Deep Overbite Correction: Biomechanics & Treatment Options

Biomechanics of Deep Overbite Correction
Charles J. Burstone
Correction of deep overbite can be accomplished in different ways depending on the treatment goals chosen for individual patients. The 2 primary
methods of correction are intrusion of anterior teeth or extrusion of posterior teeth. Successful intrusion of the incisors depends on careful control of
the force system used. Low force magnitude, force constancy, a properly
selected single point of force application, and control of force direction are
all important factors to consider. The design of the intrusion arch may be
continuous, or a 3-piece intrusion arch may be selected depending on the
needs of the patient. Alternatively, extrusion of posterior teeth may be
indicated in patients who are still actively growing and who have short
vertical facial dimensions. (Semin Orthod 2001;7:26-33.) Copyright© 2001 by
W.B. Saunders Company
A
c o m m o n finding in m a n y malocclusions is
the p r e s e n c e of d e e p overbite. Because
d e e p overbite is a s y m p t o m , it is n o t too surprising that t h e r e are n u m e r o u s etiologic factors that can lead to d e e p overbite a n d m a n y
d i f f e r e n t t r e a t m e n t goals for its c o r r e c t i o n .
Patients that show l o n g faces or a Class II p o i n t
A to p o i n t B r e l a t i o n s h i p r e q u i r e c o n t r o l of
the vertical d i m e n s i o n with no r o t a t i o n of the
m a n d i b l e d o w n w a r d a n d backward d u r i n g the
c o r r e c t i o n of the overbite. In these patients,
intrusion m e c h a n i c s of the incisors is required. O n the o t h e r h a n d , t h e r e are patients
with smaller vertical d i m e n s i o n s or individuals
showing sufficient vertical growth p o t e n t i a l for
w h o m the t r e a t m e n t of choice is the e x t r u s i o n
o f p o s t e r i o r teeth.
Two patients with a 2-year growth prediction
are shown in Figure 1. In Figure 1A, typical
maxillary-mandibular differential growth not
only improves the Class II relationship, but also
increases the vertical dimension f r o m anterior
nasal spine to m e n t o n . In this patient it is per-
From the Department of Orthodontics, Sehool of Dental Medicine, University of Connecticut Health Center, Fa,vvnington, CT.
Ad&~ss correspondence to CharlesJ. Burstone, DDS, MS, Department of Orthodontics, School of Dental Medicine, University of
Connecticut Health Center; Farmington, CT 06030.
Copyright © 2001 by W..B. Saunders Company
1073-8746/01/0701-0004535.00/0
doi:l O.1053/sodo. 2001.21059
26
fectly permissible to extrude posterior teeth because the mandible would not be hinged o p e n
during treatment. By contrast, Figure 1B shows a
patient in w h o m minimal growth is expected
during treatment. To control the vertical dimension, it is necessary in this type of patient to
intrude the incisors.
T h e decision to intrude or extrude is based
on at least 3 factors: skeletal convexity, vertical
dimension, and the interocclusal (freeway) space.
T h e estimated a m o u n t of growth during treatm e n t helps to d e t e r m i n e the a m o u n t that posterior teeth can be extruded. In some malocclusions it may be m o r e convenient and efficient to
intrude anterior teeth initially, such as in a Class
II, Division 2 patient, even t h o u g h the final plan
may not necessarily require intrusion.
Patients with fiat m a n d i b u l a r planes a n d
small vertical d i m e n s i o n s p r e s e n t an entirely
d i f f e r e n t p r o b l e m t h a n do long-faced individuals. It is desirable in m a n y o f these patients to
increase the vertical d i m e n s i o n . However, this
may n o t be practical f r o m a p o i n t of view of
stability unless future growth will occur. Even
in these patients, it may be necessary to int r u d e incisors. A b i o m e c h a n i c a l alternative to
i n t r u s i o n of a n t e r i o r t e e t h in patients with
short vertical d i m e n s i o n s is to e x t r u d e posterior teeth initially a n d m a i n t a i n fixed arches in
place d u r i n g t r e a t m e n t to allow time for adaptation to occur.
Seminars in Orthodontics, Vol 7, No 1 (March), 2001: cop 26-33
Biomechanics of Deep Overbite Correction
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Figure 1. Growth influences the decision to intrude
incisors. Two-year growth prediction shows the overbite corrected by growth. Posterior teeth can be
erupted (A). Little growth in 2-year prediction. Incisor intrusion is needed (B).
The biomechanics of 2 different types of deep
overbite correction are discussed separately in
this article. First, incisor intrusion, and second,
extrusion mechanics for posterior teeth.
Incisor Intrusion
For many years it was believed that it was impossible to intrude teeth and that if intrusion was
attempted, undesirable sequellae such as devital-
27
ization would occur. Early studies of treated patients saw little intrusion of incisors because the
mechanics used tended to extrude posterior
teeth. It has been shown that the use of light
constant forces enables the intrusion of teeth
with minimal disruption of posterior a n c h o r
units. It has also been shown that as the forces
for intrusion are increased, more root resorption but not necessarily a greater rate of intrusive m o v e m e n t may result. 1 Figure 2 shows a
patient in whom intrusion was accomplished in
both the u p p e r and lower arches using light
constant forces. The u p p e r incisors c o m m o n l y
must be intruded more than lower incisors to
maintain the original cant of the plane of occlusion. This requires controlled mechanics because in the Class II patient, the application of
Class H elastics or cervical headgear and other
similar mechanisms can steepen the plane of
occlusion and negate any intrusion effects.
There are 2 basic designs to an intrusion arch:
(1) a continuous arch, and (2) a 3-piece intrusion mechanism. 2-6 Both of these appliances are
described in this section. The application of
each is determined by the needs of the patient.7, 8
The continuous intrusion arch is shown in
Figure 3. A relatively rigid anchorage unit connects the teeth of the posterior segment. The
cuspid is bypassed by placing a small step in the
region of the cuspid or eliminating the cuspid
bracket entirely. Anterior teeth are connected
together with an incisor segment. A 0.017 ×
0.025-inch or 0.016 × 0.022-inch titanium molybdenum alloy (TMA) intrusion arch from an
auxiliary tube places the intrusive force on the
incisors. As the wire is b r o u g h t down to the
central incisors or the lateral incisors, only single
forces are directed in an intrusive direction.
The key to successful intrusion is control of
the force system. Specifically, force magnitude,
constancy, the use of only a single-point application, control of the direction of force, and the
selection of a p r o p e r point for the force application are carefully planned and delivered.
Force magnitude can be determined either
using tables or directly by a force gauge (Fig 4).
Sometimes the clinician will neglect to measure
the forces and only place a V b e n d posteriorly.
This can be dangerous because arches vary in
length and there is not a constant angulation for
a desirable activation. If too m u c h force is ap-
28
Charles J. Bu,:,tone
plied, undesirable side effects, including steepening of the occlusal plane or distal tipping of a
molar, can occur, The magnitude of force depends on the n u m b e r of teeth and their size. For
example, during intrusion of u p p e r incisors,
about 60 g of force for 4 incisors are used. Figure
5 shows a patient with a continuous intrusion
arch before and after intrusion. The use of low
forces and a stable anchorage unit will not upset
posterior anchorage and should maintain the
original plane of occlusion.
The force-deflection rate of the intrusion
arch is very low, usually u n d e r 10 g / m m , because the distance is large between the auxiliary
tube of the molar and the incisor brackets2 This
not only produces a large deflection, minimizing
the need for any reactivation, but also ensures
greater constancy of force. It also enhances the
accuracy of the appliance because any small error in activation produces a minimal change in
the delivered force.
A particularly important consideration in intrusion is to assure that the intrusion arch does
not fit into the brackets of the incisors. Instead,
a separate segment is placed. There are a nun>
bet of reasons why it is not desirable to put
either a rectangular or a r o u n d intrusion arch
wire directly into an edgewise bracket anteriorly.
The intrusive arch can change shape, p r o d u c i n g
mesial displacement of the roots of incisors.
Most importantly, any torque, labial or lingual,
can alter the intrusive force (Fig 6). If purposely
or accidentally placed lingual root torque is
present, it could completely eliminate any intrusive force. At the other extreme, labial root
torque may increase the intrusive force with a
concomitant increase of extrusive force and tip
back m o m e n t on the molar. Once an edgewise
intrusion arch wire is placed into the anterior
brackets, a precise mechanism is not present.
The clinician should carefully look at the anatomic a r r a n g e m e n t of the teeth to determine
which teeth require intrusion. The Class II, Division 2 patient may only need intrusion of 2
central incisors. Many Class II, Division 1 patients require intrusion of 4 incisors. These an-
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Figure 2. Maxillary and mandibular intrusion using a
continuous intrusion arch. Cranial base superimposition (A). Separate maxillary and mandibular superimpositions (B).
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Biomechanics of Deep Overbite Correction
29
Figure 3. Passive and active continuous intrusion arches. Separate posterior and anterior segments are placed.
The canine is bypassed. Buccal view passive (A) and active (B). Frontal view passive (C) and active (D).
a t o m i c discrepancies s h o u l d be eliminated by
segmental intrusion r a t h e r than by indiscriminate leveling. If the patient initially has leveling
wires placed in a full-arch wire, it t h e n almost
b e c o m e s impossible to p r o d u c e effective intrusion o f the incisors.
O n e o f the key aspects o f c o n t r o l l i n g the
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Figure 4. The force system. Measuring the force with
a force gauge (A). The reactive force on the posterior
anchorage unit produces potential extrusion and
steepening of the occlusal plane (B).
Figure 5. Upper incisor intrusion. Before (A) and
after (B).
Charles J. Burstone
30
A
Figure 8. Frontal view of a 3-piece intrusion arch with
hooks attached distal to the lateral incisors. Separate
right and left springs apply intrusive force distal to the
lateral incisors.
B
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the l o n g axis o f the tooth. T h e i n c i s o r will
readily i n t r u d e a n d n e i t h e r r e t r a c t n o r flare.
W i t h a typical axial i n c l i n a t i o n , the force is labial
to the c e n t e r of resistance so that the t o o t h will
i n t r u d e b u t also have a m o m e n t t h a t w o u l d retract the r o o t p r o v i d e d the intrusive arch is tied
back. For Class II, Division 2 patients, some lingual r o o t m o v e m e n t m a y be desirable. However,
i n p a t i e n t s with a l r e a d y flared incisors, p l a c i n g
a n intrusive force labial to the c e n t e r o f resist a n c e is m o r e p r o b l e m a t i c . T h e r o o t is p r o b a b l y
Figure 6. Placing an arch wire in the incisor brackets
alters the magnitude of the intrusive force. Lingual
root torque produces extrusion (A). Labial root
torque produces intrusion (B).
force system d u r i n g i n t r u s i o n is to d i r e c t the
force s o m e w h a t parallel to the l o n g axis o f the
tooth. I n F i g u r e 7, 3 d i f f e r e n t axial i n c l i n a t i o n s
of incisors are shown. W i t h a vertical incisor, a
c o n t i n u o u s i n t r u s i o n arch c a n direct the force
close to the c e n t e r o f resistance a n d parallel to
Figure 7. An intrusive force labial to tile incisors
produces different effects as axial inclinations vary.
The intrusion force unfavorably moves the incisor
root lingually in a flared incisor.
Figure 9. Three-piece intrusion arch with chain elastic (A) or spring (B) redirects the force parallel to the
long axis of the incisor.
Biomechanics of Deep Overbite Correction
31
Figure 10. Cantilever with eyelet. The direction of
the force is parallel to the ligature tie.
Figure 12. Force can be positioned either anterior or
posterior to the center of resistance of the incisor
segment to produce intrusion-protrusion, pure intrusion, or intrusion-retraction.
too far lingual to begin with, a n d f u r t h e r m o r e ,
the force is n o t d i r e c t e d a l o n g the l o n g axis o f
the tooth. Consequently, there is a large labial
c o m p o n e n t to the force. T h e t o o t h will n o t
readily i n t r u d e a n d can flare further. It is in this
type o f patient that the 3-piece intrusion arch is
used.
T h e 3-piece intrusion arch is similar to the
c o n t i n u o u s arch in that it requires a stable anc h o r a g e unit for the posterior teeth a n d a separate a n t e r i o r segment. Instead o f a c o n t i n u o u s
wire, separate tip back springs are applied o n the
right a n d left sides (Fig 8). T h e b e n t h o o k shown
in Figure 8 delivers an intrusive force distal to
the brackets o f the lateral incisors. W h e n the
force is directed at 90 ° to the occlusal plane, its
p o i n t o f a t t a c h m e n t can t h e n be p l a c e d t h r o u g h
the c e n t e r o f resistance o f the incisors so that n o
flaring o f the teeth occurs.
In addition to altering the p o i n t o f force application, with flared incisors it may be necessary
to redirect the force. T h e r e are a n u m b e r o f
possible m e t h o d s for c h a n g i n g the line o f action
o f the force so that it is parallel to the l o n g axes
o f the incisors. T h e intrusive force can be supp l e m e n t e d by a distal force f r o m a chain elastic
or a coil spring. T h e resultant force can t h e n
b e c o m e parallel to the l o n g axes o f the incisors
(Fig 9).
Two o t h e r m e t h o d s for redirecting the force
involve using separate cantilever intrusive springs.
T h e first is shown in Figure 10. T h e o r i e n t a t i o n
o f the tie is parallel to the direction o f force. By
s h o r t e n i n g the arm, the force can be directed
m o r e distally. T h e s e c o n d very simple m e t h o d
for redirecting the force is shown in Figure 12. A
posterior e x t e n s i o n to the a n t e r i o r s e g m e n t is
a n g l e d so that the force is n o w directed a l o n g
the l o n g axes o f the teeth. This assumes n o
friction a l o n g the a r c h wire so that the resulting
force only acts at 90 ° to the posterior section o f
the a n t e r i o r segment.
B
Figure 11. Angling the posterior extension redirects the
force parallel to the incisor
long axis (A). Intrusive force
on posterior extension of the
anterior segment is 90 ° to the
occlusal plane (B).
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32
Charles.]. Bu~stone
Figure 13. Extrusive mechanics. Upper bite plate on precision lingual arch (A). Bite plate attached to
the lower arch allows separated posterior teeth to be extruded with vertical elastics or allowed to
erupt (B).
By using either a continuous intrusion arch or
a 3-piece mechanism, the orthodontist can alter
not only the magnitude of the force, but also the
position of the force with respect to the center of
resistance (Fig 12). 1° Furthermore, for optimal
results, it is necessary to orient the force so it
approaches parallelism to the long axes of the
incisors. The use of a single tbrce leads to a
greater accuracy than that achieved when an
arch wire is placed into the brackets of the incisors with a continuous arch or 2 × 4 mechanism. 11q4
Key to anchorage control is the maintenance
of low-magnitude forces and the use of a rigid
posterior segment. This includes a lingual or
transpalatal arch to maintain posterior widths.
Backup with occipital headgear may be considered. A posteriorly and intrusively directed force
from the headgear acting anterior to the center
of resistance of the molar segment produces a
m o m e n t that minimizes any steepening of the
occlusal plane. O f course, headgear should not
be used to cover up mistakes in intrusion mechanics where force magnitudes are too great.
Extrusion of Posterior Segments
Figure 14. Vertical elastic applied to posterior teeth
separated by a bite plate. Individual tooth extrusion
(A). Segmental tooth extrusion (B).
The extrusion of posterior teeth for the correction of deep overbite may be less d e m a n d i n g
than intrusive mechanics but must still be accomplished carefully to avoid canting of the occlusal plane. Many continuous arches extrude
teeth. More efficiently, a 3-piece tip back mechanism with increased forces to a large anterior
segment can be used to tip back and extrude the
posterior teeth. 15 To minimize any steepening of
the u p p e r plane of occlusion with larger forces,
cervical headgear with a long and high outer
bow can p r o d u c e a m o m e n t to bring the u p p e r
plane of occlusion vertically without a change of
cant.
An u p p e r bite plate attached to a precision
lingual arch is a useful adjunct for posterior
eruption with or without other mechanics (Fig
Biomechanics of Deep Overbite Correction
13A). Unlike removable bite plates, the fixed
appliance is not under the control of the patient, which enhances its efficiency. A lower bite
plate from cuspid to cuspid can also be used to
separate the posterior teeth, allowing for vertical
extrusive mechanics to be expressed more easily
(Fig 13B). With posterior teeth separated by
either an upper or lower bite plate, vertical elastics can be u s e d either to an entire segment or to
individual teeth, b e c a u s e often n o t all teeth have
to be e r u p t e d equally (Fig 14). T h e p o s i t i o n o f
the force as well as the n u m b e r o f teeth in the
buccal s e g m e n t can be c o n t r o l l e d .
Conclusion
The correction of deep overbite requires careful
differential diagnosis and the determination of
which teeth must be intruded or extruded for
proper correction. Therefore, the mechanics for
treatment can differ radically from one patient
t o a n o t h e r . T h e k e y t o s u c c e s s f u l c o r r e c t i o n is
not only the proper treatment plan, but precise
mechanics to achieve the predetermined
treatment plan goals.
References
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Orthod 1962;48:805-822.
33
3. Burstone CJ. Mechanics of the segmented arch technique. Angle Orthod 1966;36:99-120.
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