Sensitivity of temporomandibular joint force calculations to errors in muscle force measurements

A two-dimensional, five-muscle model was used to determine the degree of precision required for accurate calculation of temporomandibular joint force magnitude and direction. The sensitivity of the calculations to each variable were assessed by incrementing each variable through its presumed biological range and were expressed as rate of change in the joint force per unit change in each variable. Sensitivity of the calculations to variables depends upon both bite force direction and bite position. The bite force direction with maximum precision for joint force magnitude produced minimal precision for joint force direction. The accuracy needed for each muscle force varied greatly. The effect of error for each muscle parameter depended upon the magnitude, direction, and moment arm length of the muscle force relative to those of the resultant muscle force. If each of the five muscle forces was known to the nearest 1% of total muscle force magnitude, 1 degree of muscle force direction, and 1 mm of moment arm length, temporomandibular joint force magnitude could be calculated to the nearest 4 kg and joint force direction to the nearest 7 degrees. It is not known whether this precision for the muscle forces is possible.     

The activity of jaw elevator muscles during peanut chewing in patients with temporomandibular joint and muscle pain dysfunction syndrome

A synchronized system of EMG and jaw motion tracking device was used to observe some chewing parameters of jaw elevator muscles in 15 patients with temporomandibular joint and muscle pain dysfunction syndrome (TMJ) and 15 normal subjects. Duration of tooth contact (DTC), duration of muscle contraction before tooth contact (DMC), total duration of muscle contraction (DTM) and velocity of jaw movement during peanut chewing were observed. Symptoms of the TMJ patients included pain and tenderness at joints and muscles, and limitation and clicking at joints during jaw movements. It was found that the TMJ patients needed more numerous breaking off strokes before trituration at the occlusal level. There was a longer DMC in the earlier trituration period and TMJ patients had longer DMC than in normals. No difference was found between right and left side chewing or between temporalis and masseter muscles. DTM in the TMJ group was only slightly longer than in normals and the difference between early and late chewing periods was statistically not significant. DTC was only slightly shorter in the TMJ group while the difference between early and late chewing periods in both groups was significant. The average and maximum closing velocities were significantly lower in the TMJ group in both right and left chewing. The difference in the opening phase was not as significant. It was concluded that DMC and jaw closing velocity are more sensitive parameters than DTM and DTC on the diagnosis of TMJ dysfunction with or without occlusal interference. DTM and DTC are parameters more closely related to the influence of occlusal factors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in loading of the temporomandibular joint during opening and closing of the jaw

Kinematics of the human masticatory system during opening and closing of the jaw have been reported widely. Evidence has been provided that the opening and closing movement of the jaw differ from one another. However, different approaches of movement registration yield divergent expectations with regard to a difference in loading of the temporomandibular joint between these movements. Because of these diverging expectations, it was hypothesized that joint loading is equal during opening and closing. This hypothesis was tested by predicting loading of the temporomandibular joint during an unloaded opening and closing movement of the jaw by means of a three-dimensional biomechanical model of the human masticatory system. Model predictions showed that the joint reaction forces were markedly higher during opening than during closing. The predicted opening trace of the centre of the mandibular condyle was located cranially of the closing trace, with a maximum difference between the traces of 0.45 mm. The hypothesis, postulating similarity of joint loading during unloaded opening and closing of the jaw, therefore, was rejected. Sensitivity analysis showed that the reported differences were not affected in a qualitative sense by muscular activation levels, the thickness of the cartilaginous layers within the temporomandibular joint or the gross morphology of the model. Our predictions indicate that the TMJ is loaded more heavily during unloaded jaw opening than during unloaded jaw closing.     

Experimental analysis of temporomandibular joint reaction force in macaques

Mandibular bone strain in the region immediately below the temporomandibular ligament was analyzed in adult and sub-adult Macaca fascicularis and Macaca mulatta. Following recovery from the general anesthetic, the monkeys were presented food objects, a wooden rod, or a specially designed bite-force transducer. Bone strain was recorded during incisal biting and mastication of food, and also during isometric biting of the rod and/or the transducer. The bone strain data suggest the following: The macaque TMJ is loaded by a compressive reaction force during the power stroke of mastication and incision of food, and during isometric molar and incisor biting. TMJ reaction forces are larger on the contralateral side during both mastication and isometric molar biting. Patterns of ipsilateral TMJ reaction force in macaques during isometric biting vary markedly in response to the position of the bite point. During biting along the premolars or first two molars a compressive reaction force acts about the ipsilateral TMJ; however, when the bite point is positioned along the M3, the ipsilateral TMJ has either very little compressive stress, no stress, or it is loaded in tension.     

Quantitative analysis and comparative regional investigation of the extracellular matrix of the porcine temporomandibular joint disc.

Characterization of the extracellular matrix of the temporomandibular joint (TMJ) disc is crucial to advancing efforts in tissue engineering the disc. However, the current literature is incomplete and often contradictory in its attempts to describe the nature of the TMJ disc matrix. The aim of this study was to identify the variation of key matrix components along the three axes of the porcine disc using ELISAs to quantify these matrix components, immunohistochemistry to identify their regional distribution, and SEM to examine collagen fiber diameter and orientation. The overall GAG content of the TMJ disc (including the dermatan sulfate proteoglycans) was 5.3+/-1.2% of the dry weight. Chondroitin sulfate, which comprised 74% of this total GAG content, was 4.4, 8.2, and 164 times more abundant than dermatan sulfate proteoglycan, keratan sulfate, and hyaluronic acid, respectively. In general, these GAGs were most concentrated in the intermediate zone of the TMJ disc, appearing in dense clusters, and least concentrated in the posterior band. Additionally, chondroitin sulfate was more abundant medially than laterally. Collagen II was discovered in trace amounts, with higher relative amounts in the intermediate zone. Collagen fibers were observed to run primarily in a ring-like fashion around the periphery of the disc and anteroposteriorly through the intermediate zone, with a mean fiber diameter of 18+/-9 mum. Characterization studies of the TMJ disc, including prior biomechanical and cell studies along with the current study of the extracellular matrix, collectively reveal a distinct character of the intermediate zone of the disc compared to its anterior and posterior bands.     

Effect of hyperactivity of the lateral pterygoid muscle on the temporomandibular joint disk

In this study, the effect of hyperactivity of the lateral pterygoid muscle (LPM) on the temporomandibular joint (TMJ) disk during prolonged clenching was examined with a mathematical model. Finite element models of the TMJ were constructed based on magnetic resonance images from two subjects with or without internal derangement of the TMJ. For each model, muscle forces were used as a loading condition for stress analysis for 10 min clenching. Furthermore, an intermittent increase of the LPM force with intervals of 1 min was applied. In the asymptomatic model, large stresses were found in the central and lateral part of the disk at the onset of clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. When the force of the LPM increased temporarily, the disk moved anteriorly and returned to its original position afterward. In the symptomatic model, large stresses were observed in both the posterior region of the disk and the retrodiscal tissue throughout clenching. Upon temporary increase of the LPM force, the disk was elongated anteriorly, which appeared to be irreversible. These results indicate that hyperactivity of the LPM may be involved in the progression of disk displacement.     

Pigmented villonodular synovitis of the temporomandibular joint. Case Report.

Pigmented villonodular synovitis is a lesion containing giant cells and, because of its tendency to recur, it is easily confused with a malignant process. However, careful review of the histological material will reveal that there is no nuclear atypism or mitotic figures. Also, there have been no reports attributing metastases or death to thid disease. The clinical course of our case was definitely benign.     

Joint reaction forces at the first MTP joint in a normal elderly population

The calculation of net ankle, knee, and hip joint reaction forces is an often applied procedure in the analysis of gait. Except for very few studies, joint reaction forces have not been measured in other joints such as the fingers, wrist, elbow, shoulder and toes. In this study the joint reaction forces between the metatarsal head and the proximal phalanx and the metatarsal head and the sesamoids are calculated for the push off phase during gait. The results of ten normal elderly subjects show that the maximum resultant loads of the two articulations lie close to the longitudinal axis of the metatarsal. The knowledge of the magnitude and direction of the joint reaction forces of a normal elderly population will be essential for the design of an optimal fixation of an artificial anatomical first MTP joint.     

A joint model of the contractile system of striated muscle (preliminary calculations)

Values of the variables of a model of the muscle contractile apparatus were calculated on the basis of a previously described theoretical system JMCSM (i.e. the Joint Model of the Contractile System of Muscle) and after introducing some necessary simplifying presuppositions. The calculations made it possible to compare the model with the original biological system and provided data needed for the subsequent stage of simulation experiments. The properties of the model are apparently not inconsistent with the properties of the original biological system. The basic equation of the theoretical model could be expressed in the form analogous to Hill's equation; the procedure by which the equations were derived and the interpretation of their parameters are mutually independent. The model also suggests a different interpretation of the dependence of the heat of shortening on other quantities of the system. It is necessary to consider these calculations and their results as preliminary with regard to the simplifying presuppositions and to the possible inaccuracies of the estimations of input data.     

The effect of perturbing body segment parameters on calculated joint moments and muscle forces during gait

This study examined the effect of body segment parameter (BSP) perturbations on joint moments calculated using an inverse dynamics procedure and muscle forces calculated using computed muscle control (CMC) during gait. BSP (i.e. segment mass, center of mass location (com) and inertia tensor) of the left thigh, shank and foot of a scaled musculoskeletal model were perturbed. These perturbations started from their nominal value and were adjusted to ±40% in steps of 10%, for both individual as well as combined perturbations in BSP. For all perturbations, an inverse dynamics procedure calculated the ankle, knee and hip moments based on an identical inverse kinematics solution. Furthermore, the effect of applying a residual reduction algorithm (RRA) was investigated. Muscle excitations and resulting muscle forces were calculated using CMC. The results show only a limited effect of an individual parameter perturbation on the calculated moments, where the largest effect is found when perturbing the shank com (MS_com,shank, the ratio of absolute difference in torque and relative parameter perturbation, is maximally −7.81 N m for hip flexion moment). The additional influence of perturbing two parameters simultaneously is small (MS_{mass+com,thigh} is maximally 15.2 N m for hip flexion moment). RRA made small changes to the model to increase the dynamic consistency of the simulation (after RRA MS_com,shank is maximally 5.01 N m). CMC results show large differences in muscle forces when BSP are perturbed. These result from the underlying forward integration of the dynamic equations.