Download Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity

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10.5005/jp-journals-10021-1161
CASE REPORT
Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region
Skeletal Anchorage using Mini-implants in the
Maxillary Tuberosity Region
1
Sundaram Venkateswaran, 2Ashwin Mathew George, 3MK Anand
4
VR Shobbana Devi, 5Sheelkumar R Vora, 6NR Krishnaswamy
ABSTRACT
Anchorage conservation has always been a challenge in orthodontics especially in cases requiring group movement of teeth. The drawbacks
of conventional anchorage conservation methods like headgears and intermaxillary elastics have been overcome with the advent of skeletal
anchorage. Mini-implants which have been proved successful in several intraoral locations for anchorage, can also be successfully placed in
the maxillary tuberosity region. However, this site is not commonly used due to the fact that the density of bone in this region is comparably
low. But with proper case selection and application of sound biomechanical principles, successful treatment results can be achieved with
mini-implants placed in this location.
The case reports discussed in the article demonstrates the ability of mini-implants when placed in the maxillary tuberosity for en masse
distalization of the entire maxillary dentition, its advantages and biomechanics.
Keywords: Skeletal anchorage, Mini-implants, Maxillary tuberosity, En masse retraction.
How to cite this article: Venkateswaran S, George AM, Anand MK, Devi VRS, Vora SR, Krishnaswamy NR. Skeletal Anchorage using
Mini-implants in the Maxillary Tuberosity Region. J Ind Orthod Soc 2013;47(4):217-224.
INTRODUCTION
It is a well-established fact that mini-implants have proven itself
as a source of absolute anchorage1,2 and it’s benefits are
innumerable, especially in biomechanically challenging cases.35
Several sites have been proposed for the placement of
miniscrew or microscrew implants. Most frequently
recommended sites are the midpalatine area, the alveolar bone
between the maxillary second premolars and first molars, and
the mandibular first and second molars6 and several case reports
with mini-implants placed at these anatomical sites have been
successfully reported and published. A relatively new protocol
of placing mini-implants in the maxillary tuberosity have
kindled interest in the clinician, because of its many biological
and biomechanical advantages.7,8 We should also take into
consideration or account the varying degrees of difficulty and
limitations that could be encountered while using tuberosity
implants.
The following case reports describe the use of maxillary
tuberosity implants for en masse retraction of the upper arch
on adult patients, with facial convexity, gummy smile line and
a deep bite. It also describes the optimal biomechanics while
using tuberosity implants to bring about desired hard and soft
tissue esthetics.
CASE REPORTS
Case 1
An 18-year-old female patient reported with the chief complaint
of lip protrusion, gummy smile and spacing between anterior
teeth. On extraoral examination, she had a convex profile,
Fig. 1A: Pretreatment extraoral photographs
1
2
3
4
5
Former Professor, Professor, Reader, Lecturer, Former
Postgraduate Student, 6Professor and Head
1
Department of Orthodontics, Chettinad Dental College and Research
Institute, Chennai, Tamil Nadu, India
2-6
Department of Orthodontics, Ragas Dental College and Hospital
Chennai, Tamil Nadu, India
Corresponding Author: Sundaram Venkateswaran, Former Professor
Department of Orthodontics, 2/102 East Coast Road, Uthandi, Chennai600119, Tamil Nadu, India, e-mail: [email protected]
Received on: 16/1/13
Accepted after Revision: 9/3/13
Fig. 1B: Pretreatment intraoral photographs
The Journal of Indian Orthodontic Society, October-December 2013;47(4):217-224
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Sundaram Venkateswaran et al
Fig. 1C: Pretreatment-lateral cephalogram and OPG
posterior divergence and lip incompetence. The interlabial gap
was 6 mm at rest and, on smiling, there was 100% incisal
showing with a 4 mm of gingival display. The nasolabial angle
was acute, mentolabial sulcus was deep, the mandibular plane
angle was reduced and the lower facial height was average
(Fig. 1A). There were no signs and symptoms of
temporomandibular joint problems.
Intraoral examination revealed a Class II molar relation on
the left side and an end on molar relation on the right side. The
overjet and overbite were 7 mm each. The upper and lower
incisors were proclined labially. The spacing in the upper arch
was 2.5 mm and, in the lower arch, it was 7 mm. The upper
midline was coincident with the facial midline, whereas the
lower midline was shifted to the left side by about 3.5 mm
(Fig. 1B). All the third molars were erupted.
The cephalometric analyses revealed a Class II skeletal
pattern (ANB-6°), reduced mandibular plane angle (Go GnSN-25°), proclined upper incisors (upper 1 to SN-113°) and
proclined lower incisors (IMPA-102°) (Fig. 1C).
Treatment Objectives
approximately around 150 to 350 Hounsfield units. The bone
in this region is typically of poor quality; the cortical layer is
thin and irregular and usually merges into the cancellous bone
with irregular distribution of lamellae. The patient was also
informed of a possible failure of mini-implant, in which case it
could to be repositioned.
Apart from these inherent disadvantages, the most potent
advantage of the maxillary tuberosity implants are that the
possibility of root contact during placement of mini-implant is
very much reduced due to its anatomical location and there is
negligible interference from the roots during tooth movement.
Treatment Progress
The upper third molars were extracted at the start of treatment in
an atraumatic manner taking care to maintain the integrity of the
buccal cortical plate to facilitate successful mini-implant
placement. Upper and lower arches were strapped up with 022
Roth prescription brackets. A transpalatal arch was fixed in the
upper arch to maintain the arch form and arch width and to
prevent rotations during retraction of the upper arch. About
5 months after the extraction of the third molars, coinciding
with the end of alignment and leveling phase, mini-implants
of 1.4 mm diameter and 10 mm length were placed on either
side in the tuberosity region.
Retraction was started immediately with 250 gm using
nickel-titanium closed coil springs extended between the
implants and the hooks crimped distal to the canines on a 0.019
× 0.025 inch stainless steel upper archwire (Figs 2A to C). For
en masse distalization of maxillary arch using sliding
The primary objective of treatment was to correct the lip
protrusion and gummy smile by intruding and retracting the
upper incisors. The other objectives were to correct the molar
relation, increased overjet and overbite, midline shift in the
lower arch and close the spaces in the upper and lower arches.
Treatment Options
The spaces present in the lower arch were sufficient for
correction of the tooth size arch length discrepancy, whereas
the spaces present in the upper arch were found to be
inadequate. The spaces needed for retraction of upper incisors
could be obtained by extraction of two upper premolars.
However, the disadvantage of extracting premolars in this case
is that the gummy smile could get worsened with further
increase in overbite. Therefore, it would be preferable to plan
for gaining space in the upper arch without premolar extraction.
The novel option of third molars extraction and retraction of
the entire upper arch using mini-implant anchorage placed in
the tuberosity region was suggested and the patient accepted
this treatment plan. It is an important criterion to assess the
bone with regard to its quantity and density before the decision
is made to place the mini-implant. It is a well-established fact
that the maxillary tuberosity region belongs to the D4 category
as classified by Lekhom and Zarb possessing a density of
218
Fig. 2A: In treatment X-rays (implant placement)
Fig. 2B: Diagrammatic representation of en masse distalization using
tuberosity implants
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Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region
Fig. 2C: Intreatment intraoral photographs
mechanics, it is preferable to solder or crimp the retraction
hooks distal to canine. This is advantageous over hooks attached
mesial to canines in that a relatively straight path of force
application can be obtained. A hook placed mesial to canine
could also cause interference with the soft tissue overlying the
canine prominence and thereby dissipate some of the force
generated by the coil spring. Also the position of hook relatively
closer to the center of resistance of maxillary dentition (near
the root apex of the maxillary first premolars) reduces the
tendency for rotation of the occlusal plane. An accentuated
reverse curve of Spee was added to the upper arch wire for
correction of deep overbite.
Treatment Results
The primary objective of correction of lip protrusion and
excessive gingival display on smile was achieved by intrusion
of the upper incisors and retraction of the entire upper arch
(Fig. 3A). The lower incisors were retracted using the spaces
available between them. The molar relationship was corrected
to Class I by distal movement of the upper arch (Fig. 3B). The
Fig. 3A: Post-treatment extraoral photographs
Table 1: Cephalometric data
Skeletal
SNA
N perpendicular to point A
SNB
N perpendicular to Pog
ANB
Sn to Go-Gn
Maxillary dentition
U1-NA
U1-SN
U6 to Ptv
Mandibular dentition
L1-NB
IMPA
L1-A Pog
Soft tissue
S line to upper lip
S line to lower lip
Lower lip—E plane
Nasolabial angle
Upper lip angle
Overjet
Overbite
Pretreatment
Post-treatment
83°
4 mm
77°
1 mm
6°
28°
81°
2 mm
76°
–1 mm
5°
30°
26°
113°
21.5 mm
20°
108°
18 mm
35°
102°
29°
27°
95°
22°
5 mm
6 mm
5 mm
85°
40°
7 mm
7 mm
3 mm
3 mm
2 mm
92°
26°
3 mm
3 mm
overjet and overbite were reduced to 3 mm each and the
duration of entire treatment took around 18 months.
Comparison between pre and post-treatment cephalogram
showed marked improvement in the facial balance (Fig. 4A)
and the cephalometric superimpositions showed bodily distalization of maxillary molars (Fig. 4B) as also seen in Table 1.
Post-treatment OPG revealed good root parallelism between
teeth (Fig. 5).
Fig. 3B: Post-treatment intraoral photographs
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Sundaram Venkateswaran et al
Case 2
Fig. 4A: Comparison between pretreatment and
post-treatment cephalogram
Fig. 4B: Superimpositions: blue—pretreatment, red—post-treatment
Fig. 5: Post-treatment OPG
An 18-year-old female presented with the chief complaint of
proclined upper incisors, protrusive lips and spacing in the
lower arch (Figs 6A to C). She reported to be having undergone
orthodontic treatment with fixed appliances 2 years earlier,
following upper and lower first premolar extractions. However,
the patient expressed her dissatisfaction with the treatment
results, especially with regard to the lip incompetence and
protrusive profile.
Clinical examination showed a convex profile, posterior
divergence, incompetent lips with incisal exposure of 5 mm at
rest, average nasolabial and mandibular plane angles, a deep
labiomental sulcus, and a normal lower facial height. Intraoral
examination revealed Class II molar and Class I canine
relationships on the left side and end-on molar and canine
relationships on the right side, with an overjet of 4.5 mm and
an overbite of 4 mm. All third molars were erupted. The patient
had mesially tipped upper posterior teeth and proclined upper
and lower incisors, with residual extraction spaces of 3 mm in
the lower left quadrant and 1 mm in the lower right quadrant.
There were no signs of TMJ problems. Cephalometric analysis
indicated a Class II skeletal pattern.
The treatment objectives were to reduce the lip protrusion
and improve the soft tissue esthetics, establish Class I molar
and canine relationships, upright the mesially tipped upper
premolars and molars, and close the residual extraction spaces
in the lower arch. These objectives could be achieved by
retracting the upper and lower anterior teeth, using one of three
options. The first option was to extract the upper and lower
first molars. But, the disadvantage of this plan was that the
first molar plays an important role in mastication and hence
could not be sacrificed. The second option was to extract all
four second molars; in this case, however, the positions of the
third molars were unfavorable to replace the second molars.
The third option was to extract all the third molars and retract
the entire maxillary and mandibular dentition into the extraction
spaces, using mini-implant anchorage placed in the tuberosity
and the retromolar regions. This was the treatment option which
was finally accepted by the patient.
Roth prescription 0.022" brackets were bonded in both
arches. After 2 months of leveling and alignment, the four third
molars were extracted. Four months later, titanium mini-
Fig. 6A: Pretreatment extraoral photographs
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Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region
Fig. 6B: Pretreatment intraoral photographs
Fig. 6C: Pretreatment lateral cephalogram and OPG. Note: Reproduced
after taking permission from JCO (J Clin Orthod 2011;45:268-73)
implants (AbsoAnchor, 1.4 mm diameter × 10 mm) were
inserted into the third molar extraction spaces in the maxillary
tuberosity and mandibular retromolar areas, as advocated by
Sung et al. The screws were placed about 6 mm apical to the
crest of the alveolar bone, so that their lines of force passed
through the centers of resistance of the first and second molars.
Retraction was initiated immediately using nickel titanium
closed-coil springs (12 mm, 200 gm) on both sides of the upper
and lower arches, extending from the mini-implant to a
retraction hook soldered distal to the canine in each quadrant
(Fig. 7A). Similar forces applied in this manner have been
shown to be adequate for en masse movement of the maxillary
or mandibular arches.
Retraction of the entire maxillary and mandibular dentition
was completed in 12 months, with a total duration for the completion of the entire treatment being 20 months (Figs 7B and C).
Post-treatment facial photographs showed a remarkable
improvement in the lip profile and facial esthetics resulting
from the retraction of the anterior teeth (Fig. 8A). Class I molar
and canine relationships were established, with a 2 mm overjet
and a 3 mm overbite. Good intercuspation was also observed
in the maxillary and mandibular distalized segment (Figs 8B
and C). Cephalometric superimposition showed that the
maxillary molars were distalized about 5 mm at the crown level
and 3 mm at the apex level; the maxillary incisors were retracted
6 mm, and the mandibular incisors 4 mm (Fig. 9). The upper
lip moved backward about 3 mm, and the lower lip about
4 mm, with both in the normal range relative to the
Fig. 7A: Miniscrews placed bilaterally in the maxillary tuberosity region and retraction hook placed distal to the maxillary canine
Fig. 7B: Intreatment intraoral photographs—occlusal views
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Sundaram Venkateswaran et al
Fig. 7C: Intreatment lateral cephalogram and OPG
Fig. 8C: Post-treatment lateral cephalogram and OPG
Table 2: Cephalometric data
SNA
SNB
ANB
SN-GoMe
U1-SN
IMPA
Wits appraisal
Upper lip to E-line
Lower lip to E-line
Nasolabial angle
Pretreatment
Post-treatment
Difference
83.0
77.0°
6.0°
32.0°
110.0°
102.0°
2.0 mm
–1.5 mm
4.0 mm
92.0°
81.5°
76.0°
5.5°
32.5°
100.0°
98.0°
1.0 mm
–4.5 mm
0.0 mm
100.0°
1.5°
1.0°
0.5°
0.5°
10.0°
4.0°
1.0 mm
3.0 mm
4.0 mm
8.0°
Fig. 9: Superimpositions (blue—pretreatment; red—post-treatment)
DISCUSSION
E-line (Table 2). The interlabial gap and incisal display at rest
were eliminated. Appropriate nasolabial, labiomental sulcus
and interincisal angles were achieved.
It took only 12 months to achieve a Class I molar
relationship, indicating that the force system and mechanics
using mini-implants placed in the tuberosity region, in this
patient were efficient, particularly since the maxillary molars
were mesially tipped at the beginning of treatment.
Fig. 8A: Post-treatment extraoral photographs
According to Chen et al, the critical factor for success of
orthodontic mini-implants is the initial mechanical stability
depending upon the bone quality and quantity.9 Crismani et al
observed that placing a mini-implant without loading it
immediately could also cause instability.10 In these (two)
patients, mini-implant were placed and retraction started only
when the arches were completely leveled and aligned thereby
preventing any sort of arch wire binding during retraction. Miniimplants were placed in these patients 5 months after extraction
of the third molars, coinciding with the end of the leveling and
alignment phase. It takes about 4 to 5 months for an extraction
socket to remodel enough to become viable for placement of a
mini-implant. Placing a screw too soon will lead to instability
due to inadequate bone support.11 Sung et al recommend using
a relatively long mini-implant with a diameter of 1.3 to 1.5
mm in areas with a predominance of cancellous bone and low
bone density,2 such as the maxillary tuberosity.12 Lee and Baek
Fig. 8B: Post-treatment intraoral photographs
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reported that orthodontic mini-implants with a diameter of 1.5
mm or more can cause greater microdamage to the cortical
bone, with a negative effect on bone remodeling and miniimplant stability.13 Therefore, we chose a mini-implant with a
diameter of 1.4 mm and a length of 10 mm. We did not
encounter any failures or fractures during placement or removal.
Being an intraoral, extradental device, mini-implants are
stationary in nature and this in itself should make one question
the considerable variations involved when compared to
anchorage using the dentition. The variation in the height of
placement of mini-implants, in relation to the center of
resistance of the dentition as a whole and, on an individual
tooth, is certain to bring about changes in the biomechanical
principles. The force system consists of multibanded
attachments on all the teeth, including the second molars,
adequately leveled and stabilized on a 19 × 25 stainless steel
wire. The force used for retraction would be preferably a nickeltitanium closed coil spring of 200 to 300 gm, extending between
the two mini-implants placed in the tuberosity regions and
retraction hooks placed on a 0.019 × 0.25 inch stainless steel
archwire distal to the canines.
In any geometry of force vectors, it is important that
biomechanical aspects are considered in all the three planes:
The horizontal, transverse and vertical planes.
• Placement and location of tuberosity implants:
Accessibility to place implants in the tuberosity region has
always been challenging due to anatomical limitations. In
our clinical experience, it is advantageous to use a contraangle driver and a mandrill available in the market.
The absence of roots in this region notwithstanding, optimal
site selection is essential. The implants may be placed at an
angulation of 20o to 40o to the occlusal plane in a vertically
directed manner. The placement should allow for sufficient
distal movement of the entire upper arch.
• Biomechanical considerations in the horizontal plane: For
en masse distalization of maxillary arch using sliding
mechanics, retraction hooks are soldered or crimped distal
to canine and it has following advantages over hooks
attached mesial to canines.
1. A straight path of force application—a hook placed
mesial to canine would cause interference with the soft
tissue overlying the canine prominence and thereby
dissipation of some of the force generated by the coil
spring.
2. The position of hook relatively closer to the center of
resistance of maxillary dentition (near the root apex of
the maxillary first premolars).
• Biomechanical considerations in the transverse plane: In
the transverse plane, the distal driving force that passes
from the miniscrew implant to the archwire can causes arch
expansion and flaring resulting in buccal crown torque.
However, this adverse effect could be overcome by using
a transpalatal arch.
•
Biomechanical considerations in the vertical plane: In the
vertical plane, the force system can cause extrusion of
incisors and clockwise rotation of the occlusal plane, which
can be countered by giving a gentle reverse curve of Spee
in the arch wire. The location of the mini-implant in the
vertical plane should be at the level of the molar tubes in
order to minimize undesirable vertical force vector.
Advantages of en masse Retraction of Entire
Maxillary Arch using Mini-implant Anchorage Over
Molar Distalization followed by Anterior Retraction
without Mini-implant Anchorage
The most appropriate advantage of mini-implants placed in
the tuberosity region is that molar distalization takes place
simultaneously along with anterior retraction and some of the
many advantages are listed below:
• Single stage of retraction
• No molar anchorage loss
• Bodily movement
• No distal tipping of molars
• Incisors and premolars not proclined
• Better patient comfort than other distalizing appliances
• If ideally placed, reduced chance of mini-implant for root
contact
• No interference with roots or any other anatomic structure
during tooth movement compared to mini-implants between
premolar and molars or between molars
• No need to reposition mini-implants as needed during molar
distalization or en masse retraction using mini-implants
placed in other locations
• Reduced treatment time.
CONCLUSION
Although the results achieved with mini-implant in the
maxillary tuberosity region could lead to a whole new realm
of orthodontic treatment options, a proper understanding of
the anatomy, implant selection and the force application
principles should be gained by the practitioner. The type of
implant selected and the vector of force application differs
considerably when using tuberosity implants, when compared
to mini-implants in other conventional locations and a thorough
evaluation must be carried out before making the final decision.
As Winston Churchill proclaimed ‘True genius resides in the
capacity for evaluation of uncertain, hazardous and conflicting
information.’
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