Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
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Skeletal stability and condylar position related to fixation method following mandibular setback with bilateral sagittal split ramus osteotomy Young-Chea Roh a, Sang-Hun Shin a, Seong-Sik Kim b, George K. Sandor c, d, Yong-Deok Kim e, f, * a
Department of Oral and Maxillofacial Surgery, School of Dentistry, Pusan National University, Yangsan, South Korea Department of Orthodontics, School of Dentistry, Pusan National University, Yangsan, South Korea Department of Tissue Engineering, Regea Institute for Regenerative Medicine, University of Tampere, Tampere, Finland d Department of Oral and Maxillofacial Surgery, University of Oulu, Oulu, Finland e Department of Oral and Maxillofacial Surgery, School of Dentistry, Pusan National University, Yangsan, South Korea f Dental Research Institute, and Institute of Translational Dental Sciences, Pusan National University, Yangsan, South Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 25 February 2014 Accepted 27 August 2014 Available online 7 September 2014
Purpose: To investigate postoperative intersegmental displacement and relapse following bilateral sagittal split ramus osteotomy (BSSRO) by comparing three different fixation methods: group A (sliding plate), group B (miniplate) and group C (bicortical screws). Materials and methods: The present retrospective study included 55 patients with mandibular prognathism who were treated with BSSRO. To evaluate skeletal changes, cone-beam computed tomography was taken before surgery (T0), three days after surgery (T1), and 6 months after surgery (T2). Differences among the three groups were assessed using a one-way analysis of variance, where P < 0.05 was accepted as statistically significant. Results: There were no significant differences among the three groups in demographic data and the amount of mandibular setback. In skeletal changes and condylar axis changes, there were no statistically significant differences among the three groups. However, there were statistically significant postoperative skeletal changes in group C (bicortical screws) at all landmarks. The mean horizontal relapse rate was 1.9% in group A (sliding plate); 4.8% in group B (miniplate); and 15.4% in group C (bicortical screws). Conclusion: The sliding plate system has good adaptability to the proximal segment after mandibular setback with BSSRO, and behaves according to semi-rigid fixation principles. © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: Mandibular prognathism Titanium Cone-beam computed tomography Orthognathic
1. Introduction Bilateral sagittal split ramus osteotomy (BSSRO) has been commonly used in orthognathic surgical procedures to correct mandibular prognathism. Throughout the history of this procedure postoperative stability has been one of the main issues. To achieve acceptable postoperative stability, either bicortical screws or miniplates have been used to position the proximal and distal segment after BSSRO. Some previous in vitro studies have shown that bicortical screw fixation tends to be more stable and less susceptible
* Corresponding author. 3-3 Beomeo, Mulgum, Department of Oral and Maxillofacial Surgery, Pusan National University, Yangsan 626-770, South Korea. Tel.: þ82 55 360 5100; fax: þ82 55 360 5104. E-mail address: [email protected] (Y.-D. Kim).
to deformation than monocortical plate fixation (Anucul et al., 1992; Hammer et al., 1995). On the other hand, many in vitro studies (Foley and Beckman, 1992; Tharanon, 1998) and comparative clinical studies (Choi et al., 2000; Chung et al., 2008) showed that there was no significant difference between bicortical screw and monocortical miniplate fixation. In addition, reports about the stability of monocortical plate fixation showed results which were as acceptable as bicortical fixation (Rubens et al., 1988; Chung et al., 2008). Semi-rigid fixation with monocortical miniplates has some advantages such as avoidance of inferior alveolar nerve injury, ease of access, and manipulation without a transbuccal fixation. The sliding plate, also known as a condylar repositionable plate, follows the same principle of semi-rigid fixation. This plate consists of two 2 mm diameter holes and an oval-shaped sliding hole. In this plating system, the oval-shaped hole allows sliding of the proximal
http://dx.doi.org/10.1016/j.jcms.2014.08.008 1010-5182/© 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
segment after BRSSO. This system had been reported to be relatively stable and convenient for the operators (Baek and Lee, 2010; Ghang et al., 2013). Up until now, however, no comparative studies comparing sliding plates versus monocortical miniplates or bicortical screws for fixation of the bone segments in BSSRO have been published. The aims of this retrospective study were to investigate postoperative intersegmental displacement and relapse by comparing three different fixation methods: sliding plate, miniplate and bicortical screws. In the present study, the authors used cone-beam computed tomography (CBCT) data to evaluate: 1) horizontal and vertical changes of mandibular position in the sagittal view following BSSRO surgery; 2) degrees of condylar axis angle change on the axial, coronal and sagittal plane of CBCT views; and 3) the stability as well as the relapse ratio after surgery and a postoperative period. 2. Patients and methods
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The bony segments were fixed with one of three different osteosynthesis methods (Figs. 1 and 2). Group A: A sliding plate was fixed with two 2.0 mm diameter monocortical screws to the proximal segment and another screw to the distal segment (Fig. 2A). Group B: Two 2.0 mm diameter monocortical screws were installed in each segment using a miniplate (Fig. 2B). Group C: Three 2.0 mm bicortical screws were placed at the superior border of the mandible (Fig. 2C). To maintain postoperative occlusion, approximately 5e7 days of intermaxillary fixation (IMF) with an interocclusal splint was applied. After releasing the IMF physiotherapy including mouth-opening exercises with orthodontic elastics was used for 4 weeks. Postoperative orthodontic treatment was started one month after surgery. 2.3. CBCT data
2.1. Patients The 55 Korean adults (25 male, 30 female) were among the patients admitted to the department of oral and maxillofacial surgery at Pusan National University Dental Hospital between March 2012 and November 2012. They were selected for the study according to the following criteria: 1) Diagnosed with mandibular prognathism with or without facial asymmetry; 2) Underwent mandibular setback BSSRO with or without either Le Fort I osteotomy or genioplasty; 3) Available preoperative and postoperative cone-beam computed tomography (CBCT) images with 6 months follow-up; 4) No history of trauma or craniofacial syndrome. Written informed consent was obtained from all patients, and the study was approved by the Institutional Review Board at Pusan National University Dental Hospital, Yangsan, Korea. 2.2. Surgery All patients received orthodontic treatment before and after their operation. All patients underwent BSSRO using the modification known as the Obwegeser-Dal Pont sagittal split of the ramus. Thirty-three patients had 1-segment Le Fort I osteotomy with BSSRO. In these patients, stabilization of the maxilla was done using rigid fixation with titanium miniplates and screws. There were no cases of inferior repositioning of the maxilla included in this study. In all cases the proximal segment of the mandible was stripped of its pterygomasseteric sling at the inferior and posterior borders.
CBCT images (PaX-Zenith 3D; Vatech, Seoul, Korea) were taken for all patients before surgery (T0), three days after surgery (T1), and 6 months following surgery (T2). The subjects were in an upright position with maximum intercuspation; the Frankfort horizontal (FH) plane of subjects was parallel to the floor. Images were obtained using a CBCT scanner (DCT Pro, Vatech, Seoul, Korea). The machine settings were as follows: 20 19 cm field of view, 90 kVp tube voltage, 4.0 mA tube current, 24 s scan time. To investigate the skeletal changes, the CBCT data was reconstructed with 3D imaging software (SimPlant 3-D Pro; Materialize, Leuven, Belgium). 2.4. CBCT analysis In this study, images were analyzed by the same investigator with preset reference points and planes (Table 1). To evaluate the horizontal and vertical movement of mandible, the distances from the FH plane and Na-perpendicular plane to point B, pogonion (Pog), and the menton (Me) were measured. Angular changes of the condyle in the axial, coronal, and sagittal images were also measured according to the method of Park et al. (2012). The axial condylar axis angle was defined as the angle between the axial condylar axis and the midsagittal plane. The axial condylar axis was drawn from the condylar lateral pole (outermost part) to the medial pole (innermost part) in the greatest mediolateral dimension of the condylar head (Fig. 3A). The coronal condylar axis angle was defined as the angle between the coronal condylar axis and the FH plane. The coronal condylar axis was drawn along the ramus from the condylar neck to the center of condyle in the slice showing the greatest mediolateral dimension of the condylar head (Fig. 3B). The sagittal condylar axis angle was defined as the angle between the sagittal condylar axis and the FH plane. The sagittal
Fig. 1. Diagrams of three different fixation methods: (A) Sliding plate, (B) Miniplate, (C) Bicortical screws.
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Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
Fig. 2. Radiographic image of: (A) Sliding plate, (B) Miniplate, (C) Bicortical screws.
condylar axis was drawn from the center of condylar neck to the center of condylar head (Fig. 3C).
3. Results 3.1. Patient distribution
2.5. Statistical analysis The data were analyzed using a statistical software package (SPSS 12.0; SPSS, Chicago, IL, USA). To evaluate differences over time, T1 and T2 values were evaluated by paired t-test and repeated measures analysis of variance (ANOVA). The difference within the three groups was assessed using one-way ANOVA. P < 0.05 was accepted as statistically significant. Table 1 Reference points and planes. Reference point/plane Nasion (Na)
Description
The most anterior and superior point of the frontonasal suture Basion (Ba) The most posterior and inferior point of the occipital bone at the anterior margin of foramen magnum Orbitale (Or) The most inferior point of orbital margin Porion (Po) The most superior point of external auditory meatus Point B Deepest point of curvature between chin and alveolar junction Pogonion (Pog) Most anterior point on contour of symphysis Menton (Me) Most inferior point on the symphysis FH plane Plane constructed by both sides of Po and (horizontal reference plane) midpoints of both Or Midsagittal plane Plane normal to FH plane and passing through (sagittal reference plane) Na and Ba Na-perpendicular plane Plane normal to FH plane and midsagittal (coronal reference plane) plane passing through Na
The distribution of cases with mandibular surgery alone versus cases with bimaxillary surgery within the three mandibular fixation groups was quite uniform with 63.2% bimaxillary surgery in group A; 57.9% in group B; and 58.8% in group C. There were no significant differences among the three groups in demographic data and the amount of mandibular setback (Table 2). The amount of setback was calculated as the average change between T0 (before surgery) and T1 (three days after surgery) by distance from the three points (B, Pog, Me) to the Na-perpendicular plane. 3.2. Linear changes in landmarks Table 3 shows mean horizontal and vertical changes during the postoperative period in each group. There were no statistically significant differences among the three groups in ANOVA. However, there were statistically significant postoperative skeletal changes in group C (bicortical screws) at all landmarks. Mean horizontal relapse rates were 1.9% in group A (sliding plate); 4.8% in group B (miniplate); and 15.4% in group C (bicortical screws), respectively. 3.3. Angular changes in condylar axis Table 4 shows mean angular changes during the postoperative period in each group. There were no statistically significant differences among the three groups in ANOVA. However, there were statistically significant postoperative angular changes in group C (bicortical screws) on both axial condylar angles.
Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
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Fig. 3. Measurement of condylar angles on CBCT images. (A) Axial condylar axis angle: angle between axial condylar axis and midsagittal plane, (B) Coronal condylar axis angle: angle between coronal condylar axis and FH plane, (C) Sagittal condylar axis angle: angle between sagittal condylar axis and FH plane.
Therefore, the type and method of fixation is the only variable responsible for postoperative relapse in our study. Many studies have reported on the sagittal and vertical postoperative stability after BSSRO setback. The reported sagittal relapse rates for mandibular setback showed great variation, from 1.0% to 91.3% (Moenning et al., 1990; Lee and Piecuch, 1992; Turvey et al., 2006; Kahnberg et al., 2007; Joss and Vassalli, 2009). In this study, horizontal postoperative relapse rates were 1.6%e15.5%, therefore within the range of the previous studies. All three fixation methods showed relatively low relapse rates compared with previous studies. In the results of the present study, horizontal and vertical mandibular movements during the postoperative period (T1eT0) averaged 0.21 mme1.11 mm, and 0.33 mm to 1.41 mm respectively, in all patients. Although there was no statistically significant difference in group comparisons, group C (bicortical screws) showed slightly higher skeletal changes during the postoperative period, compared with the other groups. There have been several reports that there were no statistically significant differences in the stability between bicortical screw fixation and monocortical plate fixation after mandibular setback (Rubens et al., 1988; Foley and Beckman, 1992; Tharanon, 1998; Ueki et al., 2001). Previous clinical studies (Anucul et al., 1992; Hammer et al., 1995; Choi et al., 2000; Chung et al., 2008) suggested that there were no significant differences between bicortical screw and monocortical miniplate fixation. This study is in agreement with previous reports, as the data obtained from this study showed no statistically significant
Table 2 Demographic characteristics of the study patients. Study variables
Group A: (sliding plate)
Group B: (miniplate)
Group C: (bicortical screws)
Sample size (n) No. of males (%) Age (years)a 1-jaw (BSSRO only)/2-jaw Amount of setback (mm)a
19 7 (36.8%) 23.6 ± 2.7 7/12 (36.8/63.2%) 6.54 ± 3.42
19 9 (47.4%) 23.6 ± 3.3 8/11 (42.1/57.9%) 7.32 ± 4.86
17 9 (52.9%) 23.0 ± 3.8 7/10 (41.2/58.8%) 6.79 ± 3.90
a
P value (ANOVA)
0.612 0.963 0.940 0.615
Expressed as mean ± SD.
4. Discussion The present study compared three fixation methods using CBCT data to evaluate postoperative intersegmental displacement and relapse. Possible factors influencing potential postoperative relapse include the magnitude of movement, control of the proximal segment, the type and methods of fixation, masticatory muscle tension, postoperative orthodontic treatment, and residual growth and remodeling (Epker and Wessberg, 1982; Will et al., 1984; Stella et al., 1986; Van Sickels et al., 1986; Mobarak et al., 2001; Reyneke and Ferretti, 2002). In this study, there were no statistically significant differences in the distribution of patients and the amount of mandibular setback, as well as the types of surgical procedures.
Table 3 Surgical and postoperative skeletal changes. Group A: (sliding plate)
Group B: (miniplate)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Mean
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
Horizontal B 6.08 Pog 6.85 Me 7.27 Vertical B 1.82 Pog 1.97 Me 1.44 a
SD
Group C: (bicortical screws)
P value (ANOVA)
SD
2.68 2.15 3.41
0.25 0.21 0.32
0.82 0.93 1.01
7.82 7.72 7.54
2.71 3.58 3.61
0.69 0.70 0.42
0.92 1.29 1.07
6.87 7.11 6.62
2.58 2.33 1.93
1.08a 1.11a 0.97a
1.09 1.13 1.06
0.507 0.510 0.498
1.03 1.21 0.98
0.52 0.33 0.61
0.89 0.71 0.76
2.11 1.79 1.52
1.39 1.41 1.08
0.77 0.39 0.92
0.82 0.91 1.00
2.01 1.49 1.44
1.33 0.91 0.97
1.31a 1.27a 1.41a
1.03 0.89 0.98
0.515 0.331 0.230
Repeated measures ANOVA (P < 0.05).
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Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
Table 4 Angular changes of the mandibular condyle. Group A: (sliding plate)
Right Axial Coronal Sagittal Left Axial Coronal Sagittal a
Group B: (miniplate)
Group C: (bicortical screws)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
2.15 1.43 0.78
1.03 1.14 1.01
1.16 0.78 0.39
2.72 1.32 1.24
2.42 1.57 1.12
1.22 0.58 1.17
0.71 0.91 0.88
2.13 1.37 0.68
2.82 1.19 0.42
0.48 0.81 1.24
4.15a 1.42 1.16
2.14 1.71 1.10
1.41 0.76 0.43
1.53 0.87 0.64
1.15 0.42 1.14
2.46 1.01 1.85
1.17 1.64 1.11
1.37 0.50 0.78
1.07 0.62 1.14
1.52 0.97 0.81
2.44 0.87 0.19
0.51 0.63 1.18
4.01a 1.21 0.97
2.25 1.17 0.35
Repeated measures ANOVA (P < 0.05).
differences among the groups. There was less skeletal change in the semi-rigid fixation groups (sliding plate and miniplate) than the rigid fixation group (bicortical screws). In measurements of condylar angles, all groups showed statistically significant inward rotation of the axial condylar angle. Although there were no significant differences among group comparisons, differences in group C (bicortical screws) were greater than in the other two groups. In bicortical screw fixation, greater torque on the proximal segment can occur than in the semirigid fixation group (Ueki et al., 2001; Kim et al., 2010). This force could be the main cause of early forward relapse because the screws tend to reduce the intersegmental gap (Kundert and Hadjianghelou, 1980; Lee and Park, 2002). The sliding plate was designed to allow repositioning of the malpositioned condyle during the early postoperative period. In this way, the sliding plate system prevents the forward relapse of the distal segment. Baek et al. reported satisfactory short-term stability after sliding plate fixation (Baek and Lee, 2010). The results of the present study show that, although there were no significant differences, skeletal changes in group A (sliding plate) were less than in group B (miniplate). Ghang et al. suggested that the sliding plate system prevents forward movement of the distal segment by buffering with its own sliding hole (Ghang et al., 2013). Another advantage of the sliding plate system is that the plate has more flexibility than conventional plates due to its reduced thickness, which results in an increased contact area due to bending of the plate. Although group C showed slightly greater amounts of skeletal change during the postoperative period than the other groups, there were no clinically noticeable orthodontic problems in group C. There were no clinically significant differences in pain or dysfunction symptoms between groups A, B or C. Over the last few years, the use of 3D rendering software for analysis of craniofacial morphology has grown rapidly. These recent advances allowed the scientific investigation of skeletal changes after orthognathic surgery. Cevidanes et al. (2009, 2010) evaluated the virtual 3D craniofacial surface models of subjects by quantification of surface distances using closest points. In our study, the subjects were analyzed with linear and planar arrays by distance and angle between points; this method of measurement was sufficient to achieve the objectives of the study. Since this method is sensitive to interobserver errors, however, careful interpretation and comparisons were required. One limitation of this study is that the patient sample included cases with bimaxillary surgery. Admittedly this mixed sample of double and single jaw surgery can potentially affect postsurgical mandibular stability, depending on the stability of the maxilla. Bimaxillary surgery involving setback and clockwise rotation or vertical impaction of the maxilla, alone or in association with a
BSSRO, has been reported as a stable procedure in published studies (Baek et al., 2009; Moure et al., 2012; Vincent et al., 2012). In this study, there was no single case of inferior repositioning of the maxilla. The distribution of maxillary surgery between the groups was not statistically different, in fact it was quite evenly distributed among the three groups (Table 2). While it seems that the inclusion of the maxillary surgery had little effect on the results in comparing these three groups, a future study will be performed with patients undergoing mandibular surgery alone with BSSRO. 5. Conclusion The results of this study suggest that there were no significant differences in postoperative skeletal stability and condylar position between to the sliding plate, miniplate and bicortical screw fixation groups after BSSRO. However, the sliding plate fixation group showed the smallest amount of postoperative skeletal change. Based on these data, the sliding plate system allows good adaptability to the proximal segment after mandibular setback BSSRO, allowing fixation along semi-rigid fixation principles. References Anucul B, Waite PD, Lemons JE: In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws. J Oral Maxillofac Surg 50: 1295e1299, 1992 Baek SH, Kim K, Choi JY: Evaluation of treatment modality for skeletal class III malocclusion with labioversed upper incisors and/or protrusive maxilla: surgical movement and stability of rotational maxillary setback procedure. J Craniofac Surg 20: 2049e2054, 2009 Baek RM, Lee SW: A new condyle repositionable plate for sagittal split ramus osteotomy. J Craniofac Surg 21: 489e490, 2010 Cevidanes LH, Motta A, Proffit WR, Ackerman JL, Styner M: Cranial base superimposition for 3-dimensional evaluation of soft-tissue changes. Am J Orthod Dentofacial Orthop 137: S120eS129, 2010 Cevidanes LH, Styner M, Proffit WR: Three-dimensional superimposition of the skull base for the longitudinal evaluation of the effects of growth and of treatment. Orthod Fr 80: 347e357, 2009 Choi BH, Min YS, Yi CK, Lee WY: A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90: 416e419, 2000 Chung IH, Yoo CK, Lee EK, Ihm JA, Park CJ, Lim JS, 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 66: 446e452, 2008 Epker BN, Wessberg GA: Mechanisms of early skeletal release following surgical advancement of the mandible. Br J Oral Surg 20: 175e182, 1982 Foley WL, Beckman TW: In vitro comparison of screw versus plate fixation in the sagittal split osteotomy. Int J Adult Orthodon Orthognath Surg 7: 147e151, 1992 Ghang MH, Kim HM, You JY, Kim BH, Choi JP, Kim SH, 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 115: 157e166, 2013 Hammer B, Ettlin D, Rahn B, Prein J: Stabilization of the short sagittal split osteotomy: in vitro testing of different plate and screw configurations. J Craniomaxillofac Surg 23: 321e324, 1995
Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963 Joss CU, Vassalli IM: Stability after bilateral sagittal split osteotomy advancement surgery with rigid internal fixation: a systematic review. J Oral Maxillofac Surg 67: 301, 2009 Kahnberg KE, Kashani H, Owman-Moll P: Sagittal split advancement osteotomy: comparison of the tendency to relapse after two different methods of rigid fixation. Scand J Plast Reconstr Surg Hand Surg 41: 167e172, 2007 Kim YI, Jung YH, Cho BH, Kim JR, Kim SS, Son WS, et al: The assessment of the shortand long-term changes in the condylar position following sagittal split ramus osteotomy (SSRO) with rigid fixation. J Oral Rehabil 37: 262e270, 2010 Kundert M, Hadjianghelou O: Condylar displacement after sagittal splitting of the mandibular rami. A short-term radiographic study. J Maxillofac Surg 8: 278e287, 1980 Lee J, Piecuch JF: The sagittal ramus osteotomy. Stability of fixation with internal miniplates. Int J Oral Maxillofac Surg 21: 326e330, 1992 Lee W, Park JU: 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 94: 305e309, 2002 Mobarak KA, Espeland L, Krogstad O, Lyberg T: Mandibular advancement surgery in high-angle and low-angle class II patients: different long-term skeletal responses. Am J Orthod Dentofacial Orthop 119: 368e381, 2001 Moenning JE, Bussard DA, Lapp TH, Garrison BT: Comparison of relapse in bilateral sagittal split osteotomies for mandibular advancement: rigid internal fixation (screws) versus inferior border wiring with anterior skeletal fixation. Int J Adult Orthodon Orthognath Surg 5: 175e182, 1990 Moure C, Qassemyar Q, Dunaud O, Neiva C, Testelin S, Devauchelle B: Skeletal stability and morbidity with self-reinforced P (L/DL) LA resorbable osteosynthesis in bimaxillary orthognathic surgery. J Craniomaxillofac Surg 40: 55e60, 2012
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Park SB, Yang YM, Kim YI, Cho BH, Jung YH, Hwang DS: Effect of bimaxillary surgery on adaptive condylar head remodeling: metric analysis and image interpretation using cone-beam computed tomography volume superimposition. J Oral Maxillofac Surg 70: 1951e1959, 2012 Reyneke JP, Ferretti C: Intraoperative diagnosis of condylar sag after bilateral sagittal split ramus osteotomy. Br J Oral Maxillofac Surg 40: 285e292, 2002 Rubens BC, Stoelinga PJ, Blijdorp PA, Schoenaers JH, Politis C: Skeletal stability following sagittal split osteotomy using monocortical miniplate internal fixation. Int J Oral Maxillofac Surg 17: 371e376, 1988 Stella JP, Astrand P, Epker BN: Patterns and etiology of relapse after correction of class III open bite via subcondylar ramus osteotomy. Int J Adult Orthodon Orthognath Surg 1: 91e99, 1986 Tharanon W: Comparison between the rigidity of bicortical screws and a miniplate for fixation of a mandibular setback after a simulated bilateral sagittal split osteotomy. J Oral Maxillofac Surg 56: 1055e1058, 1998 Turvey TA, Bell RB, Phillips C, Proffit WR: Self-reinforced biodegradable screw fixation compared with titanium screw fixation in mandibular advancement. J Oral Maxillofac Surg 64: 40e46, 2006 Ueki K, Nakagawa K, Takatsuka S, Yamamoto E: Plate fixation after mandibular osteotomy. Int J Oral Maxillofac Surg 30: 490e496, 2001 Van Sickels JE, Larsen AJ, Thrash WJ: Relapse after rigid fixation of mandibular advancement. J Oral Maxillofac Surg 44: 698e702, 1986 Vincent C, Mercier JM, Perrin JP, Khonsari RH: Stability of Le Fort I impaction osteotomies. Rev Stomatol Chir Maxillofac 113: 76e80, 2012 Will LA, Joondeph DR, Hohl TH, West RA: Condylar position following mandibular advancement: its relationship to relapse. J Oral Maxillofac Surg 42: 578e588, 1984
Contents lists available at ScienceDirect
Journal of Cranio-Maxillo-Facial Surgery journal homepage: www.jcmfs.com
Skeletal stability and condylar position related to fixation method following mandibular setback with bilateral sagittal split ramus osteotomy Young-Chea Roh a, Sang-Hun Shin a, Seong-Sik Kim b, George K. Sandor c, d, Yong-Deok Kim e, f, * a
Department of Oral and Maxillofacial Surgery, School of Dentistry, Pusan National University, Yangsan, South Korea Department of Orthodontics, School of Dentistry, Pusan National University, Yangsan, South Korea Department of Tissue Engineering, Regea Institute for Regenerative Medicine, University of Tampere, Tampere, Finland d Department of Oral and Maxillofacial Surgery, University of Oulu, Oulu, Finland e Department of Oral and Maxillofacial Surgery, School of Dentistry, Pusan National University, Yangsan, South Korea f Dental Research Institute, and Institute of Translational Dental Sciences, Pusan National University, Yangsan, South Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 25 February 2014 Accepted 27 August 2014 Available online 7 September 2014
Purpose: To investigate postoperative intersegmental displacement and relapse following bilateral sagittal split ramus osteotomy (BSSRO) by comparing three different fixation methods: group A (sliding plate), group B (miniplate) and group C (bicortical screws). Materials and methods: The present retrospective study included 55 patients with mandibular prognathism who were treated with BSSRO. To evaluate skeletal changes, cone-beam computed tomography was taken before surgery (T0), three days after surgery (T1), and 6 months after surgery (T2). Differences among the three groups were assessed using a one-way analysis of variance, where P < 0.05 was accepted as statistically significant. Results: There were no significant differences among the three groups in demographic data and the amount of mandibular setback. In skeletal changes and condylar axis changes, there were no statistically significant differences among the three groups. However, there were statistically significant postoperative skeletal changes in group C (bicortical screws) at all landmarks. The mean horizontal relapse rate was 1.9% in group A (sliding plate); 4.8% in group B (miniplate); and 15.4% in group C (bicortical screws). Conclusion: The sliding plate system has good adaptability to the proximal segment after mandibular setback with BSSRO, and behaves according to semi-rigid fixation principles. © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: Mandibular prognathism Titanium Cone-beam computed tomography Orthognathic
1. Introduction Bilateral sagittal split ramus osteotomy (BSSRO) has been commonly used in orthognathic surgical procedures to correct mandibular prognathism. Throughout the history of this procedure postoperative stability has been one of the main issues. To achieve acceptable postoperative stability, either bicortical screws or miniplates have been used to position the proximal and distal segment after BSSRO. Some previous in vitro studies have shown that bicortical screw fixation tends to be more stable and less susceptible
* Corresponding author. 3-3 Beomeo, Mulgum, Department of Oral and Maxillofacial Surgery, Pusan National University, Yangsan 626-770, South Korea. Tel.: þ82 55 360 5100; fax: þ82 55 360 5104. E-mail address: [email protected] (Y.-D. Kim).
to deformation than monocortical plate fixation (Anucul et al., 1992; Hammer et al., 1995). On the other hand, many in vitro studies (Foley and Beckman, 1992; Tharanon, 1998) and comparative clinical studies (Choi et al., 2000; Chung et al., 2008) showed that there was no significant difference between bicortical screw and monocortical miniplate fixation. In addition, reports about the stability of monocortical plate fixation showed results which were as acceptable as bicortical fixation (Rubens et al., 1988; Chung et al., 2008). Semi-rigid fixation with monocortical miniplates has some advantages such as avoidance of inferior alveolar nerve injury, ease of access, and manipulation without a transbuccal fixation. The sliding plate, also known as a condylar repositionable plate, follows the same principle of semi-rigid fixation. This plate consists of two 2 mm diameter holes and an oval-shaped sliding hole. In this plating system, the oval-shaped hole allows sliding of the proximal
http://dx.doi.org/10.1016/j.jcms.2014.08.008 1010-5182/© 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
segment after BRSSO. This system had been reported to be relatively stable and convenient for the operators (Baek and Lee, 2010; Ghang et al., 2013). Up until now, however, no comparative studies comparing sliding plates versus monocortical miniplates or bicortical screws for fixation of the bone segments in BSSRO have been published. The aims of this retrospective study were to investigate postoperative intersegmental displacement and relapse by comparing three different fixation methods: sliding plate, miniplate and bicortical screws. In the present study, the authors used cone-beam computed tomography (CBCT) data to evaluate: 1) horizontal and vertical changes of mandibular position in the sagittal view following BSSRO surgery; 2) degrees of condylar axis angle change on the axial, coronal and sagittal plane of CBCT views; and 3) the stability as well as the relapse ratio after surgery and a postoperative period. 2. Patients and methods
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The bony segments were fixed with one of three different osteosynthesis methods (Figs. 1 and 2). Group A: A sliding plate was fixed with two 2.0 mm diameter monocortical screws to the proximal segment and another screw to the distal segment (Fig. 2A). Group B: Two 2.0 mm diameter monocortical screws were installed in each segment using a miniplate (Fig. 2B). Group C: Three 2.0 mm bicortical screws were placed at the superior border of the mandible (Fig. 2C). To maintain postoperative occlusion, approximately 5e7 days of intermaxillary fixation (IMF) with an interocclusal splint was applied. After releasing the IMF physiotherapy including mouth-opening exercises with orthodontic elastics was used for 4 weeks. Postoperative orthodontic treatment was started one month after surgery. 2.3. CBCT data
2.1. Patients The 55 Korean adults (25 male, 30 female) were among the patients admitted to the department of oral and maxillofacial surgery at Pusan National University Dental Hospital between March 2012 and November 2012. They were selected for the study according to the following criteria: 1) Diagnosed with mandibular prognathism with or without facial asymmetry; 2) Underwent mandibular setback BSSRO with or without either Le Fort I osteotomy or genioplasty; 3) Available preoperative and postoperative cone-beam computed tomography (CBCT) images with 6 months follow-up; 4) No history of trauma or craniofacial syndrome. Written informed consent was obtained from all patients, and the study was approved by the Institutional Review Board at Pusan National University Dental Hospital, Yangsan, Korea. 2.2. Surgery All patients received orthodontic treatment before and after their operation. All patients underwent BSSRO using the modification known as the Obwegeser-Dal Pont sagittal split of the ramus. Thirty-three patients had 1-segment Le Fort I osteotomy with BSSRO. In these patients, stabilization of the maxilla was done using rigid fixation with titanium miniplates and screws. There were no cases of inferior repositioning of the maxilla included in this study. In all cases the proximal segment of the mandible was stripped of its pterygomasseteric sling at the inferior and posterior borders.
CBCT images (PaX-Zenith 3D; Vatech, Seoul, Korea) were taken for all patients before surgery (T0), three days after surgery (T1), and 6 months following surgery (T2). The subjects were in an upright position with maximum intercuspation; the Frankfort horizontal (FH) plane of subjects was parallel to the floor. Images were obtained using a CBCT scanner (DCT Pro, Vatech, Seoul, Korea). The machine settings were as follows: 20 19 cm field of view, 90 kVp tube voltage, 4.0 mA tube current, 24 s scan time. To investigate the skeletal changes, the CBCT data was reconstructed with 3D imaging software (SimPlant 3-D Pro; Materialize, Leuven, Belgium). 2.4. CBCT analysis In this study, images were analyzed by the same investigator with preset reference points and planes (Table 1). To evaluate the horizontal and vertical movement of mandible, the distances from the FH plane and Na-perpendicular plane to point B, pogonion (Pog), and the menton (Me) were measured. Angular changes of the condyle in the axial, coronal, and sagittal images were also measured according to the method of Park et al. (2012). The axial condylar axis angle was defined as the angle between the axial condylar axis and the midsagittal plane. The axial condylar axis was drawn from the condylar lateral pole (outermost part) to the medial pole (innermost part) in the greatest mediolateral dimension of the condylar head (Fig. 3A). The coronal condylar axis angle was defined as the angle between the coronal condylar axis and the FH plane. The coronal condylar axis was drawn along the ramus from the condylar neck to the center of condyle in the slice showing the greatest mediolateral dimension of the condylar head (Fig. 3B). The sagittal condylar axis angle was defined as the angle between the sagittal condylar axis and the FH plane. The sagittal
Fig. 1. Diagrams of three different fixation methods: (A) Sliding plate, (B) Miniplate, (C) Bicortical screws.
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Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
Fig. 2. Radiographic image of: (A) Sliding plate, (B) Miniplate, (C) Bicortical screws.
condylar axis was drawn from the center of condylar neck to the center of condylar head (Fig. 3C).
3. Results 3.1. Patient distribution
2.5. Statistical analysis The data were analyzed using a statistical software package (SPSS 12.0; SPSS, Chicago, IL, USA). To evaluate differences over time, T1 and T2 values were evaluated by paired t-test and repeated measures analysis of variance (ANOVA). The difference within the three groups was assessed using one-way ANOVA. P < 0.05 was accepted as statistically significant. Table 1 Reference points and planes. Reference point/plane Nasion (Na)
Description
The most anterior and superior point of the frontonasal suture Basion (Ba) The most posterior and inferior point of the occipital bone at the anterior margin of foramen magnum Orbitale (Or) The most inferior point of orbital margin Porion (Po) The most superior point of external auditory meatus Point B Deepest point of curvature between chin and alveolar junction Pogonion (Pog) Most anterior point on contour of symphysis Menton (Me) Most inferior point on the symphysis FH plane Plane constructed by both sides of Po and (horizontal reference plane) midpoints of both Or Midsagittal plane Plane normal to FH plane and passing through (sagittal reference plane) Na and Ba Na-perpendicular plane Plane normal to FH plane and midsagittal (coronal reference plane) plane passing through Na
The distribution of cases with mandibular surgery alone versus cases with bimaxillary surgery within the three mandibular fixation groups was quite uniform with 63.2% bimaxillary surgery in group A; 57.9% in group B; and 58.8% in group C. There were no significant differences among the three groups in demographic data and the amount of mandibular setback (Table 2). The amount of setback was calculated as the average change between T0 (before surgery) and T1 (three days after surgery) by distance from the three points (B, Pog, Me) to the Na-perpendicular plane. 3.2. Linear changes in landmarks Table 3 shows mean horizontal and vertical changes during the postoperative period in each group. There were no statistically significant differences among the three groups in ANOVA. However, there were statistically significant postoperative skeletal changes in group C (bicortical screws) at all landmarks. Mean horizontal relapse rates were 1.9% in group A (sliding plate); 4.8% in group B (miniplate); and 15.4% in group C (bicortical screws), respectively. 3.3. Angular changes in condylar axis Table 4 shows mean angular changes during the postoperative period in each group. There were no statistically significant differences among the three groups in ANOVA. However, there were statistically significant postoperative angular changes in group C (bicortical screws) on both axial condylar angles.
Y.-C. Roh et al. / Journal of Cranio-Maxillo-Facial Surgery 42 (2014) 1958e1963
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Fig. 3. Measurement of condylar angles on CBCT images. (A) Axial condylar axis angle: angle between axial condylar axis and midsagittal plane, (B) Coronal condylar axis angle: angle between coronal condylar axis and FH plane, (C) Sagittal condylar axis angle: angle between sagittal condylar axis and FH plane.
Therefore, the type and method of fixation is the only variable responsible for postoperative relapse in our study. Many studies have reported on the sagittal and vertical postoperative stability after BSSRO setback. The reported sagittal relapse rates for mandibular setback showed great variation, from 1.0% to 91.3% (Moenning et al., 1990; Lee and Piecuch, 1992; Turvey et al., 2006; Kahnberg et al., 2007; Joss and Vassalli, 2009). In this study, horizontal postoperative relapse rates were 1.6%e15.5%, therefore within the range of the previous studies. All three fixation methods showed relatively low relapse rates compared with previous studies. In the results of the present study, horizontal and vertical mandibular movements during the postoperative period (T1eT0) averaged 0.21 mme1.11 mm, and 0.33 mm to 1.41 mm respectively, in all patients. Although there was no statistically significant difference in group comparisons, group C (bicortical screws) showed slightly higher skeletal changes during the postoperative period, compared with the other groups. There have been several reports that there were no statistically significant differences in the stability between bicortical screw fixation and monocortical plate fixation after mandibular setback (Rubens et al., 1988; Foley and Beckman, 1992; Tharanon, 1998; Ueki et al., 2001). Previous clinical studies (Anucul et al., 1992; Hammer et al., 1995; Choi et al., 2000; Chung et al., 2008) suggested that there were no significant differences between bicortical screw and monocortical miniplate fixation. This study is in agreement with previous reports, as the data obtained from this study showed no statistically significant
Table 2 Demographic characteristics of the study patients. Study variables
Group A: (sliding plate)
Group B: (miniplate)
Group C: (bicortical screws)
Sample size (n) No. of males (%) Age (years)a 1-jaw (BSSRO only)/2-jaw Amount of setback (mm)a
19 7 (36.8%) 23.6 ± 2.7 7/12 (36.8/63.2%) 6.54 ± 3.42
19 9 (47.4%) 23.6 ± 3.3 8/11 (42.1/57.9%) 7.32 ± 4.86
17 9 (52.9%) 23.0 ± 3.8 7/10 (41.2/58.8%) 6.79 ± 3.90
a
P value (ANOVA)
0.612 0.963 0.940 0.615
Expressed as mean ± SD.
4. Discussion The present study compared three fixation methods using CBCT data to evaluate postoperative intersegmental displacement and relapse. Possible factors influencing potential postoperative relapse include the magnitude of movement, control of the proximal segment, the type and methods of fixation, masticatory muscle tension, postoperative orthodontic treatment, and residual growth and remodeling (Epker and Wessberg, 1982; Will et al., 1984; Stella et al., 1986; Van Sickels et al., 1986; Mobarak et al., 2001; Reyneke and Ferretti, 2002). In this study, there were no statistically significant differences in the distribution of patients and the amount of mandibular setback, as well as the types of surgical procedures.
Table 3 Surgical and postoperative skeletal changes. Group A: (sliding plate)
Group B: (miniplate)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Mean
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
Horizontal B 6.08 Pog 6.85 Me 7.27 Vertical B 1.82 Pog 1.97 Me 1.44 a
SD
Group C: (bicortical screws)
P value (ANOVA)
SD
2.68 2.15 3.41
0.25 0.21 0.32
0.82 0.93 1.01
7.82 7.72 7.54
2.71 3.58 3.61
0.69 0.70 0.42
0.92 1.29 1.07
6.87 7.11 6.62
2.58 2.33 1.93
1.08a 1.11a 0.97a
1.09 1.13 1.06
0.507 0.510 0.498
1.03 1.21 0.98
0.52 0.33 0.61
0.89 0.71 0.76
2.11 1.79 1.52
1.39 1.41 1.08
0.77 0.39 0.92
0.82 0.91 1.00
2.01 1.49 1.44
1.33 0.91 0.97
1.31a 1.27a 1.41a
1.03 0.89 0.98
0.515 0.331 0.230
Repeated measures ANOVA (P < 0.05).
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Table 4 Angular changes of the mandibular condyle. Group A: (sliding plate)
Right Axial Coronal Sagittal Left Axial Coronal Sagittal a
Group B: (miniplate)
Group C: (bicortical screws)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Surgical change (T0eT1)
Postoperative change (T1eT2)
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
2.15 1.43 0.78
1.03 1.14 1.01
1.16 0.78 0.39
2.72 1.32 1.24
2.42 1.57 1.12
1.22 0.58 1.17
0.71 0.91 0.88
2.13 1.37 0.68
2.82 1.19 0.42
0.48 0.81 1.24
4.15a 1.42 1.16
2.14 1.71 1.10
1.41 0.76 0.43
1.53 0.87 0.64
1.15 0.42 1.14
2.46 1.01 1.85
1.17 1.64 1.11
1.37 0.50 0.78
1.07 0.62 1.14
1.52 0.97 0.81
2.44 0.87 0.19
0.51 0.63 1.18
4.01a 1.21 0.97
2.25 1.17 0.35
Repeated measures ANOVA (P < 0.05).
differences among the groups. There was less skeletal change in the semi-rigid fixation groups (sliding plate and miniplate) than the rigid fixation group (bicortical screws). In measurements of condylar angles, all groups showed statistically significant inward rotation of the axial condylar angle. Although there were no significant differences among group comparisons, differences in group C (bicortical screws) were greater than in the other two groups. In bicortical screw fixation, greater torque on the proximal segment can occur than in the semirigid fixation group (Ueki et al., 2001; Kim et al., 2010). This force could be the main cause of early forward relapse because the screws tend to reduce the intersegmental gap (Kundert and Hadjianghelou, 1980; Lee and Park, 2002). The sliding plate was designed to allow repositioning of the malpositioned condyle during the early postoperative period. In this way, the sliding plate system prevents the forward relapse of the distal segment. Baek et al. reported satisfactory short-term stability after sliding plate fixation (Baek and Lee, 2010). The results of the present study show that, although there were no significant differences, skeletal changes in group A (sliding plate) were less than in group B (miniplate). Ghang et al. suggested that the sliding plate system prevents forward movement of the distal segment by buffering with its own sliding hole (Ghang et al., 2013). Another advantage of the sliding plate system is that the plate has more flexibility than conventional plates due to its reduced thickness, which results in an increased contact area due to bending of the plate. Although group C showed slightly greater amounts of skeletal change during the postoperative period than the other groups, there were no clinically noticeable orthodontic problems in group C. There were no clinically significant differences in pain or dysfunction symptoms between groups A, B or C. Over the last few years, the use of 3D rendering software for analysis of craniofacial morphology has grown rapidly. These recent advances allowed the scientific investigation of skeletal changes after orthognathic surgery. Cevidanes et al. (2009, 2010) evaluated the virtual 3D craniofacial surface models of subjects by quantification of surface distances using closest points. In our study, the subjects were analyzed with linear and planar arrays by distance and angle between points; this method of measurement was sufficient to achieve the objectives of the study. Since this method is sensitive to interobserver errors, however, careful interpretation and comparisons were required. One limitation of this study is that the patient sample included cases with bimaxillary surgery. Admittedly this mixed sample of double and single jaw surgery can potentially affect postsurgical mandibular stability, depending on the stability of the maxilla. Bimaxillary surgery involving setback and clockwise rotation or vertical impaction of the maxilla, alone or in association with a
BSSRO, has been reported as a stable procedure in published studies (Baek et al., 2009; Moure et al., 2012; Vincent et al., 2012). In this study, there was no single case of inferior repositioning of the maxilla. The distribution of maxillary surgery between the groups was not statistically different, in fact it was quite evenly distributed among the three groups (Table 2). While it seems that the inclusion of the maxillary surgery had little effect on the results in comparing these three groups, a future study will be performed with patients undergoing mandibular surgery alone with BSSRO. 5. Conclusion The results of this study suggest that there were no significant differences in postoperative skeletal stability and condylar position between to the sliding plate, miniplate and bicortical screw fixation groups after BSSRO. However, the sliding plate fixation group showed the smallest amount of postoperative skeletal change. Based on these data, the sliding plate system allows good adaptability to the proximal segment after mandibular setback BSSRO, allowing fixation along semi-rigid fixation principles. References Anucul B, Waite PD, Lemons JE: In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws. J Oral Maxillofac Surg 50: 1295e1299, 1992 Baek SH, Kim K, Choi JY: Evaluation of treatment modality for skeletal class III malocclusion with labioversed upper incisors and/or protrusive maxilla: surgical movement and stability of rotational maxillary setback procedure. J Craniofac Surg 20: 2049e2054, 2009 Baek RM, Lee SW: A new condyle repositionable plate for sagittal split ramus osteotomy. J Craniofac Surg 21: 489e490, 2010 Cevidanes LH, Motta A, Proffit WR, Ackerman JL, Styner M: Cranial base superimposition for 3-dimensional evaluation of soft-tissue changes. Am J Orthod Dentofacial Orthop 137: S120eS129, 2010 Cevidanes LH, Styner M, Proffit WR: Three-dimensional superimposition of the skull base for the longitudinal evaluation of the effects of growth and of treatment. Orthod Fr 80: 347e357, 2009 Choi BH, Min YS, Yi CK, Lee WY: A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90: 416e419, 2000 Chung IH, Yoo CK, Lee EK, Ihm JA, Park CJ, Lim JS, 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 66: 446e452, 2008 Epker BN, Wessberg GA: Mechanisms of early skeletal release following surgical advancement of the mandible. Br J Oral Surg 20: 175e182, 1982 Foley WL, Beckman TW: In vitro comparison of screw versus plate fixation in the sagittal split osteotomy. Int J Adult Orthodon Orthognath Surg 7: 147e151, 1992 Ghang MH, Kim HM, You JY, Kim BH, Choi JP, Kim SH, 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 115: 157e166, 2013 Hammer B, Ettlin D, Rahn B, Prein J: Stabilization of the short sagittal split osteotomy: in vitro testing of different plate and screw configurations. J Craniomaxillofac Surg 23: 321e324, 1995
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Park SB, Yang YM, Kim YI, Cho BH, Jung YH, Hwang DS: Effect of bimaxillary surgery on adaptive condylar head remodeling: metric analysis and image interpretation using cone-beam computed tomography volume superimposition. J Oral Maxillofac Surg 70: 1951e1959, 2012 Reyneke JP, Ferretti C: Intraoperative diagnosis of condylar sag after bilateral sagittal split ramus osteotomy. Br J Oral Maxillofac Surg 40: 285e292, 2002 Rubens BC, Stoelinga PJ, Blijdorp PA, Schoenaers JH, Politis C: Skeletal stability following sagittal split osteotomy using monocortical miniplate internal fixation. Int J Oral Maxillofac Surg 17: 371e376, 1988 Stella JP, Astrand P, Epker BN: Patterns and etiology of relapse after correction of class III open bite via subcondylar ramus osteotomy. Int J Adult Orthodon Orthognath Surg 1: 91e99, 1986 Tharanon W: Comparison between the rigidity of bicortical screws and a miniplate for fixation of a mandibular setback after a simulated bilateral sagittal split osteotomy. J Oral Maxillofac Surg 56: 1055e1058, 1998 Turvey TA, Bell RB, Phillips C, Proffit WR: Self-reinforced biodegradable screw fixation compared with titanium screw fixation in mandibular advancement. J Oral Maxillofac Surg 64: 40e46, 2006 Ueki K, Nakagawa K, Takatsuka S, Yamamoto E: Plate fixation after mandibular osteotomy. Int J Oral Maxillofac Surg 30: 490e496, 2001 Van Sickels JE, Larsen AJ, Thrash WJ: Relapse after rigid fixation of mandibular advancement. J Oral Maxillofac Surg 44: 698e702, 1986 Vincent C, Mercier JM, Perrin JP, Khonsari RH: Stability of Le Fort I impaction osteotomies. Rev Stomatol Chir Maxillofac 113: 76e80, 2012 Will LA, Joondeph DR, Hohl TH, West RA: Condylar position following mandibular advancement: its relationship to relapse. J Oral Maxillofac Surg 42: 578e588, 1984
