Skeletal stability after bilateral sagittal split osteotomy or distraction osteogenesis of the mandible: a randomized clinical trial


A randomized clinical trial was carried out to evaluate postoperative stability after mandibular advancements in non-syndromal class II patients with a bilateral sagittal split osteotomy (BSSO) or distraction osteogenesis (DO). In total 32 patients could be included in the BSSO group and 34 patients in the DO group. The BSSO was converted to a unilateral procedure for one patient, and two patients in the BSSO group were lost during follow-up. A total 63 patients could be evaluated, 29 in the BSSO group and 34 in the DO group. Advancement was comparable in the two groups (mean 7.2 mm). The mean follow-up period was 23.8 months (range 11–50 months). Lateral cephalograms were hand-traced. Horizontal relapse was measured in Y–B (mm) and SNB (°). For DO this was −0.324 mm and −0.250°, and for BSSO this was −0.448 mm and −0.259°, respectively (both not significant; NS). Vertical relapse measured in X–B was −0.074 mm for DO and −0.034 mm for BSSO (NS). The magnitude of advancement, a high mandibular plane angle, age and gender were not identified as independent risk factors for relapse. In conclusion, a BSSO and DO gave both similar stable results in advancements of the mandible up to 10 mm.

The bilateral sagittal split osteotomy (BSSO) described by Trauner and Obwegeser in 1957 and modified by Dal Pont and Hunsuck, is considered the standard procedure for advancement of the mandible in skeletal class II patients. The main complications are injuries to the inferior alveolar nerve, with numbness of the lip and chin region, and relapse. Early and long-term relapse can influence the outcome of this procedure considerably. A possible explanation for early relapse is slippage of the osteotomy segments and condylar sag. Long-term relapse can be related to changes in the morphology of the condylar head. Skeletal stability has much improved since the introduction of stable internal fixation with miniplates or screws instead of wire fixation.

McCarthy described the first clinical use of distraction osteogenesis (DO) in advancements of the mandible. Intraoral, submerged distraction devices were later introduced, which did not require percutaneous pins and thus cutaneous scars could be prevented. Some early users of DO reported stable skeletal results after mandibular DO, although this was reported in animals and primarily syndromal young children. Because of these promising results, mainly in unilateral procedures, it was hypothesized that relapse after DO was minimal due to gradual distraction of the soft tissues and could also be applied in less severe cases. Van Strijen et al. reported stable skeletal results after DO in skeletal class II non-syndromal patients with a low mandibular plane angle, although patients with a high mandibular plane angle showed more relapse in this study.

With regard to stability, DO and BSSO have been compared in only a few studies, and no significant differences were observed. However, all of these reports, except one, were retrospective in nature. To avoid selection bias and to balance known and unknown prognostic factors, a randomized clinical trial was performed to compare BSSO and DO for advancement of the mandible in non-syndromal class II patients. The primary outcomes were the occurrence of neurosensory disorders of the inferior alveolar nerve and postoperative skeletal stability. The results of skeletal stability are presented herein.

Patients and methods

Between March 2008 and July 2011, 66 patients were included in this prospective study. These patient cases with regard to skeletal stability have not been reported previously. The study design was a prospective randomized clinical trial. All patients were treated in the Department of Maxillofacial Surgery, Isala Clinics Zwolle, Netherlands. This department serves as a training centre for residents in oral and maxillofacial surgery. All surgical procedures were performed by a staff surgeon (JdeL, FB, or EB) and a resident.

For inclusion, patients had to be non-syndromal and have a hypoplastic mandible and a skeletal class II relation. They all required advancement of the mandible to obtain a skeletal class I relation. Advancement of the mandible by DO or BSSO was the only mandibular procedure executed. If indicated, a Le Fort I osteotomy was performed simultaneously. However, the assessment of relapse was correlated to the cranial base on lateral cephalograms. Patients aged >35 years and those who had undergone previous mandibular surgery were excluded. Patients were informed of the purpose of the study and all patients and/or their parents provided informed consent for participation. Patients were assigned randomly to either the BSSO or the distraction procedure (DO) ( Fig. 1 ). Randomization was done with a randomly generated list ( ) with a fixed block size of 20. No stratification was used for randomization. One person, who was not involved in the study, prepared closed envelopes (numbered 1–80) containing the allocated surgery. After informed consent was obtained, the patient was present when the surgeon opened the envelope containing the assigned type of surgery; envelopes were opened consecutively, in number order. This study was approved by the hospital medical ethics committee.

Fig. 1
Study design — randomized clinical trial.

One of the primary outcomes assessed was skeletal stability after DO or BSSO. The assessment of relapse was done radiographically. Lateral cephalometric radiographs were taken preoperatively, postoperatively, or in the DO group directly post-distraction, and at ≥11 months postoperatively. The mean follow-up was 23.8 months (range 11–50 months). An X–Y cranial base coordinate system was constructed on the lateral cephalograms. The sella–nasion line represented the x -axis. A line perpendicular to the x -axis at sella represented the y -axis (Y). Mandibular point B was used to evaluate relapse. The following measurements were made: sella–nasion–mandibular point B (SNB), sella–nasion–mandibular plane (SN–MP), X–B, and Y–B ( Fig. 2 ; previously published by Baas et al. in 2012 and Vos et al. in 2009 ). Superimposition of the radiographs was performed using the ‘manual geometric superimposition’ method, and they were hand-traced. Vertical relapse was represented by X–B and horizontal relapse by Y–B and SNB.

Fig. 2
The landmarks and measurements used for the cephalometric analysis.
Previously published by Vos et al. 2009 and Baas et al. 2012 .

The surgical procedure

Surgery was performed under general anaesthesia for the patients in both groups. Preoperatively, 2 g cefazolin and 0.5 mg/kg dexamethasone were given intravenously. Another dosage of 10 mg dexamethasone was given at 8 and 16 h postoperative.


The bilateral sagittal split advancement osteotomy was carried out according to the procedure of Trauner and Obwegeser, modified by Dal Pont and Hunsuck. The inferior alveolar nerve was identified at the medial aspect of the ramus. The osteotomy cut was made with a Lindemann bur and extended buccally to the region of the first molar and then through the lower border of the mandible. The final split of the osteotomy was performed with a Smith ramus separator and sagittal separator left/right (Biomet Microfixation, Jacksonville, FL, USA) without the use of chisels. The planned occlusion was maintained with an inter-occlusal acrylic splint (wafer). The proximal segments were positioned into the correct position in the fossa, and titanium miniplates (2.0-mm plates; Synthes GmbH, Solothurn, Switzerland) were adapted and fixed with at least four monocortical 5- to 7-mm screws. The intermaxillary fixation was then released and the occlusion was checked. After 1 week, guiding elastics were placed for 4–6 weeks, if needed.


After raising the mucoperiosteum, a buccal vertical cut was made with a Lindemann bur just behind the second molar and the third molar was removed if present. Next, the mono-directional distractor device (Zurich Distractor; KLS Martin GmbH & Co., Tuttlingen, Germany) ( Fig. 3 ) was adapted and placed parallel to the occlusal plane. The distractor was removed to complete the osteotomy at the lingual side of the mandible. The distractor device was then refitted in the marked position and fixed on each side with three monocortical screws. Before closure of the wounds, the distractor was activated to confirm proper functioning, and finally the distractor was returned to its original position. After a latency period of 5–7 days, the distractors were activated by 0.5 mm twice per day. Distraction was continued until a class I skeletal relationship was achieved. After a consolidation period of 8–10 weeks, the distraction devices were removed under general anaesthesia.

Fig. 3
The Zurich Distractor (Martin GmbH & Co., Tuttlingen, Germany) that was used in this study.
Previously published by Vos et al. 2009 and Baas et al. 2012 .

Post-surgical protocol

Postoperative guiding elastics were placed and patients were told to refrain from chewing for 6 weeks (BSSO) or 8–10 weeks (DO).

Statistical analysis

The data were analyzed using SPSS software version 18.0 (SPSS Inc., Chicago, IL, USA). Continuous data were analyzed with the Student’s t -test and dichotomous data with Pearson’s χ 2 test.


A total of 66 patients were included. After randomization, they were assigned to either the BSSO group (32 patients) or the DO group (34 patients). Two patients in the BSSO group were lost during follow-up and one patient in the BSSO group underwent a unilateral sagittal split osteotomy instead of a bilateral procedure. Therefore 29 patients in the BSSO group and 34 patients in the DO group could be evaluated for skeletal stability ( Table 1 ). A combined Le Fort I osteotomy was performed in three patients in the BSSO group and in eight patients in the DO group.

Table 1
Patient characteristics.
Patients 32 34 66
Lost to follow-up/unilateral SSO a 3 0 3
Patients for evaluation 29 34 63
Male 12 16 28
Female 17 18 35
Age, years b
Mean 18.6 21.3 20.1
Range 14.3–26.7 14.7–34.8
Advancement, mm
Mean 7.0 7.3 7.2
Range 4–12 5–12
High mandibular plane angle >38° 8 10 18
Mono/bimaxillary surgery 26/3 26/8 52/11
BSSO, bilateral sagittal split osteotomy; DO, distraction osteogenesis; SSO, sagittal split osteotomy.

a One male patient excluded because of conversion to unilateral SSO.

b Age at time of surgery.

Although patients were assigned randomly to the two groups, there was a significant difference in age between the groups. Patients in the BSSO group appeared to be 2.7 years younger ( P = 0.025).

The mean follow-up time after surgery was 23.8 months (range 11–50 months). Advancement was measured at the incisal edge of the lower incisors on serial lateral cephalograms. The mean advancement for all patients was 7.2 mm. The mean advancement in the BSSO group was 7.0 mm (range 4–12 mm) and in the DO group was 7.3 mm (range 5–12 mm) (difference not significant (NS); P = 0.506).

On the constructed X–Y cranial base coordinate system, X–B was measured to establish vertical relapse. In the DO group, relapse was −0.074 mm and in the BSSO group it was −0.034 mm. This difference was not significant ( P = 0.802) ( Table 2 ).

Table 2
Vertical relapse point B.
Operation Number Mean SD
X–B (mm) a DO 34 −0.074 0.6977
BSSO 29 −0.034 0.4988
SD, standard deviation; DO, distraction osteogenesis; BSSO, bilateral sagittal split osteotomy.

a Not significant, P = 0.802.

For the horizontal relapse, Y–B and SNB were measured. Y–B was −0.324 mm in the DO group versus −0.448 mm in the BSSO group (NS; P = 0.609). SNB was −0.250° in the DO group and −0.259° in the BSSO group (NS; P = 0.950) ( Table 3 ).

Table 3
Horizontal relapse point B.
Operation Number Mean SD
Y–B (mm) a DO 34 −0.324 1.0932
BSSO 29 −0.448 0.7716
SNB (°) b DO 34 −0.250 0.5674
BSSO 29 −0.259 0.5110
SD, standard deviation; DO, distraction osteogenesis; BSSO, bilateral sagittal split osteotomy; SNB, sella–nasion–point B.

a Not significant, P = 0.609.

b Not significant, P = 0.950.

The mandibular plane angle was measured to establish a vertical growth pattern. In total, 18 patients had a mandibular plane above 38°. Ten of the 34 patients in the DO group and eight of the 29 patients in the BSSO group had a vertical growth pattern. The difference was not significant (NS; P = 0.873) ( Table 4 ). Vertical relapse X–B was 0.028 mm in high angle patients and −0.089 mm in non-high angle patients (NS; P = 0.497). Horizontal relapse (Y–B and SNB) was −0.639 mm and −0.417° in high angle patients versus −0.278 mm and −0.189° in non-high angle patients, respectively. Although the horizontal relapse was slightly higher in high angle patients than in low angle patients, the difference was not significant (NS; P = 0.176 and P = 0.130, respectively) ( Table 5 ).

Table 4
Patients with a high mandibular plane angle. a
High angle b Total
No Yes
DO 24 10 34
BSSO 21 8 29
Total 45 18 63
DO, distraction osteogenesis; BSSO, bilateral sagittal split osteotomy.

a Not significant, P = 0.873.

b High mandibular plane angle, >38°.

Table 5
Patients with a high or low mandibular plane angle versus relapse.
High angle a Number Mean SD SEM
X–B (mm) b No 45 −0.089 0.5569 0.0830
Yes 18 0.028 0.7371 0.1737
Y–B (mm) c No 45 −0.278 0.8697 0.1296
Yes 18 −0.639 1.1220 0.2645
SNB (°) d No 45 −0.189 0.4802 0.0716
Yes 18 −0.417 0.6474 0.1526
SD, standard deviation; SEM, standard error of the mean; SNB, sella–nasion–point B.

a High mandibular plane angle, >38°.

b Not significant, P = 0.497.

c Not significant, P = 0.176.

d Not significant, P = 0.130.

An assessment of relapse was also performed for short face and long face patients separately, by treatment type. In the high mandibular plane angle patients (DO 10 patients, BSSO eight patients), there was no difference in relapse between the DO and the BSSO groups (all P > 0.448); there was also no difference for the low angle patients (DO 24 patients, BSSO 21 patients; all P > 0.322) ( Table 6 ).

Table 6
Relapse in high angle and low angle patients by treatment type.
High angle a Operation Number Mean SD SEM
No b
X–B (mm) DO 24 −0.167 0.5647 0.1153
BSSO 21 0.000 0.5477 0.1195
Y–B (mm) DO 24 −0.188 1.0715 0.2187
BSSO 21 −0.381 0.5680 0.1239
SNB (°) DO 24 −0.188 0.5863 0.1197
BSSO 21 −0.190 0.3345 0.0730
Yes c
X–B (mm) DO 10 0.150 0.9443 0.2986
BSSO 8 −0.125 0.3536 0.1250
Y–B (mm) DO 10 −0.650 1.1316 0.3578
BSSO 8 −0.625 1.1877 0.4199
SNB (°) DO 10 −0.400 0.5164 0.1633
BSSO 8 −0.438 0.8210 0.2903
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Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Skeletal stability after bilateral sagittal split osteotomy or distraction osteogenesis of the mandible: a randomized clinical trial
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