On the development, morphology and function of the temporomandibular joint in the light of the orofacial system.

The temporomandibular joint has a key role in the biocybernetic functional cycle of the orofacial system. It has developed as a "secondary joint" and displays a number of features relating to the articular tubercle, the mandibular condyle, the articular disc, the joint cartilage and the retroarticular pad. The joint cartilage of the mandibular condyle is a primary compensatory growth centre also comprising distant effects. The coordinate course of the mandibular movements is controlled by a complex reflex mechanism and neuronal controller cycles. Morphology, function and clinical aspects are of equal interest to both physicians and dentists.     

Nutrient arteries of the temporomandibular joint: an anatomical and a pathological study

We have identified an artery which is a sub-branch of the inferior alveolar artery, and propose to call it the temporomandibular branch. Mandibular bones of 36 autopsy cases (ages 23-85; 20 males and 16 females) were examined. Contrast media were injected into the inferior alveolar artery, decalcification was conducted, and photographs were taken using soft X-ray equipment (Softex: Nippon Softex, co. CSM type). Then, an examination was conducted concerning sclerosis of these arteries. Next, H.E., Azan, and Pap silver stains were used for microscopic specimens to examine arteriosclerosis of the temporomandibular joint. The artery that sub-branches toward the temporomandibular branch, branches out immediately after the inferior alveolar artery and enters the mandibular foramen, becoming the artery that supplies the temporomandibular joint. This temporomandibular branch travels slightly downward, forward of the inferior alveolar artery, and turns back toward the mandibular base. It advances to the mandibular joint almost directly. The route taken was classified into three types. Toward the head of the mandible, the temporomandibular branch, after passing over the neck of the mandible, divides into two sub-branches, anterior and posterior. In our pathological study of the temporomandibular branch, there were a small number of cases with slight intimal thickening and mild elastosis. As regards sclerotic changes, particularly in cases more than 50 years old. There were very few cases showing intimal changes. Sclerotic changes of the artery supplying the head of the mandible increase with age. The same can be said of the about the constriction rate. These findings correlated with subject age.     

偏侧咀嚼对颞颌关节影响的超微结构研究

目的　观察单侧后牙缺失偏侧咀嚼不同时期对双侧颞颌关节 (temporomandibularjoint,TMJ)的致病作用及其病理特征。方法　采取拨除Wistar雄性大鼠右侧上、下颌磨牙 ,人为造成偏侧咀嚼的动物模型 ,分别用于光镜、扫描电镜和透射电镜观察。结果　实验组TMJ出现明显的退行性改变。颞颌关节盘的胶原纤维及髁突骨小梁均出现裂隙 ,超微结构亦有明显变化。结论　长期偏侧咀嚼可引起TMJ发生病理性改变     

Influence of unilateral disc displacement on the stress response of the temporomandibular joint discs during opening and mastication

The temporomandibular joint plays a crucial role in human mastication acting as a guide of jaw movements. During these movements, the joint is subjected to loads which cause stresses and deformations in its cartilaginous structures. A perfect balance between the two sides of the joint is essential to maintain the physiological stress level within the tissues. Therefore, it has been suggested that a derangement of the joint is a contributing factor in the development of mandibular asymmetry, especially if problems of the temporomandibular joint start in childhood or adolescence. To analyze the movement of the mandible and the stresses undergone by the discs, two finite element models of the human temporomandibular joint including the masticatory system were developed, one corresponding to a healthy joint and the other with a unilateral anterior disc displacement with their movement controlled by muscle activation. A fibre-reinforced porohyperelastic model was used to simulate the behaviour of the articular discs. The stress distribution was analyzed in both models during free opening and closing, and during the introduction of a resistant force between incisors or molars. It was found that a slight unilateral anterior disc displacement does not lead to mandibular asymmetry but to a slight decrease of the maximum gape. With the introduction of a restriction between incisors, the maximum stresses moved to the anterior band in contrast to what happened if the restriction was imposed between molars where maximum stresses were located more posteriorly. Finally, the presence of a unilateral displacement of the disc involved a strong change in the overall behaviour of the joint including also the healthy side, where the maximum stresses moved to the posterior part.     

Arrangement of D-periodic collagen fibrils and association of proteoglycans with fibrils in the synovium of the mouse temporomandibular joint

The present study was performed to examine changes in the arrangement of D-periodic collagen fibrils in the synovium of the growing temporomandibular joint in mice. At 1 week of age, the mandibular condyle was undeveloped, and only a few collagen fibrils were recognizable in the subintimal layer of the synovium. At 8 weeks, the mandibular condyle was structurally developed with an increase of collagen fibrils in the synovium; a fully mature condyle was observed at 6 months of age. The close association of proteoglycans with collagen fibrils in the synovium of the growing joint was examined by both conventional and energy-filtering transmission electron microscopy of cupromeronic blue-stained specimens. Proteoglycans were associated with D-periodic collagen fibrils in the short filamentous form in random fashion at 1 week of age, but in a regular pattern with D-periodicity at 6 months. These associations in the synovium could be correlated with the mechanical character of the temporomandibular joint.     

颞下颌关节的观测

本文在２０９具成年标本上对颞下颌关节的下颌窝、下颌头、关节盘及关节囊进行了观测;对颞下颌关节的运动及弹响机制进行了讨论。     

颞下颌关节韧带的断层影像解剖研究

目的：通过cT和MRI扫描,明确颞下颌关节韧带的形态、结构及其断层影像解剖特点。方法：选取60名健康志愿者分别行颞下颌关节CT、磁共振检查,观察颞下颌关节韧带的断层影像解剖特点。结果：颞下颌关节在cT图像中显示韧带呈等密度影,而钙化的韧带呈高密度影;在磁共振T1WI和T2WI图像中,翼下颌韧带、蝶下颌韧带、茎突下颌韧带、颞下颌韧带、下颌锤骨韧带（关节盘锤骨韧带）均显示为结构清晰的低信号影像,骨皮质在T1WI及T2WI图像中均显示为结构清晰的低信号影像,骨髓质均显示为结构清晰的高信号影像。结论：CT、磁共振成像可清楚地显示颞下颌关节韧带的断层影像解剖结构。     

广东地区人群颞下颌关节解剖参数的三维分析

目的 对广东地区不同人群的下颌骨及髁突解剖参数进行三维分析。 方法 选取就诊于南方医科大学口腔医院的患者265名,利用CBCT分别测量男性和女性的髁突长度、髁突高度、下颌升支高度、下颌体高度以及下颌神经进入下颌升支的位置。 结果 所有患者髁突的平均长度（内极-外极）二维测量为19.2 mm、三维测量为20.3 mm,男性比女性长3.6 mm,两者之间无统计学差异。下颌骨高度、髁突高度和下颌升支高度分别为59.6 mm,22.8 mm和38.3 mm,其中下颌骨高度男性比女性长6.4 mm,两性之间有统计学差异。下颌升支的宽度、下颌小舌到升支前缘的距离和下颌小舌到升支后缘的距离分别为：29.4 mm,14.8 mm及14.6 mm,男女之间均无统计学差异。 结论 CBCT测量颞下颌关节有着更显著的准确性,本实验结果丰富了中国人群下颌骨解剖数据,有助于开发适合广东地区的人工颞下颌关节。 【关键词】 下颌骨; 髁突; CBCT; 人工颞下颌关节     

Functional condition of the mandible: physical structures of free mandibular movement.

Starting with the physical definition of the concept "mobile hinge axis", which only allows 2 degrees of freedom for planar mandibular movement, it will be shown that the hinge axis of the temporomandibular joint cannot be found with a small mouth-opening rotation, as is usual but erroneous. By recording cyclic mandibular movements with a measuring system which itself possesses 6 degrees of freedom, the mobile hinge axis can be found. However, there are patients which do not use a mobile hinge axis, which is indicative of latent functional disturbances of the neuromuscular system.     

下颌骨单侧前上牵引对大鼠颞下颌关节的影响

目的建一种下颌骨单侧前上牵引的大鼠动物模型,以模拟正畸不对称牵引治疗和关节外因素造成的颞下颌关节病,并研究其颞下颌关节盘和髁状突受力后表面超微结构的改变。方法利用外科手术方法在24只SD大鼠左侧下颌角与同侧颧弓前区置入镍钛拉簧,手术不破坏关节区。对照组8只,在下颌角和颧弓区分别用钢丝结扎,但不放置弹簧。弹簧施加的牵引力分别为120g和40g,使下颌骨受到前上方向的持续牵引力,在手术后3、7、14、28d安乐死法处死动物。关节盘和髁状突进行扫描电镜检查。结果本实验成功建立了下颌骨偏移导致颞下颌关节改变的大鼠动物模型。相对于对照组,实验组的加力侧和对照侧颞下颌关节均有不同程度的病理变化。关节盘病变较轻,髁状突病变以轻力组对照侧为重。结论下颌骨单侧前上牵引的大鼠动物模型可以部分模拟关节外不对称因素造成的颞下颌关节改建和病变：包括嚼肌功能紊乱、单侧的颌面肌肉挛缩、疤痕收缩以及正畸不对称牵引治疗等。     

Inconsistency of the maxilla and mandible in the Minatogawa Man No. 1 hominid fossil evaluated from dental occlusion

The Minatogawa man hominid fossils are human fossils from Japan and the oldest from the Late Pleistocene period. Of the Minatogawa skeletal remains, Minatogawa Man No. 1 is best preserved and is accompanied by the mandible. When the maxillary and mandibular dentitions of Minatogawa Man No. 1 were occluded, the dentitions did not align with one another. The attrition pattern of the maxillary teeth was of an inclined type, which tilted from the buccal to lingual side, whereas that of the mandibular dentition was of a horizontal type. Moreover, both left maxillary and mandibular third molars exhibited attrition on the distal portion of the occlusal surface. The occlusal surfaces did not complement each other in the range of mandibular movement without temporomandibular joint dislocation and the curve of Spee produced by the left maxillary and mandibular occlusal planes did not match. These findings suggest that the maxilla and mandible of Minatogawa Man No. 1 are, in fact, from different individuals.     

Functional state of the mandible and rolling-gliding characteristics in the TMJ.

For the physiological intact stomatognathic system, the three main functional states (occlusat articular functions, free mandibular movements, and ideal bolus function) were biomechanically discussed concerning the structure of movement, rolling-gliding characteristics, and force transfer in the temporomandibular joint (TMJ). In all three cases, rolling is not possible in the TMJ since the instantaneous rotational axis is positioned outside of the joint-rolling is not necessary because the TMJ is not loaded by appreciable forces. In the aged stomatognathic system with a lost discus and considerable Loads in the TMJ, however, the attrition of the joint is eased by rolling movement at the articulating surfaces. The destruction of the discus can be seen as a physiological adaptation which brings back the joint to an original odontogen condition.     

Positional relationships between the masticatory muscles and their innervating nerves with special reference to the lateral pterygoid and the midmedial and discotemporal muscle bundles of temporalis

For an accurate assessment of jaw movement, it is crucial to understand the comprehensive formation of the masticatory muscles with special reference to the relationship to the disc of the temporomandibular joint. Detailed dissection was performed on 26 head halves of 14 Japanese cadavers in order to obtain precise anatomical information of the positional relationships between the masticatory muscles and the branches of the mandibular nerve. After complete removal of the bony elements, the midmedial muscle bundle in all specimens and the discotemporal muscle bundle in 6 specimens, derivatives of the temporalis, which insert into the disc were observed. On the anterior area of the articular capsule and the disc of the temporomandibular joint, the upper head of the lateral pterygoid, the midmedial muscle bundle of temporalis and the discotemporal bundle of temporalis were attached mediolaterally, and in 3 specimens the posterosuperior margin of the zygomaticomandibularis was attached to the anterolateral area of the disc. It is suggested that these muscles and muscle bundles contribute to various mandibular movements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observed in the present study, relative positional relationships of the muscles and muscle bundles and of nerves of the mandibular nerve are consistent. A possible scheme of the developmental formation of the masticatory muscles based on the findings of the positional relationships between the muscles and the nerves is presented.     

The human temporomandibular joint region in different positions of the mandible.

The anatomy of the human temporomandibular joint region has been investigated mainly under the conditions of dental occlusion. The aim of the present study was to elucidate the topographical situations in other functional positions such as wide-open mouth, protrusion and lateral displacement. The respective mouth positions were adjusted before fixation and controlled by magnetic resonance tomography. The temporomandibular joint regions were embedded in epoxy resin, and cut serially in the sagittal or the frontal plane. WIDE OPEN MOUTH: The articular disc lies with its intermediate zone between the articular tubercle and the dorsal convexity of the condylar process, and thus adapts the articulating surfaces of the bones perfectly to each other. Massive enlargement of the retroarticular cushion is seen, whereas the loss connective tissue on the anterior side of the joint appears completely compressed. PROTRUSION: The disc lies with its intermediate zone between the convexities of the condylar process and the articular eminence. On the lateral side it appears to be compressed between mandible and temporal bone. The retroarticular cushion is moderately enlarged. The anterior compartment of loose connective tissue is smaller than in occlusion. LATERAL DISPLACEMENT: On the working side the articular disc is in a stabilized position between the bony joint elements. The balancing condyle is in a protruded position with the retroarticular cushion reaching into the dorso-lateral half of the mandibular fossa. CONCLUSION: Protrusion appears as the position with the highest mechanical stress upon the articular disc.     

Elements of a general theory of joints. 6. General kinematical structure of mandibular movements.

Movements of the mandible are recorded in vivo by a measuring system (MT 1602) that takes all 6 degrees of freedom of a rigid body into account. Class-I-patients were asked to move their mandible in the sagittal-vertical plane. The evaluation of the measurements yields an almost plane mandibular movement that only uses 2 degrees of freedom although a general plane movement normally possesses 3 degrees and although the human temporomandibular joint (TMJ) has a certain space of motion. This quantitative reduction of the degrees of freedom by one is produced by a neuro-muscularly guided dimeric link chain that cannot directly be related to anatomical landmarks. The diverse types of mandibular motion of a sound patient differ in the constant ratio of the angular velocities around the 2 axes of the dimeric link chain. Therefore, the paths of the individual mandibular points are epicycloids or hypocycloids. Patients with disorders of the TMJ and the neuromuscular feedback system do no longer show this constancy of the angular velocities' ratio. Besides that, we theoretically derive and empirically prove the fact that common axiographs do not record the "path of the hinge axis" of the TMJ, on principle. In this context we discuss some--in dentistry and anatomy widespread--fundamental misconceptions of the rigid body's kinematics.     

中国全新世女性颞下颌关节尺寸的时代变化*

目的：研究中国全新世女性颞下颌关节测量性状的时代变异问题。方法：对中国北方地区新石器时代 （47 例）、青铜铁器时代（112 例） 和近代（26 例） 成年女性13 项颞下颌关节测量性状进行测量, 并运用 SPSS19.0 软件对各时代测量性状数据进行平均值计算和不同时代间差异的假设检验。结果：髁突、冠突在全新世 厚度变薄,髁突的变薄主要在新石器- 青铜铁器时代,冠突的变薄主要在青铜铁器- 近代。髁突面积在全新世缩小, 尤其在青铜铁器时代- 近代缩小的幅度更大。下颌窝深度在全新世变化不大。髁突面积/ 下颌窝面积缩小,其变化 主要发生在新石器- 青铜铁器时代。结论：全新世女性颞下颌关节仍在进化,女性颞下颌关节的演变特点与男性 颞下颌关节有相似之处,也有差异。     

Development of the human sphenomandibular ligament.

The development and arrangement of the sphenomandibular ligament of 60 human embryos and fetuses were studied. Meckel's cartilage appeared as a single, continuous fibrous structure lying between the mandibular lingula and the malleus of the middle ear in fetuses of 210 mm crown-rump length (22 weeks of age) and over. This structure constitutes the malleolomandibular ligament, and two clearly differentiated portions bound by the tympanosquamosal fissure could be seen: a juxtaarticular portion, inserted on the posterior edge of the interpterygoid aponeurosis, and a tympanic portion, onto which the disc of the temporomandibular joint inserted. Some of the authors consider that if tension is applied to the sphenomandibular ligament this may injure the middle ear. The anatomical arrangement of the sphenomandibular ligament could explain these injuries.     

Effects of condylar fibrocartilage on the biomechanical loading of the human temporomandibular joint in a three-dimensional,nonlinear finite element model

The present study was undertaken to test a hypothesis that the addition of articular fibrocartilage in the condyle of the temporomandibular joint reduces three-dimensional stress distribution in the condyle, the disc and articular eminence. A three-dimensional, nonlinear finite-element model was developed for analysis of joint loading before and after the addition of condylar fibrocartilage to the osseous mandibular condyle reconstructed from spiral computer topography data. In the model, each of the disc, condyle and articular eminence was arbitrarily divided into five regions: the anterior, posterior, medial, lateral and central. Von Mises stresses that in virtually all regions of the disc, condyle and articular eminence became lower after the addition of condylar fibrocartilage. Especially remarkable was the approximately four-fold reduction in von Mises stresses in the anterior, central and medial regions of the mandibular condyle. In comparison, only slight to moderate stress reductions occurred in the disc and articular eminence, suggesting that condylar fibrocartilage absorbs considerable stresses and likely dampens more loads than the disc and articular eminence. The mandibular condyle demonstrated the largest total displacement in all directions after the addition of articular fibrocartilage, followed by the disc and articular eminence. We conclude that the addition of articular fibrocartilage primarily reduces loading of the mandibular condyle, rather than the disc and articular eminence. These findings lead to a hypothesis that the mandibular condyle more likely functions as a shock absorber than the disc.     

Lubrication of the Temporomandibular Joint

Although tissue engineering of the temporomandibular joint (TMJ) structures is in its infancy, tissue engineering provides the revolutionary possibility for treatment of temporomandibular disorders (TMDs). Recently, several reviews have provided a summary of knowledge of TMJ structure and function at the biochemical, cellular, or mechanical level for tissue engineering of mandibular cartilage, bone and the TMJ disc. As the TMJ enables large relative movements, joint lubrication can be considered of great importance for an understanding of the dynamics of the TMJ. The tribological characteristics of the TMJ are essential for reconstruction and tissue engineering of the joint. The purpose of this review is to provide a summary of advances relevant to the tribological characteristics of the TMJ and to serve as a reference for future research in this field. This review consists of four parts. Part 1 is a brief review of the anatomy and function of the TMJ articular components. In Part 2, the biomechanical and biochemical factors associated with joint lubrication are described: the articular surface topology with microscopic surface roughness and the biomechanical loading during jaw movements. Part 3 includes lubrication theories and possible mechanisms for breakdown of joint lubrication. Finally, in Part 4, the requirement and possibility of tissue engineering for treatment of TMDs with degenerative changes as a future treatment regimen will be discussed in a tribological context.     

Expression of caveolin-1 in the rat temporomandibular joint

This immunocytochemical study revealed the expression of caveolin-1, a major protein of caveolae, in the rat temporomandibular joint. In the synovial lining layer, immunoreactive products for caveolin-1 were detected on the cell membrane of the fibroblast-like type B cells, as confirmed by immunocytochemistry for heat shock protein 25. The cells in the articular disk, the articular layer, and zone of proliferation of the mandibular condyle also showed intense immunoreactions for caveolin-1.