Orthodontics – Retention

RETENTION  –  Period after active treatment when passive fixed / removable appliances were worn to stabilize the occlusion that had been created

—> appliance —>

RETAINER  –  Passive orthodontic appliances that help in maintaining and stabilizing the position of a single tooth or group of teeth to permit reorganizing of the supporting structures

 

WHY RETENTION IS NECESSARY?

1. The gingival and periodontal tissues are affected by orthodontic tooth movement and require time for reorganization when the appliances are removed.
2. The teeth be in an inherently unstable position after the treatment, so that soft tissue pressure constantly produce a relapse tendency.
3. Changes produced by growth may alter the orthodontic treatment results.

 

Causes of Relapse

• Failure to remove cause of malocclusion
• Lack of normal cuspal interdigitation
• Incorrect axial inclination
• Tooth size disharmony and improper contacts
• Arch expansion
• Failure to manage rotations

 

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Retention Planning

	Time of usage	Cases
NO RETENTION REQUIRED		a. Cross bite b. Dentition treated with serial extraction
LIMITED RETENTION	6 months = whole days and nights	a. Class I non-extraction cases with spacing and protrusion of maxillary incisor b. Class I and II extraction cases c. Early correction of rotated teeth to their normal position before root completion d. Cases involving ectopic eruption or the presence supernumerary teeth e. Corrected deep bites
PERMANENT RETENTION		a. After arch expansion especially in mandibular arch b. Cases of considerable generalized spacing c. Severe rotation or severe labiolingual malposition d. Spacing between maxillary central incisor with an otherwise normal occlusion

 

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Classification of Retainers

1. Fixed retainers -> cemented or bonded to the teeth

0.0195 twisted wire

 

 

2. Removable retainers -> can be removed and reinserted by the patient

 

Removable Retainers

Hawley’s retainer

• With short labial bow
• With long labial bow
• With contoured labial bow
• Continuous labial bow soldered to clasps

 

Begg’s retainer (wrap-around retainer)

 

Kesling’s tooth positioner

 

Essix (vacuum-formed retainers)

 

– end –

 

References:
Gill, D.S. 2008. Orthodontics at a Glance. Blackwell Munksgaard.
Proffit, W.R; Field, H.W; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

 

 

Orthodontics – Anchorage

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WHAT IS ANCHORAGE?

Anchorage is the resistance to the unwanted forces generated in reaction to the active component of the appliance.

 

Sources of Anchorage:

A) Intraoral sources

B) Extraoral sources

 

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Intraoral Sources

1. The alveolar bone
2. The teeth
3. The basal bone
4. The cortical bone
5. The musculature

 

1. The alveolar bone – Less dense alveolar bone offers less anchorage

 

2. The teeth –

• Root form

The distribution of the periodontal fibers on the root surface aid in anchorage

 

Tripod roots aids in increasing anchorage

 

• Size of the Root

The larger or longer the roots the more is their anchorage potential

 

• Numbers of the Roots

The greater the surface area the greater the periodontal support and hence, greater the anchorage potential.

Multirooted root provide greater anchorage

 

• Position of the tooth

The position of the teeth in the individual arches helps in increasing the anchorage potential.

 

• Axial Inclination of the Tooth

When the tooth is inclined in the opposite direction to that of the force applied, it provides the greater anchorage.

 

• Root Formation

Teeth with incomplete root formation are easier to move and are able to provide lesser anchorage.

 

• Intercuspation

Good intercuspation leads to greater anchorage potential.

 

 

3. Basal bone

Nance Palatal Button

Hard palate lingual surface -> Can be used to augment the anchorage

 

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Extraoral sources

Headgear

The anchorage unit situated outside the oral cavity.

 

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Classification of Anchorage

 

1) According to the manner of force application

• Simple anchorage
• Stationary anchorage
• Reciprocal anchorage

 

2) According to the number of anchorage units

• Single or primary anchorage
• Compound anchorage
• Reinforced anchorage

 

3) According to the jaws involved

• Intramaxillary
• Intermaxillary

 

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Simple Anchorage

Active movement of few teeth versus several anchor teeth.

 

Stationary Anchorage

Bodily movement of one group of teeth against tipping of another.

 

Reciprocal Anchorage

When two teeth or two sets of teeth move to an equal extent in an opposite direction.

 

Single or Primary Anchorage

The tooth to be moved is pitted against a tooth with a greater alveolar support area.

 

Compound anchorage

Provides for the use of more teeth with greater anchorage potential to move a tooth or group of teeth with lesser support.

 

Reinforced anchorage

The anchorage units are reinforced by use of more than one type of resistance units.

 

Intramaxillary

The elements providing the anchorage as well as those to be moved are situated within same jaw.

 

Intermaxillary

When the anchorage units situated in one jaw used to provide the force required to move teeth in the opposing jaw.

 

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Anchorage Planning

1. The number of the teeth to be moved
2. The type of the teeth to be moved
3. Type of tooth movement
4. Periodontal condition
5. Duration of tooth movement

 

Classifying Anchorage Requirements

a. Maximum anchorage

b. Moderate anchorage

c. Minimum anchorage

 

– end –

 

References:
Gill, D.S. 2008. Orthodontics at a Glance. Blackwell Munksgaard.
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Proffit, W.R; Field, H.W; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

Orthodontics – Removable Appliances

Removable appliances are orthodontic appliances that can be inserted and removed by the patient.

It is indicated when:

• Growth modification during mixed dentition
• Limited tooth movement
• Retention

 

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Active Removable Appliances

Advantages:

• Easy for cleaning
• Relatively simple, can be handled by general practitioner
• Control is less complex
• If there is a problem, the appliance can be removed by patient
• Time required by clinical to active an appliance is less
• Less expensive

 

Disadvantages:

• Success of treatment depend on patient compliance.
• Only simple malocclusion can be corrected.
• In cases requiring multiple tooth movements, treatment is prolonged.
• The chance of appliance loss or breakage is more.
• The patient must have skill to be able to remove and replace the appliance.

 

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Component of the Active Removable Appliance

A) Force or active component

• Springs
• Screws
• Elastics
• Labial bow

 

B) Fixation or retentive component

• Clasps

 

C) Base plate

• Cold curing acrylic
• Heat curing acrylic
• Orthoresin

 

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Adams Clasps

For retention on incisor, premolar and molar

Main features:

• Bridge (A)
• Arrowhead (B)
• Shoulder (C)
• Tag (D)

Diameter: SS round 0.7 mm

 

Adams Clasps Fabrication

1) Model Preparation

Draw horizontal lines that are parallel to the occlusal line

– C2 = at gingival margin (the deepest curve) mesial to distal of the tooth

– C1 = a line that divide the molar into two equal section vertically

 

2) Draw vertical lines which are parallel to each other at the right angle to horizontal lines

– On the mesial (A1) and distal (A2) contact point of molar tooth toward gingival

– Mesiobuccal cusp (B1) and distobuccal cusp (B2) of the molar towards gingival

 

3) Bridge

 

• Straight not bowing
• Bend an angle of 90° at the middle of 0.7 mm
• Mark the length of the bridge/ cusp tip to cusp tip. The bridge might be slightly longer than (B1 – B2)

 

4) Arrow head

• Mark on the wire the distance of C1 – C2
• Firmly, hold the wire at the tip of the plier. Bend an angle of 90° should not be longer from the mark point.

 

• Reduce the pressure of the plier that hold the wire. Rotate the other end of the wire (1), which the bridge will be placed towards the body of the plier. Push the wire towards the bridge and upwards (2). Repeat on the other arm.
• Adjust the shape of the arrow head.

• Hold descending arm of the arrow head with the plier and rotate the bridge, where there are about 30° of angle between the arrow head and the bridge.
• By placing the bridge at the angle 30° – 45° to the buccal surface of the tooth, make sure both arrow head are place in the undercut area.

 

5) The shoulder and palatal part

• The arrow head continuous following the embrasure at the mesial and distal of the tooth. Hold the wire on the ascending arm. Bend the wire 30° towards the bridge. Make sure the ascending arm slightly shorter than descending arm.
• Hold the wire, rotate the free end of the wire until there are 90° angle between the wire and the bridge.

• Adapt the wire on the tooth. The mesial and distal arm of the wire should be parallel and crossing the mesial and distal embrasure of the tooth when the wire are positioned at the angle of 30° – 45° with the buccal surface. The bridge should be parallel to the mesio-distal axis of the tooth.
• The wire should follow the curvature of the embrasure surface of the tooth (to make sure no high bite)

 

6) Tag

• Does not sit on the tissue (0.5 – 1 mm) away
• Does not extend over median palatine raphe (upper)
• Does not extend over sulcus

 

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Labial Bow

Uses of labial bow are:

• For retraction of anterior teeth (less than 4 mm)
• For retention

Main features:

• Bow (A)
• U loop (B)
• Tag (C)

 

Types of labial bow

• Short labial bow
• Long labial bow
• Split labial bow

Diameter: SS round 0.7 mm

 

Short Labial Bow

Bow contacts the most prominent labial surfaces of the anterior teeth. Ends in two U-shaped loops that extend as retentive arm between the canine and premolar before getting embedded in the acrylic base plate

 

Uses:

For retention (Hawley’s retainer)

Retraction of anterior teeth – minor overjet reduction and anterior space closure.

The range of action is limited because stiffness and low flexibility. The bow is activated by compressing the loops of the bow by 1 – 2 mm.

 

1) Model Preparation

 

Draw the labial bow design on the model:

• The line should be parallel to the occlusal plane.
• At the level of 1/3 incisal height
• Half round

 

2) For the canine area:

• The loop width should be 2/3 of the canine width.
• The length (A) should be the same with clinical crown of the canine.

 

3) Bow

• Bend a wire into U shape that register the average shape of the arch from canine to canine.
• Adapt the wire to the labial surface of the teeth as many as possible at the level of interdental gingival papilla.
• It should be symmetrical for both quadrant.

 

4) U loop

• At the point of 1/3 mesio-distal canine width bend the wire 90° downward (toward gingival).
• Bend the wire into U shape with the width of 2/3 of the canine posteriorly.
• Don’t touch the tissue.

 

5) Tag

• Adapted accurately between occlusal surface of 2 teeth.
• Bend the wire palatally and follow the curvature of the teeth and the palate.
• Does not sit on tissue (0.5 mm – 1 mm away).

 

Long Labial Bow

It is a modification of short labial bow design. It extends from 1st premolar of one side to that of the contralateral side. Distal arm of U loop extends between the two premolars and ends as a retentive arm.

 

Used:

• For retention (Hawley’s retainer)
• Retraction of anterior teeth – minor overjet reduction and closure to the space distal to canine
• Guidance for canine during canine retraction.

The bow is activated by compressing the loops of the bow by 1-2 mm.

 

Modification – Labial Bow soldered to Adam’s Clasp

– Retentive component in extraction cases and closely occlusion between maxilla and mandibular

 

Split Labial Bow

It is a modification of short labial bow in that is split in the middle for increased flexibility and uses 0.7 mm round SS wire.

It has 2 separate short bow, each with a U-loop ending distal to canine. It is used in anterior retraction and in closure of midline diastema.

The bow is activated by compressing the loops of the bow by 1-2 mm.

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Z-Spring

It has double cantilever where the spring is located in a box with acrylic overlying the spring. It is used to tip the tooth labially.

Main features:

• Coil (A)
• Arm (B)
• Tag (C)
• Boxing

Diameter: SS round 0.5 mm

Z-spring is activated by opening both of helical up to 2-3 mm at a time.

 

Coil:

• 2 coil
• 3 mm diameter
• Crossed coil
• Coil must be tight
• Within mesiodistal width of tooth
• Same plane with active arm

Arm:

• On top of coil
• Ends folded away from tissue
• 1/3 of whole length of tooth from gingival
• Start at mesial (if move distally)
• Spring position 90° to the palatal surface tooth

 

Z-spring Fabrication

1) Model Preparation

Divide the tooth into 3 parts equally.

 

• Draw the design of the z-spring: X1 – X2 = length of the spring, Y = midline of the mesiodistal width
• Diameter of the coils = 3 mm
• Axis of the arms A and B parallel to the mesiodistal axis of the tooth
• Z-spring position in the 1/3 gingival part

 

2) Bend wire

• Bend the first arm with a coil at one end of the wire. The arm should be parallel to mesio-distal axis of the tooth.
• Bend another coil with the same size and diameter at the other end of the tooth width.
• The wire from the first to the second coil should follow z flow.

• 1st coil is positioned under the second loop.
• For the 2nd coil, 1st loop should be on top of 2nd loop.
• From the 2nd coil, bend the wire parallel to the mesio-distal axis of the tooth. The middle part of the tooth, bend the arm towards the palate at 90° angle.

3) Tag

• Does not sit on tissue (0.5 mm – 1 mm) away
• Does not extend over median palatine raphe and not too short
• Zig zag tag to provide excellent retention
• No Acrylic stuck on the free wire

 

4) Boxing

• Active arm and coil free from acrylic
• Height of boxed acrylic at minimum

 

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Buccal Canine Retractor

Used for:

To tip canine palatally and distally

Main features:

• Perpendicular arm (A)
• Mesial limb (B)
• Coil (C)
• Distal limb (D)
• Tag (E)

Diameter: SS round 0.7 mm

Canine retractor is activated by opening the helix up to 2 mm at a time.

 

1) Model preparation

Draw the design:

• A. Long axis of the tooth
• B. Coil is located at half of the root length

 

2) Coil (A):

• 3 mm diameter
• 2 mm from sulcus
• Coiled towards tissues
• No acrylic stuck on wires

3) Mesial limb (B):

• Positioned down the long axis of tooth
• 1 mm away from tooth and tissue surface

 

4) Distal limb (C):

• Going towards of mesial of 15 or 25
• Shoulder touch mesial 15 or 25 (as a mesial stop)

 

5) Tag (D):

• Positioned towards to distal 15 or 25
• Does not sit on tissue (0.5 mm – 1  mm) away
• Does not extend over median palatine raphe (maxilla)

 

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T-Spring

Used to tip teeth buccally.

Main Features:

• Horizontal arm (A)
• Vertical arm (B)
• Loop (C)
• Tag (D)

Diameter: SS round 0.6 mm

 

T-spring Fabrication

1) Horizontal arm (A):

• 1/3 of whole length of tooth from gingival
• Full contact with tooth (follow the tooth contour)
• Width is mesio-distal of the tooth

 

2) Vertical arm (B):

• Middle of horizontal arm
• Length: 1 – 2 mm
• Positioned down the long axis of tooth

 

3) Loop (C):

• Loop should be 3/4 smaller than horizontal arm
• Both side must be equal

 

4) Tag (D):

• Zigzag tag for better retention
• Does not sit on tissue (0.5 mm – 1 mm away)
• Does not extend over median palatine raphe
• The end of the loop, bend the wires vertically toward the palate
• Follow the curvature of the palate to increase the retention of the spring
• To protect this wire the acrylic formed into ‘box’ overlying the spring

 

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Palatal / Finger Spring

Used: to tip the tooth mesially or palatally

Main features:

• Active arm (A)
• Coil (B)
• Tag (C)

Diameter: SS round 0.5 mm for incisor, 0.6 mm for canine and premolar

 

Finger Spring Fabrication

1) Active arm:

• It is placed towards the tissues
• Free end, 12  – 15 mm in length
• Should contact only on the proximal side
• It is adapted on the labial side away from the tooth surface
• The active arm is placed in the interdental area of the teeth (more than 1/2 mesio-distal width of the tooth) with a small loop.

2) Coil:

• It is positioned midway between the initial and final position of the tooth
• 3 mm diameter
• The coil should be on the opposite side of the direction of tooth movement
• Active arm of the coil is bend below the tag

 

 The active arm is placed in the interdental area of the teeth (more than 1/2 mesio-distal width of the tooth) with a small loop.

 

3) Guard wire : 0.7 mm

• The length of the wire should be longer than the mesio-distal width of the tooth
• Tags are bend at the both end of the wire
• It is placed below the active arm (in front of the coil)

 

4) Tag

• Zigzag tag
• Follow the curvature of the palate.
• Does not sit on the tissue (0.5 mm – 1 mm) away.
• Does not extend over median palatine raphe.

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Southend Clasp

Used for retention in anterior region

Diameter: SS round 0.7 mm

Main Features:

• Labial part (A)
• Palatal part (B)
• Tag (C)

 

Requirements:

• There is a minimal undercut.
• Upper incisor are not proclined.
• The wire should follow the curvature of gingival margin of the teeth.
• The mesial and distal arm adapt to the tooth and the incisal part must not interupt the occlusion of the teeth.
• The wire on the palate should follow the curvature of the palate with 1 mm relieved from palatal surface for acrylic.

 

Southend Clasp Fabrication

1) Model preparation

• Draw the design of the southend clasp on the model palatally and labially

 

2) Labial part

• Bend a V shape on the wire and adapt to the gingival area between the central incisors
• The clasp is constructed following the gingival margin and distal contour of the maxillary central incisors

 

3) Palatal part

• At the incisal part, bend the wire toward the palate
• On the palatal side make sure the wire is position at the middle between the lateral and central incisors.
• The wire are bend following the tooth and palate surface.

 

4) Tag

• Follow the curvature of the palate
• Does not sit on the tissue (0.5 mm – 1 mm) away
• Does not extend over median palatine raphe

 

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Robert Retractor

Used for correction of the severe protrusion of teeth. It produces lighter forces.

Diameter: SS round 0.5 mm

Main features:

• Horizontal bow (A)
• Vertical arm (B)
• Coil (C)
• Retentive arm reinforced with sleeve (D)
• Tag (E)

 

Robert Retractor Fabrication

1) Model preparation

Draw the horizontal bow design on the model:

• The line should be parallel to the occlusal plane
• At the level of 1/3 incisal height

 

Draw the design:

• A. Long axis of the tooth
• B. Coil is located at half of the root length at long axis of the tooth

Coil:

• 3 mm diameter
• Coil towards tissue
• No acrylic stuck on the wire

 

2) Horizontal bow

• Bend a wire into U shape that register the average shape of the arch from canine to canine.
• Adapt the wire to the labial surface of the teeth as many as possible at the level of interdental gingival papilla
• It should be symmetrical for both quadrant
• No kink

 

3) Vertical arm

• At the distal of lateral incisor, bend the wire downward (toward gingival) follow the design of vertical arm.
• Follow the tissue contour but it doesn’t touch the tissue

4) Coil

• Make the coil, 3 mm diameter, the upper arm go to canine and the lower arm go to premolar.

 

5) Retentive arm reinforced with sleeve

• Put the plastic sleeve or metal tubing through the wire at retentive arm until the tube stuck (tube length is about 3 mm)
• For retentive arm, follow the curvature of the buccal mucosa and the area of contact point between canine and premolar.
• Make sure there are gaps between the retentive arm + coil + vertical arm.

6) Tag

• Zigzag tag
• Adapted accurately between occlusal surface of 2 teeth
• Bend the wire palatally and follow the curvature of the teeth and the palate
• Does not sit on tissue (0.5 mm – 1 mm away)

 

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Base Plate

Uses:

• It incorporates both the retentive and active component into a single functional unit.
• It helps in anchorage and retention of the appliance in the mouth.
• It helps resist unwanted drift during tooth movement.
• It distributes the forces from active components over a large area.
• It protects the palatal springs against distortion in the mouth.
• Bite planes can be incorporated into the base plate and used to treat specific problems.

 

Material:

• Heat cure acrylic
• Cold cure acrylic Orthoresin

 

Thickness:

Minimum thickness to be comfortable to a patient (1 – 2 mm)

If too thick, it interferes with speech and will not be tolerated by patient.

 

Extension of Base Plate in Maxillary Arch

If too much of the palate is covered by acrylic -> produces nausea

Therefore minimizing it by

• Extending the base plate till the distal of the 1st molar.
• Slightly cutting it forward in the midline.

 

U shape Maxillary base plate

• To ensure adequate strength and gains maximum anchorage
• Easily broken

 

Extension of Base Plate in Mandibular Arch

• It is not extended too deep to avoid irritation to the sulcus and displacement by the tongue.
• Lingual undercut (should be blocked before acrylization)

 

Note:

The border should be rounded (right side)

Sharp (left side)

Undercuts should be filled (green)

 

Modification of Base Plate

Anterior bite planes

• For overbite reduction
• Should be flat
• The bite plane should be thick enough to separate the posterior teeth by 2 – 3 mm.

 

Posterior bite planes

• They are used mainly when the teeth have to be pushed over the bite
• The bite plane should be thick enough to free the teeth, that are to by moved from occlusal interference with the opposing teeth.

 

– end –

 

References:
Gill, D.S. 2008. Orthodontics at a Glance. Blackwell Munksgaard.
Isaacson, K.G; Muir, J. D, Reed, D.T. 2002. Removable Orthodontic Appliances. London: Wright.
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

 

Orthodontics – Tooth Movement

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Each tooth is attached to and separated from adjacent alveolar bone by the periodontal ligament (PDL) which are parallel collagenous fibers that resist the displacement of the tooth expected during normal function.

Component of PDL

• i) Collagenous fiber bundles
• ii) Cellular elements – osteoblast, osteoclast
• iii) Vascular blood
• iv) Neural elements

 

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Theories of Orthodontic Tooth Movement

Pressure Tension Theory – Schwartz (1932)

Whenever a tooth is subjected to an orthodontic force, it results in areas of pressure and tension. According to him, the areas of pressure show bone resorption while areas of tension show bone deposition.

 

Blood Dynamic Theory – Bien (1966)

Also known as the Fluid Dynamic Theory, the tooth movement occurs as a result of alterations in fluid dynamics in periodontal ligament.

 

Bone Bending / Piezoelectric Theory – Farrar (1876)

When the force is applied on a tooth, the adjacent alveolar bone bends. This deformation causes bone to become electrically charged and exhibits a phenomenon called piezoelectricity. Area of convexity (+) cause bone resorption, and area of concavity (-) cause bone deposition.

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WHAT IS FORCE?

It is an act upon a body that changes or tends to change the state of rest or of motion of that body.

 

WHAT IS THE OPTIMUM FORCE FOR ORTHODONTIC MOVEMENT?

The lightest force that produces a maximum or near-maximum response.

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Types of Force

 

A) Continuous forces

Force maintained at some appreciable fraction of the original from one patient visit to the next.

*Ni Ti = nickel titanium

 

B) Interrupted forces

Force level decline to zero between activation

 

C) Intermittent forces

Force level decline abruptly to zero intermittently when the orthodontic appliance is removed by patient.

 

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Type of Orthodontic Movement

A) Tipping

• Simplest form of orthodontic movement
• Produced when a single force is applied against the crown of the tooth

 

B) Translation (bodily)

• Two forces are applied simultaneously to the crown

 

C) Intrusion

 

• Light forces
• Concentrated in a small area at the apex

 

D) Extrusion

• No area for compression
• Only tension

 

– end –

 

References:
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Proffit, W.R; Field, H.W; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.

 

Orthodontics – Study Models

WHAT IS A ORTHODONTIC STUDY MODEL?

It is an essential diagnostic record which help to study the occlusion and dentition from all 3 dimensions. The models are used as pre-treatment models, stage models and post treatment models.

 

Purposes of Orthodontic Study Models

1. Represent the case prior to orthodontic treatment.
2. Aid the dentist in diagnosing and analyzing the case.
3. Permit inspection from perspectives that are impossible to obtain when looking in the patient’s mouth.
4. Permit extended observations and comparisons far beyond the patient’s endurance for holding his/her mouth open and are available for study during patient’s absence.
5. Be used in educating the patient about her/his case (dental need and treatment plan).
6. Show the orthodontic treatment progress.

 

The Criteria for Study Models

Models have 2 distinct portions:

A) Art portion : the base of the model

B) Anatomic portion : the teeth, alveolar process and palate

 

Important criteria when taking impression for a study model:

1. All detail is reproduced, including the complete peripheral turn and a portion of retromolar pads or tuberosities.
2. Detail is sharp, not blurred or indistinct.
3. Free of voids in critical areas and free of large folds of alginate.
4. No areas where alginate has pulled away from the tray.
5. Free of rips and tears except in interproximal areas.
6. Alginate thoroughly covers the tray, no tray visible through alginate.
7. Free of bulges or depressions that indicate a subsurface bubble.
8. Alginate is smooth, not sponge-like.

 

Steps in pouring the study model

1. Mix the mixture of orthodontic plaster (50% stone; 50% plaster of paris)

2. Pour the alginate impressions with orthodontic plaster.

• Flow into the tooth portions from the palate in maxilla
• Flow into the tooth position from the posterior aspect and around the arch in mandible

3. Fill the base formers with orthodontic plaster.

• Ensure a degree of centralization
• Do not push the impression tray too deeply
• Make sure the bottom of impression tray, the occlusal surface of impression, and the bottom of the base former are all parallel

4. Allow the time for orthodontic plaster to set.

5. Once it sets, remove the tray and alginate carefully to avoid fracture.

 

Steps in trimming preparation

1. Remove all nodules and imperfections with sharp instrument.

2. Soak the models in water for 5-15 minutes. Use the gentle trimmer and firm pressure.

 

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Trimming Technique

 

A) Starting with upper model

1. Occlude upper model on rubber pad.

2. Trim the base until case exhibit 1/3 art portion and 2/3 anatomic portion.

3. Check the paralellism of the occlusal plane by placing the teeth on the horizontal surface and comparing the base of cast to the horizontal surface.

 

4. Occlude the upper and lower models with wax bite in place.

5. Check the relationship of the last molars to each other. If the lower molars extend significantly further than the upper molar, mark a line the distance of the extension to the 1 cm distance from the last molar of the lower molar.

 

B) Upper model posterior side

1. Mark a light pencil line down the midline suture of the model for reference.

2. Mark the line of posterior side perpendicular to midline suture of the model.

3. Trim the posterior side following the line.

 

C) Upper model lateral sides

1. Mark the line of lateral sides at 60° from posterior side at the right and left side of the model.

2. The line should be 1 cm from buccal surfaces of the teeth (the side should not be trimmed beyond the depths of the buccal fold).

3. Trim the lateral sides following the line.

 

D) Upper model anterior sides

1. Mark the line of anterior sides at 30° from the lateral sides to a point beginning at the midline and ending at the cuspids-preserving the anterior buccal fold.

2. The line must be equal on both sides of the cast.

3. Trim the anterior sides following the line.

 

 

E) Upper model heel sides

1. Mark the line of heel sides at 120° from posterior side.

2. The line must be equal on both sides of the cast.

3. Trim the heel sides follow the line.

* All the trimming procedures, anatomy extensions should be equidistant around the entire arch for both model.

 

F) Establishing the base of mandibular cast

1. Occlude the mandibular cast with the maxillary cast using the wax.

2. With the base against the grinding wheel, cut the base of mandibular cast (parallel to maxillary cast)

3. Trim the base until case exhibit the 1/3 art  portion and 2/3 anatomic portion.

 

G) Lower model posterior sides

1. With the wax bite still in place, position the models in a vertical position on the trimming table.

2. Place the base of maxillary cast on the trimming table.

3. Trim until the posterior borders of mandibular cast.

4. Preserve the retromolar pad of mandibular cast and tuberosity of maxillary cast.

 

F) Establish lower model heel sides and lateral sides according to the upper cast

 

G) Lower model anterior side

1. With the occluded models, trim the anterior sides of the model.

2. Maintained the same amount of anatomy extension as on the upper model.

3. Both sides the same length and angulations of the corners.

4. Take the mandibular cast, trim the anterior region 3-3 cuspid to within 7 mm of the most protruded anterior tooth or from the mucobuccal fold, whichever most labial.

5. Carefully, round off the anterior borders of the cast. There is no tool to assist you in rounding the anterior border, you must use your dexterity.

6. Lightly touch all trimmed surfaces of both models on the fine wheel until heavy scratches are removed.

 

H) Model finishing

1. Sculpting and repairs can be done prior to soaping and finishing the complete models.

 

 

2. With a lab knife or other suitable instrument, even up irregularities of the maxillary cast and lingual portion.

3. Remove the bubbles and other artifacts with scale.

4. Make the depth of the vestibule visible.

5. Fill in and patch air bubbles in models where needed any small holes while the models are still wet with a thin mix of plaster.

6. Set models aside to dry.

7. After models have dried, using a wet-dry grade of fine-grit sandpaper wet sand the casts to remove the scratches left by grinding wheel.

8. When sanding the posterior borders, the sides and the heels of the models, it must be in centric occlusion and the borders made smooth at the same time.

9. Allow models to thoroughly dry (at least 24 hours).

10. Soak 20 minutes in warm concentrated soap solution.

11. Permit models to dry and rub with chamois skin or nylon until glossy.

 

I) Label the casts

Label the upper and lower casts with the following details:

• i) Patient’s name
• ii) Registration number
• iii) Patient’s date of birth
• iv) Date of impression
• v) Dental officer’s name

 

 

– end –

 

References:
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

 

 

 

 

 

Orthodontics – Etiology of Malocclusion

There are 2 factors in the etiology of malocclusion.

A) General Factors – effect the body as a whole and have a profound effect on the greater part of the dento-facial structures

They are due to…

1. Heredity
2. Congenital
3. Environment
4. Predisposing metabolic climate and disease
5. Dietary problems (nutritional deficiency)
6. Abnormal pressure habits and functional aberrations
7. Posture
8. Trauma and accident

 

B) Local Factors – responsible for malocclusion produce a localized effect confined to one or more adjacent or opposing teeth

They are due to…

1. Anomalies of number
2. Anomalies of tooth size
3. Anomalies of tooth shape
4. Abnormal labial frenum: mucosal barriers
5. Premature loss of decidious teeth
6. Prolonged retention of decidious teeth
7. Delayed eruption of permanent teeth
8. Abnormal eruption path
9. Ankylosis
10. Dental caries
11. Improper dental restoration

 

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General Factors

1) Hereditary factor

The child is a product of parents who have dissimilar genetic material. Thus the child may inherit conflicting traits from both the parents resulting abnormalities of the dentofacial region. Racial, ethnic and regional inter-mixture also might lead to a uncoordinated inheritance of teeth and jaws.

a) Neuromuscular system

b) Dentition

• size and shape of teeth
• number of teeth
• primary position of tooth germ and the path of eruption
• shedding of decidious teeth and sequence of eruption
• mineralization of teeth

c) Skeletal structures

d) Soft tissues (other than neuromuscular) – frenum

Left: Maxillary labial frenum |   Right: Ankyloglossia

 

2) Congenital defects

Developmental defects are malformations seen at the time of birth. They may be caused by variety of factors.

a) Micrognathism – abnormalities of jaw development due to intra-uterine position

b) Cleft lip and palate – most commonly seen developmental defects that occur as a result of non-fusion between the various embryonic processes. It may exhibit a number of dental problems such as missing teeth, mobile teeth, rotations and crossbite.

 

3) Environment

Various prenatal and postnatal environmental factors can cause malocclusion.

a) Prenatal factors – caused by abnormal fetal posture during gestation is said to interfere with symmetric development of the face. Other influences such as maternal fibroids, amniotic lesions, maternal diet and metabolism. Drugs for German measles (Thalidomide) can cause congenital deformities like clefts.

b) Postnatal factors –

Forceps delivery might result to injury to the TMJ area which can undergo ankylosis due to retarded mandibular growth.

Cerebral palsy is a condition whereby it has muscle incoordination. This may occur due to birth injuries and patient can display malocclusion due to muscle loss balance.

 

4) Predisposing metabolic climate and disease

i) Endocrine imbalance – e.g. gigantism, hypothyroidism etc.

ii) Infectious disease – e.g. syphilis (transmitted from infected mother to child) The child may exhibit one of the following… Hutchkinson’s incisors, Mulberry molars, enamel deficiency etc.

Hutchkinson’s incisors, peg-shaped or screw driver-shaped laterals

 

5) Dietary problems (nutritional deficiency)

i) In pregnant mother – folic acid deficiency causes cleft lip and palate, mental retardation

ii) In growing child – Protein deficiency causes delayed eruption

Common in developing countries where nutrition related disturbances such as rickets, scurvy and beriberi can produce malocclusion and upset dental development timetable.

 

 

e) Abnormal pressure habits and functional aberrations

i) Thumb and finger sucking

ii) Tongue thrust and tongue sucking

iii) Lip biting

iv) Bruxism – grinding of teeth due to emotional and psychological stresses

 

6) Posture

Poor posture habits are said to be a cause for malocclusion. It may be associated with abnormal pressure and muscle imbalance. Children who support their head by resting the chin on their hand are observed to have mandibular deficiency.

7) Trauma and accident

i) Prenatal trauma

• Hypoplasia of mandible
• Facial asymmetric

ii) Trauma at the time of delivery

• Ankylosis of the joint – severe impeded mandibular growth

iii) Postnatal trauma

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Local Factors

1) Anomalies of number

i) Supernumerary teeth

• mesiodens – usually conical shaped in a pair or as a single tooth occuring in the maxillary midline
• supplemental tooth –  most often seen in premolar and lateral incisor region

ii) Missing teeth – more common than supernumerary teeth. Usually occurs on 3rd molars, maxillary lateral incisors, mandibular 2nd premolars, mandibular incisors, maxillary 2nd premolars

• missing maxillary laterals

 

2) Anomalies of tooth size

• microdontia –  teeth that appear smaller than normal, the common affected teeth are also most often congenitally absent
• macrodontia – any teeth or tooth that is larger than normal, may result in crowding

 

3) Anomalies of tooth shape

• dilacerated – abnormal angulation between crown and root
• fusion
• gemination
• concrescence
• Talon’s cusp
• dens in dente
• peg-shaped

 

4) Abnormal labial frenum

A fibrous frenum attached to the interdental papilla region which prevents the 2 maxillary central incisors from approximating each other.

5) Premature loss of decidious teeth

Early loss of decidious teeth can cause migration of adjacent teeth into the space therefore prevent the eruption of the permanent successor.

6) Prolonged retention of decidious teeth

A decidious tooth that fails to undergo resorption will prevent the normal eruption of its permanent successor. It usually results in lingual or palatal eruption of the permanent teeth.

7) Delayed eruption of permanent teeth

May be caused by congenital absence of permanent tooth, presence of heavy mucosal barrier that prevent the tooth from emerging. Hypothyroidism can cause a delay in eruption. Presence of decidious root fragments that are not resorbed can block the eruption of tooth.

8) Abnormal eruptive path

Abnormal path might be due to arch length deficiency, presence of supernumerary teeth, impacted tooth, retained root fragments and bony barrier. The maxillary canines develop almost near the floor of orbit and travel down to final position thus are most often found erupting in an abnormal position.

9) Ankylosis

Where a part or whole of the root surface is directly fused to the bone with the absence of intervening periodontal membrane. It can be associated with certain infections, endocrinal disorders and congenital disorder such as cleidocranial dysostosis. When it fails to erupt to normal level, they are therefore submerged and causing the migration of adjacent teeth into the space.

10) Dental caries

Proximal caries that has not been restored can cause migration of the adjacent teeth into the space. A reduction in arch length as well.

11) Improper dental restorations

Over-contoured occlusal restorations cause premature contacts leading to functional shift of the mandible during jaw closure. If under-contoured, it may permits the opposing dentition to supra-erupt.

 

– end –

 

References:
Gill, D.S. 2008. Orthodontics at a Glance. Blackwell Munksgaard.
Graber, Y.M.; Vanarsdall, R.L. 2000. Orthodontics Current Principles and Technique. 2nd edition. St. Louis: Mosby Company.
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Proffit, W.R; Field, H.W; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

Orthodontics – Classification of Malocclusion

Ideal Occlusion

The relationship existing when all the teeth are perfectly placed in the arches of jaws and have a normal anatomic relationship.

 

Andrew’s Six Keys to Optimal Occlusion

Key I: Interarch Relationship

• The mesiobuccal cusp of permanent maxillary first molar occludes in the groove between the mesio buccal cusp and mesiodistal cusp of the permanent mandibular first molar as explained by Angle.
• The distal marginal ridge of the maxillary first molar occludes with the mesial marginal ridge of the mandibular second molar.
• The mesiolingual cusp of the maxillary first molar occludes in the central fossa of the mandibular first molar.

 

Key II: Crown Angulation (mesiodistal tip of the crown)

• The gingival portion of the long axes of all crowns are more distal than the incisal portion.
• Crown tiip is expressed in degrees, plus or minus.

 

Key III: Crown Inclination (Labiolingual or Buccallingual inclination)

• Crown inclination is determined from the mesial or distal perspective.
• Angle formed by a line 90° to occlusal plane & a line tangent to bracket site.
• ‘Positive’ when gingival portion of tangent line is lingual.
• ‘Negative’ when gingival portion of tangent line in labial or buccal.

 

 

Key IV: Rotations

• The fourth key to normal occlusion is that the teeth should be free of rotations.
• If molars rotated – occupies more space than normal.
• If incisors are rotated – less space.

 

Key V: Tight Contacts

• Contacts points should abut unless there is a tooth size discrepancy in mesiodistal crown diameter.

 

Key VI: Occlusal Plane

• The plane of occlusion (curve of spee) should be flat to 1.5 mm deep.
• Centric occlusion – maximum intercuspation of maxillary and mandibular teeth.
• Centric relation is the relationship of mandible to maxilla when the head of the condyle is in the most retruded unstrained position in the glenoid fossa.

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Overjet – horizontal overlap of incisors

 

Overbite – vertical overlap of incisors

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Malocclusion

• Individual tooth malpositions (intra-arch)
• Malrelation of the dental arches or dentoalveolar segment (inter-arch)
• Skeletal malrelationships

 

Individual Tooth Malpositions

A) Mesial inclination or tipping – tooth is tilted mesially | crown is mesial to the root

B) Distal inclination or tipping – tooth is tilted distally | crown is distal to the root

C) Lingual inclination or tipping – tooth is abnormally tilted toward the tongue (or palate in maxillary arch)

D) Labial / buccal inclination or tipping – tooth is abnormally inclined towards the lips/ cheeks

E) Infra-occlusion – tooth is below the occlusal plane as compared to other teeth in the arch

F) Supra-occlusion – tooth is above the occlusal plane as compared to other teeth in the arch

G) Rotation – tooth movement around the long axis of the tooth

i) Mesiolingual/ distolabial – mesial aspect of the tooth is inclined lingually

ii) Distolingual/ mesiolabial – distal aspect of the tooth is inclined lingually

iii) Transposition – 2 teeth exchange places

 

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Malrelation of Dental Arches

A) Vertical plane malocclusion

Open Bite – no vertical overlap | vertical separation is measured

Deep bite – excess overbite

 

Crossbite / reverse overjet – if the lower incisors are in front of upper incisors

 

B) Transverse plane occlusion

Posterior crossbite – buccal cusps of lower teeth occlude buccal to the buccal cusps of upper teeth

Lingual crossbite / scissor bite – buccal cusps of lower teeth occlude lingual to the lingual cusps of upper teeth

 

Crowding – condition that occurs when the tooth is not properly aligned within the arch

 

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Qualitative Accessment of malocclusion

• Angle’s classification (1899)
• British Standards Institute (1983)

 

Quantitative Accessment of malocclusion

• Index of Orthodontic Treatment Needs (IOTN)
• Peer Assessment Rating (PAR)
• Index of Complexity Outcome and Need (ICON)

 

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Angle’s Classification

• Based on anterior posterior relationship of teeth
• Considered the permanent first molars to be the key to occlusion
• Used Roman numerals
• Widely used to describe molar relationship

 

Skeletal Malocclusion

Angle’s Classification of Malocclusion (1899)

Class I Malocclusion – normal relationship of molars | line of occlusion incorrect because of malposed teeth, rotations and etc.

Angle’s Class I Occlusion – mesiobuccal cusp of upper first permanent molar occludes with the buccal groove of lower first permanent molar.

Class II Malocclusion – lower molar distally positioned relative to upper molar | line of occlusion not specific

 

Class II division 1

• Retrognathic mandible
• Proclination of upper incisor
• Retroclination of lower incisor
• Palatal bite
• Increased overjet

 

Class II division 2

• Deep bite
• Upper lateral incisors crowded and rotated mesiolabially
• Retroclination of lower anterior

 

Van der Lindon classified Class II div 2 into three types:

a) Type A – Upper central and lateral incisors are retroclined

b) Type B – Central incisors are retroclined and overlapped by lateral incisors

c) Type C – The central and lateral incisors are retroclined and overlapped by canines

 

Class II subdivision – Class II molar relationship occurs on one side of dental arch

 

Class III Malocclusion – lower molar mesially positioned relative to upper molar | line of occlusion not specific

 

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Limitations of Angle’s Classification

• First permanent molars are not fixed points
• Based only on anteroposterior relationship
• Skeletal and dental malocclusion – not differentiated
• Individual tooth malpositions cannot be visualised
• Cannot apply in cases of missing first molars

 

Modification of Angle’s Classification – Lischer’s Classification

• Neutro-occlusion (synonymous to Angle’s Class I)
• Disto-occlusion (synonymous to Angle’s Class II)
• Mesio-occlusion (synonymous to Angle’s Class III)

Individual tooth malpositions were given suffix ‘version’ . E.g.: linguo version, mesio version, infra version

 

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British Standards Institute Classification

• Based upon incisor relationship
• Class I – lower incisor edges occlude or lie below the cingulum plateau of upper central incisors
• Class II – lower incisor edges lie posterior to the cingulum plateau of upper incisors (Class II div 1 and Class II div 2)
• Class III – lower incisor edges lie anterior to the cingulum plateau of upper incisors

 

Canine Relationship

• Class I – mesial cusp slope of the upper canine overlaps the distal cusp slope of the lower canine
• Class II – upper canine is placed forward
• Class III – lower canine is placed forward

 

Other Classifications

Simon’s Classification (1926) – dental arches are related to 3 anthropologic planes

Bennet’s Classification (1912) – based on etiology

Ackermann – Proffit Classification (1960) – based on Venn diagram

Ballard’s Classification (1964) – based on skeletal classification

 

– end –

 

 

References:
Proffit, W.R.; Field, H.W.; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.
Gill, D.S. 2008. Orthodontics at a Glance. Blackwell Munksgaard.
Graber, Y.M.; Vanarsdall, R.L. 2000. Orthodontics Current Principles and Technique. 2nd edition. St. Louis: Mosby Company.
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

Orthodontics – The Introduction

6

What is orthodontics?

Orthodontics is the branch of dentistry concerned with growth of the face, development of the occlusion, the prevention and correction of irregularities of the teeth and jaws (malocclusion).

Greek derivation, termed by Le Foulon: Ortho meaning straight or correct; Odons means tooth

 

History of Orthodontics

1st recorded suggestion of active treatment of malocclusion was by Aulius Cornelius Celsus (25 B.C. to 50 A.D.).

He advocated the use of finger pressure to move the teeth.

 

Edward H.Angle is considered the father of modern orthodontics.

 

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Aims of Orthodontics Treatment

1. Functional Efficiency – increase stomatognathic system

2. Structural Balance – teeth, soft tissue, skeletal structure

3. Esthetic Harmony – increase esthetic appeal

 

Need for Orthodontic Treatment

• To intercept and correct the interferences to the normal growth
• To manage temporomandibular joint problems
• To facilitate the prosthetic rehabilitation
• To correct the speech defects
• To decompensate, prior to surgical correction of skeletal malocclusions.

 

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Treatment Types of Orthodontics

A) Preventive orthodontics

B) Interceptive orthodontics

C) Corrective orthodontics

D) Surgical orthodontics

 

Branches of Orthodontics

A) Preventive Orthodontics – to preserve integrity of what appears to be normal occlusion at the specific time

E.g.:

• Eliminate deleterious local habits
• Correction of general contributory causes
• Maintenance of tooth form
• Removal of retained decidious teeth
• Use of space maintainers

 

B) Interceptive Orthodontics – to recognize and eliminate potential irregularities and malpositions in developing dentofacial complex

E.g.:

• Space regaining
• Correction of anterior and posterior cross bites
• Elimination of oral habits
• Muscle exercise
• Removal of soft or hard tissue impediment in the pathway eruption
• Serial extraction

 

C) Corrective Orthodontics – procedures undertaken to correct fully established malocclusion, which is removable, functional (growth modification) and are fixed appliances.

 

D) Surgical Orthodontics – procedures undertaken in conjugation with or as an adjuvant to orthodontic treatment.

Aims at elimination of etiologic factors or correction of severe dento-facial deformity that cannot be corrected by orthodontic treatment alone.

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Scope of Orthodontic Treatment

• Alteration of tooth position
• Alteration of skeletal pattern
• Alteration of soft tissue pattern

 

Potential Risk of Orthodontic Treatment

• Root resorption
• Loss of periodontal support
• Decalcification and caries
• Soft tissue damage (improper use of headgear)
• Loss of vitality
• Allergies
• TMJ problems
• Relapse
• Enamel wear (ceramic brackets)

 

Limitation in Orthodontics

• Age of patient (growth and development)
• Technical limitations of orthodontic appliances (removable, functional or fixed)
• Importance of skeletal dysmorphosis
• Structural discrepancies (increase in lower inter canine width)
• Patient compliance
• Patient expectations
• Soft tissue limitations – pressure exerted on teeth by lips, cheeks and tongue | periodontal attachment | neuromuscular influences on mandibular position | contours of soft tissue facial mark (soft tissue analysis critical in orthodontic decision making)
• Allergies
• Systemic diseases (adults having type 1 diabetes may have periodontal complications)
• Oral habits (digit sucking, tongue thrusting, mouth breathing)
• Undesirable jaw growth
• Multi disciplinary approach

 

Demand for Treatment

• Females
• Higher socio-economic families/ groups
• In areas which have a smaller population to orthodontist ratio, presumably because appliances become more accepted
• More adults wanting orthodontic treatment

 

– end –

 

References:
Graber, Y.M.; Vanarsdall, R.L. 2000. Orthodontics Current Principles and Technique. 2nd edition. St. Louis: Mosby Company.
Mitchell, L. 2007. An Introduction to Orthodontic. 3rd edition. New York: Oxford University Press.
Proffit, W.R.; Field, H.W.; Sarver, D.M. 2007. Contemporary of Orthodontics. 4th edition. St. Louis: Mosby Elvevier.
Singh, G. 2008. Textbook of Orthodontics. 2nd edition. New Delhi: Unipress.

 

 

 

Class II Denture

Image source from internet

About teeth setting in abnormal jaw relations…

Upper-lower ridge relationship is an individual problem for each complete denture patient. For abnormal ridge relations, it is needed to modify normal guidelines necessary to fulfill all demands.

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Maxillary Protrusion Problems Faced & Arrangement of Teeth

Changes in anterior arrangement

1) Increased overjet – Due to maxillary prognathism, there will be increased overjet. It leads to abnormal upper and lower canine tooth relationship. No attempt should be made to reduce it by moving upper teeth palatally or lower teeth labially.

Increased Overjet

2) Changes in canine relationship – Normally, the distal surface of lower canine tooth (located at) tip of the cusp of upper canine, whereas in maxillary prognathism it leads to the lower canine tooth finishing anywhere from the tip to distal surface of upper canine. Excessive prognathism leads to distal incline of cusp of lower canine posterior to distal surface of upper canine tooth.

Changes in Canine Relationship

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Setting Upper Posterior Teeth in Class 2 Relation

Upper first premolar setting

• If necessary, the palatal cusps of the 1st premolar is flattened.
• This is done to get good intercuspation with lower premolar.

Upper second premolar setting

• Upper 2nd premolar is set with its flattened lingual cusp occluding with the flattened buccal cusp of the lower second premolar.
• There is less buccal overlap and a larger area of contact is possible between this teeth.

Setting upper molars

• Upper molars are set in normal relation as done in class 1 teeth arrangement.

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Setting Lower Anterior Teeth in Class 2 Relation

Lower anteriors are set according to normal principles. The overbite is maintained at 2mm. However, there will be increased overjet.

Setting of Lower Posteriors

• The lower first molar is placed in Class I relation. (Key of Occlusion).
• The remaining space for premolar is assessed. Usually there will be space for only 1 premolar. The lower premolar is set in the remaining space. The buccal cusp of lower premolar occludes with the palatal cusp of upper second premolar.
• The lower second molar is set in normal relation with the upper second molar.

– end –

Maxillofacial Prosthetics

Photo by Pixabay on Pexels.com

WHAT HAS MAXILLOFACIAL PROSTHETICS GOT TO DO WITH DENTISTRY?

Maxillofacial prosthodontics is the branch of dentistry that provides prostheses to treat or restore tissues of the stomatognathic system and associated facial structures, that have been affected by disease, injury, surgery, or congenital defect, providing all possible function and esthetics.

It is the art and science of functional, or cosmetic reconstruction by means of non-living substitutes for those regions in the maxilla, mandible, and
face that are missing or defective. The defects can be congenital or acquired (surgical or traumatic).

 

Objectives of maxillofacial prosthetics

• Restoration of esthetics or cosmetic appearance of the patient
• Restoration of function
• Protection of tissues
• Therapeutic or healing effect
• Psychological therapy

 

Requirements of a maxillofacial prosthesis

• The appliance must be easily and swiftly placed and held in position, both
  comfortably and securely
• Must be durable and easily cleaned
• Retain color quality
• Material should be non irritating to the surrounding tissues, strong enough
  around the periphery to endure.
• Physically resistant to sunlight, heat or cold, subject to little change in volume
  during extremes of temperatures during processing, and easily washable.

 

Types of maxillofacial defects

A. Congenital: e.g. Cleft palate , Cleft lip, Facial cleft , Missing ear

B. Acquired: e.g. Accidental injuries , Surgical resection, Pathology lesions

C. Developmental: e.g. Prognathism and Retrognathism

 

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WHAT IS THE CLASSIFICATION OF MAXILLOFACIAL PROSTHESIS?

1. Intraoral prosthesis

The intraoral prosthetic appliances are usually combined to the conventional
prosthesis (RPD, CD, FPD) that may be required for the patient.

Examples :
a. Obturators: to close a congenital or acquired defect

b. Stents: to control bleeding and promote healing, stabilize grafts, assist radiation therapy

c. Splinting appliance: to fix fractured segments until healing

d. Resection appliance: restores mandibular defects to guide mandibular closure

e. Speech aid prosthesis : Speech bulbs, Palatal lifts, Metal obturator

 

2. Extra-oral prosthesis:

Reconstructing missing parts of the facial structure

• Auricular prosthesis
• Ocular prosthesis
• Orbital prosthesis
• Nasal prosthesis
• Composite prosthesis
• Lip and cheek prosthesis

3. Combination of intra-oral and extra-oral prosthesis
4. Cranial prosthesis: Cranial onlays and inlays in cranioplasty

 

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Members of a maxillofacial team may consist of:

1. Plastic surgeon
2. Speech therapist
3. Radiotherapist
4. Dental specialist: Prosthodontist, Orthodontist, Oral surgeon, Dental Technician, Pathologist, Periodontist, Pedodontist
5. E.N.T. (Ear, Nose & Throat) Specialist
6. Psychiatrist

 

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Maxillary defects

Patients with maxillary defects will have difficulties in mastication, speech and  deglutition. The aim of a maxillofacial prosthesis should be to restore the normal physiological function in these patients. Maxillary defects can be broadly classified as follows:
A) Congenital
• Cleft lip
• Cleft palate
B) Acquired
• Total maxillectomy
• Partial maxillectomy

 

Congenital Maxillary Defects

Cleft lip and cleft palate

Cleft lip occurs due to improper fusion between the fronto-nasal and maxillary process. If this occurs on one side it leads to a unilateral cleft. If it occurs on both sides, it leads to a bilateral cleft.
Veau’s Classification of Cleft Palate:
Veau (1922) classified cleft palate into four types mainly,

Class I: Cleft involving the soft palate.

Class II: Cleft involving the soft palate and the hard palate.

Class III: Cleft involving the soft palate up to the alveolus on one side, usually involving the lip.

Class IV: Cleft involving the soft palate up to the alveolus on both sides.

Prosthetic considerations:
For young patients, a permanent prosthesis should not be provided, instead, a well fitting interim prosthesis should be provided. This interim prosthesis is replaced with a permanent one at around 25 years of age. A removable interim partial denture is preferred over a fixed prosthesis because it is more aesthetic in reproducing gingival contour, and it also helps to cover an unaesthetic residual alveolar cleft. The most important concern in the restoration of these cases is establishment of aesthetics.
Posterior cleft palate cases are usually treated using speech bulbs and palatal lift prosthesis.

 

Speech bulbs and palatal lifts

Speech bulbs and palatal lifts aid in velopharyngeal closure, which helps in raising the palate and separating the nasal cavity from the oral cavity.

A speech bulb contains a pharyngeal section, which goes behind the soft palate region, in case of a deficient soft palate.

A palatal lift prosthesis consists of an oral component that stabilizes and secures the prosthesis and an oropharyngeal extension that superiorly and posteriorly displaces the impaired soft palate. These appliances help the patient is both speech and swallowing.

 

Acquired Maxillary Defects

Acquired maxillary defects are usually classified based on their extent. If both the maxillae are resected, the defect is considered as total maxillectomy. Resection of one or a part of the maxilla or palate is considered as Partial Maxillectomy.

Aramany proposed a classification of partial maxillary defects based on their
extent.

Class I: It is a unilateral defect involving one half of the arch, extending to the
midline. It is the most common maxillary defect seen.

Class II: It is a unilateral defect involving one side of the arch posterior to the
canine (teeth posterior to the canine are absent)

Class III: It is a defect involving the central portion of the hard palate and may
also involve the soft palate (all the teeth are present) .

Class IV: It is a bilateral defect that crosses the midline and involves both sides of
the maxilla (Few posterior teeth remaining on one side)

Class V: It is a bilateral posterior defect (teeth anterior to the second premolar
are present)

Class VI: It is a bilateral anterior defect (teeth anterior to the second premolar are
absent).

 

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Obturators

The name obturator is derived from the Latin verb “obturare”, which means close or to shut off.

According to the glossary of prosthodontics , obturator is defined as prosthesis used to close a congenital or an acquired tissue opening, primarily of hard palate and or contiguous alveolar structures.

An Obturator is usually fabricated as an extension of a complete denture or a
removable partial denture.

Functions of obturator

1. Helps in separating the oral cavity from the nasal and sinus cavities, thus helping
   in speech, mastication and deglutition.
2. Can be used to keep the wound area clean and to enhance healing
3. To reshape or reconstruct the palatal contour/or soft palate
4. Can be used to correct lip and cheek position
5. Reduces the flow of exudates in the mouth
6. Can be used as a stent to hold surgical packs, post surgery.
7. Psychological benefits to the patient.
8. It also contributes to the retention and stability of the denture, by extending far
   enough into the defect and engaging some small undercuts.

 

Types of Obturators

A patient who undergoes maxillary resection is rehabilitated in 3 phases. Based on this, obturators are of 3 types :

1. Immediate Surgical Obturator
2. Interim Obturator
3. Definitive obturator

 

Surgical obturator
• Constructed from a pre operative impression cast and placed immediately after surgery.
• Enables the patient to speak, take nutrition and swallow effectively, after surgery.
• Restores the continuity of the palate
• Supports the surgical packing placed in the resection cavity.
• Usually placed until 5 to 10 days after surgery.
• They are either sutured or screwed into the edentulous arch.

 

Interim Obturator

After 5 to 10 days ,the prosthesis is removed , relined in the mouth and reprocessed with new acrylic resin and delivered on the same day.

• This serves for 4 to 6 months of the healing period.
• Periodic modifications are done as the wound heals.
• Multiple wrought wire clasps or denture adhesives can be used for retention.
• Mastication on the surgical side are avoided .
• Prosthetic teeth may be added to enhance esthetics.

 

Definitive Obturator

• It is fabricated when tissue healing and contraction are complete, usually 4 to 6 months postoperatively.
• Primary impressions using alginate and secondary impressions using a special tray using silicone are made.
• The undercuts within the defect and the lateral scar band on the side of the defect,  should be recorded well, as they contribute to the retention of the prosthesis.
• The obturator is made hollow to decrease the weight of the prosthesis.
• Dental implants and overdentures held with precision attachments can significantly improve the retention.

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Mandibular Defects

Congenital Defects of the Mandible

Congenital mandibular defects that require a maxillofacial prosthesis are uncommon. Common congenital defects of the mandible include micrognathia, mandibulofacial dysostosis, ankylosis of the temporomandibular joint etc.

Acquired Defects of the Mandible

As mentioned for the maxilla, neoplastic resection is one of the most common causes for an acquired mandibular defect. The common neoplasia which advocate the need for resection are squamous cell carcinoma of the tongue, oropharynx and floor of the mouth.

 

Types of Acquired Mandibular Defects
Based on the amount of resection or extent of bone loss, mandibular defects can be classified as follows:

1. Marginal or Continuity defect:

• Here, only the superior margin of the mandible is resected and the lower border is
left intact. So the continuity of the mandible is maintained.

• These defects do not show any deviation and are easy to restore. Reconstructed
with a split-thickness skin graft, which can behave like gingiva., over which
dentures can be made.

 

2. Discontinuity defect:

• Here, a significant segment of the mandible is resected and a condyle to condyle continuity is disrupted. Midline deviation of the mandible is commonly seen.

• These defects can be successfully reconstructed using microvascular free flaps, which makes fabrication of dentures easier.

• Because of the deviation present, a flat occlusal platform is made palatal to the existing maxillary teeth on the non resected side. This helps in guiding the mandible into the desired normal occlusion. It is known as the maxillary ramp.

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WHAT ARE EXTRAORAL DEFECTS?

•Defects occur due to trauma, neoplasm or congenital malformation.

•Aesthetics is the major principle behind the placement of these prosthetic appliances. Hence, most of these prostheses are non-functional.

• Auricular prosthesis
• Ocular prosthesis
• Orbital prosthesis
• Nasal prosthesis
• Composite prosthesis
• Lip and cheek prosthesis

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Materials used for maxillofacial prosthesis

A) Impression phase: Alginate, Silicone, Plaster of Paris

B) Modelling phase: Modelling Clay, Plaster, Plastolene, Waxes

C) Fabrication Phase:

• Extraoral materials – Acrylic resin, Vinyl chloride polymers, Polyurethane, Silicone
• Intraoral materials — Silicone, Poly (methyl methacrylate)

 

 

Summary:

Maxillofacial prosthodontics deals with the restoration of the appearance and function of patients with defects in maxilla or mandible, due to congenital, traumatic or surgical reasons.

Defects of the maxilla are more common and more complicated because of the associated anatomy and function.

Complete or partial dentures can be modified and designed to restore the intra oral defects , which helps the patients to function optimally, giving them psychological benefits.

Extra oral defects are more concerned with the appearance and a variety of biocompatible materials can be used for the same.

Dentists, together with the multidisciplinary team, can contribute significantly in the restoration of esthetics and function of patients with maxillofacial defects.

 

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References
Clinical maxillofacial prosthetics – Thomas D. Taylor
Essentials of complete denture prosthodontics. Sheldon Winkler. Second edition
Prosthodontic treatment for edentulous patients. Zarb-Bolender. Thirteenth edition
Maxillofacial rehabilitation – John Beumer
Maxillofacial prosthetics – Chalian