch Perimeter Analysis)
PROCEDURE
The arch length is measured
anterior to the first permanent
molar using a soft brass wire.
Wire
mesial aspect of
lower first permanent molar
buccal cusps of premolars till
incisal edges of the anterior
continue upto mesial of the
first molar of the contra lateral
side.
• If anteriors are proclined
brass wire should be passed along the
cingulum of anterior teeth
• If anteriors are retroclined
along the labial surface
Total tooth material
• The mesiodistal width of teeth
anterior to first molar are measured
& summed up as total tooth
material.
• The difference between the
arch length & the actual
measured tooth material gives
the discrepancy .
• INTERPRETATION If the arch
length discrepancy is:• a) 0-2.5mm:- proximal stripping
• b) 2.5-5mm:- extraction of
second premolar
• c) Greater than 5mm:extraction of first premolar
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 & mandibular arch to get ideal
interdigitation, overjet, overbite & alignment of
teeth to attain an optimum interarch relationship
• Bolton’s analysis helps to determine the
disproportion between the size of maxillary &
mandibular teeth
PROCEDURE
• The sum of mesiodistal
diameter of the12
maxillary teeth & the sum
of the mesiodistal
diameter of the
12mandibular teeth are
determined
• In same manner the sum
of 6 maxillary anterior
teeth & the sum of 6
mandibular teeth is
determined.
• OVERALL RATIO:sum of mesiodistal width of mandibular 12 teeth
sum of mesiodistal width of maxillary 12 teeth
X 100
= 91.3%
ANTERIOR RATIO:sum of mesiodistal width of mandibular 6 teeth
sum of mesiodistal width of maxillary 6 teeth MEAN
X 100
= 77.2%
• INFERENCES:
• -If the ratio is more than mean value, then the mandibular
tooth material is excessive.
• If the ratio is less than mean value, then the maxillary tooth
material is excessive.
• Bolton prefers to do proximal stripping on the upper arch if
the upper anterior tooth material is in excess & extraction of
lower incisor, if necessary to reduce tooth material in the
lower arch
• Overall ratio•
Maxillary excess = maxillary 12
Mandibular excess =
•
Mandibular 12
mandibular 12 X 100
91.3
maxillary 12 X 91.3
100
• Anterior ratio
•
•
Maxillary anterior excess= maxillary 6
•
•
Mandibular anterior excess =
mandibular 6
mandibular 6 X 100
77.2
maxillary 6 X 77.2
100
ASHLEY HOWE’S ANALYSIS
• He considered tooth crowding to be
due to deficiency in arch width rather
than arch length.
• PROCEDURE
TTM- (Total Tooth Material )
• Refers to sum of the mesiodistal width
of the teeth from first molar to first
molar
PMD- (Premolar Diameter )
• PMD- (Premolar
Diameter )
 Arch width measured
from the buccal cusp
tips of the first
premolar on one side to
the buccal cusp tip on
other side
PMBAW (Premolar basal ach Width)
• PMBAW (Premolar basal
ach Width)
 From canine fossa of one
side to the other gives the
width of dental arch at the
apical base or the junction
between the basal bone
and the alveolar process.
If canine fossae is not clearly
distinguishable the
measurement is made from a
point that is 8 mm below the
crest of the inter dental papilla
distal to the canine.
• The PMBAW and PMD are compared.
• If PMBAW is greater than PMD ---- arch
expansion is possible.
• If PMBAW is less than PMD--- arch expansion
is not possible.
• According to Ashley Howe, to achieve normal
occlusion with a full complement of teeth the
basal arch width at the premolar region should
be 44% the sum of mesiodistal widths of all the
teeth mesial to the second permanent molar.
• This ratio (expressed as %) between the apical
base width at the premolar region and the total
tooth material is called the premolar basal arch
width percentage.
• PMBAW is determined by using the formula:
• P.M. B.A.W. % = P.M. B.A.W. X 100
T.T.M.
INFERENCES
• If PMBAW > PMD :-indication that basal arch is
sufficient to allow expansion of premolars
• If PMD > PMBAW :• Can be three possibilities
• 1) contraindicated for expansion
• 2) move teeth distally
• 3) Extract some teeth
•
•
•
•
If PMBAW X100 / TTM )
A) less than 37% or less -require extraction
B) if 44% or more - extraction not required
c) if between 37-44% (border line case) may or
may not require extraction