A Long-term Comparative Study

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Clinical Paper
Orthognathic Surgery
A long-term comparative study
of two rigid internal fixation
techniques in terms of
masticatory function and
neurosensory disturbance after
mandibular correction by
bilateral sagittal split ramus
osteotomy
Y. Yamashita, T. Otsuka, M. Shigematsu, M. Goto: A long-term comparative study of
two rigid internal fixation techniques in terms of masticatory function and
neurosensory disturbance after mandibular correction by bilateral sagittal split
ramus osteotomy. Int. J. Oral Maxillofac. Surg. 2011; 40: 360–365. # 2010
International Association of Oral and Maxillofacial Surgeons. Published by Elsevier
Ltd. All rights reserved.
Y. Yamashita, T. Otsuka,
M. Shigematsu, M. Goto
Department of Oral and Maxillofacial Surgery,
Saga Medical School, Saga, Japan
Abstract. Bilateral sagittal split ramus osteotomy (BSSO) is widely used to treat
mandibular prognathism. Several methods have been described for fixation of
the bony segments. This study compared two methods of rigid fixation
(bicortical screws and monocortical miniplates) to identify differences in
postoperative masticatory function and neurosensory disturbance after 5 years of
mandibular set-back correction. 77 women who had undergone BSSO for Class
III malocclusion were reviewed, and masticatory functions and neurosensory
recovery were examined with the appropriate indicators pre- and postoperatively
(at approximately 1 month, and 1, 2, 3, 4, and 5 years). Masticatory function
exhibited similar recovery patterns in both groups. Orthognathic surgery
improved occlusal force and occlusal contact area, but longer than 4 years after
surgery may be required for postoperative occlusal functions in prognathic
patients to reach the level of healthy subjects. The groups showed no significant
differences in the recovery of parameters of masticatory functions and
neurosensory disturbance even 5 years after surgery. In the evaluation of
Int. J. Oral Maxillofac. Surg. 2011; 40: 360–365
doi:10.1016/j.ijom.2010.11.017, available online at http://www.sciencedirect.com
0901-5027/040360 +06 $36.00/0 # 2010 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
temporomandibular joint function using the Helkimo index, the score was
significantly higher for the screw group than for the miniplate group. This
suggests that BSSO fixed with miniplates may offer a relatively safe and reliable
procedure yielding adequate results and high patient satisfaction.
Keywords: long-term comparative study; sagit-
tal split ramus osteotomy; masticatory function;
neurosensory disturbance; mandibular prog-
nathism.
Accepted for publication 22 November 2010
Available online 23 December 2010
Bilateral sagittal split ramus osteotomy
(BSSO) is probably the most common
procedure currently used to correct man-
dibular deformities. Various benefits have
been reported, including better mastica-
tory function,
9,30
improved facial aes-
thetics,
6,26
and more stable results in
severe discrepancies.
18
Prevention of
relapse after this operation is important.
Several studies of BSSO have found the
two methods of internal rigid fixation
(bicortical screws or monocortical mini-
plate fixation) offer similar skeletal stabi-
lity
3,4
and their use depends on the
preference of the surgeon.
One of the main objectives of orthog-
nathic surgery is to improve masticatory
function, but the literature contains little
comparative information on postoperative
jaw functional recovery measured at given
intervals.
17,22,24
The authors have pre-
viously reported that statistical analysis
of masticatory function showed no signif-
icant difference between the two fixation
methods for 1 year postoperatively.
27
The
purpose of the present study was to com-
pare bicortical screws and miniplate fixa-
tion in terms of masticatory function and
neurosensory disturbance 5 years after
BSSO in patients who had undergone
surgical correction of Class III malocclu-
sion.
Materials and methods
77 consecutive women who underwent
BSSO for Class III malocclusion between
1996 and 2004 were studied in this retro-
spective study. All patients were selected
according to the criteria in Table 1. All
patients were fitted with the usual pre- and
postoperative orthodontics with fixed
appliances. The lower third molars were
removed several months before surgery to
allow safe splitting of the mandible.
In Group A (n = 36; mean age 23.1
years; range 16–40 years), subjects
received one miniplate on each side and
four monocortical screws. A miniplate
with monocortical screws on the lateral
surface was used to fixate the proximal
and distal fragments. In Group B (n = 41;
mean age 21.3 years; range 16–36 years),
two bicortical screws were inserted above
the inferior alveolar nerve (IAN) in the
retromolar area using a transcutaneous
approach (Fig. 1). None of the patients
exhibited a severe tear or cut of the IAN
during surgery.
In each analysis, patient groups (Groups
A and B) were also compared with a group
of controls (24 women). The mean age of
the control group was 18.7 years (range
18–23 years). All controls showed Class I
skeletal and dental relationships without
any orthodontic treatment or surgery.
A bilateral sagittal split set-back osteot-
omy was performed in all patients accord-
ing to TRAUNER & OBWEGESER,
25
as
modified by DAL PONT,
7
HUNSUCK
16
and
EPKER.
10
Briefly, a vertical osteotomy was
made in the region of the second molar.
No patients showed any complications in
splitting the mandible or nerve position
after splitting. After osteotomy and
removal of an appropriate amount of bone
from the proximal segment, the teeth were
placed in their planned position with max-
illomandibular fixation (MMF) using
stainless steel wire. The distal fragment
was set back and the desired occlusion was
fixed in two different ways, as described
above. The 3 surgeons involved in this
study were selected because they were
experienced with and regularly performed
both fixation techniques.
The MMF was released after mandibu-
lar fixation, and occlusion and position of
the condyles were checked. The wounds
were closed using resolvable sutures. The
jaws were placed in MMF with stainless
steel wires. MMF was removed after 7–20
days.
Postoperative orthodontic treatment
started within 1 month after surgery.
Patients were examined clinically and
radiographically after surgery. The clini-
cal examination was used to evaluate
changes in masticatory function and sen-
sory disturbance in patients who had
Study of two rigid internal fixation techniques 361

Fig. 1. Sagittal split ramus osteotomy showing miniplate (A) and screw (B) fixation.
Table 1. The inclusion criteria in this study.
1. No craniofacial syndromes
2. No history of jaw trauma or local nerve injury
3. Normal preoperative labiomental sensation
4. No additional osteotomies (such as genioplasty or maxillary osteotomy)
5. No TMJ surgery before and after the bilateral sagittal split set-back osteotomy
undergone BSSO, from preoperatively to
5 years postoperatively. The following
indices were assessed: occlusal contact
area; occlusal force; Helkimo index; and
sensation. All examinations were per-
formed preoperatively and 1 month and
1, 2, 3, 4 and 5 years postoperatively.
The Dental Prescale system
1
(FUJI-
FILM, Tokyo, Japan) was used to measure
occlusal contact area and occlusal force.
13
These measurements were made with the
subject seated with the head upright, look-
ing forward, in a natural position. The
subject was instructed to bite as forcefully
as possible. Maximum contact area and
contact force were recorded on Dental
Prescale
1
. Data were scanned and ana-
lyzed using an OCCLUZER 709 (GC
Corporation, Tokyo, Japan).
The Helkimo index is based on evalua-
tion of the following five groups of symp-
toms: impaired range of mandibular
movement, impaired function of the tem-
poromandibular joint (TMJ), pain on
mandibular movement, pain in the TMJ,
and pain in the masticatory muscles.
14,15
For clinical sensory testing of the lower
labiomental area, standardized Semmes-
Weinstein monofilaments
29
(Smith &
Nephew Rolyan Inc, Milwaukee, WI,
USA) were used and differences in degree
of sensory disturbance during the recov-
ery period were analyzed statistically
(S-W sensory test).
Some data were unavailable because of
absence of samples, technical problems
with analysis, and loss of patients to fol-
low-up. Missing data were considered ran-
domly lost and complete case analysis was
applied. Statistical analysis was performed
on the recovery period for each parameter.
Occlusal contact area and occlusal force
were compared between groups using Stu-
dent’s t-test. Statistical calculations were
performed using the Mann–Whitney U-test
on other parameters. Values of p < 0.05
were considered indicative of statistical
significance. Statistical analysis was per-
formed using SPSS
1
15.0 for Windows
(SPSS; Chicago, IL, USA).
Results
Operation time, blood loss, extent to
which the mandible was retracted, and
duration of MMF are presented in
Table 2. The two groups did not differ
significantly in terms of age. Both groups
showed similar morphological changes
after surgery. Mean operation time was
significantly longer for Group B
(199 Æ 45.7 min) than for Group A
(165 Æ 30.7 min; p < 0.05), but blood
loss tended to be only slightly greater in
Group B (259.7 Æ 151.4 ml) than in Group
A(222.8 Æ 141.8 ml; p > 0.05). For Group
A, mean movement in the horizontal direc-
tion was 7.3 mm on the right side, and
6.1 mm on the left side; compared with
7.0 mmand 7.0 mm, respectively, inGroup
B. Duration of MMF did not differ signifi-
cantly between groups.
Masticatory function exhibited a similar
recovery pattern in both groups. Measure-
ments decreased immediately postopera-
tively, and minimum values were reached
by 1 month after surgery. A significant
increase occurred from 1 month after sur-
gery, and masticatory function by around
1 year after surgery was greater than that
observed preoperatively.
Briefly, 1 month after surgery, occlusal
force and occlusal contact area had fallen
to approximately half of the preoperative
value or less (Figs. 2 and 3). By 1 year
postoperatively, a significant increase of
362 Yamashita et al.
Table 2. Group comparison after BSSO.
Group A (plate) Group B (screw)
Operation time (min) 165.0 Æ 30.7 199.0 Æ 45.7
*
Blood loss (ml) 222.8 Æ 141.8 259.7 Æ 151.4
Set back value
Right (mm) 7.3 Æ 3.0 7.0 Æ 2.8
Left 6.1 Æ 3.6 7.0 Æ 3.1
Duration of MMF(days) 12.2 Æ 2.6 14.9 Æ 3.1
Values are given as mean Æ SD.
*
p < 0.05 (Student’s t-test between Group A and Group B).

Fig. 2. Changes in occlusal force (N) measured with the Dental prescale
1
system. Bars
indicate Æ 1 S.D. **p < 0.01 (Student’s t-test between Group A and Group B).

Fig. 3. Changes in occlusal contact area (mm
2
) measured by the Dental prescale
1
system. Bars
indicate Æ 1 S.D. **p < 0.01 (Student’s t-test between Group A and Group B).
approximately 1.2-fold was evident. Neither
occlusal contact force nor occlusal area
differed significantly between Groups A
and B by 5 years after surgery. Although
preoperative occlusal contact area and
occlusal force were approximately half or
less compared with values in the control
group, these parameters reached the control
group average by at least 4 years after
surgery.
Changes in mean Helkimo index are
shown in Fig. 4. The trend in Group A
was comparatively stable, and always < 0.5
0.5 for 5 years. The score did not differ
significantly between pre- and postoperative
values. Group B reached a nadir in scores
(approximately 2 points) by 1 month after
surgery. Scores hadrecoveredby1year after
surgery but this score increased again from4
years after surgery. A significant difference
was apparent between types of fixation by 5
years after surgery.
The S-W sensory test was used for
clinical sensory testing of the lower
labiomental area, and differences in
degree of sensory disturbance were sta-
tistically analyzed. Scores from the S-W
sensory test exhibited a similar recovery
pattern to other parameters (Fig. 5).
Most patients experienced a marked sen-
sory disturbance in the immediate post-
operative period. These symptoms
dramatically improved within 1 year
after surgery. This gradually improved
from 1 year after surgery, and recovery
of sensation tended to be more rapid in
Group A.
Discussion
Orthognathic surgery alters occlusion and
facial appearance and affects the biome-
chanics of the craniofacial skeleton, the
muscles of mastication, and even the men-
tal state of the patient. One of the major
objectives of orthognathic surgery is to
improve masticatory function. BSSO is
commonly used to treat mandibular prog-
nathism and retrognathism. This operation
is excellent for sagittal correction of the
mandible, but can also be used for the
treatment of minor anterior open and deep
bite and mandibular asymmetry. Numerous
studies have been published on the stability
of rigid fixation in BSSOwith miniplates
1,5
or bicortical screws,
8,20
indicating that
these twodifferent methods of rigidfixation
provide equal postoperative stability.
3,4
Although the authors have previously
reported a lack of significant differences
in recovery patterns on masticatory func-
tion and neurosensory disturbance between
groups 1 year after surgery, patients treated
with miniplate fixation tended to recover
faster.
27
The present study aimed to assess
whether these two methods of rigid fixation
after mandibular correction by BSSOled to
any differences in masticatory function and
neurosensory disturbance during long-term
(5-year) observation.
Many factors affect masticatory func-
tion, including age and sex, duration of
MMF, TMJ disorders, tooth attrition, and
psychological status. Evaluating and com-
paring tooth attrition or the psychological
status of individuals was difficult in this
study. As age and sex have been demon-
strated to be significant in terms of post-
operative changes,
19,23
patient groups in
this study were age-matched to the control
group. KIM and OH
17
reported that recov-
ery of bite force was significantly affected
by the type of operation and duration of
MMF. The authors therefore standardized
the operative technique and used the same
surgeons. Two populations were selected
according to the duration of MMF. Dura-
tion of MMF did not differ significantly
between groups. The authors therefore
Study of two rigid internal fixation techniques 363

4.5
(Point)
Score of Helkimo index
2.5
3
3.5
4
Screw
Plate
0.5
1
1.5
2
-1
-0.5
0
Pre 1M 1Y 2Y 3Y 4Y 5Y
* *
Time
Fig. 4. Changes in clinical evaluation (points) of the functional state of the masticatory system
as measured by Helkimo index score. Bars indicate Æ 1 S.D. * Significant at the level of
p < 0.05.

35
Score of S-W test
(Point)
20
25
30
Screw
Plate
10
15
**
-5
0
5
Pre 1M 1Y 2Y 3Y 4Y 5Y
Time
Fig. 5. Changes in neurosensory disturbance (point) as measured by S-Wtest. Bars indicate Æ 1
S.D. ** Significant at the level of p < 0.01.
think that the sample was homogenous and
consistent with the inclusion criteria.
MMF might be recommended to allow
the paramandibular tissues to adapt, but
some reports have stressed that early
mobilization, and even complete lack of
MMF, promote rapid healing and give
more postoperative comfort to the patient.
Mean intraoperative blood loss was
higher in Group B (bicortical screw fixa-
tion) than in Group A (miniplate fixation).
This also explains the longer mean oper-
ating time in Group B(199 min) compared
with Group A (165 min, p < 0.05).
As mastication is controlled by several
complex factors, masticatory function
should be evaluated using several
approaches. The authors therefore ana-
lyzed three indicators of masticatory func-
tion before and after surgery. These are
examinations that can be applied for post-
operative evaluation of rehabilitation.
Measurements decreased immediately
after the operation, and minimum values
were reached by 1 month after surgery. A
significant increase occurred from 1
month after surgery, and masticatory func-
tion was greater than that observed pre-
operatively by around 1 year after surgery.
These findings are supported by the
authors’ previous analysis of the recovery
pattern of masticatory function.
27
The results indicate that although the
occlusal relationships of the upper and
lower teeth were greatly improved by
BSSO, postoperative occlusion was not
tight enough and more than 4 years after
surgery may be required for postoperative
occlusal function in prognathic patients to
reach the level of healthy subjects. Facet
formation and increased facet number
caused by attrition after orthognathic
treatment may be the factors allowing
postoperative occlusal function in prog-
nathic patients to reach the level of healthy
subjects.
The authors have previously reported
that statistical analysis of masticatory
functions showed no significant differ-
ences between two fixation methods for
1 year after surgery.
27
Even 5 years after
surgery, the two groups did not differ
significantly in terms of masticatory func-
tion.
The Helkimo index showed function
and dysfunction of the masticatory system
in terms of maximum mouth opening,
joint crepitus or TMJ pain. Although
achieving correct positioning of the con-
dyle in the temporal fossa during orthog-
nathic surgery is difficult, the importance
of correct positioning of the condyle is
well known and is essential if relapse on
release of MMF and postoperative TMJ
dysfunction are to be avoided. In this
study, the Helkimo index in Group B
increased again from 4 years after surgery.
Some patients had palpable TMJ sounds or
visible lateral deviation of the path of
movement during opening or closing of
the mouth and a few had pain on mandib-
ular movement. Positional screws may
lead to excessive rotation of the proximal
fragment,
12,20
and the TMJ may take up
any stress or pressure on mandibular
movement. Surgeons should compare
TMJ positions pre- and postoperatively
using several images to clarify the pre-
sence of postoperative TMJ dysfunction.
The most common complication in
BSSO is neurosensory deficit in IANfunc-
tion. The incidence of temporary and per-
manent nerve dysesthesia was similar to
the results of other studies.
2,19,21
Numb-
ness or altered function of the nerve has
been reported to occur at 9–85% of oper-
ated sites. Damage to IAN function may
be caused in several ways intraopera-
tively, for example by dissection of soft
tissues on the medial ramus, compression
of the nerve during the horizontal cut on
the medial ramus, the split itself, and
possible compression of the nerve during
fixation.
20,21,28
Nerve function is probably
more sensitive to compression than to
tension.
Rasmusson reported that one of the
most important factors influencing post-
operative nerve function is the method of
fixation.
19
Using bicortical screws, injury
to the IAN can occur during drilling or
screw placement.
11
The authors found that
miniplate fixation clearly caused less
nerve damage than bicortical screw fixa-
tion, and that patients undergoing the for-
mer method recovered sensation
significantly more rapidly. The overall
results concerning postoperative mandib-
ular nerve function were not significantly
different after long-term observation com-
pared with short-termobservation. Careful
preoperative radiographic assessment of
the mandibular anatomy and a well
planned and performed operation may
reduce the risk of nerve damage.
In the present investigation, at 5 years
after surgery, no significant differences
between groups were found regarding
masticatory function or damage to the
IAN. A clear difference was apparent in
TMJ function of the masticatory system
(Helkimo index). Overall jaw function
seemed to recover more rapidly in Group
A than in Group B. On the basis of the
present findings, the authors think that
miniplates are more forgiving and offer
advantages over positional screws. The
number of subjects in this study, however,
was too small to reach a conclusive state-
ment. Studies involving larger samples are
recommended. As both methods seem to
provide equal comfort and reliability, the
matter should remain the choice of the
individual surgeon and surgeons should
be well versed in both techniques.
Funding
None
Competing interests
None declared.
Ethical approval
Not required.
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Address:
Department of Oral and Maxillofacial
Surgery
Saga Medical School
5-1-1 Nabeshima
Saga 849-8501
Japan
Tel.: +81 952 34 2397
fax: +81 952 34 2044
E-mail: [email protected]
Study of two rigid internal fixation techniques 365

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