Selection of microimplants

 Using microimplant lengths of
more than 6mm in the maxilla,
and 5mm in the mandible is
recommended.
 A general rule of thumb is to use
the longest possible
microimplant that will not
jeopardize the health of the
adjacent tissues.

In order to obtain better mechanical retention, it is
best to choose a longer and thicker microimplant than a
shorter and thinner one. However, the soft tissue
thickness and the quality of bone at the site of
implantation and anatomical limitation always must be
considered.

 The cortical surface of the maxilla is
thinner and less compact than that of the
mandible and will require longer
microimplants.
 The proper length of the microimplants is
best selected during the pilot drilling
procedure.
 The path of insertion of a microimplant
must be considered when choosing the
correct size.

 It obviously is better and relatively easier to
place a microimplant in a direction
perpendicular to the bony surface. When the
microimplant is inserted in a diagonal direction
instead of a perpendicular direction, it is prudent
to use a slightly longer microimplant.

 Figure -1. When the microimplant is placed in a diagonal
direction (right), a portion of the microimplant is not well
covered by bone. Thus, it is better to select a slightly longer
microimplant than is used for placement in a perpendicular
direction (left).

 The Absoanchor* system uses numbers to
describe the implant series.
No. 12 series 1.2 mm in diameter

 Typically, the first Absoanchor microimplant
should be either a No. 12 or 13 of the Cylinder or
Tapered design.
 The Nos. 12 and 13 series both can withstand up
to 450 gm of orthodontic force if the patient has
sufficient cortical bone.
 In the mandible, the buccal surfaces and retro-
molar areas offer adequate thickness and high
quality cortex for the acceptance of
microimplants. Usually, microimplants of 4 to 5
mm in length and 1.2 to 13 mm in diameter
provide adequate retention.

 The maximum required intraoral orthodontic
forces seldom exceed 300 gm. When using
forces greater than 300 gm, clinicians can
select the No. 14 , 15 or 16 series.
 When there is no initial tightness following
the placement of a No. 12 or No. 13 series
microimplant the clinician should select the
next larger size until there is a close fit
between the microimplant and the bone.

 A microimplant with a 1.4 to 1.6 mm
diameter might improve retention when the
cortical bone is less dense or when greater
force is needed, e.g., when moving the entire
mandibular dentition distally. Occasionally
when mandibular lingual microimplants are
required, tori can serve as excellent implant
placement sites.

 Nos. 17 and 18 series are designed
specifically for intermaxillary fixation during
orthognathic surgery.
 When the larger diameter implants are used,
especially when they are made of low grade
pure titanium, there is a greater risk that they
will be difficult to remove due to
osseointegration.

The following guidelines for microimplant site
and size for orthodontic anchorage are
recommend.

Purpose:
 This location can be used for retracting the
entire maxillary dentition to correct Class II
canine and molar relationships.

 It also can be used for intrusion of the
maxillary molars if palatal microimplants are
used concurrently.

Surgical Considerations:
 A slightly larger incision is needed, and the
surgery is more extensive for placing
microimplants into the infrazygomatic crest area
compared to placing microimplants in the
mucogingival area. If the bone is good quality
with hard cortical tissue, however, the 5 to 6
mm long microimplant is sufficient.

 It is almost impossible to keep the head of
microimplant exposed, so a ligature wire should
be extended from the microimplant head
(closed method) to the attached gingival area.
 Bear in mind the anatomy of the maxillary sinus
when placing the microimplant in this site.

When the point of attachment for an elastic or spring auxiliary is located in a
movable soft tissue area like the alveolar mucosa, the soft tissue can grow over
the microimplant and cause inflammation (top). The coil spring was removed
following a surgical incision, and a hook made of ligature wire was extended from
the microimplant to the attached gingival area

Other Considerations:
If infrazygomatic
microimplants are being used to
retract the anterior teeth,
elastics may exert too much
vertical force and too little
horizontal force.
This area permits intrusion of the maxillary anterior teeth
during their retraction. Thus, the location of the microimplants
should be determined only after considering the point of force
application and force direction, both of which control the
mode of tooth movement.

Recommended Microimplant Size:
 Diameters of 1.3 mm. and 1.4 mm and a
length of 5 to 6 mm.

Purpose:
 This location can be used for retracting the
maxillary posterior teeth.

Surgical consideration:
 This location is used when third molars are
missing or have been extracted and healing is
complete. However, this location poses a surgical
challenge in the placement of the implant, and the
quality of cortical bone sometimes is
compromised. Thus, long microimplants usually
are required. An incision is not needed for drilling
because of the covering of attached gingiva.

 The point of insertion and angulation of
placement are critical to successful
placement of the microimplants. Only special
situations warrant using this area as a
microimplant site.

 Diameters of 1.3 to 1.5 mm and a length of 7
to 8 mm.

Purpose:
 This location is the second choice for
positioning microimplants to retract the
maxillary anterior teeth when a microimplant
placed between the first molar and second
premolar fails.

 This site also offers an excellent location for
applying intrusive forces to the maxillary
molars.

 The width of the attached gingival area
differs from patient to patient. When a
microimplant can be placed through the
attached gingiva, there is no need for an
incision.
 When a microimplant is placed in a movable
soft tissue area, a small vertical incision
must be made before drilling.

 The root of the second molar is tipped mesially, so
sometimes there is not enough space between the
first and second molar roots. To avoid root injury, a
careful surgical approach is needed. The average
distance between the first and second molar roots is
2.1 mm at a level 5 to 7 mm apical to the alveolar
crest. If the space between the roots is too narrow to
place the microimplant, it can be inserted after
creating sufficient space by moving the second molar
root distally by leveling.

 If microimplants are placed between the
maxillary first and second molar roots, elastic
materials that connect to hooks on the
archwire between the lateral incisor and
canine may impinge on soft tissue around the
canine eminence. Thus, some type of guide
bar usually is needed to prevent gingival
impingement by the elastic material.

to 8 mm.

Purpose:
 This microimplant location is the best area
for retraction of the maxillary anterior teeth
and for intrusion of the maxillary molars.

 The width of the attached gingival area differs
from patient to patient. When a microimplant
can be placed in the attached gingival area, an
incision is not required. However, when a
microimplant is placed in the movable soft
tissue area, it is necessary to make a small
vertical incision before drilling.

 When the microimplant is placed in a slightly
higher position, the path of the drill should be
angled approximately perpendicular to the
roots of the teeth. This approach is helpful in
avoiding sinus injury when the sinus wall is
very low.

 The average thickness of cortical bone is 1-
1.5 mm in this area; the quality of bone varies
among patients.
 Sometimes the mesiobuccal root of the
maxillary first molar is curved mesially. There
is danger of damaging adjacent roots during
the surgical procedure, so a careful surgical
approach is necessary.

 The average distance between the first
molar and second premolar roots is 3.2 mm
at a level 5 to 7 mm apical to the alveolar
crest. Thus, to avoid root injury, it is better to
place the microimplant diagonally and
somewhat mesial to the contact point.

 If the space between the roots is too narrow
to place the microimplant initially, it can be
inserted after creating enough space
following orthodontic movement of the tooth
roots by leveling.

 When the microimplant is placed in the
alveolar mucosa, it is better to make a hook
with ligature wire that extends to the
attached gingival area. This will prevent
inflammation around the elastic orthodontic
material.

 The vertical placement of a microimplant is
determined by biomechanics and by the
periodontal condition. Higher positioned
microimplants provide more of a vertical
component and less of a horizontal component of
force for retracting anterior teeth.

 Orthodontic elastics do not present soft
tissue impingement problems when the
microimplant is placed in an area of attached
gingiva, and it offers easy access for surgical
procedures.

 Table-1. The mean and standard deviation of
the thickness of cortical bone, the distance
between the bone surface and root, and the
distance between the roots in the maxilla
and in the mandible (from Park, 2002)

Purpose:
 This position is useful for moving the
maxillary molars distally or mesially and for
intrusion of the buccal segments.

 The quality of attached gingiva is very good
in this area, so an incision usually is not
required prior to drilling.
 It is an easy region to access.

 If the microimplants are being used to protract
or distalize the maxillary posterior teeth, it is
better to place the microimplants closer to the
gingival margin.
 If intrusion of the posterior teeth is required, it is
better to place the microimplants in a slightly
higher position.

Purpose:
 This site is used for intrusive forces and
torque control of the maxillary incisors.

 This area has very good quality cortical bone
and attached gingiva.
 The microimplant usually must be placed in
a slightly higher position to produce intrusion
of the incisors.

 An incision often is needed for drilling and easy
access.
 If the patient is young, there is a gap in the
midline suture area allowing the use of a slightly
larger diameter microimplant.
 It can be placed in a more perpendicular
direction due to the relatively larger space
available between the roots of the incisors.

 When a microimplant is placed between the
roots of the central incisors, it typically must be
placed in the labial frenum. The soft tissue often
grows around the microimplant head, so a
ligature wire extension hook from the
microimplant head extending to the attached
gingiva is required.

 Microimplants placed between the roots of
the central and lateral incisors bilaterally can
be helpful in correcting a canted occlusal
plane.

to 7 mm.

Purpose:
 This location can be used for anchorage in
lingual orthodontics and for intrusion of the
maxillary molars in treating an openbite.

 Maxillary palatal microimplants usually are
placed between the maxillary first and
second molars. However, they also can be
placed between the second premolar and
first molar and between the premolars.

 The thickness of the palatal mucosa varies
from the cervical area to the apical area. When
the palatal mucosa is anesthetized, a needle is
inserted precisely where the microimplant is to
be placed, and the thickness of the mucosa is
measured.

 Alternatively, a periodontal probe can be used to
measure the mucosal thickness of the palatal
surface. In choosing a microimplant, longer
microimplants should be selected to compensate
for the thick soft tissue. In other words, the
microimplant must be long enough to penetrate
through thick soft tissue (3 to 6 mm) and at least 6
mm into bone at this site.

 There is no need to open a flap in the palatal
area before placing a microimplant. A pilot
hole is made with the drill, and the
microimplant is inserted by rotating the
screwdriver.

 The thickness of the palatal cortical bone is
similar to the corresponding buccal area.
 The dentoalveolar spaces between the
maxillary second premolar, first molar, and
second molar provide enough space (about 4
mm) for microimplant placement.

 The positions of the greater palatine
artery and nerve should be reviewed
to avoid injuring them when placing
the microimplant in the palate. Thus,
the microimplant usually is placed
gingivally relative to the greater
palatine artery and nerve.
 The quality of bone varies among
patients, and drilling must be modified
according to the hardness of the
bone.

 The slope of the palatal
shelves varies from steep to
obtuse, and therefore, the
angulation used during
microimplant placement
should be modified according
to the contour of the alveolar
bone. In the case of steep
alveolar bone, the placement
angle of the microimplants
relative to the long axis of the
teeth may be increased from
an oblique direction to a more
perpendicular direction.

Remarks:
 When a microimplant is used for retraction of the
anterior teeth with sliding mechanics in lingual
orthodontic treatment, it is better to place the
microimplant between the roots of the first and
second molars instead of between the first molar
and second premolar. If it is placed between the
molar roots, a greater range of action for the elastic
material during en masse retraction is achieved.

 Palatal microimplants are the best choice for
intrusion of maxillary molar teeth.

 Diameters of 1.3 to 1.6 mm and a length of
10 to 12 mm.

Purpose:
 This site is used for any kind of tooth
movement of the maxillary posterior teeth,
including unilateral constriction of the arch.

 A microimplant also can be attached to a
transpalatal arch for improving anchorage
and distalizing molars.

Surgical considerations:
 No incision is needed in this area before drilling.
 Care must be taken not to penetrate the nasal
cavity during placement because the thickness
of the midpalatal area is different from site to
site and patient to patient.

 This region offers good quality cortical bone,
although it does contain the midpalatal suture.
Thicker diameter microimplants work better in
areas with patent sutures, if the suture does not
offer enough resistance in young patients; the
microimplant should be placed adjacent to the
midpalatal suture.

Remarks:
 If the transpalatal arch and microimplant are
connected, the posterior teeth can be moved
mesially and distally by applying force from the
microimplant to the transpalatal arch. However, if
the microimplant is placed in the midpalatal area,
access and applying forces are more difficult.

to 6 mm.

Purpose:
 The uprighting of tilted mandibular molars and
the retraction of mandibular teeth or the whole
mandibular dentition can be accomplished with
retromolar microimplants.

 When the mandibular second molar shows
lingual tilting, a microimplant can be placed
buccal to the second molar to provide
anchorage for buccal up-righting of the molar
and distal retraction of the teeth.

 Retromolar areas offer adequate thickness and
high quality cortical bone for good
microimplantation.
 The retromolar mucosa is thick like that of the
palate, and clinicians must select a proper
length of microimplant.
 The microimplant must be inserted at least 4
mm into bone at this site.

 Care must be taken not to fracture the
microimplant during placement, because the
bone in the mandibular arch is strong and
dense.
 Microimplants placed on the distobuccal aspect
of the mandibular second molar tend to be
covered by soft tissue.

 The thickness of retromolar soft tissue varies
from patient to patient. In choosing a
microimplant, the thickness of soft tissue
should be considered. Therefore, sometimes
a ligature wire should be extended from the
microimplants (closed method).

 Microimplants can be placed during the
same surgical procedure used to extract the
third molar.
 Microimplant used to correct a lingually tipped mandibular second molar. The
microimplant can be placed during the same surgical procedure used to
extract the third molar. The second molar was moved distally due to the
improper position of the microimplant.

Remarks:
 When planning to use microimplants for uprighting
tilted molars, the position of the microimplants
should be determined by considering the direction
and the point of force application that is coincident
with the direction of the tooth being up-righted.
Mandibular molars usually tend to be tipped
mesially and lingually when the mesial tooth is
absent. Therefore, for better control of the force
direction during uprighting, lever arm mechanics
with a bracket head type microimplant can be used.

 Occlusal contact between microimplants and
maxillary teeth occasionally occurs in patients
with small interocclusal clearance. This type of
encroachment must be checked and prevented.

to 10 mm.

Purpose:
 This location is used for
› retracting the mandibular anterior teeth,
› intrusion of the mandibular molars,
› distal movement of the mandibular molars.

 This location also provides microimplant
sites for the correction of scissors bite, i.e.,
buccal crossbite, Brodie bite.

 Placing microimplants within the zone of the
attached gingiva can prevent inflammation
and is excellent from a hygienic standpoint.
However, it is not always possible to place
microimplants in this area. Therefore, the
open method may not be a good choice here
because of the narrow band of attached
gingiva.
 Microimplants usually are placed 2 to 3 mm
apical to the attached gingiva.

 A small vertical incision is made through the
mucogingival tissue before drilling.

 A small vertical incision is made through the
mucogingival tissue before drilling.
 The cortical bone ordinarily offers enough thickness
to allow a diagonal placement of the microimplant.
 The quality of cortical bone is excellent, with an av-
erage thickness of about 3 mm, so care is required
to prevent heat generation during drilling.

 The possibility of root damage during
microimplant placement between the
mandibular first and second molars is much
less than that in the maxillary arch. The
distance between the first and second molar
roots is about 4.5 mm. In some patients, there
is sufficient alveolar bone (5.3 mm) for
placement adjacent to the second molar root
buccally.

 The microimplant can be placed in a
perpendicular direction when positioned
slightly apically.
 When microimplants are placed in the
mandible, the location of the inferior alveolar
canal and nerve must be determined.

 Fortunately, there is almost no possibility of
damaging the inferior alveolar artery and
nerve with microimplants because the
inferior alveolar canal travels some distance
away from the root apexes and
microimplants usually do not extend beyond
them.

Remarks:
 The main purpose of microimplants placed between
the mandibular first and second molars is to control the
movements of the mandibular molars vertically during
retraction of the anterior teeth. These mandibular
microimplants tend to become covered by soft tissue,
so a ligature wire extension should be connected
during the surgical procedure, even though the head of
the microimplant is exposed at the time of the surgery.

to 7 mm.

Purpose:
 This location for microimplants is used for
the retraction of mandibular anterior teeth
and for the intrusion of mandibular posterior
teeth.

 It also can be used for anchorage to move
mandibular molars distally and buccally.

 This location has a narrow attached gingiva,
so the open method is of limited use here.
 This area has good quality cortical bone, care
must be taken to prevent heat generation
during drilling into the bone.
 The distance between the roots of the first
molar and of the second premolar is about 3.4
mm.

 The volume of buccal alveolar bone in this
area, however, differs among patients. If the
alveolar bone is thin, it is very difficult to place
the microimplant diagonally in the attached
gingival area, so it should be placed slightly
lower than normal and in a perpendicular
direction.

Remarks:
 This area is the most common site for microimplants that
are used to retract mandibular anterior teeth.
 The microimplant also can be used to provide anchorage
for distal movement of mandibular molars and for controlling
the mandibular molar vertically during retraction of the
anterior teeth. When intruding molars, the microimplant is
placed a little lower than normal. The mandibular
microimplants, therefore, will be covered by soft tissue, and
a ligature wire extension should be connected during the
surgical procedure.

 Diameters of1.3 to 1.6 mm and a length of 5
to 7 mm.

Purpose:
 This site is used for the protraction of
mandibular molars.

 This area has narrow attached gingiva, so
sometimes it is difficult to employ the open
method of surgical placement.
 The distance between the canine and first
premolar roots is approximately 2.2 mm.
 The volume of buccal alveolar bone in this area
is not as thick as it is in the posterior mandible.

Remarks:
 This location is a common site for microimplant
placement, when microimplants are to be used
as anchors for the protraction of mandibular
molars. Sometimes this area presents an
opportunity for bicortical anchorage, if
required, in that the microimplant may pass
through both the buccal and lingual cortical
plates.

Purpose:
 This microimplant site is used for the
intrusion of mandibular incisors.

 This area has a very narrow band of attached
gingiva, so the open surgical approach is not
indicated here. However, the bone in this region
usually is of good quality.
 The distance between the roots of the
mandibular anterior teeth is small, however, so
it is better to place microimplants diagonally.

Remarks:
 A microimplant placed in this location usually is
used for intrusion of the anterior teeth, so it
should be placed in a slightly lower position
relative to the roots of these teeth. A ligature
wire extension hook attached to the head of
microimplant usually is required for applying
elastic traction.

 Diameters of 1.3 to 1.4mm and a length of 5
to 6 mm.

Purpose:
 This area is the best place for controlling teeth
adjacent to an edentulous space to achieve such
movements as molar uprighting.

 This is an excellent location for
microimplants because the cortical bone is of
good quality, and there is no risk of root
injury.

Remarks:
 Clinicians can place two microimplants side by
side, if needed, and can connect their upper
structures with a light-curing resin. In this way,
several attachments, including brackets, can be
bonded to the upper structures of
microimplants; they even can be used as
artificial teeth.

to 8 mm.

 The Absoanchor® microimplant system can
be used in any area of the mouth, if there is
bone. For example, the mandibular tori and
the bone adjacent to residual roots that will be
extracted at a later date can be used for the
placement of microimplants.

 Lingual microimplants placed in the mandible.

 Microimplants placed into residual roots.

MAXILLA
Cortical Bone Thickness
Mean SD Max Min
5 1.44 0.50 3.0 0.9
6 1.37 0.49 2.5 0.8
7 1.55 0.38 2.1 0.9
6-Lingual 1.40 0.27 2.0 0.9

MAXILLA
Distance Between Bone Surface and Root
Mean SD Max Min
5 2.75 1.18 4.4 1.0
6 2.24 1.12 5.3 0.9
7 2.80 1.01 5.4 1.4
6-Lingual 2.29 1.06 4.4 0.5
7-Lingual 2.08 0.94 4.9 0.9

MAXILLA
Distance Between Root
Mean SD Max Min
5-6 3.18 0.92 5.8 2.0
6-7 2.11 1.22 5.0 0.8
6-7 Lingual 4.03 0.87 5.7 2.8

MANDIBLE
Cortical Bone Thickness
Mean SD Max Min
5 1.71 0.50 2.8 0.9
6 2.48 0.71 3.1 1.3
7 3.17 0.93 4.7 1.4

MANDIBLE
Distance Between Bone Surface and Root
Mean SD Max Min
4 1.60 0.49 2.2 0.8
6 2.16 0.69 3.5 1.2
7 5.33 2.00 8.7 3.1

MANDIBLE
Distance Between Roots
Mean SD Max Min
3-4 2.20 0.92 2.8 1.4
5-6 3.47 1.09 4.8 2.0
6-7 4.57 1.41 6.5 2.7

Selection of microimplants

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