Bilateral Sagittal Split Osteotomy Research Articles

Orthosurgical synergism in the management of severe skeletal Class-III malocclusion- A case report

: What is now known as a Class-III malocclusion was initially recognized by Pierre Fauchard. True Class-III malocclusion is a genetically based condition that manifests in childhood. As the youngster reaches the teenage growth spurt, it becomes more obvious. Typically, we will discover a parent or grandparent who is dealing with the same issue. Class-III malocclusion, however, is not a disease. The abnormality itself is a compensatory mechanism to make up for variation that has happened at some point during the course of the individual's development.The case presented here demonstrates the importance of presurgical decompensation, surgical planning, including cephalometric predictions, and mock surgery in the management of severe skeletal Class-III malocclusion. The treatment included comprehensive orthodontic and surgical workup that included bilateral sagittal split osteotomy for mandibular setback of 3mm and LeFort-I osteotomy for maxillary advancement of 3mm. Class-I jaw relationships with a pleasing profile and correctly aligned arches were attained after 2 years of detailed treatment. This led to an aesthetic improvement and a significant increase in the patient's confidence. Class-III skeletal malocclusions can be corrected surgically or through camouflage. However, an ortho-surgical approach may be necessary if the issue cannot be resolved with orthodontics alone. When done correctly, bi-jaw surgery has repeatedly been shown to be quite successful.

Condylar re-positioning devices in orthognathic surgery – is there a benefit to their use?

The bilateral sagittal split osteotomy (BSSO) is the established workhorse in mandibular orthognathic surgery. Despite the frequency at which this procedure is performed, alterations in condylar position from the surgery remain a concern to the operating surgeon. Such changes in condylar positioning have long been associated with relapse. A systematic literature review was carried out to address the question: ‘condylar re-positioning devices in orthognathic surgery – is there a benefit to their use?'. As of yet there is no robust scientific evidence to suggest that these devices confer any clinical benefit over traditional manual re-positioning in orthognathic surgery cases. It would seem appropriate that future research focus on cost effective methods for intra-operative identification of a mal-positioned condyle with the aim of preventing later relapse.

Resistance and Stress Analysis of 3D Plate and Locking Plate Fixation in Bilateral Sagittal Split Osteotomy: A Comparative Finite Element Study.

This study evaluates the biomechanical properties of 3D plates and compares it with locking plates, in both set back and advancement models of bilateral sagittal split osteotomy (BSSO) using finite element model analysis. A stereolithography model of mandibular structure was imported to hypermesh to create 3D solid finite model. A BSSO was simulated on hemimandibular model and advancement and setback simulations were carried out for a distance of 4, 6, and 8mm each. 3D plates for the right side and locking plates for the left side were simulated for fixation. Meshing of the model was carried out. After meshing, the model was imported to Ansys V18.1 for analysis of it. Forces simulating the masticatory muscles were applied on both sides. The values for stress and resistance in the screws and plates were measured and the lowest and highest deformation regions were estimated using von Mises analysis. The results suggest that the tension and resistance as measured through were better distributed in 3D plates when compared with that of locking plates; the stress concentration was shown to be higher in the locking plates and deformation resistance was greater in 3D plates. The application of 3D plating system has found its place in the field of maxillofacial trauma. However, its application in the field of orthognathic surgery is yet to be explored and this study encourages us to conduct in vivo studies.

Effectiveness of hemocoagulase, tranexamic acid, and their combination for reducing blood loss in bimaxillary orthognathic surgery: a retrospective study.

Orthognathic surgery is a corrective intervention for maxillofacial deformities. Bleeding is a major concern for oral and maxillofacial surgeons. Various agents, such as hemocoagulase, tranexamic acid, and aprotinin have been developed to reduce intraoperative bleeding and transfusion requirements. Therefore, in this study we aimed to investigate the effects of hemocoagulase and tranexamic acid, as well as their simultaneous use, to reduce bleeding during orthognathic surgery. Patients and. This retrospective study included patients who had undergone simultaneous orthognathic surgery of the maxilla and mandible between January 2013 and September 2022 and were classified into three groups based on drugs administered: hemocoagulase (Botropase), tranexamic acid, and a combination of both drugs. We recorded patient age, sex, weight, blood loss, and duration of surgery. Red blood cell (RBC), hemoglobin, hematocrit, and platelet levels were measured before, immediately after, and one day after surgery. No statistically significant differences were found in blood loss, RBC, hemoglobin, hematocrit, or platelet levels between any of the groups. There were no differences in the drug effects between Le Fort I and bilateral mandibular sagittal split osteotomies, with or without double genioplasty. However, there were significant reductions in RBC, hemoglobin, hematocrit, and platelet levels during genioplasty. Tranexamic acid, hemocoagulase, and their combination had similar efficacy in patients who underwent Le Fort Ⅰ and bilateral mandibular sagittal split osteotomies with and without genioplasty.

Impact of Different Osteotomy Techniques on Bone Reserve in the Osteotomy Line in Sagittal Split Osteotomy: Experimental In Vitro Study in Caprine Mandible Model.

The objective of this study was to investigate of the effect of piezzo and conventional osteotomy techniques on bone reserve in the osteotomy line and comminuted fracture ratios that is able to compromise bone to bone contact negatively. Bilateral sagittal split ramus osteotomy was performed on 12 fresh male Thracian curly caprine mandible. In the first group (n: 12) osteotomies were performed with piezzo device. In the second group (n: 12) osteotomies were performed with micromotor and manual osteotomes. Operative time was measured. The number of comminuted fractures, length and width of the osteotomy, and the space between the osteotomy lines was evaluated from 3-dimensional computed tomography scans. The mean value of procedure duration was 320.4±10.76 seconds for piezo osteotomy and 238.8±8.29 seconds for conventional micromotor ( P <0.0001). Number of comminuted fractures was 1.41±1.3 in piezoelectric group, 1.5±1.3 in conventional group and the difference was not statistically significant (p: 0,88). Osteotomy lengths and widths were 35.58±5.2, 2.196±1.9 and 36.23±5.05, 2.27±1.85 in the piezzo and conventional groups, respectively. (p lengths :0,75; p widths :0,92) The volume of the bony interface between the distal and proximal segments of the mandible after osteotomy was 166.3±184.2mm 3 in the piezzo group and 163.5±129.3mm 3 in the conventional group (p: 0,96). The piezo surgery and the conventional osteotomy were found to be similar in terms of the gap between the distal and proximal mandible and the number of comminuted fractures. The duration to perform the conventional osteotomy was found to be shorter than the piezo surgery.

Computed Tomographic Analysis of Position of Mandibular Canal and Mandibular Foramen in Patients with Mandibular Asymmetry.

Mandibular osteotomies in facial asymmetry are complicated by the abnormal position and course of inferior alveolar nerve. This manuscript aims to evaluate the possible variations in the preoperative positions of mandibular canal and mandibular foramen in patients with mandibular asymmetry due to condylar hyperplasia or condylar hypoplasia. This study included 15 patients with mandibular asymmetry due to condylar hyperplasia or condylar hypoplasia for which bilateral sagittal split osteotomy (BSSO) was performed as a corrective procedure. The presence/absence and extent of postoperative neurosensory deficiency was recorded subjectively and objectively. The measurements were done using multiplanar reconstruction (MPR) of three-dimensional radiographic imaging and were compared to normal subjects. The results revealed that the mandibular canal was closer to the buccal cortex on the affected side and the inferior border on both sides in the region of second molar in condylar hyperplasia. In condylar hypoplasia, the canal was nearer to the inferior border and the alveolar crest in relation to second and third molars respectively on the affected and contralateral sides.The mandibular foramen was also more superior to the occlusal plane on both sides in both condylar hyperplasia and hypoplasia. Based on the study outcomes, the authors propose that assessment of the positions of mandibular canal and mandibular foramen is crucial to avoid postoperative neurosensory deficiencies.

Objective assessment of visual attention in orthognathic surgery training based on eye tracking

The aim of this study was to investigate the differences in visual attention between novices and orthognathic experts, as well as to provide evidence for use in developing and optimizing training strategies for orthognathic surgery.Novice and orthognathic experts were recruited, and their distributions of visual attention were monitored via an eye-tracking device while they watched orthognathic surgery videos. The percentages of visual fixation duration devoted to the areas of interest — surgical objects, instruments controlled by the main surgeon, and instruments controlled by the assistants — in each orthognathic surgery section were analyzed and compared between the two groups using repeated-measures factorial analysis of variance (ANOVA).In total, there were 18 participants, comprising both novices (n = 9) and experts (n = 9). For all sections of orthognathic surgery, the percentage of fixation duration on surgical objects was significantly higher for the novices than for the experts (p = 0.031, p = 0.005, p = 0.026, p = 0.047, p = 0.047, p = 0.031, p = 0.027, p = 0.034, p = 0.008, and p = 0.016). During the maxillary segment separation as part of Le Fort I osteotomy and the splitting of the mandible as part of bilateral sagittal split osteotomy, the novices also had a higher percentage of fixation duration on the instruments controlled by the main surgeon, as compared with the experts (p = 0.007 and p = 0.048, respectively).Novices invested great cognitive effort into the surgical objects in each section of orthognathic surgery, including the instruments controlled by the main surgeon in the maxillary segment separation and the splitting of the mandible. Strengthening this aspect of instruction could help novices reduce their cognitive load and achieve mastery more efficiently.

Impact of the lateral skeletal stability following bilateral sagittal split ramus osteotomy for mandibular asymmetry

This study evaluated the stability of bilateral sagittal split ramus osteotomy (BSSRO) associated with positional plagiocephaly and temporal and masseter muscles using posteroanterior cephalogram analysis and three-dimensional computed tomography (3D-CT). This retrospective cohort study included 31 patients who underwent BSSRO for mandibular asymmetry. The cranial vault asymmetry index (CVAI) and the cephalic index were used as indicators of positional plagiocephaly. The distance from the vertical reference line to the menton (Me) was measured on posteroanterior cephalograms immediately and 1 year after surgery, and postoperative stability was assessed. Temporal and masseter muscles were constructed from 3D-CT data and their volumes were measured. Simple regression analysis showed a significant correlation between postoperative changes in the vertical reference line to the Me and the CVAI (R=0.56, p=0.001), the amount of surgical movement in the vertical reference line to the Me (R=0.41, p=0.023), and the variable temporal muscle volume (R=0.27, p=0.028). There was no significant correlation between postoperative changes in the vertical reference line to the Me and the cephalic index (R=0.093, p=0.62) and variable masseter muscle volume (R=0.16, p=0.38). According to multivariate analysis, CVAI (p=0.003) and amount of surgical movement in the vertical reference line to the Me (p=0.014) were significant predictors of postoperative change in the vertical reference line to the Me. Positional plagiocephaly and amount of surgical movement influence lateral skeletal stability following BSSRO for mandibular asymmetry.

Changes of Temporomandibular Joint Morphology and Symptoms in Class II Malocclusion Patients With Bilateral Sagittal Split Ramous Osteotomy.

This study included 46 patients with class II malocclusion ranging in age from 19 to 39 years old treated with bilateral sagittal split ramous osteotomy (BSSRO). Left and right temporomandibular joints (TMJs) of each subject were evaluated independently with cone-beam computed tomography (CBCT) before operation (T1), 1 week after operation (T2), and 1 year after operation (T3) and assessed the effects of orthognathic surgery (OGS) on the temporomandibular joint disease (TMD) symptoms. Temporomandibular joint morphology evaluation included condylar volume, condylar area, cortical bone thickness, depth of the mandibular fossa, fossa thickness, joint nodule angle, joint space, and condyle-fossa relationship, which were calculated by using the Mimics software and 3-matic software. Data were statistically analyzed with SPSS software (P <0.05 means statistically significant). In our study, bilateral TMJs have no difference in T3. Bilateral sagittal split ramous osteotomy had no significant effect on the articular fossa. The condyle volume and surface area decreased from T1 to T3, but the cortical thickness of the bone did not change significantly. More anterior condyle positions in T1 and more posterior in T3.21 patients had at least 1 sign or symptom of TMD in T1 and 27 patients in T3. Four patients who were asymptomatic in T1 developed pain after surgery, 10 developed noises, 12 showed limited mouth opening, and 8 had abnormal opening patterns. It is concluded that more condylar posterior position after BSSRO and the reduction of condyle may be related to the enlargement of anterior space. The number of patients with joint symptoms increased postoperative, and the impact of BSSRO on TMD may be negative.

Clinical Stability of Bespoke Snowman Plates for Fixation following Sagittal Split Ramus Osteotomy of the Mandible.

Maxillofacial skeletal surgery often involves the use of patient-specific implants. However, errors in obtaining patient data and designing and manufacturing patient-specific plates and guides can occur even with accurate virtual surgery. To address these errors, bespoke Snowman plates were designed to allow movement of the mandible. This study aimed to compare the stability of bespoke four-hole miniplates with that of a bespoke Snowman plate for bilateral sagittal split ramus osteotomy (SSRO), and to present a method to investigate joint cavity changes, as well as superimpose virtual and actual surgical images of the mandible. This retrospective study included 22 patients who met the inclusion criteria and underwent orthognathic surgery at a university hospital between 2015 and 2018. Two groups were formed on the basis of the plates used: a control group with four-hole bespoke plates and a study group with bespoke Snowman plates. Stability was assessed by measuring the condyle-fossa space and superimposing three-dimensional virtual surgery images on postoperative cone-beam computed tomography (CBCT) scans. No significant differences were observed in the condyle-fossa space preoperatively and 1 year postoperatively between the control and study groups. Superimposing virtual surgery and CBCT scans revealed minimal differences in the landmark points, with no variation between groups or timepoints. The use of bespoke Snowman plates for stabilizing the mandible following SSRO exhibited clinical stability and reliability similar to those with bespoke four-hole plates. Additionally, a novel method was introduced to evaluate skeletal stability by separately analyzing the condyle-fossa gap changes and assessing the mandibular position.

Early and 1-year postsurgical stability and its factors in patients with complicated skeletal Class Ⅲ malocclusion treated by conventional and surgery-first approach: A prospective cohort study

This study aimed to compare postsurgical stability between conventional (CSA) and surgery-first (SFA) approaches and investigate its prognostic factors in patients with a skeletal Class Ⅲ extraction. Twenty and 19 patients treated with LeFort I osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) with premolar extraction were enrolled in SFA and CSA groups, respectively. Serial cone-beam computed tomography images obtained before surgery, immediately after surgery (T1), 3 months after surgery, and 12 months after surgery were used for 3-dimensional quantitative analysis. The condyle was segmented for analyzing volumetric changes. Repeated measures analysis of variance, independent t test, and chi-square test were used to compare time-course and intergroup differences. Pearson and Kendall correlation and multivariate linear regression analyses were used to explore prognostic factors affecting skeletal stability. In both CSA and SFA, postsurgical relapse mainly occurred in the mandible sagittal and vertical dimensions and during the first 3 months after surgery. Stability in SFA was significantly less than that in CSA. Intraoperatively, inferolateral condylar displacement with proximal segment inwards, clockwise rotation, and return movements after surgery were observed regardless of the treatment approach. The condylar volume remained stable over time. Multivariate regression analysis showed that posterior vertical dimension (VD) at T1 (-1.63mm), surgical amount of mandibular setback (-10.33 mm), surgical condylar downwards displacement (-1.28 mm), and anterior overjet at T1 (6.43 mm) were the most important predictors of early mandibular relapse (r2= 0.593). The risk of early relapse could be reduced by controlling the anterior, middle, and posterior constraints provided by the prediction model.

A finite element analysis of stress distribution with various directions of intermaxillary fixation using orthodontic mini-implants and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy.

This finite element analysis (FEA) aimed to assess the stress distribution in the mandible and fixation system with various directions of the intermaxillary fixation (IMF) using mini-implants (MIs) and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy (BSSRO). A total of nine mandibular advancement models were set according to the position of the MIs (1.6 mm in diameter, 8 mm in length) and direction of the IMF elastics (1/4 inch, 5 oz). Major and minor principal stresses in the cortical and cancellous bones, von Mises stresses in the fixation system (miniplate and monocortical screws), and bending angles of the miniplate were analysed. Compressive and tensile stress distributions in the mandible and von Mises stress distributions in the fixation system were greater in models with a Class III IMF elastic direction and a higher IMF elastic force than in models with a Class II IMF elastic direction and a lower IMF elastic force. The bending angle of the miniplate was negligible. Stress distributions in the bone and fixation system varied depending on the direction, amount of force, and position of IMF elastics and MIs. Conclusively, IMF elastics in the Class II direction with minimal load in the area close to the osteotomy site should be recommended.

Bilateral sagittal split ramus osteotomy using a conventional osteotome-hammer and a magnetic mallet device: an in vitro comparison.

The conventional chisel osteotome technique (CCOT) and the magnetic mallet osteotome technique (MMOT) with a newly manufactured custom osteotome tip for the magnetic mallet device (MMD) were compared to determine whether magneto-dynamic osteotomies are as reliable for orthognathic surgery as the conventional method. A custom osteotome tip compatible with a magnetic mallet device was manufactured. Thirty-two fresh 1-year-old sheep hemi-mandibles were chosen for osteotomy procedures to achieve the most human-like results. Sagittal split ramus osteotomies were performed, and lingual fracture pattern (LFP), basis split pattern (BSS), duration of sagittal split osteotomy, and alveolar inferior nerve injury were investigated macroscopically. Six of the defined fracture schemes were observed out of the 27 lingual split patterns. After LFP and BSS evaluation, the unfavorable fracture counts for MMOT and CCOT are 3 and 4, respectively. The macroscopic nerve damage assessment for both groups is 2 for MMOT and 1 for CCOT. Although the average durations are similar in both groups, the difference between MMOT samples is closer. None above showed a significant difference. MMOT was evaluated as a reliable alternative to CCOT in bilateral sagittal split ramus osteotomy based on the lingual and basis split patterns, duration, and nerve damage findings.

Low medial cut (Posnick modification) versus traditional bilateral sagittal split osteotomy on osteotomy split quality and complications. A comparative study

Low medial cut (Posnick modification) versus traditional bilateral sagittal split osteotomy on osteotomy split quality and complications. A comparative study

Precision of Proximal Segment Repositioning Using Digitally Planned Custom Made guide in Sagittal Split Ramus Osteotomy

Background: Orthognathic surgery is widely used surgical procedure. The most common used orthognathic surgical procedure is bilateral sagittal split osteotomy (BSSO) that is used for managing skeletal mandibular excess, deficiency or asymmetry. Objective: To correct functional and aesthetic problems. Patients and Methods: A total of (12 patients) 24 condyles have been included in our study all with cl II malocclusion, open bites and asymmetry, both genders males and females, their age ranges between18 to 40 years, all the cases had preoperative and postoperative CT scans. Results: By comparing pre and post operative CT scans regarding condylar positions for both groups. The results revealed that there was less movement of condylar head in group with device and direction of movement was more favorable. Conclusion: This study showed that the Digitally Planned Custom Made guide was useful in repositioning condyles with minimal movement post operatively and more favorable direction of movement. Keywords: Orthognathic surgery, condyles, CADCAM guides, sagittal split ramus osteotomy, proximal segment

Precision of Proximal Segment Repositioning Using Digitally Planned Custom Made guide in Sagittal Split Ramus Osteotomy

Background: Orthognathic surgery is widely used surgical procedure. The most common used orthognathic surgical procedure is bilateral sagittal split osteotomy (BSSO) that is used for managing skeletal mandibular excess, deficiency or asymmetry.&#x0D; Objective: To correct functional and aesthetic problems.&#x0D; Patients and Methods: A total of (12 patients) 24 condyles have been included in our study all with cl II malocclusion, open bites and asymmetry, both genders males and females, their age ranges between18 to 40 years, all the cases had preoperative and postoperative CT scans.&#x0D; Results: By comparing pre and post operative CT scans regarding condylar positions for both groups. The results revealed that there was less movement of condylar head in group with device and direction of movement was more favorable.&#x0D; Conclusion: This study showed that the Digitally Planned Custom Made guide was useful in repositioning condyles with minimal movement post operatively and more favorable direction of movement.

Do facial soft tissue thicknesses change after surgeries correcting dental malocclusions? An intra- and inter-patient statistical analysis on soft-tissue thicknesses in BSSO + LFI surgeries.

The aim of this study was to analyse changes in facial soft tissue thickness (FSTT) after corrective surgeries for dental malocclusion. The correlation between body mass index (BMI) and sex of patients and their FSTT before undergoing surgery was analysed. Cone beam computed tomography of seventeen patients that underwent Le Fort I osteotomy in combination with bilateral sagittal split osteotomy were collected. Hard and soft tissue landmarks were selected basing on the interventions. FSTT were computed, and measurements from pre- to post-operative were compared. The relationship between FSTT, sex, and BMI was investigated. Considering the comparison between pre- and post-operative measurements, any significant difference emerged (p > .05). The Pearson's correlation coefficient computed between BMI and the FSTT (pre-operative) showed a correlation in normal-weight patients; the region-specific analysis highlighted a stronger correlation for specific landmarks. Higher median values emerged for women than for men; the subset-based analysis showed that women presented higher values in the malar region, while men presented higher values in the nasal region. The considered surgeries did not affect the FSTT of the patients; differences related to BMI and sex were found. A collection of FSTT mean values was provided for twenty landmarks of pre- and post-operative of female and male subjects. This exploratory analysis gave insights on the behaviour of STT after maxillofacial surgeries that can be applied in the development of predictive methodologies for soft tissue displacements and to study modifications in the facial aspect of the patients.

Autoimmune diseases and orthognathic surgery: A case series of 12 patients

Autoimmune diseases result from the immune system attacking native cells and tissues due to the recognition of "self" antigens as foreign antigens. This group of disorders is associated with an increased risk of complications after surgical interventions, as the immune system may cause tissue destruction. The study aimed to investigate the risk of surgical complications in patients with autoimmune diseases, who are at a higher risk of complications due to their condition. Among 886 patients who underwent orthognathic surgery, twelve types of autoimmune diseases with 22 patients were identified. For this case-series study, 12 patients were selected with a follow-up period of at least two years. The surgical procedures were executed by a single surgical team, which involved single or multi-piece Le Fort I osteotomy, Hunsuck/Epker modification of bilateral sagittal split osteotomy (BSSO), and/or genioplasty. The recorded outcome variables were postoperative adverse events, including respiratory or blood-related complications, wound infection, neurosensory disturbances, temporomandibular joint (TMJ) complications, and relapse. Only two patients recovered after surgery without any postoperative complications, whereas others had delayed recovery from neurosensory disturbance (5/12), infection (5/12), TMJ complications (2/12), and other complications. The findings of this study suggest that patients with autoimmune diseases undergoing orthognathic surgery are at higher risk of complications, highlighting the importance of careful consideration of patient selection and risk stratification before surgical intervention. The study also emphasizes the importance of close postoperative follow-up to detect and manage complications promptly.

Effect of the magnitude of condylar head displacement on the TMJ function in skeletal class II patients undergoing different degrees of mandibular advancement: A retrospective comparative study

This study aimed to compare the condylar head displacement (CHD) after bilateral sagittal split ramus osteotomy (BSSO) between different degrees of mandibular advancement in skeletal class II patients and to evaluate whether the temporomandibular joint (TMJ) function would be affected. Fifty-nine patients (118 condyles) were included in this retrospective study and were divided into three groups based on the distance of mandibular advancement. The CHD in three directions, x (sagittal direction), y (coronal direction), and z (axial direction), was measured before operation (T0), immediately after operation (T1), and at least 6 months after operation (T2), and the TMJ function of patients was followed up and scored using the Helkimo index system. All the abovementioned data were statistically analyzed, and p<0.05 was considered the statistical difference standard. During the BSSO surgery, the condyle was predominantly displaced in a lateral, posterior, and superior direction whenever in T1 and T2, even though the degree of CHD was different. Regarding the amount of CHD, the large advancement group was higher than the other two groups in T1 and T2 (p＜0.01). The Helkimo index scores of the three groups were evaluated, and there was no significant statistical difference between the Ai and Di index of the three groups. In our center, CHD occurred in lateral, posterior, and superior directions following mandibular advancement in skeletal class II patients, with a positive correlation between the CHD and the mandibular advancement; however, the TMJ function of the three groups did not show significant differences.

Modification of Sagittal Split Osteotomy in Class II Asymmetry: Optimizing Bone Contact between Proximal and Distal Segments.

Computer-assisted surgical simulation (CASS) allows more precise orthognathic surgery. However, few studies have evaluated associations between CASS-designed bilateral sagittal split osteotomy (SSO) and bone contact surface in class II mandibular asymmetry. This study aims to evaluate the effects of using computer-assisted simulation and design modification of SSO to improve bony contact in skeletal class II asymmetry. This retrospective analysis reviewed 28 patients with class II asymmetry who underwent orthognathic surgery, including 15 with modified SSO (group CS) and 13 with conventional SSO (group C). Modified SSO was designed under CASS. Operative characteristics, postoperative outcomes, and complications were collected and compared between the two groups. Bony contact was found at the distal end of the proximal segment in all group CS patients, while bone gap was noted in all group C patients ( P < 0.05). Moreover, bone graft was used in four group C patients but was not used in all cases in group CS patients ( P < 0.05). A trend toward lower operative time or perioperative bleeding was noted in group CS, but without statistical significance. After 1-year follow-up, inferior alveolar nerve disturbances were noted in two group CS patients and one group C patient. Palpable bone gap with uneven jaw line was noted in two group C patients 1 year after surgery and one patient received fat graft treatment. The simulation-based SSO modification provides appropriate contact surface and eliminates the bone gap between proximal and distal segments in class II asymmetry. Therapeutic, III.