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Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse?
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Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse? Namiaki Takahara DDS, PhD , Atsushi Kimura DDS, PhD , Nobuyoshi Tomomatsu DDS, PhD , Koichi Nakakuki DDS, PhD , Tetsuya Yoda DDS, PhD PII: DOI: Reference:
S2212-4403(19)31556-1 https://doi.org/10.1016/j.oooo.2019.10.014 OOOO 4262
To appear in:
Oral Surg Oral Med Oral Pathol Oral Radiol
Received date: Revised date: Accepted date:
16 April 2019 2 September 2019 30 October 2019
Please cite this article as: Namiaki Takahara DDS, PhD , Atsushi Kimura DDS, PhD , Nobuyoshi Tomomatsu DDS, PhD , Koichi Nakakuki DDS, PhD , Tetsuya Yoda DDS, PhD , Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse?, Oral Surg Oral Med Oral Pathol Oral Radiol (2019), doi: https://doi.org/10.1016/j.oooo.2019.10.014
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse?
Namiaki TAKAHARA, DDS, PhD1, Atsushi KIMURA, DDS, PhD2, Nobuyoshi TOMOMATSU, DDS,PhD1, Koichi NAKAKUKI, DDS,PhD1, Tetsuya YODA, DDS, PhD3
1. Associate Professor, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan. 2. Clinical Fellow, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan. 3. Professor, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan.
*Corresponding author: Namiaki Takahara, DDS, PhD Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences， Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan Tel.: +81-3-5803-5501 Fax: +81-3-5803-0199 E-mail address: [email protected]
Funding None
Competing interests None declared
Statement of Clinical Relevance This study investigated postoperative horizontal relapse of the mandible in terms of the effects of the magnitude of setback movement and the rotation of the proximal segment after Le Fort I osteotomy and sagittal split ramus osteotomy.
Abstract Objective: To investigate postoperative horizontal relapse of the mandible in terms of the effects of the magnitude of mandibular setback movement and ramus inclination after Le Fort I osteotomy and sagittal split ramus osteotomy. Study Design: A retrospective study of patients who underwent orthognathic surgery for mandibular prognathism was performed. Postoperative relapse at point B was analyzed with
regard to the magnitude of mandibular setback and the ramus inclination. Serial cephalograms were used to measure surgical changes and evaluate postoperative relapse. Results: Nineteen men and 31 women (mean age: 23.1 years) were retrospectively enrolled. Mean surgical backward movement of the mandible at point B was 8.2 mm, mean ramus inclination was 3.56°, and mean relapse 1 year postoperatively was 0.95 mm (11.6%). Horizontal relapse of the mandible was significantly correlated with the magnitude of mandibular setback (r = -0.52, p = 0.007) and ramus inclination (r = 0.48, p = 0.014). Conclusions: Increased horizontal mandibular relapse after bimaxillary surgery was associated with greater mandibular setback movement and increased proximal segment clockwise rotation. Mandibular relapse after bimaxillary surgery may be minimized via adequate control of intraoperative clockwise rotation of the proximal segment.
Keywords: Clockwise rotation of the proximal segment, mandibular setback, sagittal split ramus osteotomy, skeletal stability
Introduction Skeletal class III deformities can result from either maxillary retrognathism or mandibular prognathism, or the simultaneous occurrence of both. Le Fort I and sagittal split ramus osteotomy are widely performed orthognathic surgical procedures used to correct mandibular
prognathism of the maxilla and the mandible, respectively. Despite technical advances and improved osteosynthesis materials, these procedures may still be associated with skeletal relapse. Several factors that potentially contribute to skeletal relapse after mandibular setback have been reported, including presurgical orthodontic alignment of dental arches to obtain stable occlusion, the magnitude of mandibular setback, the tension in the pterygomasseteric muscle sling, the method of fixation, intermaxillary fixation (IMF) duration, and positioning of the proximal segment1-3. In some studies, the magnitude of mandibular setback reportedly had a major effect on postoperative stability4, 5. It has also been reported that intraoperative clockwise rotation of the proximal segments was associated with instability after mandibular setback surgery6. However, the main factors that contribute to skeletal relapse after mandibular setback are controversial. The correlation between the degree of surgical relapse and the amount of mandibular setback or rotation of the proximal segment during bimaxillary surgery, including bilateral sagittal split ramus osteotomy (BSSO), has not yet been elucidated. The purpose of the present study was to assess whether a correlation exists between the amount of mandibular setback and postsurgical horizontal relapse of the mandible, as well as between the amount of rotation of the proximal segment and postsurgical horizontal relapse of the mandible.
Materials and Methods Study design This was a retrospective case series study. It was conducted in accordance with the Declaration of Helsinki guidelines, and was approved by the Ethics Committee of the Faculty of Dentistry, Tokyo Medical and Dental University. Study sample All patients consecutively underwent Le Fort I osteotomy and BSSO setback for correction of mandibular prognathism from January 2013 to December 2016 in the Department of Maxillofacial Surgery at Tokyo Medical and Dental University. The inclusion criteria were as follows: 1) BSSO for mandibular setback of > 5 mm; 2) preoperative and postoperative orthodontic treatment. The exclusion criteria were severe facial asymmetry associated with menton deviation of > 2 mm from the facial midline, facial cleft or any other craniofacial syndrome, a history of trauma, and the presence of any systemic disease. Procedure All patients underwent Le Fort I osteotomy and BSSO, and BSSO was performed using the short lingual technique7 for mandibular setback. In this procedure, conventional one piece Le Fort I maxillary down-fracture is performed. After mobilization, the maxilla is moved to its planned position, and MMF is applied with an intermediate splint, which is fabricated in centric relation of the condyle. The maxilla is fixed with titanium mini plates at the piriform
rim and anterior wall on each side. Following the Le Fort I osteotomy, BSSO mandibular setback was performed. Prior to separation the proximal segment was placed in the primary section by measuring from the first molar of the maxilla to the point of ascending ramus using a ruler (Fig.1). The distal segment was moved backward in accordance with the planned occlusion, and IMF was applied. After removal of the interference between the proximal and distal segments, the bony segments were fixed with titanium mini plates and monocortical screws on each side. The displacement of the proximal segment from its original position could be minimized by measuring reference points. Postoperatively, elastics were placed to maintain the ideal occlusion rather than performing IMF. Cephalometric analysis To measure surgical changes and evaluate postoperative stability, lateral cephalograms were taken in the maximum intercuspal position prior to surgery (T0), and at 1 month (T1), 6 months (T2), and 1 year (T3) after surgery. Cephalometric analysis was conducted via the superimposition technique. Each cephalogram was traced onto acetate paper. Eight cephalometric reference points (sella [S], nasion [N], PNS, point A [A], point B [B], articulare [Ar], menton [Me], pogonion [Pog], and gonion [Go]) were located on the lateral cephalogram at T0, and transferred to the lateral cephalograms taken at T1, T2, and T3. An x-y coordinate system was established in which the x-axis was constructed by rotating the S-N plane upward by 7° and the y-axis was constructed perpendicular to the x-axis and
passed through the N. The angular measurements were SNA, SNB, ANB, ramus inclination (Ar-Go to SN), and mandibular plane to SN (Fig. 2). Horizontal and vertical changes in PNS, A, B, and Me were determined between T0 and T1, T2 and T1, and T3 and T1. Rotation of the proximal segments was measured via changes in ramus inclination between T0 and T1, T2 and T1, and T3 and T1. Movement to posterior on the x-axis and to inferior on y-axis and counterclockwise rotation were defined as negative. To analyze methodological errors at each reference point, 20 randomly selected radiographs were traced and digitized twice by the same investigator, with an interval of 2 weeks. Methodological errors ranged from 0.38 mm to 0.69 mm for linear measurements, and from 0.42° to 0.83° for angular measurements. There were no significant differences between the duplicate measurements of any variables. Statistical analysis The primary predictor variable was the amount of mandibular setback at point B. The primary outcome variable was the amount of horizontal mandibular relapse at point B 1 year postoperatively. The secondary outcome variables were intraoperative change in the ramus inclination and surgical movement of the maxilla. Paired t-tests were used to analyze changes over time in the cephalometric variables. Significance was tested for comparisons between T0 and T1 (changes during surgery) and between T3 and T1 (total relapse) to avoid multiple significance testing. The following variables were analyzed as possible predictors for
postoperative horizontal relapse of the mandible at point B: (1) mandibular setback: horizontal position of B, horizontal position of Pog, SNA, SNB, ANB, mandibular plane to SN; (2) intraoperative clockwise rotation of the proximal segment: ramus inclination. Pearson’s correlational analysis was performed to investigate relationships between postoperative horizontal relapse of the mandible at point B and surgical change. All Statistical analyses were performed using the software package SPSS version 19.0.
Results The sample comprised 50 patients (19 male, 31 female) who were consecutively admitted from January 2013 to December 2016 and were followed for 1 year. Their mean age was 23.1 years (range 18 to 35 years). Cephalometric variables describing preoperative craniofacial morphology of all patients are summarized in Table 1. The mean changes in the cephalometric parameters as a result of surgery and the degree of postoperative relapse are presented in Table 2. The mean surgical backward movement of the mandible at point B at T1 was 8.2 mm, and the mean inclination of the ramus was 3.56°, indicating clockwise rotation of the proximal segment, and the distal segment was rotated clockwise by 0.99°. The mean forward movement of the maxilla was 2.37 mm at point A, and the mean upward movement was 3.07 mm at PNS. The mean horizontal change at point A during the 1-year follow-up period was 0.17 mm, and the vertical change at PNS was 0.40
mm; these changes were not statistically significant. The anterior changes at point B were 0.57
mm at 6 months after surgery and 0.95 mm at 1 year after surgery, representing respective relapses of the surgical movement of 6.9% and 11.6%. Horizontal relapse of the mandible 1 year postoperatively was significantly negatively correlated with the amount of surgical repositioning. The respective Pearson’s correlational coefficients pertaining to point B, Pog, and SNB were -0.52, -0.50, and -0.37 (p < 0.05). The mean decreases in ramus inclination were 0.9° (25.3%) 6 months postoperatively and 1.32° (37.1%) 1 year postoperatively, and the decrease in ramus inclination 1 year postoperatively was significantly correlated with horizontal relapse at point B (r = 0.48, p = 0.014) (Table 3).
Discussion BSSO is the most commonly performed surgical procedure used to correct mandibular prognathism. Despite technical advances and improved osteosynthesis materials, there is still a degree of skeletal relapse after mandibular setback surgery. It also has been reported that the relapse rates following mandibular setback surgery are among the highest for any surgical procedure8. Several potential contributory factors have been suggested, including presurgical orthodontic alignment of dental arches to obtain stable occlusion, the magnitude of mandibular setback, the tension in the pterygomasseteric muscle sling, the method of fixation, intermaxillary fixation (IMF) duration, and positioning of the proximal segment1-3.
Previous studies have reported that the amount of mandibular setback movement was a major factor affecting postoperative stability in single-jaw surgery and bimaxillary surgery4, 5. It has also been reported that intraoperative clockwise rotation of the proximal segments was associated with instability after mandibular setback surgery. Therefore, the main factors during mandibular setback surgery that contribute to skeletal relapse are still controversial. In the present study, we analyzed postoperative mandibular relapse in terms of the effects of the magnitude of setback movement and the rotation of the proximal segment because these are thought to be the main factors affecting relapse after BSSO combined with Le Fort I osteotomy. Horizontal relapse was found to be correlated with both the magnitude of mandibular setback and intraoperative clockwise rotation of the proximal segment. Previous studies have reported that early postoperative relapse (<6 months after surgery) is often associated with malpositioning of the condyles during surgery, causing condylar sag and subsequent unfavorable displacement of the mandible9. Late postoperative relapse (>12 months after surgery), however, is often related to the amount of mandibular setback4, 5. In the present study, most of the relapse after mandibular setback occurred during the subsequent 6 months. With regard to maxillary movement, Jakobsone et al.5 reported that large setback and inferior repositioning of the posterior maxilla were risk factors for postoperative relapse of the mandible after bimaxillary surgery. It has been reported that impaction of the posterior maxilla played a role in reducing postoperative mandibular relapse
after bimaxillary surgery to correct mandibular prognathism. Notably however, Kwon et al.110 reported that maxillary advancement and vertical changes of ± 2 mm did not influence postoperative mandibular stability. In the present study, the mean maxillary advancement was 2.37 mm at point A, and the mean impaction was 3.07 mm at the PNS. During the 1-year follow-up period, the mean horizontal change at point A was 0.17 mm, and the mean vertical change at PNS was 0.40 mm. These results are similar to those reported in previous studies, and in the current study, there was favorable horizontal and vertical stability of the maxilla. Neither surgical nor postoperative skeletal changes in the maxilla had any significant influence on mandibular relapse in the current study. Jakobsone et al.5 reported that skeletal relapse of the mandible increased with surgical setback in bimaxillary surgery with the following average conditions: the mean backward movement of the mandible at point B was 6.9 mm, and the mean intraoperative clockwise rotation of the proximal segment was 2.9°; the amount of postoperative relapse at point B was 1.7 mm (25%) three years postoperatively. For two-jaw surgery, Yan et al.11 reported that the intraoperative clockwise rotation of the proximal segment is a risk factor for horizontal relapse in bimaxillary surgery with the following average conditions: the mean backward movement of the mandible at point B was 11.2 mm and the mean intraoperative clockwise rotation of the proximal segment was 4.3°; the amount of postoperative relapse at point B was 2.3 mm (20.3%) six months postoperatively. In their study, the tendency of
relapse increased significantly with the intraoperative clockwise rotation of the proximal segment, but not with the amount of setback. In this study, the mean surgical backward movement of the mandible at point B was 8.2 mm, and the mean horizontal relapse was 11.6% 1 year postoperatively, which was considerably less than that reported in other studies1, 5, 12. The mean increase in ramus inclination during surgery was 3.56°, which is comparable to that reported in previous studies. Notably however, the mean counterclockwise change in inclination was 37.1%, 1 year postoperatively, which is considerably less than that reported in previous studies13, 14. These differences in results might be due to the different surgical movements and condylar guidance between the various studies. The mechanisms of early relapse after mandibular setback have been discussed in previous reports2,
15
. Clockwise rotation of the proximal segment inflicts strain on the
pterygomasseteric sling, which causes the mandible to rotate counterclockwise after surgery. In addition, the forces of the masseter and temporal muscles and the contractive force of scar tissue may contribute to postoperative instability. When the bony segments are fixed rigidly, the masticatory force can be transmitted to the whole mandible, resulting in forward movement. Hence, it can be stated that horizontal relapse of the mandible is positively correlated with the magnitude of mandibular setback and ramus inclination, and the pattern of postoperative relapse of the mandible is forward rotation. Although the magnitude of setback showed a slightly stronger correlation with horizontal
relapse of the mandible than the intraoperative clockwise rotation of the proximal segments in the present study, there may be other confounding factors present. If the vertical bony step occurs at the inferior border between the proximal and distal segments after setback movement, it is natural that surgeons will try to align the proximal segments to the distal segments. This is to ensure the formation of an optimal bone contact surface during manual condylar guidance for rigid fixation. Post distal segment setback, the vertical bony step between the inferior borders of the proximal and the distal segments at the vertical osteotomy line for sagittal split ramus osteotomy has been reported as the most predictable factor for intraoperative clockwise rotation of the proximal segments. It has also been found that the amount of mandibular setback and downward movement of the maxilla correlated positively with the vertical bony step11. In patients with a large mandibular setback, simultaneous alteration of the occlusal plane by posterior impaction of the maxilla could reduce vertical bony step and consequently increase stability. Since only a small number of cases were considered in this study, further studies with more participants are necessary to evaluate whether the setback direction of the distal segment is a contributing factor of relapse. In the present study, postoperative mandibular relapse after bimaxillary surgery for mandibular prognathism was evaluated depending on the amount of mandibular setback and the clockwise rotation of the proximal segment. Horizontal relapse was correlated with both the magnitude of mandibular setback and intraoperative clockwise rotation of the proximal
segment in the present study. Relapse of the mandible is apparently mainly influenced by the amount of mandibular setback.
Conclusion In the present study, increased horizontal mandibular relapse after bimaxillary surgery was associated with more proximal segment clockwise rotation and greater mandibular setback movement. Mandibular relapse after bimaxillary surgery may be minimized via adequate control of intraoperative clockwise rotation of the proximal segment.
References 1.
de Villa GH, Huang CS, et al: Bilateral sagittal split osteotomy for correction of mandibular prognathism: long-term results. J Oral Maxillofac Surg 63: 1584-1592, 2005.
2.
Kim CH, Lee JH, et al: Skeletal stability after simultaneous mandibular angle resection and sagittal split ramus osteotomy for correction of mandible prognathism. J Oral Maxillofac Surg 65: 192-197, 2007.
3.
Paeng JY, Hong J, et al: Comparative study of skeletal stability between bicortical resorbable and titanium screw fixation after sagittal split ramus osteotomy for mandibular prognathism. J Craniomaxillofac Surg 40: 660-664, 2012.
4.
Mobarak KA, Krogstad O, et al: Long-term stability of mandibular setback surgery: a follow-up of 80 bilateral sagittal split osteotomy patients. Int J Adult Orthodon Orthognath Surg 15: 83-95, 2000.
5.
Jakobsone G, Stenvik A, et al: Three-year follow-up of bimaxillary surgery to correct skeletal Class III malocclusion: stability and risk factors for relapse. Am J Orthod Dentofacial Orthop 139: 80-89, 2011.
6.
Han JJ, Yang HJ, et al: Relapse after SSRO for mandibular setback movement in relation to the amount of mandibular setback and intraoperative clockwise rotation of the proximal segment. J Craniomaxillofac Surg 42: 811-815, 2014.
7.
Wolford LM, Bennett MA, et al: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64: 146-155, 1987.
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Bailey L, Cevidanes LH, et al: Stability and predictability of orthognathic surgery. Am J Orthod Dentofacial Orthop 126: 273-277, 2004.
9.
Kim YJ, Lee Y, et al: Condylar positional changes up to 12 months after bimaxillary surgery for skeletal class III malocclusions. J Oral Maxillofac Surg 72: 145-156, 2014.
10.
Kwon TG, Mori Y, et al: Stability of simultaneous maxillary and mandibular osteotomy for treatment of class III malocclusion: an analysis of three-dimensional cephalograms. J Craniomaxillofac Surg 28: 272-277, 2000.
11.
Yang HJ,Hwang SJ: Contributing factors to intraoperative clockwise rotation of the proximal segment as a relapse factor after mandibular setback with sagittal split ramus osteotomy. J Craniomaxillofac Surg 42: e57-63, 2014.
12.
Hsu SS, Huang CS, et al: The stability of mandibular prognathism corrected by bilateral sagittal split osteotomies: a comparison of bi-cortical osteosynthesis and mono-cortical osteosynthesis. Int J Oral Maxillofac Surg 41: 142-149, 2012.
13.
Costa F, Robiony M, et al: Stability of sagittal split ramus osteotomy used to correct Class III malocclusion: review of the literature. Int J Adult Orthodon Orthognath Surg 16: 121-129, 2001.
14.
Costa F, Robiony M, et al: Stability of skeletal Class III malocclusion after combined maxillary and mandibular procedures: titanium versus resorbable plates and screws for maxillary fixation. J Oral Maxillofac Surg 64: 642-651, 2006.
15.
Araujo A, Schendel SA, et al: Total maxillary advancement with and without bone grafting. J Oral Surg 36: 849-858, 1978.
Legends
Figure 1 Condylar repositioning ruler Measurement method for placement of the proximal segment in the primary position The points were measured from the first molar of the maxilla to the point of ascending ramus using a ruler
Figure 2 Landmarks and reference lines on the lateral cephalogram S, sella; N, nasion, PNS, A, point A; B, point B; Ar articulare; Me, menton; Go, gonion. The x-axis was constructed by rotating the S-N plane upward by 7° and the y-axis was constructed perpendicular to the x-axis and passed through the N. The angular measurements were SNA, SNB, ANB, ramus inclination (Ar-Go to SN), and mandibular plane to SN. Positions were calculated using the x-y coordinates.
Table 1 Characteristics of subjects
Male (N=19)
Female (N=31)
Total (N=50)
Age (years)
22.8±4.4
23.2±3.5
23.1±3.9
SNA (°)
82.3±3.6
79.8±3.8
80.9±3.7
SNB (°)
87.1±5.5
84.6±3.8
85.7±4.8
ANB (°)
-4.8±2.1
-4.9±2.8
-4.9±2.5
Mandibular plane to SN (°)
35.4±7.1
38.8±6.4
37.3±6.9
Ramus inclination (°)
82.9±7.2
87.4±5.8
85.4±6.8
Data are presented as the mean ± standard deviation See Figure 1 for abbreviations.
Table 2 Surgical movement and relapse after surgery
Surgical movement
Relapse at 6 months Relapse at 1 year
T1-T0
T2-T1
T3-T1
A
2.37±2.20*
-0.11±0.92
-0.17±0.72
B
-8.20±3.69*
0.57±0.78
0.95±0.96*
Pog
-8.76±2.89*
0.68±1.50
1.37±1.07*
A
0.57±2.64
0.17±0.75
0.19±0.82
PNS
3.07±1.99*
-0.27±1.09
-0.40±0.91
Me
3.31±2.78*
0.09±0.73
0.00±0.69
SNA
1.62±1.47*
0.04±0.56
0.18±0.68
SNB
-4.49±1.83*
0.31±0.67
0.40±0.94*
Mandibular plane to SN
0.99±2.81
-0.08±1.26
-0.09±1.65
Ramus inclination
3.56±1.65*
-0.90±1.72
-1.32±1.88*
Horizontal changes (mm)
Vertical changes (mm)
Angular changes (°)
Data are presented as the mean ± standard deviation. *p < 0.05 with paired t test Linear measurement: positive value in horizontal changes indicate anterior movement and positive value in vertical changes indicate superior movement; Angular measurement: T0, prior to surgery; T1, 1 month after surgery; T2, 6 months after surgery; T3, 1 year after surgery. See Figure 1 for abbreviations.
Table 3 Correlations between mandibular horizontal relapse at 1 year post-surgery and surgical change
Surgical change
Pearson correlation
P value
Horizontal position of B
-0.52
0.007
Horizontal position of Pog
-0.50
0.036
SNB
-0.37
0.020
Ramus inclination
0.48
0.014
See Figure 1 for abbreviations.
Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse? Namiaki Takahara DDS, PhD , Atsushi Kimura DDS, PhD , Nobuyoshi Tomomatsu DDS, PhD , Koichi Nakakuki DDS, PhD , Tetsuya Yoda DDS, PhD PII: DOI: Reference:
S2212-4403(19)31556-1 https://doi.org/10.1016/j.oooo.2019.10.014 OOOO 4262
To appear in:
Oral Surg Oral Med Oral Pathol Oral Radiol
Received date: Revised date: Accepted date:
16 April 2019 2 September 2019 30 October 2019
Please cite this article as: Namiaki Takahara DDS, PhD , Atsushi Kimura DDS, PhD , Nobuyoshi Tomomatsu DDS, PhD , Koichi Nakakuki DDS, PhD , Tetsuya Yoda DDS, PhD , Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse?, Oral Surg Oral Med Oral Pathol Oral Radiol (2019), doi: https://doi.org/10.1016/j.oooo.2019.10.014
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Does the amount of mandibular setback during bimaxillary surgery correlate with the degree of surgical relapse?
Namiaki TAKAHARA, DDS, PhD1, Atsushi KIMURA, DDS, PhD2, Nobuyoshi TOMOMATSU, DDS,PhD1, Koichi NAKAKUKI, DDS,PhD1, Tetsuya YODA, DDS, PhD3
1. Associate Professor, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan. 2. Clinical Fellow, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan. 3. Professor, Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences，Tokyo Medical and Dental University, Japan.
*Corresponding author: Namiaki Takahara, DDS, PhD Department of Maxillofacial Surgery, Graduate School of Medical and Dental Sciences， Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan Tel.: +81-3-5803-5501 Fax: +81-3-5803-0199 E-mail address: [email protected]
Funding None
Competing interests None declared
Statement of Clinical Relevance This study investigated postoperative horizontal relapse of the mandible in terms of the effects of the magnitude of setback movement and the rotation of the proximal segment after Le Fort I osteotomy and sagittal split ramus osteotomy.
Abstract Objective: To investigate postoperative horizontal relapse of the mandible in terms of the effects of the magnitude of mandibular setback movement and ramus inclination after Le Fort I osteotomy and sagittal split ramus osteotomy. Study Design: A retrospective study of patients who underwent orthognathic surgery for mandibular prognathism was performed. Postoperative relapse at point B was analyzed with
regard to the magnitude of mandibular setback and the ramus inclination. Serial cephalograms were used to measure surgical changes and evaluate postoperative relapse. Results: Nineteen men and 31 women (mean age: 23.1 years) were retrospectively enrolled. Mean surgical backward movement of the mandible at point B was 8.2 mm, mean ramus inclination was 3.56°, and mean relapse 1 year postoperatively was 0.95 mm (11.6%). Horizontal relapse of the mandible was significantly correlated with the magnitude of mandibular setback (r = -0.52, p = 0.007) and ramus inclination (r = 0.48, p = 0.014). Conclusions: Increased horizontal mandibular relapse after bimaxillary surgery was associated with greater mandibular setback movement and increased proximal segment clockwise rotation. Mandibular relapse after bimaxillary surgery may be minimized via adequate control of intraoperative clockwise rotation of the proximal segment.
Keywords: Clockwise rotation of the proximal segment, mandibular setback, sagittal split ramus osteotomy, skeletal stability
Introduction Skeletal class III deformities can result from either maxillary retrognathism or mandibular prognathism, or the simultaneous occurrence of both. Le Fort I and sagittal split ramus osteotomy are widely performed orthognathic surgical procedures used to correct mandibular
prognathism of the maxilla and the mandible, respectively. Despite technical advances and improved osteosynthesis materials, these procedures may still be associated with skeletal relapse. Several factors that potentially contribute to skeletal relapse after mandibular setback have been reported, including presurgical orthodontic alignment of dental arches to obtain stable occlusion, the magnitude of mandibular setback, the tension in the pterygomasseteric muscle sling, the method of fixation, intermaxillary fixation (IMF) duration, and positioning of the proximal segment1-3. In some studies, the magnitude of mandibular setback reportedly had a major effect on postoperative stability4, 5. It has also been reported that intraoperative clockwise rotation of the proximal segments was associated with instability after mandibular setback surgery6. However, the main factors that contribute to skeletal relapse after mandibular setback are controversial. The correlation between the degree of surgical relapse and the amount of mandibular setback or rotation of the proximal segment during bimaxillary surgery, including bilateral sagittal split ramus osteotomy (BSSO), has not yet been elucidated. The purpose of the present study was to assess whether a correlation exists between the amount of mandibular setback and postsurgical horizontal relapse of the mandible, as well as between the amount of rotation of the proximal segment and postsurgical horizontal relapse of the mandible.
Materials and Methods Study design This was a retrospective case series study. It was conducted in accordance with the Declaration of Helsinki guidelines, and was approved by the Ethics Committee of the Faculty of Dentistry, Tokyo Medical and Dental University. Study sample All patients consecutively underwent Le Fort I osteotomy and BSSO setback for correction of mandibular prognathism from January 2013 to December 2016 in the Department of Maxillofacial Surgery at Tokyo Medical and Dental University. The inclusion criteria were as follows: 1) BSSO for mandibular setback of > 5 mm; 2) preoperative and postoperative orthodontic treatment. The exclusion criteria were severe facial asymmetry associated with menton deviation of > 2 mm from the facial midline, facial cleft or any other craniofacial syndrome, a history of trauma, and the presence of any systemic disease. Procedure All patients underwent Le Fort I osteotomy and BSSO, and BSSO was performed using the short lingual technique7 for mandibular setback. In this procedure, conventional one piece Le Fort I maxillary down-fracture is performed. After mobilization, the maxilla is moved to its planned position, and MMF is applied with an intermediate splint, which is fabricated in centric relation of the condyle. The maxilla is fixed with titanium mini plates at the piriform
rim and anterior wall on each side. Following the Le Fort I osteotomy, BSSO mandibular setback was performed. Prior to separation the proximal segment was placed in the primary section by measuring from the first molar of the maxilla to the point of ascending ramus using a ruler (Fig.1). The distal segment was moved backward in accordance with the planned occlusion, and IMF was applied. After removal of the interference between the proximal and distal segments, the bony segments were fixed with titanium mini plates and monocortical screws on each side. The displacement of the proximal segment from its original position could be minimized by measuring reference points. Postoperatively, elastics were placed to maintain the ideal occlusion rather than performing IMF. Cephalometric analysis To measure surgical changes and evaluate postoperative stability, lateral cephalograms were taken in the maximum intercuspal position prior to surgery (T0), and at 1 month (T1), 6 months (T2), and 1 year (T3) after surgery. Cephalometric analysis was conducted via the superimposition technique. Each cephalogram was traced onto acetate paper. Eight cephalometric reference points (sella [S], nasion [N], PNS, point A [A], point B [B], articulare [Ar], menton [Me], pogonion [Pog], and gonion [Go]) were located on the lateral cephalogram at T0, and transferred to the lateral cephalograms taken at T1, T2, and T3. An x-y coordinate system was established in which the x-axis was constructed by rotating the S-N plane upward by 7° and the y-axis was constructed perpendicular to the x-axis and
passed through the N. The angular measurements were SNA, SNB, ANB, ramus inclination (Ar-Go to SN), and mandibular plane to SN (Fig. 2). Horizontal and vertical changes in PNS, A, B, and Me were determined between T0 and T1, T2 and T1, and T3 and T1. Rotation of the proximal segments was measured via changes in ramus inclination between T0 and T1, T2 and T1, and T3 and T1. Movement to posterior on the x-axis and to inferior on y-axis and counterclockwise rotation were defined as negative. To analyze methodological errors at each reference point, 20 randomly selected radiographs were traced and digitized twice by the same investigator, with an interval of 2 weeks. Methodological errors ranged from 0.38 mm to 0.69 mm for linear measurements, and from 0.42° to 0.83° for angular measurements. There were no significant differences between the duplicate measurements of any variables. Statistical analysis The primary predictor variable was the amount of mandibular setback at point B. The primary outcome variable was the amount of horizontal mandibular relapse at point B 1 year postoperatively. The secondary outcome variables were intraoperative change in the ramus inclination and surgical movement of the maxilla. Paired t-tests were used to analyze changes over time in the cephalometric variables. Significance was tested for comparisons between T0 and T1 (changes during surgery) and between T3 and T1 (total relapse) to avoid multiple significance testing. The following variables were analyzed as possible predictors for
postoperative horizontal relapse of the mandible at point B: (1) mandibular setback: horizontal position of B, horizontal position of Pog, SNA, SNB, ANB, mandibular plane to SN; (2) intraoperative clockwise rotation of the proximal segment: ramus inclination. Pearson’s correlational analysis was performed to investigate relationships between postoperative horizontal relapse of the mandible at point B and surgical change. All Statistical analyses were performed using the software package SPSS version 19.0.
Results The sample comprised 50 patients (19 male, 31 female) who were consecutively admitted from January 2013 to December 2016 and were followed for 1 year. Their mean age was 23.1 years (range 18 to 35 years). Cephalometric variables describing preoperative craniofacial morphology of all patients are summarized in Table 1. The mean changes in the cephalometric parameters as a result of surgery and the degree of postoperative relapse are presented in Table 2. The mean surgical backward movement of the mandible at point B at T1 was 8.2 mm, and the mean inclination of the ramus was 3.56°, indicating clockwise rotation of the proximal segment, and the distal segment was rotated clockwise by 0.99°. The mean forward movement of the maxilla was 2.37 mm at point A, and the mean upward movement was 3.07 mm at PNS. The mean horizontal change at point A during the 1-year follow-up period was 0.17 mm, and the vertical change at PNS was 0.40
mm; these changes were not statistically significant. The anterior changes at point B were 0.57
mm at 6 months after surgery and 0.95 mm at 1 year after surgery, representing respective relapses of the surgical movement of 6.9% and 11.6%. Horizontal relapse of the mandible 1 year postoperatively was significantly negatively correlated with the amount of surgical repositioning. The respective Pearson’s correlational coefficients pertaining to point B, Pog, and SNB were -0.52, -0.50, and -0.37 (p < 0.05). The mean decreases in ramus inclination were 0.9° (25.3%) 6 months postoperatively and 1.32° (37.1%) 1 year postoperatively, and the decrease in ramus inclination 1 year postoperatively was significantly correlated with horizontal relapse at point B (r = 0.48, p = 0.014) (Table 3).
Discussion BSSO is the most commonly performed surgical procedure used to correct mandibular prognathism. Despite technical advances and improved osteosynthesis materials, there is still a degree of skeletal relapse after mandibular setback surgery. It also has been reported that the relapse rates following mandibular setback surgery are among the highest for any surgical procedure8. Several potential contributory factors have been suggested, including presurgical orthodontic alignment of dental arches to obtain stable occlusion, the magnitude of mandibular setback, the tension in the pterygomasseteric muscle sling, the method of fixation, intermaxillary fixation (IMF) duration, and positioning of the proximal segment1-3.
Previous studies have reported that the amount of mandibular setback movement was a major factor affecting postoperative stability in single-jaw surgery and bimaxillary surgery4, 5. It has also been reported that intraoperative clockwise rotation of the proximal segments was associated with instability after mandibular setback surgery. Therefore, the main factors during mandibular setback surgery that contribute to skeletal relapse are still controversial. In the present study, we analyzed postoperative mandibular relapse in terms of the effects of the magnitude of setback movement and the rotation of the proximal segment because these are thought to be the main factors affecting relapse after BSSO combined with Le Fort I osteotomy. Horizontal relapse was found to be correlated with both the magnitude of mandibular setback and intraoperative clockwise rotation of the proximal segment. Previous studies have reported that early postoperative relapse (<6 months after surgery) is often associated with malpositioning of the condyles during surgery, causing condylar sag and subsequent unfavorable displacement of the mandible9. Late postoperative relapse (>12 months after surgery), however, is often related to the amount of mandibular setback4, 5. In the present study, most of the relapse after mandibular setback occurred during the subsequent 6 months. With regard to maxillary movement, Jakobsone et al.5 reported that large setback and inferior repositioning of the posterior maxilla were risk factors for postoperative relapse of the mandible after bimaxillary surgery. It has been reported that impaction of the posterior maxilla played a role in reducing postoperative mandibular relapse
after bimaxillary surgery to correct mandibular prognathism. Notably however, Kwon et al.110 reported that maxillary advancement and vertical changes of ± 2 mm did not influence postoperative mandibular stability. In the present study, the mean maxillary advancement was 2.37 mm at point A, and the mean impaction was 3.07 mm at the PNS. During the 1-year follow-up period, the mean horizontal change at point A was 0.17 mm, and the mean vertical change at PNS was 0.40 mm. These results are similar to those reported in previous studies, and in the current study, there was favorable horizontal and vertical stability of the maxilla. Neither surgical nor postoperative skeletal changes in the maxilla had any significant influence on mandibular relapse in the current study. Jakobsone et al.5 reported that skeletal relapse of the mandible increased with surgical setback in bimaxillary surgery with the following average conditions: the mean backward movement of the mandible at point B was 6.9 mm, and the mean intraoperative clockwise rotation of the proximal segment was 2.9°; the amount of postoperative relapse at point B was 1.7 mm (25%) three years postoperatively. For two-jaw surgery, Yan et al.11 reported that the intraoperative clockwise rotation of the proximal segment is a risk factor for horizontal relapse in bimaxillary surgery with the following average conditions: the mean backward movement of the mandible at point B was 11.2 mm and the mean intraoperative clockwise rotation of the proximal segment was 4.3°; the amount of postoperative relapse at point B was 2.3 mm (20.3%) six months postoperatively. In their study, the tendency of
relapse increased significantly with the intraoperative clockwise rotation of the proximal segment, but not with the amount of setback. In this study, the mean surgical backward movement of the mandible at point B was 8.2 mm, and the mean horizontal relapse was 11.6% 1 year postoperatively, which was considerably less than that reported in other studies1, 5, 12. The mean increase in ramus inclination during surgery was 3.56°, which is comparable to that reported in previous studies. Notably however, the mean counterclockwise change in inclination was 37.1%, 1 year postoperatively, which is considerably less than that reported in previous studies13, 14. These differences in results might be due to the different surgical movements and condylar guidance between the various studies. The mechanisms of early relapse after mandibular setback have been discussed in previous reports2,
15
. Clockwise rotation of the proximal segment inflicts strain on the
pterygomasseteric sling, which causes the mandible to rotate counterclockwise after surgery. In addition, the forces of the masseter and temporal muscles and the contractive force of scar tissue may contribute to postoperative instability. When the bony segments are fixed rigidly, the masticatory force can be transmitted to the whole mandible, resulting in forward movement. Hence, it can be stated that horizontal relapse of the mandible is positively correlated with the magnitude of mandibular setback and ramus inclination, and the pattern of postoperative relapse of the mandible is forward rotation. Although the magnitude of setback showed a slightly stronger correlation with horizontal
relapse of the mandible than the intraoperative clockwise rotation of the proximal segments in the present study, there may be other confounding factors present. If the vertical bony step occurs at the inferior border between the proximal and distal segments after setback movement, it is natural that surgeons will try to align the proximal segments to the distal segments. This is to ensure the formation of an optimal bone contact surface during manual condylar guidance for rigid fixation. Post distal segment setback, the vertical bony step between the inferior borders of the proximal and the distal segments at the vertical osteotomy line for sagittal split ramus osteotomy has been reported as the most predictable factor for intraoperative clockwise rotation of the proximal segments. It has also been found that the amount of mandibular setback and downward movement of the maxilla correlated positively with the vertical bony step11. In patients with a large mandibular setback, simultaneous alteration of the occlusal plane by posterior impaction of the maxilla could reduce vertical bony step and consequently increase stability. Since only a small number of cases were considered in this study, further studies with more participants are necessary to evaluate whether the setback direction of the distal segment is a contributing factor of relapse. In the present study, postoperative mandibular relapse after bimaxillary surgery for mandibular prognathism was evaluated depending on the amount of mandibular setback and the clockwise rotation of the proximal segment. Horizontal relapse was correlated with both the magnitude of mandibular setback and intraoperative clockwise rotation of the proximal
segment in the present study. Relapse of the mandible is apparently mainly influenced by the amount of mandibular setback.
Conclusion In the present study, increased horizontal mandibular relapse after bimaxillary surgery was associated with more proximal segment clockwise rotation and greater mandibular setback movement. Mandibular relapse after bimaxillary surgery may be minimized via adequate control of intraoperative clockwise rotation of the proximal segment.
References 1.
de Villa GH, Huang CS, et al: Bilateral sagittal split osteotomy for correction of mandibular prognathism: long-term results. J Oral Maxillofac Surg 63: 1584-1592, 2005.
2.
Kim CH, Lee JH, et al: Skeletal stability after simultaneous mandibular angle resection and sagittal split ramus osteotomy for correction of mandible prognathism. J Oral Maxillofac Surg 65: 192-197, 2007.
3.
Paeng JY, Hong J, et al: Comparative study of skeletal stability between bicortical resorbable and titanium screw fixation after sagittal split ramus osteotomy for mandibular prognathism. J Craniomaxillofac Surg 40: 660-664, 2012.
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Mobarak KA, Krogstad O, et al: Long-term stability of mandibular setback surgery: a follow-up of 80 bilateral sagittal split osteotomy patients. Int J Adult Orthodon Orthognath Surg 15: 83-95, 2000.
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Jakobsone G, Stenvik A, et al: Three-year follow-up of bimaxillary surgery to correct skeletal Class III malocclusion: stability and risk factors for relapse. Am J Orthod Dentofacial Orthop 139: 80-89, 2011.
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Han JJ, Yang HJ, et al: Relapse after SSRO for mandibular setback movement in relation to the amount of mandibular setback and intraoperative clockwise rotation of the proximal segment. J Craniomaxillofac Surg 42: 811-815, 2014.
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Wolford LM, Bennett MA, et al: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64: 146-155, 1987.
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Bailey L, Cevidanes LH, et al: Stability and predictability of orthognathic surgery. Am J Orthod Dentofacial Orthop 126: 273-277, 2004.
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Kim YJ, Lee Y, et al: Condylar positional changes up to 12 months after bimaxillary surgery for skeletal class III malocclusions. J Oral Maxillofac Surg 72: 145-156, 2014.
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Kwon TG, Mori Y, et al: Stability of simultaneous maxillary and mandibular osteotomy for treatment of class III malocclusion: an analysis of three-dimensional cephalograms. J Craniomaxillofac Surg 28: 272-277, 2000.
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Yang HJ,Hwang SJ: Contributing factors to intraoperative clockwise rotation of the proximal segment as a relapse factor after mandibular setback with sagittal split ramus osteotomy. J Craniomaxillofac Surg 42: e57-63, 2014.
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Hsu SS, Huang CS, et al: The stability of mandibular prognathism corrected by bilateral sagittal split osteotomies: a comparison of bi-cortical osteosynthesis and mono-cortical osteosynthesis. Int J Oral Maxillofac Surg 41: 142-149, 2012.
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Costa F, Robiony M, et al: Stability of sagittal split ramus osteotomy used to correct Class III malocclusion: review of the literature. Int J Adult Orthodon Orthognath Surg 16: 121-129, 2001.
14.
Costa F, Robiony M, et al: Stability of skeletal Class III malocclusion after combined maxillary and mandibular procedures: titanium versus resorbable plates and screws for maxillary fixation. J Oral Maxillofac Surg 64: 642-651, 2006.
15.
Araujo A, Schendel SA, et al: Total maxillary advancement with and without bone grafting. J Oral Surg 36: 849-858, 1978.
Legends
Figure 1 Condylar repositioning ruler Measurement method for placement of the proximal segment in the primary position The points were measured from the first molar of the maxilla to the point of ascending ramus using a ruler
Figure 2 Landmarks and reference lines on the lateral cephalogram S, sella; N, nasion, PNS, A, point A; B, point B; Ar articulare; Me, menton; Go, gonion. The x-axis was constructed by rotating the S-N plane upward by 7° and the y-axis was constructed perpendicular to the x-axis and passed through the N. The angular measurements were SNA, SNB, ANB, ramus inclination (Ar-Go to SN), and mandibular plane to SN. Positions were calculated using the x-y coordinates.
Table 1 Characteristics of subjects
Male (N=19)
Female (N=31)
Total (N=50)
Age (years)
22.8±4.4
23.2±3.5
23.1±3.9
SNA (°)
82.3±3.6
79.8±3.8
80.9±3.7
SNB (°)
87.1±5.5
84.6±3.8
85.7±4.8
ANB (°)
-4.8±2.1
-4.9±2.8
-4.9±2.5
Mandibular plane to SN (°)
35.4±7.1
38.8±6.4
37.3±6.9
Ramus inclination (°)
82.9±7.2
87.4±5.8
85.4±6.8
Data are presented as the mean ± standard deviation See Figure 1 for abbreviations.
Table 2 Surgical movement and relapse after surgery
Surgical movement
Relapse at 6 months Relapse at 1 year
T1-T0
T2-T1
T3-T1
A
2.37±2.20*
-0.11±0.92
-0.17±0.72
B
-8.20±3.69*
0.57±0.78
0.95±0.96*
Pog
-8.76±2.89*
0.68±1.50
1.37±1.07*
A
0.57±2.64
0.17±0.75
0.19±0.82
PNS
3.07±1.99*
-0.27±1.09
-0.40±0.91
Me
3.31±2.78*
0.09±0.73
0.00±0.69
SNA
1.62±1.47*
0.04±0.56
0.18±0.68
SNB
-4.49±1.83*
0.31±0.67
0.40±0.94*
Mandibular plane to SN
0.99±2.81
-0.08±1.26
-0.09±1.65
Ramus inclination
3.56±1.65*
-0.90±1.72
-1.32±1.88*
Horizontal changes (mm)
Vertical changes (mm)
Angular changes (°)
Data are presented as the mean ± standard deviation. *p < 0.05 with paired t test Linear measurement: positive value in horizontal changes indicate anterior movement and positive value in vertical changes indicate superior movement; Angular measurement: T0, prior to surgery; T1, 1 month after surgery; T2, 6 months after surgery; T3, 1 year after surgery. See Figure 1 for abbreviations.
Table 3 Correlations between mandibular horizontal relapse at 1 year post-surgery and surgical change
Surgical change
Pearson correlation
P value
Horizontal position of B
-0.52
0.007
Horizontal position of Pog
-0.50
0.036
SNB
-0.37
0.020
Ramus inclination
0.48
0.014
See Figure 1 for abbreviations.