KING SAUD UNIVERSITY College of Dentistry

Department of Preventive Dental Sciences DIVISION OF ORTHODONTICS

431 PDS

Introduction to Orthodontics

PRACTICAL MANUAL Part I

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Introduction to Orthodontics

PRACTICAL MANUAL Part I

Contributors:

Dr. Hana AlBalbeesi Dr. Sahar AlBarakati

Dr. Laila Baidas Dr. Huda AlKawari Dr. Eman AlKofide

Re-Edited By:

Dr. Eman Alkofide 2005-2006

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Table of Contents

I. Introduction

II. Classification of Malocclusion

1. Normal Occlusion

2. Malocclusion

3. Class I Malocclusion

4. Class II Malocclusion

a. Class II Div. 1

b. Class II Div. 2

5. Class III Malocclusion

III. Diagnostic Aids:

1. Study Models

2. Radiographs;

a) Occlusal Films

b) Orthopantomographs

c) Hand and Wrist Radiographs

d) Cephalometrics

3. Model Analysis;

a) Arch Perimeter Analysis: Moyer's Analysis

b) Arch Length Analysis: Nance Analysis

c) Tooth Size Discrepancy: Bolton Analysis

IV. References

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I. Introduction

Orthodontics is one of the oldest branches in Dental Science. Orthodontics (Ortho =

Straight, Dontic = Teeth), is that branch of dental science concerned with genetic

variation, development and growth of facial form. It is also concerned with the

manner in which these factors affect the occlusion of the teeth and the function of

associated organs. Therefore we are not only concerned with straightening of the

teeth, but also of the growth, development, and function of the total orofacial

complex.

During this course, the student will be familiarized with the term Orthodontics

through a series of lectures and laboratory sessions. The lecture series of this course

will deal with the abovementioned aspects of orthodontics in more detail. The

laboratory session of this course will teach the student the technical part of

Orthodontics.

The purpose of this manual is to introduce to the student the practical part of this

course in a more simplified and understandable manner.

It is not considered a replacement of the required textbooks for the course, but as an

adjunct to help the student during the laboratory session.

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II. Classification of Malocclusion

1. Normal Occlusion

Occlusion is considered to be normal when the dental arches are in correct alignment, with

all the teeth in anatomically correct contact, and in physiologically optimal occlusion with

the corresponding teeth in the opposite dental arch. The development of normal occlusion

passes through several continuous stages from birth to the development of the permanent

dentition. The deciduous dentition begins to appear at around the age of 6 months with the

eruption of the lower central incisors. The deciduous teeth are usually complete by the age

of 2½ year of age. At this stage there is often spacing between the teeth especially distal to

the lower canines and mesial to the upper canines (primate spaces), with the distal surfaces

of the second deciduous molars in line with each other (flush terminal plane).

At 6 years of age the first molars start to erupt, and the permanent incisors develop lingual

to the roots of the deciduous incisors. At this time also, the ugly duckling state is evident.

As the child continues to grow, he/she passes through the transition period from early

mixed dentition to late mixed dentition, to the permanent dentition. Within these periods,

there lies a discrepancy between the mesiodistal widths of the deciduous molars and the

premolars which creates spacing and is termed the “leeway space”. This develops to allow

the lower permanent molars to move forward further than the upper molars and establish a

class I molar relationship.

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2. Malocclusion

Malocclusion is defined as an irregularity of the teeth (The various types of malocclusion

will be discussed briefly here; the detailed description of each will be elaborated in the next

section).

The etiology of malocclusion is generally categorized into two causes: (1) Hereditary, such as jaw-

teeth size discrepancy, and (2) Developmental, such as premature loss of teeth or habits (ex.

Thumb sucking or tongue thrusting).

Malocclusion may be associated with one or more of the following:

A) Malposition of the Teeth

This could be caused by:

• Tipped teeth – the crown of a tooth is tipped or incorrectly positioned in

comparison to the apex.

• Displaced teeth – in this situation both the crown and the apex are displaced.

• Rotated teeth – the tooth is rotated along its long axis.

• Teeth in infra-occlusion – the tooth has not reached the occlusal level.

• Teeth in supra-occlusion – the tooth has erupted pass the occlusal level.

• Transposed teeth – two teeth have reversed their positions, for example a canine

taking the place of first premolar.

B) Malrelationship of the Dental Arches

This could occur in any of the three planes of space: antero-posterior, vertical, or

transverse. The antero-posterior malrelationship is represented by the Angle Classification,

which deals with the disproportion of the teeth in an antero-posterior plane. The vertical

malrelationship is evident during the observation of overbite, while the transverse

malrelationship is presented in cases with crossbites.

The most popular and world recognized classification of malocclusion is the one described

by Edward Angle, which deals with the arch malrelationship in the antero-posterior

position.

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Angle’s Classification (Molar Classification):

This was the first useful orthodontic classification system that was developed in

1890, and it still used to our present date. Angle’s classification system was based on the

upper first molars as being the "Key to Occlusion". According to Angle, the mesiobuccal

cusp of the upper molar should occlude in the buccal grove of the lower molar. If this molar

relationship exists, and the teeth were arranged on a smoothly curving line of occlusion,

then normal occlusion would result.

Angle then described the three classes of malocclusion, based on the occlusal relationships of the

first molars, which are as follows:

• Class I Malocclusion;

The lower first permanent molar is within one-half cusp width of its correct relationship to

the upper first permanent molar (i.e. the mesiobuccal cusp of the maxillary first permanent

molar occludes with the mid-buccal groove of the lower first permanent molar.

Fig. 1

This is sometimes termed “neutro-occlusion”. There is a normal relationship of the molars,

but the line of occlusion is incorrect due to crowded, rotated, spaced teeth, or others.

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• Class II Malocclusion;

The lower arch is at least one-half cusp width posterior to the correct relationship with the

upper arch. This is also known as “disto-occlusion”. This type of malocclusion is further

categorized into two divisions according to the relationship of the upper central incisors:

Class II Div. 1 - The upper central incisors are proclined or of average inclination with an

increase in overjet (fig 2a).

Class II Div. 2 - The upper central incisors are retroclined. The overjet is usually average but

can be decreased or a little increased. Sometimes the upper laterals are proclined (fig.

2b).

Fig. 2a Fig. 2b

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• Class III Malocclusion;

The lower arch is at least one-half cusp width too far forward in relation to the upper arch.

This is also known as “mesio-occlusion” (fig. 3).

Fig. 3

In certain situations where early extraction of the first molars has occurred, the alternative

to using the Angle’s classification of malocclusion is to use the position of the canine to

determine which type of occlusion the patient has. Usually, in class I relationship, the

position of the upper canine is between the embrasure of the lower cuspid and first bicuspid.

In class II cases, we have a mesial movement of the upper canine and a distal movement of

the lower canine. In class III cases, the opposite is true. The upper canine is located more

distal, with the lower canine migrating more mesial.

Other systems have been developed to further aid in classifying a malocclusion. They are

also used when the first molars are absent. In these cases, an Incisor classification has been

developed. Its benefit is also recognized during orthodontic treatment. Since one of the

main objectives is to correct the incisor malrelationship during treatment, an understanding

of incisor position is very important.

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Incisor Classification:

This does not usually follow the buccal segment relationship. It can be divided into:

• Class I - The lower incisor edges occlude with or lie immediately below the

cingulum plateau (middle part of the palatal surface of the upper central incisors) (fig

4a).

• Class II - The lower incisor edges lie posterior to cingulum plateau of the upper

incisors. The two divisions are:

Class II Div. 1 - The upper central incisors are proclined or of average inclination and

there is an increased overjet (fig. 4b).

Class II Div. 2 - The upper central incisors are retroclined, sometimes the upper

laterals are proclined (fig 4c).

• Class III - The lower incisor edges lie anterior to the cingulum plateau of the upper

incisors. The overjet may be either reduced or reversed (fig. 4d).

a b c d

Fig. 4

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3. Class I Malocclusion:

This is the most common of all the malocclusions.

Dental Features:

• Labial Segments; The lower incisor edge should occlude with or lie directly below the

cingulum plateau of the upper incisors. Meaning that there should be a normal antero-

posterior relationship between them (fig. 5).

• Buccal Segments; The upper and lower molars are in “neutro-occlusion”. Because of the

order of eruption, if there is a crowded dental arch, the last tooth within the arch to erupt

will often be impacted or crowded out of the line of the dental arch. In some cases there

may be an associated crossbite of one or two teeth, anterior teeth crowding, spacing,

deep overbite or open bite, irrelevant of the canine and molar class I relationship.

Fig. 5

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Skeletal Relationships:

• Antero-posterior; the skeletal pattern is usually a class I, but it is possible to find a

class I malocclusion in association with a class II or class III skeletal pattern.

• Vertical and Transverse; They are usually within normal range.

• Soft Tissue; The soft tissue form and activity are usually within normal range.

Growth:

There is a harmonious growth between the upper and lower jaw, which accounts for the

skeletal and facial balance (fig. 6).

Fig. 6

Problems associated with Class I:

• Crowding: This may appear in the labial or buccal segments due to a small or narrow

arch, or in the premolar region due to early loss and drifting of teeth. It can be classified

into mild, moderate, or severe.

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There are two ways to measure crowding:

According to the broken contact: Mild = 1-2 broken contact

Moderate = 2-5 broken contact

Severe = more than 5 broken contact

According to measurement by mm’s: Mild = 1-4 lack of space

Moderate = 5-8mm lack of space

Severe = 8mm

• Spacing: This could be localized or generalized. Localized, such as a midline diastema,

could be caused by low frenal attachments, jaw-size discrepancy, or the presence of a

mesiodens. Generalized spacing is usually due to a jaw-size to teeth-size discrepancy.

• Deep Bite: Defined as the vertical overlap of the incisors (fig. 7). Normally the lower

incisal edges contact the lingual surface of the upper incisors at or above the cingulum. It

may cause traumatic occlusion and impingement of the palatal tissue.

Fig. 7

• Open Bite: There is no vertical overlap of the incisors, and there is an evident vertical

separation (fig. 8). This could be due to dental problems associated mainly with oral

habits such as thumb sucking or mouth breathing, or skeletal problems such as arch

deficiencies

Fig. 8

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• Cross Bite: It could be lingual or buccal, anterior or posterior, unilateral or bilateral,

involving one tooth or a group of teeth (fig. 9 a-e). If it present anterior, this could be due

to a pseudo-class III or a true class III. If it is posterior, it is usually due to a narrow

upper arch.

Its causes vary from thumb sucking habits to dental problems such as teeth inclinations,

to skeletal problems.

a. Normal Occlusion b. Unilateral Buccal Cross Bite

c. Bilateral Buccal Cross Bite d. Cusp relation tendency for crossbite [edge to

edge] relationship

e. Scissors Bite [lingual cross bite]

(The upper buccal teeth are occluding buccally to the lower teeth)

Fig. 9

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• Localized Teeth Problems: Such as impacted or unerupted teeth. Most commonly

observed in impacted cuspid cases.

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4. Class II Malocclusion:

a) Class II Div. 1 Malocclusion

Dental Features:

• Labial Segments; The lower incisor edge lies posterior to the cingulum plateau of the

upper incisors. There is an increased overjet which may be due to proclined upper

incisors, retroclined lower incisors, or a skeletal problem (fig. 10). Usually the overbite is

increased and complete.

Note: Overjet is defined as the horizontal overlap of the incisors. Normally the upper incisors are 2-

3mm ahead of the lower incisors.

• Buccal Segments; The upper and lower first molars are in “disto-occlusion”, meaning

that the mesiobuccal cusp of the upper first molar is anterior to the mid-buccal groove of

the lower first molar.

Fig. 10

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Skeletal Relationships:

• Antero-posterior; there is usually a class II skeletal pattern. In severe malocclusion

cases, with poor skeletal relationships, orthodontic treatment alone is compromised. In

other cases, the inclination of the lower teeth will compensate for the skeletal pattern

and thus the overjet will be less than expected.

• Vertical; The anterior skeletal face height is usually average, although it may be high. A

high angle or “dolichofacial” pattern is usually associated with an unfavorable facial

profile with little chin prominence, hence leading to a compromised orthodontic

treatment result.

Soft Tissue:

The lips are frequently incompetent, which leads to the uncontrolled proclination of the

upper incisors. Sometimes a lip seal will be maintained, but frequently there is a tongue-to-

lower lip seal with the lower lip lying behind the upper incisors.

Growth:

Patients with a class II div. 1 pattern exhibit more vertical growth. Unlike patients with a

class II div. 2 pattern who exhibit more mandibular horizontal growth. A typical class II

div. 1 case presents with a “dolichofacial” pattern or “Long Face Syndrome”, and has less

favorable growth direction of the mandible than the “brachyfacial” patient or “Square Jaw

Patient in class II div. 2 cases.

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b) Class II Div. 2 Malocclusions

Dental Features:

• Labial Segments; The upper central incisors are retroclined, while the upper laterals

may be proclined or retroclined (fig. 11). When the upper laterals are proclined, they are

usually mesially inclined and mesiolabially rotated. The lower anterior segment is

frequently retroclined, which may lead to crowding of the lower incisor area. This

increases the interincisal angle and hence has an effect on the amount of overbite. The

overjet is usually not a problem here. There is an increase in the lower curve of Spee

and the patient may appear with a gummy smile due to retroclination of the incisors.

• Buccal Segments; Here the lower arch is at least one-half cusp width post normal to the

upper arch, and there may be crowding due to early loss of the deciduous molars with a

forward drift of the lower first molars.

Fig. 11

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Skeletal Relationships:

• Antero-posterior; the profile is usually well balanced, with the chin in a good position

with the rest of the face. In some cases, the skeletal discrepancy is severe. This may

be due to an increase in the length of the anterior cranial base, leading to a more

distal positioning of the glenoid fossa and hence the mandible.

• Vertical; The lower facial height is reduced or average. The Frankfort mandibular plane

angle is often low. The lower anterior facial height may contribute to the depth of

the overbite.

• Transverse; In rare cases we may find a “scissors bite”, with the upper buccal teeth

occluding outside the lowers.

• Mandibular Positions and Paths of Closure; Usually, the path of closure is a simple

hinge movement and the habitual position of the mandible is the rest position. But in

severe cases, the mandible is habitually postured downwards and forward. With true

posterior displacements of the mandible, and where there has been a loss of posterior

teeth, patients will complain of pain in the early adult life, leading to TMJ problems.

Soft Tissue:

The lip line here is usually high, with the lower lip covering more than the occlusal half of

the upper incisors. There may be an accentuated labiomental fold, and an increased

nasiolabial angle with flattening of the upper lip profile.

Growth:

These patients exhibit a closing growth rotation, which contributes in part to the reduced

facial height and the deep overbite. Treatment in these cases is difficult.

Oral Health:

In cases with severe overbite, direct trauma (traumatic bite) to the gingival mucosa may

occur. This is due to the lower incisors occluding with the palatal mucosa and the upper

incisors occluding with the labial mucosa. In these cases proper oral hygiene is a must and

treatment of the traumatic occlusion is indicated.

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5. Class III Malocclusion:

Dental Features:

• Labial Segments; A class III incisor relationship exists when the lower incisor edge is

lying anterior to the cingulum plateau of the upper incisors. The lower incisors may lie

anterior to the upper so that there is a reverse overjet (fig. 12). The upper incisors are

often crowded and they are usually proclined. The lower incisors are usually spaced and

frequently retroclined. This inclination compensates the extent of the underlying sagittal

arch malrelationship.

• Buccal Segments; The lower arch is at least one-half cusp width too far forward relative

to the upper arch. Usually the upper arch is crowded with canines buccally excluded,

while the lower arch is well aligned. It is not uncommon to observe a crossbite in the

buccal segments because of a narrow maxilla, which may be unilateral or bilateral. A

unilateral crossbite is usually associated with lateral displacement of the mandible to

obtain maximal intercuspation.

Fig. 12

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Skeletal Relationships:

• Antero-posterior; there is a combination of factors which leads to this malrelationship.

The mandible is usually large, with a short retrognathic maxilla. The patient will

appear with a concave profile. There is a more forward position of the glenoid fossa

on the skull base so that the mandible is more anteriorly positioned than usual, with

a short anterior cranial base.

• Vertical; The Frankfort mandibular plane angle is usually high, with an associated

reduced overbite or anterior open bite. The intermaxillary height is an important

factor to consider.

• Transverse; In most cases the maxillary base is narrow with a wide mandibular base.

This transverse discrepancy is compensated for by a buccal inclination of the upper

teeth and a lingual inclination of the lower teeth. It is common to see crossbites in

the buccal segments due to a large mandible and a narrow maxilla.

• Mandibular Positions and Paths of Closure; In patients with a mild class III

malocclusion, the incisors meet edge to edge in centric relations. But in order for the

mandible to obtain a position of maximal occlusion, there is a forward displacement

of the mandible which accentuates the skeletal discrepancy. When there is a

unilateral crossbite with the teeth in occlusion, there will usually be an associated

lateral displacement of the mandible on closure.

In cases of skeletal disharmony, a more pronounced anterior displacement of the

mandible occurs. It will be more difficult if not impossible for the mandible to

retrude to obtain maximal occlusion. In fact, the only way the lower arch can meet

with the upper arch in maximum occlusion is through the forward displacement of

the mandible.

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Soft Tissue:

In cases where the lips are frequently incompetent, the anterior intermaxillary height is

large. These cases usually present with an anterior open bite with an adaptive swallowing

behavior, where the tongue comes forward into the gap between the incisors.

Growth:

Here any growth is unfavorable, since the mandible may grow more prognathic (fig. 13).

When the height of the intermaxillary space is normal or reduced, growth may worsen the

reverse overjet and the horizontal profile of the face. When the height of the intermaxillary

space is increased with growth, the tendency to a skeletal anterior open bite may become

greater.

Fig. 13

Class III Molar and Jaw Relationship

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Oral Health:

Mandibular displacements due to occlusal disharmonies eventually may be associated with

muscle pain. Also when there is a premature contact in the incisor region there may be

gingival recession around one or more lower incisors. And in cases with anterior open bite,

periodontal changes can be expected around the non-functional teeth.

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III. Diagnostic Aids

1. Study Models

In order to properly diagnose an Orthodontic case, several steps are required. These steps

allows us to gather information pertinent to developing diagnosis, and hence, treatment

planning of the case.

One aspect of orthodontic diagnosis that is part of the common knowledge of the profession,

and yet has not been described often in the literature, is the fabrication of study models (fig.

14).

Fig. 14

The following section describes in detail the process of constructing study models as advised

by the American Board of Orthodontics:

1. Impressions:

Standard aluminum trays should be used to obtain accurate impressions of the dentition and

associated soft and hard tissue structures. The edges of the trays usually are lined with a

border of wax that prevents the edge from impinging on the soft tissue. Care should be taken

to ensure that the trays are neither too wide nor too narrow, so that minimal soft tissue

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distortion occurs. The areas of tissue attachment, particularly in the area of the labial

frenum and in areas of soft tissue attachment adjacent to the upper first premolars, should

be reproduced in the impression. Obtaining a proper impression of the hard and soft tissue

of the dentoalveolar region is critical for the proper fabrication of diagnostic casts.

After the impression has been made, it should be checked thoroughly. The impression

should appear smooth with no major voids, and the borders of the impression should be

rolled with good extension into the vestibular areas. The impression also should extend

posteriorly in the palatal area and lingually in the mandibular region. Lastly, the impression

should be checked for the presence of any large air bubbles, especially on the occlusal

surfaces of the teeth. After making the impression, it should be disinfected to prevent

possible contamination of the laboratory area.

2. Wax Bite Registration

Clinicians use a wide variety of substances to record the orientation of the upper and lower

dental arches. Normally, the bite registration is taken in centric occlusion, a tooth-guided

position. In instances in which there is a substantial difference between centric occlusion

and centric relation, an additional bite registration should be taken in centric relation as

well. The clinician then must decide whether the study models are to be trimmed in centric

occlusion or centric relation. In instances in which a centric relation registration is desired, it

is often useful to mount the articulated model on an appropriate articulator, utilizing a

facebow transfer.

For routine procedures, one or two thicknesses of yellow bite registration wax are used.

The horseshoe-shaped wafers of wax are softened first in warm water and then placed on

the maxillary dental arch. The patient then closes his or her mouth so that the lower teeth

bite into the softened wax. The patient should be instructed to bite through the wax, to

avoid producing study models that “rock” or are unstable when trimmed. Using finger

pressure, the clinician then will press the wax against the teeth to achieve a three-

dimensional registration of the bite. Some clinicians advocate keeping the labial surfaces of

the upper and lower anterior teeth free of wax. The incisal edges can be registered in the

wax, but the midlines are still visible so that the lateral orientation of the wax bite (using the

midlines) can be determined.

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After the impression and wax bite have been taken, they are wrapped in moistened paper

toweling and placed in sealable plastic bag.

3. Disinfecting The Impression

A thorough rinsing of impressions reduces the number of microorganisms on the surface of

the impressions, removing plaque and secretions. The impressions should be immersed in

Biocide and then allowed to stand for approximately 10 minutes. A 1:100 solution of

chlorine bleach and water also can be used as disinfecting solution. Impressions then are

rinsed in lukewarm water and rebagged until the time they are poured.

4. Pouring The Impression

The first step in pouring the impressions is to fill in the area occupied by the tongue in the

mandibular impression. This can be accomplished by first placing a thumb or piece of

moistened paper towel or tissue in the tongue space. One scoop of alginate is mixed to

normal consistency and placed in the area normally occupied by the tongue. As the alginate

begins to harden, smoothen the alginate with finger pressure. After the initial set is

completed, the impression is put aside until a final set is completed. After that time, the

impression should be checked for accuracy, making sure that the alginate addition does not

obstruct the anatomical structures in the lingual region of the mandibular impression.

The impressions are poured using white orthodontic stone or plaster. The impression should

have been rinsed previously; not only to eliminate the residue of the disinfectant but also to

eliminate traces of saliva that otherwise might affect the integrity of the finished surface of

the stone. The stone is mixed in a vacuum mixer to eliminate bubbles that otherwise would

be trapped in the stone. The stone is poured in the tooth portion of the impression first,

using a vibrator and a waxing instrument or spatula. Additional stone is added with the

spatula to complete the anatomical portion of the impression.

After the pouring of the anatomical portion of the impression is completed, the remaining

stone is poured into a large base former, again using the vibrator. The impression tray is

turned upside down and pushed into the stone in the base former. Care should be taken to

verify that the occlusal surface of the impression remains parallel to the bottom surface of

the base former. Also, the impression tray should not be pushed into the plaster in the base

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former. If the impression tray becomes trapped in the plaster, difficulties will be encountered

in removing the tray, and the vertical thickness of the study model may be reduced.

The impression tray is removed from the poured stone after it is hardened. Ordinarily, a

wait of 30-60 minutes after the onset of the mix is adequate to make sure that the

orthodontic stone is set. Care should be taken in removing the impression from the set stone

so that the teeth (particularly the upper and lower incisors) are not fractured during tray

removal.

5. Trimming The Study Cast

The trimming needs to be done slowly and carefully. As a first step in the procedure, a

laboratory knife is used to remove any large or small chunks of plaster that interfere with the

occlusion of the cast. Such interferences include bubbles on the occlusal surfaces as well as

lateral extensions in the posterior regions, particularly behind the last erupted molar.

• Rough Trimming the Maxillary Model

The maxillary model is trimmed symmetrically with the top of the model trimmed parallel

to the occlusal plane (Fig. 15). The back of the model is trimmed perpendicular to the

midline of the palate as indicated by the orientation of the midline palatal raphe. Rough

trimming of the stone bases first can be accomplished free-hand, using the platform on the

model trimmer as a guide.

After the model is rough trimmed, the model is placed on its back so that the top of the cast

can be trimmed. The teeth rest against the attachment of the model trimmer that slides into

the groove on the trimming platform. The top surface of the model is trimmed so that it is

parallel to the occlusal plane of the teeth (fig. 15).

The anatomical base of the maxillary model should be about 1.5 cm thick (about 13 mm)

(fig. 16). If the maxillary base has been poured to an inadequate thickness, or if the base has

been trimmed excessively, the finished study models will look uneven.

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The total height of each cast should measure 3.5-4.0 cm from the occlusal surface to the top

of the model.

Fig. 15

• Trimming the Back of the Models

Once the top of the cast has been trimmed flat, the cast is placed with the top of the cast

against the trimming platform. The cast then is oriented so that the palatal raphe is

perpendicular to the wheel of the model trimmer. It is advisable to use the palatal raphe as a

guide since the dental midlines often are not coincident with the skeletal midlines.

The cast is trimmed so that there is about 5 mm of stone distal to the most posterior tooth.

In instances of severe Class II malocclusion, additional space should be allotted in the

posterior region until the final occlusion is determined.

• Establishing the Interarch Relationship

The upper and lower casts are placed together, and the operator checks for any interference

that might prevent a proper occlusion from being established. The wax bite registration is

placed on the maxillary cast, and the mandibular cast is occluded into the wax indentations.

The models then are placed on the trimming table with the casts in occlusion and the

maxillary model on the bottom, with the backs of the casts facing the trimming wheel. The

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casts are held firmly together, and the back surfaces of the models are trimmed. At this

point, only the mandibular cast touches the trimming wheel. The casts should be held gently

but firmly together as the casts are pushed into the coarse grinding wheel. Trimming

continues until both the upper and lower casts are touching the trimmer.

After it has been determined that the backs of the casts have been trimmed in a parallel

fashion, the models are removed from the trimmer, and the backs of the casts placed on a

flat surface. At this point, the models should lie flush on the surface with the wax bite in

place. If this is not the case, the models should be placed back in the trimmer with the wax

bite in place and retrimmed until both surfaces are flush against the trimmer.

The wax bite is removed and the casts occluded in a hand-held fashion. Once again, the

models should be checked for the appropriate bite orientation by placing the backs of the

models on a flat surface. If the backs of the models are not flush, they should be retrimmed

without the wax bite in place. If there is any uncertainty concerning the accuracy of the wax

bite, a new bite should be taken.

Fig. 16

• Rough Trimming the Mandibular Model

With the models in occlusion and the wax bite in place, the models are placed on the

trimming table with the lower base against the trimming wheel. Using the perpendicular

attachment of the trimming table against the top surface of the upper cast, the bottom of the

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lower cast is trimmed parallel to the top of the upper cast. The cast is trimmed so that the

base of the lower model is equal in thickness to that of the upper model (Figs. 15 and 16).

The total height of both casts in occlusion should be about 7-7.5 cm.

6. Final Trimming

• Maxillary Model

The precise angulations of the study models are determined using an angulator that can be

screwed into the trimming table. The angulator allows the operator to set the correct angle

for each surface. By placing the back of the cast against the flat surface of this device, an

angle is formed between the surface of the cast and the trimming wheel surface that allows

for the correct angulations to be determined. The screw on the angulator should be

tightened firmly to prevent slipping of the device that could result in trimming errors.

First, the angulator is set at 70° (Fig. 17). The cast is placed in the appropriate position and

the first side trimmed until the deepest extent of the vestibule is reached. The thickness of

the initial trim should be roughly the thickness of a standard wooden pencil. It is best to be

cautious at this point, because it is, of course, possible to retrim any surface. The opposite

side also is trimmed at 70°.

The angulator then is set to 25° and the front of the maxillary cast trimmed so that both

sides meet anteriorly. The tip of the cast should approximate the midline as determined by

the palatal raphe. The anterior borders of the maxillary cast are equal in length.

Fig. 17

30

The last portions of the maxillary cast to be trimmed are the back edges. These edges are

trimmed perpendicular to a line drawn from the intersection of the lateral and posterior

borders of the cast and the intersection point of the lateral and frontal surfaces of the cast on

the opposite side (Fig. 17). The length of the corner segments should be 13-15 mm. Care

should be taken to avoid trimming this area too quickly, or excess stone may be removed.

• Mandibular Model

The angulator is set at 65° when initially trimming the lower model (Fig. 18). Each side is

trimmed to the depth of the vestibule, again using the width of a standard wooden pencil as

an initial guide.

The next step in trimming is to establish the posterior angles of the mandibular cast. As with

the maxillary model, the posterior edges of the mandibular model is trimmed perpendicular

to a line bisecting the angle formed by the lateral aspect of the cast and the posterior aspect

of the cast (fig. 18). The length of this posterior surface should be 13-15 mm (fig. 19).

The anterior part of the cast is not angled but rather is rounded. The determination of the

curvature is accomplished free-hand through gentle movement of the cast in a smooth

arcing fashion. The anterior curvature is trimmed to the depth of the vestibule in most

instances. In instances of dentoalveolar protrusion, care must be taken to avoid damaging

the teeth during the trimming process.

7. Finishing Procedures

• Filling Voids

The casts are inspected carefully and any remaining bubbles removed with a cleoid-discoid

instrument or any waxing instrument. Particular attention is paid to the gingival margin as

well as to other soft tissue areas. Any airholes or voids are filled with stone and the surface

smoothed carefully, using either a finger or small brush to add plaster to the model.

31

All voids are filled, regardless of whether they are on the anatomical or artistic portions of

the model.

Fig. 18

• Finishing

The edges of the dental cast are smoothed slightly with a laboratory knife so that they are

smooth and even. If there are obvious asymmetries in the extension of the vestibule that are

due to impression technique rather than anatomical variation, these areas may be modified

using a plaster knife or a rotary instrument.

The fine polishing of the artistic portions of the dental cast is initiated using a piece of fine-

grained sand paper. The edges of the study models are smoothed under warm water. Also,

the flat surfaces of the model are smoothed in areas of voids that previously have been filled

with plaster.

The edges of the models should not be rounded. The finished models should have sharp

angles but should be generally smooth in appearance. The models are set aside in an area to

dry and allowed to dry for at least 24 hours.

• Polishing the Casts

The casts are placed in a soaping solution for one hour. The casts then are removed from the

soap bath to be rinsed under warm water and allowed to dry for approximately 20 minutes.

Using a soft rag, the bases are buffed until the casts are smooth and shiny. The casts are

32

labeled in the appropriate manner, noting the name and age of the patient, as well as the

date of the impression.

Fig. 19

33

2. Radiographs

Radiographs are very important diagnostic aids in all aspects of the field of dentistry, and

especially in orthodontics.

There are two main types of radiographs:

Intraoral Radiographs – This includes periapicals, bitewings and occlusal films.

Extraoral Radiographs – includes orthopantomographs (OPG), hand-wrist radiographs,

posteroanterior radiographs and lateral cephalometrics.

The following sections will cover the radiographs that are used mainly for

Orthodontic purposes.

a) Occlusal Films:

It is required to visualize relatively large segments of the dental arch, including the palate,

floor of the mouth, and a reasonable extent of lateral structures.

It is indicated to:

• Locate roots, supernumerary, unerupted and impacted teeth especially cavities and

third molars.

• Localize foreign bodies and stones in the salivary glands duct.

• Evaluate the integrity of the maxillary sinus outline.

• Provide information relative to the fractures of the mandible and maxilla.

• To determine to medial and lateral extent of pathosis (e.g. cysts).

34

b) Orthopantomographs (OPG):

Also termed panoramic radiography or rotational radiography. It is a radiographic

procedure that produces a single image of the facial structures, including both the maxillary

and mandibular arches and their supporting structures, such as the nasal cavity, maxillary

sinuses and the temporomandibular joints.

The principles of the panoramic radiography where first described by Numata in 1933 and

Paatero in 1948.

Originally the patient and the films rotated and the x-ray beam remained stationary. But

this method was superceded by the development of apparatus which have the tube and the

film rotating around the patient.

The x-ray source and film are simultaneously moved parallel to each other in opposite

directions. While taking the radiographs, the Frankfort Horizontal Plane (FHP), should be

parallel to the floor, and the occlusal plane should be lower anteriorly by 20-30 degrees, with

the patient biting on a bite block.

Caution should be taken on the position of the chin:

If the chin is tipped too high to the horizontal plane, the mandible will be distorted. If the

chin is tipped too low the hard palate will superimpose the roots of the maxillary teeth.

To make sure of the distortion, we can check the width of the permanent mandibular teeth

(molars) bilaterally. If one of them is wider than the other one by 20% the radiograph should

be retaken.

35

Advantages of OPG’s

• The film is extraoral, making it more comfortable for the patient.

• A broad anatomic region is imaged, which includes the maxilla and the

mandible.

• It exposes the patient to less radiation. It is quick, convenient and easy for the

assistant to take.

• It can be performed on patients who cannot open their mouths and cannot

tolerate intraoral radiographs, especially edentulous patients or patients with a

suspected pathosis.

• The time required for the procedure is short 3-4 min. including patient

positioning and actual exposure.

• Accepted by patients during presentations and education.

• Gross lesions are visible.

Disadvantages

• Does not give the fine anatomic details such as the alveolar crest, margins of

pathological lesions, bone pattern, caries, etc.

• The image may be distorted if the patient is situated outside the focus.

• Magnification, geometric distortion, overlapped images of teeth, especially

premolar region, all can occur.

• The projection can be taken only at one angle.

• The view of the temporomandibular joint is distorted.

• Expensive machine (3-4x more than the intraoral machine).

36

Indications for Usage

a. To assess the patient’s dental age based on the development and progress of

mineralization of the teeth, eruption time and exfoliation of the primary teeth.

So a comparison of the chronological and skeletal age can be done.

b. To evaluate present teeth, missing congenitally or impacted, ectopic eruption,

malpositioned teeth, the presence or absence of third molars,

supernumeraries, quality of restorations, resorption pattern of deciduous

teeth, calcification of permanent teeth, asymmetric resorption of deciduous

molars, integrity of root structures.

c. To determine the level of alveolar bone, the interdental crest, bone resorption

(horizontal, vertical), infrabony pockets, trabecular pattern wide marrow

space (esp. in young growing children), or narrow trabecular spaces (in older

children and adults).

d. To note the presence of any pathological lesions, cysts, tumors, extensive or

unique pathosis, ankylosis of deciduous teeth, susceptibility to caries, active

carious lesions, root resorption.

37

c) Hand and Wrist Radiographs:

Predicting the pattern of growth; that is the amount, direction, duration, location and timing

of the onset of pubertal growth, is important for the orthodontist when planning therapy and

coordinating orthodontic treatment with the vital growth process. Hand and wrist

radiographs can aid with this process of growth estimation.

This estimation of the skeletal age of bones or bone age, aids in determining the physical

maturation status of the child. One of the indicators to verify the pubertal growth spurt is

annual measurement of what has happened. Whereas our interest is to know what will

happen in the future to judge the development stage of the child in relation to the child’s

own growth curve, in order to decide whether the pubertal growth spurt has started or

passed.

Advantages of the Hand and Wrist Radiographs

• If differentiates the certain developmental stages towards full physical development.

The sequence of such developmental or morphological changes is equal in all

humans.

• It is technically simple to make roentgenograms of the hand. An individual will pass

through a regular series of changes in size and shape of the ossification centers of

bone during their progress towards maturity.

Several systems have been developed to evaluate these series of growth changes. One which

will be described in detail here, is a system produced by Leonard Fishman. Fishman’s

analysis is based on skeletal maturation assessment (SMA). This system uses four stages of

bone maturation located at six anatomic sites: the thumb, third finger, fifth finger and

radius. In these six sites eleven maturational indicators (SMI’s) are found to cover the entire

adolescent development period.

38

Sites of Skeletal Maturity Indicators

Which are related to: widening of the epiphyseal discs in one of the phalanges on the third

or fifth finger, visibility of the ulnarmetacarpophalangeal sesamoid on the first finger

(thumb), capping of selected epiphyses over their diaphyes, and the fusion of selected

epiphyses and diaphyses. In addition to that ossification of the hook of the hamate and

pisiform bone is also taken into consideration (figs. 20 a-d, & 21).

a. Width of Epiphysis b. Ossification

c. Capping of Epiphysis d. Fusion

Fig. 20

Sites of Skeletal Maturity Indicators

39

SMI D.S. D. F.A. M.A.

SMI 1 PP3 The epiphyses and diaphyses

in the proximal phalynx of the

third finger are equally wide.

9 11

SMI 2 MP 3 The epiphyses and diaphyses

in the middle phalynx of the

third finger are equally wide.

10 11

SMI 3 MP5 The epiphyses and diaphyses

in the middle phalynx of the

fifth finger are equally wide.

10.8 12

40

SMI 4 S Ossification of the

ulnarmetacarpophalangeal

sesamoid on the first finger.

This stage is found before

maximal growth, but can also

be found together with

maximum growth.

11 12.3

SMI 5 DP3 cap

The epiphyses form a cap

around the diaphyses on the

distal phalynx of the middle or

third finger.

11.6 12.9

SMI 6 MP3 cap

The epiphyses form a cap

around the diaphyses on the

middle phalynx of the third

finger.

12 13.7

SMI 7 MP5 cap

The epiphyses form a cap

around the diaphyses on the

middle phalynx of the fifth

finger.

12.3 14.3

41

SMI 8 DP3u Ossification of the epiphysis in

the distal phalynx on the third

finger.

13 15

SMI 9 PP3u Ossification of the epiphysis in

the proximal phalynx on the

third finger.

13.9 15.5

SMI 10 MP3U Ossification of the epiphysis in

the middle phalynx on the

third finger. This stage: DP3U

+ PP3u +MP3u = all these

stages are found after the stage

of maximum growth is

reached, most often from 1-4

years after.

14.7 16.4

SMI 11 R Complete union of epiphysis

and diaphysis of the radius.

The ossification of all the hand

bones is complete and skeletal

growth is finished.

16 17

Fig. 21 (D.S. = Developmental Stage, D = Description, F.A. = Females Age, M.A. = Males age)

42

Note: The best treatment time for orthodontic patients is 1-2 years before the growth spurt, after that

time usually no growth will occur. Hence, the advantage of growth will be missed and treatment might

be compromised

Radiographic identification of skeletal maturity indicators (fig. 22)

1. Epiphysis equal in width to diaphysis.

2. Appearance of adductor sesamoid of the thumb.

3. Capping of ephiphysis.

4. Fusion of epiphysis.

Fig. 22

Eleven Skeletal Maturity Indicators (SMIs)

43

HAND-WRIST OBSERVATION SCHEME

Fig. 23

An observational scheme for assessing SMIs on a hand-wrist radiograph

(For ease of interpretation, the first step is to determine the presence or absence of the abductor sesamoid of the

thumb).

44

d) Cephalometrics:

Cephalometrics was first introduced to the world by Hofrath in Germany and Broadbent in

the United States. Cephalometric radiography means measuring the head in the living

individual through the use of radiographs. The original purpose of cephalometrics was to

conduct research on growth patients in the craniofacial complex, but was soon used

afterwards as a method to evaluate dentofacial proportions and clarify the anatomic basis

for a malocclusion. Nowadays, lateral cephalometric radiographs are routinely used in

orthodontic practices.

A cephalograph, which is a standardized radiograph of the head (cranium and face), is

taken for the patient by the use of a machine termed the “Cephalostat” (cephalus meaning

the skull or head, and stat meaning fixed or static position).

The basic equipment required to obtain a cephalometric view consists of an x-ray source, an

adjustable cephalostat, a film cassette with radiographic intensifying screens, and a film

cassette holder.

Components of the Cephalostat:

The cephalostat consists of the following:

• Ear Rods: Two in number, one right and one left. These are tightened into the

external auditory meatuses so that the patient is maintained in the mid-sagittal plane.

Each ear rod has a metal ring of the same dimension, and in a correctly aligned

cephalostat the radiograph shows a single ring. If two rings are seen it indicates an

improperly aligned cephalostat.

• Nasal Pointer: Which rest on the bridge of the nose (usually at the soft tissue nasion).

• Orbital Pointer: This is optional, and if present it is fixed at the orbital region.

• A Metal Millimeter Scale: This is fixed vertically to the nasal pointer to indicate the

amount of magnification or distortion.

The patient is placed within the cephalostat using the adjustable bilateral ear rods placed

within each auditory meatus, usually while the patient is in a standing position (fig. 24).

The mid-sagittal plane of the patient is vertical and perpendicular to the x-ray beam. It is

45

also parallel to the film plane, which in turn is also perpendicular to the x-ray beam. The

patient's Frankfort plane (line connecting the superior border to the external auditory

meatus and the infraorbital rim) is oriented parallel to the floor. The distance between

the x-ray source and the mid-sagittal plane of the patient’s head is kept at a minimum of

5 feet (150cm), so reduce magnification.

Fig. 24

A fast Kodak blue brand 8” x 10” film is used. The film is exposed for 4/10 of 7/10 sec. at

90 KVP and 10MA, to penetrate the hard tissue and provide good details of both the hand

and soft tissue.

Two views can be used with this type of radiographic method:

1. Posteroanterior View

It shows the vertical and transverse dimensions of the head. The primary indication for

obtaining a posteroanterior cephalometric film is the presence of facial asymmetry. A

tracing is made and vertical planes are used to illustrate transverse asymmetrics. Lines are

drawn through the angles of the mandible and the outer borders of the maxillary tuberosity

46

(fig. 25). Vertical asymmetry can be observed by drawing transverse occlusal planes (molar

to molar) at various levels and observing their vertical orientation.

Fig. 25

2. Lateral Head or Profile View (lateral cephalometrics)

It shows the vertical and anteroposterior or sagittal dimensions. This type is most

commonly used during orthodontic diagnosis.

Uses of Cephalometrics:

1. Classify the type of face.

2. Show the relationship between the basal parts of the maxilla and the mandible.

3. Evaluate the soft tissue profile.

4. Evaluate the position of the incisors in relation to the basal parts and the soft tissue

profile.

47

5. A pretreatment record prior to the placement of appliance, particularly where

movement of the upper and lower incisor is planned.

6. Monitoring the Progress of Treatment.

7. To make a growth prediction when the orthodontic treatment is to be conducted

during the growth period.

8. Research Purposes; Information about growth and development by longitudinal

studies (serial cephalometric radiographs from birth to the late teens).

9. Detecting for any abnormalities or pathology e.g. a pituitary tumor of patency of the

airway as enlarged adenoids.

Tracing Technique

Certain materials are used for this purpose, which are:

• Tracing paper

• 3-H drawing pencil

• Gum eraser

• Transparent millimeter rule

• Transparent triangle

• Scotch tape

• Template

• View box

Method of Tracing

1. Place the cephalograph on the table with the profile facing to your right hand.

2. Place the tracing paper over the film (the dull surface facing you), with the lower

border of the paper extending about one inch below the chin point.

3. Tape the upper corners of the tracing paper to the radiograph.

4. The tracing should be carried out in a dark room on a light-viewing box.

5. Trace the soft tissue profile, then the hard tissue profile, and then the dentition

according to the following tracing procedure.

6. If bilateral structures are present, draw both of them and take the average of the

two.

7. Trace the reference points.

48

Tracing Procedures (fig. 26)

1. Trace the soft tissue profile starting with the forehead, then nose, then lips, then

chin till the throat angle beyond the chin.

2. Trace hard tissue profile; start with the forehead and the frontal sinus.

3. Trace the nasal bone.

4. Trace the anterior nasal spine and the anterior contour of the maxilla up to the

interdental alveolar crest between the central incisors.

5. Trace the floor of the nose and the roof of the palate. Trace the posterior nasal

spine.

6. Trace the anterior contour of the mandible starting from the interdental crest

between the lower incisors.

7. Trace the outline of the chin up to the symphysis.

8. Trace the lower border of the mandible from the symphysis to the angle of

mandible.

9. Trace the posterior border of the ramus.

10. Trace the orbit from the supra orbital ridge to the most inferior portion on the

lower border of the orbit known as orbitale.

11. Trace the zygomatic bone from the lateral contour of the orbit down to the

triangular image. The lowest projection of the triangular image is called key

ridge.

12. Trace the pterygomaxillary fissure which is seen as an inverted tear drop shape

just above the posterior nasal spine. The anterior contour of the fissure represents

the posterior surface of the maxilla and its posterior contour represents the

pterygoid bone.

13. Trace the shadow of the external acoustic meatus. It appears as an oval

radiolucency or opaque ring shadow due to ear rods and it lies behind the upper

most surface of the condylar head.

14. Trace the sella turcica (saddle shaped pituitary fossa).

15. Trace the most prominent upper central incisor from crown to root.

16. Trace the most prominent lower central incisor.

17. Trace the upper and lower permanent first molars.

49

18. Trace the occipital bone.

Note: Use the template to trace the central incisors and first molar.

50

Anatomic Points (Landmarks) of the Cephalometric Radiograph (fig. 27):

A) Cranial Base

1. Nasion (N) – The most anterior point on the fronto-nasal suture.

2. Sella (S) – The mid-point of sella turcica.

B) Mid-Face

1. Orbitale (or) – The most inferior anterior point on the bony margin of

the orbit.

2. Porion (po) – The most superior point on the bone external auditory

meatus.

In case the metal ring is present, it is located 4.5mm above the center of the metal ring.

C) Maxilla

1. Anterior Nasal Spine (ANS) – The most anterior point on the maxilla

at the level floor of the nose.

2. Posterior Nasal Spine (PNS) – The most posterior point on the maxilla

at the level floor of the nose.

3. Point A (A) – The deepest point on the anterior contour of the maxilla

between ANS and alveolar crest usually it is approximately 2mm

anterior to the apices of maxillary central incisor.

D) Mandible

1. Point B (B) – The deepest point on the anterior contour of the

mandible between the chin and alveolar crest.

2. Pogonion (pog) – The most anterior point on the curvature of bony

chin.

3. Menton (Me) – The most inferior point on the mandibular symphysis.

4. Gonion (Go) – The most inferior posterior point on the angle of the

mandible.

E) Soft Tissue

1. Upper Lip Point (UL) – The most anterior point of upper lip profile.

2. Lower Lip Point (LL) – The most anterior point of lower lip profile.

3. Soft Tissue Pogonion (pog) – The most anterior point on the profile of

soft tissue chin.

51

Fig. 26

52

Fig. 27

53

Cephalometric Horizontal Planes and Lines (fig. 28):

• SN Line – This line, connecting the mid-point of sella turcica with nasion, is taken to

represent the cranial base.

• Frankfort Plane – This is the line joining porion and orbitale.

• Maxillary Plane – The line joining anterior nasal spine with posterior nasal spine.

• Mandibular Plane – the line joining gonion and menton.

Fig. 28

54

Cephalometric Analysis:

Angular and Linear Measurements;

A series of angles in degree and a few linear distances in millimeters, are measured and

compared with normal values. The differences from the normal are noted as plus or minus.

When the differences are below or above the normal ranges, they are considered as

abnormal.

The angles used in cephalometric analysis are formed at the junction of two planes, which

could be horizontal or vertical planes.

The cephalometric analysis can be divided into three parts: Skeletal relationship, Dental

relationship and Soft tissue relationship

1. Skeletal Analysis:

a) Antero-Posterior Relationship

• SNA: Measured at the junction of SN line and NA line (fig. 29). It evaluates the

antero-posterior position of the maxilla in relation to the anterior cranial base. The

normal average is 81±3° (normal or orthognathic maxilla). When this angle is above

the normal range it would be interpreted as protruded or prognathic maxilla, and

when it is below the normal range, retruded or retrognathic maxilla.

Fig. 29

• SNB: Measured at the junction of SN line and NB line (fig. 30). It evaluates the

antero-posterior position of the mandible in relation to the anterior cranial base. The

normal average is 78±3° (normal or orthognathic mandible). When this angle is

55

above the normal range, it would be interpreted as protruded or prognathic

mandible, and when it is below the normal range, retruded or retrognathic mandible.

Fig. 30

• ANB: This angle is the difference between SNA and SNB angle and indicates the

amount of skeletal discrepancy between maxilla and mandible in antero-posterior

position (fig. 31). The normal average is 3°±2 (skeletal class I). A larger than normal

angle would indicate a skeletal class II, and smaller than 1° angle a skeletal class III.

Fig. 31

b) Vertical Relationship

• SN-Mxpl: Measured at the intersection of SN line to maxillary plane (fig. 32). It

expresses the vertical inclination of the maxilla in relation to the anterior cranial

base. The mean value is 8°±3° (normal inclined maxilla), values greater than normal

56

indicate a posterior inclination of the maxilla, and smaller values indicate an anterior

inclination of maxilla.

Fig. 32

• FH-Mnpl: Measured at the intersection of Frankfort plane and mandibular plane

and expresses the inclination of the mandible (fig. 33). The mean value is 28°±4°

(normal inclined mandible).

Angles greater than normal indicate the mandible is growing downward and

backward or the mandible is steep (posterior inclination of the mandible).

Angles less than normal indicate an anterior inclination of the mandible, (mandible

is growing forward and upward, mandible is horizontal).

Fig. 33

57

• MMpA: Measured at the intersection of the maxillary plane with the mandibular

plane and relates the inclination of the mandible and the maxilla to each other (fig.

34). The mean value is 27°±4° (normal interbasal angle). If the angle exceeds the

normal there is skeletal open bite, whereas an angle less than the mean indicates

skeletal deep bite.

Fig. 34

• Facial Proportion (FP): This is the ratio of the lower facial height to the total

anterior facial height and it is calculated as a percentage according to this equation;

FP = lower facial height

x 100 total facial height

Total facial height = lower facial height + upper facial height.

Lower facial height: This is a linear measurement from menton perpendicular to maxillary

plane.

Upper facial height: This is a linear distance is measured from Nasion perpendicular to

maxillary plane (fig. 35).

58

In normal faces this index has a value of about 50% ± 2% (normal lower height). A larger

than this ratio will indicate increased lower facial height, smaller than this value will

indicate decreased lower facial height.

Fig. 35

Note: The MMpA reflects both posterior lower facial height and anterior lower facial height.

Therefore in the case of patient who has an increased MnpA but average facial proportion it

would appear that the posterior facial height is reduced (opposed to an increased lower

facial height which result increased MMpA). This would be noticed when there is a

discrepancy between the measurements of the facial proportion and the maxillary –

mandibular plane angles (MMpA).

2. Dental Relationship

• Uinc-Mxpl: Measured at the intersection of the long axis of the upper central incisor

with the maxillary plane (fig. 36).

It evaluates the antero-posterior inclination of the most prominent maxillary central

incisor. This angle averages 109° ± 6° (normal inclination of upper incisor).

59

A larger than normal angle would indicate proclination of the upper central incisor

and smaller than normal angle would indicate retroclination of maxillary incisors.

Fig. 36

• Uinc-NA: This is a linear distance measured in millimeter from the most prominent

incisal edge of the upper incisor perpendicular to NA line (fig. 37). It averages

4±2mm (normal position of upper incisor).

A larger than normal angle would indicate protrusion of upper central incisor and a

smaller than normal angle would indicate retrusion of the central incisor.

Fig. 37

• Linc to MnPL: Measured at the intersection of the long axis of the lower central

incisor with mandibular plane (fig. 38). It evaluates the antero-posterior inclination

of the most prominent mandibular central incisor.

60

A larger than normal angle would indicate proclination of lower incisor and a smaller

than normal angle would indicate retroclination of the mandibular incisor.

Fig. 38

• Linc-NB: This is a linear distance measured in millimeter from the most prominent

incisal edge of the lower incisor perpendicular to NB line (fig. 39). It averages

4±2mm (normal position of lower incisor).

A larger than normal angle would indicate protrusion of lower central incisor and a

smaller than normal angle would indicate retrusion of the mandibular incisor.

Fig. 39

• Linc to A-Pog: This is a linear distance measured in millimeter from the incisal edge

of the lower incisor perpendicular to A-Pog line (fig. 40). This measurement averages

+1±2mm (normal position of lower incisor). A larger than normal angle would

indicate protrusion of lower central incisor and a smaller than normal angle would

61

indicate retrusion of the mandibular incisor. To have a pleasing facial appearance,

the tip of lower incisor lay on or just in front of this line.

Fig. 40

• Uinc-Linc: The interincisal angle measure at the junction of the long axis of upper

central incisor with the lower central incisor (fig. 41) It averages 135°±5° (normal

proclination of upper and lower central incisors). The angle decreases with

proclination of upper and lower incisors and increase with retroclination of incisors.

Fig. 41

62

3. Soft Tissue Relationship:

Upper Lip-EL: This is a linear distance measured from the most anterior point on the

upper lip perpendicular to esthetic plane (tip of the nose to the soft tissue pogonion) (fig.

42). It averages -2 to -4 (normal position of upper lip which is inside the line). A larger

angle indicates the protrusion of the upper lip and a smaller angle indicates the retrusion

of the upper lip.

Fig. 42

• Lower Lip-EL: This is a linear measurement from the most anterior point on the

lower lip perpendicular to esthetic plane (fig. 43). It averages from 0 to -2 inside the

esthetic line (normal position of the lower lip). A larger angle indicates the protrusion

of the lower lip and a smaller angle indicates the retrusion of the lower lip.

Fig. 43

63

431 PDS

Cephalometrics

Name : _________________________ Date : ____________

Computer No. : _________________________

Mean Patient Interpretation

1. Skeletal Relationship

A. Anteroposterior

- Maxilla to Cranium SNA 81° ± 3

- Mandible to Cranium SNB 78° ± 3

- Mandible to Maxilla ANB 3° ± 2

Skeletal Cl. II – Cl. III

B. Vertical Relation

SN – Mxpl (SN to ANS – PNS) 8° ± 3

FH – MnpL (Or – Po to (Go – me) 28° ± 4

MMpA (ANS – PNS to Go – me) 27° ± 4

Upper Facial Height (Mxpl – N) mm

Total Facial Height (Mxpl to me + Mxpl to N)

mm

FP = Lower Facial Height _______________ x 100 Total Facial Height

50% ± 2%

2. Dental Relationship Ulnc to Mxpl 109° ± 6

Ulnc – NA 4 ± 2mm

Llnc – MnPL 93° ± 6°

Llnc – NB 4 ± 2mm

Llnc to A – Pog +1 ± 2mm

Inter-incisal Angle (Ulnc- Llnc) 135° ± 5°

3. Soft Tissue Relationship

Upper lip – EL* -2 to -4mm

Lower lip – EL* 0 to -2mm

EL* = Esthetic Line (soft tissue chin pog to tip of the nose)

Overall Diagnosis: ________________________________________________________________________________

________________________________________________________________________________________________________

________________________________________________________________________________________________________

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IV. Model Analysis

The practical evaluation of the study model is an important step during the diagnosis and

treatment planning of an orthodontic case. This includes observing the model in three

different views: lateral, frontal and horizontal.

Lateral View: We can observe from this view the following:

Angle's classification

Incisal classification

Overjet (horizontal relationship)

Overbite (vertical relationship), lateral overbite or supra-eruption

Curve of Spee

Inclination of the front teeth, primary evaluation (best done on cephalometrics)

Frontal View: The following can be seen:

The midline, upper or lower. We can determine the palatal midline by using a

symmetroscope

Deviating axial inclination, meaning the mesial, distal buccal or lingual tipping of

the front teeth

Crossbite, unilateral or bilateral, including one tooth or a group of teeth

Scissors bite, also unilateral or bilateral, individual or a group of teeth

Diastemas, we should determine the amount in millimeters

Horizontal View: Determine the following:

Eruption stage, deciduous/mixed permanent

Width of the alveolar process

Shape of the dental arch, ellipsoid/parabolic

Width of the dental arch, the intercanine and intermolar distance

Deviation in tooth morphology, ex. Peg shape lateral/fusion

Space condition, Moyer’s analysis, Nance Analysis/Bolton’s Analysis

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One of the most important aspects when viewing the study models is to observe the amount

of space required for the eruption of teeth, also termed the space condition, as mentioned

above. In order to estimate if there is any arch discrepancy and space available, and whether

we need to extract, the following analysis “Model Analysis” has been developed:

Plaster Model Analysis:

The most common analysis used are: Mixed dentition analysis (Moyer’s Analysis), Arch length

analysis (Nance Analysis), Tooth size analysis (Bolton’s Analysis).

1. Mixed Dentition Analysis, “Moyer’s Analysis”

This analysis is based on measurement of the mandibular permanent incisor. A

quantitative assessment of crowding may be obtained by this mixed dentition analysis.

The space available in each dental arch is measured on the study models and the sum of

the mesiodistal dimension of the unerupted teeth is determined by measuring the

mesiodistal dimensions of the four erupted mandibular permanent incisors (fig. 44, a-d).

Thus, predicting the combined sizes of the unerupted canine and premolars from the

table. The following diagrams show the method used step by step:

a. Measuring mesiodistal tooth size of incisors b. Transferring sizes to sheet

c. Calculating sum of mandibular incisors d. Prediction of unerupted canine and premolars

Fig. 44

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How to apply Moyer’s Analysis

• Determine the maximum mesiodistal width of each of the four lower permanent

incisors in the study model. Calculate their sum.

• From the incisors value determine the predicting size for unilateral upper 3, 4 and 5

(cuspid, first and second bicuspid). This can be found from the probability charts on

the following page. The upper half of the chart is for the upper teeth, and the lower

half is for the lower teeth, this value is termed the space required.

The predicting size for unilateral lower 3, 4 and 5 is taken from the lower probability

chart (this value is termed the space required).

• Calculate the space available after alignment of upper and lower incisors each arch

separately. This value determines the space available needed to accommodate 3, 4

and 5.

Space available – space required = will give the space adequacy or inadequacy for the non-

erupted 3, 4 and 5.

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431 PDS Space Analysis in Mixed Dentition

Name: ___________________________________ Computer No.: _________________________

- Maximum Mesiodistal width of lower incisors = = mm

- Predicted size of upper unilateral 3, 4 and 5 =

- Predicted size of lower unilateral 3, 4 and 5 =

UPPER ARCH

Left Right

- Mesiodistal width of 1 and 2 = mm mm

- Space needed for alignment of 1 and 2 = mm mm

- Space left after alignment of 1 and 2 = mm mm

- Space adequacy or inadequacy (space available – space required)

= mm mm

LOWER ARCH

Left Right

- Mesiodistal width of 1 and 2 = mm mm

- Space needed for alignment of 1 and 2 = mm mm

- Space left after alignment of 1 and 2 = mm mm

- Space adequacy or inadequacy (space available – space required)

= mm mm

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ANALYSIS OF DENTITION AND OCCLUSION

Probability chart for predicting the sum of the widths of upper 345 from 2112

Σ12 12 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0

95% 21.6 21.8 22.1 22.4 22.7 22.9 23.2 23.5 23.8 24.0 24.3 24.6

85% 21.0 21.3 21.5 21.8 22.1 22.4 22.6 22.9 23.2 23.5 23.7 24.0

75% 20.6 20.9 21.2 21.5 21.8 22.0 22.3 22.6 22.9 23.1 23.4 23.7

65% 20.4 20.6 20.9 21.2 21.5 21.8 22.0 22.3 22.6 22.8 23.1 23.4

50% 20.0 20.3 20.6 20.8 21.1 21.4 21.7 21.9 22.2 22.5 22.8 23.0

35% 19.6 19.9 20.2 20.5 20.8 21.0 21.3 21.6 21.9 22.1 22.4 22.7

25% 19.4 19.7 19.9 20.2 20.5 20.8 21.0 21.3 21.6 21.9 22.1 22.4

15% 19.0 19.3 19.6 19.9 20.2 20.4 20.7 21.0 21.3 21.5 21.8 22.1

5% 18.5 18.8 19.0 19.3 19.6 19.9 20.1 20.4 20.7 21.0 21.2 21.5

Probability chart for predicting the sum of the widths of lower 345 from 2112

Σ12 12 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0

95% 21.1 21.4 21.7 22.0 22.3 22.6 22.9 23.2 23.5 23.8 24.1 24.4

85% 20.5 20.8 21.1 21.4 21.7 22.0 22.3 22.6 22.9 23.2 23.5 23.8

75% 20.1 20.4 20.7 21.0 21.3 21.6 21.9 22.2 22.5 22.8 23.1 23.4

65% 19.8 20.1 20.4 20.7 21.0 21.3 21.6 21.9 22.2 22.5 22.8 23.1

50% 19.4 19.7 20.0 20.3 20.6 20.9 21.2 21.5 21.8 22.1 22.4 22.7

35% 19.0 19.3 19.6 19.9 20.2 20.5 20.8 21.1 21.4 21.7 22.0 22.3

25% 18.7 19.0 19.3 19.6 19.9 20.2 20.5 20.8 21.1 21.4 21.7 22.0

15% 18.4 18.7 19.0 19.3 19.6 19.8 20.1 20.4 20.7 21.0 21.3 21.6

5% 17.7 18.0 18.3 18.6 18.9 19.2 19.5 19.8 20.1 20.4 20.7 21.0

Probability charts for computing the size of unerupted cuspids and bicuspids. The top chart is for the upper arch. The bottom chart is for the lower arch.

1. Measure and obtain the mesiodistal widths of the 4 permanent mandibular incisors.

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2. Find that value in the top horizontal column. 3. Reading downward in the appropriate vertical column, obtain the values for expected width

of the cuspids and premolars corresponding to the level of probability you wish to choose. Ordinarily, the 75% level of probability is used. Note that the mandibular incisors are used for the prediction of both the mandibular and maxillary cuspid and premolar widths.

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2. Arch Length Analysis, “Nance Method”:

The amount of space available is determined by adapting a length of 0.025 inch diameter

brass wire to fit from the mesial marginal ridge of the left first permanent molar around

the arch, to the mesial marginal ridge of the right mandibular first permanent molar. The

brass wire should pass over the imagined correct position of the cuspid, the center of the

occlusal surfaces of the bicuspids, and the incisal edge of the most labial of the incisor

teeth. The wire should be a smooth arch, free from kinks and should simulate the desired

arch form. Adjustment to the arch form should be made if a mandibular buccal or

lingual crossbite is present.

The length of the brass wire, determined in millimeter, is regarded as the available space

for the total complement of the dentition. This consists of the 1st and 2nd bicuspids,

cuspids and lateral and central incisors of both the right and left sides of the mandibular

arch.

It is important to recognize that the available space may or may not be adequate for the

proper alignment of the teeth. The required space is determined by measuring the

mesiodistal width of each tooth from the right 2nd bicuspid to the left 2nd bicuspid, then

calculating the sum;

The space available – space required = will give us the space adequacy or inadequacy to

accommodate the teeth.

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431 PDS Space Analysis in the Permanent Dentition

Name: ___________________________________ Computer No.: _________________________

Upper Jaw R F L

Space Available

Space Required

Difference

Lower Jaw R F L

Space Available

Space Required

Difference

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3. Tooth Size Analysis, “Bolton Analysis”:

The determination of tooth size ratios between the maxillary and mandibular teeth is

essential for proper orthodontic diagnosis, treatment planning and result prediction. This

relation determines:

a. Teeth interdigitation

b. Excessive overbite

c. Overjet

d. Spacing between teeth

The desirable ratio is necessary to attain an optimum interarch relationship. If the

analysis indicates a marked deviation, it can give an insight into the required pattern of

treatment and extraction. The Bolton procedure is used in this case to determine the

overall ratios. It is as follows:

• The sum of the mesiodistal diameter of the 12 maxillary teeth and the sum of the

mesiodistal diameter of the 12 mandibular teeth including the first molar is

calculated, this is called the overall ratio:

If the overall ratio is less than 91.3%, then the maxillary tooth material is excessive. We

can determine from the table the desired size of the mandibular 12 teeth, appropriate

for the actual size of the maxillary 12 teeth. The value represents the excessive amount

of mandibular tooth material.

Overall ratio = Sum of 12 mandibular teeth

x 100 = 91.3% Sum of 12 maxillary teeth

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We can use the same equation for the anterior 6 teeth only from canine to canine. This called

the Anterior Ratio:

If the ratio is less than 77.2%, the maxillary teeth are excessive

How to apply the Bolton’s Analysis:

If the overall ratio of the 12 mandibular and 12 maxillary teeth is more than 91.3%, then

the teeth that are at fault are the 12 mandibular teeth, meaning that they are

excess in size. From the table in the following page, we determine what the

corrected sum of the 12 mandibular teeth should be (this is achieved by

locating our actual sum of the 12 maxillary teeth which we have already the

chart, this is termed the corrected mandibular.

If the overall ratio is less than 91.3%, then the teeth that are at fault are the 12 maxillary

teeth, meaning that they are excess in size. The same procedure is done, but

here we take the actual sum of the 12 mandibular teeth instead, and locate our

corresponding maxillary value from the chart.

When determining the anterior ratio, the same procedure as above is used, calculations

are done when the amount is more than 77.2% or less than 77.25.

Anterior ratio = Sum of 6 mandibular teeth

x 100 = 77.2% Sum of 6 maxillary teeth

74

75

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II. References

1. Profitt, WR and Fields, HW. Contemporary Orthodontics. Second edition,

Mosby Yearbook Inc., St. Louis Missouri, 1993.

2. Thilander, B and Ronning, O. Introduction to Orthodontics. Fifth edition,

printed by Minab/Gotab, Stockholm, 1985.

3. Walther, DP and Houston, WJ. Orthodontic Notes. Fifth edition,

Butterworth-Heinemann Ltd., Oxford 1994.

4. Wisth, P. Introduction to the Edgewise Technique: A Technical Manual,

University of Bergen, Norway, 1985.

5. American Board of Orthodontics. Specific Instructions for Candidates,

American Board of Orthodontics, St. Louis, 1990.