Comparisons of Jaw Line and Face Line after Mandibular Setback: Intraoral Vertical Ramus versus Sagittal Split Ramus Osteotomies


Chen, C.M.; Tseng, Y.C.; Ko, E.C.; Chen, M.Y.C.; Chen, K.J.; Cheng, J.H.

Biomed Research International 2018: 1375085

2019


This study investigates the differences in the lateral profile and frontal appearance after sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO) procedures for the correction of mandibular prognathism. Sixty patients (30 SSRO and 30 IVRO) underwent mandibular setback surgery. Serial cephalograms were obtained: (1) T1: approximately 1 month before surgery; (2) T2: at least 6 months after surgery for SSRO and at least 1 year after surgery for IVRO. The landmarks, linear distances, and related angles were measured. The <i>t</i>-test was applied to the intragroup and intergroup comparisons. The null hypothesis was that SSRO and IVRO made no difference in the facial appearance. In the IVRO group, the ramus and gonial widths significantly decreased by 3.9 mm and 5.8 mm, respectively. SSRO significantly reduced the gonial angle by 2.6°, and IVRO increased it significantly by 5.3°. The postoperative increases at frontal bone levels 0 and 1 after IVRO were significantly larger than those after SSRO, but, at level 3, the increases after SSRO were larger than those after IVRO. In the frontal muscular and facial planes, SSRO and IVRO presented no difference. The frontal jaw angle and face angle were significantly larger with IVRO than with SSRO. Therefore, the null hypothesis was rejected. The ramus width and gonial width were significantly decreased in IVRO compared to SSRO. IVRO increased angles in the lateral profile (gonial angle and mandibular plane angle) and frontal appearance (jaw angle and face angle) more than SSRO did.

Hindawi
BioMed
Research
International
Volume
2018,
Article
ID
1375085,
7
pages
https://doi.org/10.1155/2018/1375085
Hindawi
Research
Article
Comparisons
of
Jaw
Line
and
Face
Line
after
Mandibular
Setback:
Intraoral
Vertical
Ramus
versus
Sagittal
Split
Ramus
Osteotomies
Chun-Ming
Chen
)
142
Yu-Chuan
Tseng1,
23
Edward
Chengchuan
Ko,
1
'
2
Michael
Yuan-Chien
Chen,
4
'
5
Kwei-Jing
Chen,
4
'
3
and
Jung-Hsuan
Chenge
3
Department
of
Oral
and
Maxillofacial
Surgery,
Kaohsiung
Medical
University
Hospital,
Kaohsiung
Medical
University,
Kaohsiung
Taiwan
2
School
of
Dentistry,
College
of
Oral
Medicine,
Kaohsiung
Medical
University,
Kaohsiung
Taiwan
3
Department
of
Orthodontics,
Kaohsiung
Medical
University
Hospital,
Kaohsiung
Taiwan
4
School
of
Dentistry,
College
of
Medicine,
China
Medical
University,
Taichung
Taiwan
5
Department
of
Dentistry,
China
Medical
University
Hospital,
China
Medical
University,
Taichung
Taiwan
Correspondence
should
be
addressed
to
Jung-Hsuan
Cheng;
zinglontion@hotmail.com
Received
17
August
2018;
Accepted
3
December
2018;
Published
18
December
2018
Academic
Editor:
Marilia
G.
de
Oliveira
Copyright
CO
2018
Chun-Ming
Chen
et
al.
This
is
an
open
access
article
distributed
under
the
Creative
Commons
Attribution
License,
which
permits
unrestricted
use,
distribution,
and
reproduction
in
any
medium,
provided
the
original
work
is
properly
cited.
Background.
This
study
investigates
the
differences
in
the
lateral
profile
and
frontal
appearance
after
sagittal
split
ramus
osteotomy
(SSRO)
and
intraoral
vertical
ramus
osteotomy
(IVRO)
procedures
for
the
correction
of
mandibular
prognathism.
Methods.
Sixty
patients
(30
SSRO
and
30
IVRO)
underwent
mandibular
setback
surgery.
Serial
cephalograms
were
obtained:
(1)
Tl:
approximately
1
month
before
surgery;
(2)
T2:
at
least
6
months
after
surgery
for
SSRO
and
at
least
1
year
after
surgery
for
IVRO.
The
landmarks,
linear
distances,
and
related
angles
were
measured.
The
t-test
was
applied
to
the
intragroup
and
intergroup
comparisons.
The
null
hypothesis
was
that
SSRO
and
IVRO
made
no
difference
in
the
facial
appearance.
Results.
In
the
IVRO
group,
the
ramus
and
gonial
widths
significantly
decreased
by
3.9
mm
and
5.8
mm,
respectively.
SSRO
significantly
reduced
the
gonial
angle
by
2.6°,
and
IVRO
increased
it
significantly
by
5.3%
The
postoperative
increases
at
frontal
bone
levels
0
and
1
after
IVRO
were
significantly
larger
than
those
after
SSRO,
but,
at
level
3,
the
increases
after
SSRO
were
larger
than
those
after
IVRO.
In
the
frontal
muscular
and
facial
planes,
SSRO
and
IVRO
presented
no
difference.
The
frontal
jaw
angle
and
face
angle
were
significantly
larger
with
IVRO
than
with
SSRO.
Therefore,
the
null
hypothesis
was
rejected.
Conclusions.
The
ramus
width
and
gonial
width
were
significantly
decreased
in
IVRO
compared
to
SSRO.
IVRO
increased
angles
in
the
lateral
profile
(gonial
angle
and
mandibular
plane
angle)
and
frontal
appearance
(jaw
angle
and
face
angle)
more
than
SSRO
did.
1.
Introduction
Facial
aesthetics
is
an
essential
factor
that
determines
inter-
personal
relationships,
affects
social
and
psychological
devel-
opment,
and
plays
an
important
role
in
a
person's
employ-
ment
and
social
status.
Mandibular
prognathism
is
an
Angle's
Class
III
malocclusion
commonly
characterized
by
a
concave
facial
shape.
In
addition
to
abnormalities
in
the
growth
between
the
maxilla
and
the
mandible,
patients
with
Angle's
Class
III
malocclusion
have
a
shorter
anterior
cranial
base,
an
acute
cranial
base
angle,
and
a
more
obtuse
gonial
angle
[1,
2].
Moreover,
patients
with
mandibular
prognathism
present
with
anterior
crossbite
leading
to
difficulty
in
mastication.
This
further
results
in
problems
with
malnutrition
and
vocal-
ization.
The
unaesthetic
profile
and
malocclusion
often
lead
to
social
dysfunction
and
psychological
disorders.
However,
the
etiology
of
mandibular
prognathism
is
still
uncertain.
It
has
been
thought that
environmental
and
genetic
factors
are
involved
in
the
growth
and
development
of
mandibular
prognathism
[1]
.
Treatment
for
patients
with
mandibular
prognathism
not
only
requires
mandibular
setback
to
correct
the
malocclusion
7
°
Po
Or
Co
Y
x
SIG
65
°
Go
\
Ag
Not›-
RP
Pog
2
BioMed
Research
International
and
restore
the
masticatory
function
but
also
requires
con-
sideration
of
the
harmony
of
facial
patterns
after
surgery.
Numerous
types
of
mandibular
setback
methods
exist,
sagit-
tal
split
ramus
osteotomy
(SSRO)
and
intraoral
vertical
ramus
osteotomy
(IVRO)
being
the
most
commonly
used
at
present.
Both
SSRO
and
IVRO
have
their
share
of
advantages
and
disadvantages
due
to
the
difference
in
osteotomy
line
designs.
Most
reports
in
the
literature
have
investigated
the
postoperative
skeletal
stability
[3-6]
and
profile
changes
[7-
11]
after
these
two
types
of
surgery,
but
rarely
have
studies
compared
the
designs
of
osteotomy
in
both
procedures
and
their
effects,
especially
regarding
differences
in
bone
tissue,
muscular
tissue,
and
skin
surface.
This
study
aims
to
investigate
and
compare
changes
between
the
SSRO
and
IVRO
procedures
regarding
the
frontal
and
lateral
bone
plane
(jaw
line),
muscular
line,
and
the
skin
surface
(face
line).
2.
Materials
and
Methods
This
study
enrolled
60
patients
with
mandibular
prog-
nathism.
The
exclusion
criteria
were
as
follows:
(1)
patients
with
craniofacial
malformations
such
as
a
cleft
lip
and
palate;
(2)
patients
who
have
had
facial
trauma
or
tumors;
(3)
patients
who
underwent
surgeries
like
genioplasty
or
maxillary
surgery.
Thirty
patients
(17
men
and
13
women),
with
an
average
age
of
24
years
(range
of
18-33
years),
under-
went
SSRO
setback
mandible
and
miniplate
rigid
fixation
at
the
Department
of
Oral
and
Maxillofacial
Surgery,
China
Medical
University
Hospital.
The
other
30
patients
(12
men
and
18
women),
with
an
average
age
of
20.6
years
(range
of
17-34
years),
underwent
modified
IVRO
[12]
and
6-week
intermaxillary
fixation
(IMF)
at
the
Department
of
Oral
and
Maxillofacial
Surgery,
Kaohsiung
Medical
University
Hospital.
Serial
cephalograms
were
obtained:
(1)
Tl:
approximately
1
month
before
surgery;
(2)
T2:
at
least
6
months
after
surgery
for
SSRO
and
at
least
1
year
or
more
after
surgery
for
IVRO.
The
following
landmarks
were
identified:
sella
(S),
nasion
(N),
orbitale
(Or),
porion
(Po),
condylion
(Co),
the
posteriormost
and
inferiormost
points
of
the
ramus
(RP),
gonion
(Go),
pogonion
(Pog),
antegonial
notch
(Ag),
sigmoid
notch
(SIG),
and
menton
(Me).
This
coordinate
system
had
its
origin
at
point
N
and
its
x-axis
at
an
upward
of
the
sella-nasion
(S-
N)
line
as
the
horizontal
axis.
The
y-axis
was
the
line
passing
through
the
S
and
perpendicular
to
the
x-axis
(Figure
1).
The
ramus
width
(ramus
distance
through
the
SIG
parallel
to
the
FH
line)
and
gonial
width
(gonial
distance
through
the
Ag
point
65°
to
the
FH
line)
[13]
were
measured
(Figure
1).
The
three
angles
(ramus
angle,
gonial
angle,
and
mandibular
plane
angle)
were
investigated
using
lateral
cephalography.
In
the
posteroanterior
film,
the
Lo
(lateral
orbitale)
is
the
intersection
of
the
Lo
contour
with
the
innominate
line.
The
Lo-Lo
line
is
as
the
horizontal
plane
and
the
z-axis
is
a
midsagittal
line
perpendicular
to
the
horizontal
plane.
RO
(ramus
origin)
is
the
most
lateral
inferior
point,
where
the
mastoid
process
outline
crosses
the
condylar
neck.
R1
is
10
mm
below
RO
and
so
on.
From
clinical
observation,
the
long
axis
of
the
canine
was
a
junction
with
the
mandibular
inferior
border
at
the
CBI
(chin
bone
inferior;
5
mm
above
FIGURE
1:
Cephalometric
landmarks,
linear
and
angular
measure-
ments.
N:
nasion,
S:
sella,
Po:
porion,
Or:
orbitale,
Pog:
pogonion,
Me:
menton,
SIG:
sigmoid
notch,
Ag:
antegonial
notch,
Go:
gonion,
Co:
condylion,
and
RP:
the
posteriormost
and
inferiormost
points
of
the
ramus.
x-axis
(horizontal
line:
to
NS
line),
y-axis
(vertical
line
through
S).
FH
plane:
a
line
connecting
Po
to
Or.
Pterygomasseteric
sling
(PMS)
plane:
a
line
through
Ag
point
65°
to
FH
plane.
Red
arrow
(angle):
1:
mandibular
plane
angle;
2:
ramus
angle;
3:
gonial
angle.
Green
lines
(distances):
4:
ramus
width;
5:
gonial
width.
Me).
The
long
axis
of
the
second
molar
was
a
junction
with
the
mandibular
inferior
border
at
the
CBS
(chin
bone
superior;
20
mm
above
Me).
Therefore,
the
study's
design
was
as
follows:
CSI
(chin
skin
inferior)
and
the
CBI
are
5
mm
above
the
MeS
(skin
of
menton)
and
the
Me
(bone
of
menton),
respectively.
The
CSS
(chin
skin
superior)
and
the
CBS
(chin
bone
superior)
are
20
mm
above
the
MeS
and
Me,
respectively.
The
R
line
(bone
plane)
is
connected
with
RO
and
R3.
The
M
line
(muscular
plane)
is
connected
with
MO
and
M3.
The
S
line
(skin
plane)
is
connected
with
SO
and
S3.
The
chin
bone
line
is
connected
with
the
CBS
and
the
CBI.
The
chin
skin
line
is
connected
with
the
CSS
and
the
CSI.
The
angles
(A:
Or-ramus
angle,
B:
Or-muscle
angle,
and
C:
Or-
skin
angle)
are
the
intersection
of
the
Lo-Lo
line
with
the
R
line,
M
line,
and
S
line,
respectively.
The
jaw
angle
(angle
D)
is
the
angle
between
the
R
line
and
CBS-CBI
line.
The
face
angle
(angle
E)
is
the
angle
between
the
S
line
and
CSS-CSI
line.
In
this
study,
bilateral
frontal
distances
were
measured
in
the
bone,
muscle,
and
skin
planes.
The
postoperative
changes
in
frontal
dimensions
and
angles
were
measured
(Figure
2).
The
data
in
this
study
were
analyzed
using
the
IBM
SPSS
20
statistical
software
at
a
statistically
significant
value
p
<
0.05.
The
t-test
was
applied
to
the
intragroup
and
intergroup
comparisons.
The
null
hypothesis
was
that
SSRO
and
IVRO
made
no
difference
in
the
facial
appearance.
The
systematic
error
and
accidental
error
from
the
two
data
collections
were
calculated.
The
systematic
error
was
calculated
using
the
paired
t-test
to
determine
whether
there
Pog
(horizontal)
Pog
(vertical)
Ramus
width
Gonial
width
Ramus
angle
Gonial
angle
Mandibular
plane
angle
<
0.0001
0.008
0.1252
0.2198
0.0006
0.0010
0.5173
*
-11.9
-0.2
-
-3.9
-
-5.8
0.9
5.3
-
6.2
<
0.0001
0.7355
<
0.0001
<
0.0001
0.3288
<
0.0001
<
0.0001
<
0.0001
0
.0774
<
0.0001
<
0.0001
0.3011
<
0.0001
<
0.0001
t,
IVRO
>
SSRO
t,
IVRO
>
SSRO
t,
IVRO
>
SSRO
t,
IVRO
>
SSRO
t,
IVRO
>
SSRO
-
5.0
3.41
-
1.4
2.73
-
0.6
2.16
-
0.9
3.65
2.2
3.03
-
2.6
3.77
-
0.4
3.42
4.15
2.68
3.05
2.66
4.97
4.45
4.39
Lo
D
CBS
D
CBS
SM
M
S
A
B
RO
0
SO
121M
I
SI
R
3M
2M
S
I
S2
3
R
SO
0
S2
R2
S3
R3
CSS
CSS
CBI
CBI
e
CSI
CSI
MeS
4
BioMed
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3
TABLE
1:
Comparison
of
lateral
dimensions
after
mandibular
setback
operations
(SSRO
vs.
IVRO).
Postoperation
changes
SSRO
IVRO
SSRO
vs.
IVRO
Mean
SD
p
value
Mean
SD
p
value
p
value
*:
intragroup
comparison:
statistically
significant,
p
<
0.05.
t:
intergroup
comparison:
statistically
significant,
p
<
0.05.
-:
not
significant.
FIGURE
2:
Lo:
lateral
orbitale,
horizontal
plane
(Lo-Lo
line),
z-axis
(red
line):
midsagittal
line
perpendicular
to
Lo-Lo
line,
Me:
menton,
MeS:
soft
tissue
of
Me,
R
line
(bone
plane:
RO-R3
line),
M
line
(muscular
plane:
MO-M3
line),
and
S
line
(skin
plane:
SO-S3
line).
CSI:
chin
skin
inferior,
CBI:
chin
bone
inferior,
CSS:
chin
skin
superior,
and
CBS:
chin
bone
superior.
Green
lines
(distances):
R
line,
M
line,
and
S
line
at
level
0
to
level
3.
Yellow
double
arrow
(angles):
A:
Or-ramus
angle,
B:
Or-muscle
angle,
and
C:
Or-skin
angle.
Pink
arrow
(angles):
D:
jaw
angle
(angle
between
R
line
and
CBS-CBI
line),
E:
face
angle
(angle
between
S
line
and
CSS-CSI
line).
was
a
significant
difference
between
the
two
descriptions
and
measurements.
The
accidental
error
was
calculated
based
on
the
following
formula
(Dahlberg's
formula).
The
Dahlberg
formula
is
expressed
as
follows:
accidental
errors
=
d
2
/
2
n,
where
d
represents
the
difference
between
the
two
sets
of
data
and
n
represents
the
number
of
measurements.
Statistical
analysis
showed
no
statistically
significant
difference,
and
thus
there
were
no
systematic
and
accidental
errors.
This
was
a
retrospective
study,
approved
by
the
human
investigation
review
committee
of
both
hospitals.
3.
Results
Table
1
shows
the
comparative
outcomes
of
the
SSRO
and
IVRO
groups.
Both
groups
revealed
significant
changes
regarding
the
amount
of
setback
after
surgery.
The
setback
in
IVRO
(11.9
mm)
was
more
significant
than
that
in
SSRO
(5
mm).
In
the
vertical
direction,
the
SSRO
group
had
significantly
superior
movement
whereas
the
IVRO
did
not.
In
the
SSRO
group,
ramus
width
decreased
by
0.6
mm
and
gonial
width
by
0.9
mm,
and
these
changes
were
not
4
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International
TABLE
2:
Comparison
of
frontal
distances
after
mandibular
setback
operations
(SSROvs.
IVRO).
Bilateral
sides
Mean
SSRO
SD
p
value
Postoperation
changes
IVRO
Mean
SD
p
value
p
value
SSRO
vs.IVRO
Bone
plane
0
1.9
3.07
0.0030
*
4.4
3.51
<
0.0001
0.0040
t,
IVRO
>
SSRO
1
1.9
2.91
0.0012
*
4.7
4.14
<
0.0001
0.0044
t,
IVRO
>
SSRO
2
2.7
2.79
<
0.0001
*
3.3
4.91
0.0010
0.5938
3
3.2
4.07
0.0002
*
-0.9
7.37
0.5005
0.0207
t,
SSRO
>
IVRO
Muscle
plane
0
0.1
4.29
0.8846
0.9
3.84
0.2341
0.6025
1
0.9
3.90
0.2505
0.7
4.10
0.3548
0.7963
2
0.9
4.24
0.2606
0.0
4.03
0.9648
0.3837
3
1.2
5.75
0.2578
-0.5
6.19
0.6877
0.2604
Skin
plane
0
0.5
4.14
0.5345
1.2
5.18
0.2284
0.6785
1
-0.5
4.09
0.5580
0.3
5.61
0.7874
0.6460
2
0.2
5.18
0.8635
-0.9
5.75
0.4063
0.4108
3
1.3
5.00
0.1720
-1.4
6.70
0.2751
0.0995
*:
intragroup
comparison:
statistically
significant,
p
<
0.05.
t:
intergroup
comparison:
statistically
significant,
p
<
0.05.
-:
not
significant.
\
FIGURE
3:
Jaw
line
(dotted
line):
preoperation
(blue);
postoperation
(red:
SSRO);
postoperation
(yellow:
IVRO).
Face
line
(solid
line):
preoperation
(blue);
postoperation
(red:
SSRO);
postoperation
(yel-
low:
IVRO).
statistically
significant.
In
the
IVRO
group,
ramus
width
and
gonial
width
significantly
decreased
by
3.9
mm
and
5.8
mm,
respectively.
In
addition,
the
IVRO
group
values
(ramus
width
and
gonial
width)
decreased
significantly
more
than
did
the
SSRO
group
values.
The
postoperation
mandibular
patterns
of
the
SSRO
and
IVRO
groups
were
shown
in
Figure
3.
Investigation
of
the
changes
in
related
angles
revealed
that
SSRO
significantly
increased
the
ramus
angle
by
2.2°
and
IVRO
had
an
insignifi-
cant
increase
of
0.9°.
SSRO
significantly
reduced
the
gonial
angle
by
2.6°
and
IVRO
significantly
increased
it
by
5.3°.
The
change
in
the
mandibular
plane
angle
with
SSRO
was
minimal,
whereas
IVRO
significantly
increased
it
by
6.2°.
The
increases
in
both
the
gonial
and
the
mandibular
angles
were
significantly
larger
with
IVRO
than
with
SSRO.
Table
2
reveals
significantly
increased
postoperative
frontal
distance
at
levels
(levels
0,
1,
and
2)
of
the
bone
plane
after
both
SSRO
and
IVRO.
At
bone
level
3,
SSRO
significantly
increased
the
frontal
distance
by
3.2
mm,
whereas
IVRO
decreased
it
by
0.9
mm,
but
the
difference
was
not
significant.
On
intergroup
comparisons,
the
postoperative
increases
at
bone
levels
0
and
1
were
significantly
larger
after
IVRO
than
after
SSRO,
but,
at
level
3,
the
increases
after
SSRO
were
larger
than
after
IVRO.
At
levels
(levels
0,
1,
2,
and
3)
of
the
muscular
plane,
no
significant
difference
existed
in
the
postoperative
frontal
distance
after
both
SSRO
and
IVRO,
and
no
difference
existed
for
intergroup
comparisons
either.
However,
SSRO
increased
the
frontal
distance
by
1.2
mm
at
muscular
level
3,
whereas
IVRO
decreased
it
by
0.5
mm.
At
levels
(levels
0,
1,
2,
and
3)
of
the
facial
plane,
no
significant
difference
existed
in
the
postoperative
frontal
distance
after
both
SSRO
and
IVRO,
and
no
difference
existed
for
intergroup
comparisons
either.
However,
SSRO
increased
the
frontal
distance
by
1.3
mm
at
facial
level
3,
whereas
IVRO
decreased
it
by
1.4
mm.
The
postoperation
frontal
appearances
of
the
SSRO
and
IVRO
groups
were
shown
in
Figure
3.
Table
3
reveals
that
SSRO
significantly
increased
the
frontal
Or-ramus
angle
by
2.3°
and
significantly
decreased
the
jaw
angle
by
3.8°.
IVRO
significantly
decreased
the
Or-ramus
angle
by
7.3
°
and
face
angle
by
5.4°.
On
intergroup
comparisons,
the
amount
of
decrease
in
the
Or-ramus
angle
and
face
angle
was
greater
with
IVRO
than
with
SSRO.
IVRO
significantly
increased
the
jaw
angle
and
face
angle
by
7.1°
and
3.4°,
respectively,
whereas
SSRO
decreased
the
jaw
angle
and
face
angle
by
3.8
°
and
3.5°,
respectively.
Intergroup
comparisons
showed
that
the
BioMed
Research
International
5
TABLE
3:
Comparison
of
frontal
angles
after
mandibular
setback
operations
(SSROvs.
IVRO).
Bilateral
sides
Mean
SSRO
SD
p
value
Postoperation
changes
IVRO
Mean
SD
p
value
p
value
Or-ramus
angle
2.3
5.53
0.0326
*
-7.3
11.15
0.0015
*
0.0001
Or-muscle
angle
2.9
11.36
0.1749
-
-0.5
9.56
0.7874
-
0.1917
Or-skin
angle
0.7
7.50
0.5965
-
-5.4
6.51
0.0001
*
0.0010
Jaw
angle
-3.8
6.95
0.0052
*
7.1
9.99
0.0007
*
0.0001
Face
angle
-3.5
11.48
0.1073
-
3.4
7.66
0.0229
*
0.0054
SSRO
vs.1VRO
t,
SSRO
>
IVRO
-
t,
SSRO
>
IVRO
t,
IVRO
>
SSRO
t,
IVRO
>
SSRO
*:
intragroup
comparison:
statistically
significant,
p
<
0.05.
t:
intergroup
comparison:
statistically
significant,
p
<
0.05.
-:
not
significant.
increases
in
jaw
angle
and
face
angle
were
larger
with
IVRO
than
with
SSRO.
Therefore,
the
null
hypothesis
was
rejected.
4.
Discussion
Both
SSRO
and
IVRO
have
advantages
and
disadvantages
due
to
the
use
of
different
osteotomy
line
designs.
Generally,
IVRO
has
a
significantly
lower
probability
of
injuring
the
inferior
alveolar
nerve
than
does
SSRO
[14,
15],
but
IVRO
requires
IMF
for
6
weeks,
which
allows
the
proximal
and
distal
segments
to
maintain
stability
and
undergo
bone
healing.
Unlike
IVRO,
SSRO
uses
rigid
internal
fixation
to
bind
the
distal
and
proximal
segments
and
does
not
need
IMF.
In
the
meta-analysis,
Al-Moraissi
and
Ellis
[16]
found
that
there
was
no
statistically
significant
difference
in
skeletal
stability
between
bicortical
screw
fixation
and
plate
fixation
of
the
SSRO
when
used
for
mandibular
setback.
After
SSRO,
the
patients
can
open
their
mouths
facilitating
oral
intake
and
experience
minimal
hindrance
in
social
interaction.
The
main
disadvantages
after
IVRO
are
that
patients
can
only
consume
liquid
food
and
challenges
in
oral
hygiene
maintenance.
Ideally,
the
surgeon
and
the
patient
should
discuss
the
degree
of
injury
to
the
inferior
alveolar
nerve
and
the
effects
of
each
method
on
oral
intake
and
social
interaction
before
proceeding
with
either
of
the
treatment
options.
The
major
differences
between
the
osteotomy
design
of
SSRO
and
IVRO
are
as
follows.
(1)
In
SSRO,
the
ramus
is
split
into
two
halves
and
the
osteotomy
line
extends
to
the
mandibular
molar
area,
but
the
external
appearance
of
the
ramus
is
unchanged.
In
IVRO,
the
ramus
is
cut
through
behind
the
mandibular
foramen
from
the
sigmoid
notch
to
the
mandibular
angle,
and
the
external
appearance
of
both
the
ramus
and
the
mandibular
angle
is
changed.
(2)
The
patterns
of
bone
overlap
are
different.
The
two
halves
are
reunited
in
SSRO,
whereas,
in
IVRO,
the
two
intact
segments
are
overlapped
and
its
thickness
doubled
resulting
in
a
changed
frontal
appearance.
Investigating
the
computed
tomography,
Rokutanda
et
al.
[6]
reported
that
osseous
healing
was
similar
in
patients
undergoing
SSRO
and
IVRO
at
the
postoperative
one
year.
The
present
study
reveals
that
the
morphological
change
in
lateral
ramus
width
and
gonial
width
is
small
and
insignificant
after
SSRO.
In
IVRO,
the
characteristics
of
bone
overlap
are
apparent
as
the
lateral
ramus
and
gonial
widths
are
significantly
decreased,
and
the
external
appearance
of
the
ramus
significantly
changed.
Therefore,
the
changes
in
external
appearance
associated
with
the
changes
in
the
lateral
ramus
and
angle
produced
by
IVRO
are
more
obvious
than
changes
produced
by
SSRO.
As
the
amount
of
setback
in
IVRO
increases,
the
amount
of
bone
overlap
and
the
decrease
in
ramus
width
both
increase.
In
addition,
modified
IVRO
excises
the
inferior
portion
of
the
proximal
segment
preventing
the
proximal
segment
from
protruding
beyond
the
mandibular
inferior
border
and
preventing
the
patient
from
having
a
sensation
of
protrusion
when
touching.
The
present
study
reveals
that
the
ramus
angle
is
still
significantly
increased,
although
Pog
is
setback
by
counterclockwise
rota-
tion
in
SSRO.
The
reasons
are
that
the
proximal
segment
moves
clockwise
backward
after
distal
segment
setback
or
the
condyle
of
the
proximal
segment
must
be
pushed
into
the
glenoid
fossa
posteriorly
and
superiorly
during
rigid
fixation
of
both
segments,
producing
a
significant
increase
in
the
ramus
angle.
There
is
still
controversy
that
the
gonial
angle
was
increased
or
decreased
after
mandibular
rami
osteotomies.
Jonsson
et
al
[17]
reported
that
the
gonial
angle
was
found
to
increase
in
SSRO
and
to
decrease
3.3°
in
oblique
sliding
osteotomy.
Kitahara
et
al.
[8
]
reported
inverse
results
in
which
the
gonial
angle
was
found
to
decrease
by
4.4°
in
SSRO
and
to
increase
by
3.3°
in
IVRO.
Despite
the
significant
decrease
in
the
gonial
angle
in
SSRO
in
our
study,
the
ramus
angle
and
gonial
angle
exhibit
a
complementary
relationship,
and
hence
the
small
change
in
the
mandibular
plane
angle
is
reasonable.
However,
IVRO
has
no
fixation
of
the
proximal
and
distal
segments,
so
the
ramus
angle
returns
to
the
new
physiological
position
based
on
its
functional
needs
and
the
action
of
bone
remodeling.
This
position
corresponds
to
bone
movement
and
muscle
attachment,
and
thus
the
postoperative
ramus
angle
does
not
change
significantly,
which
is
entirely
different
from
what
occurs
with
SSRO.
Similarly,
the
gonial
angle
is
significantly
increased
following
postoperative
remodeling
in
IVRO,
which
is
unlike
what
takes
place
with
SSRO.
In
addition,
the
gonial
angle
is
significantly
larger
following
IVRO
than
SSRO.
Similarly,
the
mandibular
plane
angle
is
significantly
increased
following
IVRO,
and
not
with
SSRO.
Additionally,
the
mandibular
plane
angle
is
significantly
6
BioMed
Research
International
larger
following
IVRO
than
that
following
SSRO.
Regarding
the
external
appearance
of
the
mandibular
angle
area,
the
increases
in
the
gonial
angle
and
mandibular
plane
angle
result
in
a
smoother
profile
of
patients.
Yoshioka
et
al.
[18]
reported
that
intergonial
width
increased
by
1.21
mm
in
the
IVRO
group
and
0.45
mm
in
the
SSRO
group.
However,
Yeo
et
al.
[19]
showed
that
intergonial
width
decreased
2.59
mm
after
mandibular
setback
by
SSRO.
Choi
et
al.
[20]
investigated
long-term
changes
in
mandibular
and
facial
widths
after
mandibular
setback
surgery
using
IVRO.
They
found
that
frontal
mandibular
width
increased
after
IVRO
but
seemed
to
normalize
within
approximately
3
years.
In
our
study,
the
bone width
at
levels
0
and
1
was
significantly
increased
in
IVRO
compared
to
SSRO
and
the
bone
width
at
level
3
was
significantly
increased
in
SSRO
compared
to
IVRO. Therefore,
the
Or-ramus
angle
significantly
increased
by
2.3°
in
SSRO
but
significantly
decreased
by
7.3°
in
IVRO.
These
result
in
a
significantly
larger
Or-ramus
angle
with
SSRO
than
with
IVRO.
Upon
investigating
the
frontal
muscle
plane,
no
signifi-
cant
change
existed
for
any
of
the
four
levels
with
SSRO
or
IVRO.
Although
the
width
in
the
bone
plane
was
significantly
increased
with
IVRO
and
SSRO,
the
muscle
plane
integrated
the
increased
thickness
in
the
bone
resulting
in
insignificant
increases
in
the
muscle
plane
with
IVRO
and
SSRO.
The
Or-muscle
angle
in
SSRO
was
observed
to
be
similar
to
the
increase
in
its
Or-ramus
angle.
Comparatively,
in
IVRO,
the
muscle
plane
integrated
the
change
in
bone
thickness
resulting
in
significantly
smaller
change
in
the
Or-muscle
angle
than
the
Or-ramus
angle.
Choi
et
al.
[20]
reported
that
frontal
facial
width
did
not
reflect
underlying
skeletal
changes
after
IVRO.
Upon
evaluating
the
frontal
facial
plane,
no
significant
change
existed
for
any
of
the
four
levels
with
SSRO
or
IVRO,
which
signifies
that
there
was
no
significant
increase
in
frontal
facial
width
following
significant
frontal
bone
changes
in
SSRO
and
IVRO.
It
was
observed
that
the
increases
in
the
level
3
bone,
muscle,
and
facial
plane
widths
were
similar
in
SSRO,
whereas
the
decreases
in
the
level
3
bone,
muscle,
and
facial
plane
widths
were
similar
in
IVRO.
Our
findings
were
similar
to
the
report
of
Choi
et
al.
[20].
The
change
in
the
Or-
face
angle
in
SSRO
was
small,
whereas
it
was
significantly
decreased
in
IVRO. Therefore,
the
Or-face
angle
with
SSRO
was
significantly
larger
than
with
IVRO.
Regarding
the
jaw
angle,
the
significant
increase
in
the
Or-ramus
angle
in
SSRO
led
to
a
significant
decrease
in
the
jaw
angle.
However,
the
significant
decrease
in
the
Or-ramus
angle
in
IVRO
led
to
a
significant
increase
in
the
jaw
angle.
Hence,
the
jaw
angle
was
significantly
larger
in
IVRO
than
in
SSRO.
In
IVRO,
there
was
considerable
increase
in
the
face
angle
because
of
the
significant
decrease
in
the
Or-face
angle.
In
SSRO,
there
was
small
increase
in
the
Or-face
angle,
and
hence
the
face
angle
decreased
correspondingly
but not
significantly.
Therefore,
the
face
angle
was
significantly
larger
with
IVRO
than
with
SSRO.
In
other
words,
both
the
jaw
angle
and
face
angle
were
significantly
larger
with
IVRO
than
with
SSRO.
In
conclusion,
ramus
width
and
gonial
width
were
signif-
icantly
decreased
in
IVRO
than
SSRO.
The
frontal
muscular
and
skin
surface
planes
presented
no
significant
difference
between
IVRO
and
SSRO.
IVRO
increased
angles
in
the
lateral
profile
(gonial
angle
and
mandibular
plane
angle)
and
frontal
profile
(jaw
angle
and
face
angle)
relative
to
SSRO.
Data
Availability
The
data
used
to
support
the
findings
of
this
study
are
available
from
the
corresponding
author
upon
request.
Conflicts
of
Interest
There
are
no
conflicts
of
interest.
Authors'
Contributions
Chun-Ming
Chen
and
Edward
Chengchuan
Ko
equally
contributed
to
this
paper.
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