A comparative study of stabitity after mandibular advancement surgery Ekaterina Douma,* M. M. Kuftinec,** and Farhad M6shiri*** Louisville, Ky., and Athens, Greece. The postsurgical stability of two groups of patients treated with different fixation techniques after mandibular advancement was evaluated retrospectively. Sixteen patients (group 1) underwent rigid osseous fixation, and another group of 16 patients (group 2) underwent intraosseous wiring fixation. Our findings suggested that skeletal and dental changes occurred in both groups as a result of adaptation to the altered functional equilibrium. Relapse resulting in a percentage loss of the initial advancement occurred primarily 6 to 8 weeks postsurgically. No statistically significant difference was found to exist in,the short-term and long-term rates between the two groups. For the population studied, relative stability after mandibular advancement surgery was affected more by individual variability than by the fixation technique. (AM J ORTHODDENTOFACORTHOP1991 ;100:141-55.)
The application of combined surgicalorthodontic procedures for the treatment of major facial deformities and associated malocclusions has become an increasingly prevalent treatment modality over the past 2 decades. Development of sound conjoint treatment principles made possible the correction of skeletal and dental dysplasias that were unyielding to either surgical or orthodontic treatment alone? "2 The orthognatbic surgery option gives a clinician the ability to correct skeletal dysplasias in nongrowing patients, as well as to treat severe progressive deformities in adolescents and young adults. 3 Skeletal Class II malocclusions resulting from mandibular retrognathism often require a combined orthodontic-surgical approach for optimal function and best esthetic results. The sagittal split ramus osteotomy is currently one of the most favored surgical techniques for the management of mandibular retrognathism. 2 The technique has been successfully used by many clinicians over the years. Despite its popularity, however, one factor still remains a major concern in the surgical correction of mandibular retrognathism: its potential for relapse3 In fact, several investigations have shown that skeletal relapse is the most often encountered sequela of mandibular advancement surgery; it usually occurs early in the postsurgical period. *Former resident, now in practice in Athens, Greece. **Professor of Orthodontics, Director of Postgraduate Program, University of Louisville, Louisville, Ky. ***Clinical Professor of Orthodontics, University of Louisville, Louisville, Ky. 8/1/21619
Although skeletal relapse seems to be a multifactorial phenomenon, according to short-term and longterm follow-up of clinical cases, different.studies have suggested a link between certain etiologic factors. Positional change of the proximal segment was found to be the most important parameter in determining stability of the advanced mandible. According to recent studies,58 intraoperative distraction of the mandibular condyles from their functional position in the glenoid fossae results in a dramatic skeletal relapse immediately on release of intermaxillary fixation. The relapse occurs because a large discrepancy between the functional occlusal position and the terminal hinge position is created. Paramandibular connective tissue tension from the skin, interstitial connective tissue components, and enveloping periosteum have also been reported as etiologic factors in relapse. Recent reports indicate that the relapse seen after mandibular advancement surgery is a result of paramandibular connective tissue tension, lack of control of the proximal segment during surgery, condylar distraction, inadequate fixation periods, magnitude of advancement, t/nfavorable growth postsurgically, and preexisting internal derangement of the temporomandibular joints. 9'2 To minimize relapse, intraosseous fixation of the bone segments with stainless steel wires was used for a period of 6 to 8 weeks after surgery. Histologic studies have shown that wiring of the proximal and distal segments provide semirigid fixation at best. 13~7 The patient with an osteotomy is at risk of relapse for as long as 25 weeks after surgery. In an effort to prevent intersegment movement and to promote primary bone healing, a technique for rigid approxi141
142
Douma, Kttftinec, atzd Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
Po
(3
Or
G~
Me
Fig. 1. Hard tissue cephalometric landmarks used in study.
mation and fixation of the bony segments has evolved. The objective was tO prevent a major source of relapse while simultaneously reducing the length of intermaxillary dental fixation. Rigid fixation after sagittal split osteotomy for mandibular advancement was accomplished by means of compression screws, usually inserted through a small skin incision at a 90 ° angle to the osteotomy site. z8-2~ Recent investigations of rigid fixation reported a good postsurgical stability, with a capability o f e a r l y masticatory function, improved nutrition, and a faster rate of recovery. When the relapse rates in intermaxillary and rigid fixation groups were compared, skeletal changes in the rigid fixation group were statistically smaller than those in the intermaxillary group. The relatively new technique was thus reported to be effective and stable. However, sufficient clinical documentation to support the theoretical concepts is not readily available. The purpose o f this study was to investigate any significant differences between rigid and intraosseous wiring fixation techni~tues in patients treated with bi-
lateral sagittal split ramus osteotomy for mandibular advancement. Comparisons were to be made of any short-term and long-term skeletal and dental changes between the two groups. METHOD AND MATERIALS
Two groups of 16 patients each who underwent mandibular advancement by means of bilateral sagittal split ramus osteotomy for correction of mandibular retrognathism were selected for this study. Patients who had any additional surgery (e.g., genioplasty or two jaw procedures) were not included in our sample. All the surgical procedures were performed by two "members of the same oral surgery group in an attempt to eliminate major technical differences. No maxillary surgical procedures were performed in any of the patients. The cephalograms were taken in norma lateralis, on the same cephalometers, so that magnification factors would remain constant, and reasonable comparisons could be made.22.23 Group 1 consisted of 14 females and 2 males with a mean age of 30.68 years (range, 14 to 50 years). Stabilization of the segments was achieved postsurgically by means of bone compression screws, which were consistently placed through
Stability after mandibular advancement surgery
Volume 100 Number 2
o \
143
1
UFH
:L
L~L
I
Fig. 2. Soft tissue landmarks and constructed parameters (after Moshiri F. J Clin Orthod 1982;16:3759): UFH, upper face height; NLA, nasolabial angle; ULL, upper lip length; LLL, lower lip length; FCA, facial contour angle. Table I. P e r c e n t a g e s o f r e l a p s e
Group 1 (rigid fi.ration) Mean (SD)
Group 2 (wire firation) Mean (SD)
Group 1 to group 2
20.7 (21.6)
17.6 (20.2)
0.70 (NS)
10.1 (17.8)
6.1 (20.4)
0.62 (NS)
31.4 (30.4)
23.0 (31.5)
0.49 (NS)
t tests
Short-term relapse (Ar - PgT,) - (Ar - PgT0 *100 (Ar - PgT2) - (Ar - PgT0
Long-term relapse (Ar - PgT3) - (Ar - PgT4)*100 (Ar - PgT2) - (Ar - PgT0
Total relapse (Ar - PgT2) - (Ar - PgT4) *100 (Ar - PgTz) - (Ar - PgTO No'rE: For explanation of T, - T4, see Fig. 3.
an intraoral approach. Interdental fixation with an occlusal splint in place was u s e d for up to 2 weeks. 2' G r o u p 2 c o n s i s t e d o f 13 female and 3 male patients w h o also u n d e r w e n t m a n d i b u l a r a d v a n c e m e n t t h r o u g h bilateral sagittal split r a m u s o s t e o t o m y . In this group, inferior border
intraosseous wiring o f the b o n y s e g m e n t s was e m p l o y e d to a s s u r e stability a n d e n s u r e a g a i n s t m a j o r skeletal relapse. 2~ In addition, interdental fixation with an acrylic occlusal splint w a s routinely m a i n t a i n e d for a period o f 6 to 8 weeks.
144
Dottma, Kt~inec, and Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
GROUP RIGID
I
SURGICAL CHANGE
FIXATION
-I
JI¢
FIXATION CHANGE
I I"
4
NET T1 PRESURGERY
MEAN [S.DI
A
MINIMUM MAXIMUM
POSTFIXATION CHANGE
"1
NET POSTSURGICAL CHANGE
'l
LONG-TERM CHANGE
T2 IMMEDIATE POSTSURGERY 3.3 DAYS 11.541 2 8
T3 SHORT-TERM
2.15 MOSII.071 1 4
T4 LONG-TERM
11.15 MOSI3.601 7 18
Fig. 3. A, Regimen of sampling and descriptive statistics for rigid fixation group.
Cephalometric analysis
RESULTS
Nine hard tissue anatomic landmarks (Fig. 1) and five soft tissue landmarks (Fig. 2) were located on each tracing. Sixteen variables were selected to facilitate quantitative interpretation of customarily reported clinical parameters. 23'~27
Skeletal changes
Statistical analysis Statistical computations were made and analyzed with an SPSS package on an IBM 3081-D computer. Means and standard deviations were recorded for 16 variables, the change in each variable for both groups at four different times (TI, T2, T3, and 'I"4) as shown in Fig. 3. The significance of changes over the four points in time was determined by the Student t test for paired data. Spearman's rank order correlation coefficient (p) was used to test significant relationships between variables. Statistical significance was established at p = 0.05 and a correlation of r = 0.6 Was considered of clinical significance. Errors in landmark identification and digitizing were evaluated statistically, suggesting a linear error of approximately 0.02 mm and an angular error of 0.2".
Skeletal changes were demonstrable postsurgically in both groups. Short-term relapse was found to be comparable at 20.7% and 17.6% for group 1 and group 2, respectively. Similarly, a long-term relapse was 10.1% and 6.1% for the same respective groups. A mean total relapse of 31.4% for group 1 and 23% for group 2 was Observed (Table I). Overall, changes expressed in inillimeter values were relatively small, measuring 1.4 m m and 1.8 mm for the two groups, respectively. Relapse rates were compared at all four time intervals by the Student t test, and differences were found to be statistically significant.
Magnitude of advancement Overall, the two groups had a similar amount of surgical advancement (5.6 mm and 7.0 mm, respectively). Associations between the magnitude o f ad-
Volume I00 Number 2
Stability after mandibular advancenzent s,+rgery GROUP
2
INTERMAXIL LARY
SURGICAL CHANGE
"1 I-
FIXATION
FIXATION CHANGE
I14
+
t NET T1 PR ESURGERY
B
145
NET
POSTSURGICAL
LONG-TERM
MEAN IS.D.I
6.06 DAYS 13.711
MINIMUM MAXIMUM
2 18
ii I
CHANGE
"1
CHANGE
T2 IMMEDIATE POSTSURGERY
POSTF|XAT|ON CHANGE
T3
T4
SHORT-TERM
LONG-TERM
2.43 MOS I1.111 1 5
22.85 MOS 111.091 12 46
Fig. 3. B, Regimen of sampling and descriptive statistics for intermaxi~lary fixation group.
Posterior facial height
vancement measured at pogonion and the total relapse were calculated for both groups by means of Pearson's correlation coefficient. Fig. 4 indicates a moderate association between the variables, indicating that as the magnitude of advancement increased, a tendency for postsurgical relapse was also likely to increase.
The surgical change in posterior facial height resulted in a slight net decrease in both groups. The mean long-term loss in posterior facial height was 0.9 mm for the rigid fixation group and 2.5 mm for the intermaxillary fixation group (Fig. 7).
Mandibular plane angle
Dental changes
A weak association was shown between mandibular plane angle and postsurgical relapse in group 1 and a moderate association in group 2 (Fig. 5). In both groups greater postsurgical skeletal relapse occurred in the high-angle cases than in the low-angle cases.
A slight posterior decompensatory movement of the maxillary incisors was achieved in preparation for surgery in both groups. The net long-term change was 0.7 ° and 2.6 ° for the two groups, respectively (Fig. 8). The pattern of dental decompensation for the mandibular incisors after surgery differed in the two groups, but some proclination of the mandibular incisors was seen in most of the patients in both of the groups (Fig. 9). Although the occurrence of dental changes has been reported to compensate for postsurgical skeletal changes, such conclusions should be made with caution because of the large individual variability and also be-
Anterior facial height Both groups showed a demonstrable degree of anteroinferior surgical advancement of the distal segment, resulting in an increase in anterior facial height, which was sustained after surgery (Fig. 6). The differences between the groups showed no statistical significance.
146
Douma, Kuftinec, and Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
SURGICAL ADVANCEMENT VS. RELAPSE Group i - R i g i d F i x a t i o n X
i8i5-
i
i4 o
J / .1
c
m
It
The application of combined surgicalorthodontic procedures for the treatment of major facial deformities and associated malocclusions has become an increasingly prevalent treatment modality over the past 2 decades. Development of sound conjoint treatment principles made possible the correction of skeletal and dental dysplasias that were unyielding to either surgical or orthodontic treatment alone? "2 The orthognatbic surgery option gives a clinician the ability to correct skeletal dysplasias in nongrowing patients, as well as to treat severe progressive deformities in adolescents and young adults. 3 Skeletal Class II malocclusions resulting from mandibular retrognathism often require a combined orthodontic-surgical approach for optimal function and best esthetic results. The sagittal split ramus osteotomy is currently one of the most favored surgical techniques for the management of mandibular retrognathism. 2 The technique has been successfully used by many clinicians over the years. Despite its popularity, however, one factor still remains a major concern in the surgical correction of mandibular retrognathism: its potential for relapse3 In fact, several investigations have shown that skeletal relapse is the most often encountered sequela of mandibular advancement surgery; it usually occurs early in the postsurgical period. *Former resident, now in practice in Athens, Greece. **Professor of Orthodontics, Director of Postgraduate Program, University of Louisville, Louisville, Ky. ***Clinical Professor of Orthodontics, University of Louisville, Louisville, Ky. 8/1/21619
Although skeletal relapse seems to be a multifactorial phenomenon, according to short-term and longterm follow-up of clinical cases, different.studies have suggested a link between certain etiologic factors. Positional change of the proximal segment was found to be the most important parameter in determining stability of the advanced mandible. According to recent studies,58 intraoperative distraction of the mandibular condyles from their functional position in the glenoid fossae results in a dramatic skeletal relapse immediately on release of intermaxillary fixation. The relapse occurs because a large discrepancy between the functional occlusal position and the terminal hinge position is created. Paramandibular connective tissue tension from the skin, interstitial connective tissue components, and enveloping periosteum have also been reported as etiologic factors in relapse. Recent reports indicate that the relapse seen after mandibular advancement surgery is a result of paramandibular connective tissue tension, lack of control of the proximal segment during surgery, condylar distraction, inadequate fixation periods, magnitude of advancement, t/nfavorable growth postsurgically, and preexisting internal derangement of the temporomandibular joints. 9'2 To minimize relapse, intraosseous fixation of the bone segments with stainless steel wires was used for a period of 6 to 8 weeks after surgery. Histologic studies have shown that wiring of the proximal and distal segments provide semirigid fixation at best. 13~7 The patient with an osteotomy is at risk of relapse for as long as 25 weeks after surgery. In an effort to prevent intersegment movement and to promote primary bone healing, a technique for rigid approxi141
142
Douma, Kttftinec, atzd Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
Po
(3
Or
G~
Me
Fig. 1. Hard tissue cephalometric landmarks used in study.
mation and fixation of the bony segments has evolved. The objective was tO prevent a major source of relapse while simultaneously reducing the length of intermaxillary dental fixation. Rigid fixation after sagittal split osteotomy for mandibular advancement was accomplished by means of compression screws, usually inserted through a small skin incision at a 90 ° angle to the osteotomy site. z8-2~ Recent investigations of rigid fixation reported a good postsurgical stability, with a capability o f e a r l y masticatory function, improved nutrition, and a faster rate of recovery. When the relapse rates in intermaxillary and rigid fixation groups were compared, skeletal changes in the rigid fixation group were statistically smaller than those in the intermaxillary group. The relatively new technique was thus reported to be effective and stable. However, sufficient clinical documentation to support the theoretical concepts is not readily available. The purpose o f this study was to investigate any significant differences between rigid and intraosseous wiring fixation techni~tues in patients treated with bi-
lateral sagittal split ramus osteotomy for mandibular advancement. Comparisons were to be made of any short-term and long-term skeletal and dental changes between the two groups. METHOD AND MATERIALS
Two groups of 16 patients each who underwent mandibular advancement by means of bilateral sagittal split ramus osteotomy for correction of mandibular retrognathism were selected for this study. Patients who had any additional surgery (e.g., genioplasty or two jaw procedures) were not included in our sample. All the surgical procedures were performed by two "members of the same oral surgery group in an attempt to eliminate major technical differences. No maxillary surgical procedures were performed in any of the patients. The cephalograms were taken in norma lateralis, on the same cephalometers, so that magnification factors would remain constant, and reasonable comparisons could be made.22.23 Group 1 consisted of 14 females and 2 males with a mean age of 30.68 years (range, 14 to 50 years). Stabilization of the segments was achieved postsurgically by means of bone compression screws, which were consistently placed through
Stability after mandibular advancement surgery
Volume 100 Number 2
o \
143
1
UFH
:L
L~L
I
Fig. 2. Soft tissue landmarks and constructed parameters (after Moshiri F. J Clin Orthod 1982;16:3759): UFH, upper face height; NLA, nasolabial angle; ULL, upper lip length; LLL, lower lip length; FCA, facial contour angle. Table I. P e r c e n t a g e s o f r e l a p s e
Group 1 (rigid fi.ration) Mean (SD)
Group 2 (wire firation) Mean (SD)
Group 1 to group 2
20.7 (21.6)
17.6 (20.2)
0.70 (NS)
10.1 (17.8)
6.1 (20.4)
0.62 (NS)
31.4 (30.4)
23.0 (31.5)
0.49 (NS)
t tests
Short-term relapse (Ar - PgT,) - (Ar - PgT0 *100 (Ar - PgT2) - (Ar - PgT0
Long-term relapse (Ar - PgT3) - (Ar - PgT4)*100 (Ar - PgT2) - (Ar - PgT0
Total relapse (Ar - PgT2) - (Ar - PgT4) *100 (Ar - PgTz) - (Ar - PgTO No'rE: For explanation of T, - T4, see Fig. 3.
an intraoral approach. Interdental fixation with an occlusal splint in place was u s e d for up to 2 weeks. 2' G r o u p 2 c o n s i s t e d o f 13 female and 3 male patients w h o also u n d e r w e n t m a n d i b u l a r a d v a n c e m e n t t h r o u g h bilateral sagittal split r a m u s o s t e o t o m y . In this group, inferior border
intraosseous wiring o f the b o n y s e g m e n t s was e m p l o y e d to a s s u r e stability a n d e n s u r e a g a i n s t m a j o r skeletal relapse. 2~ In addition, interdental fixation with an acrylic occlusal splint w a s routinely m a i n t a i n e d for a period o f 6 to 8 weeks.
144
Dottma, Kt~inec, and Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
GROUP RIGID
I
SURGICAL CHANGE
FIXATION
-I
JI¢
FIXATION CHANGE
I I"
4
NET T1 PRESURGERY
MEAN [S.DI
A
MINIMUM MAXIMUM
POSTFIXATION CHANGE
"1
NET POSTSURGICAL CHANGE
'l
LONG-TERM CHANGE
T2 IMMEDIATE POSTSURGERY 3.3 DAYS 11.541 2 8
T3 SHORT-TERM
2.15 MOSII.071 1 4
T4 LONG-TERM
11.15 MOSI3.601 7 18
Fig. 3. A, Regimen of sampling and descriptive statistics for rigid fixation group.
Cephalometric analysis
RESULTS
Nine hard tissue anatomic landmarks (Fig. 1) and five soft tissue landmarks (Fig. 2) were located on each tracing. Sixteen variables were selected to facilitate quantitative interpretation of customarily reported clinical parameters. 23'~27
Skeletal changes
Statistical analysis Statistical computations were made and analyzed with an SPSS package on an IBM 3081-D computer. Means and standard deviations were recorded for 16 variables, the change in each variable for both groups at four different times (TI, T2, T3, and 'I"4) as shown in Fig. 3. The significance of changes over the four points in time was determined by the Student t test for paired data. Spearman's rank order correlation coefficient (p) was used to test significant relationships between variables. Statistical significance was established at p = 0.05 and a correlation of r = 0.6 Was considered of clinical significance. Errors in landmark identification and digitizing were evaluated statistically, suggesting a linear error of approximately 0.02 mm and an angular error of 0.2".
Skeletal changes were demonstrable postsurgically in both groups. Short-term relapse was found to be comparable at 20.7% and 17.6% for group 1 and group 2, respectively. Similarly, a long-term relapse was 10.1% and 6.1% for the same respective groups. A mean total relapse of 31.4% for group 1 and 23% for group 2 was Observed (Table I). Overall, changes expressed in inillimeter values were relatively small, measuring 1.4 m m and 1.8 mm for the two groups, respectively. Relapse rates were compared at all four time intervals by the Student t test, and differences were found to be statistically significant.
Magnitude of advancement Overall, the two groups had a similar amount of surgical advancement (5.6 mm and 7.0 mm, respectively). Associations between the magnitude o f ad-
Volume I00 Number 2
Stability after mandibular advancenzent s,+rgery GROUP
2
INTERMAXIL LARY
SURGICAL CHANGE
"1 I-
FIXATION
FIXATION CHANGE
I14
+
t NET T1 PR ESURGERY
B
145
NET
POSTSURGICAL
LONG-TERM
MEAN IS.D.I
6.06 DAYS 13.711
MINIMUM MAXIMUM
2 18
ii I
CHANGE
"1
CHANGE
T2 IMMEDIATE POSTSURGERY
POSTF|XAT|ON CHANGE
T3
T4
SHORT-TERM
LONG-TERM
2.43 MOS I1.111 1 5
22.85 MOS 111.091 12 46
Fig. 3. B, Regimen of sampling and descriptive statistics for intermaxi~lary fixation group.
Posterior facial height
vancement measured at pogonion and the total relapse were calculated for both groups by means of Pearson's correlation coefficient. Fig. 4 indicates a moderate association between the variables, indicating that as the magnitude of advancement increased, a tendency for postsurgical relapse was also likely to increase.
The surgical change in posterior facial height resulted in a slight net decrease in both groups. The mean long-term loss in posterior facial height was 0.9 mm for the rigid fixation group and 2.5 mm for the intermaxillary fixation group (Fig. 7).
Mandibular plane angle
Dental changes
A weak association was shown between mandibular plane angle and postsurgical relapse in group 1 and a moderate association in group 2 (Fig. 5). In both groups greater postsurgical skeletal relapse occurred in the high-angle cases than in the low-angle cases.
A slight posterior decompensatory movement of the maxillary incisors was achieved in preparation for surgery in both groups. The net long-term change was 0.7 ° and 2.6 ° for the two groups, respectively (Fig. 8). The pattern of dental decompensation for the mandibular incisors after surgery differed in the two groups, but some proclination of the mandibular incisors was seen in most of the patients in both of the groups (Fig. 9). Although the occurrence of dental changes has been reported to compensate for postsurgical skeletal changes, such conclusions should be made with caution because of the large individual variability and also be-
Anterior facial height Both groups showed a demonstrable degree of anteroinferior surgical advancement of the distal segment, resulting in an increase in anterior facial height, which was sustained after surgery (Fig. 6). The differences between the groups showed no statistical significance.
146
Douma, Kuftinec, and Moshiri
Am. J. Orthod. Dentofac. Orthop. August 1991
SURGICAL ADVANCEMENT VS. RELAPSE Group i - R i g i d F i x a t i o n X
i8i5-
i
i4 o
J / .1
c
m
It
