Three-dimensional finite element analysis of the mandible and temporomandibular joint on simulated occlusal forces before and after vertical ramus elongation by distraction osteogenesis

Distraction osteogenesis has recently become a mainstay for treatment of mandibular hypoplasia. Thorough knowledge about changes in the temporomandibular joint (TMJ) and the surrounding parts of the mandible and the skull after mandibular distraction is still lacking. The purpose of the current study was to investigate the stress distribution in the mandible and the TMJ before and after skeletal correction by intraoral unilateral vertical mandibular ramus distraction, using a finite element (FE) model. The FE models were based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the mandible and TMJ before and after skeletal correction by 15 mm of vertical distraction of the mandibular ramus was analyzed quantitatively and compared during centric occlusion. Before the distraction osteogenesis treatment, the condyles, articular discs, and glenoid fossa regions are loaded with a different stress pattern. The affected right condyle, disc, and fossa are loaded diffusely and externally in comparison with the anterior and with centralized loading on the normal left side. After unilateral mandibular distraction osteogenesis, the load became more centric and symmetrical. The results suggest that correction of the mandibular deformity by distraction osteogenesis tends to normalize the stress patterns in the TMJ.     

Mandibular distraction osteogenesis using an intraoral device and bite plate for a case of hemifacial microsomia.

OBJECTIVE: To present orthodontic treatment combined with mandibular distraction osteogenesis using an intraoral device and a bite plate in a patient with hemifacial microsomia, severe facial asymmetry, and unilateral mandibular hypoplasia. PATIENT: An 8-year-old girl exhibited mandibular deviation resulting from hypoplasia of the mandibular condyle and ramus on the left side. The patient was treated with an intraoral device for mandibular distraction osteogenesis, bite plate, and hybrid-type functional appliance. Facial asymmetry was improved, and the mandibular ramus was elongated in an anterior and primarily posterior direction with slightly posterior and superior displacement of the proximal segment. Postdistraction treatment results have been stable for 1 year. At the 1-year follow-up, the volume of the lateral and medial pterygoid muscles on the left side had increased. The condyle and disc on the right temporomandibular joint moved well and in harmony at open mouth position, and a rotational movement of the left temporomandibular joint was observed.     

Effects of tissue-engineered articular disc implants on the biomechanical loading of the human temporomandibular joint in a three-dimensional finite element model

The purpose of this study was to evaluate biomechanical loading of the temporomandibular joint when using a biodegradable laminate implant to replace the articular disc and to test the hypothesis that the use of the implant reduces stress distribution in the condyle, implant, and glenoid fossa. A finite element model of a female human mandible, including the temporomandibular joint, which had two standard endosseous implants inserted bilaterally in the premolar region, was constructed from computed tomography scan images using a commercially available finite element software. The disc, condyle, and glenoid fossa were arbitrarily divided into five regions: the anterior, posterior, medial, lateral, and central. The disc was then replaced with a poly-L/DL-lactide biodegradable laminate. The finite element model was then used to predict principal and Von Mises stresses. The use of poly-L/DL-lactide implant resulted in remarkable reduction in Von Mises stresses (approximately threefold) in the anterior, central, and medial regions of the mandibular condyle in comparison with slight to moderate stress reductions in the corresponding regions of the implant and glenoid fossa. The mandibular condyle also demonstrated the largest total displacement in all directions followed by the implant and glenoid fossa. The use of an alloplastic implant such as the bioresorbable, poly-L/DL-lactide laminate to replace the articular disc reduces loading of the mandibular condyle rather than the implant and glenoid fossa. These findings lead to support the hypothesis that the mandibular condyle more likely functions as a shock absorber than the disc. The use of bioresorbable laminate implants might prove an efficient technique to replace the articular disc and promote normal function of the temporomandibular joint.     

下颌支后缘垂直切开上移重建髁突治疗骨软骨瘤

目的:评价下颌支后缘垂直骨切开术用于治疗髁突骨软骨瘤的临床效果.方法:对我院2004-2009年间9例应用髁突切除术及带蒂下颌支后缘上移重建髁突治疗髁突骨软骨瘤的患者进行随访,并通过影像学、咬合关系及颞下颌关节功能进行综合评估.结果:经过至少8个月的随访,所有患者髁突重建后的咬合关系、面形及关节功能均恢复良好.影像学检...     

颞下颌关节强直的牵引成骨治疗

目的探讨牵引成骨技术在颞下颌关节强直治疗中的应用。方法应用内置式牵引器治疗8例单侧颞下颌关节强直患者,患侧升支区制备一个1.5～2.0cm颊舌向等宽的骨间隙,并去除喙突,恢复开口度,升支后缘方块截骨,截骨块保留翼内肌附着,与下颌骨间安装牵引器,术后采用升支牵引成骨术,每日牵引1mm,分2次完成,重建颞下颌关节结构及恢复颞下颌关节功能,并坚持开口训练18个月以上。结果经牵引成骨后,患者牵引间隙成骨良好,新形成的关节形态得到改建,升支高度延长1.2～2.1cm,开口度达到正常。结论牵引成骨是治疗颞下颌关节强直的有效方法。     

Micro-computed tomography evaluation of the glenoid fossa and mandibular condyle bone after bilateral vertical ramus mandibular distraction in a canine model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (microCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.     

Micro-computed tomography evaluation of the glenoid fossa and mandibular condyle bone after bilateral vertical ramus mandibular distraction in a canine model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (muCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.     

牵张力作用下颞下颌关节受力的三维有限元研究

目的 研究不同方向牵张力作用下颞下颌关节的受力状况,探讨下颌骨牵张成骨过程中牵张力合理的方向.方法 通过建立颞下颌关节及下颌骨的三维有限元模型,在模型上模拟牵张力的作用,得到下颌骨牵张成骨过程中,颞下颌关节的受力状况.牵张力的方向为平行于下颌骨下缘或平行于正中矢状面.分别观察牵张延长1 mm、3 mm、5 mm的应力分布状况.结果 不同方向牵张力作用下颞下颌关节的受力情况是不同的.当牵张力平行正中矢状面时,颞下颌关节的受力较大.结论 在下颌骨牵张成骨过程中,牵张力的方向具有重要的生物力学效果.     

Transport distraction osteogenesis as a method of reconstruction of the temporomandibular joint following gap arthroplasty for post-traumatic ankylosis in children: a clinical and radiological prospective assessment of outcome

This clinical and radiographic study investigated the use of transport distraction osteogenesis in unilateral temporomandibular joint (TMJ) ankylosis patients. Six patients aged between 4 and 8 years were selected for the study; the mean preoperative maximal inter-incisal opening (MIO) was 3.5 mm without lateral and protrusive mandibular movements. The ankylotic mass along with the posterior border of the ascending ramus was exposed via ‘lazy-S’ incision. A gap arthroplasty was performed, followed by a ‘reverse L’ osteotomy on the posterior border of the ramus. In-house manufactured extraoral distraction devices were used for this prospective study. Follow-up clinical and radiographic evaluation was carried out for 13–27 months after completion of the activation period. After a mean follow-up of 19 months, the mean MIO was 29.1 mm and the lateral and protrusive movements changed from none to slight. Cone beam computed tomography images of all patients showed remodelled neocondyle created by transport distraction osteogenesis with no statistically significant differences observed for average cancellous bone density, trabecular number, and trabecular spacing between the neocondyle of the operated side (test) and the condyle of the non-operated side (control). Neocondyle formation by transport distraction osteogenesis using the in-house distraction device is a promising treatment option for TMJ reconstruction in ankylosis patients.     

Long-term evaluation of the stability of reconstructed condyles by transport distraction osteogenesis

This retrospective longitudinal study evaluated the long-term stability of reconstructed condyles by transport distraction osteogenesis of the mandibular ramus in patients with unilateral temporomandibular joint (TMJ) ankylosis. 7 patients were followed up for 16–92 months (mean 39.4 months). The mean age of the patients at the time of distraction was 22.9 years (range 7–44 years). Maximal mouth opening and panoramic radiographs were recorded preoperatively, at the time of device removal and several years after removal of distraction device. At follow-up, cone beam CT images of the TMJ were obtained to confirm the changes of the reconstructed condyle. Absolute height (Co–Inc) and relative height (Co–Inc/Co–Go) of the reconstructed condyle and the asymmetric difference ratio (AR) were examined to assess the changes of condylar height and mandibular symmetry. The mean maximal mouth opening was stable during the period of follow-up. The mean absolute height and relative height of the reconstructed condyle decreased significantly (P < 0.05). Although no significant difference was found, the mandibular asymmetry difference ratio increased by 16.7%. These results suggested that the heights of reconstructed condyles were not stable in the long-term, and the mandible tended to be asymmetrical.     

Treatment of temporomandibular joint ankylosis and facial asymmetry with bidirectional transport distraction osteogenesis technique

Transport distraction technique is a good treatment modality for unilateral temporomandibular joint ankylosis. However, with a unidirectional distraction, it is not possible to correct facial asymmetry that results from mandibular hypoplasia associated with early-onset unilateral temporomandibular joint ankylosis. For this purpose, gap arthroplasty and simultaneous bidirectional transport distraction was used to correct these deformities. Although vertical distraction corrects vertical deficiency of the ramus and creates a neocondyle, the simultaneous anteroposterior distraction of the transport segment corrects facial asymmetry resulting from horizontal shortness of mandible. Three patients, whose mean mouth opening was 8.6 mm, were successfully treated with this technique. Mean advancements in vertical and anteroposterior direction were 14.7 and 7.7 mm, respectively. Mean maximal mouth opening was 29.7 mm postoperatively. The average follow-up period was 13 months (range, 12-15 mo). During this period, reankylosis was not observed, and the interincisal distance did not decrease. Gap arthroplasty and bidirectional transport distraction of the mandibular ramus is a good and effective therapeutic option in treatment.     

Craniofacial morphology and inclination of the posterior slope of the articular eminence in female patients with and without condylar bone change

This study investigated the association of craniofacial and glenoid fossa shapes and temporomandibular joint (TMJ) pathology in 39 orthodontic patients with signs and symptoms of TMJ disorders, using helical CT scans. Cephalometric measurements showed that 21 subjects with bilateral condylar bone change (BBC) had significantly smaller SNB angles, ramus heights and S-Ar/N-Ba ratios, as well as larger mandibular plane angles and lower anterior facial height than the 18 subjects with no condylar bone change (NBC). The average posterior slope of the left and right articular eminence in their central and lateral sections was significantly steeper in NBC than in BBC. Condylar bone change might, therefore, not only be related to the morphology of the mandible, but also of the glenoid fossa and cranial base. This appears to reflect adaptive changes in the condyle, articular eminence and cranial base in response to changes in loading.     

牵张成骨术矫正单侧真性关节强直偏颌畸形1例

对1例因关节强直导致的偏颌畸形患者行下颌骨体牵张成骨器植入术,术后1周开始牵张右侧下颌骨,牵张20 d后右侧下颌升支及下颌体高度明显增加,牵张器维持4个月,右侧上颌骨自动向下生长,上下颌咬合关系恢复正常,取出下颌牵张成骨器,在牵张成骨新骨上植入MEDPOR假体并行颏成形术。手术完成后患者颜面不对称及畸形咬合关系均得到明显改善。     

Mandibular distraction in the absence of an ascending ramus and condyle

The introduction of distraction osteogenesis (DO) as a method of mandibular elongation has provided the craniofacial surgeon with a valuable tool in the approach to patients with mandibular deficiencies. A growing number of case reports and clinical series have proven the efficacy of mandibular DO as an augmentative technique in patients with hemifacial microsomia (HFM). Although DO has become a part of the treatment algorithm for many patients with HFM, surgeons have been reluctant to apply the technique in patients with complete agenesis of the ascending mandibular ramus and condyle (grade III HFM). In the following cases, mandibular DO was successfully performed in two patients with grade III HFM. Preoperative images and intraoperative findings confirmed that both patients lacked the entire ascending mandibular ramus and condyle on the affected side. After unilateral multiplanar DO, both patients showed new bone formation within the distraction gap and development of a pseudoarthrosis between the proximal segment of the mandible and the skull base. Facial symmetry improved dramatically, and speech and mandibular excursion were maintained. The patients have been followed for 1 to 2 years after distraction with durable functional and esthetic outcomes. Mandibular DO offers many advantages compared with rib grafting, including avoidance of donor site morbidity, application in patients who are not candidates for graft harvest, and use after rib graft failure. The following cases support the use of mandibular DO as a mechanism of endogenous tissue engineering in patients with complete agenesis of the ascending mandibular ramus and condyle.     

Backward distraction osteogenesis of condylar segment in patient with mandibular ramus deficiency--report of a case

A backward distraction osteogenesis (BDO) of the condylar segment for treatment of mandibular ramus deficiency was developed. This report describes the clinical progress of a patient with mandibular ramus deficiency in whom satisfactory occlusion was achieved and maintained by gradual posterosuperior repositioning of the displaced condyles into the glenoid fossae during intermaxillary fixation. Findings of pre- and postoperative clinical and magnetic resonance imaging indicate that the effect of BDO on the temporomandibular joint was negligible.     

Histological changes in the temporomandibular joint in rabbits depending on the extent of mandibular lengthening by osteodistraction

We studied the histological changes in the temporomandibular joint (TMJ) after unilateral mandibular distraction osteogenesis in rabbits. Eight rabbits were used, two of which served as controls and the other six had distraction of the left mandibular body after a latency period of 7 days at a rate of 0.5mm a day for a total of 2mm (n = 2), 3.5mm (n = 2), and 5mm (n = 2) of distraction. After a 14-day consolidation period, TMJs from both sides were harvested and prepared for histological examination under an optical microscope using haematoxylin and eosin stain. We found no degenerative or inflammatory changes in either TMJ in any of the groups. Endochondral ossification in the condyle was greater on the opposite side in the experimental group than in the condyles of the control group. Endochondral ossification was active in the 3.5-mm group.     

Treatment of painful temporomandibular joint dysfunction with the sagittal split ramus osteotomy.

PURPOSE: We describe a new indication for the sagittal split ramus osteotomy with rigid fixation to treat patients with painful dysfunction of the temporomandibular joint. PATIENTS AND METHODS: Ten patients for whom nonsurgical management failed were found to have a mandibular condyle positioned postero-superior within the glenoid fossa with reduced joint space on corrected-axis tomograms. The sagittal split ramus osteotomy was used to reposition the proximal segment and to increase joint space. Preoperative and long-term postoperative (average, 44.7 months) symptoms and tomographic findings were retrospectively compared. RESULTS: Significant pain relief occurred postoperatively in all patients. One patient had a relapse after initial improvement. No patient developed a malocclusion. The long-term radiographic condyle-fossa relationship tended to return to its preoperative position with no relapse of clinical symptoms, except in the 1 patient. CONCLUSION: The sagittal split ramus osteotomy with rigid fixation is another procedure that can be used to treat painful temporomandibular joint dysfunction by changing the position of the mandibular condyle in the glenoid fossa.     

Condylar osteochondroma manifesting as Class III skeletal dysplasia: diagnosis and surgical approach

This is a case report of a 21-year-old man who had a gradually progressive Class III malocclusion and crepitation of the right temporomandibular joint. Routine TMJ tomograms revealed a radiopaque-radiolucent lesion of the right mandibular condyle with a compensatory anteroinferior displacement of the left mandibular condyle. Nuclear bone scans confirmed increased asymmetric technetium 99 tracer uptake in the region of the right temporomandibular joint. A two-stage surgical approach was undertaken; this consisted of excision of the condylar lesion to correct the Class III malocclusion and posterior crossbite and a LeFort I osteotomy to correct the slight transverse maxillary cant and anterior open bite. A histopathologic diagnosis confirmed osteochondroma of the mandibular condyle.     

Biomechanical evaluation of mandibular midline distraction osteogenesis by using the finite element method.

The aim of this study was to evaluate the biomechanical effects of mandibular midline distraction osteogenesis on the mandibular complex by using a 3-dimensional finite element model, whose construction was based on computer tomography scans of the mandible of a 22-year-old man. The computer tomography pictures were transferred and converted to the finite element model by means of a procedure developed for this study. The final mesh consisted of 1314 solid elements with 3076 nodes. The distraction was performed on the middle intersection point of the vertical and horizontal planes on the mandibular symphysis. The mechanical response in terms of displacement and von Mises stresses was determined by widening the mandible up to 5 mm on both sides. The results indicate that the mandible was separated almost in a parallel manner (4.45-5.0 mm separation from the mandibular incisors to the lower border of the mandibular symphysis and 4.09-4.92 mm from the mandibular canines to the symphyseal border at the canine region), superoanteriorly. Anteroposterior evaluation demonstrated that the greatest widening was achieved at the symphyseal region, and the widening effect gradually decreased from anterior to posterior. Viewed occlusally, the width of the mandibular bone at the symphyseal region increased remarkably, whereas the ramal and gonial regions of the mandible and the condyle had shown minimal displacement. Mandibular bone was displaced forward and slightly downward. The highest stress levels were observed bilaterally below the condylar areas. High stress levels were also observed in the ramal region of the mandible.     

有限元法探讨犬下颌不全截骨牵张的最佳截骨量

目的 利用不完全截骨牵张成骨重建犬下颌节段缺失的有限元模型,控制截骨程度,探讨最佳截骨量.方法 有限元模型模拟不完全截骨,在加力(12N)牵张过程中观察犬下颌皮质骨逐渐加大截骨量时截骨部位的Von Mises应力,并与犬下颌骨的极限抗拉强度比较,以获得牵引时不发生断裂(骨折)的最少剩余皮质骨量.结果 牵张过程中当连接处骨片剩余1mm时,滑动骨块和骨片的连接处Von Mises应力是47.76MPa,最接近犬下颌骨的极限抗拉强度(约49.35MPa).结论 犬下颌行半侧不全截骨牵张成骨时,当连接骨片的剩余宽度小于1mm时,将大大增加牵张区骨折的危险性.