Journal of Oral & Facial Pain and Headache, 02/1994

Two temporomandibular joints originating from one specimen were investigated using magnetic resonance imaging and cryosectioning. Magnetic resonance images, photographs of the surface of the tissue block, and on-tape sections were compared. The left joint was imaged and sectioned in a sagittal plane, the right joint in a plane perpendicular to the long axis of the condyle. The densely plaited fibrous tissue of the disc proper correlated extremely well with the low signal intensity in magnetic resonance imaging. The transition between the densely plaited fibrous tissue and the looser tissue of the posterior attachment was located anterior to the thickest part of the intra-articular tissues in most sections of the specimen. The temporomandibular joint disc could be seen in angulated as well as in sagittal magnetic resonance scans. The posterior band was imaged best in angulated magnetic resonance scans throughout the temporomandibular joint.

The distribution and arrangement of extracellular matrix proteins were examined in the primate temporomandibular joint disc and posterior attachment using a combination of light microscopic, immunohistochemical, and biochemical techniques. The band areas of the disc contain a complex collagenous (type I) fiber network consisting of a mediolaterally directed fiber bundle system that interlaces or becomes continuous with an anteroposteriorly directed collagenous fiber array that runs through the intermediate zone. Thin, branching, elastic fibers are a significant component of the disc and are generally oriented parallel to the collagenous fiber network. Interfibrillar spaces in band areas contain numerous chondrocytes encased within a matrix that is rich in a high molecular weight, predominantly chondroitin-sulfate proteoglycan and type II collagen. The intermediate zone appears tendinous in its construction and is composed of anteroposteriorly oriented elastic and collagenous fibers, scattered chondrocytes, and reduced amounts of chondroitin-sulfate proteoglycan and type II collagen. The posterior attachment is composed of fibrocytes, larger caliber elastic fibers, loosely organized type I collagenous fibers, and low molecular weight dermatan-sulfate proteoglycan. These results indicate that the primate temporomandibular joint disc is a microheterogenous tissue with distinct regional specializations.

The purpose of this study was to measure, under laboratory conditions, the noise level of the optoelectronic jaw-tracking system JAWS-3D, which records the movement of the whole mandible from extraorally placed landmarks. Also, an assessment was made of its accuracy in measuring positions, angles, and velocities. The results showed that the accuracy of JAWS-3D decreased when the distance between the recorded point and the extraoral landmarks increased. The path of a point near to the landmarks was estimated with an error of 0.11%, whereas the error increased to 1.33% when the point was far from the landmarks. The maximum error in angle computation was 0.7 degrees. The velocities calculated by JAWS-3D corresponded closely to the actual ones: mean error of 3 mm/s for velocities up to 80 mm/s. Thereafter, the error increased to reach 26 mm/s at a speed of 210 mm/s.

It is essential to know the limitations of any equipment used for research or clinical purposes. Clinical electronic equipment is commonly sold for lack box use without specification of artifacts. This study tested the technical and clinical limitations of the Sirognathograph, which is a device used for recording mandibular movement. From a technical point of view, the Sirognathograph's slow sampling speed and sample artifacts have been shown to be the system's main limitations; however, it was possible to eliminate sampling artifacts by using a customized pulse generator and software for controlled data acquisition. Clinically, the Sirognathograph appears to have some inherent limitations in its accuracy. The effect of cranial movements during mastication can cause a baseline drift with consequent errors in the recording of mandibular position. This problem was controlled in this study by using a headband to stabilize the cranial movements during mastication. Also, the spatial relationships between the aerial and both the cranial base and the magnet were found to be critical for repeatability of the recordings.

Differential, functional loading of the mandibular condyles has been suggested by several human morphologic studies and by animal strain experiments. To describe articular loading and the simultaneous forces on the dental arch, static bites on a three-dimensional finite element model of the human mandible were simulated. Five clenching tasks were modeled: in the intercuspal position; during left lateral group effort; during left lateral group effort with balancing contact; during incisal clenching; and during right molar clenching. The model's predictions confirmed that the human mandibular condyles are load-bearing, with greater force magnitudes being transmitted bilaterally during intercuspal and incisal clenching, as well as through the balancing-side articulation during unilateral biting. Differential condylar loading depended on the clenching task. Whereas higher forces were found on the lateral and lateroposterior regions of the condyles during intercuspal clenching, the model predicted higher loads on the medial condylar regions during incisal clenching. The inclusion of a balancing-side occlusal contact seemed to decrease the forces on the balancing-side condyle. Whereas the predicted occlusal reaction forces confirmed the lever action of the mandible, the simulated force gradients along the tooth row suggest a complex bending behavior of the jaw.

The effects of fulcrum-type splints on the temporomandibular joints are unclear. An analysis of bilateral temporomandibular joint linear tomograms of 20 volunteers was made. This study was carried out to evaluate and quantify the condylar distraction caused by the use of interocclusal splints with pivots located simultaneously on second molars. Statistical results showed an average condylar lowering of 1.3 mm in 87.5% of the subjects (P .05) while clenching with lips closed and wearing this splint. A real bilateral condylar distraction was shown in 30% of the subjects, 35% showed both condyles in a protruded position, and 35% of the subjects showed a combined situation.

This study assessed the ability of electronic thermography to identify internal derangement of the temporomandibular joint. The study population consisted of 30 patients with internal derangement verified by temporomandibular joint arthrotomography. Electronic thermography was conducted using an Agema 870 thermographic unit. Thermal assessments included: (1) pattern recognition; (2) pattern symmetry; (3) absolute temperature measurements; (4) delta T measurements; and (5) mean temperature measurements and differences within five designated anatomic zones. Results indicated: (1) low levels of thermal symmetry in patients with internal derangement of the temporomandibular joint, and (2) absolute temperature measurements and mean temperature zone measurements showing large delta T values (0.4 degrees C to 0.8 degrees C). Demonstration of characteristic thermal temporomandibular joint changes suggests that electronic thermography may have potential for assessing internal derangement of the temporomandibular joint. However, more extensive studies are needed before thermographic procedures can be accepted clinically.

An epidemiologic sample of 84 subjects was followed longitudinally from the age of 15 to 25 years concerning clinical signs of craniomandibular dysfunction. There was an obvious fluctuation of the clinical signs of craniomandibular disorders over the 10-year period. No statistically significant change of any of the separate clinical signs or the clinical dysfunction index was noted, and no subject had severe signs of dysfunction. Muscle pain on palpation was still the most common clinical sign and was noted in nearly half of the subjects after 10 years. Temporomandibular joint clicking was common at the ages of 15 and 25 years, but no subject had developed locking of the temporomandibular joint during the 10-year period. Occlusal interferences in the retruded contact position and on the nonworking side increased during the 10-year period and were now present in 74% and 32% of the participants, respectively. A slight increase of occlusal wear was noted, but more pronounced wear was still a rare finding at the age of 25 years. Twenty-one subjects (25%) were judged by the examiners to be in need of some kind of functional treatment. The treatment advocated was in most cases minor, however, and could, with few exceptions, be incorporated in the subjects' ordinary dental treatment.

To assess the knowledge and beliefs of practicing dentists regarding temporomandibular disorders and chronic pain, a random sample of dentists in the Kansas City metropolitan area was surveyed. A survey instrument examining knowledge and beliefs in four domains (psychophysiological, psychiatric disorders, chronic pain, and pathophysiology) was used. The responses of the practicing dentists were compared to the responses of panels of experts. Results indicated that dentists generally agreed with experts in the psychophysiological and psychiatric disorders domains but disagreed with the experts in the chronic pain and pathophysiology domains. Specialists and general dentists did not differ from one another in their responses. The findings partially replicate an earlier, similar survey of dentists in the Seattle, Washington, area. The findings suggest that the role of psychiatric disorders and psychophysiologic factors in the etiology of temporomandibular disorders is widely acknowledged by practicing dentists. However, there is considerable discrepancy between practicing dentists and temporomandibular disorder experts on the pathophysiology of temporomandibular disorders and how best to diagnose and treat these chronic conditions.

Traumatic myositis ossificans, also known as myositis ossificans circumscripta or fibrodysplasia ossificans circumscripta, is a form of dystrophic calcification leading to heterotopic ossification of intramuscular connective tissue. This is usually due to a single severe injury or repeated minor injuries to muscle, although cases without a history of injury have been reported. Heterotopic ossification is rare in the orofacial region, especially in the medial pterygoid muscles. A case of medial pterygoid myositis ossificans with unique computed tomography findings is described.