Download Clinical Applications of the Miniscrew Anchorage

Clinical Applications of the
Miniscrew Anchorage System
ALDO CARANO, DO, MS
STEFANO VELO, MD
PAOLA LEONE, DO, MS
GIUSEPPE SICILIANI, MD, DMD
M
ight skeletal anchorage be applied to orthodontic tooth movement and orthopedic jaw
movement?” With this question in 1983, Creekmore and Eklund were the first orthodontists to
suggest in print that a small metal screw could
withstand a constant force of sufficient magnitude and duration to reposition an entire anterior
maxillary dentition without becoming loose,
painful, infected, or pathologic.1 Their case
opened an entirely new area for managing orthodontic anchorage, but may have been too progressive and too invasive for its time.
Toward the end of the 1980s, a number of
clinicians focused on the use of standard dental
implants as temporary anchorage for orthodontic
tooth movement and then as permanent abutments for tooth replacement.2-5 The major advantage of these implants is that they make it possible to move multiple teeth without loss of
anchorage. They can be placed in areas where
natural anchorage or conventional orthodontic
appliances are impractical, including the edentulous spaces in the alveolus of either arch, the
palate, the zygomatic process, the retromolar
regions, and the ramus. Disadvantages of dental
Dr. Carano
Dr. Velo
implants are the need for an invasive surgical procedure, the limitations on placement sites imposed by the implants’ 10mm length, the time
required for osseointegration prior to force application, and cost. In addition, they are not recommended for female patients younger than 16 or
males younger than 18.
More recently, new onplants, miniplates,
and palatal implants have been developed specifically for use in orthodontics.6-8 The miniplates
have been advocated as anchorage for molar intrusion7,9-11; palatal implants have been used for
space closure, and most effectively for distalization of maxillary molars.5,7 Because these new
devices still have many of the same limitations as
standard dental implants, however, most orthodontists have now turned to miniscrews.12-17 Repeating the experience of Creekmore, they have
found that small screws, like those used for rigid
fixation in maxillofacial surgery, work well for
orthodontic anchorage.14,15 The size of the screws
has been reduced even further in the last few
years.16,17
The material generally used for miniscrews
is medical grade 4 or 5 titanium, although stain-
Dr. Leone
Dr. Siciliani
Dr. Carano is an Adjunct Professor, Department of Orthodontics, University of Ferrara, Ferrara, Italy; an Adjunct Professor, Department of Orthodontics,
St. Louis University; and in the private practice of orthodontics in Taranto and Bari, Italy; e-mail: [email protected]. Dr. Velo is an Adjunct Professor,
Department of Orthodontics, University of Ferrara, and in the private practice of orthodontics in Padua, Italy. Dr. Leone is an Assistant Professor,
Department of Orthodontics, University of Washington, Seattle, and in the private practice of orthodontics in Seattle. Dr. Siciliani is Chairman,
Department of Orthodontics, University of Ferrara, and in the private practice of orthodontics in Rome.
VOLUME XXXIX NUMBER 1
© 2005 JCO, Inc.
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Clinical Applications of the Miniscrew Anchorage System
less steel has been proposed as an alternative.
Recent histological studies in animals have
shown that the osseointegration of titanium miniscrews is less than half that of conventional dental implants.7,18,19 There was no significant difference in the bone surrounding the miniscrew sites
whether the miniscrews were loaded or unloaded
with force.9,18,20 The presence of more compact
bone in the mandible may account for some differences in miniscrew performance found between the maxillary and mandibular arches.7,18-21
Incomplete osseointegration represents a
distinct advantage in orthodontic applications,
allowing for effective anchorage with easy insertion and removal. The miniscrew material and the
specific design of the self-tapping portion are still
important, however, in determining resistance to
breakage. Even though orthodontic forces are not
normally great enough to break the screws, the
rotational forces associated with placement and
removal can cause miniscrew failure, especially
if the bone consistency is high or a partial integration has occurred. Differences among various
miniscrew head designs have also been noted
with regard to soft-tissue healing.
This article illustrates the clinical applications of a new titanium miniscrew designed for
orthodontic anchorage.
Fig. 1 Miniscrew Anchorage System (MAS) screws
are available in three conical sizes. Screw head
consists of two fused spheres with internal hexagon for insertion of screwdriver. Slot can be used
for attachment of elastics, coil springs, ligature
wires, or auxiliary hooks.
the attachment of elastics, chains, coil springs,
ligature wires, or auxiliary hooks.
Miniscrew Design
The conical screws used in the Miniscrew
Anchorage System* (MAS), made of medical
grade 5 titanium, are available in three sizes (Fig.
1). Type A has a diameter of 1.3mm at the top of
the neck and 1.1mm at the tip. Type B is 1.5mm
in diameter at the neck and 1.3mm at the tip.
Both types are 11mm long. Type C, which is
9mm long, has a diameter of 1.5mm at the neck
and 1.3mm at the tip.
The screw head consists of two fused
spheres (the upper 2.2mm in diameter, the lower
2mm), with an internal hexagon for insertion of
the placement screwdriver. A .6mm horizontal
slot at the junction of the two spheres allows for
*Micerium, S.p.a., Via Marconi 83, 16030 Avegno, Italy; www.
micerium.it.
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Mechanical Testing
Two methods were chosen to test these
screws mechanically, representing two potential
modes of failure during insertion and removal:
torsional strength and bending strength. The tests
were conducted in the Department of Mechanical
Engineering at the University of Genoa, Italy, by
seating the screws in a tapped brass block at a
thread depth of 6mm. For torsion-to-failure testing, a dial torque wrench with a recording device
was turned in a clockwise direction, perpendicular to the long axis of the screw. For bending-tofailure testing, a dial bending arm with a recording device was used to deform the screw along its
long axis in a clockwise direction. Six screws
were used for each test.
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Carano, Velo, Leone, and Siciliani
A
B
Fig. 2 A. Surgical guide made from segment of
rectangular wire. B. Metallic marker helps avoid
root damage during miniscrew placement.
appliances such as headgear and lingual arches in
cases where absolute anchorage is necessary.
From a biomechanical standpoint, miniscrews
allow more bodily tooth movement during space
closure by placing the force vectors closer to the
center of resistance of the teeth.
The sites most often utilized for MAS insertion in the maxilla include:
• Interradicular spaces, both buccal and lingual
• Extraction spaces
• Inferior surface of the anterior nasal spine
In the mandible, the most common miniscrew placement sites are:
• Interradicular spaces, both buccal and lingual
• Lateral to the mentalis symphosis
• Extraction spaces
In our experience, the most useful locations
are the interradicular spaces, either buccal or lingual, between the second premolars and first molars in both arches, or the buccal space between
the upper lateral incisor and canine.
Surgical Procedure
The mean resistance to breakage in torsion
was 48.7Ncm for the 1.5mm-diameter miniscrew
and 37.4Ncm for the 1.3mm-diameter miniscrew.
The mean resistance to breakage in flexion was
120.4N for the 1.5mm-diameter miniscrew and
91.7N for the 1.3mm-diameter miniscrew.
These results suggest that the MAS screws
can resist a force much greater than that of any
orthodontic application. It is possible, however,
to apply a torsional force of more than 40Ncm
during insertion or removal and thus to break the
screw. To limit this torsional force, the clinician
should use a small screwdriver and hold it by the
fingertips. If the self-tapping screw encounters
extreme resistance during insertion, additional
pilot drilling may be required. At the time of
removal, if the screw seems to be osseointegrated, a minor surgical procedure may be needed to
remove it completely.
Placement Sites
Miniscrews are used in place of traditional
VOLUME XXXIX NUMBER 1
A surgical guide can be made from a rectangular wire segment to help identify the miniscrew location on the intraoral x-ray (Fig. 2A).
The self-tapping screw often requires no preparation of the medullary bone. If the bone is too
dense, however, a bur (.9mm for Type A, 1.1mm
for Type B) should be used to drill a pilot hole
through the gingival and cortical bone under
local anesthesia. We recommend placing a stop
on the bur to limit the depth of insertion to 23mm, but it is critical that the depth be 2mm
shorter than the miniscrew. The axial inclination
of the bur must be the same as the desired inclination of the miniscrew.
Special attention is required during screw
placement to reduce the chance of injury to delicate anatomic structures such as vessels, nerves,
and dental roots. A metallic marker, which can be
attached to a vacuum-formed retainer or directly
to the brackets, can be used to show the position
of the miniscrew relative to the roots on the preand post-placement panoramic or periapical radiographs (Fig. 2B). To date, we have not seen
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Clinical Applications of the Miniscrew Anchorage System
usually not needed. To the best of our knowledge, no post-surgical complications have been
reported in the literature. Once the orthodontic
anchorage is no longer required, the screw can be
easily removed with the manual screwdriver,
usually without local anesthesia. The mucosa
generally heals within a few days, and new bone
fills in the placement site.
any trauma to anatomic structures during screw
placement. Vessels and nerves are easily avoided
by proper interpretation of the x-ray images. The
roots are more difficult to identify, but damage
can be eliminated by limiting any pilot drilling to
the cortical plate of the alveolar bone (2-3mm). If
a self-tapping screw encounters a root during
insertion, it will stop, and can then be redirected
by the clinician.
A manual screwdriver is used to insert the
miniscrew, preferably between the free and attached gingiva. When properly placed, the screw
head will protrude through the soft tissue. Once
the initial stability of the miniscrew has been
confirmed, an orthodontic force of 50-250g can
be applied immediately. The head of the miniscrew has been designed to prevent compression
of the mucosa, but if this occurs after placement
of a chain or nickel titanium coil spring, we suggest using Monkey Hooks** instead.
Post-operative antibiotics or analgesics are
Closure of Extraction Spaces
Loss of posterior anchorage during extraction space closure can exacerbate the curve of
Spee and deepen the bite. Miniscrews provide
reliable skeletal anchorage for anterior retraction
in either arch, whether a single tooth at a time or
en masse.
Maxillary miniscrews are usually placed
between the roots of the first and second premolars, where the large interradicular space typically allows easy insertion without root interference. The screw heads can be situated at or above
the mucogingival line, depending on the desired
**American Orthodontics, Inc., 1714 Cambridge Ave., Sheboygan,
WI 53082.
A
B
C
D
Fig. 3 A. Case requiring both intrusion and distal space closure. B. Miniscrew positioned above mucogingival
line. C. Elastomeric chain attached to Monkey Hook instead of directly to miniscrew. D. After space closure.
12
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Carano, Velo, Leone, and Siciliani
the maxillary sinus (Fig. 5). If the alveolar
process is prominent, an auxiliary such as a
Monkey Hook can be used to keep the chain or
coil spring away from the soft tissue, thus avoiding discomfort and gingival irritation (Figs. 3,4).
In the mandibular arch, miniscrews can be
useful in patients where maximum anchorage is
needed, such as bialveolar protrusion and Class
line of action. If both intrusive and distalizing
forces are needed, the miniscrew should be positioned above the mucogingival line (Fig. 3). If
the primary movement is to be a distalizing vector, however, the miniscrew should be placed at
the mucogingival line (Fig. 4). The higher the
screw is placed in the maxilla, the more perpendicular to the bone it must be to avoid damage to
A
B
C
D
Fig. 4 A. Patient requiring distal vector of space closure. B. Miniscrew placed at mucogingival line. C. En
masse retraction of anterior teeth. D. Miniscrews in place after retraction, with no sign of inflammation.
A
B
Fig. 5 A. Miniscrew placed high in maxilla must be more perpendicular to bone to avoid damaging maxillary
sinus. B. If screw head is at mucogingival level, it should be inclined at 30-45° to interradicular bone.
VOLUME XXXIX NUMBER 1
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Clinical Applications of the Miniscrew Anchorage System
A
B
C
D
Fig. 6 A. Adolescent patient with deep bite. B. After leveling and alignment, miniscrews placed between upper
lateral incisors and canines to reinforce anchorage during incisor intrusion. C. Bite opening with biteplanes
bonded to lingual surfaces of upper incisors. D. After incisor intrusion.
III cases. We do not recommend placing miniscrews between the roots of the lower first and
second premolars, however, because of the proximity of the mentalis foramen.
Symmetrical Incisor Intrusion
Many patients present with moderate-tosevere deep bites requiring pure intrusion of the
anterior teeth to level the occlusal plane. Unless
the deep bite is so extreme that absolute anchorage is needed, it may be inadvisable to place
miniscrews simultaneously in both arches in
young patients. In these cases, miniscrews can be
used to reinforce conventional orthodontic mechanics. One of our most common treatment methods involves the use of biteplanes bonded to the
lingual surfaces of two or all four upper
incisors.22
To provide anchorage during incisor intrusion, miniscrews can be placed between the
upper lateral incisors and canines (Fig. 6). The
insertion should not be performed until after leveling and alignment, however, so that the maximum amount of interradicular space will be
available. To avoid tipping the upper incisors
buccally during intrusion, the ends of the archwire should be cinched back.
14
Correction of a Canted Occlusal Plane
A canted occlusal plane is often considered
impossible to level with traditional orthodontic
treatment. Miniscrews, on the other hand, provide skeletal anchorage for intrusion of the
appropriate teeth on the canted side (Fig. 7). The
screws can be inserted between the upper lateral
incisors and canines, the upper canines and premolars, or the lower lateral incisors and canines.
To avoid interference with the teeth to be intruded, it is important to center the miniscrews between their roots (Fig. 8).
Alignment of Dental Midlines
When an entire arch needs to be moved laterally to correct the posterior malocclusion, the
dental midlines are usually aligned with intermaxillary elastics, requiring considerable patient
compliance. Vertical forces may be contraindicated in some cases, or the intermaxillary elastics
may decompensate the arches from a frontal
prospective, causing the bite to open. In these
more complex cases of midline deviation, miniscrews may be a useful alternative. A screw can
be placed either lingually or buccally so that the
head stands out at the crown margins (Fig. 9).
JCO/JANUARY 2005
A
B
C
D
Fig. 7 A. Patient with canted occlusal plane. B. Miniscrew centered between roots of upper lateral incisor and
first premolar on canted side (ankylosed impacted canine was extracted). C. Intrusion of upper lateral incisor
and first premolar. D. After leveling of occlusal plane.
Thus, the line of force is directed more occlusally, with an enhanced horizontal vector.
Extrusion of Impacted Canines
Various procedures have been suggested to
prevent anchorage loss and avoid canting of the
occlusal plane while an impacted canine is pulled
down into occlusion. Some authors have recommended inserting auxiliaries such as Kilroy
Springs** on the main archwire.23 Others have
proposed using superelastic overlay archwires.24
**American Orthodontics, Inc., 1714 Cambridge Ave., Sheboygan,
WI 53082.
VOLUME XXXIX NUMBER 1
Fig. 8 Miniscrew must be centered between roots
of teeth to be intruded to avoid interference
between teeth and screw.
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Clinical Applications of the Miniscrew Anchorage System
A
B
C
D
Fig. 9 A. Patient requiring lateral movement of entire maxillary arch to correct posterior malocclusion.
B. Miniscrew placed in existing space between upper right canine and first premolar. C. Elastomeric chain
attached between screw and archwire, directing force more occlusally and horizontally. D. After alignment of
dental midlines.
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Carano, Velo, Leone, and Siciliani
A
B
C
D
Fig. 10 A. Patient with palatally impacted maxillary right canine. B. Miniscrew placed as anchorage for appropriate force vector without involving other teeth. C. After uprighting and partial extrusion using only miniscrew, case completed with maxillary fixed appliance. D. Final results, showing root parallelism.
In both systems, the teeth must be leveled and
aligned before they can be combined into an
anchorage unit.
Miniscrews can be used instead when
heavy forces are required to bring an impacted
canine into occlusion, without relying on the rest
of the teeth for anchorage (Fig. 10). Treatment
time may be shortened—in fact, there is no need
VOLUME XXXIX NUMBER 1
to bond the entire arch during canine extrusion—
and there are no undesirable side effects on the
other teeth. Whether the canine is impacted palatally or lingually, the miniscrew can be placed
to provide the most appropriate force vector; it
can even be removed and relocated as the canine
is extruded. Auxiliaries can be used to make the
miniscrew mechanics even more versatile.
17
Clinical Applications of the Miniscrew Anchorage System
A
B
C
Fig. 11 A. Patient requiring intrusion of maxillary right posterior segment for leveling of occlusal plane. B. Miniscrew inserted in interradicular space between upper right first and second molars, with elastomeric chain
used for intrusion. C. After seven months of intrusion, treatment completed with mandibular implants.
A
B
C
Fig. 12 A. Patient requiring intrusion of upper right second molar. B. Miniscrew inserted in edentulous space
of upper first molar. C. After leveling of anterior teeth, upper arch was prepared with .017" × .022" stainless
steel archwire, and elastomeric chain was used for intrusion. Case was completed in five months.
Molar Intrusion
Opinions have differed regarding the efficacy of orthodontic intrusion of posterior teeth.
Although miniscrews can be a reliable source of
anchorage, it is difficult to place them precisely
in the narrow space between the roots of the first
and second molars without interfering with the
roots.25 In some cases, more than one screw
might even be needed to withstand a relatively
high intrusion force. Therefore, we suggest lim-
18
iting the use of miniscrews to situations where
simple intrusion of one or two molars is needed
and where placement will be unproblematic
(Figs. 11,12). In open-bite cases requiring bilateral intrusion of the posterior segments, miniscrews are not an ideal solution.26
Molar Distalization
Fixed and removable maxillary molar distalization devices for the correction of Class II
JCO/JANUARY 2005
Carano, Velo, Leone, and Siciliani
B
A
C
D
E
F
G
Fig. 13 A. Patient with asymmetrical Class II malocclusion. B. Distal Jet appliance placed and activated.
C. Miniscrew positioned mesial to activation locks, blocking mesial movement of appliance. D. After distal
molar movement, further compression of coil spring moves lock away from miniscrew; anchorage loss is prevented by bonding light-cured composite between screw head and lock. E. Maxillary left canine moved distally by elastic attached to Distal Jet, then built up with composite for esthetic purposes. F. After completion
of molar distalization, Distal Jet converted to passive retainer, and lingual brackets bonded to posterior teeth.
G. Five months later, Distal Jet retainer removed, and Class II correction completed.
malocclusions without the need for special patient compliance have become increasingly popular over the past decade. These appliances range
from fixed devices that are activated by the
orthodontist27-30 to open-coil springs,31-34 but
most utilize some form of palatal coverage to
provide anchorage and prevent incisor flaring.
Nevertheless, studies of molar distalization have
VOLUME XXXIX NUMBER 1
shown a considerable amount of anterior anchorage loss.35
The ideal site for skeletal anchorage would
be the palate, but this requires a surgical procedure to place the implant and another to remove
it. In our experience, screws less than 2mm in
diameter are unstable when used for palatal
anchorage and routinely fail.
19
Clinical Applications of the Miniscrew Anchorage System
A
B
Fig. 14 A. During molar distalization, compression of Distal Jet’s coil spring moves activation lock distally,
away from miniscrew (blue). B. Loss of anchorage can be prevented by bonding light-cured composite (yellow) between screw head and lock.
A
B
Fig. 15 A. Patient with asymmetrical Class II malocclusion treated with Distal Jet, with miniscrews placed
mesial to activation locks to block mesial movement.
B. After molar distalization and removal of Distal Jet,
miniscrew repositioned just mesial to distalized molar
to stabilize it while the remaining teeth are moved distally.
20
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Carano, Velo, Leone, and Siciliani
A
C
B
Fig. 16 A. Patient requiring closure of upper and lower residual spaces.
B. Miniscrew placed distally to mandibular canine for application of
mesial force against lower molars. C. Class III elastics used for molar
mesialization.
The MAS + Distal Jet** may be a solution.
After the Distal Jet appliance has been placed
and activated, palatal miniscrews are inserted
between the roots of the first and second premolars, mesial to the activation locks attached to the
anterior rests (Fig. 13A-C). The miniscrews
block mesial movement of the appliance during
distalization, thus preventing loss of anterior
anchorage. Further compression of the Distal
Jet’s coil springs will move the locks distally,
away from the miniscrews (Fig. 14); during this
phase, anchorage loss can be prevented by bonding light-cured composite between the screw
heads and the locks (Fig. 13D). After molar distalization, the Distal Jet is converted to a passive
retainer, and brackets are bonded to the teeth for
completion of the Class II correction (Fig. 13EG). Another option is to remove the miniscrew
after molar distalization and replace it just mesial
to the distalized molar, where it will stabilize the
molar while the remaining teeth are moved posteriorly (Fig. 15).
**American Orthodontics, Inc., 1714 Cambridge Ave., Sheboygan,
WI 53082.
VOLUME XXXIX NUMBER 1
The MAS + Distal Jet should not be used in
the mixed dentition, because the palatal screw
may interfere with developing permanent teeth.
Molar Mesialization
Molars are often moved mesially in orthodontic treatment to close extraction spaces or
edentulous spaces. Molar mesialization is not a
simple movement and can lead to problems such
as loss of anterior anchorage and molar tipping.
Furthermore, if there is a knife-edge alveolar
ridge in the space to be closed, alveolar bone
may be lost.
A miniscrew placed mesial to the space, at
a height that will produce a force vector approximating the center of resistance of the molar, can
be a valuable source of anchorage. If the screw is
inserted after the initial leveling and alignment
have been completed, a full-size archwire can be
used to prevent mesial crown tipping of the
molar during space closure. Because mesial
movement is usually slow, especially in the
mandibular arch, no more than 2-3mm of molar
mesialization should be attempted (Fig. 16).
21
A
B
Fig. 17 A. Class III patient with intermaxillary elastics attached from upper second molars to miniscrew inserted between lower canines and first premolars. B. After protraction of maxillary arch.
A
B
C
D
Fig. 18 A. Patient needing upper third molar, which was severely compromised periodontally and in Brodie
bite, to be brought into occlusion and uprighted for prosthetic reasons. B. Sectional rectangular wire used to
upright third molar, with fixed biteplane bonded for immediate bite opening. C. Palatal miniscrew used for
skeletal anchorage to allow application of inward and upward force vector, limiting molar extrusion and correcting Brodie bite. D. Third molar alignment after less than five months of treatment.
Intermaxillary Anchorage
Miniscrews are a convenient source of
anchorage in both extraction and nonextraction
therapy when intermaxillary forces are applied
with Class II elastics or anterior repositioning
appliances. Many undesirable side effects can be
produced by such mechanics, including bite
opening and excessive proclination and protrusion of the lower incisors. One possible solution
22
is to place a miniscrew between the roots of the
lower first and second molars or the second premolar and first molar. The location between the
second premolar and first molar (as close as possible to the first molar) is generally preferable,
because the screw must be inserted perpendicular to the alveolar process, which can be difficult
in more posterior regions where access is limited. In addition, the interradicular space between
the second premolar and first molar is wider than
JCO/JANUARY 2005
Carano, Velo, Leone, and Siciliani
the space between the first and second molars.
Placement of the miniscrew mesial to the first
molar may also prevent mesial movement of the
entire lower arch, although care must be taken to
avoid contact with the molar roots.
In Class III treatment, when the maxillary
arch needs to be advanced, miniscrews can be
placed between the roots of the lower canines
and first premolars for elastic attachment (Fig.
17). If the mandibular arch needs to be repositioned distally, the miniscrews can be placed
between the roots of the upper first and second
molars or second premolars and first molars.
Upper Third Molar Alignment
Miniscrews can also be useful in cases with
multiple missing teeth where conventional orthodontic mechanics are difficult to apply. For
example, an upper third molar can be uprighted
with a fixed sectional wire, utilizing a palatal
miniscrew for skeletal anchorage to limit unwanted extrusion of the molar (Fig. 18).
Discussion
Miniscrews are already widely used in
Europe and Asia, but there is still some skepticism in the United States, where many orthodontists consider them too invasive to be part of their
daily practice routines. One concern is whether
placement of a miniscrew should be performed
by the orthodontist or the oral surgeon. Most
American orthodontists refer out any procedure
that is not strictly orthodontic, such as oral hygiene or extraction of permanent teeth, even if it
is part of the orthodontic treatment plan. In our
opinion, however, placement of a miniscrew is
not simply a surgical procedure, but requires specific planning based on orthodontic considerations such as force vectors and the types of anchorage and tooth movement required. Sometimes
the screw needs to be relocated to a better position during treatment, which may become complicated if the patient has to be referred to a specialist.
Histological studies have confirmed that
titanium screws are biocompatible and are easily
VOLUME XXXIX NUMBER 1
removed because of their incomplete osseointegration.10,25 What is still unknown is whether differences in size, shape (conical or cylindrical),
head design, pilot drilling, and physical properties can influence the likelihood of successful
treatment or minimize potential complications
such as breakage at the neck during the application of orthodontic forces. One potential problem
is the trend toward reduced diameters of self-tapping screws. We believe this could lead to a dangerous reduction in their mechanical resistance,
and therefore consider testing to breakage in torsion and flexion to be a fundamental step before
the clinical application of any new miniscrews.
In our preliminary testing of the MAS screws, we
found they were able to resist forces much
greater than any applied in orthodontic treatment, but that caution was required during insertion and removal to avoid applying torsional
forces that might break the screws.
Conclusion
Although more research is needed into
many aspects of miniscrew application, the cases
presented in this article and elsewhere in the literature clearly demonstrate the versatility and
technical advantages of skeletal anchorage. In
our opinion, orthodontic treatment using a skeletal anchorage system is not only more effective,
but offers a variety of treatment alternatives in
challenging cases where traditional mechanics
cannot be used. Advantages of miniscrews over
other forms of anchorage include:
• Optimal use of traction forces, regardless of
the number or positions of the teeth
• Applicability at any stage of development, including interceptive therapy
• Shorter treatment time, with no need to prepare
dental anchorage
• Independence of patient cooperation
• Patient comfort
• Low cost
Of course, there are potential complications
common to all implant procedures, including:
• Damage to anatomic structures such as nerves,
vessels, and roots
• Loss of a screw during placement or loading
23
Clinical Applications of the Miniscrew Anchorage System
• Breakage of a screw within the bone during
insertion or removal
• Inflammation around implant sites
With the MAS, we have experienced none
of these problems except for the loss of three
screws during force loading. Breakage may be
more likely with screws of smaller diameter.
Furthermore, the MAS offers several advantages
compared to more invasive osseointegrated systems:
• Increased selection of insertion sites
• Ease of insertion and removal
• Ability to withstand immediate loading
• Applicability in growing patients
• Low cost
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3. Celenza, F. and Hochman, M.N.: Absolute anchorage in orthodontics: Direct and indirect implant-assisted modalities, J.
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anchorage, J. Clin. Orthod. 34:659-666, 2000.
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