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Surgical-Orthodontic
Cases
Part 2: Class III Treatment
Dr. Terry McDonald
Interviews Dr. Richard McLaughlin
See Part I of this interview (Winter 2009 PCSO
Bulletin), where Dr. Terry McDonald interviewed
Dr. Richard McLaughlin about Surgical-Orthodontic
Cases — Class II Treatment.
Dr. McLaughlin
Dr. McDonald
CURRICULUM VITAE:
RICHARD P. McLAUGHLIN, DDS
D
R. RICHARD MCLAUGHLIN completed his
orthodontic training at the University of
Southern California in 1976. Since then, he
has been in the full time practice of orthodontics in San Diego, CA. He has lectured extensively
in the United States as well as internationally. He is a
member of the Pacific Coast Society of Orthodontists,
the American Association of Orthodontists, and a
Diplomate of the American Board of Orthodontics.
He is the Component Director of the Southern California Component of the Edward H. Angle Society. He is
the 2009 American Board of Orthodontics recipient
of the Dale Wade Award. In addition, Dr. McLaughlin
is a clinical professor at the University of Southern
California, Department of Orthodontics, in Los Angeles, California, and an associate professor at St. Louis
University, Department of Orthodontics.
Terry McDonald: What are you general comments
on Class III surgical cases?
Richard McLaughlin: Thinking among orthodontists and oral
surgeons has somewhat changed over the years concerning
Class III surgical treatment. In the early days of orthognathic
surgery, most severe Class III cases were treated with mandibular setbacks. With time, and the awareness that many Class
III cases showed a component of midface deficiency, maxillary
surgical techniques were developed to address the mid face
concerns. With this advancement, Class III cases could be
treated with either lower jaw surgery or upper jaw surgery, or
a combination of both. As knowledge of the causes of sleep apnea has increased along with the awareness that sleep apnea
patients are being significantly helped by combined orthodontic-surgical procedures, the pendulum for Class III surgery
has swung more toward forward and downward placement of
the maxilla with resultant backward mandibular rotation, and
minimal need for mandibular setback.
TM: With this as a background, please give us
your ideas for Class III surgical treatment that
can be accomplished with mandibular surgery only.
RM: In terms of diagnosis and treatment planning, many of
the principles described in Part I of this discussion (Class II
surgical treatment) are applicable to Class III treatment as
well. In order for Class III cases to be treated with mandibular
surgery only, the maxilla must be in an ideal or at least an acceptable position in three planes of space.
Transversely, the maxilla must be wide enough posteriorly
Transversely
to accommodate the retracted mandibular position. A high
percentage of Class III cases are narrow in the maxilla relative
to the corrected mandibular position. As with most cases, the
Curve of Wilson should be level in the upper arch, which is
very difficult to achieve in the maxilla in Class III cases. Also,
cants in the maxilla must be minimal, or at least acceptable to
the patient.
Horizontally, the airway should be evaluated to assure that
carrying out a mandibular setback will continue to assure an
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adequate airway. The upper incisors must be located in an
acceptable position, or be movable to that position orthodontically. Correct incisor torque position must be achievable
orthodontically (110o to 115o to the palatal plane, and 55o to
59o to the maxillary occlusal plane). Ideally, with normal lip
thickness, the upper central incisors should be positioned approximately 9mm behind the true vertical line. (Editor’s note:
see part one of this interview regarding the true vertical line.)
With thin lips, the incisors can be positioned slightly more
anteriorly, and with thick lips, slightly more posteriorly.
Crowding must be managed either with interproximal reduction or extractions to accommodate upper incisor horizontal
position. Distal lateral spaces may be needed along with
lower incisor stripping to assure proper overbite and overjet
in the corrected Class I position.
Vertically, the maxillary dentition should be relatively flat.
When vertical “steps” are present, surgical leveling is preferred over orthodontic leveling. Vertical incisor exposure
should be in the range of 2mm to 5mm. (Class III patients frequently show inadequate vertical development of the maxilla
and lack of incisor exposure). In order to avoid post-surgical disappointment, it is critical that modifications from
this range be thoroughly discussed with the patient prior to
surgery. The maxillary occlusal plane should be close to a
normal range (94o to 98o to the true vertical line), as it cannot
be adjusted when surgery is confined to the mandible only.
When the occlusal plane is very flat or very steep in these
cases, the distally positioned mandible may be either too
prominent or too retrusive. Chin reductions can be helpful in
this regard, but this procedure has its limitations. In summary, for mandibular surgery only to be successful, maxillary
tooth and jaw position requirements are significant, and the
above three-dimensional considerations should be carefully
evaluated.
In the mandible, Transversely, the Curve of Wilson should
be leveled, usually with buccal uprighting. Horizontally, the
incisors should be positioned as close to an ideal position as
possible, 90o to 95o to the mandibular plane and 62o to 66o to
the mandibular occlusal plane. Frequently the lower incisors
are retroclined in Class III cases, and it is a challenge to procline them far enough forward. The shape of the symphisis
and lower lip pressure create a resistance to this movement.
Crowding should be managed either with interproximal re-
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duction or extractions to accommodate correct lower incisor
position.
Vertically, mandibular Curve of Spee leveling should be
completed orthodontically prior to surgery. This allows for
more accurate positioning of the occlusion by the surgeon,
and minimizes the need for a surgical splint. As with Class
II cases, when teeth are properly aligned, including Curve of
Spee leveling, the occlusion acts as an excellent splint, and very
little orthodontic tooth movement is required post-surgically.
For general upper and lower tooth alignment in these cases,
as with Class II cases, the American Board requirements
serve as excellent guidelines for the orthodontist. Concerning mandibular surgical fixation technique, there is great
controversy among surgeons concerning fixation screws
versus mini-plates. My experience has been that the use of
mini-plates allows for more accurate condyle positioning,
with fewer post-surgical symptoms, than do fixation screws.
TM: What are your indications and requirements
for Class III maxillary surgery only?
RM: As stated above, this is becoming a far more common
surgical procedure than in the past. This is due to the awareness that: 1. when possible, eliminating mandibular setback
surgery and treating the Class III patient with maxillary
surgery only can contribute to the prevention of that patient
developing sleep apnea, and 2. Class III malocclusions are
more frequently the result of maxillary deficiency versus
mandibular prognatism. So, when surgery is completed
in the maxilla only, the mandible must be located in an
adequate position in the face, or in a position where it can
be rotated clockwise to an acceptable position by forward
and downward positioning of the maxilla. This is often a
good choice, as frequently the maxilla in Class III patients
is short vertically, with inadequate incisor exposure. Care
must be taken to reduce or eliminate clenching during the
healing process (with anti-clenching medication) so that
re-impaction of the maxilla does not occur. Asymmetries in
the mandible eliminate the alternative of maxillary surgery
only. Finally, in cases where surgery is limited to the maxila
only, the steepening of the occlusal plane can be achieved by
moving the maxilla down such that the mandible rotates in
a clockwise direction. Segmental maxillary surgery may be
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required in these cases because of a vertical “two-step” occlusion, a transverse maxillary discrepancy or both. Segmental
maxillary surgery will be discussed below under two-jaw
surgery. If maxillary surgical positioning and the resultant
mandibular rotation produces a good occlusion and a satisfactory facial result, but does not produce an adequate airway,
then two-jaw surgery is indicated. Pre-surgical orthodontic
tooth alignment can be carried out in a manner similar to
mandibular setback cases, as described above.
TM: Please discuss your ideas on two-jaw Class III
surgical cases.
RM: The limitations and indications for single Class III jaw
surgery were described above. When the limitations present
themselves, then two-jaw surgery is indicated. Such cases
require maximum attention and skill, but they do allow for the
most amount of flexibility and, hence, the best possible facial,
airway and occlusal results. More specifically, the corrected
occlusion can be properly placed between the airway posteriorly and the face anteriorly. This is greatly aided by setting
the occlusal plane in an ideal position, which is frequently not
possible with single-jaw surgeries.
Pre-surgical orthodontic alignment considerations in the
mandible were described above in the discussion on mandibular surgical only and apply similarly in two-jaw surgeries. The
maxillary surgical portion of the treatment can be completed
with a single piece LeForte procedure if there are no vertical or transverse discrepancies in the maxilla. Segmental
maxillary surgery is required in cases that have a “two-step”
occlusion vertically in the maxilla. The most common area
where vertical steps occur is between the lateral incisors and
cuspids. Therefore, this is the most common area (about 90%
of segmental cases) for sectioning the arch wires pre-surgically. The step may also occur between the cuspids and first
bicuspids (about 10% of the time) in which case arch wire sectioning would occur in this location. Very infrequently, other
segmental locations may be required. Arch wire segments can
be properly shaped by first coordinating the upper and lower
arch wires, and then sectioning the upper arch wire in the
appropriate locations. This allows the positioned maxillary
segments to fit the lower arch properly at the time of sur-
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gery. When there is a transverse discrepancy in the maxilla
(usually maxillary narrowing), a significant surgical decision
is required. Many surgeons are uncomfortable with large
segmental expansions (5mm to 10mm) in the maxilla. Their
concerns are related to the tendency for transverse relapse to
occur. Therefore, some surgeons prefer to do a SARPE procedure prior to orthodontic alignment to correct the maxillary
transverse problem, and then a second surgery for vertical
and horizontal positioning of the arches after orthodontic
alignment. However, a second surgery is not popular with patients. Fortunately, surgeons are improving their techniques
in dealing with transverse discrepancies so that all needed
maxillary correction can be accomplished with a single surgical procedure with stable results. In particular, rather than
single sectioning in the mid-palatal suture area, a cut can be
made on each side of the suture. This divides the amount of
widening into two areas, thereby increasing the chances for
stability. Final surgical splints are also not required in these
two-jaw cases if the pre-surgical orthodontic alignment is
satisfactory and the upper arch wire segments are connected
during surgery using acrylic across the upper surgical sites.
This method forms a single stable upper arch because of the
formation of a very solid single arch wire.
Most surgeons complete upper jaw surgery first in these
cases, using the original mandiblar position and an interim
surgical splint as a baseline for maxillary positioning. Others
complete mandibular surgery first, contending that there
are frequently discrepancies between seated positions of the
condyles in patients that are awake versus the positions in
patients that are anesthetized (no matter how much care is
taken). When this discrepancy occurs, the usual result is a
mandible that is seated more posteriorly than planned. Thus,
the more retrusive anesthetized mandibular reference position and interim splint set the maxilla more posterior than
desired. While completing mandibular surgery first requires
great accuracy, the argument for this approach is valid and
compelling.
TM: Thank you, Dr. McLaughlin, for your
experienced and valuable comments.
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