Sagittal Split Ramus Osteotomy Setback Research Articles

Evaluation of Intersegmental Displacement After Mandibular Setback Split Ramus Osteotomy Using Modified L-Shaped Monocortical Plate: Cone-Beam Computed Tomography Superimposition.

The purpose of the current study is to compare intersegmental displacements after mandibular setback sagittal split ramus osteotomy (SSRO) using 4 types of osteosynthesis methods. This is a retrospective study of 53 subjects who presented underwent bilateral setback SSRO at Pusan National University Hospital from January 2009 to December 2013. The subjects were divided into 4 groups according to the osteosynthesis method applied: group A-modified L-type monocortical plate; B-conventional miniplate; group C-bicortical screws; group D-metal and absorbable screws. To obtain the intersegmental displacement, the mean of the differences of the 3-dimensional from T0 (2 days after surgery) to T1 (6 months after surgery) was calculated for the right and left condylar heads (condylion, Cd) and the right and left coronoid processes (Cps) using 3-dimensional imaging software (Ondemand 3D; Cybermed Co, Seoul, Korea). For the condylion in the x, y, z coordinate system, in group A, there were significant differences in the y-axis for the right and left Cd; in group B, significant differences in the y-axis for the right Cd and in the y- and z-axes for the left Cd; in group C, no significant differences in the axis for the Cd; and in group D, there were significant differences in the y- and z-axes for the right Cd and in the x- and y-axes for the left Cd. For the Cps, the results are not much different from the condylion movement in all group. In the current study, group C manifested the greatest displacement for the healing period. Group A did not show the significant difference to group B. In view of these results, modified L-shaped monocortical plate can be applied for osteosynthesis effectively.

Stability of biodegradable metal (Mg–Ca–Zn alloy) screws compared with absorbable polymer and titanium screws for sagittal split ramus osteotomy of the mandible using the finite element analysis model

Mg–Ca–Zn alloy has been suggested for the application of fixation materials during maxillofacial surgery. We investigated the stability of Mg–Ca–Zn alloy for clinical application during orthognathic surgery. The finite element model for the fixation of sagittal split ramus osteotomy was constructed. In the bicortical screw fixation of the mandible setback condition, the stress distributions of Mg–Ca–Za alloy, polylactic acid polymer, and titanium were evaluated using the virtual model with occlusal loading of 132 N. The deformations of the three different materials of fixation screw were observed according to masticatory force ranging from 132 to 1,000 N. When comparing the stress distribution placed on cortical bone between the polymer and magnesium alloy groups, the magnesium alloy screws could bear more stress, thereby decreasing the stress, which might be distributed to other biologic components, such as the condyle and cortical ramus of the mandible. Deformations of the screws according to functional load were minimal, and the deformation remained <0.21 mm at the initial functional load of the mandible after surgery, regardless of materials used. The biodegradable magnesium alloy screw can bear more stress and decrease the detrimental effect on the stability of sagittal split ramus osteotomy setback surgery.

Cone-beam computed tomography evaluation on the changes in condylar long axis according to asymmetric setback in sagittal split ramus osteotomy patients.

To determine whether the condylar rotation is affected by asymmetric setback in patients undergoing sagittal split ramus osteotomy. Thirty patients who underwent bilateral sagittal split ramus osteotomy setback surgery were divided into the two groups, symmetric setback and asymmetric setback, according to the right/left difference of setback amount (<2.0, ≥2.0 mm). Condylar long axis changes were evaluated using the three-dimensional superimposition of before and immediately after surgery cone-beam computed tomography volume images. Evaluations were performed separately in lesser setback and greater setback side in patients undergoing asymmetric setback, whereas both side condyles were evaluated together in patients undergoing symmetric setback. Condylar axis changes on axial view were correlated with setback amount or right/left setback difference using Pearson correlation analysis. In general, the condylar axis change occurred in a pattern of inward rotation. The condyles in patients undergoing symmetric setback showed 3.4° rotation in average. In case of asymmetric setback, the lesser setback side showed larger value (4.3°) than the greater setback side (2.3°) with a statistical significance. In the correlation analysis, setback amount showed no significant correlation with the condylar axis changes in both groups. However, correlation with right/left setback difference showed a positive correlation in lesser setback side of patients undergoing asymmetric setback. The findings of this study indicate that large amount of setback alone does not contribute to the change in condylar long axis, but asymmetric setback might cause a change in condylar long axis, particularly on the lesser setback side.

Comparison of postoperative changes in the distal and proximal segments between conventional and sliding mini-plate fixation following mandibular setback.

ObjectiveThe purpose of the present study was to evaluate the postoperative three-dimensional (3D) changes in the proximal segments after mandibular setback sagittal split ramus osteotomy and to compare the changes between the conventional mini-plate fixation and semi-rigid sliding plate fixation.MethodsCone-beam computed tomography (CBCT) images were used to evaluate the postoperative 3D changes in the proximal segments during the healing process. CBCT images were superimposed using the symphysis and the lower anterior mandible as references.ResultsThere were no statistically significant differences between the conventional mini-plate and semi-rigid sliding plate groups (p > 0.05). With respect to the distribution of changes greater than 2 mm in the landmarks, the right condylion, right coronoid process, and left condylion showed ratios of 55.6%, 50.0%, and 44.4%, respectively, in the semi-rigid sliding plate group; however, none of the landmarks showed ratios greater than 30% in the conventional mini-plate group.ConclusionsThere were no statistically significant differences in postoperative changes in the segments between the conventional mini-plate and semi-rigid sliding plate groups. Nevertheless, while selecting the type of fixation technique, clinicians should consider that landmarks with greater than 2 mm changes were higher in the semi-rigid sliding plate group than in the conventional mini-plate group.

Stability of Condyle Position after Bilateral Sagittal Split Ramus Osteotomy Setback with Rigid Internal Fixation by 2 Screws Case Series

Stability of Condyle Position after Bilateral Sagittal Split Ramus Osteotomy Setback with Rigid Internal Fixation by 2 Screws Case Series

Orthognathic Surgery for Correction of Patients With Mandibular Excess: Don’t Forget to Assess the Gonial Angle

To evaluate the gonial angle (GA) and associated factors that can contribute to stability after bilateral sagittal split ramus osteotomy setback and Le Fort I advancement osteotomy for the treatment of patients with mandibular excess. This retrospective study included 42 randomly selected, adult patients. Lateral cephalometric radiographs were obtained before and 1 week and 1 year after surgery. Patients in group 1 (n= 18) had a GA smaller than 125° and those in group 2 (n= 24) had a GA larger than 125°. Data were analyzed by analysis of variance and Pearson correlations. Multivariate linear regression analysis was used to identify factors that influenced postsurgical stability. Mean surgical changes were similar in the 2 groups. The mandible was set back an average of 5.4mm in group 1 and 6.4 mm in group 2, whereas the maxilla was advanced 2.5 mm in group 1 and 1.7mm in group 2. Statistically significant postoperative changes were noted for group 1 only. Relapse was found at the innermost point of the contour of the mandible between the incisor tooth and bony chin and the pogonion for the horizontal landmarks; the innermost point of the contour of the maxilla between the anterior nasal spine and incisor tooth and the menton for the vertical landmarks; and the GA, the angle between the sella-nasion line and the innermost point of the contour of the mandible between the incisor tooth and bony chin, and the esthetic plane to the upper lip for the dimensional landmarks. No statistically significant changes were noted for group 2 (GA >125°). Patients with a preoperative GA smaller than 125° have a greater risk of relapse after receiving bilateral sagittal split ramus osteotomy setback and Le Fort I advancement for the treatment of mandibular excess. Patients with a preoperative GA larger than 125° appear to have a more predictable procedure.

Effect of setback Le Fort I osteotomy on midfacial soft-tissue changes as evaluated by cone-beam computed tomography superimposition for cases of skeletal Class III malocclusion

This study employed the cone-beam computed tomography (CBCT) superimposition method to evaluate postoperative midfacial soft-tissue changes in cases of skeletal Class III malocclusion after double-jaw surgery with setback and vertical reduction Le Fort I osteotomy. A retrospective study was carried out on 15 patients who had undergone maxillary setback Le Fort I osteotomy and mandibular setback sagittal split ramus osteotomy with alar cinch suturing and V-Y soft-tissue closure. Three dimensional CBCT volume scans were recorded preoperatively (T0) and 6 months postoperatively (T1) to measure soft-tissue changes of the upper lip and midface. Post-surgery, soft-tissue landmarks in the cheek and paranasal areas had moved forward; the soft-tissue thickness at the A-point had markedly increased (P<0.05); there was no significant change in the subnasale, and the midline of the soft-tissue of the upper-lip area had moved backward. The extent of the mean soft-tissue change at the labrale superius was greater than that at the other soft-tissue landmarks of the upper lip. The results suggest that maxillary setback movement of the maxilla by alar cinch suturing has a beneficial effect on paranasal soft-tissue and lip contours for patients with protrusive lip and acute nasolabial angle.

Cone-beam computed tomographic evaluation of the condylar remodeling occurring after mandibular set-back by bilateral sagittal split ramus osteotomy and rigid fixation

ObjectiveTo evaluate condylar head remodeling after mandibular set-back sagittal split ramus osteotomy (SSRO) with rigid fixation in skeletal class III deformities. The correlation between condylar head remodeling and condylar axis changes was determined using cone-beam computed tomography (CBCT) superimposition.MethodsThe CBCT data of 22 subjects (9 men and 13 women) who had undergone mandibular set-back SSRO with rigid fixation were analyzed. Changes in the condylar head measurements and the distribution of the signs of condylar head remodeling were evaluated by CBCT superimposition.ResultsThe subjects showed inward rotation of the axial condylar angle; reduced condylar heights on the sagittal and coronal planes; and resorptive remodeling in the anterior and superior areas on the sagittal plane, superior and lateral areas on the coronal plane, and anterior-middle and anterior-lateral areas on the axial plane (p < 0.05).ConclusionsThe CBCT superimposition method showed condylar head remodeling after mandibular set-back SSRO with rigid fixation. In skeletal class III patients, SSRO with rigid fixation resulted in rotation, diminution, and remodeling of the condylar head. However, these changes did not produce clinical signs or symptoms of temporomandibular disorders.

Midfacial soft-tissue changes after mandibular setback surgery with or without paranasal augmentation: Cone-beam computed tomography (CBCT) volume superimposition

The aim of this article is to compare the soft-tissue changes in the midfacial areas of patients who had undergone mandibular setback sagittal split ramus osteotomy (SSRO) with that of mandibular setback SSRO with paranasal augmentation. The subjects included 15 patients (group I), SSRO with paranasal augmentation and 20 patients (group II), SSRO alone. To evaluate the difference of the midfacial soft-tissue changes between groups, cone-beam computed tomography superimposition was utilized and the soft-tissue changes were measured both preoperatively and postoperatively by a 10 × 27 grid. In group I, the soft tissues were changed at the areas bounded superiorly by the infraorbital foramen, zygomatic eminence, posteriorly by the masseteric muscle and medially by the lateral aspect of the nose and following the nasolabial fold. In group II, the midfacial soft-tissue measurements were unchanged. This study may help clinicians to predict improvement in the midfacial region from mandibular setback SSRO with or without a paranasal augmentation procedure in class III deformities.

Evaluation of Intersegmental Displacement According to Osteosynthesis Method for Mandibular Setback Sagittal Split Ramus Osteotomy Using Cone-Beam Computed Tomographic Superimposition

To compare intersegmental displacements after mandibular setback sagittal split ramus osteotomy with reference to the fixation system applied: miniplate with monocortical screw, 3 bicortical screws, and 1 bicortical screw and 2 resorbable screws. The 42 subjects were divided into 3 groups according to the osteosynthesis method applied. To evaluate the intersegmental displacements from immediately after surgery (T0) to 6 months after surgery (T1), 2 cone-beam computed tomographic data sets were superimposed on the symphyseal area and the lower part of the mandible below the root apex. On the superimposed 3-dimensional images, the mean and standard deviation of the differences of the coordinates (x, y, z) between T0 and T1 were calculated. From T0 to T1, group B (bicortical screws) manifested the greatest condylion (Cd) and coronoid process (Cp) displacements (P < .05). In group A, the right Cd moved anteriorly and the left Cd moved anteriorly and inferiorly, whereas the right and left Cps moved anteriorly. In group B, the right and left Cps moved laterally and inferiorly. In group C, the right Cd moved anteriorly and inferiorly, the left Cd changed laterally and anteriorly, the right Cp moved anteriorly, and the left Cp moved anteriorly and inferiorly. In the present study, group B (bicortical screws) showed the greatest displacement after the healing period. In view of these findings, surgeons should consider carefully their choice of osteosynthesis method to effectively decrease intersegmental displacement.

Midfacial soft tissue changes after leveling Le Fort I osteotomy with differential reduction

To compare the short- and long-side soft tissue changes in the midfacial areas of patients who have undergone superior repositioning Le Fort I osteotomies for the correction of occlusal cant. The null hypothesis was that there were no significant differences in the midfacial soft tissue changes between the greater- and lesser-reduction sides. The subjects included 25 patients who had undergone Le Fort I osteotomy with superior repositioning and mandibular setback sagittal split ramus osteotomy. Using the cone-beam computed tomography volume superimposition method, the soft tissue changes were measured and determined both preoperatively and postoperatively. A 10 × 27 grid at 4.5-mm (vertical) and 5-mm (horizontal) intervals was used for the hard to soft tissue response. The mean difference in the reduction from leveling Le Fort I osteotomy was 3.2 ± 1.2 mm between the short and long sides (P < .05). The mandibular setback movement averaged 5.4 ± 3.3 mm on the long side and 5.0 ± 3.6 mm on the short side (P > .05). The soft tissue areas below the Frankfort horizontal (FH) plane to 13.5 mm showed different changes after the differential leveling Le Fort I osteotomies. The distinctly changed areas, which showed differences between the greater- and lesser-reduction sides beyond the 2.5-mm average for the soft tissue response, were below the FH plane to 13.5 mm and lateral to the midsagittal reference plane to 30 mm. In light of this, oral surgeons and orthodontists should be concerned about the volumetric midfacial difference after leveling the maxillary occlusal plane at the preoperative stage and thus should take appropriate measures to improve it.

An In Vitro Evaluation of Rigid Internal Fixation Techniques for Sagittal Split Ramus Osteotomies: Setback Surgery

The aim of this study was to evaluate the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomy for mandibular setback in vitro. Sixty polyurethane replicas of human hemimandibles were used as substrates, simulating a 5-mm setback surgery by sagittal split ramus osteotomy. These replicas served to reproduce 3 different techniques of fixation, including 1) a 4-hole plate and 4 monocortical screws (miniplate group), 2) a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3) 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). After fixation, hemimandibles were adapted to a test support and subjected to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge with an Instron 4411 mechanical testing unit. Peak loadings at 1, 3, 5, and 10 mm of displacement were recorded. Means and standard deviation were analyzed using analysis of variance and Tukey test with a 5% level of significance, and failures during tests were recorded. Regardless of the amount of displacement and direction of force, the miniplate group always showed the lowest load peak scores (P < .01) compared with the other fixation techniques. The hybrid group demonstrated behavior similar to the inverted-L group in lateral and vertical forces at any loading displacement (P > .05). Molar load tests required more force than incisal load tests to promote the same displacement in the mandibular setback model (P < .05). For mandibular setback surgery of 5 mm, this study concluded that the fixation technique based on the miniplate group was significantly less rigid than the fixation observed in the hybrid and inverted-L groups. Mechanically, adding 1 bicortical positional screw in the retromolar region in the miniplate technique may achieve the same stabilization offered by inverted-L fixation for mandibular sagittal split ramus osteotomy setback surgery in vitro.

Midfacial Soft-Tissue Changes After Advancement of Maxilla With Le Fort I Osteotomy and Mandibular Setback Surgery: Comparison of Conventional and High Le Fort I Osteotomies by Superimposition of Cone-Beam Computed Tomography Volumes

To compare the soft-tissue changes in the midfacial areas of patients who underwent conventional and high Le Fort I osteotomies with maxillary advancement, using voxel-by-voxel registration at the cranial bases, and to evaluate the influence of the level of the osteotomy cut on those soft-tissue changes. The subjects included 42 patients (28 in group 1 and 14 in group 2) who had undergone conventional or high Le Fort I osteotomy with maxillary advancement and mandibular setback sagittal split ramus osteotomy. Using the method involving superimposition of 3-dimensional cone-beam computed tomography volumes, we evaluated the soft-tissue changes preoperatively and postoperatively. The midfacial area was measured with a 10 × 27 grid at 4.5-mm (vertical) and 5-mm (horizontal) intervals. The maxillary advancement in group 1 averaged 3.35 ± 1.06 mm at the A-point and 3.23 ± 0.98 mm at the same location in group 2. Both of the Le Fort I osteotomies induced an overall hard-to-soft tissue response in the midfacial area (P < .05). In group 1, the distinctly changed soft tissue was marked near the osteotomy line and upper lip. The distribution of the changed points was within a roughly triangular area between the 2 nasolabial folds and the upper lip. In group 2, the soft-tissue changes were concentrated just below the infraorbital foramen. The distribution of the affected soft tissue after the high Le Fort I osteotomy was within the rectangular malar region between the 2 infraorbital foramens and the upper lip.

Surgery-First Approach in Skeletal Class III Malocclusion Treated With 2-Jaw Surgery

The purpose of this study was to evaluate the surgical movement and postoperative orthodontic treatment (POT) of the surgery-first approach for the correction of skeletal class III malocclusion. The samples consisted of 11 patients with skeletal class III malocclusion who underwent nonextraction treatment and 2-jaw surgery (Le Fort I osteotomy impaction of the posterior maxilla, IPM; bilateral sagittal split ramus osteotomy setback of the mandible). The wafer was removed 4 weeks after surgery. Mean (SD) durations of POT and total treatment were 8.91 (3.14) and 12.18 (3.57) months, respectively. Lateral cephalograms were obtained during the initial examination (T0), immediately after surgery (T1), and after debonding (T2). Sixteen variables were measured. Paired t-test was performed for statistical analysis. The maxilla rotated clockwise, and the nasolabial angle increased by IPM (FH-palatal plane angle, FH-occlusal plane angle, P < 0.01; nasolabial angle, P < 0.05) and well maintained during POT. The mandible was repositioned backward by bilateral sagittal split ramus osteotomy setback of the mandible (SNB, Pog-N perp, P < 0.001) and relapsed forward during POT (SNB, P < 0.01; Pog-N perp, P < 0.05). U1-SN decreased by IPM (P < 0.001) and relapsed labially owing to class III mechanics during POT (P < 0.01); eventually, no significant difference was found between T0 and T2 stages. Although IMPA increased by POT, there was no significant difference between T0 and T2 stages. The mandible seems to relapse forward immediately after wafer removal and before labioversion of the lower incisors. Accurate prediction of POT is crucial in controlling dental alignment, incisor decompensation, arch coordination, and occlusal settling. Long-term wearing and selective grinding of the wafer for labioversion of the lower incisors and use of miniplates/miniscrews to control the inclination of the upper incisor and to prevent relapse of the mandible are needed.

Position of Mandibular Canal and Ramus Morphology Before and After Sagittal Split Ramus Osteotomy

The purpose of this study was to evaluate changes in the mandibular canal and ramus morphology before and after a sagittal split ramus osteotomy. The subjects were 30 patients (60 sides) with mandibular prognathism who had undergone bilateral sagittal split ramus osteotomy setback surgery. The mandibular canal position and ramus morphology were measured at the 3 horizontal planes under the mandibular foramen level (level A), 1 cm lower than level A (level B), and 2 cm lower than level A (level C) preoperatively and 1 year postoperatively by computed tomography. Postoperative ramus width, lateral distance, lateral marrow distance, and canal length were significantly larger than the preoperative values at the foramen, 1 cm lower, and 2 cm lower. The mandibular canal completely contacted the lateral cortex without lateral bone marrow in 6 sides (10%) in levels A and B and 4 sides (6.7%) in level C preoperatively and 6 sides (10%) in level C postoperatively. This study suggested that postoperative mandibular canal position was located more posteriorly and the postoperative lateral bone marrow became thicker compared with the preoperative state.

The effect of mandibular setback or two-jaws surgery on pharyngeal airway among different genders

Cephalometric studies show significant gender differences in the size of the pharyngeal airway space. This study aimed to investigate and compare morphologic changes after mandibular setback or two-jaws surgery on the pharyngeal airway in men and women using computed tomography (CT). The sample included 34 women and 13 men diagnosed with Class III skeletal deformities, who had been treated by mandibular setback or bimaxillary surgery (maxillary advancement and mandibular setback). Anteroposterior, lateral and cross-sectional area dimensions of the airway, at the level of soft palate and base of tongue, were measured pre- and postoperatively on CT images. In the mandibular setback group, the anteroposterior and cross-sectional area of the pharyngeal airway at the level of the soft palate and base of tongue were significantly reduced for men or women (P<.05). In the two-jaws surgery group, only midsagittal anteroposterior dimensions at the same levels were significantly decreased for men or women (P<.05). The difference between any values measured between men and women who received bilateral sagittal split ramus osteotomy setback surgery or two-jaws surgery for the treatment of class III anteroposterior discrepancy were not statistically significant (P>.05). This study suggests that oropharyngeal airway measurements, important for airway patency, do not demonstrate sex dimorphism.

Effect of bilateral sagittal split ramus osteotomy setback on the soft palate and pharyngeal airway space

To evaluate the effect of bilateral sagittal split ramus osteotomy setback on the morphology of the pharyngeal airway, especially the structures of the soft palate and pharyngeal airway space (PAS), lateral cephalograms obtained from 49 women before treatment and 1 year after surgery were traced and compared. All patients underwent this osteotomy to correct mandibular hyperplasia. The data were corrected with the use of regression equations for the PAS, taking into account head posture. On average, the SNB angle decreased by 3.9 degrees, resulting in an increase of 4.1 degrees in OPT/NSL (head posture, defined as the craniocervical angulation at the uppermost part of the cervical spine). The morphology of the PAS and soft palate changed significantly ( p < 0.01). The mean reduction in the PAS was 2.6 mm retropalatinally and 4.0 mm retrolingually. On average, the soft-palate length increased by 3.2 mm and the soft-palate angle increased by 4 degrees. These results show that mandibular setback surgery markedly decreases the PAS and changes the morphology of the soft palate.

Changes in the inferior alveolar nerve following sagittal split ramus osteotomy in monkeys: A comparison of monocortical and bicortical fixation

We aimed to observe the changes in the inferior alveolar nerve (IAN) after bilateral sagittal split ramus osteotomy (SSRO) using monocortical or bicortical screw fixation. Bilateral SSRO for setback of the mandible was done in 12 monkeys, and monocortical or bicortical fixation was applied on opposing sides of each mandible. Sensory nerve action potentials were tested before and immediately after operation, and at 2, 4, 8, and 12 weeks. Six animals selected randomly were killed at 4 and 12 weeks after the operation. Specimens of nerve were harvested and processed for histological examination and electron microscopic analysis. Obvious prolongation of latency and diminution of amplitude in the IAN were found postoperatively. At 4 weeks after operation, Wallerian degeneration was apparent, and there were signs of axonal regeneration in the nerves. The IAN had more abnormalities of evoked potentials and pathological changes after bicortical than after monocortical fixation. Although considerable recovery was found after both forms of fixation at 12 weeks, the function of the nerve after plate fixation was better than after screw fixation. Our results suggest that the nerve damage during SSRO could be temporary and reversible, and monocortical fixation may result in restoration of the nerve function sooner than bicortical fixation.

Effect of Mandibular Setback via Bilateral Sagittal Split Ramus Osteotomy on Transverse Displacement of the Proximal Segment

The purpose of this study was to evaluate if a correlation exists between: a) transverse changes in the proximal segments because of mandibular setback surgery and b) postsurgical horizontal relapse of the mandible. A total of 42 patients underwent bilateral sagittal split ramus osteotomy setback with rigid fixation and Le Fort I osteotomy performed by 1 surgeon between 1986 and 2000. The radiographic material for this study consisted of posteroanterior and lateral cephalometric radiographs for each patient taken preoperatively (T1), early postoperatively (T2), and late postoperatively (T3). Twenty-four of the 42 identified patients had T1, T2, and T3 radiographs, while the remainder of the patients had only T1 and T2 radiographs available. The posteroanterior radiographs were used to evaluate the angulation of the proximal segment and the intergonial width. Statistically significant increases in intergonial width and proximal segment angulation occurred from T1 to T2. In fact, all 42 patients had an increased intergonial width from T1 and T2. From T2 to T3, most patients underwent some relapse in their transverse dimension changes (21 of 24 patients had a decrease in their intergonial width). Overall, the intergonial width and the proximal segment angulations were significantly increased from T1 to T3. However, there was no significant correlation between the amount of transverse displacement of the proximal segment and horizontal postsurgical relapse of the mandible. The results show that statistically significant changes in the transverse width and angulation between proximal segments occur in patients undergoing bilateral sagittal split ramus osteotomy for mandibular setback with rigid fixation. However, the magnitude of the changes was small, and it is still uncertain as to whether these changes are of any clinical significance.