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.     

Centers of rotation during jaw movements

Anatomists consider the articulation of movable joints to be complex, involving movable instantaneous centers of rotation (ICR). However, prosthodontists often treat the temporomandibular joint (TMJ) as a model of a simple hinge. The aim of this study was to examine the case for a movable ICR during habitual opening and closing jaw movements. Young, dentate subjects were examined with a kinesiograph. Jaw movements were performed and recorded. The center of rotation of each movement pattern was identified, and its location related to the position of the TMJ. The results showed that opening and closing jaw movements were predominantly non-coincident, with a movable ICR located at a variable distance and direction from the TMJ. There was no evidence to suggest that the TMJ functioned as a simple hinge during jaw movements.     

Synovial fluid dynamics with small disc perforation in temporomandibular joint

Summary The articular disc plays an important role as a stress absorber in joint movement, resulting in stress reduction and redistribution in the temporomandibular joint (TMJ). The flow of synovial fluid in the TMJ may follow a regular pattern during movement of the jaw. We hypothesised that the regular pattern is disrupted when the TMJ disc is perforated. By computed tomography arthrography, we studied the upper TMJ compartment in patients with small disc perforation during jaw opening–closing at positions from 0 to 3 cm. Finite element fluid dynamic modelling was accomplished to analyse the pattern of fluid flow and pressure distribution during the movements. The results showed that the fluid flow in the upper compartment generally formed an anticlockwise circulation but with local vortexes with the jaw opening up to 2 cm. However, when the jaw opening–closing reached 3 cm, an abnormal flow field and the fluid pressure change associated with the perforation may increase the risk of perforation expansion or rupture and is unfavourable for self‐repair of the perforated disc.     

Jaw closing movement and sex differences in temporomandibular joint energy densities

Energy densities (ED, mJ/mm³) quantify mechanical work imposed on articular cartilages during function. This cross‐sectional study examined differences in temporomandibular joint (TMJ) ED during asymmetric versus symmetric jaw closing in healthy females versus males. ED component variables were tested for differences between and within sexes for two types of jaw closing. Seventeen female and 17 male subjects gave informed consent to participate. Diagnostic criteria for temporomandibular disorders and images (magnetic resonance (MR), computed tomography) were used to confirm healthy TMJ status. Numerical modelling predicted TMJ loads (F_normal) consequent to unilateral canine biting. Dynamic stereometry combined MR imaging and jaw‐tracking data to measure ED component variables during 10 trials of each type of jaw closing in each subject's TMJs. These data were then used to calculate TMJ ED during jaw closing asymmetrically and symmetrically. Paired and Student's t tests assessed ED between jaw closing movements and sexes, respectively. Multivariate data analyses assessed ED component variable differences between jaw closing movements and sexes (α = 0.05). Contralateral TMJ ED were 3.6‐fold and significantly larger (P < .0001) during asymmetric versus symmetric jaw closing, due to significantly larger (P ≤ .001) distances of TMJ stress‐field translation in asymmetric versus symmetric movement. During asymmetric jaw closing, contralateral TMJ ED were twofold and significantly larger (P = .036) in females versus males, due to 1.5‐fold and significantly smaller (P ≤ .010) TMJ disc cartilage volumes under stress fields in females versus males. These results suggest that in healthy individuals, asymmetric compared to symmetric jaw closure in females compared to males has higher TMJ mechanical fatigue liabilities.     

Implant-supported mandibular splinting affects temporomandibular joint biomechanics

Objectives: Mandibular functional movements lead to complex deformations of bony structures. The aim of this study was to test whether mandibular splinting influences condylar kinematics and temporomandibular joint (TMJ) loading patterns. Materials and methods: Six subjects were analyzed by means of dynamic stereometry during jaw opening–closing with mandibles unconstrained as well as splinted transversally by a cast metal bar fixed bilaterally to two implant pairs in the (pre)molar region. Statistical analysis was performed by means of ANOVAs for repeated measurements (significance level α=0.05). Results: Transversal splinting reduced mandibular deformation during jaw opening–closing as measured between two implants in the (pre)molar region on each side of the mandible significantly by 54%. Furthermore, splinting significantly reduced the distance between lateral condylar poles (average displacement vector magnitude of each pole: 0.84±0.36 mm; average mediolateral displacement component: 45±28% of the magnitude) and led to a medial displacement of their trajectories as well as a mediolateral displacement of stress‐field paths. Conclusions: During jaw opening–closing, splinting of the mandible leads to a significant reduction of mandibular deformation and intercondylar distance and to altered stress‐field paths, resulting in changed loading patterns of the TMJ structures. To cite this article:
Zaugg B, Hämmerle CHF, Palla S, Gallo LM. Implant‐supported mandibular splinting affects temporomandibular joint biomechanics.
Clin. Oral Impl. Res. 23 , 2012; 897–901
doi: 10.1111/j.1600‐0501.2011.02241.x     

Stress analysis during jaw movement based on vivo computed tomography images from patients with temporomandibular disorders

The purpose of this study is to develop three-dimensional (3D) finite element models of temporomandibular joints (TMJs) and to investigate stress distributions. To determine the causes of temporomandibular disorders (TMDs), the magnitude and location of the maximum stresses under physiological loading must be considered. Stress analysis TMD models were reconstructed from computed tomography (CT) data. Several studies have investigated finite element TMJ models, but few have used a bilateral mandible model that includes jaw closing and maximum opening. In this study, the authors defined an asymmetry index for the different stress values on each side joint; this index has not yet been investigated. According to clinical observation, one joint affects the other side joint during mastication. Three symptom-free volunteers and three symptomatic patients were selected as the control group (CG) and TMD group (TG), respectively. For the TG, data analysis indicated that the condyle was asymmetrical during jaw closing, while both the condyle and disc were slightly asymmetrical during jaw opening. The maximum stresses did not significantly differ between the CG and TG for either closing or opening of the jaw. The results of this study have a potential clinical benefit in terms of proving superior biomechanical behaviour.     

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.     

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.     

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.     

肋骨移植治疗生长期患者单侧颞下颌关节强直合并颌骨畸形效果评价

目的 评价肋骨移植治疗生长期患者单侧颞下颌关节强直合并颌骨畸形的效果。方法 对2010年1月—2014年12月采用肋骨移植同期治疗单侧颞下颌关节强直合并颌骨畸形的生长期患者进行CT影像学分析,采用ProPlan CMF 1.4软件对术前、术后1周和随访1年以上的下颌支高度、肋骨长度和颏点偏斜程度进行测量和比较。采用SPSS 17.0软件包对数据进行配对t检验。结果 6例患者纳入研究,年龄3~7岁,平均5岁。肋骨术后平均延长下颌支高度6.2 mm,颏点偏斜平均矫正5.3 mm;术后平均随访2.7 a,肋骨平均生长6.9 mm,健侧下颌支平均生长4.4 mm,患侧4.3 mm（P>0.05）。结论 肋骨移植可以同期治疗颞下颌关节强直及合并的颌骨畸形,具有生长潜能,但是长期效果有待于进一步观察。     

Correlation of clinical parameters to the arthrographic depiction of temporomandibular joint internal derangements

This prospective clinical investigation of 188 patients with signs and symptoms of temporomandibular joint (TMJ) pain and dysfunction examines the correlation between clinical signs and symptoms versus the arthrographic characteristics of intracapsular disease related to displacement of the meniscus. An attempt has been made to establish which specific clinical signs and symptoms, as determined by arthrography, best predict the condition of the joint. Our findings suggest that most of the clinical signs and symptoms are not sufficiently reliable in themselves to permit prediction of the condition of the meniscus. Those clinical parameters that did show a strong correlation were tested in combinations using stepwise discriminant analysis to evaluate clinical tendencies. Thus, patients with normal meniscal position and function were often noted to have normal mandibular ranges of movement, no joint noises on opening and closing of the jaw, and no tomographic evidence of degenerative joint disease. Subjects with meniscal displacement with reduction were often found to have joint clicking, deviation of the jaw upon opening, and an absence of degenerative joint disease by multidirectional tomography. Patients who had meniscal displacement without reduction were often found to have limitation in jaw movement, crepitation on opening and closing of the jaw, and associated degenerative changes on multidirectional tomograms. If specific treatment plans are to be tailored for different stages of TMJ internal derangements, clinical findings alone or clinical findings in conjunction with plain radiographs of the TMJ are not consistently accurate.     

翼外肌在创伤性颞下颌关节强直中的作用机制研究

目的 揭示翼外肌在创伤性颞下颌关节（temporomandibular joint, TMJ）强直发病中的作用机制。 方法 本研究纳入6个月大的雄性绵羊8只,双侧髁突均通过手术建立复合创伤继发TMJ强直动物模型,即手术造成双侧髁突矢状骨折、关节盘移位及关节窝损伤。此外,左侧切除部分翼外肌作为实验组,右侧保留翼外肌作为对照组。术后12周,通过用大体观察、螺旋CT扫描、Micro-CT扫描、组织学观察等方法对TMJ样本进行评估与分析。 结果 肉眼观察可见：对照组发生了TMJ骨性强直而实验组仅仅是纤维强直。螺旋CT和Micro-CT结果显示：与实验组相比,对照组关节面粗糙、有新骨形成并突入到关节腔内,且关节腔内有钙化的骨痂形成;对照组髁突的最大内外径和前后径均明显大于实验组（P＜0.05）;Micro-CT扫描结果还显示：对照组新生骨小梁的方向与翼外肌牵拉方向一致,而实验组无此特征。组织学结果也印证了对照组关节内发生了纤维-骨性强直,而实验组仅为纤维强直。 结论 在髁突矢状骨折的愈合过程中,翼外肌发挥了类牵张成骨的作用,从而参与创伤性TMJ强直的发生。     

最大闭口咬合状态下颞下颌关节的接触特征分析

目的研究颞下颌关节在最大闭口咬合状态下的接触方式和应力分布。方法用可视化人体图像数据先建立颞下颌关节的三维实体模型,在Marc中再进行有限元模型的建立,定义髁状突、关节盘、关节窝三者之间的接触关系,观察其接触特征。结果在最大闭口咬合接触下,髁状突先与关节盘后带与双板区交界处发生接触,同时,关节盘相对髁状突作向前滑动,髁突的等效应力值大于关节盘,而关节窝的应力水平最小。结论在最大闭口咬合状态下,关节盘后带与双板区的交界处以及中间带均为重要的应力缓冲区域。     

Non-surgical treatment of sports-related temporomandibular joint disorders in basketball players

Abstract –  In this study, 18 basketball players (11 female, seven male; age range 14–32 years) with temporomandibular joint (TMJ) problems who had a history of sport injuries related to head or jaw region were evaluated and the results of the treatment were presented. A standardized functional examination of the masticatory system was performed including measurement of maximal jaw movements, recording of joint sounds, pain on movement of the jaw as well as tenderness to palpation of the both TMJ or masticatory muscles. Patients were also evaluated periodontally. Diagnosis was made according the criteria, described by Okeson, and appropriate treatment was applied using different kind of splints. At the end of treatment only one patient continued with right TMJ reduction with slight pain. Except for that patient, none of the patients had pain after treatment. The maximum opening of the jaws and the maximal jaw movements were statistically increased after treatment. Patients with TMJ problems also showed periodontal problems, most likely due to inadequate oral hygiene because of the limited jaw movements and pain. Periodontal parameters including probing depth (PD), Plaque index (PI), and Sulcus Bleeding Index (SBI) improved after treatment. Sports-related TMJ injuries may result in complex problems such as pain, TMJ sounds, limitation in maximal jaw movements and maximum opening of the mouth, difficulty in chewing. With the appropriate diagnosis this could be treated non-surgically in 6–8 months. This study also showed that the TMJ disorders may cause periodontal problems, which may affect all teeth and also the general health of the athlete.     

Osteoblastic activity of the rabbit temporomandibular joint during distraction osteogenesis assessed by [18F]fluoride positron emission tomography

The purpose of the study was to evaluate the effects of irradiation and hyperbaric oxygenation (HBO) on osteoblastic activity of the temporomandibular joint (TMJ) region during mandibular distraction osteogenesis. Unilateral distraction was performed on 19 rabbits, which were divided into five groups. One group served as a control group, while the others received either high- or low-dose irradiation in the TMJ region before surgery. Some of the animals were also given HBO 18 times at 2.5 ATA x 90 min preoperatively. Osteogenesis was assessed by [18F]fluoride positron emission tomography at the end of the distraction. Osteoblastic activity was higher on the distracted side in all groups, except in the high-dose irradiated group without preceding HBO. HBO increased osteogenesis on both sides after radiotherapy. It is concluded that increased osteoblastic activity reflects increased pressure on the TMJ region of the distracted side, resulting from lengthening. It seems that more remodeling is required after irradiation than without preceding radiotherapy. After radiotherapy, HBO increased osteoblastic activity.     

Biomechanical calculation of human TM joint loading with jaw opening

A three-dimensional, static mathematical calculation of the stomatognathic system was done to predict total temporomandibular joint (TMJ) loading at different levels of jaw opening. The model assumed that muscle forces acting on the mandible could be simulated by a combination of contractile components (CCs) and elastic components (ECs) and that static equilibrium existed within the body of the mandible. The model also imposed the constraint that any generated joint reaction force would act on the centre of the condyle. The results of the model demonstrated that under all conditions of opening and for all values of the elastic modulus selected, the forces between the TMJ condyle and the articular eminence were compressive in nature. The compressive force magnitude increased from 2.7 to 27.6 N incrementally as the jaw opened from 10 to 40 mm. Overall data in this study indicated that the TMJ tissues undergo low levels of compression at open positions up to 40 mm. Finally, the condition of trismus (increased jaw closing activation with opening) was simulated, the joint reaction force at 20 mm opening increased from 7.7 to 64.9 N with only a 20% activation of the closers.     

A Retrospective Study on the Clinical Results of Temporomandibular Joint Surgery

A retrospective study on the results of temporomandibular joint (TMJ) surgery was performed in 74 patients with total menisectomy, 90 patients with partial menisectomy with disk repair, and 66 patients with arthroscopic lysis of adhesion and lavage of the joint space. TMJ pain during jaw movement, TMJ noise and maximum jaw opening was evaluated one year after surgery. TMJ pain and TMJ noise were significantly reduced by all three procedures. However, TMJ clicking was more significantly observed in patients with arthroscopy. Maximum jaw opening was significantly increased by all three procedures. However, maximum opening of patients with total menisectomy was significantly smaller than in the other two procedures.     

Influence of distraction rates on the temporomandibular joint position and cartilage morphology in a rabbit model of mandibular lengthening

PURPOSE: Although various aspects of bone formation during distraction osteogenesis have been studied extensively, there are only limited experimental data concerning the influence of mandibular distraction rates on structural alterations in the temporomandibular joint (TMJ). In this study, a rabbit model of unilateral mandibular distraction was used to test the effects of various strain schedules on the position and morphology of the TMJ. MATERIAL AND METHODS: Fifty-two immature white female rabbits were used. The distraction procedure was performed using physiologic (2,000 microstrains, 1 per day) and elevated strain magnitudes (20,000 microstrains, 1 per day), as well as high strain magnitudes (200,000 and 300,000 microstrains, 1 per day). The investigation of the TMJ included clinical, radiologic, and histologic aspects. RESULTS: Clinical and radiologic examinations at the end of the distraction period showed no evidence of joint luxation even at maximal distraction rates. Histologic and ultrastructural analyses revealed a positive correlation between the degree of mechanical loading and the development of degenerative alterations in the cartilage. In samples distracted at hyperphysiologic strain magnitudes, all cartilaginous layers were reduced in the regions of the TMJ that had been exposed to the higher pressure forces. The fibrous layer became nearly completely destroyed. CONCLUSIONS: These experimental data show that distraction schedules with single but hyperphysiologic loads may lead to degenerative or even early arthrotic changes in the condyle. These data support the principle that distraction protocols should be performed without extensive mechanical loading on the TMJ.     

Timing of temporomandibular joint sounds in orthodontic patients

The consistency of occurrence and also the timing of TMJ sounds during jaw opening and closing were studied by means of an audio-visual sound recording system in an attempt to address the possible causes of temporomandibular joint (TMJ) sounds. From a group of 347 orthodontic patients, 104 were found to have medium- or high-amplitude TMJ sounds during jaw opening or closing. Most patients (53%) had reciprocal clicking--that is, a single sound on opening and on closing; another 12% had multiple sounds on opening or closing; 22% had a single closing sound; and 13% had a single opening sound. Sounds occurred at all degrees of jaw opening throughout this sample, but in most patients opening sounds tended to be closer to maximum opening, whereas closing sounds tended to occur in the middle of the closing movement. No statistically significant association was found between the timing of the opening and closing sounds. In 42.3% of patients, the sound was inconsistent in its occurrence on successive opening and closing cycles. Twenty-three percent of patients reported pain, jaw locking, or limitation of movement, but these were not associated with the timing of the opening sound. The findings suggest that the reciprocal click, widely associated with anterior disc displacement with reduction, was relatively common, but that other explanations for the joint sounds should also be considered. Conversely, a large variation may exist in the timing and the occurrence of sounds in patients with anterior disc displacement in the absence of pain and limitation of movement.     

Healing following conventional and cryosurgical discoplasty in the monkey temporomandibular joint

The techniques of conventional discoplasty and the scar producing potential of cryosurgical treatment of the bilaminar region were examined in a study of 17 adult female cynomologous monkeys. Temporomandibular joint (TMJ) tissues were obtained at four and 10 days, four, 20, 52, and 78 weeks after surgery, and compared to TMJ tissues in unoperated control animals. No clinically observable changes in weight, occlusion, or jaw function were identified. All the surgical sites healed normally. At necropsy, lesions of the articular surface of the condyle were apparent in areas that had been surgically "shaved." The anterior, intermediate, and posterior zones of the surgically-treated discs were generally free of change. Two cryosurgically-treated discs showed lesions and perforations. Histologic and autoradiographic observations suggested that the bilaminar area heals quickly with minimal scarring, following both conventional surgical manipulation and cryosurgery. Under the conditions of this experiment the cryosurgical technique was judged not to be superior to the conventional surgical approach.