下颌前突的三维非线性有限元应力分析

下颌前突是最常见的颌面畸形,其下颌骨的力学环境不同于正常人。基于一位下颌前突患者的头部CT片,建立下颌骨的三维有限元模型,关节盘和关节软骨层间考虑接触,对其施加模拟正中咬合的载荷,分析下颌骨不同部位的应力分布特点,为下颌前突的治疗提供参考。结果表明:下颌骨的高应力区出现在乙状切迹和下颌角,分别为13.337MPa和13.850MPa;下颌骨的最大变形发生在颞下颌关节(TMJ)区域。通过与正常人下颌骨的比较,发现下颌骨大部分区域的应力分布较为吻合,但TMJ内的应力分布存在较大的差异,表明下颌前突可能导致TMJ内紊乱症,甚至髁突吸收、关节盘穿孔。可见,除了必要的矫形或手术治疗外,有时还需要针对TMJ进行治疗。     

上颌扩弓对颞下颌关节应力影响的有限元分析

目的 通过三维有限元法对比扩弓前和放置扩弓器时颞下颌关节（temporomandibular joint, TMJ）内部各组织应力分布情况。方法 根据1名上颌牙弓狭窄患者CBCT影像资料，构建扩弓前和包含扩弓器的TMJ三维有限元模型，对模型加载相同的肌力和边界约束，观察TMJ髁突、关节盘、关节窝的等效应力、最大主应力和最小主应力。结果 扩弓前TMJ等效应力主要分布在下颌支前缘、髁突前斜面、关节盘中间带和后带以及关节窝顶部。放置扩弓器时,TMJ应力分布特征与扩弓前基本一致，应力虽然明显增加，但应力分布区域更加均匀；髁突和关节盘应力向前、向外侧移动，髁突后斜面表现出更加均匀的最大主应力分布范围。结论 上颌扩弓器产生的矫形力能够使TMJ应力增加，诱导髁突发生组织改建，协调髁突和关节盘的关系。临床上对于牙弓狭窄的患者应该采用合适的手段进行扩弓矫治。     

不同稳定咬合板厚度对可复性前移位患者颞下颌关节应力分布影响

目的 利用三维有限元方法比较双侧颞下颌关节（temporomandibular joint,TMJ）可复性前移位（anterior disc displacement with reduction,ADDwR）患者在佩戴两种不同厚度稳定性咬合板后紧咬时TMJ应力分布改变。方法 根据患者CT、MRI影像数据,依次构建ADDwR患者牙尖交错位（工况1）与戴3、5 mm稳定咬合板咬合（工况2、3）时共3个TMJ有限元模型。分别给予3种工况中的下颌骨施加最大肌力60 s,之后对各工况中关节窝和髁突软骨表面、关节盘表面及双板区的最大等效应力进行评估。结果 各工况左侧TMJ内各结构等效应力均大于右侧。戴3 mm咬合板后,双侧关节盘均未发生复位,关节盘应力仍旧集中在后带及双板区,双侧关节软骨表面应力显著增加;戴5 mm咬合板后,右侧关节盘复位,关节盘最大应力位于中间带,关节软骨和双板区等效应力降低约40%,左侧关节盘未复位,关节窝软骨和双板区等效应力下降约6%。结论 ADDwR患者佩戴不同厚度咬合板,TMJ内应力及其分布模式均发生改变;5 mm稳定性咬合板可以减小ADDwR患者关节窝软骨及双板区表面应力,关节盘复位有利于缓解ADDwR患者TMJ应力。临床为ADDwR患者选择稳定性咬合板治疗时,在保证舒适前提下,较厚的咬合板可以获得更有利的应力分布。     

正常及关节盘移位后颞下颌关节滑膜OPG/OPGL的表达及意义

目的： 观察正常及关节盘移位后颞下颌关节滑膜内护骨素OPG及其配体OPGL的表达及意义。方法： 32只日本大耳白兔，25只建立颞下颌关节盘前移位的动物模型，术后1、2、4、8、12周处死，5只行模拟手术作为假手术对照，另2只不行手术作为空白对照。取颞下颌关节标本，HE染色观察镜下结构， S-P免疫组化法检测滑膜中OPG和OPGL的表达与分布。结果： 各实验组动物术后体重无减轻，伤口愈合良好，大体及显微镜下观察关节盘明显前移位。对照组OPG主要表达于滑膜下层血管内皮细胞及部分滑膜衬里细胞，滑膜内 OPGL无表达或鲜有表达。关节盘移位后，仅1、2周各1个样本滑膜下层少量OPGL表达，其它样本未见明显OPGL阳性细胞；OPG表达强度无减弱。结论： 正常颞下颌关节滑膜内OPG表达明显强于OPGL，对正常状态骨软骨代谢平衡的维持有重要意义；关节盘移位后OPG和OPGL无明显变化，保证了关节盘移位后骨软骨代谢能维持平衡。     

颞下颌关节盘前移位对髁状突软骨中纤溶酶原激活剂系统表达的影响

目的研究颞下颌关节盘前移位对关节软骨组织中尿激酶型纤溶酶原激活剂（uPA）系统的影响.方法24只日本大耳白兔在不打开关节囊的情况下建立右侧颞下颌关节盘前移位动物模型,分别于术后4、1、2、4、8d和12周各处死4只动物.常规HE染色观察髁突软骨的形态学变化,并以原位杂交法检测髁突软骨细胞中uPA和纤溶酶原激活剂抑制剂-1（PAI-1）的基因表达变化.结果术后髁突受力区出现一过性的软骨变薄、各层排列紊乱等病理变化.uPA和PAI-1基因转录水平在术后即开始上调,至2周时达到最高水平,至12周时基本恢复至正常水平,与髁突软骨的适应性改建相一致.结论颞下颌关节盘前移位后,关节软骨内uPA系统的变化与关节软骨的适应性改建密切相关.     

颞下颌关节骨骼肌肉系统三维有限元模型的构建

目的探讨基于影像学与解剖学构建颞下颌关节(temporomandibular joint,TMJ)骨骼肌肉系统三维有限元模型的可行性,为TMJ生物力学研究提供建模的新思路。方法采集第2代中国虚拟人男性第23号头颅CT图像、咀嚼肌及TMJ关节盘MRI图像,以DICOM格式导入Mimics软件进行三维重建,再通过Geomagic Studio软件配准模型、优化模型及构建关节软骨和关节囊,最后由ANSYS软件定义各组织的材料属性,建立TMJ骨骼肌肉系统的三维有限元模型。结果建立了一个包含关节盘、关节软骨、关节囊、上颌骨(包括颧骨及鼻骨)、下颌骨、颞骨(包括部分顶骨)、蝶骨、上牙列、下牙列、颞肌、咬肌、翼内肌、翼外肌、颞下颌韧带、蝶下颌韧带及茎突下颌韧带的TMJ骨骼肌肉系统的三维有限元模型。结论根据CT、MRI图像和解剖学,利用Mimics、Geomagic Studio及ANSYS可以精确、可行地构建TMJ骨骼肌肉系统的三维有限元模型。模型更加真实还原TMJ的生物力学环境,为TMJ生物力学研究提供新的建模方法,为临床上TMJ疾病的可视化治疗提供仿真平台。     

包含颞下颌关节的下颌骨有限元建模

为获得颞下颌关节下颌骨的应力分布提供更为有效的有限元模型。用Mimics10．0导入正常人的颌面CT建立其下颌各部位的有限元模型,通过CAE软件ABAQUS 6．10进行有限元分析。获得了完整的下颌骨、颞下颌关节有限元模型,及后牙咬合状态下模型各部位应力分布等数据。通过分析数据发现,关节盘高应力区主要集中在关节盘中带和后带,而关节盘各部分应力表现为关节盘颊侧应力高于舌侧,顶部应力高于底部,中带平均应力最大,后带次之,前带最小。     

不同牙 合 位时翼外肌对颞下颌关节盘的生物力学影响

目的　研究在牙尖交错位和最大张口位时可复性关节盘前移位中翼外肌对关节盘的生物力学影响及两牙合 位之间的差异。 方法　对已经建立的可复性关节盘前移位的颞下颌关节数字化仿真模型,在不同牙合 位时进行翼外肌加载,通过三维有限元的方法进行生物力学分析。 结果　最大张口位时,关节盘应力集中区较牙尖交错位时向前外侧移动,集中于关节盘中间带偏外侧区;关节盘中间带与关节盘后带之间存在明显位移差,形成位移撕裂带,而在牙尖交错位时则无类似位移差现象。 结论　在可复性关节盘前移位中,最大张口位时翼外肌可导致关节盘中间带偏外侧区的应力集中,在关节盘中间带形成位移撕裂带,导致此区域变薄、穿孔甚至撕裂。     

不同位时翼外肌对颞下颌关节盘的生物力学影响

目的研究在牙尖交错位和最大张口位时可复性关节盘前移位中翼外肌对关节盘的生物力学影响及两位之间的差异。方法对已经建立的可复性关节盘前移位的颞下颌关节数字化仿真模型,在不同位时进行翼外肌加载,通过三维有限元的方法进行生物力学分析。结果最大张口位时,关节盘应力集中区较牙尖交错位时向前外侧移动,集中于关节盘中间带偏外侧区;关节盘中间带与关节盘后带之间存在明显位移差,形成位移撕裂带,而在牙尖交错位时则无类似位移差现象。结论在可复性关节盘前移位中,最大张口位时翼外肌可导致关节盘中间带偏外侧区的应力集中,在关节盘中间带形成位移撕裂带,导致此区域变薄、穿孔甚至撕裂。     

成人颞下颌关节的矢状张口运动分析

作者采用X线电影摄影技术和运动生物力学研究方法,对14例正常人颞下颌关节的矢状张、闭口运动进行了分析。本文进一步肯定了下颌运动的瞬时运动中心理论,确定了瞬心曲线的形态、位置和趋势,并提出了下颌张口运动的两阶段模式,提供了各标志点的运动轨迹和范围。这些结论对颞下颌关节的理论分析和病理分析,均有参考价值。由于张口运动一开始髁突就向前下滑动,滑动在该阶段约占整个运动的70～86%,而转动仅占14～30%,因此在咀嚼运动中,髁突前斜面与关节结节后斜面通过关节盘,始终保持接触并承受主要的咀嚼压力,故可解释关节窝顶骨板菲薄及髁嵴形成的原因。     

Three-dimensional finite element analysis of human temporomandibular joint with and without disc displacement during jaw opening

The aim of this study was to evaluate the differences of stress distribution in the temporomandibular joint (TMJ) disc during jaw opening between the subjects with and without internal derangement of TMJ (TMJ-ID). Three symptom-free volunteers and three symptomatic patients with anterior disc displacement were selected as normal and TMJ-ID subjects, respectively. For each subject, magnetic resonance images (MRI) were taken in the axial, sagittal and coronal directions. Using MRI taken, six three-dimensional finite element models of TMJ were developed. For each subject, the condylar movements during jaw opening were recorded and used as the loading condition for stress analysis. By comparing the calculated disc displacement to the measured one from MRI, the frictional coefficients were mu = 0.001 for the normal subjects, but mu = 0.01-0.001 for the TMJ-ID subjects. For the normal subjects, relatively high stresses were found at the anterior and lateral portions of the disc throughout jaw opening. In the connective tissues, the stress level was higher in the TMJ-ID than in the normal subjects. It is suggested that the disc displacement induces the change of stress distribution in the disc and the increase of frictional coefficients between articular surfaces, resulting in the secondary tissue damage.     

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.     

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.     

A Surface–Regional and Freeze–Thaw Characterization of the Porcine Temporomandibular Joint Disc

The temporomandibular joint (TMJ) disc is a central element in several TMJ disorders. Tissue-engineered TMJ disc replacements may alleviate discomfort associated with TMJ disorders; however, prior to developing a replacement, a thorough understanding of the native disc must be attained. Toward this end, we developed an unconfined compression, incremental stress relaxation viscoelastic model which simultaneously incorporates the strain increment magnitude and total deformation in the stress relaxation solution. This multiple strain step model was fit to stress relaxation data from (i) 80 test sites from eight porcine TMJ discs for the purposes of a surface–regional characterization and (ii) 30 test sites from five porcine TMJ discs for the purposes of a freeze–thaw characterization. The model estimated viscoelastic parameters accurately and surface–regional variations were detected throughout the TMJ disc. Regionally, the medial and anterior regions have the largest relaxation moduli, and the posterior and anterior regions have the largest instantaneous moduli. The inferior surface was found to have higher instantaneous modulus values than the superior surface. Furthermore, material properties were retained over five freeze–thaw cycles. The results of this study allow for the creation of design and validation criteria for future engineering efforts and shed light on the disc’s role in TMJ function and dysfunction.     

An accurate simulation model of anteriorly displaced TMJ discs with and without reduction

Internal derangement of the temporomandibular joint (TMJ) is defined as an abnormal positional relationship of the disc relative to the mandibular condyle and the glenoid fossa. Among others, the anterior disc displacement is the most common disorder, however its origin and consequences are still unclear. Several finite element simulations of the TMJ have been developed, but none of them has reported dynamic simulations of the disc as a three-dimensional, fiber-reinforced biphasic material under finite deformations, during the opening movement of a pathologic joint affected of an anterior displacement of the disc with and without reduction, using a realistic geometry of the ligaments in the joint. The aim of the work presented here was to compare the stress distribution in the healthy joint and in two pathologic situations, one joint affected of an anterior disc displacement with reduction (ADDWR) and one without reduction (ADDWOR) during an opening movement of the mouth. It was found that, while in the healthy disc the highest compressive stresses were located in the intermediate zone, in the pathologic joints the maximum compressive stresses were located in the posterior band both in the ADDWOR case and in the ADDWR before the reduction. Moreover, although the final stress distribution in the ADDWR was similar to that in the healthy case, the collateral ligaments supported higher stresses, a fact that could lead to degeneration of these components and subsequently to the total anterior displacement of the disc. Finally, the results suggest that an anterior displacement of the disc would lead to higher compressive and tangential stresses in the posterior band of the disc than in the healthy one, and as a consequence, to possible perforations in that zone of the disc which would modify its geometry if no treatment is applied.     

Electrical Conductivity Method to Determine Sexual Dimorphisms in Human Temporomandibular Disc Fixed Charge Density

To investigate potential mechanisms associated with the increased prevalence of temporomandibular joint (TMJ) disorders among women, the study objective was to determine sex-dependent and region-dependent differences in fixed charge density (FCD) using an electrical conductivity method. Seventeen TMJ discs were harvested from nine males (77 ± 4 years) and eight females (86 ± 4 years). Specimens were prepared from the anterior band, posterior band, intermediate zone, medial disc and lateral disc. FCD was determined using an electrical conductivity method, assessing differences among disc regions and between sexes. Statistical modeling showed significant effects for donor sex (p = 0.002), with cross-region FCD for male discs 0.051 ± 0.018 milliequivalent moles per gram (mEq/g) wet tissue and 0.043 ± 0.020 mEq/g wet tissue for female discs. FCD was significantly higher for male discs compared to female discs in the posterior band, with FCD 0.063 ± 0.015 mEq/g wet tissue for male discs and 0.032 ± 0.020 mEq/g wet tissue for female discs (p = 0.050). These results indicate FCD contributes approximately 20% towards TMJ disc compressive modulus, through osmotic swelling pressure regulation. Additionally, FCD regulates critical extracellular ionic/osmotic and nutrient environments. Sexual dimorphisms in TMJ disc FCD, and resulting differences in extracellular ionic/osmotic and nutrient environments, could result in altered mechano–electro-chemical environments between males and females and requires further study.     

The regional difference of viscoelastic property of bovine temporomandibular joint disc in compressive stress-relaxation

An in vitro experimental technique was performed to measure the viscoelastic properties of the bovine disc. Thirteen TMJ discs from young cattle (3-year-old) were used. Each disc was divided into five specimens of anterior, central, posterior, lateral and medial regions, and they were used for compression tests. A series of stress-relaxation tests was conducted for each specimen from 5% strain up to 20% strain with 5% intervals. The stress-relaxation was monitored over a period of 5 min. Each region exhibited a different biomechanical behavior, which is presumably related to the organization and distribution of proteoglycans that indirectly modulate the stiffness of the collagen network. It is suggested that an improved understanding of the viscoelastic properties of the disc under function may guide consideration for design and selection of biomaterials for TMJ reconstruction.     

颞下颌关节可复性盘前移患者的MR表现

目的:研究颞下颌关节可复性盘前移（ADDWR）患者的磁共振（MR）成像表现。方法:纳入颞下颌关节ADDWR患者55例作为观察组,另纳入30例牙齿排列整齐的健康志愿者作为对照组。所有研究对象均接受MR成像检查,记录颞下颌关节ADDWR患者关节盘前移程度,比较不同严重程度患者关节盘形态和关节渗出情况。结果:55例颞下颌关节ADDWR患者中,轻症35例,重症20例。对照组、轻症组及重症组关节盘形态分型比较,差异有统计学意义（P<0.05）。3组对象颞下颌关节渗出情况比较,差异有统计学意义（P<0.05）。不同程度关节渗出患者视觉模拟评分法（VAS）评分差异有统计学意义（P<0.05）。3组对象关节盘长度差异有统计学意义（P<0.05）。轻度组关节盘前移度较重症组显著减轻,差异有统计学意义（P<0.05）。结论:MR有助于颞下颌关节ADDWR患者病情判断,可为临床治疗提供依据。