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MODEL ANALYSIS MODEL ANALYSIS UNDER THE GUIDANCE OF:-
Dr. Suresh
Dr. Vishwanath Patil
Dr. B. C. Patil
Dr. Aaquib Hashmi
Dr. Vijaya
Submitted by:-
Tahera. Ahmednasirwala

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INTRODUCTION Model analysis is one of the essential diagnostic aids.
The important purpose of the orthodontic study model is to help in model analysis.
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.
Model analysis are used for determination of space discrepancies in the arch, i.e., to determine the difference between the space available and the space required for tooth alignment

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REQUIREMENTS TO DO MODEL ANALYSIS
Well prepared study models
Vernier calipers
Divider
Ruler
Brass wire

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CLASSIFICATION

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ARCH PERIMETER ANALYSIS 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.

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PROCEDURE CALCULATION OF SPACE REQUIRED: measure the mesiodistal dimension of all the teeth mesial to the first molar (54321¦12345)
CALCULATION OF SPACE AVAILABLE: 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.
Mark the wire and measure the wire, which gives the space available.

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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.

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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.

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INTERPRETATION

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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.

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PROCEDURE STEP I: DETERMINATION OF ARCH LENGTH (total space available)
Measure the arch perimeter using brass wire.
From mesio-buccal line angle of the mandibular right first molar, pass the wire along the buccal cusp and cingulum in the anterior region, pass the wire on the left quadrant like a mirror image till the mesiobuccal line angle of the left mandibular first molar.

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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 in the anterior region.
If the teeth are well aligned, the wire passes over the incisal edges of the anteriors.
Mark the wire, straighten the wire and measure the wire which gives the space available.

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STEP II: DETERMINATION OF TOOTH MATERIAL (total space required)
Measure the mesiodistal dimension of all teeth mesial to the first molar and add. This value gives the total space required
STEP III: DETERMINATION OF DISCREPANCY
The discrepancy refers to the difference between the arch length and tooth material

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INTERPRETATION

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ASHLEY HOWE ANALYSIS Ashley Howe considered the crowding of teeth to be the result of deficiency in arch width rather than arch length.
He found the relationship between the twelve teeth anterior to the permanent second molars and the width of the dental arch in first premolar region.
This is usually done in the upper arch.

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ANALYSIS DETERMINATION OF TOOTH MATERIAL (TTM): mesodistal width of all the teeth anterior to the permanent second molars are measured with the help of callipers and all the values are summed up.
DETERMINATION OF PREMOLAR DIAMETER (PMD): it refers to the distance or arch width from the tip of the buccal cusp of one fiirst premolar to the tip of the buccal cusp of opposite first premolar.
DETERMINATION OF PREMOLAR BASAL ARCH WIDTH (PMBAW): measurement of width from canine fossa of one side to another gives us the width of the dental arch at the apical base or junction between the basal bone and the alveolar process.

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INFERENCE There are two inferences derived in Ashley Howe’s analysis.
First one is the comparison of PMBAW and PMD
Second one is the relationship between the PMBAW and TTM

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INFERENCE I The PMBAW and PMD are compared.
If the PMBAW is greater than the PWD, then it is indicated that arch expansion is possible.
If on the other hand, the PMBAW is less than PMD, then arch expansion is not possible.

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INFERENCE II To achieve a normal occlusion with a full complement of teeth, the basal arch width at the premolar region (PMBAW) should be 44% of the sum of the mesiodistal widths of all the teeth mesial to the second molar (TTM)

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INFERENCE

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PONT’S INDEX 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 upper maxillary incisors

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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 incisors.
Determining the need for lateral arch expansion.
Determining whether the expansion is possible or not at the premolar and molar regions.

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AIM The mesiodistal width of maxillary central and lateral incisors predicts the width of the dental arch in the premolar and molar area.
Relationship exists between the form of the skull and the form of the dental arch.
He determined a constant ratio between:
Sum width of the four maxillary incisors (SI)
Width of the maxillary arch as measured from the center of the occlusal surfaces of first premolars (MPV) and first molars (MMV)

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The ratio of the combined incisor width to transverse arch width was 80 in the premolar area and 64 in the molar area.
He also suggested that the maxillary dental arch should be expanded one or two millimeters more than that found in normal occlusion to allow for relapse.

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ANALYSIS DETERMINATION OF SUM OF INCISORS(SI): the greatest mesiodistal width of the incisors is measured with calipers, recorded on a line and their sums then recorded (in mm)
DETERMINATION OF MEASURED PREMOLAR VALUE(PMV): width of the arch in the premolar region from the distal pit of upper first premolar to the distal pit of the second opposite first premolar.
DETERMINATION OF THE MEASURED MOLAR VALUE (MMV): width of the arch in the molar region from the mesial pit of the upper first molar to the mesial pit of the opposite first molar.

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CALCULATED PREMOLAR VALUE (CPV): or the ideal arch width in the premolar region is determined by:
CPV = SI X 100
80
CALCULATED MOLAR VALUE (CMV): or ideal arch width in the molar region is determined by:
CMV = SI X 100
64

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If calculated value or expected value is more than measured value, it indicates the need for expansion.
Thus, it is possible to determine how much expansion is needed in the premolar and molar regions.
Pont’s analysis gives us approximate indications of the degree of narrowness of dental arches in case of malocclusion and the amount of lateral expansion required for the arch to be of sufficient size to accommodate the teeth in perfect alignment.

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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.

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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

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FORMULA The calculated premolar value (CPV):
CPV = SI X 100
85
The calculated molar value (CMV):
CMV = SI X 100
65

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KORKHAUS ANALYSIS This analysis is similar to Pont’s analysis.
Only difference is that it makes use of Linder Harth’s formula to determine the ideal width in the premolar and molar regions.
In addition this analysis also utilizes a perpendicular measurement made from a point in between the two maxillary incisors to the midpoint of the inter proximal line.

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According to Korkhaus for a given width of the upper incisors a specific value of the distance between the mid point of the inter premolar line to the point between the two maxillary incisors should exist.
An increase in this perpendicular measurement denotes proclination of the upper anterior teeth, while a decrease in this value denotes retroclined upper anteriors.

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BOLTON’S ANALYSIS It helps to determine the disproportion between the size of mandibular and maxillary teeth.
In well aligned upper and lower arches with normal overjet and overbite, there exists a definite proportionality of tooth size between the two arches.
If the proportionality is met, the maxillary dentition fits well with the mandibular teeth.
The presence of disproportionately sized teeth in either arch can make it difficult to obtain an occlusion with good alignment, ideal overjet, ideal overbite, and a class I molar relationship.

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AIM The primary purpose of Bolton’s analysis is to determine mathematical ratios between total lengths of dental arches ( total tooth material) as well as between segments of tooth material (anterior tooth material).
Three inch needle pointed dividers are used to determine the greatest mesiodistal diameter of all the teeth on each cast.

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Cast analysis

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TOTAL TOOTH RATIO / OVER ALL RATIO The ratio of the percentage relationship of sum width of mandibular tooth material as measured from first molar to first molar width to that of corresponding maxillary dentition.

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STEPS SUM OF MANDIBULAR 12: the mesiodistal width of all the teeth mesial to the mandibular second permanent molars is measured and summed up.
SUM OF MAXILLARY 12: the mesiodistal width of all the teeth mesial to the maxillary second permanent molars is measured and summed up.

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Anterior Bolton analysis Full archBolton analysis

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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

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If the overall ratio is more than 91.3%, it indicates mandibular tooth material excess.
The amount of mandibular tooth material excess is determined by using the formula

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ANTERIOR TOOTH RATIO The ratio of the percentage relationship of mandibular anterior width to the maxillary anterior width.

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SUM OF MANDIBULAR 6: the mesio distal width of all the anterior six teeth are measured and summed up
SUM OF MAXILLARY 6: the mesio distal width of all the anterior six teeth are measured and summed up

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The anterior ratio is determined using the following formula:

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If the anterior ratio is less than 77.2%, it indicates maxillary anterior tooth material excess.
The amount of maxillary tooth material is determined using the formula:

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If the anterior ratio is more than 77.2%, it indicates mandibular anterior tooth material excess.
The amount of mandibular tooth material is determined using the formula:

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PECK AND PECK INDEX The mandibular incisors in people with no crowding will have similar mesio distal width and large labio lingual width than in people with incisal crowding.
The proportion of the mesio distal width of each tooth to the labio lingual thickness is calculated using the formula:
MDW X 100
LLW

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Mean value for lower central incisor should be 88 to 92%
Mean value for lower lateral incisor should be 90 to 95%
If the calculated value is greater than the mean value, it indicates that the mesio distal width is more than labio lingual width and hence proximal stripping is indicated.

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MIXED DENTITION ANALYSIS

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AIM The purpose of mixed dentition analysis is to evaluate the amount of space available in the arch for succeeding permanent teeth and necessary occlusal adjustments.

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ANALYSIS OF SUPPORTING ZONES Is done to determine the difference between space available and space required as for the as yet un-erupted permanent canines and first and second premolars.
Three assumptions are made:
Incisors are neither protrusive nor retrusive
Does not predict the amount of natural decrease in perimeter.
Growth changes will not significantly affect the treatment.

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DETERMINATION OF SIZE OF UNERUPTED PERMANENT TEETH This is either done with the help of prediction tables or radiographic assessment of mesiodistal widths of unerupted permanent canines, and first and second premolars.
Thus, Moyer’s analysis is based only on casts and prediction tables, whereas Hixon and old father is based on radiographs as well as prediction tables.

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MOYER’S MIXED DENTITION ANALYSIS This analysis requires only study models
By measuring the mesiodistal widths of erupted lower incisors one can predict the mesiodistal width of un-erupted upper and lower canines and premolars from 75% level of the probability chart.

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INTRODUCTION There is a high degree of co-relation between the sizes of different groups of teeth in the particular individual; by measuring one group of teeth it is possible to make prediction of the size of the other group of teeth with a fair degree of accuracy.
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.

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PROCEDURE STEP I: 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.
STEP II: SPACE AVAILABLE- measure the distance between the distal surface of permanent lateral incisors and mesial surface of permanent first molar. Determine the amount of space required for the proper alignment of mandibular incisors. The amount of space left behind gives the space available.

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TANAKA AND JOHNSTON ANALYSIS 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 derived the following formula based on 75% level prediction values.
The sum of widths of mandibular permanent incisors is measured and divided by 2
For the lower arch, 10.5mm is added to the result
For the upper arch, 11mm is added to the result to obtain the total estimated widths of the canines and premolars.

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NANCE’S MIXED DENTITON ANALYSIS This analysis is similar to arch perimeter analysis of the permanent dentition

PROCEDURE SPACE REQUIRED:
measure the mesio distal width of the erupted permanent teeth.
Measure the width of each unerupted tooth, cuspids and bicuspids from the IOPA.
The total mesiodistal width of all the teeth in each quadrant will indicate space required to accommodate the permanent teeth.

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B = measurement of un-erupted canines and premolars on radiograph

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SPACE AVAILABLE:
using brass wire, measure the arch perimeter from the mesial surface of permanent first molar to the mesial surface of the permanent first molar on the other side.
Compare the space required and space available to arrive at the arch length discrepancy

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ADVANTAGES
It results in minimal errors
It can be performed with reliability
It allows analysis of both arches
LIMITATION
It is time consuming
Complete mouth radiograph is needed.

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HUCKABA’S MIXED DENTITION ANALYSIS (RADIOGRAPHIC METHOD) This analysis makes use of a radiograph and study cast to determine the width of unerupted teeth

PRINCIPLE With any type of radiograph, it is necessary to compensate for enlargement of radiographic image.
This can be done by measuring an object that can be seen both in the radiograph and on the cast, such as primary molar tooth.
It is possible to determine the measurements of un-erupted teeth by studying the teeth that have already erupted in a radiograph and on a cast

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A simple proportional relationship can be established as follows:

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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

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ADVANTAGES Accuracy of this method of determining the width of the unerupted tooth is fair to good depending upon the quality of the radiographs and their position in the arch
The technique can be used in the maxillary and mandibular arches for all ethnic group

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CONCLUSION Mixed dentition analysis forms an integral aspect of orthodontic diagnosis to determine whether the treatment plan is going to involve serial extraction, space maintenance, space gaining or simply periodic observation of the patient.

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RECENT ADVANCES IN MODEL ANALYSIS

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Cast analysis by software

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ADVANTAGES OF COMPUTERIZED ANALYSIS Accurate
Easy
More information:
Arch form
Loop distance (Bolton analysis)
Determine asymmetric Arch
Space analysis
Rotation
Prediction