Download Uprighting impacted mandibular permanent second molars with the

Uprighting impacted mandibular permanent second molars with
the tip-back cantilever technique－cases report
PO-SUNG FU1
CHERN-HSIUNG LAI2
YI-MIN WU1
CHING-FANG TSAI3
TA-KO HUANG4
JIN-HUANG ZENG5
WEN-CHENG CHEN4
CHUN-CHENG HUNG3
1
Department of Family Dentistry, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan,
ROC.
2
Research Center for Anaerobic and Oral Microbiology, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
3
Department of Prosthodontics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan,
ROC.
4
Faculty of Dentistry, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
5
Private practice, Kaohsiung, Taiwan, ROC.
Very severe inclination of the mandibular second molar is a difficult challenge for dentists. Severe
impaction of the mandibular second molars often leads to their extraction to avoid potential damage to
the root of the first molars and provide space for the eruption of the third molars. An ideal treatment is
orthodontic uprighting with or without surgical uncovering, and one of the effective appliances for molar
uprighting is the tip-back cantilever technique. This paper presents the successful tip-back sectional
archwire orthodontic treatment of impacted mandibular second molars. （J Dent Sci, 3(3)：174-180 , 2008）
Key words: molar impaction, molar uprighting, tip-back cantilever, pole arm.
Impaction of the second permanent molars is not
common, and usually occurs in the mandibular arch
with a incidence of about 0.3%1-3. The etiology of
impaction may be related to an insufficient arch length,
excessive tooth size, or excessive axial inclination1,4,5.
In the normal growth and development process, the
second permanent molar tooth buds are distal to the
first permanent molar and have a mesial inclination.
This inclination is usually self-correcting as the
resorption of the anterior border of the mandibular
ramus occurs and the first permanent molar migrates
into the leeway space for angular adjustment and
eruption. However, this correction does not always
happen, and the second molar can become impacted.
Received: June 7, 2008
Accepted: August 19, 2008
Reprint requests to: Dr. Chun-Cheng Hung, Department of Prosthodontics, Kaohsiung Medical University Hospital,
No.100, Tzyou 1st Road, Kaohsiung, Taiwan 80756,
ROC.
174
Extraction of impacted second molars has been
suggested to make room for unerupted third molars.
Unfortunately, there is no guarantee that the third
molar will erupt in an upright position6,7.
Severe impaction of lower second/third molars
often leads to difficulty in cleaning and necessitates
extraction in order to avoid potential damage to the
roots of first/second molars. The management of
impacted molars used to be a complicated problem.
Separating wires and threaded pins have been
advocated8-10. Other clinicians have soldered helical
loop springs to the distal end of a lingual arch or
constructed loop springs from the distal end of labial
arch wires11-16.
Surgical approaches for impacted second molars
include surgical extraction to allow eruption of the
third molars, surgical uprighting of the impacted
second molars, surgical uncovering with orthodontically assisted eruption and transplantation of the
third molars to the second molar sockets17-23. However,
orthodontic uprighting might be a better alternative
J Dent Sci 2008‧Vol 3‧No 3
Molar uprighting with a tip-back cantilever
with a lower risk to the teeth. With the recent
development of miniscrews, its clinical application
has became various and predictable24-27.
While it is recognized that any of the uprighting
techniques previously mentioned can possibly be
applied in a given situation, the technique should be
determined by factors such as the severity of the molar
impaction, the accessibility of the coronal surface of
the impacted molar, the desired type of movement, the
undesirable side effects, as well as the simplicity and
convenience of the uprighting mechanics4-6.
The proper time to treat impacted second molars
is when the patient is 11~14 years old, while second
molar root formation is still incomplete and before the
third molars complete their development in close
proximity to the second molars4,5. In this study, cases
of successfully uprighting impacted molars using a
0.016 x 0.022-inch titanium molybdenum alloy (TMA)
tip-back sectional archwire, which we termed the
“pole arm”, are presented.
MATERIALS AND METHODS
Biomechanical considerations
The pole arm cantilever produces effects on the
tooth in 3 dimensions, principally in the mesiodistal
(distal crown tipping) and vertical directions (molar
extrusion). The force acting on the impacted molar is
of the same magnitude as, but of opposite direction to,
the force acting on the main wire. Therefore, the
intrusive force is on the anterior segment and the
extrusive force on the impacted molar, and the couple
distally tips the impacted molar (Figure 1).
Figure 1. Force delivered to the pole arm and force as well as moment acting on the
impacted molar. Fa, active force acting on the pole arm; Fr, reciprocal force acting on the
impacted molar; Frv, vertical (extrusive) component of Fr; Frh, horizontal (distal) component
of Fr; M, moment acting on the impacted molar.
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P.S. Fu, C.H. Lai, Y.M. Wu, et al.
Appliance design
The pole arm appliance is fabricated at chairside
with 0.016 x 0.022-inch TMA wire (Figure 2). A
periapical or panoramic radiograph should be taken of
the impacted molar before and after applying the
technique to confirm the severity of the impaction and
the position of the uprighting spring of the inserted
pole arm. Before insertion of the pole arm appliance,
we recommend applying local anesthesia to the buccal
and lingual gingiva which are between the impacted
molar and adjacent tooth. The buccal arm (D) is
inserted from the lingual side, passing beneath the
contact area between the adjacent tooth and impacted
molar and is pulled out buccally. Activation of the
uprighting spring is accomplished by bending the
distal contact between the first molar tube and buccal
arm (D), when the buccal arm is ligated by wire to the
anchor teeth. As the contact works towards restoring
its original form, it produces a distal uprighting force
against the mesial surface of the impacted molar.
Finally, a lingual rest (A) is fixed with glass-ionomer
or composite resin on the occlusal surface close to the
lingual groove of the first molar to avoid it sliding out
of position (Figures 2, 3).
Moving the pole arm gingival activates the
appliance. The pole arm can be reactivated in the
mouth by lifting, gently squeezing the buccal arm
occlusally, and ligating the buccal arm again. After the
initial adjustment at 3~4 weeks, adjustments every 6
weeks seem to be adequate.
CASE PRESENTATIONS
Case 1
A 13-year-old male presented with impaction of
the mandibular left second molar. The patient had a
Class I, bimaxillary protrusive malocclusion. The
mandibular left second molar was tipped mesially and
was obliquely impacted under the distal surface of the
first molar. A panoramic radiograph revealed the
presence of all permanent teeth and a severe mesial
inclination of the mandibular left second molar and
developing third molars (Figure 4). The root formation
of the impacted molar was still incomplete.
The treatment plan was for extraction of four first
premolars and a germectomy of the mandibular left
third molar. After initial leveling and alignment, we
inserted the 0.016 x 0.022-inch TMA pole arm
uprighting spring into the impacted mandibular
second molar and ligated it mesially to the anchor
teeth. Ten weeks following insertion of the pole arm,
the impacted mandibular second molar had been
uprighted to some degree, and a bracket was bonded
to it for further alignment. Posttreatment intraoral
photographs and a panoramic radiograph (Figure 5)
show the corrected inclination of the impacted
mandibular left second molar with proper interdigitation. A Hawley retainer and a lingual fixed
retainer were respectively used as retentive devices for
the maxilla and mandible.
Case 2
Figure 2. Pole arm uprighting spring. A, Lingual rest bending; B,
occlusogingival bending with length according to the impaction
depth; C, buccolingual bending with length according to the
buccolingual width of the impacted molar; D, mesial extension
following the buccal curve of the anchor teeth.
176
An 18-year-old female presented with Class I,
mild crowding and bilateral impactions of the
mandibular second molars. A panoramic radiograph
revealed that both mandibular second molars were
obliquely impacted under the distal contour of the first
molars. The root formation of the impacted second
molars was complete. The mandibular third molar
buds were located on top of the second molar distal
roots (Figure 6).
The treatment plan was a germectomy of the
mandibular third molars. After initial leveling and
alignment, the pole arm uprighting springs were
placed into both impacted mandibular second molars.
J Dent Sci 2008‧Vol 3‧No 3
Molar uprighting with a tip-back cantilever
Figure 3. Intraoral photographs and periapical radiograph at insertion of pole arm.
Figure 4. Pretreatment photograph and panoramic radiograph showing impacted mandibular left
second molar.
Figure 5. Posttreatment photographs and panoramic radiograph showing corrected inclination of the mandibular left
second molar.
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P.S. Fu, C.H. Lai, Y.M. Wu, et al.
Figure 6. Pretreatment photograph and panoramic radiograph showing bilaterally impacted mandibular second molars.
At 8 (for the right side) and 10 weeks (for the left side)
following insertion of the pole arms, the impacted
mandibular second molars had been uprighted to some
degree, and brackets were bonded to them for further
alignment. Posttreatment intraoral photographs and a
panoramic radiograph (Figure 7) show the corrected
inclination of the impacted lower molars with proper
interdigitation and root parallelism. A Hawley retainer
and a lingual fixed retainer were respectively used as
retentive devices for the maxilla and mandible.
DISCUSSION
The impaction of molars is difficult to prevent
and detect early due to its multifactorial etiologies.
Apart from the well-known etiologies, probably
iatrogenic factors of second molar impaction are
incorrectly fitted bands cemented onto the first molars,
prevention of mesial drift of the first molar caused by
a lip bumper or lingual arch therapy, and excessive
tip-back of the first molar during previous orthodontic
treatment4,28-30.
Figure 7. Posttreatment photographs and panoramic radiograph showing corrected inclination of the mandibular left
second molar.
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Molar uprighting with a tip-back cantilever
Before uprighting the impacted second molar, the
need for third molar extraction must be well evaluated.
Usually, the third molar can hinder the distal
movement of the impacted second molar, implying the
need for extraction. Nevertheless, if the root formation
of the impacted second molar is incomplete and the
degree of impaction is mild, extraction of the third
molar is not so urgent until otherwise deemed
necessary4,31,32.
The biomechanics of the pole arm are similar to
those of the pole vault. The fulcrum is on the distal
contact of the first molar tube and the pole arm, while
the activation force is on the canine and first/second
premolar wire fixation and is opposed by the mesial
surface of the impacted molar. As the tooth is being
uprighted, a space develops between the uprighting
molar and the tooth anterior to it. Crowns of the
impacted molar and its front molar are properly
ligated together with a figure 8 steel ligature or
elastometric chain. Roots of the impacted molar are
brought mesially without further reciprocal distal
movement of the crowns. In additions, the impacted
molar is usually infraoccluded and requires an
eruptive force to bring the teeth into occlusion with
their antagonist. The tooth should be banded/
bracketed to accomplish space closure, buccolingual
correction, and occlusion detailing.
There may be slight occlusal interference
between the impacted molar and its antagonist or the
wire during the uprighting process, but this problem
rapidly resolves itself. The pole arm uprighting spring
elevates the mesial marginal ridge of the impacted
molar to the functional occlusal plane. However, if
vertical development of the impacted molar is
impeded by its antagonist, then the overerupted
antagonist must be intruded.
Since treatment planning in individual cases
varies greatly, each malocclusion and associated
periodontal involvement should be evaluated on an
individual case basis. The selection of an appliance
should be based on a correct evaluation of the
impacted molars and their adjacent teeth as well as
their antagonists. The innovation of the pole arm
uprighting spring eliminates the need for early
bonding or a banding apparatus on the impacted
molars, which is difficult and may cause occlusal
interference. Furthermore, no demand for surgical
exposure of adequate crown surfaces for bonding or
banding has increased patient acceptance.
This article presents an uprighting technique on
J Dent Sci 2008‧Vol 3‧No 3
impacted second molars that can be used equally
effectively on impacted first or third molars. It has the
following advantages: (1) simple to construct, (2)
inexpensive, (3) requires no considerable patient
cooperation, (4) is easily activated, (5) provides rapid
treatment, and (6) does not rotate molars (as often
occurs with finger springs).
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