Effects of the closing and opening muscle groups on jaw condyle biomechanics after prominent mandibular angle osteotomy

ObjectivesThe aim of this study was to determine the effect of closing and opening muscle groups of the jaw on mandibular stability after prominent mandibular angle osteotomy, through three-dimensional finite element analysis (FEA).Materials and methodsSix patients with prominent mandibular angles, without malocclusion, were selected as finite element models of preoperative and postoperative prominent mandibular angle surgery. Computed tomographic (CT) scans were undertaken of the patients before and after surgery and three-dimensional images reconstructed using Simpleware software. The images were imported into an FEA software. Boundary-constrained and load conditions were applied. The solution process was run, and actions of closing and opening muscle groups were simulated and calculated.ResultsThe Von Mises stresses on the condyle position after the operation were higher than those before the operation. A significant difference was found between the stress distributions in the condyle position between prominent mandibular angle patients and mandibular angle ostectomy patients (P < 0.05).ConclusionsAfter osteotomy, the variation in force exerted by the closing and opening muscle groups of the jaw is one of the major factors affecting mandibular stability. FEA is a promising strategy in pre-surgical planning for improving surgical success and reducing complications.     

下颌升支矢状劈开截骨术后髁突和下颌角横向变化的研究

目的 观察下颌升支矢状劈开截骨后退术后下颌骨近心骨段的横向变化及长期稳定性。方法 对42例行双颌手术＋坚固内固定治疗的Ⅲ类错[牙合]畸形患者术前、术后一周以及术后12个月以上的后前住头颅定位片进行描记、定点测量，并作统计学分析。结果 下颌角间距及髁突间距在术中分别增加了4．04mm（P〈0．01）和2．11mm（P〈0．01）；在术后观察期，二者分别减小了1．45mm（P〈0．01）和1．80mm（P〈0．01）；下颌角间距术中增宽量越大，观察期减小的幅度越大。结论 经过升支矢状劈开截骨后退下颌骨远心骨段后，下颌骨近心骨段在横向上发生了一定的移位，后前住头颅定位片上表现为下颌角间距及髁突间距的明显增加；在平均20个月的观察期内，二者有不同程度的回复，下颌角间距较术前呈明显的净增宽。     

骨性下颌前突正畸—正颌联合治疗前后髁突位置变化的研究

目的:研究骨性下颌前突正畸-正颌联合治疗前后髁突位置的变化,探讨下颌双侧升支矢状劈开后退术对于治疗骨性下颌前突的可靠性和安全性。方法:15例骨性下颌前突的安氏Ⅲ类错牙合畸形病人,行下颌双侧升支矢状劈开后退术(bilateral sagittal split ramus osteotomy,BSSRO)与正畸矫治联合治疗,分别在术前两周和术后半年拍摄许勒式X线片,测量BSSRO术前、术后双侧髁突在关节窝内前、后、上间隙的距离,进行统计学分析比较术前术后髁突位置的变化情况。结果:15例病例经BSSRO配合正畸治疗后均达到正常的咬合关系,恢复了口腔功能,改善了面部容貌;正颌术前:左侧关节前、后、上间隙均数为1.91、2.30、2.51 mm;右侧前、后、上间隙均数为2.14、2.65、2.98 mm;正颌术后:左侧关节前、后、上间隙均数为1.99、2.38、2.62 mm;右侧前、后、上间隙均数为2.14、2.66、2.60 mm。术后半年双侧髁突在关节窝内的上、前、后间隙与术前两周相比,差异均无统计学意义。结论:下颌双侧升支矢状劈开后退术(BSSRO)配合正畸治疗,能够安全有效的矫治骨性下颌前突,并且未使其出现新的关节症状。     

下颌前突患者下颌支矢状劈开截骨术后髁突运动轨迹的改变

目的:研究双侧下颌支矢状劈开截骨术对下颌前突患者髁突运动轨迹的影响。方法:采用ARCUSdigma下颌三维运动轨迹描记仪,以髁突运动中心为参考点,研究30例正常受试者、14例下颌前突患者手术前后开口、前伸和左右侧向髁突运动的轨迹。用SPSSV11.0统计软件包进行配对t检验和成组t检验。结果:下颌前突患者术前、术后、正常组左侧髁突的运动轨迹与右侧基本相同,左侧髁突与右侧的开口、前伸和侧方运动范围无显著性差异(P>0.05)。术前组与正常组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均小于正常组(P<0.05);术后与正常组髁突运动轨迹接近,术后开口、前伸和侧方运动范围与正常组无统计学差异;术前与术后组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均显著小于术后组(P<0.05)。结论:下颌前突患者手术后,随着术后正畸治疗及咬合自我调整,建立了正常的咬合引导关系,使下颌功能运动趋向正常。     

Facial nerve palsy following bilateral sagittal split ramus osteotomy for setback of the mandible

Sagittal split osteotomy of the mandible is frequently used to correct dentofacial deformities. Postoperative facial palsy is one of the most serious complications because it reduces the quality of life and significantly reduces social interaction. The case of a 22-year-old patient who underwent sagittal split setback osteotomy is described. The medical records, perioperative photographs and literature were reviewed in detail to collect data on the clinical course, treatment and outcomes.     

Horizontal rotation of the condyle after sagittal split osteotomy of the mandible

Displacement of the proximal segment of the condyle such that the condyle is no longer in its correct position has been cited as a major factor in postsurgical skeletal relapse after mandibular, sagittal split osteotomy. This study examined the effects of sagittal split osteotomy on the horizontal rotation of the condyle in 16 dissected mandibles for which clamp, screw, and wire fixations were used to advance the mandible or set it back. The results showed that, after sagittal split osteotomy, horizontal rotation usually occurred, regardless of the position of the distal segment or the type of fixation used. Our finding that 82% of the condylar angles increased after surgery indicates that the lateral pole of the condyle had rotated anteriorly, while the medial pole had rotated posteriorly. There were no consistent differences in horizontal rotation between the condyles on the side where the proximal segment had been fixed first and those on the side where it had been fixed second; nor did the sizes of the original intercondylar angles affect the magnitudes of change in the postoperative intercondylar angles. The only statistically significant difference (p = 0.005) between the angles after fixation by the three different methods was between screw and wire osteosyntheses when the distal segments were in the forward position. The reason for this difference is unclear.     

Intraoperative diagnosis of condylar sag after bilateral sagittal split ramus osteotomy

PURPOSE: To evaluate a method to identify condylar sag intraoperatively by clinical examination after bilateral sagittal split osteotomy (BSSO). METHODS: We prospectively studied 184 patients (121 female, 63 male) who had BSSO. The same surgeon operated all patients over a period of 15 months using the same technique. All patients had mandibular advancements. A standard condylar seating technique was used. The occlusion was evaluated at operation and 1 week later. RESULTS: Eighteen patients had an incorrect occlusion diagnosed during the operation after removal of the IMF. Peripheral condylar sag (type II) had developed in three of these patients. In 15 patients central sag was diagnosed. One-week postoperatively, three patients had a malocclusion as a result of condylar sag. CONCLUSION: Meticulous examination of the occlusion and an understanding of the occlusal changes secondary to condylar sag can reliably identify condylar sag intraoperatively. The use of suitable corrective measures during the primary operation can substantially reduce the postoperative complication rate of condylar sag.     

New techniques for reproduction of the condyle relation and reduction of complications after sagittal ramus split osteotomy of the mandible

One hundred three patients underwent a modified sagittal ramus split osteotomy of the mandible. Maintenance of the temporomandibular joint relationship prior to the procedure was achieved postoperatively by using a three-dimensionally adaptable fixation bar. Techniques were also developed to avoid damage to the inferior alveolar nerve during the osteotomy and application of lag screws. These procedures avoided the disadvantages of lag screw osteosynthesis, and reduced relapse.     

双侧下颌支矢状劈开截骨术后咽腔气道的变化

目的：通过头影测量分析骨性下颌前突患者双侧下颌支矢状劈开截骨术后咽腔气道的变化,为术后保持与防止复发提供依据。方法骨性下颌前突患者20例,均接受口内入路的下颌支矢状劈开截骨术。术前1周、术后1周、术后6个月拍摄标准颅颌侧位片进行头影测量,通过治疗前、后对照,比较下颌支矢状劈开截骨术后咽腔气道的改变。采用SPSS 17.0 软件包对数据进行统计学分析。结果术后1周与术前1周相比,软腭长度显著增加,咽腔气道显著减小;术后6个月咽腔气道有所恢复,与术后1周相比软腭长度显著减小,咽腔气道显著增加;术后6个月与术前1周相比,软腭长度及咽腔气道变化无显著差异。结论骨性下颌前突患者行双侧下颌支矢状劈开截骨术后短期内咽腔气道较术前显著减小,可能加大发生睡眠呼吸暂停综合征的几率。但经过一段时间的组织适应和改建后,咽腔气道有恢复至术前宽度的趋势。     

The influence of bilateral sagittal split ramus osteotomy on submental‐cervical aesthetics

The effect of orthodontic‐surgical treatment on submental‐cervical region was evaluated in a very limited number of studies. The aim of this study was to evaluate submental‐cervical soft tissue contour changes following mandibular advancement and set‐back procedures via bilateral sagittal split ramus osteotomy. Sixty‐seven patients were included in this study. Group 1 consisted of 27 skeletal Class II patients who underwent mandibular advancement surgery, whereas Group 2 consisted of 40 skeletal Class III patients who underwent mandibular set‐back surgery. Various linear and angular measurements were performed on pre‐operative and sixth month post‐operative cephalometric radiographs. A new method was used to evaluate the amount of sagging at submental region. The submental length did not change in Group 1; however, it decreased significantly in Group 2 (P < 0·05). The angle between submental plane and facial plane decreased to 95·9° from 98·8° in Group 1(P < 0·05), whereas it increased to 93·1° from 88·2° in Group2 (P < 0·05). The change of submental soft tissue sag was almost stable in Group 1, while 0·34 mm increase of sag was observed in Group 2. This increase was not statistically significant (P > 0·05). Mandibular set‐back and advancement procedures do not remarkably change the submental sag following approximately 6 mm jaw movement. Although mandibular advancement did not significantly effect submental length, soft tissue followed mandibular set‐back with a ratio of 1:1 at C‐point to projection of soft tissue pogonion and 1:0·7 at C‐point to soft tissue menton distances.     

Mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy: comparing 2 different fixation techniques.

PURPOSE: Using finite element (FE) computer model simulation, we compared the mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy (BSSRO) through the use of 2 different techniques to stabilize the osteotomy. MATERIALS AND METHODS: Based on the reconstructed geometry from computed tomography scans of dry adult skull with a mandibular deformity requiring surgical correction, we developed 3-dimensional FE models that simulate BSSRO with 2 different techniques to stabilize the osteotomy. Technique 1 uses 3 bicortical titanium screws. Technique 2 uses a curved titanium plate with 4 monocortical screws. Five different load cases were applied to the mandible after the simulated BSSRO with the mandible being constrained at both temporomandibular joints. To evaluate the efficacy of these 2 stabilization techniques, we compared 1) the resulting deflections at the central incisor, 2) the mechanical stresses developed in the bone in the vicinity of the stabilizing implants, and 3) the mechanical stresses developed within the screw/plating system themselves. RESULTS: Technique 1, using 3 bicortical titanium screws, leads to smaller deflections at the central incisor for all 5 load cases, suggesting higher mechanical stability. Technique 1 also leads to lower mechanical stresses in the bone and in the implanted screws, whereas technique 2 is associated with higher values in each of these quantities. CONCLUSIONS: To stabilize osteotomies after a 3-dimensional simulated BSSRO, 3 bicortical screws forming an inverted-L configuration are shown to offer more effective load transmission in the mandibular construct. This technique, when examined in an FE model, leads to higher stability with lower mechanical stresses in the bone near the bicortical screws.     

Three-dimensional evaluation of positional change of the condyle after mandibular setback by means of bilateral sagittal split ramus osteotomy

OBJECTIVE: The aim of this study was to evaluate condylar displacement in 3 dimensions by means of computed tomography after mandibular setback by sagittal split ramus osteotomy with rigid fixation and to compare these results with those from patients with mandibular advancement. STUDY DESIGN: Thirty Korean subjects with skeletal class III malocclusion who had undergone mandibular setback by sagittal split ramus osteotomy had computed tomographs taken. Tomographs were taken to evaluate the temporomandibular joint 1 month before and approximately 1 month after surgery. The position and angulation of the condyle were measured on axial or sagittal views. These measurements were analyzed to determine any correlations between the amount of mandibular movement and condylar displacement. RESULTS: The results of this study show that the condyle tends to move inferiorly and rotate inward on the axial view and backward on the sagittal view by a statistically significant amount. CONCLUSION: The positional change of the condyle after sagittal split ramus osteotomy was not correlated with the amount of the setback.     

Peripheral facial palsy after bilateral sagittal split ramus osteotomy: case report

Bilateral sagittal split ramus osteotomy (BSSRO) is commonly used in orthognathic surgery. Although abnormal sensation in areas that are innervated by the inferior alveolar nerve is a well-known neurological complication of mandibular osteotomy, facial palsy is rare postoperatively. We present a case of peripheral facial palsy that developed the day after BSSRO to correct a mandibular protrusion in a 42-year-old man. Oral prednisolone was begun on the second day postoperatively, and was gradually tapered off over time. One month after operation, he had gradually recovered all movements in his right facial muscle and, after two months, had completely recovered without residual asymmetry. Possible causes of the palsy were compression of the facial nerve as a result of the insertion of a retractor around the posterior border of the ramus, and postoperative oedema. Peripheral facial palsy after BSSRO should be considered a rare, but possible, complication and as such, should be mentioned in consent forms.     

Comparison of osseous healing after sagittal split ramus osteotomy and intraoral vertical ramus osteotomy

The sagittal split ramus osteotomy (SSRO) is generally associated with greater postoperative stability than the intraoral vertical ramus osteotomy (IVRO); however, it entails a risk of inferior alveolar nerve damage. In contrast, IVRO has the disadvantages of slow postoperative osseous healing and projection of the antegonial notch, but inferior alveolar nerve damage is believed to be less likely. The purposes of this study were to compare the osseous healing processes associated with SSRO and IVRO and to investigate changes in mandibular width after IVRO in 29 patients undergoing mandibular setback. On computed tomography images, osseous healing was similar in patients undergoing SSRO and IVRO at 1 year after surgery. Projection of the antegonial notch occurred after IVRO, but returned to the preoperative state within 1 year. The results of the study indicate that IVRO is equivalent to SSRO with regard to both bone healing and morphological recovery of the mandible.     

Mandibular remodeling after bilateral sagittal split osteotomy for prognathism of the mandible.

PURPOSE: To describe the postoperative remodeling changes in the mandible after bilateral sagittal split osteotomy to correct mandibular prognathism. PATIENTS AND METHODS: Twenty patients who underwent bilateral sagittal split osteotomy for the correction of mandibular prognathism were studied for postoperative remodeling changes within the mandible. The 6-week, 1-year, and long-term postoperative cephalometric mandibular tracings of 12 patients were superimposed using the fixation wires as the stable reference points to demonstrate the specific locations of the intrabony remodeling. RESULTS: There was a general direction of remodeling at the condylion and gonion anteriorly and superiorly, while the B point and pogonion did not show much change in remodeling. At the condylion, 60% and 40% of the cases showed significant horizontal and vertical remodeling, respectively. At the gonion, 50% and 55% of the cases showed significant horizontal and vertical remodeling, respectively. No correlation was found between the remodeling changes at condylion and gonion and the surgical movement or relapse at B point and pogonion. There was a significant correlation between the observed horizontal relapse at gonion and the horizontal remodeling changes at this point showing that the postoperative displacement of this point is a result of both positional translocation and remodeling changes. CONCLUSION: The results of this study show that there are intrabony remodeling changes that occur in the mandible after sagittal split osteotomy and that these continue for a long period of time in some patients. This remodeling occurred more in the condylar and gonial areas, while the chin remained relatively stable.     

The sagittal split osteotomy of the mandible

Modifications of the sagittal split osteotomy of the mandible have essentially reduced the major drawbacks of the procedure, such as condyle displacement, short-term skeletal relapse, and protracted maxillomandibular fixation and mental nerve dysesthesia. These techniques have proved effective over a period of 4 years in fifty-seven patients treated.     

Prediction of neurosensory alterations after sagittal split ramus osteotomy

Prediction of neurosensory deficit in the lower lip and chin after sagittal split ramus osteotomy (SSRO) is challenging. This study aimed to elucidate factors related to the development and improvement of neurosensory disturbance (NSD) after SSRO with respect to surgical procedure and the anatomical and structural characteristics of the craniomaxillofacial skeleton. Subjects comprised 50 patients treated by a single experienced surgeon. Anatomical data and landmarks were obtained by computed tomography (CT) imaging. There was a significant difference between patients with or without NSD for the surgical space on the medial side of mandibular ramus 1 week after SSRO (P = 0.006). Less than 15.0 mm between the lingula and mandibular notch (relative risk, 6.7; 95% CI, 1.7–33.8) and 195.0 mm² or more space on the medial side of the mandibular ramus (relative risk, 17.2; 95% CI, 3.9–100.4) indicated a significant risk of NSD development at 6 months postoperatively. These results suggested that the development of NSD is related to the surgical space on the medial side of the mandibular ramus and subsequent manipulation of the inferior alveolar nerve (IAN) in that region. Limited periosteal degloving prevents excessive stretching of the IAN during SSRO, thus lowering NSD incidence.     

下颌升支矢状截骨术后肌功能康复训练的临床探讨

目的 探讨肌功能康复训练对下颌升支矢状截骨术后功能恢复的作用.方法 利用自行研制的张口训练器,借鉴国外的功能训练方法 ,对接受下颌升支矢状截骨术的27例患者进行被动张口训练和有阻力的肌肉耐力训练,在颌间牵引拆除后2～3 d,使用张口训练器插入牙列间锻炼张口度,5 min/次,3～4次/d.在张口度达到20～25 mm后进行肌肉耐力训练.患者用后牙咬合施加阻力后的张口器并维持5 s后,松弛5 s再咬合,反复进行,5 min/次,3～4次/d,持续3～4周.27例康复训练结果 与20例接受同类手术未行功能康复训练的患者对比.结果 接受肌功能训练的患者术后4周时张口度[(34.72±3.75)mm]已接近术前水平,8周时(牙合)力[(231.08±62.52)N]达到术前水平.未接受肌功能训练的患者在术后4、8周时张口度[(28.42±4.11)mm]和(牙合)力[(210.90±73.40)N]均值仍低于术前,差异有统计学意义(P＜0.05).结论 系统和规范的肌功能康复训练,并配合使用新型张口训练器,能加速下颌升支矢状截骨术患者口颌系统功能的恢复速度.