BDS [Orthodontics] course

1. Model Analysis
PROF (Dr.) SAIBEL FARISHTA

2. The study casts are essential diagnostic aids. They provide a three
dimensional view of the maxillary and mandibular dental arches. Model
analysis involves the study of the maxillary and mandibular arches in all
the three planes of space [Sagittal, Vertical and Transverse] and is a
valuable tool in orthodontic diagnosis and treatment planning.
Ashley Howe’s Analysis
He considered tooth crowding to be due to deficiency in arch length.
He founded a relationship between the total width of the 12 anterior
teeth to the second molars and the width of the dental arch in the first
premolar region.
Determination of the Total Tooth Material [TTM]
Procedure –
The mesio-distal width of all the teeth, mesial to the second permanent
molars is measured with the help of dividers and all the values are
summed up. This value is called the total tooth material.

3. Determination of PreMolar Diameter [PMD]
It refers to the arch width from the tip of the buccal cusp of one first
premolar to the tip of buccal cusp of the opposite first premolar.
Determination of PreMolar Basal Arch Width [PMBAW]
The canine fossa is found distal to the canine eminence. The
measurement of the width from canine fossa of one side to the other
gives us the width of the dental arch at the apical base or the junction
between the basal bone and alveolar process. If the canine fossa 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.

4. Inference -
Determination of the possibility of Arch expansion
The PMBAW and the PMD are compared. If the PMBAW is greater than
PMD, then it is an indication that arch expansion is possible. If on the
other hand the PMBAW is less than PMD, then arch expansion is not
possible.
Calculation of PreMolar Basal Arch Width Percentage
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 mesio-distal widths of all the teeth mesial to
the second permanent molar [TTM]. This ratio [expressed as %]
between the apical base width at the premolar region and TTM is called
the premolar basal arch width percentage. It is determined using the
formula :
PMBAW % = PMBAW x 100
TTM

5. • If PMBAW % is 37% or less, it indicates a need for extraction
• If PMBAW % is 44% or more, the case can be treated without extractions
• If PMBAW % is 37% - 44% the case is referred to as a borderline case

6. Ponts Analysis
Ponts in 1909 presented a system where the measurement of the four
maxillary incisors automatically established the width of the arch in
Premolar and molar regions. This analysis helps in –
• Determining whether the dental arch is narrow or normal
• Determining the need for lateral arch expansion
• Determining how much expansion is possible at Premolar & molar regions
Procedure –
Determination of Sum Of Incisors [SI]
The mesio distal width of the 4 maxillary incisors is measured and the
values summed up. This value is called sum of incisors [SI]

7. Determination of Measured Premolar Value [MPV]
The width of the arch in the premolar region from the distal pit of one
upper first premolar to the distal pit of the opposite first premolar is
measured. This is called the measured premolar value.
Determination of Measured Molar Value [MMV]
The width of the arch in the molar region from the mesial pit of one
upper first molar to the mesial pit of the opposite first molar is
measured. This is called the measured molar value.
Determination of Calculated Premolar Value [CPV]
The calculated premolar value or the expected arch width in the
premolar region is determined by the formula :
SI x 100
80

8. Determination of Calculated Molar Value [CMV]
The calculated premolar value or the expected arch width in the molar
region is determined by the formula :
SI x 100
64
Inference –
If measured value is less than the calculated value, it indicates the
need for expansion. Thus it is possible to determine how much
expansion is needed in molar and premolar regions.

9. Ponts Analysis

10. Linder Harth Index
This analysis is quite similar to Pont’s analysis, except that a new
formula has been proposed to determine the calculated premolar and
molar values.
The calculated premolar value is determined using the formula –
SI x 100
85
The calculated molar value is determined using the formula –
SI x 100
64

11. Korkhaus Analysis
This is similar to pont’s analysis. According to this,for a given width of
upper incisor,a specific value of the distance b/n midpoint of inter
premolar line to point in b/n the max.incisor exist.
Inference - Increase in this measurement denotes proclined upper
anteriors, while reduced value indicates retroclined upper anteriors.

12. Carey’s Analysis
Many malocclusions occur as a result of discrepancy between arch
length and tooth material. This analysis helps in determining the extent
of the discrepancy. It is performed on the lower cast. The same
analysis on the upper cast is called Arch perimeter analysis.
Procedure –
Determination of Arch Length
The arch length anterior to the first permanent molar is measured
using a soft brass wire. The wire is placed touching 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. It 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 in the anterior segment passes labial to the
teeth. If the anterior teeth are well aligned, the wire passes over the
incisal edge of anteriors.

13. 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
It refers to the difference between the arch length and tooth material.
Inference –
• If the discrepancy is 0 to 2.5 mm, it indicates minimal tooth material
excess. Proximal stripping can be done in these cases.
• If the discrepancy is between 2.5 to 5 mm, it indicates the need to
extract the second premolars
• A discrepancy of more than 5 mm indicates first premolar extraction.

14. Carey’s Analysis

15. Bolton’s Analysis
According to Bolton there is a ratio between the mesio distal widths of
maxillary and mandibular teeth. Many malocclusions occur as a result
of abnormalities in tooth size. This analysis helps in determining
disproportion in size between maxillary and mandibular teeth.
Procedure –
Sum of Mandibular 12
The mesio distal width of all the teeth mesial to the mandibular second
permanent molars is measured and summed up.
Sum of Maxillary 12
The mesio distal width of all the teeth mesial to the maxillary second
permanent molars is measured and summed up.

16. Sum of Mandibular 6
The mesio distal width of all the teeth mesial to the mandibular first
premolars is measured and summed up.
Sum of Maxillary 6
The mesio distal width of all the teeth mesial to the maxillary first
premolars is measured and summed up.
Determination of Overall Ratio
According to Bolton, the sum of mesio distal widths of the mandibular
teeth anterior to the second permanent molars is 91.3% the mesio
distal width of the maxillary teeth mesial to the second molars. The
overall ratio is determined using the formula:
Overall ratio = sum of mandibular 12 x 100
Sum of maxillary 12

17. If the overall ratio is less than 91.3% it indicates maxillary tooth
material excess. The amount of maxillary excess is determined using
the formula:
Sum of maxillary 12 = sum of mandibular 12 x 100
91.3
If the overall ratio is more than 91.3% it indicates mandibular tooth
material excess. The amount of mandibular excess is determined using
the formula:
Sum of mandibular 12 = sum of maxillary 12 x 91.3
100
Determination of Anterior Ratio
The sum of mesio distal width of the mandibular anteriors should be
77.2% of the mesio distal width of the maxillary anteriors. The anterior
ratio is determined using the following formula:
Anterior ratio = sum of mandibular 6 x 100
Sum of maxillary 6

18. If the anterior ratio is less than 77.2% it indicates maxillary anterior
excess. The amount of maxillary anterior excess is determined by the
following way:
Sum of maxillary 6 - sum of mandibular 6 x 100
77.2
If the anterior ratio is more than 77.2% it indicates mandibular anterior
excess. The amount of mandibular anterior excess is determined using
the formula:
Sum of mandibular 6 - sum of mandibular 6 x 77.2
100

19. Bolton’s Analysis

20. Bolton’s Analysis

21. Moyer’s Mixed Dentition Analysis
The purpose of a mixed dentition analysis is to evaluate the amount of
space available in the arch for the erupting permanent canines and
premolars. In this analysis, the size of the unerupted permanent
cuspids and premolars are predicted from the knowledge of the sizes of
certain permanent teeth already erupted in the mouth.
This analysis predicts the combined mesio distal width of 3, 4 and 5
based on the sum of the widths of the four lower permanent incisors.
Procedure –
The mesio distal width of the four lower incisors are measured and
summed up.
The amount of space available for 3, 4 and 5 after incisor alignment is
determined by measuring the distance between the distal surface of
lateral incisor and the mesial surface of first permanent molar.
Based on the mesio distal width of the four mandibular incisors, the
expected widths of the canines, first and second premolars are
predicted by referring the probability chart. 75% level of probability is
considered reliable.

22. The predicted tooth size of 3, 4 and 5 is compared with the arch length
available for them so as to determine the discrepancy. If the predicted
value is greater than the available arch length, crowding of teeth can
be expected.

23. Mixed Dentition Analysis – Radiographic Method
This technique makes use of a radiograph as well as a study cast to
determine the width of the unerupted teeth. Radiographic
measurements of unerupted teeth are by themselves unreliable due to
the distortions that can occur. It is possible to determine the
measurements of the unerupted teeth by studying the teeth that have
already erupted in a radiograph and on a cast.
The following formula is used:
Y1 = X1 x Y2
X2
Y1 = width of unerupted tooth, whose measurement is to be determined
Y2 = width of unerupted tooth on a radiograph
X1 = width of a tooth that has erupted, measured on a cast
X2 = width of a tooth that has erupted, measured on a radiograph

24. THANK YOU