Download Clinical Applications and Efficiency of Miniscrews

ORIGINAL ARTICLE
Fortini, Arturo1
Cacciafesta, Vittorio2
Sfondrini, M. Francesca3
Cambi, Stefano4
Lupoli, Massimo5
_ Department of Orthodontics,
University of Insubria,
Varese, Italy
_ Private Practitioner,
Florence, Italy
_ Department of Orthodontics,
Università Cattolica “S. Cuore”
of Rome, Rome, Italy
Clinical Applications and Efficiency of
Miniscrews for Extradental Anchorage
Purpose: The purpose of this article is to describe the use and clinical applications of a new type
of miniscrew in several different anchorage situations.
Participants: 12 patients (age 13 to 51 years; 3 male, 20 female) with anchorage problems.
Materials and Methods: Lateral head films, panoramic radiographs, photos, and study casts were
obtained before treatment. The site of insertion was chosen individually depending on a number of
factors. Nineteen miniscrews were inserted for various types of tooth movements. Recently, a new
design of miniscrew with a different head has been introduced that allows attachment of elastic
modules, power chains, or metallic ligatures.
Results: Miniscrews were successfully used in several different clinical situations, such as: intraarch
intrusion of anterior teeth; intraarch intrusion of posterior teeth; extrusion and alignment of impacted teeth; anchorage for distalization; retention after distalization; molar protraction; retraction of
maxillary and mandibular anterior teeth with concomitant poor dental support in the posterior segments; intrusion and proclination of lower front teeth in the absence of posterior support; and space
closure with maximum anchorage.
Conclusion: The new miniscrews presented here have shown an excellent efficacy as an extradental
anchorage in several clinical situations where conventional anchorage can not be applied.
Keywords: osseointegrated implants, miniscrews, immediate loading, extradental anchorage, noncompliance treatment
(Orthodontics 2:?–?, 2004)
INTRODUCTION
Submitted for publication
17 August 2003; accepted for
publication 1 November 2003.
Reprint requests:
Dr. Vittorio Cacciafesta,
Studio Prof. Giuseppe Sfondrini,
Via Libertà 17, 27100 Pavia, Italy.
E-mail: [email protected]
In order to solve the problems related to anchorage for orthodontic tooth movements in periodontally involved patients or subjects with
mutilated dentitions, various solutions have been
suggested. These include: osseointegrated implants, onplants, miniplates, zygoma wires and
anchors. However, all these systems have some
limitations and drawbacks.
In this article a new type of miniscrew is presented as an alternative anchorage, and possible applications for various types of tooth movements are demonstrated. Miniscrews are small
enough to be placed between the roots of adjacent teeth in the alveolar bone. They are easily inserted and removed without a mucoperiosteal flap, and can be loaded immediately
after insertion.
In orthodontics anchorage may be defined as
the amount of allowed movement of the reactive unit. In critical anchorage situations, the reactive unit must not be moved (Freudenthaler et
al, 2001).
Traditionally, anchorage has been classified as
either extraoral or intraoral. In the case of ex-
traoral anchorage, the reactive forces are transferred to the head or to the neck. The methods
commonly employed in orthodontics to control
and reinforce the anchorage, particularly extraoral devices, are constrained by some limits
in their application and use, such as patient compliance and discomfort. For example, a headgear is often rejected by adult patients. The intraoral anchorage systems are sub-classified further as intraarch, interarch, and extradental. The
intraarch anchorage is based on the assumption that more teeth offer greater anchorage
than fewer teeth and that tipping is easier than
translation. Conversely, the interarch anchorage is based on the need to move teeth in one
direction in e.g. the upper jaw, and in the opposite direction in the lower jaw. Intraoral, extradental anchorages are characterized by the
transfer of reactive forces to the interface between metallic anchorages and bone (Melsen
and Verna, 1999).
The growing demands for orthodontic treatment
methods that require minimal compliance, particularly by adults with prosthetic and/or periodontal problems, and the importance placed
on aesthetic considerations by those patients,
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Fortini et al., Miniscrews for Extradental Anchorage
have led researchers to investigate several different alternative anchorage systems (Favero et
al, 2002). Their common feature is that they use
the alveolar bone for anchorage. Therefore,
they have been defined as extradental. The clinical indications for the use of these systems are:
• Lack of quantity or quality of dental anchorage units (periodontally involved teeth, partial edentulism).
• Necessity to minimize or completely neutralize undesired reactive forces during tooth
movements.
removed easily after use by simply unscrewing
them in the opposite direction (Figs. 2a and b).
Miniscrews can be used for direct anchorage
in the anterior and posterior region of the oral
cavity and can be attached with elastics or NiTi superelastic coils to the fixed appliance. Their
cost is much reduced compared to conventional implants.
The purpose of this article is to describe the use
and clinical applications of this new type of miniscrew in several different anchorage situations.
There are some differences between the various
extradental anchorage systems available: the
type of metallic composition (from pure titanium
to conventional stainless steel), the surgical procedure for insertion (major or minor surgical
trauma), the possibility of osseointegration, and
the application of immediate loading.
Several reports on different systems have been
published: osseointegrated implants (Douglass
and Killiany, 1987; Roberts et al, 1989, 1990,
1996; Higuchi and Slack, 1991; Kokich,
1996); onplants (Block and Hoffman, 1995;
Janssens et al, 2002); zygoma wires (Melsen
et al, 1998) and anchors (De Clerck et al,
2002); mini-plates (Nagasaka et al, 1999;
Umemori et al, 1999; Sherwood et al, 2002);
and miniscrews (Kanomi, 1997; Costa et al,
1998; Freudenthaler et al, 2001; Melsen and
Garbo, 2004; Park et al, 2001).
The experience of recent years has indicated
that several of these anchorage systems may
present some disadvantages, including:
• difficulty in determining the most appropriate
location for each individual patient (implants,
miniplates) (Smalley, 1995)
• limited availability of sites (implants, onplants)
• absolute necessity of waiting for osseointegration before applying any load (implants,
onplants)
• extensive surgical trauma during insertion
and removal (implants, onplants, miniplates)
• excessive cost (particularly implants and onplants).
SUBJECTS, MATERIALS AND METHODS
The recently introduced miniscrews presented
in this paper are manufactured in stainless steel
(Fig. 1) and do not require osseointegration. Also, they are small enough to be inserted between the roots of adjacent teeth in the alveolar bone and can be loaded immediately. The
surgical procedure is uncomplicated because
the screws are placed directly through the gingiva, without a mucoperiosteal flap, and can be
2
The sample consisted of 12 patients, 3 males
and 9 females. They all presented with anchorage problems (periodontally involved teeth,
partial edentulism, or the necessity of absolute
control of reactive forces). Their mean age was
29.5 years (minimum 13 years and 4 months;
maximum 52 years and 6 months). All patients
received detailed information about the treatment objectives and signed a written consent
form.
Lateral head films, panoramic radiographs,
photos, and study casts were obtained before
treatment. The site of insertion was chosen individually, depending on the availability of sufficient bone, the amount of space between two
adjacent roots, soft tissue conditions, and the
type of tooth movement to be performed.
Nineteen miniscrews1 (Fig. 1) were inserted for
various types of tooth movements.
The introductory kit (Fig. 3) contains a screwdriver, the burrs for drilling the bony hole, different sizes of miniscrews (6 mm, 8 mm, 10 mm,
12 mm in length, 1.5 to 2.0 mm in diameter)
(Fig. 4), and two different screw head designs
(Fig. 5, 6a and b).
Surgical Procedure
In order to achieve better bony access, 10 out
of the 19 miniscrews were inserted under local
anaesthesia, through a mucosal incision of
about 2 mm. The periosteum was reflected from
the underlying bone, and a hole was drilled into the bone with the twist drill under continuous
irrigation. The miniscrew was inserted manually with the screwdriver (Figs. 7a to c). Two miniscrews were inserted using a mucosa punch,
which allows for the creation of transmucosal
access to the bone without any flap, followed
by manual insertion with a screwdriver (Figs. 8a
and b). The remaining 7 miniscrews were inOrthodontics Vol 1, No 2, 2004
Fortini et al., Miniscrews for Extradental Anchorage
Fig. 1 Technical drawing of one type of the miniscrews that were used in the patients presented in
this article. (Fig. 1 ist Datei “Fig. 1a.TIF”
Figs. 2a and b Seating a miniscrew with a screwdriver (a) is as
simple as removing it by turning in
the opposite direction (b).
a
b
Fig. 3 Introductory kit containing
a screwdriver, drills, and the miniscrews.
Fig. 4 Miniscrews of different lengths.
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Fig. 5 Two screws with different lengths
of the transmucosal shafts.
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Fortini et al., Miniscrews for Extradental Anchorage
a
b
Figs. 6a and b New design of
miniscrew with a circular groove
around the head (a), for attachment of elastic modules, power
chains (b) and metal ligatures.
Figs. 7a to c Miniscrew insertion by mucosal incision: (a) 810 mm long incision, (b) placing
the miniscrew, (c) two sutures for
wound closure.
b
a
c
a
4
b
Figs. 8a and b Mucosa punch
(a) for creating transmucosal access to the bone (b).
Orthodontics Vol 1, No 2, 2004
Fortini et al., Miniscrews for Extradental Anchorage
b
Figs. 9a to c Miniscrew insertion
directly through the attached gingiva using a drill (a and b) and
the screwdriver mounted on a
low-speed handpiece (c).
Figs. 10a and b Loading the
miniscrews with Ni-Ti coil springs
(a) or elastic modules (b).
a
c
a
b
serted directly through the mucosa without any
flap dissection, using the drill mounted on a lowspeed handpiece. In these cases a low-speed
handpiece was also used for screwing the
screws into the bone (Figs. 9a to c).
ameter allows its insertion in almost every desired location, particularly between adjacent
roots. It is recommended that force levels are
maintained between 25 cN and 100 cN during the entire treatment.
Orthodontic Procedure
CLINICAL EXAMPLES
As the miniscrews are made of stainless steel,
there is no need to wait for osseointegration;
thus, the orthodontic forces can be applied immediately after insertion. However, we recommend waiting for 8–10 days before loading the
screw – but only if a flap was raised. This is recommended to allow the healing of soft tissues
and the maintenance of good oral hygiene.
Subsequently, superelastic Ni-Ti coil springs,
power chains, or elastic modules are attached
to the head of the miniscrew, through the hole
or to the groove (Figs. 10a and b). The small diOrthodontics Vol 1, No 2, 2004
We have successfully used miniscrews in several different clinical situations, such as:
Intrusion (Fig. 10a) and retrusion of anterior
teeth (Fig. 10b)
In this scenario, anterior teeth can be intruded
placing the screws between the roots of the lateral incisor and canine, or distal of the canine.
The screws are connected with Ni-Ti superelastic coil springs to a stiff stainless steel segment
that consolidates all the anterior teeth as one
unit.
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Fortini et al., Miniscrews for Extradental Anchorage
b
a
c
Figs. 11a to l Intrusion of a maxillary right first molar. Pre-treatment photograph (a) and panoramic radiograph (b). Insertion (c
to e) and loading of two miniscrews (buccally and palatally)
with Ni-Ti superelastic coil springs
(f to h). Intrusion achieved after 4
months (i to l). Note appearance
of the implant sites immediately
after the uncomplicated removal
of the miniscrews (j and k). (Die
gespiegelten Zugfedern in Fig.
11f.TIF und Fig. 11i.TIF sollten
entfernt werden! Vgl. Ausdruck!)
d
e
f
g
h
i
6
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Fortini et al., Miniscrews for Extradental Anchorage
k
j
l
a
Figs. 12a to c Extrusion and alignment of an impacted maxillary right canine using a miniscrew in
the opposing arch. (a) Clinical situation before extraction of the primary canine and surgical exposure
of the permanent canine in the first quadrant. (b) Elastic attached to impacted canine in miniscrew in the
mandible. (c) Situation after forced eruption of the
canine and prior to orthodontic alignment.
Intrusion of posterior teeth (Figs. 11a to l)
The use of miniscrews is highly indicated as anchorage for the intrusion of maxillary molars. One
screw is inserted labially, whereas one is placed
palatally, in order to apply the load from both
sides and achieve a pure intrusion of the tooth.
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b
c
Extrusion and alignment of impacted
teeth (Figs. 12a to c, 13a and b)
Miniscrews can be employed to extrude and
align impacted teeth in the opposing arch with
vertical elastics.
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Fortini et al., Miniscrews for Extradental Anchorage
a
Figs. 13a and b Extrusion (a)
and alignment (b) of an impacted mandibular left premolar using a miniscrew in the opposing
arch.
b
Figs. 14a and b Premolar distalization with absolute anchorage
against a miniscrew; (a) lateral
view, (b) occlusal view.
a
b
Fig. 15 Retention of maxillary molars after their distalization. The anchorage for retention is provided
by means of a Nance button and two miniscrews.
(Same patient as in Figs. 14a and b.)
a
b
Anchorage for distalization (Figs. 14a and b)
Molar protraction (Figs. 16a to l)
After the use of a molar distalizing appliance,
premolars can be subsequently distalized using
miniscrews as anchorage.
Particularly in the mandibular arch, protraction
of molars is an anchorage-demanding type of
movement. Therefore, the use of miniscrews in
combination with Ni-Ti superelastic coil springs
and hinge-mechanic systems allows a bodily forward movement of the tooth without side effects
on adjacent teeth.
Retention after distalization (Fig. 15)
Another possible application of miniscrews is
the anchorage reinforcement of molars that
have been distalized.
8
Figs. 16a to l Protraction of lower right second and third molar.
Pre-treatment photographs (a to
c) and panoramic radiograph
(d) of an adult missing the
mandibular right first molar. Insertion (e) and loading of a
miniscrew with a Ni-Ti superelastic coil spring for molar protraction using rotatory mechanics (f
to g). Panoramic radiograph after 5 months (h). Post-treatment
photographs (i to k) and
panoramic radiograph (l).
Orthodontics Vol 1, No 2 2004
Fortini et al., Miniscrews for Extradental Anchorage
c
e
f
g
h
i
j
k
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d
l
9
Fortini et al., Miniscrews for Extradental Anchorage
Fig. 17 Retraction and intrusion of maxillary anterior teeth with concomitant poor dental support in the
posterior segments using a miniscrew as anchorage.
Retraction of maxillary and mandibular anterior teeth with concomitant poor dental
support in the posterior segments (Fig. 17)
In this scenario, the application of miniscrews in
the posterior regions allows a force vector with
both intrusive and retractive components, thus
correcting a deep bite and closing extraction
spaces simultaneously. This system can replace
the use of zygoma wires, which were used in
the maxilla with the same clinical indications before the introduction of miniscrews.
Intrusion and proclination of lower front
teeth in the absence of posterior support
The insertion of two miniscrews in the mandibular symphysis enables the clinician to intrude
and procline the mandibular front teeth even
when posterior teeth are missing or periodontally compromised.
On average after 5 months, when the miniscrews were no longer required for anchorage,
they were removed under local anaesthesia
without difficulty, with the same screwdriver
used for insertion (Figs. 2a and b).
COMPLICATIONS
Some patients develop local inflammations, often due to a patient’s poor oral hygiene, which,
if present, can be controlled by daily rinsing with
chlorhexidine. The risk of root damage during
the surgical procedure or from subsequent tooth
movement is minimal.
A more common event can be the loosening of
the miniscrew during orthodontic treatment. In
their investigation, Melsen and Costa (2000)
reported that 2 miniscrews out of 16 were lost
immediately after insertion. This was generally
caused by incorrect positioning, either by the
use of excessively high forces, or by the pro10
duction of torsional moments on the miniscrew
allowing it to come unscrewed.
In our sample, 3 miniscrews out of 19 were lost.
Based on our experience from this study, the
cause of the loss was incorrect positioning of
one miniscrew in the maxillary arch, and to the
use of two short miniscrews in the mandible. In
fact, we repositioned the miniscrew in the maxillary arch, and they remained absolutely stable
as in the contralateral side.
Regarding the two miniscrews (8 mm) lost in the
mandible, it was enough to replace them with
two longer screws (12 mm) with bicortical retention without changing the location.
DISCUSSION
The miniscrews used in the present study proved
to be efficient in maintaining the type of extradental anchorage required in several different clinical situations. Apart from a slight local
irritation at the site of insertion, neither discomfort nor allergic reactions were reported by the
patients. All miniscrews were well accepted and
tolerated throughout treatment.
Today, stainless steel is one of the most frequently used biomaterials for internal fixation
devices and implants because of its favourable
combination of mechanical properties, corrosion resistance and cost effectiveness when
compared to other metallic implant materials
(Disegi and Eschbach, 2000). The biocompatibility of implant-quality stainless steel has been
proven by successful animal and human implantation for decades (Lemons et al, 1976; Disegi and Wyss, 1989; Ellerbe and Frodel, 1995;
Kallela et al, 1999; Disegi and Eschbach,
2000). Composition, microstructure and tensile
properties of stainless steel used for internal fixation are standardized in ISO and ASTM specifications (ISO 5832-1, 1997; ASTM, 1992).
Metallurgical requirements are stringent to enOrthodontics Vol 1, No 1, 2004
Fortini et al., Miniscrews for Extradental Anchorage
sure sufficient corrosion resistance, non-magnetic response, and satisfactory mechanical
properties. Metallic materials, such as stainless
steel, pure titanium, and titanium alloys have
demonstrated an acceptable combination of
strength, ductility, corrosion resistance, and biocompatibility (Disegi and Wyss, 1989). Torsional properties of stainless steel screws are different from titanium screws. Stainless steel bone
screws are easier to handle because the surgeon can feel the onset of plastic deformation
and this provides adequate prewarning to avoid
overtorquing the screw while titanium screws
break suddenly (Disegi and Eschbach, 2000).
Tissue reaction adjacent to the screws shows fibrous tissue capsules (Lemons et al, 1976). Stability is ensured by mechanical retention.
The advantages of miniscrews are the ease of
insertion and removal. Both procedures can be
performed by orthodontists, without any need
of referrals, at any time during orthodontic therapy. Loading can be initiated immediately after
insertion, thus shortening treatment time. Other advantages over osseointegrated implants include
the availability of sites and the reduced cost.
The clinical possibilities offered by this type of
Orthodontics Vol 1, No 1, 2004
anchorage make miniscrews a very interesting
and fascinating therapeutic option that is well
accepted by patients, and in particular by adults
who wish reduced treatment times.
As regards severe periodontally involved or
pre-prosthetic patients, it is clear that this method
represents one of the best anchorage options
that can be offered by the clinician for reinforcing anchorage.
CONCLUSIONS
Based on our experience from this study, the
new miniscrews presented here have shown an
excellent efficacy as an extradental anchorage
in several clinical situations where conventional anchorage can not be applied. They represent a valuable alternative to osseointegrated
implants, onplants, miniplates, zygoma wires
and anchors. Neither discomfort, nor side effects have been reported. Therefore, the orthodontist has a new efficient and safe tool for the
control and reinforcement of the anchorage for
different types of tooth movements – without relying on patient compliance.
11
Fortini et al., Miniscrews for Extradental Anchorage
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