Study models and its uses

Study models and itsStudy models and its
usesuses
www.indiandentalacademy.comwww.indiandentalacademy.com

IntroductionIntroduction
Objectives of ideal orthodontic study models .Objectives of ideal orthodontic study models .
Why we make study models?Why we make study models?
Uses of study modelsUses of study models
Parts of the study modelsParts of the study models
Study model fabrication and trimmingStudy model fabrication and trimming
Model analysisModel analysis

INTRODUCTIONINTRODUCTION
Orthodontic study models are an essentialOrthodontic study models are an essential
diagnostic records, which helps to studydiagnostic records, which helps to study
the occlusion and dentition from all threethe occlusion and dentition from all three
dimensions. They are accurate plasterdimensions. They are accurate plaster
reproductions of the teeth and theirreproductions of the teeth and their
surrounding soft tissues.surrounding soft tissues.

OBJECTIVES OF STUDY MODELSOBJECTIVES OF STUDY MODELS
Models accurately reproduce the teeth and theirModels accurately reproduce the teeth and their
surrounding soft tissues.surrounding soft tissues.
Models should be trimmed, symmetrical andModels should be trimmed, symmetrical and
pleasing to the eye .pleasing to the eye .
Models are to be trimmed that the dental occlusionModels are to be trimmed that the dental occlusion
shows by setting the models on their backs.shows by setting the models on their backs.

Models are to be trimmed to meet theModels are to be trimmed to meet the
measurements and angles proposed formeasurements and angles proposed for
trimming them.trimming them.
Models should have clean, smooth, bubble-Models should have clean, smooth, bubble-
free surfaces with sharp angles where the cutsfree surfaces with sharp angles where the cuts
meet.meet.
The finished models are treated with a soapThe finished models are treated with a soap
solution to give it a glassy, mar-proof finish.solution to give it a glassy, mar-proof finish.

WHY WE MAKE STUDY MODELS?
Visual aid for the dentist as he monitorsVisual aid for the dentist as he monitors
changes taking place during tooth movement.changes taking place during tooth movement.
Needed for comparison purposes at the end ofNeeded for comparison purposes at the end of
treatment and act as a reference for post-treatment and act as a reference for post-
treatment changes.treatment changes.
They serve as a reminder for the parent and theThey serve as a reminder for the parent and the
patient of the condition present at the start ofpatient of the condition present at the start of
treatment.treatment.

Possible to view the occlusion from every aspect.Possible to view the occlusion from every aspect.
Occlusion can be visualized from the lingualOcclusion can be visualized from the lingual
aspect.aspect.
Enable accurate measurements to be made of theEnable accurate measurements to be made of the
dental arches.dental arches.
Assessment of treatment progress at a later date.Assessment of treatment progress at a later date.
Are a permanent record of the inter -maxillaryAre a permanent record of the inter -maxillary
relationships and the occlusion at the start ofrelationships and the occlusion at the start of
therapy; this is necessary for medico legaltherapy; this is necessary for medico legal
considerations.considerations.

Necessary to assist another practitioner toNecessary to assist another practitioner to
whom the patient may require to be transferredwhom the patient may require to be transferred
In explaining the treatment plan and progressIn explaining the treatment plan and progress
to a patient or parent. To motivate the patientto a patient or parent. To motivate the patient
as the patient can visualize the treatmentas the patient can visualize the treatment
progressprogress
 In planning treatment, as they are the onlyIn planning treatment, as they are the only
three dimensional records of the patient'sthree dimensional records of the patient's
dentition. Simulation of treatment can also bedentition. Simulation of treatment can also be
donedone www.indiandentalacademy.comwww.indiandentalacademy.com

USES OF STUDY MODELSUSES OF STUDY MODELS
Assist and record dental anatomyAssist and record dental anatomy
Assist and record inter cuspationAssist and record inter cuspation
Assess and record arch formAssess and record arch form
Assess and record the curves of occlusionAssess and record the curves of occlusion
Evaluate occlusion with the aid of articulatorsEvaluate occlusion with the aid of articulators
Measure progress during treatmentMeasure progress during treatment
Detect abnormality, e.g. localizedDetect abnormality, e.g. localized
enlargements, distortion of arch form, etc.enlargements, distortion of arch form, etc.
Calculate total space analysisCalculate total space analysis
Provide record before, immediately, after andProvide record before, immediately, after and
several years following treatment for theseveral years following treatment for the
purpose of studying treatment procedures andpurpose of studying treatment procedures and
stability.stability.

Tray selectionTray selection
Good models are only made from goodGood models are only made from good
impressions which in turn require selection ofimpressions which in turn require selection of
the right tray inserted in the most advantageousthe right tray inserted in the most advantageous
manner in this waymanner in this way
The excess alginate impression material, insteadThe excess alginate impression material, instead
of penetrating the pharynx, over-extends theof penetrating the pharynx, over-extends the
sulcussulcus
The average box tray's rim is too shallow toThe average box tray's rim is too shallow to
achieve this result ad it is recommended thatachieve this result ad it is recommended that
orthodontic trays are used since their rim theorthodontic trays are used since their rim the
labial region is at least 34 inch (20 mm) andlabial region is at least 34 inch (20 mm) and
their edge is beaded to secure the alginate.their edge is beaded to secure the alginate.www.indiandentalacademy.comwww.indiandentalacademy.com

The size of trays selected should not only coverThe size of trays selected should not only cover
the last molars but also be 14 inch (3 mm)the last molars but also be 14 inch (3 mm)
clear of the outer aspect of the teeth andclear of the outer aspect of the teeth and
alveolar process. As the tray is being insertedalveolar process. As the tray is being inserted
in an oblique sagittal direction , the patient'sin an oblique sagittal direction , the patient's
lip is held forward and the excess alginatelip is held forward and the excess alginate
impression material pushed into the sulcus toimpression material pushed into the sulcus to
expel any air.expel any air.
In the production of good study models aIn the production of good study models a
further aid to the technician is the provision offurther aid to the technician is the provision of
a wax bite taken with the teeth in the usuala wax bite taken with the teeth in the usual
occlusion for that patient. This should beocclusion for that patient. This should be
obtained as accurately as possible with a roll ofobtained as accurately as possible with a roll of
wax, between the posterior teethwax, between the posterior teeth

A tray with a 34 inch (2 cm) high flange isA tray with a 34 inch (2 cm) high flange is
suitable for orthodontic impressions. Here it issuitable for orthodontic impressions. Here it is
being inserted for an upper impression in anbeing inserted for an upper impression in an
upward and backward direction in order toupward and backward direction in order to
extend over the alveolar process.extend over the alveolar process.
Following the upward and backward insertionFollowing the upward and backward insertion
the excess material flows into the labial sulcusthe excess material flows into the labial sulcus
and is supported by the high flange of the tray.and is supported by the high flange of the tray.

PARTS OF THE STUDY MODELSPARTS OF THE STUDY MODELS
The study models can beThe study models can be
divided into two partsdivided into two parts
The Anatomic portionThe Anatomic portion
The Artistic portionThe Artistic portion

Anatomic portionAnatomic portion
The anatomic portion is that partThe anatomic portion is that part
which is the actual impression of thewhich is the actual impression of the
dental arch and its surrounding softdental arch and its surrounding soft
structures. This is the part, which must bestructures. This is the part, which must be
preserved when trimming the modelpreserved when trimming the model
Artistic portionArtistic portion
The artistic portion is the stoneThe artistic portion is the stone
base supporting the anatomic portion.base supporting the anatomic portion.
This portion is trimmed in a manner, whichThis portion is trimmed in a manner, which
depicts, in a general way, the dental archdepicts, in a general way, the dental arch
form and is pleasing to the eye.form and is pleasing to the eye.

STUDY MODEL FABRICATIONSTUDY MODEL FABRICATION
AND TRIMMINGAND TRIMMING
Preliminary proceduresPreliminary procedures
Remove any excess flash or obviouslyRemove any excess flash or obviously
excessive bulk on the periphery of the modelsexcessive bulk on the periphery of the models
Remove any nodules that may be present onRemove any nodules that may be present on
thethe occluding surfaces of the teethoccluding surfaces of the teeth
 Remove any extensions in the posterior areasRemove any extensions in the posterior areas
that prevent occluding of the modelsthat prevent occluding of the models
Using the wax bite, occlude the models.Using the wax bite, occlude the models.

STEPS IN ART PORTION FABRICATION
Determine the occlusal plane of the dentition.
Once this has been determined, the base of the
lower model is trimmed parallel to the occlusal
plane
The occlusal plane is considered to be the highest
three points of the erupted teeth.

Trim the back of the lower model
perpendicular to the midline . Done on a near
symmetrical model by measuring the distance
from the distal of the first molar teeth or
second bicuspids to the back of the model on
both the left and right sides.
On a model that is not symmetrical,
compensation must be made to keep the back
as near perpendicular to the midline as
possible.

To trim the back of the upper model, occlude
the models utilizing the wax bite. The wax bite
not only maintains the correct interrelationship
but will also help to prevent fracturing of the
teeth. Carefully trim the posterior surface of
the occluded models so that the upper model
matches that of the lower model .
The back of the upper and lower models
should now be 90° to the base of the lower
model. Trim the posterior surfaces of both
models until just posterior to the hamular
notch which should be several millimeters
posterior to the last tooth.

Trim the base of the upper model so that it is
parallel to the base of the lower model. Trim
until the top base is flat, but leave several
millimeters of extra height so the occlusal plane
of the models can be centered.
The occlusal plane should be centered between
the top of the maxillary model and the base of
the mandibular model.

Two bases are parallel to each other and to theTwo bases are parallel to each other and to the
occlusal plane .occlusal plane .
The backs of both the upper and lower basesThe backs of both the upper and lower bases
are at right angles to the bases, the occlusalare at right angles to the bases, the occlusal
plane and to the mid-palatal aponeurosis.plane and to the mid-palatal aponeurosis.
From here on, the upper and lower modelsFrom here on, the upper and lower models
shall be trimmed independently of each other.shall be trimmed independently of each other.

Lower model
Make the buccal cuts to the edge of the vestibule
using a 60° angle.
The edge of the vestibule is taken as a point
approximately 5 to 6 mm away from the most
prominent point of the lower canine or first bicuspid
tooth. The model is trimmed to this point provided
that this does not cut beyond the deepest point of the
vestibule in the region of the first or second molar.

The anterior segment of the lower arch is
trimmed into a curve, which should follow the
arc of a circle. The finished model should have
this curve trimmed to within 5 to 6 mm of the
anterior teeth.
The heels of the lower model are cut at
approximately 115° to the back of the model.
The floor of the mouth should be leveled and
smoothed to form a flat surface.

Upper model
Make the buccal cuts to the edge of the
vestibule at an angle of 60° .
Make the anterior cuts so that the ends are at
the midline and approximately in the canine
area . This cut should be approximately 5 to 6
mm from the labial surface of the anterior
teeth, with both sides of equal length and their
intersection on the midline.www.indiandentalacademy.comwww.indiandentalacademy.com

The heels of the upper model are formed by
occluding both the models and finishing them
such that they are flush with the heels of the
lower models at 115°. The heels of the upper
model may not be the same length as those of
the lower model.
The finished height of the occluded models
should be 7 cm

Finishing the modelsFinishing the models
The surface must be made smooth, absolutely flat
and at right angles to the bases of the models.
In the carborandum stone technique, the model is
rubbed over the stone with an even pressure
under a stream of water until a smooth surface
results. The method is to rub the model on a
frosted glass surface.
Dry for 48 hours or dried overnight in an
orthodontic oven. Model should be labeled with
the patient's name and date on the back surface.

The final glazing is put on the models by
immersing them in a commercial gloss solution
for half an hour.
Holding under cold water, the models are
polished and soap solution removed by
buffing with cotton.
The models are set on their occlusal surfaces to
dry for another twelve hours, then buffed with
a very light but rapid motion using slightly
damp cotton. www.indiandentalacademy.comwww.indiandentalacademy.com

The models should assume a high, even luster
which will then resist soiling while handling.
The models should be placed on a flat surface
with their backs down.
They should be picked up together and always
returned together.
Individual handling of the models is more
likely to result in damage to the models.

Digital study modelsDigital study models
DIGITAL STUDY MODELSAny Orthodontist who has been in practice for a number of years, experiences a problem about storage space in his office besides it is aDIGITAL STUDY MODELSAny Orthodontist who has been in practice for a number of years, experiences a problem about storage space in his office besides it is a
consuming time procedure. For this reason, the additional advantage of saving space of digital models is a welcome advance (911).Begole (12) was one of the firstconsuming time procedure. For this reason, the additional advantage of saving space of digital models is a welcome advance (911).Begole (12) was one of the first
authors introducing a computer program to aid the direct analysis of study models as a clinical diagnostic and using dental cast photos.Rudge (13) devised anotherauthors introducing a computer program to aid the direct analysis of study models as a clinical diagnostic and using dental cast photos.Rudge (13) devised another
computer system using an electroniccomputer system using an electronic
XY reader in order to relate changes in dentition as a result of orthodontic treatment.At the same time, Yen (14) proposed a simple computer programXY reader in order to relate changes in dentition as a result of orthodontic treatment.At the same time, Yen (14) proposed a simple computer program
using a study model photocopy. This program predicts “required space” and compares it to “available space”. This analysis also includes Bolton ratios, intercanineusing a study model photocopy. This program predicts “required space” and compares it to “available space”. This analysis also includes Bolton ratios, intercanine
distances, intermolar distances, arch length and arch discrepancy.The introduction of digital image in our society and especially in orthodontics permits the use of, either adistances, intermolar distances, arch length and arch discrepancy.The introduction of digital image in our society and especially in orthodontics permits the use of, either a
regular scanner, or a digital camera, to digitalize stone dental casts and to measure several measurements as mesiodistal tooth size, arch length, intercanine distance orregular scanner, or a digital camera, to digitalize stone dental casts and to measure several measurements as mesiodistal tooth size, arch length, intercanine distance or
intermolar distance by a computer programintermolar distance by a computer program
prepared to use these obtained digital images in 2D.Rivero et al (15), used a regular scanner to digitalize dental stoneprepared to use these obtained digital images in 2D.Rivero et al (15), used a regular scanner to digitalize dental stone
casts while Carter et al (16), introduced another new digital method to measure tootharch width, length and perimeter and to evaluate longitudinal arch changes withcasts while Carter et al (16), introduced another new digital method to measure tootharch width, length and perimeter and to evaluate longitudinal arch changes with
age.Gouvianaski et al (17) were one of the first authors using a digital camera linked to a computer program to photograph and measure stone dental casts whileage.Gouvianaski et al (17) were one of the first authors using a digital camera linked to a computer program to photograph and measure stone dental casts while
Trankmann et al (18) measured dental models by digitalizing tables.Ho and Freer (19), designed a computer program that permits direct input of toothwidthTrankmann et al (18) measured dental models by digitalizing tables.Ho and Freer (19), designed a computer program that permits direct input of toothwidth
measurements per patient from study casts using digital calipers instead of traditional ones.Mok and Cooke (20) compared the reproducibility of mesiodistalmeasurements per patient from study casts using digital calipers instead of traditional ones.Mok and Cooke (20) compared the reproducibility of mesiodistal
total tooth widths and arch perimeter values, on plaster casts, given by sonic digitization and by digital calipers.Redmond (9,10) introduced a new computerized system intotal tooth widths and arch perimeter values, on plaster casts, given by sonic digitization and by digital calipers.Redmond (9,10) introduced a new computerized system in
which impressions are sent to the company where they are scanned and emailed to the Orthodontist back. This new systemwhich impressions are sent to the company where they are scanned and emailed to the Orthodontist back. This new system
allows five simultaneous views of the model in 3D, can be incorporated into computer patient records and eliminating the need for model storage.Tomassetti (21)allows five simultaneous views of the model in 3D, can be incorporated into computer patient records and eliminating the need for model storage.Tomassetti (21)
compared three digital measuring methods with the traditional method for calculating the Bolton Index and concluded that digital methods were much quicker.Garino (22)compared three digital measuring methods with the traditional method for calculating the Bolton Index and concluded that digital methods were much quicker.Garino (22)
also compared dental arch measurements between stone and digital casts concluding that digital program were as easy and accurate as traditional ones with thealso compared dental arch measurements between stone and digital casts concluding that digital program were as easy and accurate as traditional ones with the
additional advantage of saving storage space.In McKeown´s study (23) tooth dimensions were compared between index patients with severe hypodontia, their relativesadditional advantage of saving storage space.In McKeown´s study (23) tooth dimensions were compared between index patients with severe hypodontia, their relatives
with a full of complement of teeth and a control group. All formed teeth were imaged buccally and occlusally from study models with a digital camera linked to a computer.with a full of complement of teeth and a control group. All formed teeth were imaged buccally and occlusally from study models with a digital camera linked to a computer.
The camera was mounted horizontally above the model on an adjustable rod with the lens focused parallel to the tooth surface and parallel to the long axis of the clinicalThe camera was mounted horizontally above the model on an adjustable rod with the lens focused parallel to the tooth surface and parallel to the long axis of the clinical
crown for occlusal views.Tran (24) compared Little index results with traditional calipers and a digital program concluding that the digital system was a very good option forcrown for occlusal views.Tran (24) compared Little index results with traditional calipers and a digital program concluding that the digital system was a very good option for
this measurement.But most of the digital programs reviewed, give teeth measurementthis measurement.But most of the digital programs reviewed, give teeth measurement
information as a group and not individually.In the present study, we introduce a new, fast and accurate 2D computerizedaid system, already introduced and proved by usinformation as a group and not individually.In the present study, we introduce a new, fast and accurate 2D computerizedaid system, already introduced and proved by us
(25), to measure mesiodistal tooth size, intercanine and intermolar distance, arch perimeter and calculate Overall and Anterior Bolton ratios, arch discrepancy and teeth(25), to measure mesiodistal tooth size, intercanine and intermolar distance, arch perimeter and calculate Overall and Anterior Bolton ratios, arch discrepancy and teeth
asymmetries automatically.All the study casts were digitized with a conventional scanner (Figure 3). But before making any measurement, it is important to use anasymmetries automatically.All the study casts were digitized with a conventional scanner (Figure 3). But before making any measurement, it is important to use an
accurate and easy calibration system to obtain dental casts tooth real dimensions in millimetres. With the aid of the mouse as a user interface of the digital method,accurate and easy calibration system to obtain dental casts tooth real dimensions in millimetres. With the aid of the mouse as a user interface of the digital method,
we marked the points of the mesiodistal size of each permanentwe marked the points of the mesiodistal size of each permanent
tooth on the image of the casts. The software designed for this purpose, which we have tested and found accurate and reliable (25) determines dental measurements intooth on the image of the casts. The software designed for this purpose, which we have tested and found accurate and reliable (25) determines dental measurements in
millimetres automatically. From this data, we were able to predict the rest of teeth measurements (Figure 4, 5A and 5B).ADVANTAGES OF DIGITAL STUDY MODELSmillimetres automatically. From this data, we were able to predict the rest of teeth measurements (Figure 4, 5A and 5B).ADVANTAGES OF DIGITAL STUDY MODELS
•These virtual casts can be kept in digital format and also eliminating•These virtual casts can be kept in digital format and also eliminating
the storage problem with study models in our offices.• Digital images can be made bigger and localizing anatomic points easily.• Digital photos are suited for immediatethe storage problem with study models in our offices.• Digital images can be made bigger and localizing anatomic points easily.• Digital photos are suited for immediate
data transmission for instance to a colleague by Internet for an orthodontic diagnosis.• Digital study casts can be showed to patients in order to motivate them in theirdata transmission for instance to a colleague by Internet for an orthodontic diagnosis.• Digital study casts can be showed to patients in order to motivate them in their
treatments.• Measurements can be made on digital casts in an easy, accurate and automatic way.• Digital casts and their measurements can be accessed at any timetreatments.• Measurements can be made on digital casts in an easy, accurate and automatic way.• Digital casts and their measurements can be accessed at any time
and at any distance for diagnostic, clinical and informationand at any distance for diagnostic, clinical and information
purposes.In Spain, an orthodontics survey (1) reported that digital programspurposes.In Spain, an orthodontics survey (1) reported that digital programs
for dental casts are just used by 10%.DISADVANTAGES OF DIGITAL STUDY MODELSfor dental casts are just used by 10%.DISADVANTAGES OF DIGITAL STUDY MODELS
•• If we have poor dental casts, digitalized images can be altered during digitalizing even if a good calibration system is made.• Sometimes, some dental images in mixedIf we have poor dental casts, digitalized images can be altered during digitalizing even if a good calibration system is made.• Sometimes, some dental images in mixed
dentition are difficultdentition are difficult
to recognize and measure.• Digitalizing dental casts is a laborious process that has always to be made under the same conditions.Nowadays, digital study models can beto recognize and measure.• Digitalizing dental casts is a laborious process that has always to be made under the same conditions.Nowadays, digital study models can be
viewed from any angle, turned through 360º in all planes of space and even opened to allow upper and lower models to be viewed separately. Measurements can beviewed from any angle, turned through 360º in all planes of space and even opened to allow upper and lower models to be viewed separately. Measurements can be
carried out to allow space analyses to be conducted (2628).sscarried out to allow space analyses to be conducted (2628).ss

Well finished study modelWell finished study model

Requisites of a study modelRequisites of a study model
Study models should always have a neatStudy models should always have a neat
appearanceappearance
They should depict not only the teeth but alsoThey should depict not only the teeth but also
as much of the alveolar process as possibleas much of the alveolar process as possible
For protection they are mounted on basesFor protection they are mounted on bases
which also help the upper and lower teeth towhich also help the upper and lower teeth to
be placed in correct occlusion.be placed in correct occlusion.
It is customary to trim the bases in such a wayIt is customary to trim the bases in such a way
that the models fall into the patient's occlusionthat the models fall into the patient's occlusion
when standing on their rear surfaces or sideswhen standing on their rear surfaces or sides
on a level surface.on a level surface.

Model AnalysisModel Analysis

IntroductionIntroduction
ConceptsConcepts
Analysis of arch formAnalysis of arch form
Analysis of arch symmetryAnalysis of arch symmetry
Tooth size discrepanciesTooth size discrepancies
Analysis of apical basesAnalysis of apical bases
Lower incisor space analysisLower incisor space analysis
Arch length –tooth material discrepancyArch length –tooth material discrepancy
Mixed dentition analysisMixed dentition analysis
Recent advancesRecent advances

IntroductionIntroduction
Study cast analysis is a 3dimensionalStudy cast analysis is a 3dimensional
assessment of maxillary and mandibular dentalassessment of maxillary and mandibular dental
arches and occlusal relationshiparches and occlusal relationship
Traditionally mesiodistal tooth dimension areTraditionally mesiodistal tooth dimension are
measured with vernier gauage as opposed tomeasured with vernier gauage as opposed to
subjective visual estimation of space on dentalsubjective visual estimation of space on dental
castscasts
Wiith present knowledge this method is oftenWiith present knowledge this method is often
considered to only minimal diagnostic valueconsidered to only minimal diagnostic value
.nevertheless space analysis ,remains important.nevertheless space analysis ,remains important
part orthodontic diagnostic procedure.part orthodontic diagnostic procedure.
Manual measurements that use calibrated gaugeManual measurements that use calibrated gauge
produces the most accurate and reproducibleproduces the most accurate and reproducible
result.result.

ConceptsConcepts
Basal arch is arch formed by corpus madibularisBasal arch is arch formed by corpus madibularis
and maxillaris.dimension probably are unaltered byand maxillaris.dimension probably are unaltered by
loss of all premanent teeth and resorption ofloss of all premanent teeth and resorption of
alveolar process.alveolar process.
Alveolar arch is the arcal measurement ofAlveolar arch is the arcal measurement of
alveolar process. Dimension of alveolar arch mayalveolar process. Dimension of alveolar arch may
not coincide with those of basal arch when teethnot coincide with those of basal arch when teeth
are tipped labially off the basal archare tipped labially off the basal arch
Dental arch usually is measured through contactDental arch usually is measured through contact
points of teeth and represents a series of pointspoints of teeth and represents a series of points
where the muscle force acting against the crownswhere the muscle force acting against the crowns
of teeth are balanced.of teeth are balanced.

When the crowns tip markedly of basal bone theWhen the crowns tip markedly of basal bone the
dental arch and alveolar arch are not synonymousdental arch and alveolar arch are not synonymous
Our aim is to align the teeth In such a way thatOur aim is to align the teeth In such a way that
width of the teeth are identical with dental archwidth of the teeth are identical with dental arch
measurement and the dental arch well positionmeasurement and the dental arch well position
over basal bone .over basal bone .

ANALYSIS OF ARCH FORMANALYSIS OF ARCH FORM
MAXILLARY EXPANSION INDICESMAXILLARY EXPANSION INDICES
Numerous indices have been proposed to helpNumerous indices have been proposed to help
the clinician decide how much maxillary expansionthe clinician decide how much maxillary expansion
will be required to alleviate crowding.will be required to alleviate crowding.
If the indices and guides to be considered useful,If the indices and guides to be considered useful,
the amount of crowing in any given untreated casethe amount of crowing in any given untreated case
should correlate with the discrepancy betweenshould correlate with the discrepancy between
observed arch width and predicted orobserved arch width and predicted or
recommended arch width.recommended arch width.
Research support the contention that intermolarResearch support the contention that intermolar
arch width is associated with amount of crowding inarch width is associated with amount of crowding in
males and interpremolar width in males andmales and interpremolar width in males and
females

It was stated by Ricketts et al tat each eachIt was stated by Ricketts et al tat each each
millimeter of canine expansion provides for 1mmmillimeter of canine expansion provides for 1mm
increase in arch perimeter and 1 mm of molarincrease in arch perimeter and 1 mm of molar
expansion increased peripheral arch length 0.25expansion increased peripheral arch length 0.25
mm.mm.

PONTS INTEXPONTS INTEX
Pont in 1909 devised a method of prePont in 1909 devised a method of pre
determining an ideal arch width based ondetermining an ideal arch width based on
mesiodistal widths of the crowns of maxillarymesiodistal widths of the crowns of maxillary
incisors.incisors.
Pont suggested that the ratio of combined incisorPont suggested that the ratio of combined incisor
to transverse arch width, as measured form centerto transverse arch width, as measured form center
of occlusal surfaces of the teeth was ideally 0.8 nof occlusal surfaces of the teeth was ideally 0.8 n
the first bicuspid area and 0.64 in the first molarthe first bicuspid area and 0.64 in the first molar
area in an ideal uncrowded dentititon.area in an ideal uncrowded dentititon.

MethodMethod::
 mesiodistal widths of four maxillary incisors aremesiodistal widths of four maxillary incisors are
measured and added. This forms sum ofmeasured and added. This forms sum of
incisors (SI).incisors (SI).
 width of the arch in the premolar region fromwidth of the arch in the premolar region from
the deepest point in the transverse fissure ofthe deepest point in the transverse fissure of
first premolar to its counterpart on the otherfirst premolar to its counterpart on the other
side is measure.side is measure.
 width of the arch in the molar region from thewidth of the arch in the molar region from the
point of intersectionof tranverse fissure withpoint of intersectionof tranverse fissure with
buccal fissure of first permanent molar to itsbuccal fissure of first permanent molar to its
counterpart on the other side is measured.counterpart on the other side is measured.www.indiandentalacademy.comwww.indiandentalacademy.com

 If the upper central or, lateral incisors areIf the upper central or, lateral incisors are
missing as hypoplastic determinations may bemissing as hypoplastic determinations may be
made based on sum of lower incisors widthmade based on sum of lower incisors width
using ‘Tonn’ formula of all four upper incisorsusing ‘Tonn’ formula of all four upper incisors
which calculates appropriatewhich calculates appropriate
width.width.
 Expected arch width in the premolar region isExpected arch width in the premolar region is
SI/80x100. Expected arch width in the molarSI/80x100. Expected arch width in the molar
region is SI/64x100.region is SI/64x100.
If measured value is less than the calculatedIf measured value is less than the calculated
value it indicates the need for expansion. Pontvalue it indicates the need for expansion. Pont
suggested that maxillary arch be expanded 1-2suggested that maxillary arch be expanded 1-2
mm more than required to account for relapse.

Disadvantages.Disadvantages.
At best , ponts index is only a crude guideAt best , ponts index is only a crude guide
eventhough it is widely used. Researched at theeventhough it is widely used. Researched at the
University of Washington found very poorUniversity of Washington found very poor
correlations between combined maxillary incisorscorrelations between combined maxillary incisors
width and the ultimate arch width in the bicuspidwidth and the ultimate arch width in the bicuspid
and molar areas.and molar areas.
Its was found in subsequent studies by Nimkaran,Its was found in subsequent studies by Nimkaran,
milesm O’Reilly & weyant that points index overmilesm O’Reilly & weyant that points index over
estimate interpremolar and intermolar width by 2.5estimate interpremolar and intermolar width by 2.5
mm- 4.7. mm.mm- 4.7. mm.
Ponts index does not take into account with thePonts index does not take into account with the
alignmebt of teeth or malformations (peg laterls).alignmebt of teeth or malformations (peg laterls).

Anatomic variations are seen with moreAnatomic variations are seen with more
frequency among upper incisors than lowerfrequency among upper incisors than lower
incisors.incisors.
This study was conducted on French population .This study was conducted on French population .
it may not apply to other ethnic groupsit may not apply to other ethnic groups
Finally clinical validity of this index is unproven.Finally clinical validity of this index is unproven.
 LinderharthLinderharth modified original ponts formulamodified original ponts formula
for anterior and posterior arch width.for anterior and posterior arch width.

Ideal anterior arch width= SI/85x100Ideal anterior arch width= SI/85x100
Ideal posterior arch width = SI/65x100Ideal posterior arch width = SI/65x100
Schmuth, Ritter, Werse and Benthake haveSchmuth, Ritter, Werse and Benthake have
suggested different anterior and posterior ideal archsuggested different anterior and posterior ideal arch
widths for a given sum of upper incisors.widths for a given sum of upper incisors.

SCHWARZ ANALYSISSCHWARZ ANALYSIS
Schwarz presented an analysis for ideal inter-Schwarz presented an analysis for ideal inter-
premolar and intermolar widths that were correlatedpremolar and intermolar widths that were correlated
for particular facial type.for particular facial type.
Facial types were classified as narrow, normal orFacial types were classified as narrow, normal or
broad by him.broad by him.
The intermolar measured width of Schwarz differsThe intermolar measured width of Schwarz differs
from Pont’s. it is the distance between central pitsfrom Pont’s. it is the distance between central pits
of occlusal fissures of first molarsof occlusal fissures of first molars
Scharz analysis is calculated with appropriateScharz analysis is calculated with appropriate
formula.formula.
 In narrow faces, the first premolar width is SI+In narrow faces, the first premolar width is SI+
6mm while intermolar width is SI+12mm.6mm while intermolar width is SI+12mm.www.indiandentalacademy.comwww.indiandentalacademy.com

In an average face intermolar width is SI+7mmIn an average face intermolar width is SI+7mm
and intermolar width SI=14mm.and intermolar width SI=14mm.
 Inter-premolar widths SI+8mm and intermolarInter-premolar widths SI+8mm and intermolar
widths of SI+16mm are seen in broad faces.widths of SI+16mm are seen in broad faces.
But’ further research has conclusively proved thatBut’ further research has conclusively proved that
Schwarz analysis over estimated interpremolarSchwarz analysis over estimated interpremolar
widths of male and females by 2.5mm. –4.3mm.widths of male and females by 2.5mm. –4.3mm.

Mc. NAMAR’S ANALYSISMc. NAMAR’S ANALYSIS
McNamaa proposed a simple rule of thumbMcNamaa proposed a simple rule of thumb
indicating an idea average intermolar width I maleindicating an idea average intermolar width I male
of 37.4mm and in females of 36.2mm.of 37.4mm and in females of 36.2mm.
This ideal value is compared to the measuredThis ideal value is compared to the measured
value.value.
The intermolar width is measured from midpointThe intermolar width is measured from midpoint
of lingual surface of maxilla first molars to itsof lingual surface of maxilla first molars to its
counterpart on the other side.counterpart on the other side.
 McNamara collected data from study of HoweMcNamara collected data from study of Howe
and co-workers who compared arch widths of twoand co-workers who compared arch widths of two
subjectively selected groups of dental casts-subjectively selected groups of dental casts-
crowded and un-crowded.crowded and un-crowded.

But the original study is open to subjectiveBut the original study is open to subjective
selection bias (personal concepts of whatselection bias (personal concepts of what
constitutes a desired or ideal arch form mayconstitutes a desired or ideal arch form may
unknowingly impact selection of cases).unknowingly impact selection of cases).
 Hence, McNamara’s rule of thumb overHence, McNamara’s rule of thumb over
estimated required molar width by 2.7-3.5mm inestimated required molar width by 2.7-3.5mm in
sample of males in the study of Nimkaran, Miles,sample of males in the study of Nimkaran, Miles,
O’Reilly and Weyant.O’Reilly and Weyant.
 In the sample of females it over estimatedIn the sample of females it over estimated
intermolar widths by 3.7mm on average.intermolar widths by 3.7mm on average.
The lack of statistical significance depicts highThe lack of statistical significance depicts high
variability of intermolar width in females.variability of intermolar width in females.

KORKHAUS ANALYSISKORKHAUS ANALYSIS
According to Korkhaus (1938). There is a specificAccording to Korkhaus (1938). There is a specific
value of distance from labial surface of centralvalue of distance from labial surface of central
incisors interpremolar line for a particular addedincisors interpremolar line for a particular added
width of incisors.width of incisors.
This value called as anterior arch length isThis value called as anterior arch length is
defined as the perpendicular from most anteriordefined as the perpendicular from most anterior
labial surface of incisors to connecting line oflabial surface of incisors to connecting line of
reference points of anterior arch width.reference points of anterior arch width.
This measurement reveals the anterior-posteriorThis measurement reveals the anterior-posterior
malpositioning of incisors, the formula for anteriormalpositioning of incisors, the formula for anterior
arch length by Korkhaus is as followsarch length by Korkhaus is as follows

Similar methods were put forward by Weise andSimilar methods were put forward by Weise and
Brune.Brune.
 Korkhaus analysis is applicable to bothKorkhaus analysis is applicable to both
arches. The anterior arch length of mandible isarches. The anterior arch length of mandible is
shorter than Masxilla’s.shorter than Masxilla’s.

ANALYSIS OF ARCH SYMMETRYANALYSIS OF ARCH SYMMETRY
These symmetry analyses estimate the right-leftThese symmetry analyses estimate the right-left
differences in transverse and antero-posterior toothdifferences in transverse and antero-posterior tooth
positions. Mid-palatal raphae is used as thepositions. Mid-palatal raphae is used as the
reference plane for transverse symmetry analysis ofreference plane for transverse symmetry analysis of
maxilla.maxilla.
 Similarly lingual freenum (Korkhuas, 1939) toSimilarly lingual freenum (Korkhuas, 1939) to
form the anterior mark of the reference plane. Theform the anterior mark of the reference plane. The
posterior mark is the perpendicular drawn fromposterior mark is the perpendicular drawn from
posterior extend of mid-palatal raphae of maxillaryposterior extend of mid-palatal raphae of maxillary
case on to mandibular case.case on to mandibular case.
 The tuberocity plane that passes throughThe tuberocity plane that passes through
distal most tuberocity is the reference plane fordistal most tuberocity is the reference plane for
comparing antero-posterior symmetry.comparing antero-posterior symmetry.www.indiandentalacademy.comwww.indiandentalacademy.com

SymmetrographSymmetrograph
Bernklau introduced a transpartent measuringBernklau introduced a transpartent measuring
grid of 2mm square scale and two metal rods.grid of 2mm square scale and two metal rods.
The calibrated grid is sturdily fixed on mid palatalThe calibrated grid is sturdily fixed on mid palatal
raphae.raphae.
 Since it is well oriented to midpalatal raphae,Since it is well oriented to midpalatal raphae,
tuberocity plane and occlusal plane, thetuberocity plane and occlusal plane, the
asymmetrical arch shape is transverse and antero-asymmetrical arch shape is transverse and antero-
posterior directions can be assessed.posterior directions can be assessed.
Analysis of transverse symmetry is important inAnalysis of transverse symmetry is important in
the following cases:the following cases:

 In cases of unilateral cross bite to assess left-In cases of unilateral cross bite to assess left-
right asymmetry.right asymmetry.
 Incase of asymmetric arches with crowding.Incase of asymmetric arches with crowding.
 Midline shift cases (dental)Midline shift cases (dental)
 Differentiation between dental and skeletalDifferentiation between dental and skeletal
midline shift in the mandible.midline shift in the mandible.
Analysis of antero-posterior symmetry is importantAnalysis of antero-posterior symmetry is important
inin
 Suspected mesial migration of posterior teeth.Suspected mesial migration of posterior teeth.
 In the cases of rotated molars.In the cases of rotated molars.

TOOTH SIZE DISCREPANCIESTOOTH SIZE DISCREPANCIES
 Tooth size discrepancies are thought to existTooth size discrepancies are thought to exist
frequently in the human dentition.frequently in the human dentition.
If a patient has significant tooth size discrepancy,If a patient has significant tooth size discrepancy,
orthodontic algiment of the teeth into idealorthodontic algiment of the teeth into ideal
occlusion may not be possible.occlusion may not be possible.
 Prior to discovery of different mathematicalPrior to discovery of different mathematical
formulation, diagnosis plaster set-ups were the onlyformulation, diagnosis plaster set-ups were the only
diagnostic tool available.diagnostic tool available.
But, now due to its’s convenience and relativeBut, now due to its’s convenience and relative
usefulness, Bolton analysis is most widely used.usefulness, Bolton analysis is most widely used.
 However, when a large anterior tooth-sizeHowever, when a large anterior tooth-size
problem is suspected a set up is likely indicated.problem is suspected a set up is likely indicated.www.indiandentalacademy.comwww.indiandentalacademy.com

BOLTON ANALYSISBOLTON ANALYSIS
The Bolton analysis based on ratio’s between theThe Bolton analysis based on ratio’s between the
mesio-distal tooth diameter sums of mandibular andmesio-distal tooth diameter sums of mandibular and
maxillary dentitions, remains the most recognizedmaxillary dentitions, remains the most recognized
and widely used method for detecting inter-archand widely used method for detecting inter-arch
tooth size discrepancies.tooth size discrepancies.
Study of the ratio proposed by him help inStudy of the ratio proposed by him help in
estimating the overjet and overbite relationshipsestimating the overjet and overbite relationships
that will likely obtain after the treatment is finished,that will likely obtain after the treatment is finished,
the effect of contemplated extration on posteriorthe effect of contemplated extration on posterior
occlusion and incisor relationship and identificationocclusion and incisor relationship and identification
of occlusal misfit produced tooth sizeof occlusal misfit produced tooth size
incompatibilities.incompatibilities.

Method:Method:
 The width of all teeth mesial to permanen molars areThe width of all teeth mesial to permanen molars are
measured an added up individually for both arches.measured an added up individually for both arches.
 Sum of the widths of mandibular 12 is divided by sumSum of the widths of mandibular 12 is divided by sum
of the widths of maxillary12 an multiplied by 100 to getof the widths of maxillary12 an multiplied by 100 to get
“overall ratio” (a mean ratio of 91.3 according to Bolton“overall ratio” (a mean ratio of 91.3 according to Bolton
will result in ideal overbite overjet relationship as well aswill result in ideal overbite overjet relationship as well as
posterior occlusion.posterior occlusion.
 A similar anterior ratio can be calculated by dividing theA similar anterior ratio can be calculated by dividing the
sum of mandibular anterior by sum of maxillarysum of mandibular anterior by sum of maxillary
anteriors and multiplying by 100. An anterior ratio ofanteriors and multiplying by 100. An anterior ratio of
77.2 will provide ideal overbite and overject relations if77.2 will provide ideal overbite and overject relations if
the angulation of incisors is correct and if thethe angulation of incisors is correct and if the
labiolingual thickness of mesial edges are notlabiolingual thickness of mesial edges are not
excessive.excessive.

 The equations to quantity the tooth materialThe equations to quantity the tooth material
excess are as followsexcess are as follows
Maxillary tooth material excessMaxillary tooth material excess
== Sum of max 12- sum of mandSum of max 12- sum of mand
12x10012x100
91.391.3
Mandibular tooth material excessMandibular tooth material excess
= Sum of mand 12= Sum of mand 12-sum of max-sum of max
12x91.312x91.3

Mandibular anterior excessMandibular anterior excess
= Sum of mand 6= Sum of mand 6- Sum of max- Sum of max
6x77.26x77.2
100100

DisadvantageDisadvantage
 Accuracy and dependability of bolton’s have beenAccuracy and dependability of bolton’s have been
challenged. Good occlusal relationships have beenchallenged. Good occlusal relationships have been
demonstrated in cases with significant Boltondemonstrated in cases with significant Bolton
discrepancies.discrepancies.
 Bolton analysis predictions do not take into account theBolton analysis predictions do not take into account the
sexual dimorphism in maxillary canine widths.sexual dimorphism in maxillary canine widths.
 population and gender composition of Bolton samplepopulation and gender composition of Bolton sample
are not specified. This implies potential selection bias.are not specified. This implies potential selection bias.
 Bolton estimates of variation were underestimatedBolton estimates of variation were underestimated
because his sample was derived from prefect class Ibecause his sample was derived from prefect class I
occlusions.occlusions.

 Blacks have larger maxillary canines premolarsBlacks have larger maxillary canines premolars
and first molars than whites and Asians. Soand first molars than whites and Asians. So
blacks differ markedly in posterior archblacks differ markedly in posterior arch
relationship.relationship.
 Lavella (1972) studied the tooth sizes inLavella (1972) studied the tooth sizes in
different populations and concluded that blacksdifferent populations and concluded that blacks
have larger overall and anterior ratios thanhave larger overall and anterior ratios than
whites and Asians.whites and Asians.
 Whites had the least. He also showed thatWhites had the least. He also showed that
overall and anterior ratios are consistentlyoverall and anterior ratios are consistently
larger in males than females, regardless oflarger in males than females, regardless of
race.race.

 In the University of Michigan growth studyIn the University of Michigan growth study
separate anterior and overall ratios wereseparate anterior and overall ratios were
established for males and females.established for males and females.
MaleMale FemaleFemale
Anterior ratioAnterior ratio 73.573.5 73.473.4
Overall ratioOverall ratio 9191 90.690.6

TOOTH THICKNESS INTERMAXILLARYTOOTH THICKNESS INTERMAXILLARY
TOOTH SIZETOOTH SIZE DISCREPANCIESDISCREPANCIES
 In a study by Rudolph, Dominguez, Ahn & Thinh toothIn a study by Rudolph, Dominguez, Ahn & Thinh tooth
thickness proved to have strong correlation with interthickness proved to have strong correlation with inter
maxillary tooth size ratio (Y = 0.57).maxillary tooth size ratio (Y = 0.57).
 They divided tooth setups into thick, having an averageThey divided tooth setups into thick, having an average
maxillary incisor thicknessmaxillary incisor thickness ≥≥2.75mm and thin, having2.75mm and thin, having
average maxillary incisor thicknessaverage maxillary incisor thickness << 2.75mm.2.75mm.
 Two prediction equations were developed by plotting aTwo prediction equations were developed by plotting a
liner regression of thickness on inter maxillary ratio forliner regression of thickness on inter maxillary ratio for
each data set.each data set.
 Then both predictions methods were applied to theThen both predictions methods were applied to the
models to test their accuracy in predicting existence ofmodels to test their accuracy in predicting existence of
tooth size discrepancies.tooth size discrepancies.

 Predicted =-7.053 (tooth thickness)+ 95.024 ifPredicted =-7.053 (tooth thickness)+ 95.024 if
tooth thicknesstooth thickness<< 2.75mm.2.75mm.
 Predicted =-1.928 (tooth thickness)+81.874, ifPredicted =-1.928 (tooth thickness)+81.874, if
tooth thicknesstooth thickness≥≥2.75mm.2.75mm.
 The new method has greater sensitivity andThe new method has greater sensitivity and
specificity than Boltons. The mean absolutespecificity than Boltons. The mean absolute
error is significantly lower than Bolton’s inerror is significantly lower than Bolton’s in
predicting ideal inter maxillary ratio.predicting ideal inter maxillary ratio.

SANIN- SAVERA TOOTH SIZESANIN- SAVERA TOOTH SIZE
ANALYSISANALYSIS
 Sanin and savera and collegues at the university ofSanin and savera and collegues at the university of
Oregon, devised a simple and ingenious procedure toOregon, devised a simple and ingenious procedure to
identify individual and group tooth size disharmonies.identify individual and group tooth size disharmonies.
 It makes use of precise measiodistal measurements ofIt makes use of precise measiodistal measurements of
crown size of each tooth, appropriate tables for toothcrown size of each tooth, appropriate tables for tooth
size distribution in the population and a chart or plottingsize distribution in the population and a chart or plotting
partint’s measurements.partint’s measurements.

ANALYSIS OF APICALBASESANALYSIS OF APICALBASES
REES ANALYSISREES ANALYSIS::
 The relation between overall extend of apical baseThe relation between overall extend of apical base
and the length of dental arch is expressed metrically forand the length of dental arch is expressed metrically for
upper and lower jaws according to Rees (1953).upper and lower jaws according to Rees (1953).
 Erase lip and check freena on the casts.Erase lip and check freena on the casts.
 Construction of 3 perpendiculars to the occlusal plane,Construction of 3 perpendiculars to the occlusal plane,
mesial to first permanent molars and the contact pointmesial to first permanent molars and the contact point
of central incisors. The lives should extend 8-10mm toof central incisors. The lives should extend 8-10mm to
vestibular fold.vestibular fold.
 Measure the distance from mesial of first permanentMeasure the distance from mesial of first permanent
molar on one side to that on the other side through themolar on one side to that on the other side through the
tips of vertical lines with the aid of a thin adhesive tape.tips of vertical lines with the aid of a thin adhesive tape.

 Determine the arch length by measuring the ach perimeterDetermine the arch length by measuring the ach perimeter
mesial to first permanent molar using apiece of brass wire.mesial to first permanent molar using apiece of brass wire.
 The measured values are compared to actual values byThe measured values are compared to actual values by
Rees.sRees.s
 Maxillary apical base-maxillary dental arch==1.5mm-+5mmMaxillary apical base-maxillary dental arch==1.5mm-+5mm
 Madibular apical base –Mandibular dental arch = +2mm-Madibular apical base –Mandibular dental arch = +2mm-
+7mm+7mm
 Maxillary apical base-Mandibular apical base = +3mm-Maxillary apical base-Mandibular apical base = +3mm-
+9.5mm+9.5mm
 Maxillary dental arch-Mandibular dental arch =+5mm-+10mmMaxillary dental arch-Mandibular dental arch =+5mm-+10mm
 The analysis provides information for treatment planning inThe analysis provides information for treatment planning in
borderline cases.borderline cases.

ASHLEY HOWES ANALYSISASHLEY HOWES ANALYSIS
 Howes devised a formula for determiningHowes devised a formula for determining
whether apical bases could accommodatewhether apical bases could accommodate
patients teeth.patients teeth.
 He considered tooth crowdind to be due toHe considered tooth crowdind to be due to
deficiency in arch width rather than arch length.deficiency in arch width rather than arch length.
 He proposed a relationship between the toothHe proposed a relationship between the tooth
width of 12 teeth anterior to second permanentwidth of 12 teeth anterior to second permanent
molars and width of arch in the first premolarmolars and width of arch in the first premolar
region.region.
 This analysis is applicable to both arches.This analysis is applicable to both arches.

MethodMethod::
 Add the widths of all the teeth from firstAdd the widths of all the teeth from first
permanent molars forward on both sides to getpermanent molars forward on both sides to get
tooth material (T.M)tooth material (T.M)
 Determine premolars diameter (P.M.D)) byDetermine premolars diameter (P.M.D)) by
measuring the arch width between buccal cuspmeasuring the arch width between buccal cusp
tips of first premolars on either side.tips of first premolars on either side.
 Premolar basal arch width (P.M.B.A.W)is thePremolar basal arch width (P.M.B.A.W)is the
diameter of apical base. The measurement ofdiameter of apical base. The measurement of
the distance from canine fossa on one side ofthe distance from canine fossa on one side of
the arch to the other side gives PMBAW (If thethe arch to the other side gives PMBAW (If the
canine fossa is not clearly distinguishable takecanine fossa is not clearly distinguishable take
the point 8mm below interdental papilla distal tothe point 8mm below interdental papilla distal to
canine.canine. www.indiandentalacademy.comwww.indiandentalacademy.com

 Basal arch length is measured at the midline from theBasal arch length is measured at the midline from the
estimated anterior limits of apical base to aestimated anterior limits of apical base to a
perpendicular that is tangent to distal surfaces of firstperpendicular that is tangent to distal surfaces of first
molars. The ratio of basal arch length to tooth materialmolars. The ratio of basal arch length to tooth material
BAL/TM is obtained by dividing arch lengths by sum ofBAL/TM is obtained by dividing arch lengths by sum of
widths of 12 teeth.widths of 12 teeth.
 If the PMBAW is greater than PMD, the it is anIf the PMBAW is greater than PMD, the it is an
indication that arch expansion is possible.indication that arch expansion is possible.
 According to Howe, to achieve normal occlusion with fullAccording to Howe, to achieve normal occlusion with full
complement of teeth the basal arch width at thecomplement of teeth the basal arch width at the
premolar region should be44% of the sum ofpremolar region should be44% of the sum of
mesiodistal width of all the teeth mesial to secondmesiodistal width of all the teeth mesial to second
molar.molar.

 This condition can be treated without extraction.This condition can be treated without extraction.
 If it goes below 37% that indication need forIf it goes below 37% that indication need for
extraction of premolars. 37-44% is treated asextraction of premolars. 37-44% is treated as
border line case.border line case.
 Since this method was introduced rapidSince this method was introduced rapid
palatal expansion has come into more commonpalatal expansion has come into more common
use, Now the clinicians can alter the apical baseuse, Now the clinicians can alter the apical base
itself by rapid palatal expansion.itself by rapid palatal expansion.

LOWER INCISOR SPACELOWER INCISOR SPACE
ANALYSISANALYSIS
 An assessment of amount of crowding orAn assessment of amount of crowding or
spacing of the anterior teeth in one of the firstspacing of the anterior teeth in one of the first
steps in orthodontic diagnosis and treatmentsteps in orthodontic diagnosis and treatment
planning.planning.
 Objective information on the amount of archObjective information on the amount of arch
size tooth size discrepancy in the incisor regionsize tooth size discrepancy in the incisor region
often tips the balance for or against premolaroften tips the balance for or against premolar
extraction.extraction.

ANTERIOR SPACE ANALYSIS OFANTERIOR SPACE ANALYSIS OF
MERRIFIELDMERRIFIELD
 The mesiodistal widths of each of six anterior teeth,The mesiodistal widths of each of six anterior teeth,
canine to canine is measured with at least 0.1mmcanine to canine is measured with at least 0.1mm
accuracy. The sum of these six measurement is theaccuracy. The sum of these six measurement is the
space required in the anterior segment.space required in the anterior segment.
 Then the anterior space available is measured whichThen the anterior space available is measured which
is a mill metric assessment of amount of bony supportis a mill metric assessment of amount of bony support
present anterior segment for tooth alignment.present anterior segment for tooth alignment.
 Measurement of space available requires theMeasurement of space available requires the
knowledge of whether incisors are to be moved bodilyknowledge of whether incisors are to be moved bodily
(Subjective measurement or if alignment and(Subjective measurement or if alignment and
intercuspation of anterior teeth can be achieved throughintercuspation of anterior teeth can be achieved through
tipping and torquing.tipping and torquing.

 The space can be measured with a pliable rulerThe space can be measured with a pliable ruler
that can be held in the arch form, a photocopythat can be held in the arch form, a photocopy
of the cast that can be measured with a digitizerof the cast that can be measured with a digitizer
of brass ligature wire which can be shaped toof brass ligature wire which can be shaped to
arch form, then 8 traightened and measured.arch form, then 8 traightened and measured.
 The difference between available space minusThe difference between available space minus
required space is then calculated.required space is then calculated.
 A negative value indicates the amount by whichA negative value indicates the amount by which
the mid arch has to be modified to alleviatethe mid arch has to be modified to alleviate
anterior crowding.anterior crowding.
 A positive value confirms that adequate spaceA positive value confirms that adequate space
exists for alignment of anterior teeth.exists for alignment of anterior teeth.

 The correlation between required space andThe correlation between required space and
available space is positive and high (r=0.87).available space is positive and high (r=0.87).
 anterior space analysis is a sensitive indicatoranterior space analysis is a sensitive indicator
on the amount of space actually needed foron the amount of space actually needed for
alignment.alignment.
 But, it disregards the axiversions of anteriorBut, it disregards the axiversions of anterior
teethteeth

IRRAGULARITY INDEX BY LITTLEIRRAGULARITY INDEX BY LITTLE
 Instead of measuring anterior crown diameters, thisInstead of measuring anterior crown diameters, this
method calculates sum of distances between toothmethod calculates sum of distances between tooth
contact points measured parallel with occlusal planecontact points measured parallel with occlusal plane
 In other words it is the sum of liner displacements ofIn other words it is the sum of liner displacements of
the anatomic contact points of each of the lower incisorsthe anatomic contact points of each of the lower incisors
from adjacent tooth’s contact point.from adjacent tooth’s contact point.
 Irregularity index is a measure of irregularity alone.Irregularity index is a measure of irregularity alone.
 When the axial inclinations of teeth diverge or when theWhen the axial inclinations of teeth diverge or when the
teeth are displaced or when the teeth are displaced butteeth are displaced or when the teeth are displaced but
not overlap, this index does not mention about thenot overlap, this index does not mention about the
space available for alignment which might readily bespace available for alignment which might readily be
there.there.

PECK & PECK INDEXPECK & PECK INDEX
 Peck and peck observed that persons with idealPeck and peck observed that persons with ideal
incisal arrangement had smaller mesiodistalincisal arrangement had smaller mesiodistal
width and comparatively larger labiolingualwidth and comparatively larger labiolingual
width than persons with lower incisor crowding.width than persons with lower incisor crowding.
 Based on this finding they suggested certainBased on this finding they suggested certain
guidelines for lower arch.guidelines for lower arch.

Method:Method:
 Calculate the mesiodistal and labiolingual widthCalculate the mesiodistal and labiolingual width
of mandibular incisors.of mandibular incisors.
 Calculate the proportion of mesiodistal width ofCalculate the proportion of mesiodistal width of
each tooth to labiolingual width.each tooth to labiolingual width.
 Mean value for lower central incisor-88% toMean value for lower central incisor-88% to
92%92%
 Mean value for lower lateral incisor –90% toMean value for lower lateral incisor –90% to
95%95%
 If the value for a given case is more than meanIf the value for a given case is more than mean
value then, mesiodistal width of the tooth isvalue then, mesiodistal width of the tooth is
greater than laniolingual width and hencegreater than laniolingual width and hence
proximal stripping is indicated.proximal stripping is indicated.www.indiandentalacademy.comwww.indiandentalacademy.com

ARCH LENGTH TOOTH MATERIALARCH LENGTH TOOTH MATERIAL
DISCREPANCYDISCREPANCY
ARCH PERIMETER ANALYSISARCH PERIMETER ANALYSIS
 Many malocclusions occur as a result of discrepancyMany malocclusions occur as a result of discrepancy
between arch length and tooth material.between arch length and tooth material.
 Arch perimeter analysis helps in determining theArch perimeter analysis helps in determining the
extend of this discrepancy in maxillary arch.extend of this discrepancy in maxillary arch.
 Same method on the lower arch is called “CAREY’S”Same method on the lower arch is called “CAREY’S”
Analysis method.Analysis method.

 Sum the mesiodistal widths of all the teethSum the mesiodistal widths of all the teeth
mesial to first permanent molars to find themesial to first permanent molars to find the
tooth material.tooth material.
 Determine the arch perimeter start from theDetermine the arch perimeter start from the
mesiobuccal line angle of first molar, along themesiobuccal line angle of first molar, along the
contacts of premolars, through incisive papillacontacts of premolars, through incisive papilla
on an imaginaily respositioned arch form in theon an imaginaily respositioned arch form in the
incisor segment, the again through premolarincisor segment, the again through premolar
contacts on the other side to mesiobuccal linecontacts on the other side to mesiobuccal line
angle of first molar.angle of first molar.
 Find out the discrepancy. If tooth material ismFind out the discrepancy. If tooth material ism
more this leads to crowding.. on the other handmore this leads to crowding.. on the other hand
excess of arch perimeter result in spacing.excess of arch perimeter result in spacing.

CAREYS ANALYSIS ON LOWERCAREYS ANALYSIS ON LOWER
ARCHARCH
 Essentially the same procedure and inference.Essentially the same procedure and inference.
 But while assessing the arch perimeter the wireBut while assessing the arch perimeter the wire
is passes along the incisal edges of loweris passes along the incisal edges of lower
incisors.incisors.
 If they are proclined, the wire is passesIf they are proclined, the wire is passes
through angular and if they are retroclined wirethrough angular and if they are retroclined wire
is passed labially.is passed labially.
 If the discrepancy is 0-2.5mm proximalIf the discrepancy is 0-2.5mm proximal
stripping is carried out.stripping is carried out.

LUNDSTROM’S SGMENTALLUNDSTROM’S SGMENTAL
ANALYSISANALYSIS
 Segmental analysis involves an indirectSegmental analysis involves an indirect
assessment of dental arch perimeter.assessment of dental arch perimeter.
 The dental arch is divided into six straight lineThe dental arch is divided into six straight line
segments of tow teeth per segment, includingsegments of tow teeth per segment, including
first permanent molas, the record thefirst permanent molas, the record the
mesiodental width of the teeth and sum themmesiodental width of the teeth and sum them
for each segment and add them up for netfor each segment and add them up for net
discrepancy.discrepancy.

DISCREPANCY CALCULATIONDISCREPANCY CALCULATION
 The difference between the actual and idealThe difference between the actual and ideal
arch length, on the alignment of the teeth isarch length, on the alignment of the teeth is
determined by amount of dental crowding anddetermined by amount of dental crowding and
antero-posterior positioning of incisors inantero-posterior positioning of incisors in
relation to the facial skeleton.relation to the facial skeleton.
 So comprehensive spaceanalysis requiresSo comprehensive spaceanalysis requires
cephalogram.cephalogram.
 Performed on both arches.Performed on both arches.

Methods:Methods:
 Make out the difference between the actual and idealMake out the difference between the actual and ideal
arch length on the case. Also find out the amount ofarch length on the case. Also find out the amount of
depth of curve of spee, separately on left and right side.depth of curve of spee, separately on left and right side.
Add the 3 values to get dental discrepancy.(D.D)Add the 3 values to get dental discrepancy.(D.D)
 The distance of incisor to N-Pog line s calculated theThe distance of incisor to N-Pog line s calculated the
variation fromte standard value is noted down asvariation fromte standard value is noted down as
sagittal discrepancy. (S.D). [ Standard value in thesagittal discrepancy. (S.D). [ Standard value in the
maxillary in the mandibular arch-2 to+2mm].maxillary in the mandibular arch-2 to+2mm].
 discrepancy per arch side is equal todiscrepancy per arch side is equal to DDDD +SD+SD
22
 This method is applicable to mixed dentition if theThis method is applicable to mixed dentition if the
growth related changes of N-Pog line are taken intogrowth related changes of N-Pog line are taken into
account.account.

CROWDING INDEXCROWDING INDEX
 The widest mesiodistal dimensions of all teethThe widest mesiodistal dimensions of all teeth
and the available space for each tooth wereand the available space for each tooth were
measured and used to calculate the crowdingmeasured and used to calculate the crowding
index.index.
 In occlusal view, the C1 was determined byIn occlusal view, the C1 was determined by
measuring the available horizontal spacemeasuring the available horizontal space
parallel to occlusal plane, between the leastparallel to occlusal plane, between the least
displaced interproximal contact points.displaced interproximal contact points.
 The least displaced contact in that point onThe least displaced contact in that point on
adjacent mesial and distal surfaces, that is mostadjacent mesial and distal surfaces, that is most
in line with overall arch form.in line with overall arch form.

 The actual widths of corresponding tooth wasThe actual widths of corresponding tooth was
then deducted from available space to givethen deducted from available space to give
resultant amount of crowding (Positiveresultant amount of crowding (Positive
measure) or spacing (negative measure) formeasure) or spacing (negative measure) for
each tooth, mesial to first molars, the XI waseach tooth, mesial to first molars, the XI was
then calculated by summing the individualthen calculated by summing the individual
differences,differences,
 The crowding index is a valid and moreThe crowding index is a valid and more
reproducible measure of dental crowding thanreproducible measure of dental crowding than
objective measurementobjective measurement

MIXED DENTITION ANALYSISMIXED DENTITION ANALYSIS
 The purpose of mixed dentition analysis is toThe purpose of mixed dentition analysis is to
evaluate the amount of space available in theevaluate the amount of space available in the
arch or succeeding permanent teeth andarch or succeeding permanent teeth and
necessary occlusal adjustments.necessary occlusal adjustments.
 It requires accurate prediction of theIt requires accurate prediction of the
mesiodental widths of unerupted permanentmesiodental widths of unerupted permanent
teeth.teeth.
 Mixed dentition analysis is an importantMixed dentition analysis is an important
criterion in determining whether treatment plancriterion in determining whether treatment plan
is going to involve serial extraction, guidance ofis going to involve serial extraction, guidance of
eruption, space maintenance, space regainingeruption, space maintenance, space regaining
or just periodic observation of patient.or just periodic observation of patient.

 To complete an analysis 3 factors are noted.To complete an analysis 3 factors are noted.
 Sizes of permanent teeth anterior to firstSizes of permanent teeth anterior to first
permanent molar.permanent molar.
 Arch perimeterArch perimeter
 Expected changes in the arch perimeter withExpected changes in the arch perimeter with
growth.growth.

 To predict the mesiodistal crown widths ofTo predict the mesiodistal crown widths of
unerupted permanent teeth 4 approaches areunerupted permanent teeth 4 approaches are
employedemployed
 Use of measurement from erupted teeth.Use of measurement from erupted teeth.
 Use of measurements from radiograph.Use of measurements from radiograph.
 Use of combination of measurements (these areUse of combination of measurements (these are
considered at most accurate).considered at most accurate).
 Use of mean values for supporting zoneUse of mean values for supporting zone

MOYERS ANALYSISMOYERS ANALYSIS
 Moyers method makes use of the permanentMoyers method makes use of the permanent
teeth already erupted in the month to predict theteeth already erupted in the month to predict the
sizes of unerupted cuspids and premolars. Itssizes of unerupted cuspids and premolars. Its
is a widely used method and emplys predicationis a widely used method and emplys predication
tables. Lower incisor mesiodistal widths aretables. Lower incisor mesiodistal widths are
measured and added to predict the sizes ofmeasured and added to predict the sizes of
unerupted teeth from the table.unerupted teeth from the table.
 Its has minimal systematic error and range ofIts has minimal systematic error and range of
such error is knownsuch error is known
 Does not require sophisticated clinicalDoes not require sophisticated clinical
judgement.judgement.
 Not time consumingNot time consuming

 No radiographic projectionsNo radiographic projections
 Allows for sexual dimorphisms with equalAllows for sexual dimorphisms with equal
accuracyaccuracy
 It can be used directly inside patients month.It can be used directly inside patients month.
 Used for both archesUsed for both arches

Methods:Methods:
 Record the mesiodistal width of each of theRecord the mesiodistal width of each of the
mandibular incisors with Boley’s guagemandibular incisors with Boley’s guage
 Add the values of the incisors on one side of theAdd the values of the incisors on one side of the
arch. Transfer the value to the guage. Placearch. Transfer the value to the guage. Place
one tip of the guage in the midline and other inone tip of the guage in the midline and other in
the precise point where the distal surface of thethe precise point where the distal surface of the
lateral incisor will be when it will have beenlateral incisor will be when it will have been
aligned. Repeat this on the other side. Thisaligned. Repeat this on the other side. This
step is very important in the case of incisorstep is very important in the case of incisor
crowding where second mark will be oncrowding where second mark will be on
deciduous canine.deciduous canine.
 Compute the amount of space available afterCompute the amount of space available after
incisor alignment. It is the distance molar.incisor alignment. It is the distance molar.www.indiandentalacademy.comwww.indiandentalacademy.com

 Predict the size of unerupted cuspids andPredict the size of unerupted cuspids and
premolars from probability chartpremolars from probability chart
 Commpute the amount of space left in the archCommpute the amount of space left in the arch
fro molar adjustment by substracting estimatedfro molar adjustment by substracting estimated
of incisorsof incisors

 Two important differences are there when this method isTwo important differences are there when this method is
applied to upper jawapplied to upper jaw
 Different probability chart is employedDifferent probability chart is employed
 Allowance must be made for overjet correction whenAllowance must be made for overjet correction when
measuring the space to be occupied by aligned incisors.measuring the space to be occupied by aligned incisors.
 7575thth
level of probability is preferred by most clinicianslevel of probability is preferred by most clinicians
since crowding is a more severe clinical problem andsince crowding is a more severe clinical problem and
use of 75use of 75thth
level of probability takes the clinician to saferlevel of probability takes the clinician to safer
side.side.
 However, experienced clinician with precisionHowever, experienced clinician with precision
appliances and cephalometrics may use 50appliances and cephalometrics may use 50thth
level oflevel of
probability since it is more of a precise estimate.probability since it is more of a precise estimate.
Similar tables are given by Dorschl et al.Similar tables are given by Dorschl et al.

TANAKA JOHNSON ANALYSISTANAKA JOHNSON ANALYSIS
 Developed another way to predict the sizes ofDeveloped another way to predict the sizes of
unerupted canines and premolars based onunerupted canines and premolars based on
lower incisor measurementslower incisor measurements
 It is very convenient in the sense that noIt is very convenient in the sense that no
radiographs or reference tables are needed.radiographs or reference tables are needed.

Methods:Methods:
 Sum up the widths of lower incisors.Sum up the widths of lower incisors.
 Divide the value by two and add 10.5 mm to obtainDivide the value by two and add 10.5 mm to obtain
estimated width of mandibular canine and premolars inestimated width of mandibular canine and premolars in
one quadrant.one quadrant.
 Divide the same value by two and add 11mm to obtainDivide the same value by two and add 11mm to obtain
estimated width of maxillay canine and premolars in oneestimated width of maxillay canine and premolars in one
quadrant.quadrant.
 Space available =Total arch length –combined width of-Space available =Total arch length –combined width of-
2x (Calculate width of canine & premolars.)2x (Calculate width of canine & premolars.)

 This method is similar to Moyer’s (their correctionThis method is similar to Moyer’s (their correction
coefficient werecoefficient were γγ=0.63 for maxillary arch and=0.63 for maxillary arch and γγ=0.65 for=0.65 for
mandibular arch).mandibular arch).
 Unlike Moyer’s who separtated the sexes, Tavala &Unlike Moyer’s who separtated the sexes, Tavala &
Johnson combined the sexes in their study.Johnson combined the sexes in their study.
 They originally advocated use of 75They originally advocated use of 75thth
percentile.percentile.
 But now it is evident that even 50But now it is evident that even 50thth
percentile overpercentile over
predicts unerupted tooth width by 0.6mm in the upperpredicts unerupted tooth width by 0.6mm in the upper
arch and 0.4mm in the lower arch.arch and 0.4mm in the lower arch.
 So 50So 50thth
percentile gives a reasonable hedge againstpercentile gives a reasonable hedge against
under predicting the tooth size.under predicting the tooth size.

REVISED HIXON OLDFATHERREVISED HIXON OLDFATHER
APPROACH BY STALEY & KERBERAPPROACH BY STALEY & KERBER
 Hixon and old-father were the first to develop anHixon and old-father were the first to develop an
equation to predict the mesiodistal width uneruptedequation to predict the mesiodistal width unerupted
mandibular canine and premolars in children whomandibular canine and premolars in children who
participated in IOWA growth study 91946-19600.participated in IOWA growth study 91946-19600.
 In a cross validation on the same subjects in 1980In a cross validation on the same subjects in 1980
Hixon & old father performed poorly than expected.Hixon & old father performed poorly than expected.
 The means of predicted widths were significantlyThe means of predicted widths were significantly
smaller then the actual widths.smaller then the actual widths.
Rigth side= -0.41mmRigth side= -0.41mm
Left side = -0.43mmLeft side = -0.43mm
 This finding is apparent in the studies of Moyers,This finding is apparent in the studies of Moyers,
Kaplan, Smith karavek etcKaplan, Smith karavek etc

 The predictor or independent variable asThe predictor or independent variable as
developed by Hixon & oldfather consist of thedeveloped by Hixon & oldfather consist of the
sum of case widths of mandibular central andsum of case widths of mandibular central and
lateral incisors thelateral incisors the
 long cone periapical radiopgraphic widths oflong cone periapical radiopgraphic widths of
unerpted first and second premolars, theunerpted first and second premolars, the
original equation took into accountoriginal equation took into account
measurements from left side of the arch.measurements from left side of the arch.
 (high degree of bilateral symmetry exists in(high degree of bilateral symmetry exists in
canine an premolar widths) Revised equationcanine an premolar widths) Revised equation
takes measurements from both sides.takes measurements from both sides.

Methods;Methods;
 Measurement the mesiodistal widths of lowerMeasurement the mesiodistal widths of lower
right central incisors on the casr.right central incisors on the casr.
 Measure the widths of lower right first andMeasure the widths of lower right first and
second premolars on the Periapical film.second premolars on the Periapical film.
 Take sum of these widths to the predictionTake sum of these widths to the prediction
graph to determine combined predicted width.graph to determine combined predicted width.
The simple computation convenient graphThe simple computation convenient graph
make this accuratge prediction method suitablemake this accuratge prediction method suitable
for clinical use.for clinical use.
 Add one standard error of estimate to theAdd one standard error of estimate to the
predicted sum as hedge against underpredicted sum as hedge against under
predicting true size of teeth.predicting true size of teeth.

 Use the same procedure on the left side.Use the same procedure on the left side.
 Add the predicted widths of rights and leftAdd the predicted widths of rights and left
canines and premolars to width of eruptedcanines and premolars to width of erupted
incisors to compute lower arch tooth size mesialincisors to compute lower arch tooth size mesial
to first permanent molars.to first permanent molars.
 The graph is accurate to nearest of 0.1mm .The graph is accurate to nearest of 0.1mm .
 Sum of the predictor variable are in horizontalSum of the predictor variable are in horizontal
axis.axis.
 Following the value upward will intersect theFollowing the value upward will intersect the
prediction line in the graph.prediction line in the graph.
 Corresponding prediction value is made outCorresponding prediction value is made out
from vertical axis.from vertical axis.www.indiandentalacademy.comwww.indiandentalacademy.com

 The predicted value is compared to the archThe predicted value is compared to the arch
length available.length available.
 The arch length available is made out byThe arch length available is made out by
adding the length of deciduous canine part ofadding the length of deciduous canine part of
the arch to the length measured betweenthe arch to the length measured between
mesial surface of first permanent molar to distalmesial surface of first permanent molar to distal
surface of deciduous canine.surface of deciduous canine.
 Addition of one standard error of estimate toAddition of one standard error of estimate to
the predicted sum would yield a predicted sumthe predicted sum would yield a predicted sum
of widths at the 84of widths at the 84thth
percentile.percentile.
 This would provide assurance that canine andThis would provide assurance that canine and
premolar widths are larger than true sum inpremolar widths are larger than true sum in
84% of cases.84% of cases.

 A mean difference of zero is required forA mean difference of zero is required for
unbiased, accurate prediction.unbiased, accurate prediction.
 When the original Hixon & old father producedWhen the original Hixon & old father produced
significant differences, the newer approachsignificant differences, the newer approach
values are not significantly different from zero.values are not significantly different from zero.
 The equation for right and left sides areThe equation for right and left sides are
different.different.
 The differences between the equation wereThe differences between the equation were
moderated in this study using averages ofmoderated in this study using averages of
independent and dependent variables,independent and dependent variables,
 Finally, this analysis is was successfully cross-Finally, this analysis is was successfully cross-
validated.validated. www.indiandentalacademy.comwww.indiandentalacademy.com

IOWA PREDICTION METHODIOWA PREDICTION METHOD
 Another prediction method using data from Iowa growth studyAnother prediction method using data from Iowa growth study
was developed by staley et al to predict the mesiodistalwas developed by staley et al to predict the mesiodistal
widths of unerupted canines and premolars in both upper andwidths of unerupted canines and premolars in both upper and
lower arches.lower arches.
 Only measurements of radiographic widths of uneruptedOnly measurements of radiographic widths of unerupted
canines and premolars are used as predictor variable.canines and premolars are used as predictor variable.
 Sum of these widths are transferred to prediction graph toSum of these widths are transferred to prediction graph to
obtain predicted sum of canine and premolars widths.obtain predicted sum of canine and premolars widths.
 For the most accurate prediction measurements should beFor the most accurate prediction measurements should be
repeated for the other side.repeated for the other side.
 Different graphs are used for maxilla and mandible.Different graphs are used for maxilla and mandible.
 This analysis has been cross-validated successfullyThis analysis has been cross-validated successfully

PROPOTIONAL EQUATION PREDICTIONPROPOTIONAL EQUATION PREDICTION
METHODMETHOD
 It is the alternative method used to estimate theIt is the alternative method used to estimate the
unerupted tooth’s width if most of the canines andunerupted tooth’s width if most of the canines and
premolars are crupted.premolars are crupted.
 The width of unerupted tooth (a second premolar0 anedThe width of unerupted tooth (a second premolar0 aned
erupted too (Primary second molar ) are measured onerupted too (Primary second molar ) are measured on
same Periapical film.same Periapical film.
 The width of decidious second molar is measured onThe width of decidious second molar is measured on
the plaster cast. The width of unerupted tooth can bethe plaster cast. The width of unerupted tooth can be
made out by following propotional equation.made out by following propotional equation.

Unerupted tooth widthUnerupted tooth width Erupted toothErupted tooth
width(cast)width(cast)
Unerupted tooth width (X-ray) = Erupted tooth width (X-Unerupted tooth width (X-ray) = Erupted tooth width (X-
ray)ray)
Unerupted tooth width =Unerupted tooth width =
Erupted tooth width (cast) x unerupted tooth width (x-Erupted tooth width (cast) x unerupted tooth width (x-
ray)ray)
Erupted tooth width (x-ray)Erupted tooth width (x-ray)

 The radiographic widths of unerupted teeth byThe radiographic widths of unerupted teeth by
themselves are unreliable.themselves are unreliable.
 Accuracy of this method of determining theAccuracy of this method of determining the
width of unerupted tooth is fair to goodwidth of unerupted tooth is fair to good
depending on the quality of radiographs anddepending on the quality of radiographs and
their position in the arch.their position in the arch.
 All exposures should be made with parallelingAll exposures should be made with paralleling
technique.technique.

NANCE MIXED DENTITIONNANCE MIXED DENTITION
ANALYSISANALYSIS
 Nance (1949) proposed a method that takesNance (1949) proposed a method that takes
into account the degree of rotation orinto account the degree of rotation or
displacement of lower anterior teeth.displacement of lower anterior teeth.

Method;Method;
 An 0.012 brass wire is adapted to lower mixed dentitionAn 0.012 brass wire is adapted to lower mixed dentition
model so that one and engages mesiobuccal line anglemodel so that one and engages mesiobuccal line angle
of the lower left permanent molar near the marginalof the lower left permanent molar near the marginal
ridge.ridge.
 The wire then passes over buccal cusps of deciduousThe wire then passes over buccal cusps of deciduous
molars, Though normal position of cuspids, then overmolars, Though normal position of cuspids, then over
the anterior teeth at the ridge center where incisalthe anterior teeth at the ridge center where incisal
edges of anterior teeth are normally found, then aroundedges of anterior teeth are normally found, then around
the same course on the opposite side, ending in thethe same course on the opposite side, ending in the
mesiobuccal line angle of lower right first permanentmesiobuccal line angle of lower right first permanent
molar.molar.
 The wire is measured and recorded. Then theThe wire is measured and recorded. Then the
mesiodistal width of four permanent mandibular incisorsmesiodistal width of four permanent mandibular incisors
are measured.are measured.

 Corresponding predicted widths of canines andCorresponding predicted widths of canines and
premolars are derived from the table..If thepremolars are derived from the table..If the
predicted widths are X, brass wire lengths ispredicted widths are X, brass wire lengths is
LD, sum of incisors LA, then LA+LD, sum of incisors LA, then LA+
2x=3.4mm=LD2x=3.4mm=LD
 Plus 3.4 mm applies to inevitable mesial drift.Plus 3.4 mm applies to inevitable mesial drift.

PEDICTION METHOD BASED ONPEDICTION METHOD BASED ON
MEAN VALUES FOR SUPPORTINGMEAN VALUES FOR SUPPORTING
ZONESZONES
 Different investigations have analysed casts and haveDifferent investigations have analysed casts and have
predicted mean values of supporting base .predicted mean values of supporting base .
 supporting base is the distance from distal surface ofsupporting base is the distance from distal surface of
permanent lateral incisors and mesial surface ofpermanent lateral incisors and mesial surface of
permanent first molar in the mixed dentition .permanent first molar in the mixed dentition .
 It decreases in the permanent dentition due to lateIt decreases in the permanent dentition due to late
mesial shift .mesial shift .
 The measured values in the patient are compared toThe measured values in the patient are compared to
mean values.mean values.

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