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CLINICIAN'S CORNER
A surgery-first approach using single-jaw
rotational mandibular setback in
low-angle mandibular prognathism
Gyeong-Su Kim,a Sung-Hoon Lim,a Seo-Rin Jeong,a and Jae Hyun Parkb
Gwangju and Seoul, South Korea, and Mesa, Ariz
For the treatment of low-angle mandibular prognathism, rotational mandibular setback surgery is usually performed with Le Fort I maxillary osteotomy to rotate the maxillomandibular complex simultaneously. However,
this maxillary surgery can be replaced with the orthodontic intrusion of maxillary posterior teeth. Single-jaw rotational mandibular setback surgery can be done with a surgery-first approach by planning orthodontic rotation of
the maxillary occlusal plane with the simulation of the postsurgical forward mandibular rotation. This case report
describes this approach applied to a 19-year-old female patient with low-angle mandibular prognathism but
without maxillary deficiency. A Class II open bite was formed by the rotational setback surgery. During postsurgical orthodontic treatment, the maxillary total arch was distalized with maxillary molar intrusion using palatal
mini-implants and lever. This case report demonstrates that orthodontic rotation of the maxillary occlusal plane
and simulation of mandibular rotation can replace maxillary surgery and enable single-jaw rotational mandibular
setback surgery with a surgery-first approach. (Am J Orthod Dentofacial Orthop 2021;-:---)
M
andibular setback surgery is used to correct
mandibular prognathism. This mandibular
setback is usually performed along the occlusal
plane to prevent bite opening at the anterior or posterior
teeth.1 During this setback along the occlusal plane, the
vertical bony step (VBS) develops inevitably at the
mandibular border between the proximal and distal
bony segments because of the difference between the
occlusal plane and the mandibular plane. The VBS
stretches the pterygomasseteric sling, causing postsurgical forward rotation of the mandible.2-6 In patients
with a low mandibular plane angle, simple mandibular
setback along the occlusal plane cannot improve the
a
Department of Orthodontics, College of Dentistry, Chosun University, Gwangju,
South Korea.
b
Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health,
A.T. Still University, Mesa, Ariz; Graduate School of Dentistry, Kyung Hee University, Seoul, South Korea.
All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported.
This study was supported by research funds from Chosun University Dental Hospital, South Korea, 2020.
Address correspondence to: Sung-Hoon Lim, Department of Orthodontics, College of Dentistry, Chosun University, 303, Pilmun-daero, Dong-gu, Gwangju
61453, South Korea; e-mail, [email protected].
Submitted, January 2021; revised, February 2021; accepted, April 2021.
0889-5406/$36.00
Ó 2021 by the American Association of Orthodontists. All rights reserved.
https://doi.org/10.1016/j.ajodo.2021.04.017
prominence of the chin and mandibular border relative
to the basal bone. In addition, the smile arc, which is
deficient in most low-angle mandibular prognathism
patients, may not be improved.7,8 Instead, mandibular
setback with a backward rotation is required in these patients to improve a square-looking mandible. To rotate
the mandible during mandibular setback, maxillary Le
Fort I osteotomy is generally performed to rotate the
occlusal plane clockwise.7,9 However, maxillary molar
intrusion during presurgical orthodontic treatment also
can change the maxillary occlusal plane, allowing rotational mandibular setback along the changed maxillary
occlusal plane.10,11
The demand for the surgery-first approach12 is
increasing in favor of early surgical correction. Because
presurgical intrusion of the maxillary molars is not available with the surgery-first approach, double-jaw surgery, including posterior impaction of the maxilla and
rotational mandibular setback, is usually performed in
patients with low-angle mandibular prognathism. However, intruding maxillary molars is possible during postsurgical orthodontic treatment after single-jaw
mandibular setback surgery with a backward rotation
of the distal segment of the mandible. This case report
demonstrates that the surgery-first approach can be
applied successfully for single-jaw rotational mandibular setback surgery.
1
Kim et al
2
Fig 1. Pretreatment facial and intraoral photographs.
DIAGNOSIS AND ETIOLOGY
A 19-year-old female presented to our department
with the chief complaint of a protruded chin (Fig 1).
Her profile was concave with a protruded chin. Her
maxillary incisor exposure was deficient in both resting
posture and smiling. In addition, there were Class III
end-on molar relationships on both sides.
Cone-beam computed tomography showed that the
patient’s maxillary dental midline coincided with the
midsagittal reference plane, and her mandibular dental
midline shifted 1.5 mm to the left, and the pogonion
also shifted 2.5 mm to the left (Fig 2). Her left gonion
was positioned 3.3 mm buccally relative to her right
gonion. As a transverse dentoalveolar compensation to
the mandibular shift to the left, her maxillary left first
molar was positioned 2.5 mm more buccally than the
maxillary right first molar. Her airway was quite broad
(Fig 2, B), and there was no snoring or sleep apnea.
Lateral cephalometric analysis showed low-angle
skeletal Class III with a normal maxilla and prognathic
mandible (Table). She had a flat occlusal plane angle,
proclined maxillary incisors, and retroclined mandibular
incisors as an anteroposterior dentoalveolar compensation to the mandibular prognathism. Because of these
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excellent dentoalveolar compensations, there was no
crossbite.
TREATMENT OBJECTIVES
Treatment objectives were (1) to establish a skeletal
and dental Class I relationship by resolving the mandibular prognathism, (2) to decompensate the anteroposterior and transverse compensations, (3) to correct the
mandibular asymmetry, and (4) to increase the occlusal
and mandibular plane angles to give the patient a less
square-looking face and to increase her smile arc and
maxillary incisor exposure.
TREATMENT ALTERNATIVES
The following alternatives were presented to the patient and her parents, including rotational mandibular
setback surgery to improve the protuberance of the
chin and mandibular border relative to the mandibular
basal bone: (1) double-jaw surgery for clockwise rotation (posterior impaction) of the maxillomandibular
complex was the first option. This would result in anteroposterior decompensation of the incisor inclinations
and thus reduce the required amount of orthodontic
decompensation; (2) single-jaw mandibular rotational
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Fig 2. Pretreatment records: A, lateral cephalogram; B, lateral and frontal cone-beam computed tomography (CBCT) views; C, panoramic view constructed from CBCT; D, maxillary digital model superimposed on the CBCT model shows transverse dentoalveolar compensation to the mandibular shift to
the left; E, CBCT model shows mandibular translation to the left.
Table. Cephalometric measurements
Parameter
SNA ( )
SNB ( )
ANB ( )
Wits (mm)
FMA ( )
Occlusal plane (Tweed) to FH ( )
Maxillary occlusal plane to FH ( )
Occlusomandibular plane angle ( )
U1 to SN ( )
U1 to FH ( )
IMPA ( )
Interincisal angle ( )
Upper lip to E-plane (mm)
Lower lip to E-plane (mm)
A0 B0 to FH ( )
Norm
81.1
79.2
2.5
0.0
29.6
10.0
14.0
19.6
105.3
113.8
91.6
125.4
0.8
0.1
81.0
Pretreatment
80.6
87.3**
6.7****
14.5****
14.6**
6.5
8.4*
8.2
118.2*
125.8*
62.9****
156.7***
4.9*
3.7*
101.7****
Postsurgery
80.7
77.5
3.2
0.5****
30.4
8.9
7.5*
21.5
117.1*
124.3*
69.4****
135.8
0.2
2.9*
76.7*
Posttreatment
80.8
80.4
0.3*
6.3****
26.5
12.3*
13.9
13.2*
100.5
108.1
80.2**
146.2**
2.4
5.0**
81.9
2-year retention
80.5
80.2
0.3*
8.3****
26.7
11.1
13.1
15.6*
102.8
110.6
80.8**
141.9*
3.5*
5.7**
82.1
FMA, Frankfort mandibular plane angle; IMPA, incisor mandibular plane angle.
*.1 standard deviation from the norm; **.2 standard deviations from the norm; ***.3 standard deviations from the norm; ****.4 standard
deviations from the norm.
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Fig 3. Three-dimensional surgical simulation: A, presurgery (blue); B, simulation of ideal mandibular
position (yellow); C, additional 3.5 clockwise rotation of distal segment to resolve vertical overlap of
maxillary and mandibular molars (green). Linear measurements shown in the figure are in millimeters.
The oblique lines in the left column show the A0 B0 to FH angle of 81 . In addition, a computer-aided
design–computer-aided manufacturing surgical splint (pink) was fabricated from the surgical occlusion,
and a surgical stent (pale pink) for angle shaving was also fabricated.
setback surgery after intrusion of maxillary posterior
teeth to increase the maxillary occlusal plane angle
was the second option. Although this option avoids
maxillary surgery, presurgical orthodontic treatment is
needed; (3) a surgery-first approach with single-jaw
mandibular rotational setback surgery was the third option. This option would bring immediate improvement
of the low-angle mandibular prognathism. However,
this approach results in VBS and stretching of the pterygomasseteric sling, causing postsurgical forward
mandibular rotation. Therefore, overcorrection of the
rotational setback is required to accommodate this postsurgical forward rotation.
With all options, maxillary molar distalization is
necessary to decompensate the proclined maxillary
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incisors. In the first option, double-jaw surgery would
reduce the need for orthodontic decompensation and
could thereby reduce the treatment duration. However,
the patient and her parents wanted to minimize the
risk of surgery, so they rejected the first option. In addition, because the patient had a long break between her
high school graduation and admission to the university,
she really wanted to have the surgery during this interval.
Therefore, the third option was chosen.
TREATMENT PROGRESS
Three-dimensional surgical simulation was made for
the surgery-first approach (Fig 3). To that end, digital
dental models were registered on the mesh models extracted from the pretreatment cone-beam computed
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Fig 4. Surgical simulation and surgery results: A-C, superimposition of presurgery (gray) and postsurgery (red); D and E, superimposition of surgery simulation (yellow) and postsurgery (red). Angle
shaving was done as planned; F, color map of mesh deviation. Correction of mandibular asymmetry
was 0.5 mm deficient, and bite was opened 0.8 mm more; G to I, superimposition of presurgery
(gray) and postsurgery (red) mandibles. Although the backward rotation of the proximal segment
was minimal, condylar sagging occurred because of the inward roll and yaw rotation of the proximal
segments.
tomography. Bilateral sagittal split ramus osteotomies
were simulated. Then, the distal segment of the
mandible was setback so that the A0 B0 to FH angle was
81 .13,14 In addition, the distal segment was rotated by
11.5 backward (clockwise), resulting in a Frankfort
mandibular plane angle of 27.1 . This simulation resulted in a 14 mm setback at the pogonion and an
8 mm setback at the mandibular incisal edge. In addition, a 2 mm transverse shift to the right was made to
correct the asymmetry. During this simulation, the antegonial notch depth was maintained to prevent stretching
of the pterygomandibular sling that could cause a forward mandibular rotation.5,6,15
In this simulated position, the occluding molars overlapped each other. When double-jaw surgery is done,
this overlap can be removed by the impaction of the posterior maxilla. However, with mandibular single-jaw surgery, the overlap of the occluding teeth cannot be solved
without increasing the vertical dimension. Therefore, the
mandible was rotated 3.5 backward with the center of
rotation at the medial pole of the condyle until the tooth
overlaps were resolved. Because of this rotation, a Class
II open bite was created, and the mandibular setback was
increased to 19 mm at the pogonion and 11 mm at the
mandibular incisal edge. To place passive surgical wires,
0.017 3 0.025-in stainless steel (SS) archwires were tied
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Fig 5. One-month postsurgery. Severe Class II open bite was formed as intended.
with 0.018-in slot standard edgewise brackets
and adapted to the pretreatment model passively by
bending the archwires. Subsequently, these archwire
and bracket assemblies were transferred to the dentition
using transfer jigs.
Surgery was done as planned except for a 0.5 mm
deficient transverse correction and 0.8 mm more bite
opening (Fig 4).16 Postsurgical orthodontic treatment
was started 1 month after surgery (Fig 5). For maxillary
molar distalization, two 2.0 3 8-mm mini-implants
were placed in the midpalate, and a lever plate was
placed over the platforms of the mini-implants. Then
nuts were fastened to fix the plate to the mini-implant
heads (LIM plate system; Jeil Medical, Seoul, South
Korea) (Fig 6).11,17,18 Brackets were bonded on the
lingual surfaces of the maxillary first molars, and a
0.0215 3 0.028-in SS transpalatal arch (TPA) was
placed. Intrusive distalization forces were generated on
both sides by applying elastomeric chains from the
TPA to the hooks of the lever plate. For transverse
decompensation, an elastomeric chain was applied
from the crimpable hook on the right side of the TPA
to the center of the lever plate.
At 5-month postsurgery, brackets were also bonded
on the lingual surfaces of the maxillary first premolars,
and a 0.019 3 0.025-in SS TPA was placed for
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constriction of the premolar width to improve arch coordination. At 9-month postsurgery, elastomeric chains
were also connected from the premolar TPA to the lever
plate to retract the premolars into the space created by
the molar distalization. At this time, en-masse retraction
of the anterior teeth was performed on the buccal side
using a 0.020-in SS archwire to allow lingual tipping
of the maxillary incisors as an anteroposterior decompensation. At 1-year and 10-month postsurgery, appliances were debonded, and fixed retainers were bonded
(Fig 7).
TREATMENT RESULTS
Posttreatment facial photographs showed the correction of the protrusive and asymmetric chin and improvement of the smile arc (Fig 7). Intraoral photographs
showed Class I molar relationships on both sides with
optimal overjet and overbite. On the panoramic radiograph, good root parallelism was seen, and root resorption was not distinct (Fig 8). Superimposition
immediately after surgery and posttreatment (Fig 8, C)
showed 3.6 forward mandibular rotation (Fig 8, C).
The center of rotation located by the Reuleaux method
was at 16 mm superior and 11 mm posterior to the condylion. This 3.6 mandibular forward rotation with this
center of rotation was greater than the simulation of
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Fig 6. Treatment progress. Top row, palatal mini-implants and lever plate assembly were placed for
maxillary molar distalization, transverse decompensation, and molar intrusion; middle row, premolar
TPA was also placed and distalization forces were applied; bottom row, closure of the spaces created
by molar distalization was completed. M, months of treatment; Y, years of treatment.
the 3.5 mandibular rotation with the center of rotation
at the condyle, resulting in an additional 1.8 mm of
anterior movement of the pogonion and 1.6 mm of superior movement of the menton beyond the ideal jaw
position simulation (Fig 8, D). As a result of this additional forward mandibular rotation, the ANB angle was
improved from 6.7 to 0.3 , and Wits appraisal was
improved from 14.5 mm to 6.3 mm, leaving a mild
skeletal Class III relationship. Model superimposition of
pretreatment and posttreatment maxillary models
showed intrusion and distalization of molars and
retraction and extrusion of incisors resulting in steepening of the maxillary occlusal plane. In addition, teeth
on the right moved buccally and on the left moved
lingually, achieving decompensation of the transverse
dentoalveolar compensation to mandibular asymmetry
(Fig 9).11,19
After 2 years 6 months of retention, the improved
facial appearance was maintained, and the occlusion
was stable (Fig 10). However, the superimposition of
posttreatment and the 2-year 6-month retention lateral
cephalograms showed a slight forward rotation of the
mandible and 1 mm of flaring of the maxillary incisors
(Fig 8, F). This flaring was far greater than the
posttreatment mandibular rotation, indicating a mild
relapse tendency of the maxillary total arch
distalization.
DISCUSSION
Although good stability of both the surgery-first
approach and conventional orthognathic surgery was reported,20 VBS inevitably increases because of the
increased occlusal interferences at the surgical occlusion
with the surgery-first approach.11,12,15 VBS increases as
the bite opens, and as the occlusomandibular plane
angle increases, it stretches the pterygomasseteric sling,
resulting in a forward rotation of the mandible during
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Fig 7. Posttreatment facial and intraoral photographs. Treatment was finished 1 year 10 months after
surgery.
postsurgical orthodontic treatment.2 In the present patient, there was more actual postsurgical forward rotation than simulated rotation; 1.8 mm more forward
movement of the mandible than predicted. During simulation of the ideal jaw position, there was still VBS,
although it did not decrease the antegonial notch depth.
When measured at the antegonial notch, there were
4.7 mm of VBS on the right side and 2.8 mm on the
left side immediately after surgery, and they were larger
than the simulation of surgery (Fig 4). This increased
VBS stretched the pterygomasseteric sling more, resulting in more forward rotation than in the simulation.
The superimposition of the pretreatment and posttreatment lateral cephalograms showed that the posttreatment mandibular border was up to 2 mm below the
pretreatment mandibular border. However, the simulated ideal jaw position was up to 4 mm below the pretreatment mandibular border. Therefore, it seems that
the postsurgical forward rotation varies among patients.
No guideline or consensus was made on the prediction
of postsurgical mandibular rotation. Further studies
are needed to improve the accuracy of this prediction.
During the postsurgical forward rotation of the
mandible, the mandibular incisor rises more than the
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posterior teeth. This can cause intrusion and flaring of
the maxillary incisors, exacerbating the already deficient
smile arc and incisor exposure. To avoid this problem,
rotation of the mandible should be reflected in the surgical simulation, and an anterior open bite should be
created on the surgical occlusion. This postsurgical anterior open bite should be increased as the occlusal interferences at the surgical occlusion increase, and also the
overjet should be increased because forward rotation decreases overjet. This requires additional setbacks to
accommodate the postsurgical forward rotation. Unfortunately, this additional setback can make the setback
surgery becomes more difficult and may reduce the stability of the mandibular setback.21 Therefore, the
surgery-first approach is more suitable to patients in
which the required amount of mandibular setback is
not severe, and the anticipated amount of VBS is not
great. If a patient does not satisfy these conditions,
double-jaw surgery with impaction of the posterior
maxilla should be considered to reduce the VBS and
postsurgical forward rotation of the mandible. In the
present patient, the mandible was setback 19 mm during
surgery, and 13.6 mm (72%) of this setback remained after postsurgical forward rotation.
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Fig 8. Comparison of radiographs: A, panoramic radiograph at 5-weeks postsurgery; B, posttreatment
panoramic radiograph; C, cephalometric superimposition of postsurgery (red) and posttreatment (blue)
showed forward rotation of mandible; D, superimposition of posttreatment lateral cephalogram and
3-dimensional surgical simulation (blue and yellow); E, superimposition of pretreatment (yellow) and
posttreatment (blue) lateral cephalograms; F, superimposition of posttreatment (blue) and 2-year
6-month retention (orange) lateral cephalograms. M, months of treatment; Y, years of treatment.
Mandibular setback surgery decreases the airway
measurements.22-24 However, patients with prognathic
mandible tend to have a larger upper pharyngeal
airway,25,26 and mandibular setback surgery may not
degrade the upper airway patency,24,27,28 resulting in a
very low incidence of obstructive sleep apnea (OSA) after
mandibular setback surgery.28 In the present case, pretreatment oropharyngeal volume and minimal crosssectional area were larger than average for non-OSA
subjects,29,30 and the values decreased at 5-day postsurgery (Fig 11). Irani et al22 showed that this diminished
airway could be improved during postsurgical orthodontic treatment even without significant relapse of
mandibular setback surgery. In the present case, the
diminished minimal pharyngeal width on the cephalogram was not improved even with the 5.4 mm
postsurgical forward movement of the chin. This may
have been caused by the superior movement of the
mandibular plane during postsurgical orthodontic treatment. However, all airway measurements were within
one standard deviation from the mean values of nonOSA patients.29-32 The present patient did not have
any OSA-related symptoms and had a normal body
mass index at both pretreatment and posttreatment.
When planning mandibular setback surgery, OSArelated symptoms, body mass index, and airway measurements should be considered in the surgery plan to
prevent the development of the OSA.
After treatment, the improvement of the facial esthetics was similar to the results that can be achieved
by double-jaw surgery. In other words, the doublejaw-surgery-like effect of rotational mandibular setback
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Fig 9. Model superimposition. Top row, superimposition of pretreatment model (blue) and posttreatment model (red); bottom row, posttreatment model superimposed on pretreatment maxilla. Arch symmetry was improved by transverse decompensation.
Fig 10. Intraoral photographs at 2-year 6-month retention.
was achieved with single-jaw surgery.11 This method demands more role of the orthodontist because the effect
of maxillary surgery must be achieved orthodontically.
Future studies are needed to improve this single-jaw
rotational setback with a surgery-first approach.
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CONCLUSIONS
Single-jaw rotational setback surgery for low-angle
mandibular prognathism can be performed using a
surgery-first approach. A Class II open bite was created
on the surgical occlusion on the basis of a simulation
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Fig 11. Airway measurements. Cone-beam computed tomography measurements29,30 and cephalometric measurements31,32 showed values within one standard deviation from the mean values for
non-OSA subjects.29-32
of postsurgical forward rotation of the mandible. During
postsurgical orthodontic treatment, the maxillary total
arch was distalized with maxillary molar intrusion. This
case report demonstrates that orthodontic rotation of
the maxillary occlusal plane and simulation of mandibular rotation can replace maxillary surgery and enable
single-jaw rotational mandibular setback surgery with
a surgery-first approach.
2.
3.
4.
AUTHOR CREDIT STATEMENT
5.
Sung-Hoon Lim contributed to treatment and manuscript revisions; Gyeong-Su Kim contributed to data
collection and original draft preparation; Seo-Rin Jeong
and Jae Hyun Park contributed to manuscript revisions.
6.
7.
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