Temporomandibular Joint Loading Research Articles

A three-dimensional mathematical model of temporomandibular joint loading

Objective. A mathematical model of the temporomandibular joint was developed to study the magnitude and direction of the compressive loading experienced at the temporomandibular joint during clenching. Design. The model was based on the principles of static equilibrium in three dimensions. Background. Direct measurement of temporomandibular joint loading in humans is extremely difficult. Animal models have provided an alternative in the past. However, evidence suggests that primates are not the most accurate human analogues for temporomandibular joint studies. A mathematical model was used as an alternative to direct measurement. Methods. The EMG activity of two masticatory muscles was combined with their cross-sectional areas to calculate the force exerted by each muscle. Experimentally determined forces were implemented into a quadratic programming model to solve for the compressive forces on the joint. Two objective functions were chosen and their ability to predict muscle and joint forces was evaluated. Results. The maximum bite forces for normal men, normal women, and women with temporomandibular joint disorders were 300 N (SD 102 N), 210 N (SD 57.7 N), and 120 N (SD 77.1 N), respectively. The calculated joint force for normal males was 260 N (SD 84.1 N). Normal females and female temporomandibular joint disorder patients produced temporomandibular joint forces of 172 N (SD 37.5 N) and 152 N (SD 44.2 N), respectively. Relevance Over 10 million Americans suffer from disorders/diseases affecting the temporomandibular joints. It is important to know the magnitude of joint loading for treatment and prevention of temporomandibular joint disorders. This work is of interest to clinicians treating temporomandibular joint disorders and for designing artificial temporomandibular joints.

Mechanical properties of human articular disk and its influence on TMJ loading studied with the finite element method

The present study was designed to investigate the elastic modulus of human temporomandibular joint (TMJ) disk under tension and its influences on TMJ loading. Seven human TMJ disks served as specimens. Continuous tensile stress was applied to each specimen, and the elastic moduli of human TMJ disks were calculated at 2% strain. Furthermore, using a three-dimensional finite element model of the mandible including the TMJ, changes in the TMJ stresses during clenching were evaluated in association of varying elastic moduli of the articular disk determined by the tensile tests. The elastic moduli at 2% strain varied from 27.1 to 65.2 MPa with a mean of 47.1 MPa. A significant correlation was found between the elastic moduli and age (P < 0.01). On the surface of condyle, compressive stress in the anterior area and tensile stress in the posterior area increased when the elastic moduli of the TMJ disk was varied from 25 to 65 MPa. In the TMJ disk, shear stresses in all the areas became larger with greater stiffness. In conclusion, it is shown that the elastic modulus of human TMJ disk is increased with age and that higher stiffness of the disk exerts substantial influences on mechanical loading for the TMJ structures.

A study on analysis of temporomandibular joint loading by a simplified three-dimensional finite element model

A study on analysis of temporomandibular joint loading by a simplified three-dimensional finite element model

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.

顎関節負荷の調節メカニズムの静力学的解析 : 咬合点の違いによる咀嚼筋協調活動の変化

Masticatory or bite forces applied to the teeth are known to generate compressive forces in the temporomandibular joint (TMJ), which are referred to as "TMJ loading." Normal TMJs are both tolerant and adaptable to a certain amount of loading, but excessive loading is believed to be one of the causes of TMJ dysfunctions. Thus TMJ loading can be considered to be controlled to a certain extent by the stomatognathic system, so as not to exceed a certain limit. In an attempt to clarify that control mechanism during biting, we previously analyzed TMJ loading using a two-dimensional static jaw model and then proved, by computer simulation, that the TMJ loading is minimized when the load vector points in a certain direction. This minimization can be achieved merely by coordinating the activities of the masseter and the temporalis. We then analyzed the modification of such coordinated activities of masticatory muscles by changing the bite point and validated the jaw model by comparing our simulation results with somatometric data. Our jaw model comprises two rigid bodies, the upper and lower jaws, and a spring-element model of the articular disk, including masticatory muscles as follows: 1) the masseter, including the internal pterygoid; 2) the temporalis; and 3) the lateral pterygoid, all of which function dominantly during biting. Bite force is assumed to be applied to a single point on the occlusal plane. Muscle forces applied to our model were determined by referring to morphological and electromyographic data reported previously. First, we carried out experiments in order to obtain masseter and temporalis forces minimizing TMJ loading under various locations of bite point on the occlusal plane. Simulation results indicated that 1) the location of the bite point solely affects the activity of the masseter under the condition that the magnitude and direction of bite force are both constant and TMJ loading is minimized; and 2) the activity balance between the masseter and the temporalis minimizing TMJ loading is sensitive to the direction of bite force. Comparison of our simulation results with EMG data for the masseter and temporalis and biteforce data demonstrated that our results almost coincided with somatometric data for biting at the canine or the premolar, and for biting weakly at the first molar. This strongly suggests that minimization of TMJ loading is actually realized by the stomatognathic system under certain bite conditions.

Functions of masseter and temporalis muscles in the control of temporomandibular joint loading--a static analysis using a two-dimensional rigid-body spring model.

Masticatory forces or bite forces applied to the teeth are known to generate a compressive force on the temporomandibular joint (TMJ). This intra-articular force is referred to as TMJ loading. TMJ loading is considered to be controlled to a certain extent by the stomatognathic system, so as not to exceed a certain limit. In order to clarify the control mechanism of the TMJ during biting, the controllability of TMJ loading through coordinated activities of the masticatory muscles has been numerically analyzed using a static two-dimensional jaw model. This model consists of a rigid-body model of the jaws and a spring model of the articular disk, which includes three dominant muscle force vectors representing the masseter, temporalis and lateral pterygoid muscles. The bite force vector is assumed to be applied solely at the first molar. Static equilibrium analyses suggest that coordinated activities of the masseter muscle and anterior portion of the temporalis muscle can minimize TMJ loading and concentrate the stress within the articular disk to the intermediate zone of the disk, and that the activity of the posterior portion of the temporalis muscle has the possibility of reducing TMJ loading.

Estimation of temporomandibular joint loading by use of measured values of occlusal force and time-integrated electromyogram

Estimation of temporomandibular joint loading by use of measured values of occlusal force and time-integrated electromyogram

Modeling of jaw biomechanics in the reconstructed mandibulectomy patient

Statement of problem. Biomechanics of occlusal force and indirect calculation of temporomandibular joint loading in patients after surgery for head and neck cancer is poorly understood. Purpose. This study compared occlusal force values of 6 mandibulectomy subjects with reconstructed mandibles to 6 noncancer subjects with intact mandibles and reports occlusal force predictions from a developed computer model simulation of both a mandibulectomy subject with a reconstructed mandible and noncancer subject with an intact mandible. Material and methods. Maximum occlusal force was recorded at the first molar and incisal edge in 6 mandibulectomy subjects who had bony reconstruction of the mandible and 6 noncancer subjects with an intact mandible. Clinical data were then qualitatively compared with occlusal force values generated from an existing computer model simulating an average adult, and a developed model simulating an average mandibulectomy subject who had bony reconstruction of the mandible. The biomechanical parameters modeled also included an estimation of joint force magnitude and direction when biting with maximal force on the first molar. Results. Clinical data revealed no significant differences in occlusal force between the 6 mandibulectomy subjects with bony reconstruction of the mandible and 6 noncancer subjects with an intact mandible; however, average molar and incisal occlusal force values were 22% and 32% less in mandibulectomy subjects with bony reconstruction. Computer simulations of a reconstructed mandibulectomy subject predicted that reconstructed subjects would have 45% less molar occlusal force, 50% less incisal occlusal force, and a higher joint/tooth force ratio compared with a simulated noncancer patient with an intact mandible. Conclusions. There were no significant differences in first molar or incisal occlusal force between reconstructed mandibulectomy subjects and noncancer subjects with intact mandibles. Trends calculated from computer simulations were consistent with clinical findings. (J Prosthet Dent 1999;81:167-73.)

In vitro strain measurements in the condylar process of the human mandible

Although there have been a number of experimental studies of temporomandibular joint loading, the precise relation between condylar load and condylar strain is incompletely understood. This in vitro study determined the magnitudes and directions of the principal components of strain on the four surfaces of the condylar process of human cadaver mandibles during loading with selected simulated muscle forces, with simultaneous measurement of occlusal and joint forces. Rosette strain gauges were placed on each of the four surfaces and the mandibles were loaded by a load cell to simulate the action of the masseter and medial pterygoid muscles. Force and strain values were measured at five different bite positions and nine different positions of the resultant muscle force. Forces and strain values were highest when the resultant muscle force was closest to the joint and the bite position was furthest from the joint. The ratios of bite force to joint force and the ratios of forces between the two joints conformed to theoretical predictions of many previous models, with the balancing-side joint being loaded more heavily than the working-side joint. At all gauge positions the maximum principal strain was tensile, the minimum principal strain was compressive, and the absolute strain values were correlated with the magnitude of the force on the condyle. However, under the chosen loading regimen, the ratio of compressive to tensile strain differed among the four surfaces. The highest levels of tensile strain occurred on the anterior and lateral surfaces and the highest compressive strain occurred on the posterior surface. It was not possible to detect significant changes in strain patterns due to bite position or muscle force position, that were independent of the force magnitudes.

Effect of bilateral asymmetric tooth clenching on load distribution at the mandibular condyles

The effects of balancing-side tooth contacts on temporomandibular joint loads are unclear. We used a 3-D computer model to calculate the magnitude and direction of temporomandibular reaction forces during simulated clenching on interocclusal acrylic resin shims and between natural teeth. Muscle tensions were proportioned according to the task modeled. Working-side tooth contacts included the canine alone, as well as group function, and occlusal loads were progressively shifted toward a posterior contralateral simple balancing contact. In the acrylic resin shim experiments, group function with simple balancing contact yielded the highest forces at the load point and at both temporomandibular joints. Movement of the occlusal load toward the balancing side produced greater, anteriorly oriented forces on the working condyle. For natural teeth, changes in the angle of resultant tooth force (simulating facet angulation) greatly influenced condylar forces. As the occlusal load moved toward the balancing side, greater and more laterally oriented forces were produced on the balancing condyle. Unilateral clenching on the canine produced the least condylar and bite forces. The simulation involving natural teeth offers a possible explanation for deviations in form and osteoarthrosis at the temporomandibular joints.

Muscle activity patterns and control of temporomandibular joint loads

The strategy used by the neuromuscular system to distribute reaction forces to the temporomandibular joints on the working and balancing sides has not been fully defined. Theoretical studies and experimental measurements suggest that the two joints are unevenly loaded during unilateral biting or closures for posterior teeth. However, previous electromyographic studies suggest that muscle activity patterns may attempt to balance the distribution of the two joint forces. This study measured bilateral activity in the anterior temporal, posterior temporal, and superficial masseter muscles during isometric bites or closures and chewing at five different positions along the teeth. The resulting ratios of muscle activity on the working/balancing sides were compared with ratios required to maintain equal joint forces. The values of the muscle activity were also used to estimate the ratio of joint forces on the working/balancing side at each tooth position. Results indicate that the muscle activity patterns do not maintain equal joint forces, nor are the muscles responding to joint forces exceeding critical limits. These results suggest that patterns of muscle activity are designed to control the position and magnitude of occlusal forces rather than temporomandibular joint forces. If these same patterns of activity are maintained following repositioning of dental and skeletal elements, adverse temporomandibular joint forces could result.

Muscle activity patterns and control of temporomandibular joint loads

Muscle activity patterns and control of temporomandibular joint loads

A theoretical model of loading and eminence development of the postnatal human temporomandibular joint.

The objectives of the present study were to characterize the loading of the immature TMJ, and to develop a theoretical model to explain the relationship between joint loading and development of the eminence of the human TMJ. The osteological remains of forty individuals, ages ranging from birth to twenty years, were used to provide metric coordinates of the three-dimensional relationships of the anatomy of the biting apparatus. The data were used, in a numerical model of TMJ loading (Smith et al., 1986), to calculate the magnitudes and directions of condylar loading. The following conclusions were drawn: (i) static equilibrium cannot be satisfied unless the immature TMJ is loaded; (ii) in the neonate, the direction of condylar loading is approximately vertical but, as the child matures, the angle of condylar loading becomes more oblique; and (iii) evidence is given in support of the hypothesis that early development of the eminence is consequent upon the stimulation of bone growth by the appropriate position and timing of loading of the immature condyle on the temporal component of the joint.

A three-dimensional investigation of temporomandibular joint loading

A mathematical model of the muscle groups applied to the human mandible is developed to study the forces developed on the condyles during maximum unilateral occlusion. The results show that the reaction forces are in approximately a 2:1 ratio with the balancing side condyle carrying the greater load. Furthermore, the direction in which these condylar reactions occur is presented.

A numerical model of temporomandibular joint loading.

A numerical model of the mandible, its articulating surfaces, and the forces exerted by the primary masticatory muscles has been developed for the purpose of investigating loading of the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint is a load-bearing joint over the normal functional range of bite-force positions and angles. In this investigation, temporomandibular joint loads were found to vary from a maximum appositional force of 60% of the bite force (when bite forces were applied to the incisors) to a distracting force of about 5% of the bite force (when applied to the distal surfaces of the third molars). TMJ loads tended to reach a minimum as a result of vertically directed bite forces positioned at the second molars. A range of conditions in which bite forces were directed parallel to or within approximately 20 degrees of the mid-sagittal plane was found to be conducive to stability of the temporomandibular joint. This stability included symmetry in the direction and in the magnitude of condylar loads as well as the presence of small forces tending to oppose the condyle and articular eminence. TMJ loads tended to reach a maximum in response to mediolaterally directed bite forces. This result is consistent with the fact that no muscle of mastication exhibits a spatial orientation in which the muscle fibers are predominantly mediolateral in direction.

Development of mechanical and mathematic models to study temporomandibular joint loading

Development of mechanical and mathematic models to study temporomandibular joint loading