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Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?
Accepted Manuscript Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position? Reza Tabrizi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Fereydoun Pourdanesh, DMD, Associate Professor of Oral and Maxillofacial Surgery, Hassan Mirmohammad Sadeghi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Sholeh Shahidi, DMD, Professor of Oral and Maxillofacial Radiology, Behnaz Poorian, DMD, Senior Resident of Oral and Maxillofacial Surgery PII:
S0278-2391(17)31154-0
DOI:
10.1016/j.joms.2017.08.031
Reference:
YJOMS 57966
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 7 May 2017 Revised Date:
21 July 2017
Accepted Date: 16 August 2017
Please cite this article as: Tabrizi R, Pourdanesh F, Sadeghi HM, Shahidi S, Poorian B, Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?, Journal of Oral and Maxillofacial Surgery (2017), doi: 10.1016/j.joms.2017.08.031. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
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Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?
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Reza Tabrizi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Fereydoun Pourdanesh, DMD, Associate Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hassan Mirmohammad Sadeghi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Sholeh Shahidi, DMD, Professor of Oral and Maxillofacial Radiology, Biomaterial Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
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Behnaz Poorian, DMD, Senior Resident of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Corresponding author: Behnaz Poorian, DMD
Address: OMFS Department, Shahid Beheshti Dental School, Velenjak, Tehran, Iran. Tel: +989203022038 Email: [email protected]
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Keywords: Condyle, rigid fixation, relapse, osteotomy
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Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?
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Reza Tabrizi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Fereydoun Pourdanesh, DMD, Associate Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hassan Mirmohammad Sadeghi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Sholeh Shahidi, DMD, Professor of Oral and Maxillofacial Radiology, Biomaterial Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
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Behnaz Poorian, DMD, Senior Resident of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Corresponding author: Behnaz Poorian, DMD
Address: OMFS Department, Shahid Beheshti Dental School, Velenjak, Tehran, Iran.
Abstract:
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Tel: +989203022038 Email: [email protected]
Purpose: Fixation methods are important for condylar position and stability in sagittal split osteotomy (SSO) procedures. The aim of this study was to compare changes of the condylar position and stability following SSOs for mandibular setback in plate fixation with monocortical screw and bicortical screws.
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Materials and Methods: In this retrospective cohort study, patients who underwent mandibular setback were studied in two groups. In group 1, fixation was done via miniplate with four monocortical screws and in group 2, this was done via 3 bicortical screws. Cone beam computed tomography (CBCT) scans were taken before and immediately after SSOs and one year later. Condylar position was evaluated linearly (mediolateral movement in the coronal view) and angularly (condylar axis with Frankfort plane in the coronal view). Stability of the mandible was determined at the B point horizontally and vertically. Results: Forty-eight patients were studied in two equal groups. A significant difference for the mediolateral changes of the condyle before and after osteotomies was detected between the two groups (P=0.003). There was no difference between the two groups for angular changes of the condyle before and after SSOs in the coronal view (P=0.45). Analysis of the data did not reveal any differences for vertical relapse at the B point (P=0.47) or horizontal relapse between the two groups (P=0.21). Conclusion: According to this study, bicortical screw fixation may be associated with more condylar displacement. However, we could not find significant differences in surgical stability between miniplate fixation with monocortical screws or bicortical screw fixation after one year of follow-up.
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Introduction
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Sagittal split osteotomy (SSO) is a conventional treatment modality for correction of mandibular deformities. Condylar position after the osteotomy and fixation methods are two main factors in stability of SSO [1]. Various fixation methods including miniplates and positional screws have been recommended [2]. The monocortical screws with a miniplate are less rigid than bicortical screws [3]. Contradictory results have been reported in stability of the mandible after SSOs with miniplate fixation compared with bicortical screws [4-6]. Changes of condylar position are unavoidable following SSOs [7]. The change in condylar position in bicortical screw fixation is more than that in plate fixation with monocortical screws. Correction of condyle position and the proximal segment may be easily done during SSO [5].
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We sought to see if there is any difference between monocortical plate fixation and bicortical screw fixation in terms of condylar position following SSO for mandibular setback and if so which fixation method has more stability in SSOs. We hypothesized that plate fixation with monocortical screws would have less condylar positional changes with more stability. Materials and Methods:
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The authors designed a retrospective cohort study. The sample was derived from patients who were referred to the Oral and Maxillofacial Surgery Departments of Shiraz University of Medical Sciences and Shahid Beheshti University of Medical Sciences between September 1 ,2012 and October 31, 2016. The committee of the medical ethics group of Shahid Beheshti University of Medical Sciences approved the study. Patients eligible for study inclusion had skeletal class III deformity with U shape mandible and underwent bilateral SSO and had pre- and post-surgical cone beam computed tomography (CBCT) scans. Patients were excluded from the study if they had asymmetry, bad split during osteotomies, previous trauma or fracture of the mandible, previous orthognathic surgery, surgical augmentation, congenital deformities or needed bimaxillary orthognathic surgery. None of the patients had impacted third molars in the mandible. All patients signed an informed consent form prior to taking CBCT scans (instead of lateral cephalometry, posterior-anterior cephalometry and orthopantomography) before and after the surgery.
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CBCT scans were taken via NewTom VGi (Image works) CBCT unit. A standardized protocol of the NewTom device for the extended (15 ×15 cm) field of view with 0.3 mm slice thickness and 26.9 s acquisition time was applied. The raw images were exported using the NewTom native software (NNT viewer) into DICOM multifiles. For measurement analysis, we used image-processing software, MIMICS Innovation suite (version 15, developed by Materialise). To evaluate changes in condylar position, two observers assessed all radiographs on two separate occasions with one-week interval. DICOM files of the pre- and postoperative images were evaluated using the CBCT software (QR NNT v2.0.4, Quantitative Radiology), which had a linear measurement capability. To obtain the optimal cross-sectional image of the condyle, the axial section of the condylar process that had the widest mediolateral diameter was chosen as the reference view. (Figure 1) On this reference view, a line parallel to the long axis of the condylar process was drawn. On coronal section, a line was drawn parallel to the Frankfort plane from the widest point of the condyle to the medial wall of the fossa.(Figure 2) The coronal condylar axis angle was determined as the angle between the coronal condylar axis and the FH plane. (Figure 3) The coronal condylar axis was drawn along the ramus of the mandible from the condylar neck to the center of the
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condyle on the slice with the widest mediolateral dimension of the condylar head. In liner measurement, negative movement was considered as a medially movement and positive for a laterally movement of the condyle. To evaluate relapse, another CBCT scan was taken 12 months after surgery. To assess the vertical change of the mandible, the distance from the B point perpendicular to the FH plane was measured. Horizontal change of the mandible was determined by measuring the B point perpendicular to the N-perpendicular plane. (Figure 4) The amount of mandibular set back was measured by a caliper from the upper and lower incisal edges before and immediately after completion of surgery.
Surgical approach:
Statistical analyses:
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The surgical method defined by Epker [8] was used. The incision was made over the anterior part of the vertical ramus, extending to the mesial aspect of the first molar. Subperiosteal dissection was done in the inferior border of the mandible, where a lateral channel retractor was placed. A long bur was used to create a horizontal bone cut through the medial cortex of the ramus, right above and approximately posterior to the lingula. The medial osteotomy line was extended 3 to 4 mm beyond the lingula. The vertical osteotomy cut was made through the buccal cortex, distal to the second molar. The two osteotomies were then connected with a 701-fissure bur. A spreader and a narrow osteotome were applied to gently separate the lateral cortex, and the osteotome was used to step along the connecting cut to ensure that the split stays close to the lateral cortex. Patients were assigned to two groups. In group 1, a miniplate with four monocortical screws was used to fix the distal and proximal segments in the desired occlusion after placement of the final surgical split and intermaxillary fixation (IMF). In group 2, three bicortical screws were placed in the inverted L model at the maximum bone contact. IMF was released after fixation in both groups. Age, gender and the amount of setback were variables and type of fixation was the predictive factor of the study. The amount of vertical and horizontal relapse and condylar changes (linear and angular) were the outcomes of the study. All surgeries were performed by five academic surgeons with more than 7 years experience.
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The statistical analyses were performed using the SPSS version 19 (SPSS Inc., IL, USA). Independent ttest was used to compare the amount of relapse at the B point (vertically and horizontally), the amount of mandibular set back and condylar changes (linear and angular). The Fisher's Exact test was used to compare any difference between the two groups of males and females. An inter-examiner reliability analysis was performed using the Kappa statistic to determine the level of agreement between the examiners. Results:
Fifty patients were studied in two groups (n=25 in each group). In group 2, two patients were lost to follow-up. Group 1 included 13 males and 12 females (total of 25) and group 2 included 11 males and 12 females (total of 23). There was no significant difference between the two groups of males and females (P=0.5). The mean age of the patients was 24.48±4.08 years in group 1 and 24.47±3.81 years in group 2. The results did not demonstrate any difference for age between the two groups (P=0.66). The mean
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setback was 4.84±0.90 mm in group 1 and 4.83±1.11 mm in group 2. There was no difference for the amount of setback between the groups (P=0.27). The mean of pre-surgical orthodontic treatment time was 12.88±2.42 months in group 1 and 11.78±3.27 in group 2.Analysis of the data did not demonstrate any difference for pre-surgical orthodontic treatment between group 1 and 2.(P=0.19). The mean of post-surgical orthodontic treatment time was 8.52±1.73 months in group 1 and 8.30±1.83 months in group 2. No significant difference was detected statistically between two groups for post-surgical orthodontic treatment.(P=0.68)(Table1) The amount of mediolateral change of the condyle before and after SSOs in the coronal view was
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-0.47±0.35 mm in group 1 and -0.90±0.22 mm in group 2. Assessment of the data demonstrated a significant difference for mediolateral change of the condyle before and after osteotomies between the two groups (P= 0.003).
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The amount of angular change of the condyle before and after SSOs was 2.2±1.11° in group 1 and 3.56±1.37° in group 2. There was no difference between the groups for angular changes of the condyle before and after SSOs in the coronal views (P=0.45).
Discussion:
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None of patients had obvious immediate relapse after releasing IMF. The amount of vertical relapse at the B point was 2± 0.82 mm in group 1 and 2.43 ±0.79 mm in group 2. Analysis of the data did not reveal any difference for vertical relapse at the B point (P=0.47). The amount of horizontal relapse at the B point was 1.40± 0.76 mm in group 1 and 1.96± 0.71 mm in group 2. Results did not show a significant difference for horizontal relapse between the groups (P=0.21). (Table2)The inter-examiner reliability for the examiners was found to be Kappa=0.48 (P<0.001) with 95% confidence interval, which showed a moderate agreement between the examiners. None of patients needed re-operation or post-operation infection or hardware failure.
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Failure to position the condyle properly can lead to rotation of the proximal segment, condylar sag and condylar torque [9]. Condylar malposition can result in skeletal relapse, hypomobility, malocclusion, and remodeling of the condylar head [10, 11]. Position of the condyle may change during SSOs [2]. When the mandible is setback, interference at the anterior part of the osteotomy and a gap posteriorly can cause problems during rigid fixation. Use of lag screws can cause narrowing of the posterior gap and move the condyle medially [12]. In this study, we compared two fixation methods: Three-screw fixation and miniplate with monocortical screws. The results demonstrated greater linear change medially in the coronal view in bicortical screw fixation than the miniplate group. Angular change did not differ between the fixation methods. Surgical stability was the same after one year in both groups. Condylar displacement after SSOs can be due to the fixation method, direction and amount of distal segment movement [7] as well as the amount of bone interference between the proximal and distal segments [13]. Insufficient removal of bony interference and improper reposition of the proximal segment can lead to condylar torque and displacement; this can result in postoperative relapse and temporomandibular joint disorders [14]. Undesirable condylar torque with or without mediolateral displacement can occur during adaptation of the proximal and distal segments with condylar guidance, when bony interference is between the two osteotomy segments or inter-ramus width has increased or
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decreased [15, 16]. This event may differ in osteotomy methods and the condyle may rotate inwards after SSO [16].
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Gang et al. studied 3D mandibular changes after SSO with a semirigid sliding plate system in mandibular setback surgery in 26 patients. They reported inward rotation of the condyle on the axial computed tomography view immediately after surgery and outward rotation on the axial computed tomography view six months to one year after osteotomies [17]. Han and Hwang suggested that stronger rigid internal fixation in orthognathic surgery using SSO reduces flexibility of postoperative functional adjustment of the displaced condyle relative to the preoperative condylar position [15].
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Some authors reported that rigidity of monocortical screw with a miniplate was less than that of three bicortical screws in fixation of SSOs [18-20]. Al-Moraissi and Ellis in a meta-analysis study mentioned that there was no statistically significant difference in skeletal stability between bicortical screw fixation and plate fixation in SSO for mandibular setback [1]. Use of miniplate with monocortical screws has been advocated in fixation of SSOs [9, 17, 21]. Long-term follow-up studies over two years also demonstrated that miniplate fixation method was associated with stable results [22, 23]. Chen et al. studied condylar position after SSOs with lefort I osteotomy. They reported obvious changes in condylar position after osteotomies. According their study, Condyles have a tendency to be placed in a concentric position in the glenoid fossa 3 months after osteotomies and stayed stable during the 1year follow-up. These changes did not result in an increase of TMD signs.[24] Small number of patients in our study was a limitation of this study. We suggest further multicenter studies with larger sample size to increase the reliability of results.
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Conclusion:
References:
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Al-Moraissi, E. and E. Ellis, Stability of bicortical screw versus plate fixation after mandibular setback with the bilateral sagittal split osteotomy: a systematic review and meta-analysis. International journal of oral and maxillofacial surgery, 2016. 45(1): p. 1-7. Kim, Y.I., et al., The assessment of the short- and long-term changes in the condylar position following sagittal split ramus osteotomy (SSRO) with rigid fixation. J Oral Rehabil, 2010. 37(4): p. 262-70. Brasileiro, B.F., et al., An in vitro evaluation of rigid internal fixation techniques for sagittal split ramus osteotomies: setback surgery. Journal of Oral and Maxillofacial Surgery, 2012. 70(4): p. 941-951. Fujioka, M., T. Fujii, and A. Hirano, Comparative study of mandibular stability after sagittal split osteotomies: biocortical versus monocortical osteosynthesis. Cleft Palate Craniofac J, 2000. 37(6): p. 551-5.
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According to the study results, bicortical screw fixation may be associated with greater condylar displacement. We did not find a significant difference in surgical stability between miniplate fixation with monocortical screws and bicortical screw fixation at the one-year follow-up visit.
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Chung, I.H., et al., Postoperative stability after sagittal split ramus osteotomies for a mandibular setback with monocortical plate fixation or bicortical screw fixation. J Oral Maxillofac Surg, 2008. 66(3): p. 446-52. Nooh, N., Stability of the mandible after bilateral sagittal split osteotomy: Comparison between positioning screws and plate. Saudi Dent J, 2009. 21(3): p. 123-6. Lee, W. and J.U. Park, Three-dimensional evaluation of positional change of the condyle after mandibular setback by means of bilateral sagittal split ramus osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2002. 94(3): p. 305-9. Epker, B., Modification in the sagittal osteotomy of the mandible. J Oral Surg, 1977. 35: p. 157159. Lupori JP, K.J., Van Sickels JE, Bilateral sagittal split osteotomy advancement and setback, in Oral and Maxillofacial Surgery, F. RJ, Editor. 2000, Saunders. p. 297-311. Ueki, K., et al., Condylar and disc positions after sagittal split ramus osteotomy with and without Le Fort I osteotomy. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 2007. 103(3): p. 342-348. Franco, J.E., J.E. Van Sickels, and W.J. Thrash, Factors contributing to relapse in rigidly fixed mandibular setbacks. Journal of Oral and Maxillofacial Surgery, 1989. 47(5): p. 451-456. Schardt-Sacco, D., Rigid internal fixation in orthognathic surgery, in Oral and Maxillofacial Surgery, R.J. Fonseca, Editor. 2000, Saunders. p. 433-446. Yang, H.J. and S.J. Hwang, Change in condylar position in posterior bending osteotomy minimizing condylar torque in BSSRO for facial asymmetry. Journal of Cranio-Maxillofacial Surgery, 2014. 42(4): p. 325-332. Wolford, L.M., O. Reiche-Fischel, and P. Mehra, Changes in temporomandibular joint dysfunction after orthognathic surgery. Journal of oral and maxillofacial surgery, 2003. 61(6): p. 655-660. Han, J.J. and S.J. Hwang, Three-dimensional analysis of postoperative returning movement of perioperative condylar displacement after bilateral sagittal split ramus osteotomy for mandibular setback with different fixation methods. Journal of Cranio-Maxillofacial Surgery, 2015. 43(9): p. 1918-1925. Ueki, K., et al., Condylar and temporomandibular joint disc positions after mandibular osteotomy for prognathism. Journal of oral and maxillofacial surgery, 2002. 60(12): p. 1424-1432. Ghang, M.H., et al., Three-dimensional mandibular change after sagittal split ramus osteotomy with a semirigid sliding plate system for fixation of a mandibular setback surgery. Oral Surg Oral Med Oral Pathol Oral Radiol, 2013. 115(2): p. 157-66. Anucul, B., P.D. Waite, and J.E. Lemons, In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws. J Oral Maxillofac Surg, 1992. 50(12): p. 1295-9. Peterson, G.P., R.H. Haug, and J. Van Sickels, A biomechanical evaluation of bilateral sagittal ramus osteotomy fixation techniques. J Oral Maxillofac Surg, 2005. 63(9): p. 1317-24. Choi, B.H., et al., A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2000. 90(4): p. 416-9. Ozden, B., et al., In vitro comparison of biomechanical characteristics of sagittal split osteotomy fixation techniques. Int J Oral Maxillofac Surg, 2006. 35(9): p. 837-41. Borstlap, W.A., et al., Stabilisation of sagittal split advancement osteotomies with miniplates: a prospective, multicentre study with two-year follow-up. Part II. Radiographic parameters. Int J Oral Maxillofac Surg, 2004. 33(6): p. 535-42. Borstlap, W.A., et al., Stabilisation of sagittal split set-back osteotomies with miniplates: a prospective, multicentre study with 2-year follow-up. Int J Oral Maxillofac Surg, 2005. 34(5): p. 487-94.
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Chen, S., et al., Short- and long-term changes of condylar position after bilateral sagittal split ramus osteotomy for mandibular advancement in combination with Le Fort I osteotomy evaluated by cone-beam computed tomography. J Oral Maxillofac Surg, 2013. 71(11): p. 195666.
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Legends for tables: Table 1: Patients’ demographics. Table2: Comparison of outcomes between the two groups Legends for figures:
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Figure 1: Axial section of the condylar process that had the widest mediolateral diameter and used as a reference.
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Figure 2: A line was drawn parallel to the Frankfort plane from the widest point of the condyle to the medial wall of the fossa to determine mediolateral change of the condyle and the angle between the coronal condylar axis and the FH plane. Figure 3: To assess the vertical change of the mandible, the distance from the B point perpendicular to the FH plane was measured. Horizontal change of the mandible was determined by measurement of the distance from the B point perpendicular to the N-perpendicular plane.
Group 1 13 males, 12 females 24.48±4.08 4.84±0.90 12.88±2.42
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Variables Gender Age (years) Setback(mm) Pre-surgical orthodontic treatment time(months)
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Post-surgical orthodontic 8.52±1.73 treatment time (months) * Fisher's Exact test **Independent t-test
Group 2 11 males, 12 females 24.47±3.81 4.83±1.11 11.78±3.27
P value P=0.5* P=0.66** P=0.27** P=0.19**
8.30±1.83
P=0.68**
2.2±1.11
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3.56±1.37
P=0.45
2± 0.82 1.40± 0.76
2.43 ±0.79 1.96± 0.71
P=0.47 P=0.21
Table 2 Group 1
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Medially movement
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Independent t-test p= 0.003
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Mediolateral change of the condyle before and after SSOs (mm) Angular change of the condyle before and after SSOs (degrees) Vertical relapse at the B point (mm) Horizontal relapse at the B point (mm)
Group 2
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S0278-2391(17)31154-0
DOI:
10.1016/j.joms.2017.08.031
Reference:
YJOMS 57966
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 7 May 2017 Revised Date:
21 July 2017
Accepted Date: 16 August 2017
Please cite this article as: Tabrizi R, Pourdanesh F, Sadeghi HM, Shahidi S, Poorian B, Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?, Journal of Oral and Maxillofacial Surgery (2017), doi: 10.1016/j.joms.2017.08.031. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
ACCEPTED MANUSCRIPT
Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?
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Reza Tabrizi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Fereydoun Pourdanesh, DMD, Associate Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hassan Mirmohammad Sadeghi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Sholeh Shahidi, DMD, Professor of Oral and Maxillofacial Radiology, Biomaterial Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
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Behnaz Poorian, DMD, Senior Resident of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Corresponding author: Behnaz Poorian, DMD
Address: OMFS Department, Shahid Beheshti Dental School, Velenjak, Tehran, Iran. Tel: +989203022038 Email: [email protected]
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Keywords: Condyle, rigid fixation, relapse, osteotomy
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Does Fixation Method Affect Stability of Sagittal Split Osteotomy and Condylar Position?
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Reza Tabrizi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Fereydoun Pourdanesh, DMD, Associate Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hassan Mirmohammad Sadeghi, DMD, Assistant Professor of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Sholeh Shahidi, DMD, Professor of Oral and Maxillofacial Radiology, Biomaterial Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
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Behnaz Poorian, DMD, Senior Resident of Oral and Maxillofacial Surgery, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Corresponding author: Behnaz Poorian, DMD
Address: OMFS Department, Shahid Beheshti Dental School, Velenjak, Tehran, Iran.
Abstract:
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Tel: +989203022038 Email: [email protected]
Purpose: Fixation methods are important for condylar position and stability in sagittal split osteotomy (SSO) procedures. The aim of this study was to compare changes of the condylar position and stability following SSOs for mandibular setback in plate fixation with monocortical screw and bicortical screws.
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Materials and Methods: In this retrospective cohort study, patients who underwent mandibular setback were studied in two groups. In group 1, fixation was done via miniplate with four monocortical screws and in group 2, this was done via 3 bicortical screws. Cone beam computed tomography (CBCT) scans were taken before and immediately after SSOs and one year later. Condylar position was evaluated linearly (mediolateral movement in the coronal view) and angularly (condylar axis with Frankfort plane in the coronal view). Stability of the mandible was determined at the B point horizontally and vertically. Results: Forty-eight patients were studied in two equal groups. A significant difference for the mediolateral changes of the condyle before and after osteotomies was detected between the two groups (P=0.003). There was no difference between the two groups for angular changes of the condyle before and after SSOs in the coronal view (P=0.45). Analysis of the data did not reveal any differences for vertical relapse at the B point (P=0.47) or horizontal relapse between the two groups (P=0.21). Conclusion: According to this study, bicortical screw fixation may be associated with more condylar displacement. However, we could not find significant differences in surgical stability between miniplate fixation with monocortical screws or bicortical screw fixation after one year of follow-up.
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Introduction
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Sagittal split osteotomy (SSO) is a conventional treatment modality for correction of mandibular deformities. Condylar position after the osteotomy and fixation methods are two main factors in stability of SSO [1]. Various fixation methods including miniplates and positional screws have been recommended [2]. The monocortical screws with a miniplate are less rigid than bicortical screws [3]. Contradictory results have been reported in stability of the mandible after SSOs with miniplate fixation compared with bicortical screws [4-6]. Changes of condylar position are unavoidable following SSOs [7]. The change in condylar position in bicortical screw fixation is more than that in plate fixation with monocortical screws. Correction of condyle position and the proximal segment may be easily done during SSO [5].
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We sought to see if there is any difference between monocortical plate fixation and bicortical screw fixation in terms of condylar position following SSO for mandibular setback and if so which fixation method has more stability in SSOs. We hypothesized that plate fixation with monocortical screws would have less condylar positional changes with more stability. Materials and Methods:
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The authors designed a retrospective cohort study. The sample was derived from patients who were referred to the Oral and Maxillofacial Surgery Departments of Shiraz University of Medical Sciences and Shahid Beheshti University of Medical Sciences between September 1 ,2012 and October 31, 2016. The committee of the medical ethics group of Shahid Beheshti University of Medical Sciences approved the study. Patients eligible for study inclusion had skeletal class III deformity with U shape mandible and underwent bilateral SSO and had pre- and post-surgical cone beam computed tomography (CBCT) scans. Patients were excluded from the study if they had asymmetry, bad split during osteotomies, previous trauma or fracture of the mandible, previous orthognathic surgery, surgical augmentation, congenital deformities or needed bimaxillary orthognathic surgery. None of the patients had impacted third molars in the mandible. All patients signed an informed consent form prior to taking CBCT scans (instead of lateral cephalometry, posterior-anterior cephalometry and orthopantomography) before and after the surgery.
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CBCT scans were taken via NewTom VGi (Image works) CBCT unit. A standardized protocol of the NewTom device for the extended (15 ×15 cm) field of view with 0.3 mm slice thickness and 26.9 s acquisition time was applied. The raw images were exported using the NewTom native software (NNT viewer) into DICOM multifiles. For measurement analysis, we used image-processing software, MIMICS Innovation suite (version 15, developed by Materialise). To evaluate changes in condylar position, two observers assessed all radiographs on two separate occasions with one-week interval. DICOM files of the pre- and postoperative images were evaluated using the CBCT software (QR NNT v2.0.4, Quantitative Radiology), which had a linear measurement capability. To obtain the optimal cross-sectional image of the condyle, the axial section of the condylar process that had the widest mediolateral diameter was chosen as the reference view. (Figure 1) On this reference view, a line parallel to the long axis of the condylar process was drawn. On coronal section, a line was drawn parallel to the Frankfort plane from the widest point of the condyle to the medial wall of the fossa.(Figure 2) The coronal condylar axis angle was determined as the angle between the coronal condylar axis and the FH plane. (Figure 3) The coronal condylar axis was drawn along the ramus of the mandible from the condylar neck to the center of the
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condyle on the slice with the widest mediolateral dimension of the condylar head. In liner measurement, negative movement was considered as a medially movement and positive for a laterally movement of the condyle. To evaluate relapse, another CBCT scan was taken 12 months after surgery. To assess the vertical change of the mandible, the distance from the B point perpendicular to the FH plane was measured. Horizontal change of the mandible was determined by measuring the B point perpendicular to the N-perpendicular plane. (Figure 4) The amount of mandibular set back was measured by a caliper from the upper and lower incisal edges before and immediately after completion of surgery.
Surgical approach:
Statistical analyses:
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The surgical method defined by Epker [8] was used. The incision was made over the anterior part of the vertical ramus, extending to the mesial aspect of the first molar. Subperiosteal dissection was done in the inferior border of the mandible, where a lateral channel retractor was placed. A long bur was used to create a horizontal bone cut through the medial cortex of the ramus, right above and approximately posterior to the lingula. The medial osteotomy line was extended 3 to 4 mm beyond the lingula. The vertical osteotomy cut was made through the buccal cortex, distal to the second molar. The two osteotomies were then connected with a 701-fissure bur. A spreader and a narrow osteotome were applied to gently separate the lateral cortex, and the osteotome was used to step along the connecting cut to ensure that the split stays close to the lateral cortex. Patients were assigned to two groups. In group 1, a miniplate with four monocortical screws was used to fix the distal and proximal segments in the desired occlusion after placement of the final surgical split and intermaxillary fixation (IMF). In group 2, three bicortical screws were placed in the inverted L model at the maximum bone contact. IMF was released after fixation in both groups. Age, gender and the amount of setback were variables and type of fixation was the predictive factor of the study. The amount of vertical and horizontal relapse and condylar changes (linear and angular) were the outcomes of the study. All surgeries were performed by five academic surgeons with more than 7 years experience.
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The statistical analyses were performed using the SPSS version 19 (SPSS Inc., IL, USA). Independent ttest was used to compare the amount of relapse at the B point (vertically and horizontally), the amount of mandibular set back and condylar changes (linear and angular). The Fisher's Exact test was used to compare any difference between the two groups of males and females. An inter-examiner reliability analysis was performed using the Kappa statistic to determine the level of agreement between the examiners. Results:
Fifty patients were studied in two groups (n=25 in each group). In group 2, two patients were lost to follow-up. Group 1 included 13 males and 12 females (total of 25) and group 2 included 11 males and 12 females (total of 23). There was no significant difference between the two groups of males and females (P=0.5). The mean age of the patients was 24.48±4.08 years in group 1 and 24.47±3.81 years in group 2. The results did not demonstrate any difference for age between the two groups (P=0.66). The mean
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setback was 4.84±0.90 mm in group 1 and 4.83±1.11 mm in group 2. There was no difference for the amount of setback between the groups (P=0.27). The mean of pre-surgical orthodontic treatment time was 12.88±2.42 months in group 1 and 11.78±3.27 in group 2.Analysis of the data did not demonstrate any difference for pre-surgical orthodontic treatment between group 1 and 2.(P=0.19). The mean of post-surgical orthodontic treatment time was 8.52±1.73 months in group 1 and 8.30±1.83 months in group 2. No significant difference was detected statistically between two groups for post-surgical orthodontic treatment.(P=0.68)(Table1) The amount of mediolateral change of the condyle before and after SSOs in the coronal view was
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-0.47±0.35 mm in group 1 and -0.90±0.22 mm in group 2. Assessment of the data demonstrated a significant difference for mediolateral change of the condyle before and after osteotomies between the two groups (P= 0.003).
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The amount of angular change of the condyle before and after SSOs was 2.2±1.11° in group 1 and 3.56±1.37° in group 2. There was no difference between the groups for angular changes of the condyle before and after SSOs in the coronal views (P=0.45).
Discussion:
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None of patients had obvious immediate relapse after releasing IMF. The amount of vertical relapse at the B point was 2± 0.82 mm in group 1 and 2.43 ±0.79 mm in group 2. Analysis of the data did not reveal any difference for vertical relapse at the B point (P=0.47). The amount of horizontal relapse at the B point was 1.40± 0.76 mm in group 1 and 1.96± 0.71 mm in group 2. Results did not show a significant difference for horizontal relapse between the groups (P=0.21). (Table2)The inter-examiner reliability for the examiners was found to be Kappa=0.48 (P<0.001) with 95% confidence interval, which showed a moderate agreement between the examiners. None of patients needed re-operation or post-operation infection or hardware failure.
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Failure to position the condyle properly can lead to rotation of the proximal segment, condylar sag and condylar torque [9]. Condylar malposition can result in skeletal relapse, hypomobility, malocclusion, and remodeling of the condylar head [10, 11]. Position of the condyle may change during SSOs [2]. When the mandible is setback, interference at the anterior part of the osteotomy and a gap posteriorly can cause problems during rigid fixation. Use of lag screws can cause narrowing of the posterior gap and move the condyle medially [12]. In this study, we compared two fixation methods: Three-screw fixation and miniplate with monocortical screws. The results demonstrated greater linear change medially in the coronal view in bicortical screw fixation than the miniplate group. Angular change did not differ between the fixation methods. Surgical stability was the same after one year in both groups. Condylar displacement after SSOs can be due to the fixation method, direction and amount of distal segment movement [7] as well as the amount of bone interference between the proximal and distal segments [13]. Insufficient removal of bony interference and improper reposition of the proximal segment can lead to condylar torque and displacement; this can result in postoperative relapse and temporomandibular joint disorders [14]. Undesirable condylar torque with or without mediolateral displacement can occur during adaptation of the proximal and distal segments with condylar guidance, when bony interference is between the two osteotomy segments or inter-ramus width has increased or
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decreased [15, 16]. This event may differ in osteotomy methods and the condyle may rotate inwards after SSO [16].
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Gang et al. studied 3D mandibular changes after SSO with a semirigid sliding plate system in mandibular setback surgery in 26 patients. They reported inward rotation of the condyle on the axial computed tomography view immediately after surgery and outward rotation on the axial computed tomography view six months to one year after osteotomies [17]. Han and Hwang suggested that stronger rigid internal fixation in orthognathic surgery using SSO reduces flexibility of postoperative functional adjustment of the displaced condyle relative to the preoperative condylar position [15].
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Some authors reported that rigidity of monocortical screw with a miniplate was less than that of three bicortical screws in fixation of SSOs [18-20]. Al-Moraissi and Ellis in a meta-analysis study mentioned that there was no statistically significant difference in skeletal stability between bicortical screw fixation and plate fixation in SSO for mandibular setback [1]. Use of miniplate with monocortical screws has been advocated in fixation of SSOs [9, 17, 21]. Long-term follow-up studies over two years also demonstrated that miniplate fixation method was associated with stable results [22, 23]. Chen et al. studied condylar position after SSOs with lefort I osteotomy. They reported obvious changes in condylar position after osteotomies. According their study, Condyles have a tendency to be placed in a concentric position in the glenoid fossa 3 months after osteotomies and stayed stable during the 1year follow-up. These changes did not result in an increase of TMD signs.[24] Small number of patients in our study was a limitation of this study. We suggest further multicenter studies with larger sample size to increase the reliability of results.
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Conclusion:
References:
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Al-Moraissi, E. and E. Ellis, Stability of bicortical screw versus plate fixation after mandibular setback with the bilateral sagittal split osteotomy: a systematic review and meta-analysis. International journal of oral and maxillofacial surgery, 2016. 45(1): p. 1-7. Kim, Y.I., et al., The assessment of the short- and long-term changes in the condylar position following sagittal split ramus osteotomy (SSRO) with rigid fixation. J Oral Rehabil, 2010. 37(4): p. 262-70. Brasileiro, B.F., et al., An in vitro evaluation of rigid internal fixation techniques for sagittal split ramus osteotomies: setback surgery. Journal of Oral and Maxillofacial Surgery, 2012. 70(4): p. 941-951. Fujioka, M., T. Fujii, and A. Hirano, Comparative study of mandibular stability after sagittal split osteotomies: biocortical versus monocortical osteosynthesis. Cleft Palate Craniofac J, 2000. 37(6): p. 551-5.
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According to the study results, bicortical screw fixation may be associated with greater condylar displacement. We did not find a significant difference in surgical stability between miniplate fixation with monocortical screws and bicortical screw fixation at the one-year follow-up visit.
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Chung, I.H., et al., Postoperative stability after sagittal split ramus osteotomies for a mandibular setback with monocortical plate fixation or bicortical screw fixation. J Oral Maxillofac Surg, 2008. 66(3): p. 446-52. Nooh, N., Stability of the mandible after bilateral sagittal split osteotomy: Comparison between positioning screws and plate. Saudi Dent J, 2009. 21(3): p. 123-6. Lee, W. and J.U. Park, Three-dimensional evaluation of positional change of the condyle after mandibular setback by means of bilateral sagittal split ramus osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2002. 94(3): p. 305-9. Epker, B., Modification in the sagittal osteotomy of the mandible. J Oral Surg, 1977. 35: p. 157159. Lupori JP, K.J., Van Sickels JE, Bilateral sagittal split osteotomy advancement and setback, in Oral and Maxillofacial Surgery, F. RJ, Editor. 2000, Saunders. p. 297-311. Ueki, K., et al., Condylar and disc positions after sagittal split ramus osteotomy with and without Le Fort I osteotomy. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 2007. 103(3): p. 342-348. Franco, J.E., J.E. Van Sickels, and W.J. Thrash, Factors contributing to relapse in rigidly fixed mandibular setbacks. Journal of Oral and Maxillofacial Surgery, 1989. 47(5): p. 451-456. Schardt-Sacco, D., Rigid internal fixation in orthognathic surgery, in Oral and Maxillofacial Surgery, R.J. Fonseca, Editor. 2000, Saunders. p. 433-446. Yang, H.J. and S.J. Hwang, Change in condylar position in posterior bending osteotomy minimizing condylar torque in BSSRO for facial asymmetry. Journal of Cranio-Maxillofacial Surgery, 2014. 42(4): p. 325-332. Wolford, L.M., O. Reiche-Fischel, and P. Mehra, Changes in temporomandibular joint dysfunction after orthognathic surgery. Journal of oral and maxillofacial surgery, 2003. 61(6): p. 655-660. Han, J.J. and S.J. Hwang, Three-dimensional analysis of postoperative returning movement of perioperative condylar displacement after bilateral sagittal split ramus osteotomy for mandibular setback with different fixation methods. Journal of Cranio-Maxillofacial Surgery, 2015. 43(9): p. 1918-1925. Ueki, K., et al., Condylar and temporomandibular joint disc positions after mandibular osteotomy for prognathism. Journal of oral and maxillofacial surgery, 2002. 60(12): p. 1424-1432. Ghang, M.H., et al., Three-dimensional mandibular change after sagittal split ramus osteotomy with a semirigid sliding plate system for fixation of a mandibular setback surgery. Oral Surg Oral Med Oral Pathol Oral Radiol, 2013. 115(2): p. 157-66. Anucul, B., P.D. Waite, and J.E. Lemons, In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws. J Oral Maxillofac Surg, 1992. 50(12): p. 1295-9. Peterson, G.P., R.H. Haug, and J. Van Sickels, A biomechanical evaluation of bilateral sagittal ramus osteotomy fixation techniques. J Oral Maxillofac Surg, 2005. 63(9): p. 1317-24. Choi, B.H., et al., A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2000. 90(4): p. 416-9. Ozden, B., et al., In vitro comparison of biomechanical characteristics of sagittal split osteotomy fixation techniques. Int J Oral Maxillofac Surg, 2006. 35(9): p. 837-41. Borstlap, W.A., et al., Stabilisation of sagittal split advancement osteotomies with miniplates: a prospective, multicentre study with two-year follow-up. Part II. Radiographic parameters. Int J Oral Maxillofac Surg, 2004. 33(6): p. 535-42. Borstlap, W.A., et al., Stabilisation of sagittal split set-back osteotomies with miniplates: a prospective, multicentre study with 2-year follow-up. Int J Oral Maxillofac Surg, 2005. 34(5): p. 487-94.
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Chen, S., et al., Short- and long-term changes of condylar position after bilateral sagittal split ramus osteotomy for mandibular advancement in combination with Le Fort I osteotomy evaluated by cone-beam computed tomography. J Oral Maxillofac Surg, 2013. 71(11): p. 195666.
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Legends for tables: Table 1: Patients’ demographics. Table2: Comparison of outcomes between the two groups Legends for figures:
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Figure 1: Axial section of the condylar process that had the widest mediolateral diameter and used as a reference.
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Figure 2: A line was drawn parallel to the Frankfort plane from the widest point of the condyle to the medial wall of the fossa to determine mediolateral change of the condyle and the angle between the coronal condylar axis and the FH plane. Figure 3: To assess the vertical change of the mandible, the distance from the B point perpendicular to the FH plane was measured. Horizontal change of the mandible was determined by measurement of the distance from the B point perpendicular to the N-perpendicular plane.
Group 1 13 males, 12 females 24.48±4.08 4.84±0.90 12.88±2.42
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Variables Gender Age (years) Setback(mm) Pre-surgical orthodontic treatment time(months)
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Table 1
Post-surgical orthodontic 8.52±1.73 treatment time (months) * Fisher's Exact test **Independent t-test
Group 2 11 males, 12 females 24.47±3.81 4.83±1.11 11.78±3.27
P value P=0.5* P=0.66** P=0.27** P=0.19**
8.30±1.83
P=0.68**
2.2±1.11
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3.56±1.37
P=0.45
2± 0.82 1.40± 0.76
2.43 ±0.79 1.96± 0.71
P=0.47 P=0.21
Table 2 Group 1
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Medially movement
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Independent t-test p= 0.003
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Mediolateral change of the condyle before and after SSOs (mm) Angular change of the condyle before and after SSOs (degrees) Vertical relapse at the B point (mm) Horizontal relapse at the B point (mm)
Group 2
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