- Email: [email protected]
A procedure for midline correction
A procedure for midline correction Anthony Boston,
A.
Gianelly,
D.M.D.,
Ph:D.,
and
Irving
A.
Paul,
D.D.S.
Ma.w.
D
uring orthodontic treatment, teeth are repositioned according to the dictates of both skeletal and dental harmony. The dental component indicates that the final arrangement of the teeth should conform to a Class I dental pattern with perfect alignment, proximal contact, proper axial inclination, and maximum intercuspation. These occlusal relationships will exist only under certain conditions which coordinate the dentition and the dental arches. For example, the sizes of the maxillary and mandibular teeth must be a perfect match for each other. Similarly, the maxillary and mandibular midlines must be coincident. In this instance there will be equal amounts of tooth substance on either side of the midline. Accordingly, cusp position should be suitable for maximum interdigitation. If the midlines are not coincident, maximum intercuspation is improbable because the cusp position on the side of the midline “shift” will be more posterior to its “normal” location ; on the side away from the shift, the cusps will be situated somewhat anterior to the proper position. Midline coincidence, therefore, is an essential factor in dental harmony. For this reason, the position of the midlines receives a considerable degree of attention during therapy. With this in mind, the following report will describe a procedure which may be useful to correct a midline imbalance which may be present in the final stages of treatment after alignment, space closure, etc. AS an example, let us assume that the maxillary midline is “correctly” situated and the mandibular midline is deviated to the right. As indicated, the right mandibular segment is posterior to its “correct” position and the left buccal segment is anterior. Therefore, a force system capable of applying a mesially directed component of force on the right side and a distally directed force on the left should aid in midline correction. If these movements are coordinated in a continuous arch, the incisors should move to the left, correcting the midline problem. One such system is illustrated in Fig. 1. A round wire was inserted in the mandibular arch with the following configuration: A second-order bend was formed and inserted into the right canine bracket to drive the crown of the From A.04
Boston
University
School
of
Graduate
Dentistry.
Procedure
for midline
correction
265
Fig. 1. Photographs
illustrating a biomechanical “system” for midline correction. A, The maxillary midline is correctly situated, while the mandibular midline is deviated 2 to 3 mm. to the right. B, A second-order bend, designed to move the crown of the mandibular right canine mesially, is placed in the wire, which is inserted into the bracket of the mandibular right canine. The action of the wire is augmented by the use of a Class II elastic on the right side. C, second-order bend designed to move the crown of the mandibular left canine distally. This photograph was taken approximately one week after placement of the midline correction system to illustrate a small space mesial to the left canine. Normally, no space becomes apparent, because the wire is tied back to maintain arch continuity. For purposes of demonstration, the wire was not tied back, so that a space, indicative of the tooth movement involved, might appear. Movement of this nature is necessary to allow the incisors to move to the left to correct the midline discrepancy. D, Midline coincidence approximately 7 weeks after the application of the midline correction system.
canine mesially (Fig. 2). The second-order bend produces a couple force which, assuming the ability of the tooth to rotate freely, will presumably rotate the toot,h around a center of rotation located at the centr0id.l In the present illustrarim, i,he cc&r uf rotation will probably br lorated close to the bracket area of couple. In addiihe tooth because the second-order bend produces a “friction” is limited by proximal contact. tion, the ability of the canine to rotate freely Accordingly, the rules of pure couple application must be modified. If the canine is then ligated to the rest of the teeth in t,he buccal segment, the force directing t-he crown of the canine mesially will act over the entire segment, directing the crowns of all the teeth in that quadrant mesially. Placement of a Class II elastic tends to enhance the activity of the force system, since it also applies an ant,erior component of force on the right buccal segment.
Amer.
J. Orthodorct. Se&?mbsr 1970
Fig. 2. Diagrammatic
illustration of a wire with a second-order bend ready for placement in the bracket of the mandibular left canine to move the crown of the canine distally. As long as the “arms” of the second-order bend are equidistant, both horizontally and vertically, from the midpoint of the bracket, the introduction of the wire into the bracket applies a “couple” force to the tooth.
A similar approach is followed on the left side. An appropriate second-order bend to direct the crown of the canine distally is formed and placed into the canine bracket. The canine is then ligated to the other teeth in the left buccal segment so that the distal force is applied to all the teeth. (This step may not be totally necessary, since a distally directed force on the other posterior teeth will occur as a result of proximal contact when the canine crown moves distally.) Finally, a Class III elastic with its distally directed force on the lower posterior teeth is attached in the canine region. Thus, the force system entails a continuous mandibular arch wire with a second-order force on the right side directing the crowns of the teeth in the right buccal segment mesially. The second-order force on the left side directs the crowns of the teeth in the left buccal segment distally. To enhance the activity of these forces, a Class II elastic with its mesial component of force on the right buccal segment and a Class III elastic with its distal component of force on the left buccal segment are used. Since both sides generally move at the same time, the incisors will have to be moved toward the left. These tooth movements usually occur in 2 months or less. Once the crowns are positioned, root control is then necessary for proper completion of the case. For more activity, second-order forces can also be applied to the molars (as well as the canines) at the same time. On the right, the force would direct the crown mesially; on the left, the crown could be displaced distally. This force system can also shift midlines in the presence of spaces and in conjunction with closing loops.
Volume Number
38 3
Procedure
midhze
for
267
correction
Fig. 1, D illustrates the midline correction. The procedure was accomplished in 7 weeks. In the example cited in this report, the maxillary arch was used as the anchor unit for elastic traction. Since the maxillary midline was “correct,” the maxillary arch should be stabilized. One method would be to combine the use of a passive rectangular wire with a headgear on the anterior part, of the arch with more force in the Class Ill traction side. Another would bc the use of second-order forces to counteract the traction forces. For instance, on the left side, a force tlirecting the crowns distally would tend to balance the mesial component of the Class III elastic. In addition, the relatively short time that is usually necessary to complete the midline adjustment procedure might suggest that the maxillary arch jrould tend to remain in plncc as long as this procedure is performed with some caution. REFERENCES
1. Burstone, Reidel, 197-213.
R.
Truly
we
have
such
rapid
not
men,
clude still
as
that
accepted
theory
so
the
very
The in
good be
and
more further of
road feel
remains superior
today of
may
tooth movement. Philadelphia, 1962,
in
a
that
to
opportunity
B. Frank: Society
of
the us to
a certain
practice
American
on
cause
much no
(Gray,
biomechanics Ort,hodontics,
way to
contemplate remains
progress. of
a may
they
there
further
meeting
come
progress
hand-that for
C. J.: Mechanics: (editors) : Vistas
be
the
become
time,
end
and
of
the
accomplished.
method of
brief
of
doing
address,
Orthodontists,
July
the is
Transaction to
15,
thing, making
of 1910,
of
almost
common
direction.
tomorrow,
13
is
a
and pp.
tendency
a stated in that
obsolete
B. S., Febiger,
journey It
advancement
President’s
In. Xraus, Lea &
the p.
at thing
to But
conthe
way
tenth 11.)
annual
for
A.
Gianelly,
D.M.D.,
Ph:D.,
and
Irving
A.
Paul,
D.D.S.
Ma.w.
D
uring orthodontic treatment, teeth are repositioned according to the dictates of both skeletal and dental harmony. The dental component indicates that the final arrangement of the teeth should conform to a Class I dental pattern with perfect alignment, proximal contact, proper axial inclination, and maximum intercuspation. These occlusal relationships will exist only under certain conditions which coordinate the dentition and the dental arches. For example, the sizes of the maxillary and mandibular teeth must be a perfect match for each other. Similarly, the maxillary and mandibular midlines must be coincident. In this instance there will be equal amounts of tooth substance on either side of the midline. Accordingly, cusp position should be suitable for maximum interdigitation. If the midlines are not coincident, maximum intercuspation is improbable because the cusp position on the side of the midline “shift” will be more posterior to its “normal” location ; on the side away from the shift, the cusps will be situated somewhat anterior to the proper position. Midline coincidence, therefore, is an essential factor in dental harmony. For this reason, the position of the midlines receives a considerable degree of attention during therapy. With this in mind, the following report will describe a procedure which may be useful to correct a midline imbalance which may be present in the final stages of treatment after alignment, space closure, etc. AS an example, let us assume that the maxillary midline is “correctly” situated and the mandibular midline is deviated to the right. As indicated, the right mandibular segment is posterior to its “correct” position and the left buccal segment is anterior. Therefore, a force system capable of applying a mesially directed component of force on the right side and a distally directed force on the left should aid in midline correction. If these movements are coordinated in a continuous arch, the incisors should move to the left, correcting the midline problem. One such system is illustrated in Fig. 1. A round wire was inserted in the mandibular arch with the following configuration: A second-order bend was formed and inserted into the right canine bracket to drive the crown of the From A.04
Boston
University
School
of
Graduate
Dentistry.
Procedure
for midline
correction
265
Fig. 1. Photographs
illustrating a biomechanical “system” for midline correction. A, The maxillary midline is correctly situated, while the mandibular midline is deviated 2 to 3 mm. to the right. B, A second-order bend, designed to move the crown of the mandibular right canine mesially, is placed in the wire, which is inserted into the bracket of the mandibular right canine. The action of the wire is augmented by the use of a Class II elastic on the right side. C, second-order bend designed to move the crown of the mandibular left canine distally. This photograph was taken approximately one week after placement of the midline correction system to illustrate a small space mesial to the left canine. Normally, no space becomes apparent, because the wire is tied back to maintain arch continuity. For purposes of demonstration, the wire was not tied back, so that a space, indicative of the tooth movement involved, might appear. Movement of this nature is necessary to allow the incisors to move to the left to correct the midline discrepancy. D, Midline coincidence approximately 7 weeks after the application of the midline correction system.
canine mesially (Fig. 2). The second-order bend produces a couple force which, assuming the ability of the tooth to rotate freely, will presumably rotate the toot,h around a center of rotation located at the centr0id.l In the present illustrarim, i,he cc&r uf rotation will probably br lorated close to the bracket area of couple. In addiihe tooth because the second-order bend produces a “friction” is limited by proximal contact. tion, the ability of the canine to rotate freely Accordingly, the rules of pure couple application must be modified. If the canine is then ligated to the rest of the teeth in t,he buccal segment, the force directing t-he crown of the canine mesially will act over the entire segment, directing the crowns of all the teeth in that quadrant mesially. Placement of a Class II elastic tends to enhance the activity of the force system, since it also applies an ant,erior component of force on the right buccal segment.
Amer.
J. Orthodorct. Se&?mbsr 1970
Fig. 2. Diagrammatic
illustration of a wire with a second-order bend ready for placement in the bracket of the mandibular left canine to move the crown of the canine distally. As long as the “arms” of the second-order bend are equidistant, both horizontally and vertically, from the midpoint of the bracket, the introduction of the wire into the bracket applies a “couple” force to the tooth.
A similar approach is followed on the left side. An appropriate second-order bend to direct the crown of the canine distally is formed and placed into the canine bracket. The canine is then ligated to the other teeth in the left buccal segment so that the distal force is applied to all the teeth. (This step may not be totally necessary, since a distally directed force on the other posterior teeth will occur as a result of proximal contact when the canine crown moves distally.) Finally, a Class III elastic with its distally directed force on the lower posterior teeth is attached in the canine region. Thus, the force system entails a continuous mandibular arch wire with a second-order force on the right side directing the crowns of the teeth in the right buccal segment mesially. The second-order force on the left side directs the crowns of the teeth in the left buccal segment distally. To enhance the activity of these forces, a Class II elastic with its mesial component of force on the right buccal segment and a Class III elastic with its distal component of force on the left buccal segment are used. Since both sides generally move at the same time, the incisors will have to be moved toward the left. These tooth movements usually occur in 2 months or less. Once the crowns are positioned, root control is then necessary for proper completion of the case. For more activity, second-order forces can also be applied to the molars (as well as the canines) at the same time. On the right, the force would direct the crown mesially; on the left, the crown could be displaced distally. This force system can also shift midlines in the presence of spaces and in conjunction with closing loops.
Volume Number
38 3
Procedure
midhze
for
267
correction
Fig. 1, D illustrates the midline correction. The procedure was accomplished in 7 weeks. In the example cited in this report, the maxillary arch was used as the anchor unit for elastic traction. Since the maxillary midline was “correct,” the maxillary arch should be stabilized. One method would be to combine the use of a passive rectangular wire with a headgear on the anterior part, of the arch with more force in the Class Ill traction side. Another would bc the use of second-order forces to counteract the traction forces. For instance, on the left side, a force tlirecting the crowns distally would tend to balance the mesial component of the Class III elastic. In addition, the relatively short time that is usually necessary to complete the midline adjustment procedure might suggest that the maxillary arch jrould tend to remain in plncc as long as this procedure is performed with some caution. REFERENCES
1. Burstone, Reidel, 197-213.
R.
Truly
we
have
such
rapid
not
men,
clude still
as
that
accepted
theory
so
the
very
The in
good be
and
more further of
road feel
remains superior
today of
may
tooth movement. Philadelphia, 1962,
in
a
that
to
opportunity
B. Frank: Society
of
the us to
a certain
practice
American
on
cause
much no
(Gray,
biomechanics Ort,hodontics,
way to
contemplate remains
progress. of
a may
they
there
further
meeting
come
progress
hand-that for
C. J.: Mechanics: (editors) : Vistas
be
the
become
time,
end
and
of
the
accomplished.
method of
brief
of
doing
address,
Orthodontists,
July
the is
Transaction to
15,
thing, making
of 1910,
of
almost
common
direction.
tomorrow,
13
is
a
and pp.
tendency
a stated in that
obsolete
B. S., Febiger,
journey It
advancement
President’s
In. Xraus, Lea &
the p.
at thing
to But
conthe
way
tenth 11.)
annual
for