The use of microimplants in orthodontics

Characteristics and clinical
significance Of temporary
anchorage devices
Mechanics using temporary anchorage devices (TADs)
follow general biomechanical principles, but, compared
with conventional mechanics, they have several characteristic
features. These features not only make handling
treatment with conventional methods easier and more
efficient but also make treatment of seemingly impossible
cases with challenging anchorage preparation feasible.
A good understanding of TAD mechanics with the
proper biomechanical treatment principles can minimize
side effects while maximizing the efficiency of TAD mechanics .

Characteristics of Temporary
Anchorage Device Mechanics
Characteristics of TAD mechanics can be divided into
three categories: mechanics using rigid anchorage, intrusive
mechanics, and high efficiency
mechanics.
Rigid Anchorage. When the TAD achieves bony
support via a stable osseous interface, immobile rigid
anchorage to the orthodontic load can be supplied within
physiologic thresholds.
Segmented Canine Retraction
with indirect anchorage

This means that use of a TAD
can secure rigid anchorage easily without any additional
preparation of the dentition while relieving the limitations
of anchorage found with conventional orthodontic
mechanotherapy.
Intrusive Mechanics. Conventional mechanics essentially
consist of characteristics of extrusive mechanics.
Conversely, the TAD is generally located apically
compared
with the brackets, and in this location, the mechanics
are advantageous in achieving intrusion .

• Buccal and palatal mini-
implants were placed and two-
single continuous forces
without moments were applied
for
• efficient molar intrusion.A-c
Intraoral views prior to
treatment. D–F, Intraoral views
after 3 months of maxillary
molar intrusion..

Cephalometric superimposition
shows intruded upper molars and
mandible mandibular autorotation.
G, Cephalometric radiograph prior
to treatment. H, Cephalometric
radiograph after 3 months of molar
intrusion. I, Cephalometric
superimposition

High Efficiency Mechanics. TAD mechanics generally
use a single force without moments, which is very
efficient for tooth movement
The line of action, point of application, and direction of force can
be designed for efficient tooth movement by controlling
the location of TAD placement.

The characteristics of TAD mechanics contribute to the
following three features of clinical treatment .
Clinical Significance of Temporary
Anchorage Device Mechanics
The mesially angulated second molar was uprighted and
protracted to the first molar position with
a mini-implant and bonding of sectional orthodontic
attachments bonding. The third molar was guided to erupt
into the second molar position. A, Intraoral view before
treatment. B, A single orthodontic mini-implant was placed
between the canine and first premolar and splinted to the
first premolar. First and second premolars and the second
molar were bonded and common tied to prevent distal
uprighting of the second molar. C, The second molar was
uprighted and mesially protracted to the first molar
position by root movement. D, The third molar was guided
into the second molar position. E, Panoramic radiograph
before treatment. Notice the residual roots of the first
molar (black arrow). F, Panoramic radiograph after
treatment

Easy and Simple Anchorage Preparation. Orthodontic
anchorage can be easily prepared using TADs,
regardless of the condition of the dentition. Treatment
mechanics can also become simpler. For example, designing
mechanics for asymmetric tooth movement is comparatively
convenient because the teeth are not providing
the anchorage Furthermore, adjunctive treatment of
tooth loss or impacted teeth can be addressed with the
use of TADs and sectional orthodontic attachments.

A 22-year-old female patient had an impacted second
molar blocked by the third molar. When the
third molar was extracted, a mini-implant was placed on
the retromolar area simultaneously. The maxillary second
molar was extracted due to supereruption, and the third
molar would be guided into second molar position. The
mandibular second molar was guided to erupt to the
proper position, and the a tube was bonded on the
second
molar to level and align. The alveolar bone level of the
guided second molar was in good condition. A, Intraoral
view of the extraction of the third molar and TAD
placement. B, Intraoral view at the start of molar
uprighting.
C, Attachments were bonded on the first and second
molar for leveling. D, Intraoral view after molar uprighting.
E, Panoramic radiograph prior to treatment. F, Panoramic
radiograph while the molar was uprighting with TAD.
G, Panoramic radiograph at the completion of treatment.
H, Close-up radiograph shows healthy bone level
between the molars.

Increase of Treatment Efficiency. Due to rigid anchorage
supplied by the TAD, orthodontic treatment can be
conducted more easily and efficiently. Moreover,
mechanotherapy can be designed using a treatment
objective centered approach as opposed to a mechanics
centered approach. This frees orthodontic mechanotherapy
from the biomechanical limitations of anchorage.

Molar distalization becomes simpler and more predictable,
even in adult patients, and can be a very useful
option for treatment of cases with moderate crowding
or camouflage treatment of anteroposterior skeletal
discrepancies. Furthermore, all of the anterior and
posterior teeth can be moved at the same time using rigid
anchorage .
Two mini-implants 2mm in diameter and 10 mm in length
were placed in paramedian midsagittal raphe. A transpalatal
bar (0.38-in) was fabricated which was soldered to the bands
cemented on maxillary molars. Anchorage was provided
from the mini-implants to distalize the maxillary molars and
at the same time prevent extrusion of maxillary molars.
The Use of Mini-Implants
(Temporary Anchorage
Devices) in Resolving
Orthodontic Problems
March 2012

A 25-year-old female patient had the chief
complaint of protrusion of the lips and a
“gummy”
smile. After four first premolar extractions,
anteroposterior and vertical disharmony
was improved by anterior
retraction and molar intrusion. The chin
position was also changed by molar
intrusion and subsequent autorotation.
A, Frontal smile view before treatment. B,
Lateral facial view before treatment. C,
Intraoral view before
treatment. D, Frontal smile view at the
completion of treatment. E, Lateral facial
view at the completion of active
treatment. F, Intraoral view at the completion
of treatment. G, Cephalometric radiograph
before retraction and
intrusion. H, Cephalometric radiograph at
the completion of treatment. I,
Superimposition of cephalometric
radiograph.

Expansion of the Range of Orthodontic Mechanotherapy.
TAD mechanics can expand the range of
orthodontic mechanotherapy. One of the most significant
changes is the potential for intrusion of posterior
teeth. By intrusion of the entire dentition or
intrusion of the posterior teeth, orthodontic mechanotherapy
can indirectly change the position of the chin
point, similar to that seen by surgical repositioning of
the maxilla Additionally, occlusal plane inclination can also be controlled
without maxillary surgery when the posterior
teeth are intruded. The stability of molar intrusion is
clinically acceptable if proper treatment protocols are followed .
Hyper-extruded maxillary first molar before
temporary anchorage device intrusion
Maxillary first molar following temporary
anchorage device intrusion

A 25-year-old woman presented
with an anterior open bite. Using
maxillary buccal and palatal and
mandibular buccal TADs, the
molars were intruded and the
vertical excess problem was
improved. The chin moved
upward and forward. A, D, Intraoral
view prior to treatment. B, C,
Intraoral view at the completion of
active treatment.
E, Cephalometric radiograph
superimposition.

TAD mechanics are useful in solving mechanical problems
but have restrictions when addressing the biological
limitations encountered with mechanotherapy.
Considerations for Temporary Anchorage
Device Mechanics
Mandibular second
molar distalization
with the use of direct
miniscrew anchorage
for the correction of
mild Class III
malocclusion

TAD Stability. TAD mechanics is entirely based on the
stability of the TAD. The success rate of TADs is greater
than 80%, which is clinically acceptable.34–40 Loosening
of a TAD is not uncommon clinically. The more favorable
alternative when loosening occurs is to modify the
location of TAD placement. However, if the location of
the TAD cannot be compromised, a 3 to 6 month
waiting period is essential for cortical bone formation
before replacing the TAD in the same location.41–43 In
cases of repeated failure, alteration of the treatment plan
may be required.
Design of the retraction unit may differ because of
anatomic limitations, although the miniscrew is
placed in the same region; (a) the distalizing force
passes through the center of resistance of the first
molar, which may provide parallel distalization
rather than the system used in (b).

TAD Positioning. Selection of a TAD position is very
important for the design of TAD mechanics. In some
instances, TADs cannot be placed in a desired position
due to limitations of anatomic structures and accessibility.
Moreover, TADs placed in interdental areas may
restrict tooth movement of adjacent teeth because of the
lack of the space between the roots.44
Miniscrew-supported pendulum application

The orthodontic load bearingcapacity is closely related to the
size and
biocompatibility (i.e., bonding strength at the implant–
bone interface) of the TAD. According to a finiteelement
model (FEM) analyses study, a miniscrew–type
TAD made of titanium alloy can withstand approximately
200 to 400 g of orthodontic force depending on
the bone condition and diameter of the miniimplant.
However, splinting two implants or placing extra
implants can allow for heavier forces to be applied. The
use of wider and longer TADs may also be helpful.
Load-Bearing Capacity of the TAD.
Miniscrews used as direct
anchorage in canine
distalization. Canine
distalization with (a) a
segmental arch and (b) a
hybrid retraction arch

The TAD itself can
provide favorable orthodontic anchorage but cannot
offer an ideal force system for all types of tooth movement.
Rigid anchorage is just one of the contributing
factors to ideal treatment. However, rigid anchorage
itself does not guarantee successful tooth movement;
anchorage loss and unwanted side effects can result
even with TAD mechanics. For example, the intrusive
force vector of TAD mechanics can produce side effects
unforeseen with conventional mechanics).
.
Biomechanical Considerations.
The use of a miniscrew
as indirect anchorage
during the distalization
of the premolars and
canine

These consequences are very difficult to
correct. Therefore, it is necessary to remove or control
unwanted force vectors from the TAD in all three
dimensions of space
Orthodontic force was applied to protract the
molar unilaterally from the TAD to close the
space
of the upper right deciduous canine.
However, an open bite resulted due to mesial
tipping of the molar as well
as the intrusive force vector in the premolar
area. Using lever arm mechanics,
intermaxillary elastics can prevent
such side effects and can solve the problem.
A, B, Intraoral views prior to treatment. C, D,
Intraoral views during
treatment. Occlusal canting developed.

Bilateral, symmetric retraction and intrusive
forces were applied, but occlusal canting
developed
due to different anchorage values on either
sides. That is, there was more intrusion on
the left anterior area because
the left first molar prosthodontic implant was
not included in the full bonding. Using
intermaxillary elastics, canting
was improved. Conventional extrusive
mechanics are useful to compensate the
disadvantages of the intrusive
components from TAD mechanics. A, Intraoral
views prior to treatment. B, Panoramic
radiograph prior to treatment.
C, D, Intraoral views during treatment.
Occlusal canting developed. E, F, Intraoral
views during the canting
correction.

Biological Limitations as a Fixed Mechanotherapy.
TAD mechanics move teeth using the same principles as
conventional mechanotherapy and must be used with
consideration to biological limitations. Tooth movement
should take place within the periodontal complex, as
with all mechanotherapy.
a and b: Miniscrew
in the palate to
achieve intrusion of
over-erupted
posterior teeth.

Although research and clinical trials have been
Reported, a clear protocol of the orthopedic effects
to the basal bone using TAD mechanics is not yet established.
Further studies are needed to clarify the orthopedic
effects of TAD mechanics. With regard to transverse
orthopedic expansion, several studies to expand the
lateral envelope of movement of the posterior teeth have
been conducted, but no definite conclusions have
been established.
Canine distalization
combined with
miniscrew use as (a)
indirect anchorage
and (b) direct
anchorage

Unexpected
iatrogenic side effects such as root injuries and penetration
into the nasal cavity or maxillary sinus
may occur during surgical placement of the TAD.
Root injuries are reversible in many cases; however,
a crack to a root is considered irreversible. Proper
surgical protocols can prevent iatrogenic injuries to
anatomic structures.
Side Effects Related to TAD Mechanics.
Cone beam CT scans (A: 3D
reconstructed; B: axial; C: panoramic)
shows fractured tip of microimplant
(arrows) and its incorrect positioning
into the tooth ligament. (D) Tip (arrow)
of the fractured microimplant after
removal (magnification, × 10)
simultaneously with supernumerary
tooth 2.9 (asterisk: crown of the
removed tooth 2.9)

TAD mechanics can expand the envelope of discrepancies
of tooth movement, but may also contribute
some negative aspects. Side effects, which are related
to intrusive mechanics and are not common to conventional
mechanics, can develop. Additionally, TAD
mechanics may worsen the conventional side effects of
orthodontic treatment.
Typical reactions of maxillary sinus
membrane to different depths of
penetration: A and C are the CBCT
images obtained immediately after
insertion. The penetration depths were
1.9 mm in A and0.4 mm in C .B and Dare
the images obtained at the end of mini-
implant placement, corresponding to A
and C,respectively.
he incidence of an
infrazygomatic crest mini-
implant penetrating into the
maxillary sinus may be high.
Penetrating through double
cortical bone plates and
limiting the penetration depth
within 1 mm are
recommended for
infrazygomatic crest mini-
implant anchorage

Root resorption and periodontal
problems, particularly, may occur due to large amounts
of tooth movement using rigid anchorage. Side effects
resulting from misdiagnosis and overtreatment should
be avoided.

TAD mechanics can also increase the expectation level
of patients and may cause further dissatisfaction in a
subjective patient. For satisfactory and successful treatment,
the operator should engage in thorough communication
with the patient regarding the effectiveness and
limitations of the TAD.

Clinical and Biomechanical
application Of temporary
anchorage devices
General Principles in Biomechanical
Application of Temporary Anchorage
Device Mechanics
Establishment of an Individualized and Optimal
Treatment Plan. The individualized treatment plan
should be determined by collecting an adequate database
of information with regard to the patient and interviewing
the patient and any persons concerned. Cost benefit
analyses should also be considered when deciding
between treatment options.
A screw failed during
loading. Slight inflammation
was shown around the
screw.

Various TAD systems are available on the dental
market, and there are numerous reported clinical
applications. A specific TAD system and insertion
site should be selected according to the individual
treatment plan.
The Selection of a TAD System and an Insertion
Site.
A screw obliquely placed at an interradicular area.

Anatomic Factors. The cortical bone must be thick
enough to provide sufficient primary stability (mechanical
stabilization from cortical bone immediately after
implantation), and thus adequate cortical bone is required
for early stability and favorable healing Edentulous
areas have low bone quality, sometimes due to atrophy.
In these areas, bone probing is necessary following
anesthesia to check the quality of cortical bone.
Mini-implant near the dental
root.
Mucositis around a
mini-implant.
Food debris around a
mini-implant.

Attached gingiva is not always necessary for TAD
maintenance but is more favorable compared with the
oral mucosa. However, the stability may be compromised
if the TAD is irritated by the oral mucosa and can
lead to unfavorable conditions as well.
Appropriate mini-implant placement. Mini-implant placed in the periodontal ligament.

TAD placement in areas where significant stress is
applied should be avoided when possible. For example,
stability of a TAD near the mandibular first molar may
be compromised due to masticatory stress. Good
accessibility during surgical placement is advantageous
in achieving primary stability. Risks of irreversible injury
to important anatomic structures should be minimized.
Furthermore, the TAD itself should not be an obstacle
for planned tooth movement.

Biomechanical Factor. The TAD should be placed in
a biomechanically suitable position for planned tooth
movement. Moreover, the TAD position must be primarily
favorable for the main target tooth.

Clinical Factor. Pain and discomfort following
surgical placement of TADs are clinically acceptable.
Furthermore, the TAD should be placed in areas that
result in minimal discomfort for the patient during
treatment.
Counterclockwise
orthodontic
implant thread
with bracket head

Treatment Strategy. First, to efficiently achieve treatment
objectives, a strategy should be planned .The priority of tooth
movement should be decided
before instituting a plan to move the target tooth. In
other words, the teeth to be moved and the establishment
of an anchorage unit at each stage of treatment should
be identified before movement begins.
Upper canine retraction using a miniscrew, elastic force andsectional/segmented arch.Pre-
treatment (a), during treatment (b) and post-treatment (c) photograph

There are two methods for molar distalization: the entire dentition can be distalized (A) or the
second molars can be moved distally first and with the rest of the dentition following (B). When the entire dentition
is distalized, only TADs provide anchorage for movement of all the teeth. On the other hand, when only the
molars are moved distally first, the rest of the dentition and the TADs both provide anchorage. When distalizing
the entire dentition at once, treatment mechanics may be simpler and treatment time shorter. However, there is
also less treatment predictability as more teeth are involved. Conversely, when distalizing the molars separately, it
is more predictable due to more anchorage and less teeth being moved. But, more steps in treatment processes
are needed and it will make treatment more complex. (Green indicates an anchorage unit; red, a unit to be moved.)

Design of Mechanotherapy. To obtain the desired
tooth movement according to the treatment strategy,
mechanics with an optimized orthodontic force system
should be designed .
During this process,
two things need to be considered: how to produce tooth
movement and how to control this movement.
A screw through
non-keratinized oral
mucosa. Slight
inflammation was
shown around the
screw head.

Diverse methods to use a TAD. A, Direct application of a
single force: When using a single force,
precise calibration is possible. Moreover, the whole force
system does not change significantly even as the tooth
is moved. To control the tooth movement, the line of action
should be adjusted. B, Indirect application of a single
force: Using attachments on TADs, the line of action can be
controlled. C, Direct application of force and moment:
If wires can be engaged to TADs, TADs can produce not
only a force but also a moment. When the wire attached
to the TAD is engaged into the bracket slot at the opposite
side, it becomes a statically indeterminate force system
and the force system cannot be predicted precisely. When
the tooth is moved, the total force system will be altered
as well. Additionally, complex use of a TAD can negatively
affect its stability. D, Indirect application of force and
moment: The combination of a TAD and tooth can be
considered a total anchor unit. It can provide
threedimensional
anchorage, but there is little movement of the anchorage
unit. When using this unit for an indirect
application, the operator has to take into consideration that
the tooth with a PDL can be moved but the stable
TAD with an osseous interface cannot be moved. This
means that if the TAD is splinted with a wire of higher
stiffness to a tooth receiving heavier occlusal forces, there
will be a detrimental effect to the stability of the TAD.

With regard to producing tooth movement, the operator
needs to determine what kind of orthodontic force
system will be used. The force system of the mechanics
at the start of treatment and any changes in the force
system that come about when the tooth is moving are
important, which is related to mechanical efficiency and
to the speed of tooth movement. This is especially
imperative in difficult types of tooth movements.
Indirect anchorage configuration for anterior
retraction using temporary anchorage devices
Final occlusion following indirect anchorage
retraction with temporary anchorage devices

The operator should also decide how to control the
teeth three dimensionally
during treatment. There are
unwanted movements that occur as treatment progresses,
even in an ideally designed force system.
Gingival inflammation
caused by touch of a
closing
coil spring. The
spring has already
replaced to a ligature
wire.

For successful
application of TAD mechanics, proper monitoring and
Three dimensional
adjustments should be made upon
tooth movement
Direct anchorage configuration for
anterior retraction using temporary
anchorage devices
Final occlusion following direct anterior
retraction with temporary anchorage devices

There are several different ways to
make such modifications: the use of a single force with
or without an additional TAD, the use of brackets and
wires, and the combination of both.
Direct anchorage configuration for
protraction of a mandibular right first molar
Mandibular arch after protraction
of tooth #30.

More specifically, there are two types of mechanics
that can be used :
Force driven
mechanics,
which uses just a single force, and shape driven
mechanics,
which uses the shapes of the archwires engaged in
the brackets.
Molar intrusion can be achieved by force-
driven
mechanics (A) or shape-driven mechanics
(B). A, Force-driven
mechanics use only single forces without
moment. B, Shapedriven
mechanics use continuous archwires, which
are engaged into
the brackets. As a consequence, forces and
moments are produced
and they cannot be calculated chairside

Force driven
mechanics have a statistically determinate
force system, whereas shape driven
mechanics
have a statistically indeterminate force system. From the
standpoint of efficiency, force driven
mechanics are more
advantageous because the force system can be designed
precisely and does not change significantly even with
tooth movement.
Intrusion of maxillary right
buccal occlusion with
temporary anchorage
devices prior to
orthognathic surgery.

The force system of shape driven
mechanics cannot
be designed precisely and changes significantly with
tooth movement because it is a statistically indeterminate
force system. Therefore, shape driven
mechanics are not
efficient in cases of difficult types of tooth movement
such as molar intrusion. However, shape driven
mechanics
are more effective in detailed adjustments of tooth
positions clinically.
First molar intrusion

Decision-making. When considering the effects of
molar intrusion to
decide whether a molar should be intruded, three major
factors should be evaluated.
Molar Intrusion
First molar intrusion

Local effects of molar intrusion: As the molars are intruded, the
alveolar bone crest and free
gingival margin move together eventually if there is proper oral
hygiene control. But the mucogingival junction is
not changed, so the width of the attached gingiva decreases.

General effects of molar intrusion: After molar intrusion (A), the mandible rotates around the
horizontal condylar axis to align itself to maintain interocclusal rest space. Consequently,
the chin moves upward
and forward and the interlabial space (ILS) at rest decreases (B).

Local Factors. The intermaxillary occlusal relationship
should be considered. The condition of alveolar
bone and attached gingiva should also be evaluated.
General Factors. In addition to occlusal relationships,
facial and smile esthetics should be assessed. To
reduce lower facial height, the upper and lower dentition
should be controlled at the same time; if only one arch
is intruded, unwanted extrusion of posterior teeth occurs
in the opposing arch.
A simple method of intruding a molar
is to apply an intrusive force from the
adjacent teeth, which, in turn, are
connected to a micro-implant

Factors for Stability. Stability of molar intrusion
and anterior facial height reduction can be achieved by
overcorrection. For retention of an anterior open
bite correction, functional improvement of the musculature
following treatment is essential. Tongue
thrust during swallowing should especially be controlled
for increased stability.
Biomechanics.
A. Appliance design. B.
Palatal button. C. Mini-
implants placed on the
palate. D. Appliance
cemented with resin.
Mini-implants placed on the
maxilla (palate and molar buccal
area) intrusion movement
activation with a closed
elastomeric chain.

Mechanical Efficiency. Molar intrusion is one of the
most difficult tooth movements to achieve. Therefore,
mechanical efficiency is very important in the design of
molar intrusion mechanics. That is, force driven
mechanics
should be included considering its efficiency and
predictability.

Posterior torque and arch form control during molar intrusion: Posterior torque and arch form
(buccolingual positioning) control are related. A, Buccal intrusive forces away from the center of resistance cause
buccal tipping and arch expansion. B, Lingual crown torque may be used to offset the tendency of buccal tipping
for bodily movement. However, it is difficult to calculate the precise amount of moment (palatal crown torque)
needed. Theoretically, even if palatal crown torque is applied precisely, slight tooth movements can generate
changes to the force system, rendering it biomechanically inefficient. In order to apply lingual crown torque, the
archwire can be torqued or brackets with sufficient lingual crown torque can be used. C, In the case of using
buccal intrusive forces, a constriction force can be applied to reduce the tendency of buccal tipping. The degree
of constriction force should be similar to that of the intrusion force, but this force system is difficult to control
precisely. D, An active or passive transpalatal archwire (TPA)/lingual archwire (LA) is effective for controlling torque
and arch form. However, these appliances may be uncomfortable for patients while lowering the rate of tooth
movement as well. E, Labial and lingual combined intrusion forces are most effective for torque control. This
system
can also control the arch form.

Three-dimensional Control. Mechanics for posterior
intrusion should be designed to achieve threedimensional
control of the molar and the molar must be
monitored in all dimensions during movement .
More specifically, rotations,
tipping, torque, mesiodistal positioning, and inferosuperior
positioning of the tooth all need to be controlled.
Arch form, inclination of the occlusal plane, and the
frontal occlusal plane should also be evaluated.
Mini-implant placement on the mandible, active lingual arch and in the maxilla, active buccal
accessory arch.

Biomechanical efficiency of posterior intrusion: As seen with anterior intrusion, use of a single
force (i.e., force-driven mechanics) for posterior intrusion is effective and efficient as opposed to use of just the
brackets and wires. Intrusion can also be achieved more quickly with a single force. A single force, however, is not
effective for controlling arch form, tooth axis, inclination of the occlusal plane, and detailed adjustments. A continuous
arch, which is a statically determinate force system, is advantageous for controlling the arch form, tooth
axis, and individual tooth positions yet disadvantageous from the viewpoint of efficiency. If a combination of the
two force systems is used, the disadvantages of each of the systems are mutually compensated. For maxillary molar
intrusion, force-driven mechanics (i.e., single force) were used to increase efficiency on the palatal side, and shapedriven
mechanics (archwire with compensating curve) were used on the labial side to adjust in detail. A, B, Intraoral
views prior to treatment. C, D, Intraoral views after 3 months of molar intrusion with buccal and palatal TADs and
a continuous archwire.

Control from a lateral view: Clinically, control of
the inclination of the occlusal plane is one of the most important
considerations in posterior intrusion and more specifically, the
intrusion
of the maxillary second molar is key. Occlusal plane inclination
is related to molar axis control. A, To maintain the inclination of
the occlusal plane, the premolars and anterior teeth should also be
intruded approximately the same amount as the molars. This is
especially indicated in the correction of a gummy smile or long
face.
B, The second molars should be intruded more than the premolars
if the occlusal plane is to be steepened, especially in the correction
of open bites. Steepening of the occlusal plane would be difficult
to achieve. Note the change in the inclination of the posterior
occlusal plane and the changes of the axes of the individual
posterior
teeth. This suggests that axis control is related to occlusal plane
control. Furthermore, the individual posterior teeth should be
tipped back to aid in steepening of the occlusal plane.

Second-order control: The single force
generated
from the TAD near the second molar is
effective for the intrusion
of the second molar (A). TADs may not
always be positioned ideally,
but the mechanical design can
compensate for such limitations in
placement. For example, tip back bends
and/or step down bends
(B) or L-loops (C) can be used to
increase efficiency.

There are several ways in
which three dimensional
control can be managed: the
use of a single force from the TAD, the use of brackets
and archwires, and both of these methods combined .
For example, the use of a single force
generated from a TAD in an appropriate position (i.e.,
Force driven
mechanics) is more effective for gross
control.

Treatment Mechanics.
Maxillary Molar Intrusion. Palatal root control is
important for upper molar intrusion because the center
of resistance of the maxillary molar is located on the
palatal side.96 A palatal intrusion force is very effective
for palatal root control and for an increase in biomechanical
efficiency.
Brackets bonded on the buccal and palatal surfaces to apply intrusion
force from both sides.
At 5 months of treatment, the second molar was intruded

Mandibular Molar Intrusion. Mandibular molar
intrusion is different from maxillary molar intrusion;
biologically, the mandible is composed of harder and
denser bone, contributing to a slower bone turnover
rate. Clinically, the success rate of a miniscrew–type
TAD placed between the mandibular molars may be
lower than a TAD positioned between the maxillary
molars.34,39 The mandibular lingual area is especially
difficult for TAD insertion.

However, lingual intrusive forces are of less necessity
in mandibular molar intrusion than in maxillary molar
intrusion because buccal intrusive forces in the mandible
produce less buccal tipping. This is due to the fact that
there is more lingual inclination in mandibular molars
compared with maxillary molars .Considering
these obstacles, control of the second molars should
be a priority from the very beginning.
Root inclination of the mandibular molar:
From a lingual view, threedimensional
CT reconstruction shows that the lingual
inclination of the roots of the
posterior teeth increases from the premolars
to molars. In other words, the mandibular
First molar second molar is tipped more
lingually than the mandibular first molar

Molar Distalization
Decision-making. Three major factors should be considered
when deciding whether to distalize a molar
or not6:
• Required space: If more than 3 mm of space per side
is required to achieve the treatment objectives, premolar
extraction may be preferable from the standpoint
of treatment efficiency.
• Hard tissue conditions: There must be enough space
for distalization. Second or third molar extraction
should be considered before distalization to secure
adequate space.
• Soft tissue conditions: A clinically acceptable amount
of attached gingiva must be present following distalization,
especially on the distobuccal aspect of the
molar after mandibular molar distalization.
Mini-screw
combined with
Nitinol springs
placed buccaly

Biomechanics
Mechanical Efficiency. Distalization forces need to be
efficiently applied to the molar itself as opposed to the
other teeth. The distalization forces can be applied en
masse or singly to each tooth.
In the maxilla, TADs placed on the palatal side can
apply distalization forces directly to the molar. Moreover,
these TADs can also control the mesiodistal axis of
the molar through manipulation of the line of action.
Implant supported molar distalization

With a shallow palatal vault, mechanics that consist of TADs in the midpalatal suture area and a
transpalatal arch are simple and effective. With this anatomical structure, distalization forces from TADs travel
through the center of resistance of the molar, which produce distalization by bodily movement. In this clinical case,
the patient was in a growing period. Thus, parasagittal TADs were placed, not the midsagittal TAD, because palatal
suture growth was not completed. A, Intraoral view prior to treatment. B, Intraoral view during treatment.
C, Cephalometric radiograph during molar distalization. Distalization force (green arrow) is through the center of
resistance of the molar (red dot).

By modulating the line of action, distalization by bodily movement can be produced. With deep
palatal vaults, TADs in the palatal interdental area and a transpalatal arch can produce distalization forces that
travel through the center of resistance of the molars (red dot). A, Intraoral view prior to molar distalization.
B, Intraoral view after 5 months of molar distalization. C, Cephalometric radiograph during molar distalization.
Distalization force (green arrow) is through the center of resistance of the molar (red dot). The line of action is
moved occlusally by TAD positioning when compared with the case in Figure 12-18.

With deep palatal vaults, TADs in the midpalatal suture area and an attachment on them can
modulate the line of action to produce distalization forces (C, green arrow), which travel through the center of
resistance of the molars (C, red dot). If the distalization force is coming directly from the midpalatal TADs, as in
this clinical case, the line of action passes more apically (C, black arrow) than the center of resistance of the molar.
A, Intraoral view prior to distalization. B, Intraoral view during molar distalization. C, Cephalometric radiograph
during molar distalization.

Although adjacent teeth may limit mesiodistal tooth
movement, buccal interdental miniscrew–
type TADs are
very useful in molar distalization because of ease of
placement and simple application during treatment.
With a properly positioned
TAD, 3 mm of distal movement per side can be
achieved.
Mini-screw
with the sliding
jig mechanics
for molar
distalization.

Buccal alveolar bone can provide enough space for a half-cusp width of distalization if the TAD
is properly placed. However, narrow interradicular widths cannot provide enough space for
mesiodistal movement.
Angular placement of the TAD to the occlusal plane (A, B), as opposed to parallel to the occlusal
plane (C, D),
can take advantage of a wider buccal space.

Off-center placement of the TAD to the distal is also important in molar distalization. However,
the protocol for the prevention of root injury should be followed in order to minimize the possibility of
root injury.
Normal insertion site on buccal alveolus: The orthodontic mini-implant is usually placed on the midline
between
the adjacent teeth and at the connecting point of mucogingival junction (MGJ) (A). The TAD is placed 1.0
to
1.5 mm distal from the midline (yellow line) because molar distalization is planned (B).

The patient was a 12-year-old boy whose chief complaint
was protrusion. Severe overjet and Class II canine
and molar relationship were corrected by molar
distalization using TADs placed in the buccal interdental
area. Initial positions
of the TADs at the beginning of treatment were close to
the first molars. But, after distalization, the TADs seemed
to be on the same line as the root of the second premolar
(D, E). If placed with proper angulation in order to make
use
of the buccal space and placed closer to the distal
portion rather than in the middle of the interproximal
space, buccal
implants are also useful in molar distalization. A,
Occlusal relationship prior to treatment. B, Intraoral view
during molar
distalization. C, Occlusal relationship at the completion
of active treatment. D, E, Intraoral view during treatment.
Buccal
TADs were on the same line as the second premolar
(black arrows). F, Cephalometric radiograph prior to
treatment.
G, Cephalometric radiograph at the completion of active
treatment.

As with molar intrusion,
Three dimensional
control of the molar is important in
molar distalization using TAD mechanics .
Thus, the mechanics should be designed
to manage the threedimensional
position of the molar.
Once again, there are several ways to achieve this control:
the use of a single force from the TAD, the use of brackets
and archwires, and the combination of both systems.
Three-dimensional Control.

Mesiodistal axis control: A, B, If the second molar is not included, it may tip back due to distal
movement of the first molar and marginal ridge discrepancies can be created. The second molar
should be controlled
simultaneously whenever possible during molar distalization to prevent any vertical discrepancies. C,
Even
with strap-up including the second molar, bodily distalization of the second molar is not easy to attain
because
tipping can occur easily. A clinical sign of tipping is second molar mesial marginal ridge elevation
(green arrow).
To prevent distal tipping while distalizing, the use of wires of adequate stiffness is also a practical
consideration.

Arch form (buccolingual positioning) and torque
control: During distalization, the maxillary second
molar can be easily tipped buccally, while the
mandibular second molar can be easily tipped
lingually, due to the
respective buccolingual inclinations of these
molars. In addition, posterior torque control and
arch form (buccolingual
positioning) control are related. If the second
molar is tipped to the buccal, the palatal cusps fall
inferiorly
and the torque of the second molar worsens. A
slight toe-in bend may aid in controlling the
buccolingual positioning
of the second molar and, as a result, also be
useful in controlling torque. A, Schematic
illustration of arch form
changes and the relationship between
buccolingual position and torque. B, Intraoral
view after molar distalization.
The second molar torque worsened because of
buccal tipping (green arrow).

Arch form control: Sectional mechanics
without cross-arch splinting is not
adequate for arch form
control because of the tendency for
mesial-out rotation of the posterior
segment. A, B, Schematic illustrations of
rotation of the buccal segment by
distalizing forces. C, D, Intraoral views
before molar distalization. E, F, Intraoral
views during molar distalization. Notice
the mesial-out rotation (black arrow).

Vertical control: Distalization forces may have intrusive
force vectors because of geometric positions of the TADs. Intrusive force
vectors, in turn, may cause unwanted intrusion such as anterior biteopening
or occlusal plane canting, which are difficult to correct once
developed. Therefore, such intrusive force vectors should be controlled.
The use of lever arms is one way to effectively eliminate intrusive force
vectors (black arrow, retraction force; purple arrow, distalizing force
vector; red arrow, intrusive force vector).

Arch form and vertical control: A, B, Lever arms are used for vertical control. Applying buccal and
palatal distalizing force simultaneously is also effective for arch form control and useful for asymmetric
distalization.
C, D, Lever arms were used for vertical control (C) and cross-arch splinting for arch form control (D).

According to geometric positions of the
TADs, distalizing forces have a horizontal
force vector. In
addition to distal movement, buccolingual
tipping is more likely to occur than distal
movement because the sum
of the circumcemental area of the molar
roots is greater than the sum of the
anterior teeth. These horizontal force
vectors may develop arch expansion (A,
B) or constriction (C, D).

En Masse Distalization. All of the anterior and
posterior teeth can be distalized at the same time using
rigid anchorage. The same principles are applied for full
dentition distalization as for single tooth movement.
Considerations for mechanical efficiency and threedimensional
control are necessary as well. With regard
to threedimensional
control, the center of resistance
of the total dentition can be estimated.97 Theoretically,
if the force is applied through the center of resistance of
the whole dentition, translation of the entire dentition
will be achieved. Clinically, however, there is a greater
tendency for the teeth to move individually as opposed
to entirely .
The entire dentition was distalized to correct
protrusion. Even though twin brackets were used,
distal tip back of the individual teeth was observed. A,
Cephalometric radiograph prior to treatment. B,
Cephalometric
radiograph after molar distalization.

Furthermore, if the dentition
moves as a whole body and does not allow for tipping
of individual teeth, movement will be very slow. Even in
en masse distalization, the key point is molar control. If
the molars are well controlled threedimensionally,
moving the remaining teeth is comparatively easy. En
masse movement is indicated when intrusion is needed
in addition to distalization.

Molar Protraction
Decision-making. TADs can provide stable anchorage
for molar protraction. However, molar protraction
toward an edentulous area can be affected more by
biological conditions than by biomechanics.102–104
When the first molar or second premolar is missing,
protraction in the maxilla is somewhat predictable. But
in the mandible, there are various individual differences.

According to research conducted by Roberts et al., the
rate of molar traction can be as low as 0.2 mm per
month. Extra caution should also be taken when moving
teeth into edentulous areas in the mandible because
severe periodontal attachment loss can be induced during
protraction depending on the condition of the alveolar
bone.

Therefore, the following precautions should be
considered when protraction into an edentulous area is
planned, especially in the mandible, to prevent loss of
attachment. It is necessary to evaluate the periodontal
condition of the area where protraction is planned.
Vertical and transverse bone quantity influences the periodontal
prognosis. Low alveolar bone levels and narrow
alveolar bone have a higher chance of attachment
loss.

An inadequate amount of attached gingiva has a
higher chance of attachment loss as well. The patient’s
chronologic and dental ages should be also considered
because growing children and patients with incomplete
third molar development have a lower chance of
attachment loss.

Rotation control: Buccal protraction forces produce
a moment of mesial-in rotation (A). Adding
lingual protraction force (B) is a simple and effective
way to offset this mesial-in rotation tendency.
Biomechanics. Three dimensional
control is also
important for successful protraction .

Molar axis and vertical control from a
lateral view:
A, Protraction forces away from the center
of resistance cause an
inclination for mesial tipping. B, Generally,
TADs are placed apically,
and as a result, protraction forces have
intrusive force vectors. If
intrusion occurs on only one side, occlusal
canting can develop and
this is very difficult to correct if it occurs.
C, A lever arm engaged
in an auxiliary tube on the first molar is
effective in vertical control.

The patient was an 18-year-old girl, whose
problem was the severely mutilated upper fist
molar.
Because of prolonged inflammation, there was
little alveolar bone left in the upper fist molar
area. Using TADs,
the second molar was protracted after
extraction of the first molar and the third
molar erupted to the proper
position. The periodontal tissue of the
protracted second molar was in good
condition. Indirect application is also
effective in vertical control, and this same
application can also provide stable anchorage
in cases of unilateral molar
protraction. A, B, Intraoral view at the start of
treatment. C, D, Intraoral view at the
completion of treatment.

Anterior Retraction
in Extraction Treatment
A unique feature of TAD mechanics in premolar
extraction cases is the ability to adjust the anteroposterior
position of the anterior teeth and molars.
Moreover, TAD mechanics can correct vertical
disharmony simultaneously during anterior retraction.

A 25-year-old female patient had the chief
complaint of protrusion of the lips and a
“gummy”
smile. After four first premolar extractions,
anteroposterior and vertical disharmony was
improved by anterior
retraction and molar intrusion. The chin position
was also changed by molar intrusion and
subsequent autorotation.
A, Frontal smile view before treatment. B, Lateral
facial view before treatment. C, Intraoral view
before
treatment. D, Frontal smile view at the
completion of treatment. E, Lateral facial view at
the completion of active
treatment. F, Intraoral view at the completion of
treatment. G, Cephalometric radiograph before
retraction and
intrusion. H, Cephalometric radiograph at the
completion of treatment. I, Superimposition of
cephalometric
radiograph.

Decision-making. First, adequate alveolar space is necessary
for bodily retraction of the roots of the anterior
teeth. Verification of the amount of alveolar bone is
necessary during treatment planning procedures. When
a large amount of retraction is planned, there is higher
risk for root resorption and periodontal attachment
loss; therefore, risk management is important. Also,
precaution is greatly needed to avoid overretraction
and overintrusion of the anterior teeth when using rigid
anchorage.

Biomechanics. Biomechanically speaking, there is no
significant difference between conventional mechanics
and TAD mechanics with regard to anterior retraction.
The general principles in extraction treatment with
conventional edgewise techniques are also important in
extraction treatment with miniimplants.

The TAD can supply rigid anchorage for maximum
anterior retraction and anterior torque adjustment.
Moreover, TADs are generally placed apically, making it
advantageous to control the line of action for canine axis
and torque control during retraction .
The line of action can be moved apically by using
long lever arms for anterior torque control
during retraction. A, Intraoral view at the start of
the anterior retraction. B, Intraoral view during
anterior
retraction.
The proper
force system should be designed, and monitoring this
system is especially important, as it is with conventional mechanics

To achieve successful anterior retraction, canine axis
control and anterior torque control are imperative, even
with TAD mechanics. Canine lingual tipping, which is
loss of canine torque, should be closely followed in cases
with large amounts of anterior retraction .
Distal tipping of the canine causes deflection of the archwire (A). As a consequence, extrusion
force develops in the anterior teeth and it worsens anterior torque. Moreover, by the deflection (twisting) of the
archwire, lingual crown torque has been produced in the anterior teeth and this induces loss of anterior torque.
The posterior segments are intruded by deflection of the main archwire caused by distal tipping of the canine and
the intrusive force vector from retraction force (B, C).

When the retraction force is generated directly
and only from the TAD, some considerations are ended.
Canine control becomes more critical. Additionally, the intrusive
force vector of TAD mechanics is available for vertical
control of the anterior teeth, but when left improperly
monitored, side effects such as occlusal plane canting can occur .
One should remember that the TAD itself is not
controlling the canine axis and anterior torque.

Canine axis control and control of the intrusive force vector are important in preventing posterior
bite opening. A posterior bite opening was corrected by canine axis control and wire engagement into the second
molar. A, Intraoral view prior to treatment. B, Intraoral view during anterior retraction. Posterior bite opening was
noted. C, An attachment was bonded to the second molar. A leveling archwire was placed, and the retraction
force was removed. D, Intraoral view during anterior retraction. Posterior bite opening improved.

When a TAD is used for anterior retraction, particularly
with a curved main archwire, the retraction force can be delivered
to the posterior teeth by friction of the archwire. As a consequence,
the posterior teeth can be distalized (A). This distal movement of the
posterior teeth can be monitored by checking the intermaxillary
occlusal relationship. Application of a light force to the molar is useful
in maintaining molar position (B).

nonsurgical Correction of vertical excess
Retraction and Intrusion of Maxillary and Mandibular
Dentition
The patient was a 28-year-old woman whose chief complaint was
protrusion of the lips, even after orthodontic treatment with three
premolar extractions. She exhibited an acceptable occlusion and a nice
posed smile but had the typical features of a long-faced patient: a
long lower third of the face, lip incompetence, extreme mentalis strain
upon lip closure, and a recessive chin. Cephalometric analysis confirmed
anterior vertical excess with a flat occlusal plane. Surgical
correction may have been an option, but the patient desired a nonsurgical
approach. Therefore, maxillary and mandibular molar intrusion
and distalization with orthodontic mini-implants were planned
to correct the protrusion and vertical excess and to improve the facial
aesthetics.

In an effort to distalize and intrude the entire dentition, continuous
arch mechanics were used. To provide the proper space for the lower
dentition, lower third molars were extracted. The mechanics consisted
of buccal mini-implants (Orlus mini-implants, 1.8 mm in diameter and
7.0 mm in length in the maxilla, 1.6 mm in diameter and 7.0 mm in
length in the mandible) and 0.017 × 0.025-inch TMA wire
with a tip back bend to intrude the molars and control occlusal plane
inclination. A constriction bend was also applied to control arch form.
Palatal or lingual TADs were not used.

Active treatment to the desired position was completed after
months. The entire dentition was distalized and intruded with only the
use of buccal mini-implants. The cephalometric superimposition shows
that the upper and lower anteriors were retracted and that the chin
point moved upward and forward .
Fixed retainers extending from first premolar to first premolar were
used in the maxilla and mandible. A maxillary circumferential retainer
was also worn at night.
At 18 months post-treatment follow-up, the results were well
maintained .

A–C, Facial views prior to treatment. D–F, Intraoral views prior to treatment. G–I, Intraoral view
during treatment.

J–L, Facial views at the completion of active treatment. M–O, Intraoral views at the
completion of active treatment. P–R, Intraoral views 18 months after completion of active
treatment.

S, Profile view prior to treatment. T, Profile view at the completion of active treatment.
U, Cephalometric radiograph prior to treatment. V, Cephalometric radiograph at the completion of
active
treatment. W, Cephalometric superimpositions.

Correction Of occlusal Cant and midline
Maxillary Molars Intrusion with Mandibular Molars
Extrusion
The patient was a 22-year-old man whose chief complaint was “my
orthodontic treatment was finished 2 months ago, but my chin has
slanted to one side after treatment.”
He presented with TMJ symptoms of intermittent pain and clicking
on the left TMJ and the upper left first premolar had been extracted.
Clinically, the patient’s maxillary dentition was canted downward on
the right. The patient also exhibited upper and lower midline deviations
of approximately 2 mm to the left from the facial midline at
maximum intercuspation . A significant lateral shift
was noted from centric relation to maximum intercuspation, while the
lower dental midline coincided with the facial midline in centric relation .

deviated to the left with canted lips at maximum intercuspation, but
this deviation was alleviated once in centric relation.
Radiographic examination confirmed that the mandibular asymmetry
was due to a significant lateral shift from centric relation to
maximum intercuspation. The upper right first molar was 3.3 mm
lower than the upper left first molar .
There are two possible options to correct such canting. The first is
surgical correction of the maxilla, and the second is nonsurgical correction
using TADs to intrude the maxillary molars. The patient opted
for the nonsurgical treatment plan.
The treatment plan called for intrusion and distalization of the
upper right molars in order to correct maxillary canting as well as the
Facial examination revealed that the chin

A–C, Extraoral views prior to treatment. D, The patient exhibited occlusal plane canting with a
tongue blade. E–G, Intraoral views prior to treatment in centric occlusion (CO). H–J, Intraoral views
prior to treatment
in centric relation (CR).

K, PA cephalometric radiograph in centric occlusion. L, PA cephalometric radiograph in
centric relation. M–P, During treatment, the maxillary working archwire and mini-implants were placed and
intrusion
of the upper right molars was initiated.

midline deviation, and to guide the mandible to the centric relation position .
Five mini-implants, 1.8 mm in diameter and 7.0 mm in length,
were placed in the buccal and palatal area .
After 10 months of treatment, the upper right molars were intruded
and distalized. The canting of occlusal plane improved and the mandible
was also guided into centric relation .
After 12 months of treatment, one Orlus mini-implant, 1.6 mm in
diameter and 7.0 mm in length, was placed on the right buccal slope
of the mandible. Then an extrusion spring, made of 0.016 × 0.022-inch
TMA (Ormco) wire, was positioned to extrude the lower right posterior
teeth. The spring was connected and bonded to the TADs and then
applied to the bracket bases to produce an extrusive force .

Q, R, 12 months of treatment. The right maxillary molars were intruded and the differential
interocclusal space is shown. S, T, 12 months of treatment. Intraoral view with mandibular mini-
implants
and extrusion spring.

At 18 months after the start of treatment, the appliances were
removed and fixed retainers were used . Additionally,
an active retainer using mini-implants in the maxillary arch was
worn at night .
The occlusal and mandibular planes rotated 6.2 degrees and 7.5
degrees, respectively.
Menton, therefore, moved 6.4 mm to the right and the facial asymmetry
improved .
At a follow-up examination 27 months after the end of treatment,
the results were well maintained .

A, B, Extraoral views at the completion of treatment. C, A flat occlusal plane shown with a tongue
blade. D–F, Intraoral views at the completion of treatment, G, Superimposition of PA cephalometric
radiographs.

H–J. Intraoral view with active retainer. K–M, Intraoral
views at 27 months’ retention.

The use of microimplants in orthodontics

The use of microimplants in orthodontics

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