Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars

http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

A NOVEL TREATMENT APPROACH FOR EXTRUDED MAXILLARY MOLARS

Julia Elodie Vlachojannis1*, Margherita Santoro2
1. Dr. Med. Dent., M. Sc., Lofou 4A Ekali, Athens 14578, Greece.
2. D.D.S., M.A., Division of Orthodontics, Columbia University, School of Dental and Oral Surgery, 635 W 168th St, P&S Box 20, New York,
NY 10032, US.

Abstract

Two approaches are currently used to correct overerupted/extruded posterior teeth, the
“prosthodontic” and the “orthodontic” one. This report presents a novel orthodontic approach for
selective molar intrusion.
In two females (26 and 20 years), a modified transpalatal arch (TPA, equivalent to a couple with
a 30 g net force) was used to move the tooth bodily. A 50 g force was applied to the overerupted
maxillary second molar by means of a short length elastomeric chain from the helix to the palatal
sheath and replaced every three weeks. Sufficient intrusion of the maxillary second molar was
obtained within two months.
For intrusion of a single tooth, a modified TPA together with a short length elastomeric chain is
a non-invasive and cost-effective alternative to traditional edgewise mechanics, temporary
anchorage devices, or removable appliances.
Case report (J Int Dent Med Res 2011; 4: (2), pp. 77-86)

Keywords: Case report, unopposed molar, selective molar intrusion, modified transpalatal arch
appliance.

Received date: 14 May 2011 Accept date: 08 August 2011

Introduction prior endodontic treatment might be necessary.

The orthodontic approach aims to intrude
Unopposed molar teeth are frequently the tooth; however, due to the great root surface
subject to overeruption, and are believed to be area of molars, the resistance to intrusion forces
related to impaired masticatory function and to is high. A good anchorage system is necessary
development of temporomandibular disorders.1 to counteract the unwanted effect of extrusion on
In a longitudinal study over 10 years with the adjacent tooth. This report presents two
12 adults, Christou and Kiliaridis found that cases successfully treated with an orthodontic
unopposed molars showed more vertical approach using a modified transpalatal arch
displacement (0.8mm) than opposed molars (TPA) for selective molar intrusion.
(0.4mm). They concluded that the observed
changes were either the result of late growth Biomechanical Background
remodeling or a consequence of altered dental Intrusion is described as an apical
equilibrium following antagonist tooth loss.2 movement in the direction of its long axis into the
Two approaches are currently in use to alveolus in the same direction that forces are
correct overerupted (extruded) posterior teeth. imposed by physiologic occlusion by means of
The prosthodontic approach reduces the vertical positive tension and positive pressure applied to
height of the crown of the extruded tooth; the contents of the periodontal apparatus.
however, depending on the amount of extrusion The periodontal ligament system is most
resistant to orthodontic forces applied in vertical
direction towards the apex of the root due to the
*Corresponding author: unique combination of simultaneous hydraulic
Julia Elodie Vlachojannis, Dr. Med. Dent., M. Sc.
Lofou 4A Ekali, Athens 14578, Greece pressure and fibrous tension applied to the
periodontal ligaments. Very light continuously
E-mail: jvlachojannis@gmail.com applied forces are most effective. They result in
small increases in fiber tension without elevating
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 Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars
http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

hydraulic pressures beyond the physiologic level orthodontic forces are the deflection of wires, the
and thus preventing the compressed tissues to activation of springs and auxiliaries such as
be traumatized.3 elastics.8
Positive continued tension stretches the An intrusive force on the molars’ buccal
periodontal ligaments in a semi-elastic way. tube creates a moment tipping the crown buccaly
Small forces are required to maintain the (Figure 1).
extension until the fibers fatigue.3 Positive
pressure on the bone results in resorption. A
continuous intrusive light force of 0.5N was also
associated with significantly reduced basal blood
flow in the pulp in 13 incisors (p<0.05).4 After
resorption of the bone, the tooth will move into
the space closest to the tooth. The whole cycle is
then repeated several times during orthodontic
treatment.3
It is most important to know the center of
resistance of the tooth to be intruded. This center
is dependent on root length and morphology,
number of roots and level of alveolar bone
support. This center is usually located at about
one-fourth to one-third the distance from the
cemento-enamel junction to the root apex.5 On
upper incisors the center of resistance is located
at 0.24 times the root length measured apically to
the level of alveolar crest.6
Due to the delicate balance of the
periodontal ligament fiber systems, the force Figure 1. The intrusive force on the molar
applied needs to be well chosen, keeping in mind creates a moment tipping the crown buccaly.
that these calculations are only approximate in
individual cases. A force is equal to mass times An orthodontic force of higher magnitude
acceleration (F = ma) and is measured either in will be required on molars than on incisors
Newton or clinically in gram x millimeter (mm). If because of the larger area of periodontal
the force passes through the center of resistance attachment. There is a general agreement that
the tooth translates without tipping (so-called this force should not exceed 100 gm.9 Forces in
bodily movement). The further away the point of conventional orthodontics are transmitted
force application is from the center of resistance, through the archwire. A very stiff archwire has a
the greater are the rotational and the linear steep load-deflection curve with a high initial
moments; the rotation moment is to be force that decays rapidly even with small tooth
determined by multiplying the magnitude of force movements. The study by Kohno and co-workers
by the perpendicular distance of the line of action suggests that molar movements induced by light
to the center of resistance. The ratio between the forces with modern clinical appliances are close
net moment and net force on a tooth (M/F ratio) to physiological movements.5
with reference to the center of resistance Intrusion of a tooth will result in unwanted
determines the center of rotation.7 effects: (i) extrusion of the adjacent tooth, often
An M/F ratio of 10:1 generally produces seen when engaging an archwire while brackets
sole translation with the center of rotation located height differs. This is associated with clockwise
at infinity.8 rotation of the mandible and an anterior open bite
The force presents magnitude (size) and when the extrusion takes place in the molar area
direction and is described as a vector with a line (Figure 2);9 (ii) molar transversal width expansion
of action and point of application. The magnitude when the intrusion is caused by a high pull
of the moment force has 2 variables: the headgear. This can be counteracted by
magnitude of the force and the distance from the constricting the inner bow of the high pull
center of resistance. Common ways of obtaining headgear or by using a TPA.9

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 Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars
http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

adjusted by cutting it in half and a helix was bent

parallel to the roof of the palate. The removable
palatal bar was then adjusted to a 60-90° angle
so that the helix laid at the height of the center of
resistance of the extruded molar. The helix was
kept open facing the gingiva, just enough to
activate the appliance by slipping through a
power-chain or other elastomeric auxiliaries of
choice. In combination with a main guiding
stainless steel archwire 0.022′′ or 0.022” x 0.028”
(which is run through the buccal tube) a balanced
force system was achieved to create an
equilibrium between buccal and palatal root
torque (Figure 3).
Figure 2. This step bend between the two
terminal molars produces extrusion and lingual
tipping of the first maxillary molar and intrusion
combined with buccal tipping of the second
maxillary molar. It does not only create couples in
the same direction (green) but also distal tipping
of the terminal molar with a 25° vertical force
vector. Since the forces are applied to the buccal
tube, it is important to compare equivalent force
systems at the center of resistance in order to
predict tooth movement. The resultant vector is
indicated (orange). The unilateral extrusion of the
adjacent maxillary first molar can cause an open
bite if this unwanted effect is not sufficiently
controlled.

This study proposes a different approach

to molar intrusion and displays more anchorage Figure 3 A. Palatal view of force system: At the
than conventional biomechanics in which the risk palatal sheath (B) we connected an elastomeric
of extruding the adjacent posterior tooth is auxiliary to the helix from the semi-palatal arch
prevalent. It can be considered a modification of appliance (located at the height of the center of
previous designs, such as the Kucher and resistance to obtain pure translation). Note that
Weiland’s appliance that uses similar during intrusion the height of the hook became
biomechanics in combination with a transpalatal more incisal and a couple is being created which
arch to reduce the prominence of the palatal brings the center of rotation from infinity toward
cusp of the upper second molar.18 the tooth. If this couple is large enough relative to
the forces the amount of translation could
Materials and methods become negligible in comparison to the tipping
and the center of rotation would be near the
Appliance fabrication & design: An center of resistance.
impression was taken of the arch with the
extruded molar. The teeth were bonded/banded Forces: When representing a vector as an
with edgewise fixed appliances. A band was fit arrow, the point of application is indicated as the
on the adjacent molar including a soldered origin of the arrow and the length of the arrow is
palatal attachment for a prefabricated removable proportional to the magnitude of the force and is
palatal bar (GAC International Inc., Islandia, NY). arbitrary. The arrowhead indicates the direction
The removable palatal bar was made of and the body indicates the line of action. All
0.036′′ stainless steel round wire and was forces have the same scale. Our two applied

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http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

forces acted on three planes of space as This force system was equivalent to a
illustrated in the two-dimensional graph (Figure couple with a 30 gm net force to move the tooth
2). To determine the single net force or resultant bodily (Figure 3 A). Note that during intrusion the
affecting the maxillary second molar, both height of the hook became more incisal and a
applied net-effect forces had to be combined. couple was being created which moved from
The two vectors acted as sides of a infinity to a more incisal position. If this couple
parallelogram and the resultant was the diagonal. was large enough relative to the forces the
Its length indicated the magnitude of the resultant amount of translation could become negligible in
force on the same scale as the original force. The comparison to the tipping and the center of
final movement of the maxillary molar was rotation would be near the center of resistance
identical to the resultant. (Figure 3 C).10
The two vectors had their point of
application in point A – the buccal tube and in
point B – the palatal sheath (Figures 3A and 3B):
On point A we used a step bend, which created a
moment tending to rotate the tooth and also
created two couples in the same direction
regardless of the step bend location between the
brackets. As the line of action did not pass
through the center of resistance, tipping of the
maxillary second molar was expected. We
applied 45 gm force on the tube 6 mm from the
center of resistance and produced 270 gm-mm
moment (Mf – moment of the force), tipping the
tooth.

Figure 3 C. Molar cut view and application of the

force: The resultant vector (green) indicates a
slight palatal crown tipping.

In our model, we obtained an intrusive

force of 92.8 gm combined with clinically
negligible distal and palatal crown tipping each of
less than 15° (Figure 3 B). However, according to
the individual environment, each clinical
application might produce other unwanted effects.

Figure 3 B. Resultant vector (thin red arrow) in

combining all forces (orange arrows) at the
center of resistance: An intrusive force combined
with slight distal and palatal crown tipping is
obtained.

To obtain bodily movement we needed to

create a moment of the couple (Mc) equal in
magnitude and opposite in direction to the
original movement. On point B we used a hook at
the height of the center of resistance to obtain
pure translation. We applied 50 gm force on the
tube 6 mm from the center of resistance and Figure 4 A1. Pre-treatment intra-oral
produced 300 gm-mm moment (Mf – moment of
assessment, buccal view.
the force), tipping the tooth very slightly palatally.

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 Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars
http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

Patient A.J.
A 26 year 10-months-old female patient
was referred by a general dentist for orthodontic
evaluation. Her chief complaint was the missing
tooth in the lower right arch. She presented with
mild upper and lower anterior crowding, missing
mandibular right second molar and extruded
maxillary right second molar (Figures 4 A1 and
A2).

Figure 4 B2. Appliance in place (occlusal view).

After 2 months of intrusive force we

obtained space for implant placement of
mandibular right second molar (Figures 4 C - F).

Figure 4 A2. Pre-treatment study model

assessment.
After evaluating the patient’s periodontal
health condition, the following treatment plan was
designed: Full-arch-bonding with edgewise
appliances, including the modified semi-palatal
bar appliance for intrusion of maxillary right
second molar, mandibular right second molar
Figure 4 C. Lateral view 2 months post
implant placement and retention of the maxillary
orthodontic intrusion.
right second molar in its new position.After the
patient’s treatment plan approval, the semi-
palatal bar appliance was placed (Figure 4 B1)
and an Ormco Power Chain (Ormco, Glendora,
USA) was tied palatally from the palatal sheath of
the maxillary right second molar through the
semi-palatal bar helix and back onto the sheath
(Figure 4 B2).

Figure 4 D. Occlusal view 2 months post

orthodontic intrusion.
Cephalometric and panoramic evaluation
indicate the successful intrusion (Figures 5 A and
B and Figures 6 A and B). The cephalometric
superimposition along the palatal plane
Figure 4 B1. Appliance in place (buccal view). registered at ANS shows successful intrusion of

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 Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars
http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

the second molar (Figure 7 A) and no

measurable extrusion of the adjacent molar that
was used as anchorage (Figure 7 B).

Figure 4 E. Lateral view after implant placement

and temporary crown insertion. Figure 5 B. Post-treatment cephalogram.

Figure 6 A. Pre-treatment panoramic radiograph

of patient 1.

Figure 4 F. Lingual view after implant placement

and temporary crown insertion.

Figure 6 B. Post-treatment panoramic

radiograph with implant placement of patient 1.

Figure 7 A. Cephalometric superimposition along

Figure 5 A. Pre-treatment cephalogram. the palatal plane registered at ANS shows
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http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

successful intrusion of upper second molar in and panoramic evaluation indicate the successful
patient 1. intrusion. The cephalometric superimposition
shows no measurable extrusion of the adjacent
molar used as anchorage. Both maxillary right
first and second molar were slightly mesially
displaced.

Figure 7 B. Cephalometric superimposition along

the palatal plane registered at ANS shows no
measurable extrusion of the adjacent upper first
molar in patient 1.

Patient D.S.
A 20-year-old female patient presented in
2000 for surgical treatment evaluation of her Cl III Figure 8 B. Post-treatment occlusal view of
malocclusion. After performing orthodontic clinical successful intrusion of UR7 in patient 2.
decompensation, her maxillary right second
molar was bucally tipped out of the arch and
needed intrusion and correct alignment before
performing mandibular setback surgery (Figure 8
A).

Figure 8 C. Palatal view of clinical successful

intrusion of UR7 in patient 2.

Figure 8 A. Pre-treatment occlusal view of

decompensated maxillary arch in patient 2.

The semi-palatal bar appliance was

placed and a power-chain was tied palatally from
the palatal sheath of maxillary right second molar
through the semi-palatal bar helix and back onto
the sheath. After 2 months of intrusive force the
correct alignment was achieved. Clinical (Figures
8 B and C), cephalometric (Figures 9 A and B) Figure 9 A. Cephalometric superimposition along

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http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

the palatal plane registered at ANS shows superimpositions, the expected extrusive force
successful intrusion of upper second molar in on the adjacent tooth - in this cases the first
patient 2. molar - was not observed in our patients. This
may be due to occlusal forces, the stabilizing
effect of the buccal guiding archwire, and the use
of light force generated by the power chain over
an extended period of time. The intrusion of a
single tooth concentrates on a small area at the
apex. Only extremely light and continuous forces
(5 to 15 gm per tooth) should be employed with
the line of action of the force directed through or
close to the tooth’s center of resistance.13,14
There is general agreement that forces on
posterior teeth should not exceed 100 gm.15,16
Maintaining a light force application may avoid
other unwanted effects of intrusion, e.g. the
Figure 9 B. Cephalometric superimposition along resorption of the intruding tooth in the apical third.
the palatal plane registered at ANS shows no In an animal skeletal anchorage system model,
measurable extrusion of the adjacent upper first Daimaruya and coworkers found a minimum root
molar in patient 2. resorption of 0.1 mm ± 0.1 mm (mean ± SD) after
7-months of treatment. Root resorption reached
Results the dentin at one-third of the apical area of the
roots.11 Thus, even minimum external apical root
Our results confirm that the modified TPA resorption can be considered aggressive when
technique is an alternative to conventional localized at the apical region. We could not
methods for selective molar intrusion. In detail, detect root resorption in our patients; however a
patient A.J. showed an intrusion of 3.5 mm and much larger number of patients will be needed to
patient D.S. an intrusion of 1.5 mm over 2 exclude unwanted effects generated by this
months and 3 appointments. appliance.
Discussion Auxiliary anchorage has been used to
control the intrusive force, e.g. a base arch
In 2001, Daimaruya examined molar (rectangular stainless steel archwire), which
intrusion in dogs through a skeletal anchorage includes all teeth except the extruded tooth,
system. Canine mandibular molars intruded by together with a buccal intrusion arch. The
an average of 3.4 mm over the 7 months of intrusion arch is segmentally attached to the
observation.11 The intrusion of about 3.5 mm base appliances. To achieve pure molar intrusion
observed in our patient A.J. is in accordance with it is necessary to position the point of application
previous observations and also with the intrusion of the force more anteriorly (Figure 10).14
observed by Moon and co-workers12 who
achieved first and second molar intrusion in
selected patients by the more invasive means of
corticotomy and orthodontic skeletal anchorage.
Our proposed method includes full arch
bonding to gain a solid anchor during treatment.
The previously extruded tooth should be
maintained for 6 months in its new position to
allow the periodontal ligament fibers to
restructure. During treatment, the intrusion
surrounding gingival tissue and bony structures
were clinically monitored and remained healthy.
Permanent retention needs to be
preserved by the restorative substitution of the
opposing teeth. Based on cephalometric Figure 10. Example of an intrusion arch: this

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arch is not inserted into the posterior brackets reduce the prominence of the palatal cusp of the
and unwanted effects are a large tip back upper second molar.27 In contrast to this
moment and a small extrusive force at the appliance we could eliminate the laboratory step.
incisors. Gianelly had employed a removable
appliance, which anchored on the remaining
The extrusive force on incisors can be dentition, pulling from the buccal and the palatal
counteracted by an anterior bite plate, by side. He concluded that this type of anchorage
occlusal forces and / or by an anterior vertical was inadequate for restoring an occlusal plane
pull (J-hook) headgear.17 Intrusion of teeth when the overerupted tooth is a terminal tooth.
adjacent to the molar may occur as unwanted Due to the fact that the occlusal plane is restored
effect, when those teeth are not connected to the by a combination of extrusion / intrusion and
appliances.18 extrusion was an easier and quicker movement
Orthodontic intrusion of posterior teeth is to be produced orthodontically, Gianelly preferred
difficult to achieve in adults due to missing surgery instead of restoring the occlusal plane.18
growth compensation, histological changes in the The use of removable appliances instead of fixed
alveolar bone, smaller marrow spaces and a appliances may be the cause of the discrepancy
reduced blood supply when compared with between the results of our study and previous
growing patients.19 To improve anchorage, a studies.
combination of corticotomy, miniplates and Some intrusive forces on the adjacent
orthodontic miniscrews has been proposed.5 molar have also been observed by Gianelly18,
Corticotomy was performed by incising and could be justified by the presence of the
the cortical bone surrounding the tooth to reduce horizontal periodontal fibers attached apically to
resistance during intrusion. The method is the crown. However, this phenomenon is only
expensive, rarely covered by dental plans and noticeable when the adjacent molar is not the
associated with pain, swelling and infection. By direct source of anchorage, in which case
combining corticotomy with rare earth magnets, extrusive forces will prevail. In our study, the first
Hwang and Lee achieved an intrusion of 3.5 mm molar was the direct source of anchorage, and
during 2 months of treatment without observing was stabilized by a separate archwire system
adverse events such as discomfort, root encompassing the whole maxillary arch. Intrusion
resorption and/or extrusion of the adjacent was not observed on the maxillary first molars,
teeth.20 and extrusion was not observed either.
Temporary anchorage devices (TAD) are Another reaction to the intrusion force is
preferable because they provide maximum that the periodontal pocket might deepen.
anchorage control and minimize the need for full Caution must be given to the presence of
arch appliances. The success rate of more than periodontal diseases as these may aggravate
75% has been considered favorable.21 Putative and lead to periodontal damage.13,14 In case of
adverse events of TAD’s include pain, infection, normal intrusion the periodontal fibers are
trauma of anatomical and vascular structures, expected to build a junctional epithelium at best,
fracture, dislodgement and gingival but there is no basis for expecting true re-
overgrowth.22,23 attachment of the periodontal fibers in response
Use of 2 TADs to successfully correct an to orthodontic treatment. Melsen et al. described
overerupted upper first molar was described by the formation of a tight epithelial cuff in
Kravitz and coworkers.24 In another study using histological slides of a dog’s lower first premolar
TADs, overerupted maxillary first molars were that was first extruded and then intruded.28
intruded by 3 to 8mm over 7.5 months (about With our patients, the position of the
0.5-1.0 mm per month), without loss of tooth gingiva relative to the crown was left unchanged
vitality, adverse periodontal response or while periodontal probing depths did not increase.
radiographically evident root resorption 25,26
In order to reduce the risk of extruding the Conclusions
adjacent posterior tooth, we employed a
modification of previous appliances, such as the Extruded upper second molars are often
Kucher and Weiland’s appliance that used similar encountered in adult patients. The modified TPA
biomechanics in combination with a TPA to appliance presents a clinically elegant, non-

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 Journal of International Dental and Medical Research ISSN 1309-100X Extruded Maxillary Molars
http://www.ektodermaldisplazi.com/journal.htm Julia Elodie Vlachojannis and Margherita Santoro

invasive and cost-effective procedure. 21. Crismani AG, Bertl MH, Celar AG, Bantleon HP, Burstone CJ.
Miniscrews in orthodontic treatment: review and analysis of
The TPA is rapidly bent in the office and published clinical trials. Am J Orthod Dentofacial Orthop
is cost-effective because it does not require 2010;137(1):108-13.
22. Papadopoulos MA, Tarawneh F. The use of miniscrew implants
laboratory work. This appliance can be inserted for temporary skeletal anchorage in orthodontics: a comprehensive
in one session chair-side. review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod
2007;103(5):6-15.
23. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical
Declaration of Interest success of screw implants used as orthodontic anchorage. Am J
Orthod Dentofacial Orthop 2006;130(1):18-25.
The authors report no conflict of interest 24. Kravitz ND, Kusnoto B, Tsay PT, Hohlt WF. Intrusion of
and the article is not funded or supported by any overerupted upper first molar using two orthodontic miniscrews. A
case report, Angle Orthod 2007;77(5):915-22.
research grant. 25. Kravitz ND, Kusnoto B, Tsay TP, Hohlt WF. The use of
temporary anchorage devices for molar intrusion. J Am Dent Assoc
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