CLEAR ALIGNER THERAPY IN ORTHODONTICS .pptx

CLEAR
ALIGNER
THERAPY
Under The Guidance Of:
P R O F ( D R . ) M O H A M M A D M U S H T A Q .
H E A D O F T H E D E P A R T M E N T ,
D E P A R T M E N T O F O R T H O D O N T I C S A N D
D E N T O F A C I A L O R T H O P E D I C S .
Presented by:
Dr. Zanab Farheen
Fayaz

Contents
 History of Aligners.
 Introduction
 Reasoning from first principle.
 Materials - structures and Properties
 Basic principles with Aligners.
 A Comparison Between fixed Appliances and Clear Aligners .
 Case selection
 Pillars of Clear Aligners
Aligners
Software
Clinchek
Auxiliaries
 Power ridges and pressure areas in the invisalign system
 Digital workflow
 Shape moulding effect
 Watermelon Effect
 Drawbridge Effect
 References

Moya SP , Zafra JL .Aligner Techniques in Orthodontics.
Hoboken(NJ).Wiley Blackwell;2021. p. 1-10

Definition
• Clear Aligner therapy is an orthodontic technique that uses a
series of computer-generated custom plastic aligners to gradually
guide the teeth into proper alignment
(Graber 5th Edition)
• Clear Aligner Therapy (CAT) embraces a wide range of
appliances with differing modes of action, methods of
construction, and applicability to various malocclusion
treatments.
• All share the use of clear thermoformed /3D printed plastic
aligners but there are major and significant differences which
affect the ability of any given system to treat a wide range of
orthodontic problem.

Histo
ry
• In 1924 Orrin Remen Snyder developed the ‘Flex-o-Tite’ , meant to
stimulate gums through home use combined with toothpaste,
convenient for periodontally compromised patients.
• In 1946, Harold Kesling was responsible for developing what he
called the ‘Tooth Positioner’, a device made from Vulcanite meant
to prevent relapse after orthodontic treatment.
• In 1963 ,Shanks developed a technique for producing mouth guard
style transparent retainers, with a machine capable of producing
them.
• In 1964, Nahoum patented his ‘vacuum formed dental contour
appliance.
Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021. p.
1-10

• In 1994, Sheridan developed an aligner system, called
ESSIX, using clear , polymeric shell appliances with
thermoplastic divots to reposition teeth, meant to solve minor
anterior mal-positions.
• In 1997, together with Schwartz, they standardized this by
patenting a system that would be implemented in many
dental offices until now, an ‘in-office’ vacuum system.
• In1990s, a computerized aligner system was developed
namely, Invisalign, created by two Stanford students, Zia
Chishti and Kelsey Wirth.
Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021.
p. 1-10

Orthoclear
● Founded in 2005 by Zia Chishti, one of the Invisalign system founders, based in
Pakistan, ended its operations in 2006 after a corporate agreement with Align
Technology that followed litigations related to trademark.
ClearCorrect
● Founded in 2006 in Texas, it was developed by one of the practitioners using Ortho
clear, after it ended its operations, to be able to finish his patient treatments not using
the ortho clear system, offered to old Orthoclear customers.
Orthocaps
● Founded in 2006 in Germany , this system has a ‘method of combining two different
soft aligners for day and night time use’.
These two types differ from one another in both their composition and the amount of
pressure they exert. This innovation is called the Twin Aligner system.
Inman aligner
● Developed by a dental technician, Donal P. Inman in 2000 , initially for minor
alignments.
p. 1-10

Materials –Structures And
Properties
 Aligner materials are resin polymers.
 Currently, aligner manufacturers use polyethylene terephthalate
(PET) , glycol-modified (PETG), polyurethane (PUR),
polypropylene (PP), polycarbonate (PC), thermoplastic
polyurethanes (TPU), ethylene vinyl acetate (EVA), polyethylene
(PE), and many other materials for the construction of the
aligners.
 Structurally, thermoplastic polymers are divided into either
amorphous or semicrystalline.
 PETG, PC, and co-polyester are amorphous polymers.
 PP, PE, and EVA are semicrystalline polymers.
Nanda S, Castroflorio T , Garino F , Oijma K.Princioles and biomechanics of Aligner treatments.St. Louis,
Missouri:Elsevier;2022.p.30-34

 Most of the thermoplastic materials has been extensively used for the construction of orthodontic retainers too.
 The new generation of Invisalign aligner material is SmartTrack, a thermoplastic polyurethane with an integrated
elastomer.
 According to the manufacturer, this is highly elastic material that delivers low and constant force to improve control of
tooth movements

ies
 The development of instrumented indentation testing (IIT) is used to yield a variety of mechanical properties (elastic modulus,
creep, relaxation, different expression of hardness, and others), from a simple hardness measurement.
 Water Absorption
Water absorption through humidity in the air, immersion in water, or intraoral application generally causes expansion of the
thermoplastic material, causing the irreversible degradation of the mechanical properties of the polymer.
 During the first 48 hours of immersion, water absorption rate was high for two common PETG products and several
PETG/PC/TPU polymer blends.
 This was followed by a slowdown and a plateau after 2 weeks of immersion, at about 0.5 to 0.8% weight increase.

Transparency
 A high degree of transparency is required, which should be stable
during the orthodontic treatment periods .
 The transparency of the aligner decreases when the layer
thickness increases and in PETG blended with TPU.
Nanda S, Castroflorio T , Garino F , Oijma K.Princioles and biomechanics of Aligner treatments.St.
Louis, Missouri:Elsevier;2022.p.30-34

Basic principles of
aligners
 Forces
Aligners move teeth by exerting a push force. When the aligner is
inserted over teeth, the aligner deforms over the teeth and the
elasticity in the aligner material pushes the teeth into position.
Optimized attachments provide an active, flat surface that the
aligner may push against to provide effective tooth movements.
 Anchorage
Aligners offer extremely good control of anchorage because the
anchoring teeth can become immovable at different stages of
treatment.
Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021. p. 1-
10

 Engagement
Aligners engage teeth by enclosing the tooth in aligner
material. The more material wrapped around a tooth, the
better the engagement.
In teeth with a long clinical crown there will be better
engagement therefore better expression of tooth movement.
In contrast, in teeth with short clinical crowns , there is
less engagement and less expression of tooth movement.

p. 1-10
Case selection
In order to develop confidence with the technique, it is
paramount in the beginning to follow a suitable learning
curve to allow familiarization with the system and
working with the following malocclusions is
recommended:
● Class I with minor or moderate crowding or spacing
● Half-cusp Class II with minor crowding
● Class III with minimal overbite/overjet non-
extraction cases
● Deep bite that can be solved by proclination and
anterior intrusion (without posterior extrusion)
● Open bite that can be solved by retroclination and
anterior extrusion (without posterior intrusion)
● Lower incisors extractions

Comparison of fixed
orthodontics and aligners
Force
 As the archwire returns to its original shape, it
pulls on the lingually erupted tooth to move it
into the arch .
 In contrast, clear aligners move teeth by
exerting a push force.
 The aligner deforms over the teeth, and the
elasticity in the aligner material pushes the
teeth into position
Tai S.Clear Aligner Technique.Quintessence Publishing Co, Inc:Hanover Park, IL;2018.p.
7-16

Engagements
 Fixed appliances engage teeth via an archwire
ligated into the bracket slot. The thicker and more
rigid the archwire , the better the engagement.
 Clear aligners engage teeth by having aligner
material wrapped around teeth. The more aligner
material wrapped around a tooth, the better the
engagement.
Tai S.Clear Aligner Technique.Quintessence Publishing Co, Inc:Hanover Park,
IL;2018.p. 7-16

age
 In fixed edgewise appliances, the most common anchorage model is
that of reciprocal anchorage, based on Newton’s third law.
 One segment of teeth will act as an anchorage unit for another
segment of teeth
 In clear aligner treatment, the anchorage segments can be
predetermined and may change at different stages in treatment.
 In this respect, clear aligners offer extremely good control of
anchorage because the anchorage teeth may be made immovable at
different stages of treatment.
Tai S.Clear Aligner Technique.Quintessence Publishing Co, Inc:Hanover Park, IL;2018.p. 7-16

E X T R U SI ON
 In fixed edgewise appliances, extrusion of a single
tooth may be accomplished relatively easily.
 Extrusion of a single tooth is a moderately difficult
tooth movement for clear aligners, depending on the
amount of extrusion required.
 At times, some auxiliary treatment such as buttons
and elastics may have to be placed to assist with
single-tooth extrusion.
 However, extrusion of groups of teeth, for example
when maxillary incisors are extruded to close an
anterior open bite, may be performed successfully with
clear aligners.
Tai S.Clear Aligner Technique.Quintessence Publishing Co, Inc:Hanover Park, IL;2018.p. 7-
16
on

I N T R U SI O N
INTRUSION:
 In fixed edgewise appliances, dental arches are leveled
through relative intrusion with reverse curves in the
archwire .
 In clear aligner treatment, entire segments of teeth may
be intruded successfully, or selective intrusion of
individual teeth may also be programmed to correct an
occlusal cant or level out gingival margins.
 This may be performed without concurrent extrusion of
the posterior segments if so desired.
IL;2018.p. 7-16

TO RQ U E
TORQUE
 In fixed edgewise appliances, torque is
built into the bracket slot.
 The amount of torque expressed is
related to the size of the archwire and
the amount of torque built into the
bracket slot.
 Clear aligners offer the power ridge
feature for lingual root torque .
7-16

 The incisor torque in the finished occlusion may be predetermined for individual patients depending on
the initial malocclusion, desired final occlusion, and soft tissue lip support.
 Excessive torque may be undesirable in cases with mild incisor protrusion that are treated non-
extraction.

RO OT M O V E M EN T S
 In fixed edgewise appliances, tip is built into the bracket slot. If
further adjustment to root inclinations is required, then root-tip
bends may also be made in the archwire.
 In clear aligner treatment, optimized root control attachments
offer control of root inclinations .
 Long, vertical rectangular attachments will offer control of root
inclinations as well.
 In lower incisor or premolar extraction cases, virtual gable bends
may be requested to ensure careful management of root
inclinations as the extraction spaces are closed.
IL;2018.p. 7-16
ROOT TIP:

• Incisor Position
 In fixed appliance treatment, incisors tend to procline on alignment.
 Clear aligners, on the other hand, offer excellent control of incisor inclination.
 The labiolingual pre- and posttreatment positions of the maxillary and mandibular incisors may also be
monitored using the superimposition tool .
7-16

Tooth size discrepancy
 In fixed appliance treatment, an anterior Bolton tooth size discrepancy is usually calculated or
adjusted for midway through treatment.
 In clear aligner treatment, the treatment planning software accurately calculates the tooth size
discrepancy and will resolve it according to the clinician’s preference, either by leaving space around
the lateral incisors or by including interproximal reduction in the opposing arch.
 This is decided at the treatment-planning stage and built into the final occlusion.

Vertical control
 In fixed appliance treatment, overbite and overjet tend to decrease as the incisors procline during
alignment.
 Clear aligners offer excellent vertical control in cases with minimal overbite and overjet.
 The occlusal coverage of the aligners on teeth as well as the ability to program intrusive mechanics
into the treatment plan allow for leveling and alignment with excellent control of the vertical
dimension
Midline correction
 Intraoral anterior cross elastics are commonly worn with fixed appliances for midline correction.
 Midline correction with clear aligners is more predictable, as interproximal reduction is commonly
incorporated into the treatment plan to correct the dental midlines.
IL;2018.p. 7-16

IL;2018.p. 7-16
CLINCHECK PRESCRIPTION FORMS FOR SELECTING THE MECHANICS FOR RESOLUTION OF
VARIOUS MALOCCLUSIONS

IL;2018.p. 7-16

Pillars of Clear Aligner
Therapy
 Aligners
 Software
 Attachments and features of SmartForce
 Auxiliary techniques
 Technicians Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021.
p. 1-10

Aligners
Aligners are made from SmartTrack material, a patented plastic formula exclusively designed for this purpose,
while attachment templates are made with EX 15 and Vivera retainers with EX 40.
Characteristics of the SmartTrack technology:
• soft and constant force.
• more elastic hence longer working period.
• Better adjustment to the teeth
• Easier to use
Every aligner makes:
0.25 mm of linear movement
2 degrees of angular movement to correct rotations
1 degree of torque movement (lingual–root torque or labial–root torque)
 Aligners are created to be used 22 hours per day, with changes depending on the amount of movement every
7, 10 or 14 day.

First-generation aligners
 The earliest forms of clear aligner systems were solely reliant on the thermoformed plastic aligner
material without any auxiliary elements being incorporated into the aligner system.
Second-generation aligners
 With advances in aligner systems, manufacturers incorporated the use of attachments to provide
better control of planned tooth movement.
 Clinicians could also request for composite buttons to be bonded on the teeth and utilize inter-
maxillary elastics.
 Other features, including SmartForce™ attachments, Power Ridge™, Velocity Optimization, and
interproximal reduction (IPR) became universal in the Invisalign system.
Bichu YM , Alwafi A , Liu X , Andrews J , Ludwig B , Bichu AY , Zou B. Advances in orthodontics clear aligner materials. Bioactive Materials.2023 Apr
1;22:384-403

Third-generation aligners
 In 2010, the third-generation aligners included SmartForce™ features , such as optimized
attachments, designed and placed automatically by commercial software as well as indentations in
the polyurethane plastic that placed increased pressure on specified points on the crown to produce
a moment of a couple and root torque (Power Ridge).
 Further , the clinician could also prescribe non-precision attachments to be placed on the teeth
wherever needed, to improve movements such as derotation and extrusion.
 New precision cuts were introduced to help with Class II and Class III inter arch elastics .
Fourth-generation aligners
 In 2011, G4 attachments were released to facilitate the clinical outcomes in open bite cases.
 This new material provides better performance, such as a gentle and more constant force, more
long-term action and improved adhesion , which eases the use for patients.

Fifth-generation aligners
• In late 2013, fifth-generation enhancement improved the predictability of deep bite correction by
introducing pressure areas on the lingual of the upper and lower anterior teeth, precision bite ramps
on the lingual of the upper incisors, and bevelled dome-shaped retention attachments on the
premolars
Sixth-generation aligners
 In late 2014, sixth-generation clinical innovation for orthodontic treatment of first premolar
extractions was introduced using new SmartStage™ technology and Smart Force™ features to
provide vertical control and root parallelism that optimize the progression of tooth movements for
extraction treatment planned for maximum anchorage.

Seventh-generation aligners
 Invisalign G7, a set of features designed to deliver greater control of tooth movements and
improved treatment outcomes was released in 2016.
 It aimed to deliver better upper lateral incisor control, and improve root control and features
to address the prevention of posterior open bites
Eighth-generation aligners
 Around late 2020, the eighth-generation enhancements were announced aiming to further
improve the predictability of deep-bite correction with SmartForce™ aligner activation for
anterior intrusion and improvements in the ClinCheck virtual proprietary software setup to
level the Curve of Spee.
 G8 also minimizes unwanted crown tipping during posterior arch expansion with optimized
expansion support and rotation attachments to reduce the potential for buccal crown tipping
Bichu YM , Alwafi A , Liu X , Andrews J , Ludwig B , Bichu AY , Zou B. Advances in orthodontics clear aligner materials. Bioactive Materials.2023 Apr
1;22:384-403

1-10
Software
 In orthodontic therapy with clear aligners, the judicious manipulation of the software constitutes
a significant aspect of treatment planning and is critical for successful outcomes

Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021. p. 1-

ClinCheck
 ClinCheck is the proprietary software by Align Technology that simulates the tooth movement
sequence into the final occlusion.
 It is a powerful digital treatment-planning tool by which the clinician may determine the sequence
of tooth movement, the final tooth positions, and the final occlusion.
 Clear aligners utilize digital treatment planning that allows the clinician to determine and set up
the sequence of tooth movement leading to the finished occlusion in a software program before a
single tooth is moved.
 The attachments acted as “handles” to increase aligner engagement to move teeth or control root
inclinations
1-10

Attachments
 Certain types of tooth movements (eg, intrusion) require anchorage in different parts
of the dental arch. Other tooth movements, such as translation, may require root
control to maintain root inclinations.
 Rotations on teeth with circular crown morphology, such as premolars, may require
additional engagement of the aligner through the use of attachments to help these
tooth movements express fully clinically.
 Attachments may be classified into two categories:
 (1) conventional attachments
 (2)optimized attachments

 Conventional attachments are passive attachments that increase
the engagement of the aligner onto the tooth.
 They act as handles for the aligners to move teeth.
Ellipsoid attachments
 Ellipsoid attachments are passive attachments that are primarily
used for retention or anchorage.
 They are the original attachments , used especially when the
tooth surface area is limited.

R E C T A N G U L A R A T T A C H M E N T S
 Rectangular attachments are passive attachments and may be vertical or horizontal.
 Vertical rectangular attachments are useful for root control.
 Horizontal rectangular attachments may also be used for root control, particularly in the buccolingual
dimension to effect buccal root torque on molars.
 They may also be used where a short clinical crown or occlusal interference does not allow placement of
a vertical rectangular attachment.

 Beveled attachments
 Both the vertical and horizontal attachments may also
be beveled . The beveled surface is the active surface.
 The bevel provides a flat surface for the aligner to
push against to effect the desired tooth movement.
 For extrusive tooth movements , a horizontal
attachment that is beveled on the gingival will be
effective.
 For intrusion, use a horizontal attachment beveled on
the occlusal.

Optimized attachments
 Automatically placed by the software when it detects certain thresholds of tooth movement.
 They are designed to control the point of application of force, the direction of the force, and the amount of force
applied, which is customized for each individual tooth.
 All optimized attachments have an active surface that varies in geometry based on the unique morphology of each
tooth.
Moya SP , Zafra JL .Aligner Techniques in Orthodontics. Hoboken(NJ).Wiley Blackwell;2021. p. 1-10

POWER RIDGES
They might be placed alone, and are not compatible with attachments, usually
stablishing a force couple, for example, for incisorstorque:
● Buccal
○ Available on upper and lower incisors
○ They produce lingual root torque (LRT)
○ Threshold for placement is 3 degrees LRT
○ 1 degree/aligner
● Buccal + lingual
○ Available on upper incisors
○ They produce LRT + incisor retraction
○ Threshold for placement is 3 degrees LRT + anterior retraction
○ 1 degree/aligner +0.25mm retraction
1-10

Precision Ramps
 These are usually dynamic, changing on every aligner,
adapting to tooth movement, and constitute a
differential aspect to braces, which can only change
when the practitioner has the patient in office.
 This is especially useful for precision bite ramps which
help create only the required tooth disocclusion, being
more comfortable for the patient’s TMJ .

Precision
wings
 This is the latest innovation from Align Technology
on Smart Forces applied to the aligners, developed
for Mandibular Advancement Features.
 They help the patient by advancing the mandible on
a preset basis, which is now the gold standard
whenever mandibular hypoplasia is found in young,
growing patients.
Moya SP , Zafra JL .Aligner Techniques in
Orthodontics. Hoboken(NJ).Wiley Blackwell;2021.
p. 1-10

Clincheck plan
review

1. Review the initial occlusion.
2. Review the Comments tab.
Moya SP , Zafra JL .Aligner Techniques in
Orthodontics. Hoboken(NJ).Wiley
Blackwell;2021. p. 1-10

3. Review the number of stages in treatment.
4. Review the animation and Staging tab.

5. Review the final occlusion.

6. Review the superimposition tool.
7. Review the
Tooth Movement
Assessment (TMA).

8. Review the attachment design.
9. Review the interproximal
reduction.

10. Review the design of precision cuts.

Eight tips on communication with the
technician
1. Read the Comments tab.
2. Identify the view.
3. Identify the tooth.
4. Quantify the tooth movement.
5. Specify the direction of tooth movement.
6. State the problem and give the solution.
7. Use reference points.
1-10

Lingually displaced teeth
Staging
 Open space first, then start uprighting or moving labially.
Principle
 The software is programmed for simultaneous tooth movement for
alignment, meaning every tooth moves at the same time.
 If there is inadequate space, then teeth will collide into adjacent
teeth and tooth movements may not be fully expressed.
 Therefore, it is preferable to delay the movement of a lingually
displaced tooth until after space has been opened;
TREATMENT STAGING

Expansion versus
distalization
Staging
First expand, then distalize.
Principle
When teeth are distalized , the maxillary arch already becomes narrow
relative to the mandibular arch.
Thus, teeth need to be distalized into a wider arch form so that the
maxillary arch will coordinate with the mandibular arch form

Deep Bite With Hypererupted ,
Retroclined Maxillary Incisors
Staging
 First procline , then intrude, and finally retract.
Principle
 It is difficult mechanically to execute tooth
movements in several planes of space
simultaneously.
 By staging the tooth movements in different planes
of space separately, there is an increased probability
that such difficult tooth movements will be
expressed clinically.

Uneven Intrusion Of Maxillary
Central Incisors
Staging
 Review the Clin Check plan stage by stage to verify tooth positions in the interim stages.
 Restage tooth movements as necessary to maintain level incisal edges throughout treatment.
Principle
 When a patient initially presents with maxillary central incisors with level incisal edges , one central incisor
may be intruded or extruded relative to the contralateral incisor,during the treatment.
 Although the incisal edges may be level in the finished occlusion, sometimes the staging creates uneven incisal
edges midway through treatment.

Sequential Versus Enmasse
Distalization
Staging
 Sequential distalization is a more predictable way of correcting an anteroposterior discrepancy in the buccal occlusion.
Principle
 When the software is programmed for enmasse distalization , this may be viewed on the ClinCheck plan as the entire arch
drifting distally.
 In sequential distalization, the second molar is distalized first, with the entire dental arch from first molar to first molar acting
as an anchorage segment to push the second molar distally.
 When the second molar is distalized halfway, the first molar starts to move distally.
 When the first molar stops moving, the second premolar starts to move distally,.

Managing
Overjet
Staging
 In certain cases, it may be advantageous to delay the start of treatment in one arch in order to manage
occlusal interferences or excessive overjet.
Principle
 In Class II malocclusions, there are often more stages in the maxillary arch, where sequential
distalization has been programmed.
 This may result in interim stages in the ClinCheck plan with an increased overjet.
 Similarly , for Class III malocclusions, there may be occlusal interferences in the interim stages of
correcting an anterior crossbite.

Round Tripping Mandibular Incisors
Staging
Restage tooth movements and perform posterior IPR to avoid round
tripping.
Secondly, a fixed reference point such as the most labially mandibular
incisor may be specified for tooth movement.
Principle
In clear aligner treatment, often times the mandibular incisors are
aligned until there is adequate access to the interproximal contacts to
perform IPR.
Once IPR is carried out, the incisors are retracted.
The ClinCheck treatment plan should be reviewed stage by stage to
ensure that significant round tripping does not occur in the interim
stages, as this may result in detrimental periodontal complications .

Auxiliary Elements
 Auxiliary elements, such as attachments and power ridges, are used to enhance predictability of
specific tooth movements.
 The strategic arrangement of these auxiliaries in aligners or on the teeth can enhance force delivery.
 They are used strategically to deliver forces at specific areas on the tooth surface.

Digital
Workflow
 The term workflow, first introduced in 1921,is
usually defined as procedural sequences of steps
involved to accomplish a working process.
 Since the introduction of CEREC (Chairside
Economical Restoration of Esthetic
Ceramics/Ceramic Reconstruction), digitalization
in dentistry has been extensively discussed, and its
rising popularity has also increasingly influenced
orthodontics.

p. 1-10

Designing Aligners And
Management Portals

Biomechanics In Clear Aligners
 Tooth movement in aligners is more complex that it is
with fixed appliances.
 The difference can be attributed to the absence of
specific points of force application , tooth anatomy ,
aligner material property , mismatch between aligners
and dentition geometry, slipping motion between
contact shapes and other biomechanical factors.
Upadhyay M, Arqub SA. Biomechanics of clear aligners: hidden truths & first principles. Journal of the World Federation
of Orthodontists. 2021 Dec 26

• Plastic encapsulates the tooth :
1.Retention-undercuts.
2.Elastic deformation of the aligner material.(less than the retentive forces).
The total desired movement is then sub-divided in such a way that the aligners remain withing the range of elastic
deformation and a sequence of aligners is made to accomplish this.
1.Faciolingual movements:
This movement if fairly predictable because the entire body of the aligner can be distorted elastically and the it
returns to its original shape carrying the tooth with it.
2.Vertical movements:
Vertical movement would require the aligner to essentially stretch within the matrix of the plastic and at the
same time maintain retention of the tooth it is attempting to move . Because there is very limited ability for such
elasticity withing the plastic itself ,these movements must be divided into small increments thus are considered
difficult.
HOW DO ALIGNERS MOVE TEETH ?

Shape Moulding
Effect
 The method has been the primary means of force application since the inception of clear aligners
treatment in 1940s.
 The method involves the movement of the target according to the shape of the aligners used.
 Pre established mismatch(activation) between the aligner shape and the dental crown geometry
generates 3D force systems distributed all over the contact surfaces.
Upadhyay M, Arqub SA. Biomechanics of clear aligners: hidden truths & first principles. Journal of the World Federation of Orthodontists. 2021 Dec 26

Drawbridge
Effect
 Simple tipping of anterior teeth can lead to
pseudo correction of the overbite, known as the
“drawbridge effect”.
 This impact does not involve a “true” extrusion of
anterior teeth (a movement along the
longitudinal axis of teeth) but rather just a
relative movement of the incisor crown
downward and backward.

WAT ER M ELO N S E E D E F F E CT
Aligners have the inherent ability to simultaneously engage
the occlusal , buccal and lingual surfaces.
This ability provides them with a unique ability to apply
comprehensive forces from all direction , hence , the term
“Watermelon seed effect”
The idea behind this effect is to create a resultant force vector
that is directed through the center of resistance of target
teeth.

HOW DO ALIGNERS MOVE TEETH ?
Force and displacement
There are several types of forces that can be applied to the teeth:
translation, torque, rotation, and extrusion require heavy forces of 50-150g,
rocking motion requires 50-75g, intrusion requires light forces of 10-25g.
Barbagallo et al. concluded that thermoplastic aligners have similar effects
on root surface as light fixed orthodontic forces (25g). This is explained by
the discontinuous and removable nature of the force . To this end, aligners
can induce the same biological response described for other fixed appliances
at least during early treatment phases.

TYPES OF MOVEMENTS

This is the easiest move to obtain when a force is applied against the crown.
a) The uncontrolled tipping
A study was carried out by Baldwin et al. in 2006 to describe the
movement of teeth adjacent to a premolar extraction spaces during space
closure with aligner appliances and then fixed appliances. In this study,
treatment with aligners resulted in significant tipping of the teeth
adjacent to premolar extraction sites .
a) The controlled tipping
Tipping is predictable with thermoplastic aligners, but it remains difficult
to establish comparable root control .
The tipping movement

An in vitro study was performed by Elkholy et al. in 2016 to study the forces and moments
delivered by the new thinner PETG aligners during the labio-palatal translational movement
of a maxillary central incisor led to the conclusion that for aligners without specific
modifications such as pressure points ,specific or more rigid cervical regions to create a counter
moment, the translational movement of the maxillary central incisors in the vestibular or
palatal direction is impossible to achieve.
According to Zhang et al. the coronal movement was relatively greater compared to the root
movement (~ 0.4mm). These results indicate that the aligners cannot perform translational
movements well, which explains the lower quality of treatment and the high recurrence rates
compared to the fixed multi brace treatment
a) Labiolingual/mesiodistal movements:
Translational movement:
Translational movement is required in three main situations:

Closure of space at the extraction sites requires “root
control” attachments on the teeth adjacent to the
extraction sites.
The study by Li et al. whose aim was to evaluate the
results of Invisalign treatment compared to the fixed
multi brace treatment showed no significant
difference between the two groups in the translation
of the roots and the achievement of good root
angulation.
The results of this study could be due to the correct
use of attachments to control the movement of the
roots.
This study confirmed that Invisalign can give good
results in extraction cases.
b) CLOSURE OF EXTRATION SPACES:

c)Molar Distalization:
A retrospective study was performed by Ravera et al.
the results of which showed that the translational
movement of the maxillary molars was achievable with
the use of aligners in combination with composite
attachments and class II elastics .
The aligners allowed the maxillary second molars to be
distalized by 2.25mm without any significant vertical
crown movement.

The intrusion movement
The aligners have advantage in this type of
movement because they cover all the teeth thus
preventing the extrusion of the posterior teeth .
Intrusion normally does not require composite
attachments on the affected teeth. However,
the anchor teeth should be fitted with
horizontal rectangular attachments for
anchoring.
Another method is to position two buttons on
the aligner buccally and lingually at the gum
level of the target tooth. Two 1.5 to 2 mm deep
grooves are then made on the incisal edge with
a 1 mm diameter to hook the elastics in case of
intrusion of the anterior tooth in the case of a
posterior tooth , the occlusal part of the aligner
is cut.

The extrusion movement seems to be
difficult to obtain. Indeed, in a prospective
clinical study carried out by Kravitz et al.
[12] the efficiency of tooth movement with
removable polyurethane aligners was
evaluated and the least accurate movement
was the extrusion (29.6%) - specifically,
extrusion of specifically, extrusion of the
maxillary (18.3%) and mandibular
(24.5%) central incisors.
The extrusion movement
Also, an observational study by Tuncay et al. examining
tooth movement during upper lateral incisor eruption by
aligners found that pure extrusion along the long axis is
extremely difficult. This movement takes place in a non-
linear movement for both the root and the crown, referred
to as “wobbling”.

It is then necessary to use attachments that
have a so-called active flat surface to apply
force-Beveled attachments. Beveled
attachments are most often used when
extruding a tooth. They can be 3, 4, or 5mm
wide, 2mm high, and 0.25 to 1.25mm thick .
In open bite cases requiring absolute
extrusion of the incisors, the attachments are
automatically placed on the incisors by the
software when a pure extrusion of 0.5mm or
more is detected.
Another method is to use a Power grip bonded to the
buccal surface of the tooth affected by the extrusion,
two buttons on the aligner at the adjacent teeth, and
intra-jaw elastics.
In open bite cases,requiring 2-3mm
extrusions,intermaxillary elastics can be used.

The torque movement
Torque movement with aligners can be done
using Power Ridges. They are supposed to
apply a lingual or palatal force on the cervical
part of the crown, which, when constrained
by the plastic covering the incisal edge of the
same tooth, creates a couple of forces, this
couple is supposed to produce the lingual
torque.
Another method used in the Essix system is
also effective: using Hilliard thermoplier or
one layer of composite, two forces are applied
simultaneously buccally and lingually of the
target tooth.
Controlling the torque of an upper central
incisor requires the creation of effective couple
of forces.

The rotation movement
Hahn et al. [27] found that only a slight activation
of ± 0.17mm or 0.5 ° per step during rotation
could produce ideal forces between 0.36-0.6 N.
There are 2 methods to perform the rotation:
i. A couple of forces can be created to rotate a
tooth by bonding buttons to the buccal and palatal
surface of the rotated tooth and use elastic chains
between them before or during the aligner
treatment.
ii. It is also possible to perform canine and
bicuspid rotations in a more predictable way
using optimized rotation attachments.
These attachments have different shapes
depending on the direction of force required to
rotate the affected tooth.

Efficacy Of Tooth Movement With
Clear Aligners
 The overall mean accuracy of invisalign was 50%.
 The highest accuracy was achieved with a buccal-lingual crown tip (56%).
 The lowest accuracy occurred with the extrusion (29.6%) and with rotation (46%) and this movement
was difficult for canines , premolars and molars.
 Maxillary incisor intrusion improved , but single incisor intrusion still remained a challenge .
 The percent accuracy determined by a best-fit analysis on a predicted Clinchek digital model may
underestimate the product’s overall clinical efficacy.
 As such, the actual number of 50% accuracy may be less important than the confirmation that the
invisalign appliance is improving but still struggles with specific types of tooth movements.
Haouili N , Kravitz ND , Vaid NR , Ferguson DJ , Makki L. Has Invisalign improved ? A prospective follow up study on the efficacy of tooth movement with invislaign . American
Journal Of Orthodontics and dentofacial Orthopaedics.2020 Sep 1;158(3):420-5

References
 Aligner Techniques in Orthodontics(Susana Palma Moya Javier Lozano Zafra Ed 1)
 Clear Aligner Technique (Sandra Tai Ed 1)
 Orthodontic Aligner Treatment : A Review of Materials, Clinical Management, and
Evidence(Theodore Eliades , Athanasios E. Athanasiou)
 PRINCIPLES and BIOMECHANICS of ALIGNER TREATMENT(Ravindra Nanda , Tommaso
Castroflorio , Francesco Garino , Kenji Ojima,)
 Kesling HD. The philosophy of the tooth positioning appliance . American journal of
Orthodontics an Oral surgery. 1945 Jun 1;31(6):297-304.
 Haouili N , Kravitz ND , Vaid NR , Ferguson DJ , Makki L. Has Invisalign improved ? A
prospective follow up study on the efficacy of tooth movement with invislaign . American
Journal Of Orthodontics and dentofacial Orthopaedics.2020 Sep 1;158(3):420-5.
 Upadhyay M, Arqub SA. Biomechanics of clear aligners: hidden truths & first principles.
Journal of the World Federation of Orthodontists. 2021 Dec 26.
 Bichu YM , Alwafi A , Liu X , Andrews J , Ludwig B , Bichu AY , Zou B. Advances in
orthodontics clear aligner materials. Bioactive Materials.2023 Apr 1;22:384-403

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