Mechanical tension in distraction osteogenesis regulates chondrocytic differentiation

Differentiation of chondrocytes to cells of osteoblastic phenotype occurs during an interim period of bone development, fracture repair and distraction osteogenesis. To study the relationship between tension-stress and chondrogenesis, uniaxial strains (0 microstrains, 2000 microstrains, 20000 microstrains, 200000 microstrains, 300000 microstrains) were applied in a rabbit model of mandibular distraction osteogenesis. The results demonstrated that cell differentiation, apoptosis and tissue development in the newly formed gap tissue showed a correlation to the applied strain magnitudes. Only strains of 20000 microstrains resulted in a statistically significant (P<0.05) formation of cartilage struts with embedded chondrocyte-like cells. However, chondrocyte-like cells were rarely detected in samples distracted at lower or higher strain magnitudes. Osteoblasts appeared to replace cartilaginous matrix by mineralized bone matrix. The phenotypic change from chondrocytes to osteoblasts was accompanied by a decreased proteoglycan synthesis. a change in the expression from type II collagen towards type I and involved asymmetric cell divisions and apoptotic cell death. Therefore, we suggest that mechanical strain is an external stimulus responsible for phenotypic cell alterations.     

Changes in the temporomandibular joint after mandibular lengthening with different rates of distraction

This study assessed the changes in the condyle after mandibular lengthening with 2 different rates of distraction (1 mm/day and 2 mm/day). Unilateral mandibular distraction was performed in 8 young adult goats. The animals were sacrificed 8 weeks after the completion of distraction, and the temporomandibular joint (TMJ) specimens were harvested and processed for histologic examination and histomorphometric analysis. Adaptive changes in the condyle were observed in the goats distracted at a rate of 1 mm/day, whereas degenerative alterations were found in those distracted at a rate of 2 mm/day. This study suggests that the TMJ is able to withstand the impact of distraction at a rate of 1 mm/day, but more rapid distraction may induce degeneration in the condylar cartilage.     

Histologic, histomorphometric and immunohistologic changes of the gingival tissues immediately following mandibular osteodistraction

OBJECTIVES: Even though osteogenesis after osteodistraction has been investigated in numerous experimental studies, there is limited information focusing on the influence of well-defined mechanical distraction forces on the associated gingival tissues. MATERIAL AND METHODS: In a study including 48 rabbits, mandibular osteodistraction was performed in vertically osteotomized mandibular body, using defined distraction protocols with physiologic, moderate and hyperphysiologic forces. The soft tissues overlying the distraction gap were harvested finally for histologic, immunohistologic and histomorphometric investigations. RESULTS: The control group without distraction showed the typical architecture and thickness of normal gingiva. In groups with distracted mandibles, an accelerating atrophy of gingiva depending on the degree of mechanical loading was obvious, characterized by decreasing thickness of epithelial layer, loss of rete ridges and disorganization of the different cell layers with a high number of apoptotic cells. In lamina propria collagen fibres were reduced and elastic fibres increased. Histomorphometric analysis revealed significant correlation between degree of distraction and atrophy in overlying soft tissues. CONCLUSION: This rabbit model of mandibular lengthening shows an accelerating atrophy in the covering soft tissues following hyperphysiologic distraction. The long-term outcome of these distraction-related soft-tissue alterations remains unclear. The atrophic changes may likely be of temporary nature.     

Mechanical work during stress-field translation in the human TMJ

The pathomechanics of degenerative joint disease of the temporomandibular joint (TMJ) may involve fatigue produced by mechanical work on the articulating tissues. This study tested the hypotheses that mechanical work in the TMJ (i) varies with the type of mandibular activity, and (ii) is evenly distributed over TMJ surfaces. Ten healthy human participants were recorded with Magnetic Resonance Imaging (MRI) and jaw tracking. The data were used to reconstruct and animate TMJ activity. Aspect ratios, instantaneous velocities, and distances of stress-fields translation were used to calculate work (mJ). The results were analyzed by least-squares polynomial regression and ANOVA. Work magnitudes were related to peak velocity (R(2) = 0.92) and distance of stress-field translation (R(2) = 0.83), and were distributed over the joint surfaces (p < 0.03). During mandibular laterotrusion, average mechanical work was 1.5 times greater in the contralateral joint. Peak magnitudes of work (> 3000 mJ) were 4 times that previously reported.     

牵张成骨延长一侧下颌骨对颞下颌关节的影响

目的：研究牵张成骨（DO）延长一侧下颌骨对双侧颞下颌关节（TMJ）的影响。方法：用DO技术将8只山羊的一侧下颌骨延长10mm，在牵张完成后第8和16周分别处死4只动物，取双侧关节作组织学和扫描电镜研究。结果：下颌一侧DO术后双侧髁状突发生适应性改建，髁突表面超微结构正常。结论：在适当的牵张条件下延长一侧下颌骨不会对TMJ造成病理性损害。     

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 temporomandibular joint ankylosis in children: is it necessary to perform mandibular distraction simultaneously?

Temporomandibular joint (TMJ) ankylosis in children disturbs not only mandibular growth, but also facial skeletal development. Costochondral graft was used to ensure growth, but it had proven to be unpredictable. The authors evaluate retrospectively 41 patients who underwent temporomandibular joint reconstruction during the last 10 years. Twenty were treated by costochondral graft, 15 by arthroplasty, and 6 by other surgical procedures, and they were excluded. The etiology was septic in 54% of the cases. Follow-up was at least 12 months in all cases. Arthroplasty was a quicker and easier procedure than the costochondral graft, reducing operating time, risk of blood transfusion, and hospital stays and costs. It also was associated with less risk of reankylosis, 13%vs 25%. Furthermore, it was associated with a minor morbidity and secondary complications. Seventy-five percent of the patients treated with bone graft required additional secondary surgery. Radiographically, the authors observed a remodeled neocondyle at the level of proximal mandibular end in cases treated by arthroplasty. On clinical examination, patients showed variable degrees of facial deformity and an unknown potential of mandibular growth after TMJ arthroplasty. The authors also observed improved clinical and radiologic appearance after ankylosis correction. Is it reasonable to perform ankylosis release and mandibular distraction simultaneously without knowing which patients will be able to experience growth with time? In that case it would be necessary a predict growth to apply the exact amount of mandibular distraction for obtaining stable results. Timing of mandibular distraction, after TMJ arthroplasty is performed and mandibular function restored, must be specific to each patient's needs, assuring the best distraction conditions and planning. The authors present their treatment protocol, including TMJ joint arthroplasty with temporal muscle interposition, and mandibular distraction osteogenesis, as a second procedure, to correct residual asymmetry or retrognathism if necessary.     

下颌双侧体部牵引成骨联合上颌手术辅助快速扩弓治疗双侧髁突自溶性吸收继发重度骨性Ⅱ类错畸形伴上牙弓狭窄的效果

目的 介绍一种治疗双侧髁突自溶性吸收（ICR）继发重度骨性Ⅱ类错畸形伴上牙弓狭窄的方法。方法 纳入6例双侧ICR继发重度骨性Ⅱ类错畸形伴上牙弓狭窄的病例,进行下颌双侧体部牵引成骨（DO）联合上颌手术辅助快速扩弓（SARME）。依照计算机辅助手术模拟（CASS）技术标准流程进行下颌体部DO术模拟,根据临床检查及影像学检查,设计牵引方向及距离。在T0、T1、T2及T3分别进行头颅CT、颞下颌关节（TMJ）问卷、TMJ磁共振、多导睡眠监测（PSG）等检查,从面型、咬合关系、颞下颌关节情况及睡眠呼吸功能4个方面评估手术效果、二期手术必要性及关节稳定性等。结果 纳入病例中,3例已完成全部治疗。下颌体部分别牵引13.0 mm、6.7 mm和8.1 mm,二期颏成形分别前移7.2 mm、0（未做）和11 mm,上颌分别扩弓5.3 mm、7.3 mm和4.9 mm,PSG数据显示重度阻塞性睡眠呼吸暂停低通气综合征（OSAHS）痊愈。最终面型及咬合关系均达到预期,改建期无复发,TMJ亦无明显变化。结论 下颌体部DO联合SARME,可有效纠正双侧ICR继发重度骨性Ⅱ类错畸形伴上牙弓狭窄。运用CASS技术进行手术设计及模拟,可有效预计牵引方向及距离,使治疗效果及稳定性更加可靠。     

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.     

Postsurgical temporomandibular joint hypomobility: Rehabilitation technique

Specific techniques to treat temboromandibular joint (TMJ) hypomobility caused by capsular restriction are explained. Initially inflammation must be controlled. TMJ manipulation by condylar distraction during opening, protrusion, and lateral movements, and a simple stretching exercise to maintain increased mandibular range of motion, are described. Resistive opening and closing exercises at full opening to relax the lateral pterygoid muscles are prescribed. For all exercises five repetitions, repeated five times per day, are prescribed. These techniques are demonstrated in the successful treatment of a child with a presurgically and postsurgically hypomobile right TMJ.     

同期关节重建及下颌体牵张成骨治疗颞下颌关节强直3例报道

目的:对伴有严重牙颌面畸形的颞下颌关节强直患者,采用自体肋骨软骨移植重建关节,同期运用牵张成骨术行下颌骨牵张成骨延长下颌体长度,治疗下颌后缩和阻塞性睡眠呼吸暂停低通气综合征(OSAHS),评价治疗计划的可行性及短期效果。方法:3例颞下颌关节强直患者,平均年龄17.5岁,发生关节强直的平均年龄为3.6岁,病程平均为13.9a,开口度均为0,均伴有严重牙颌面畸形和OSAHS。根据头影测量结果,预先设计患侧下颌支下降的长度和下颌体延长长度;采用关节成形术加双侧冠突切除,术中取模制备板,进行同期自体肋骨软骨移植重建颞下颌关节和双侧下颌体牵张成骨术。术后第7天开始牵引,每天2次,牵引速率为0.8mm/d。结果:3例患者均顺利完成手术,术后未出现感染等严重并发症。顺利完成牵张成骨。下颌骨牵引长度平均为22.5mm(20.5～25mm)。术后3个月开口度平均为28mm(26～32mm),患者面形及OSAHS获得良好改善。结论:肋骨软骨移植关节重建同期进行下颌体牵张成骨具有良好的稳定性,该设计有利于缩短治疗周期和治疗费用,在短期内可同时解决开口、面形和OSAHS等问题,为后续矫正咬合关系奠定了基础。     

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.     

Microscopic changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible.

PURPOSE: Unilateral mandibular distraction osteogenesis (DO) has been shown to cause gross changes in the mandibular condyle and articular disc. The purpose of this study was to correlate histologic findings with these gross changes in a minipig distraction model. MATERIALS AND METHODS: Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0-day latency and rates of 1, 2, or 4 mm/day for a 12-mm gap. After the minipigs were killed (at 0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested, decalcified, prepared for standard paraffin embedding, and evaluated to determine changes in 1) morphology and thickness of the articular cartilage and subchondral bone and 2) morphology of the disc. RESULTS: In control animals, there were no degenerative changes in the articular cartilage and underlying condylar bone; there were no significant differences in the mean articular cartilage thickness. The temporomandibular joint discs were normal. In experimental animals, distracted condyles showed increasing degenerative changes and mean articular cartilage thickness as the DO rate increased. The discs were thinner. These changes were present, but to a lesser degree, in the contralateral condyles. After 90 days, degenerative changes in the condyles and discs were reduced, after remodeling, except in the 4 mm/day DO group. CONCLUSIONS: Histologic changes in the condyles and temporomandibular joint discs in response to mandibular DO correlated with previously reported gross changes. These changes were greater at higher distraction rates and remodeling back to normal occurred in mandibular condyles distracted at 1 mm/day.     

Histological evaluation of the temporomandibular joint after bilateral vertical ramus mandibular distraction in a canine model

The aim of this pilot study was to histologically evaluate the effect of bilateral vertical mandibular distraction osteogenesis (DO) on the temporomandibular joint (TMJ) in a canine model. Eight male beagle dogs underwent DO, with the placement of single-vector internal distractors. One unoperated animal served as control. After a latency period of 7 days, distraction was performed at a rate of 1 mm a day for an average of 12 days. The animals were divided into two groups (n = 4) and sacrificed after one or two months of consolidation. Eighteen TMJs were prepared for histological evaluation. Control TMJs surfaces were smooth, with no irregularities and trabecular bone was thick and multiply connected. In the one-month group, thinning of the trabecular bone was evident. The trabeculae were long, not multiply connected, parallel to each other and perpendicular to the articular surface. Although overall fibrous-cartilaginous tissues covering the TMJs were maintained with no signs of degenerative changes, one condyle from the one-month group had depressions and erosions of the fibro-cartilage layer and subcortical bone. In the two-month group, overall bone and cartilage architecture was more similar to the control specimens. This study indicates that, in the short term, gross changes can occur in the TMJ after bilateral mandibular vertical ramus distraction. These changes seem to be a process of biological adaptation to the pressure and functional changes secondary to surgery and distraction. However, long-term studies are needed to confirm whether the changes are completely reversible.     

Maintenance of condylar position using an occlusal splint after mechanical vibrating-traction of the TMJ

Although adequate relief of excess mechanical loading to the joint has been accepted as one of the important treatment concepts in the orthopaedic field, a treatment method for the temporomandibular joint (TMJ) to relieve excess mechanical loading has not yet been established. This study aimed to clarify the effect of an occlusal splint on the maintenance of the distracted condylar position achieved by vibrating-traction method. Vibrating dynamic traction force was applied for 5 min to the right TMJ using vibrating-traction apparatus. A flat stabilization splint was adjusted to keep the mandibular position and the condylar displacement was evaluated for 6 h after the dynamic traction procedure. Mean vertical displacement of the mandibular right first molar immediately after the vibrating-traction for the six subjects was 156 microm (ranging from 141 to 179 microm). The calculated mean condylar displacement immediately after the traction was 480 mum and could be kept to be 381 mum even after 6 h by wearing the flat stabilization splint. From the results of this study, it was revealed that the mechanically tracted condylar position could be maintained by a flat occlusal splint. It was suggested that the vibrating-traction method followed by the provision of occlusal support might have a possibility to work as a mechanical relieving procedure for the TMJ.     

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。     

Decreased expression of osteocalcin and osteonectin in relation to high strains and decreased mineralization in mandibular distraction osteogenesis.

In a rabbit model of mandibular distraction osteogenesis, high strains resulted in a substantial reduction in the expression rate of the two osteogenic marker proteins, osteocalcin and osteonectin. In non-distracted samples and mandibles exposed to 2000 microstrains, staining for osteocalcin in the osteotomized area was detected in osteoblasts and diffusely dispersed in the mineralized matrix of the surrounding bone. However, in osteotomized mandibles distracted at strains above physiological levels (200,000 and 300,000 mustrains, respectively) the majority of osteoblast-like cells failed to express immunodetectable amounts of osteocalcin. Similarly, in the extracellular matrix of the distraction area the expression of osteonectin decreased by applying higher strains. Ultrastructural analyses of mandibular samples exposed to hyperphysiological strains revealed that the reduced expression rate of osteocalcin and osteonectin was paralleled by a significant loss of crystal formation, suggesting a functional role of both proteins related to mechanical loading.     

安氏Ⅱ1类患者颞下颌关节三维有限元分析

目的:对比分析安氏Ⅱ¹类错牙合与正常牙合在牙尖交错位紧咬牙时颞下颌关节的应力分布。方法:运用相关软件将志愿者的CT及MRI数据融合,构建个别正常牙合及安氏Ⅱ¹类错牙合颞下颌关节有限元模型,分别对其进行边界约束和力学加载,分析描述两者颞下颌关节各个部位的应力分布。结果:正常牙合两侧颞下颌关节应力分布基本对称,安氏Ⅱ¹类错牙合颞下颌关节的应力分布特征与正常牙合基本一致,但下颌骨、髁突及颞骨关节窝的等效应力值比正常牙合增大;关节盘的等效应力有所下降,但其上下表面的中间带应力值比正常牙合增大。结论:安氏Ⅱ¹类错牙合患者在牙尖交错位时的应力分布增大了其罹患颞下颌关节紊乱病的危险性,应及时矫治为其颞下颌关节提供一良好的生物力学环境。     

Comparative study of the temporomandibular joint space in maximum intercuspation and canine edge-to-edge positions in deep bite and non-deep bite subjects

In order to study the relationship between morphological properties of the TMJ and the mathematically predicted force distribution in the TMJ, the geometric distribution of the joint space on top of the condylar surfaces was evaluated. Seven deep bite subjects and seven non-deep bite subjects were used, and the joint space in the maximum intercuspation and canine edge-to-edge positions was analysed in each group. Standardized images of the TMJ were taken with computed tomography (CT) using a mandible positioner. The comparative ratio of joint space (CRJS) between the maximum intercuspation and the canine edge-to-edge positions was calculated and summarized on the map of the mean morphological outline of the condyle. On the balancing-side condyle, the CRJS of small value was distributed mainly on the anterior edge of the condyle in the non-deep bite group, whereas, in the deep bite group, it was distributed on the centre of the condyle. On the working-side condyle, the small CRJS was distributed around the lateral pole of the condyle in the non-deep bite group, whereas, in the deep bite group, it was found around the posterior part of the condyle. The distribution pattern of CRJS on the upper surface of the condyle in the non-deep bite group was consistent with the results of previous studies on mathematical simulation of TMJ loading. From the results of this study, it was suggested that the distribution of mechanical loading on the TMJ in the eccentric mandibular position would be highly affected by the comparative ratio of joint space. As the comparative ratio of joint space would be highly affected by the condylar position, the analysis of the morphology of the TMJ in relation to mechanical joint loading, in a future investigation, should be carried out on specific mandibular positions in relation to the function of the TMJ to be studied.     

Gap arthroplasty combined with distraction osteogenesis in the treatment of unilateral ankylosis of the temporomandibular joint and micrognathia

Our aim was to evaluate the efficacy of simultaneous gap arthroplasty and distraction osteogenesis (DO) in the treatment of unilateral ankylosis of the temporomandibular joint (TMJ) in patients with micrognathia. During the period January 2000-December 2006, 11 patients with unilateral ankylosis of the TMJ and micrognathia were treated with simultaneous gap arthroplasty, mandibular osteotomy, and implantation of a distractor. Mouth opening exercises were started on the first postoperative day and distraction on the fifth postoperative day. All patients had satisfactory mouth opening at follow-up, the mean (range) being 32.4 (28-37) mm in 13 to 58 months' follow-up. Mean length (range) of the mandibular body increased by DO was 12.4 (7-15) mm. Facial asymmetry was corrected and satisfactory occlusions achieved with the help of postoperative orthodontic treatment. We conclude that DO and gap arthroplasty can be used simultaneously in the treatment of patients with ankylosis of the TMJ and micrognathia.