Russell W. Bessette

Magnetic resonance imaging of the temporomandibular joint meniscus

This report describes early experience with magnetic resonance imaging (MRI) of the temporomandibular joint meniscus in which surface coil technology was used. The results suggest remarkable imaging capabilities and speed with noninvasive methods.

Mandibular retrusion, temporomandibular joint derangement, and orthognathic surgery planning.

One-hundred consecutive orthognathic surgery candidates with mandibular retrusion were selected for retrospective analysis. Patients had undergone imaging studies that included magnetic resonance imaging (MRI) of both temporomandibular joints to assess the presence or absence, stage, and activity of suspected internal derangement(s). Patients were divided into stable and unstable deformity groups based on the presence or absence of change in their facial contour and/or occlusal disturbances in the 24 months prior to evaluation. Each of the 58 unstable and 30 of 42 stable patients were found to have internal derangements of at least one temporomandibular joint. The degree of joint degeneration directly paralleled the severity of retrognathia in most cases. We concluded that temporomandibular joint internal derangement is common in cases of mandibular retrusion and leads to the facial morphology in a high percentage of patients. Preoperative temporomandibular joint imaging with MRI is recommended prior to orthognathic surgical correction of retrognathic deformities.

Effect of Biting Force on the Duration of the Masseteric Silent Period

The relationship of biting force to the duration of the masseteric silent period was studied. After introduction of a bite transducer in ten individuals, the jaw jerk reflex was elicited at specific decreases in biting force. No significant alteration in the duration of the silent period was observed.

Contribution of Periodontal Receptors to the Masseteric Silent Period

Quadrant local anesthesia was sequentially administered to the maxillary and mandibular teeth and periodontium in three healthy individuals. After anesthesia the duration of the silent period was shortened. Total anesthesia of all quadrants abolished the silent period in every individual, demonstrating that sensory impulses from periodontal receptors provide a major source of inhibition, and disfacilitation or active inhibition from intact muscle receptors is insufficient to produce a silent period.

Diagnosis and reconstruction of the human temporomandibular joint after trauma or internal derangement.

This study reviewed the standardized records of 1100 patients with the symptoms of temporomandibular joint syndrome. Of these patients, only 4.5 percent required surgical intervention. The remaining patients were found to have masticatory muscle spasm and were treated by conservative dental methods. Over half the surgical patients had significant macrotrauma to the jaws in their past history. In addition, electromyographic measurement of the masseteric silent period duration in these patients did not reveal muscle spasm. These factors further serve to differentiate the surgical patient from the patient with myofascial pain dysfunction. The patients selected for surgery demonstrated moderate to severe joint disease and required arthroplasty with partial meniscectomy. A surgical technique is presented demonstrating the reconstruction of the meniscus with silicone implant. This same surgical technique is studied in 10 monkeys, and their joints are examined histologically. The results of surgery reveal that 87 percent of the patients reported improvement 1 year after surgery. In all patients complaining of temporomandibular joint clicking or crepitus, surgery produced complete alleviation of these symptoms. The results of surgery were also associated with a 62 percent increase of jaw opening. Histologic evaluation of the human meniscal resections revealed that in addition to an anatomic displacement of the meniscus, there are also significant cellular changes. These changes consisted of calcification, a decrease in cellularity, hyperemia, and a decrease in elastin content.

Chewing pattern analysis in TMD patients with and without internal derangement: Part I.

In order to investigate the chewing movement of temporomandibular disorders (TMD) patients with and without internal derangement of the temporomandibular joint (TMJ), analysis of the envelope of motion during chewing was performed in 103 TMD patients with unilateral internal derangement (ID group), 94 TMD patients without internal derangement (NID group) and 10 normal subjects (normal group). The analysis of numeric parameters revealed that the ID group demonstrated a significantly restricted range of motion compared to the NID or normal groups, and the NID group demonstrated significant irregularity of chewing compared to the ID or normal groups. The analysis of chewing also demonstrated that the chewing pattern for the ID group demonstrated more frequent deviation of the turning point to the nonchewing side in the frontal plane and a narrow anteroposterior pattern in the sagittal plane compared to the other groups. No characteristic chewing patterns were identified for the NID group.

Vibration analysis of the temporomandibular joints with meniscal displacement with and without reduction

The vibrations of 102 joints demonstrating meniscal displacement with either early or late reduction (MDR-early/MDR-late) and 70 joints displaying meniscal displacement without reduction either incomplete or complete (MD-incomplete/MD-complete) were analyzed and compared to 83 arthrographically normal but symptomatic joints (NID) using electrovibratography (EVG). The total power density of the vibration [I(T)], peak power density [I(max)] and power density at each 50Hz range between O to 600 Hz [I(f)] showed the highest in the MDR-late group followed by the MDR-early group, suggesting that the level of vibration is related to the degree of disk displacement and reduction. The wave characteristic parameters such as the correlation coefficients between I(T) and each I(f) showed higher correlation at higher frequency ranges as the degree of disk displacement progressed, from MDR-early to MDR-late to MD-incomplete. The diagnostic sensitivity of EVG when using I(T) as a determining parameter was 96.6% for the MDR-early group, 91.8% for the MDR-late group, 77.8% for the MD-incomplete group and 57.4% for the MD-complete group with the specificity for the NID group at 75%.

Vibration Analysis of the Temporomandibular Joints with Degenerative Joint Disease

The surface vibrations of 42 temporomandibular joints (TMJ) with degenerative joint disease (DJD) and/or perforation of the disk were evaluated using electrovibratography and compared to the surface vibrations of 83 joints with normal TMJ imagings and 61 joints with meniscal displacement without reduction. Through the frequency spectrum analysis, TMJs with DJD showed higher vibration energy above 350-450 Hz and TMJs with perforation showed higher vibration energy between 100-150 and 300-450 Hz. The presence of perforation did not seem to affect the characteristic of vibrations when TMJs were associated with DJD. A threshold was set for the total vibration energy as described in our previous report and used as a parameter in order to separate patients with internal derangement from a pool of TMJ dysfunction patients (diagnostic specificity = 75%, diagnostic sensitivity = 80.2%). Using this criteria, the following were correctly identified as internal derangement and/or DJD: a) 100% of the TMJs with meniscal displacement without reduction associated with DJD; b) 87.0% of the TMJs with meniscal displacement without reduction associated with perforation; c) 88.9% of the TMJs with meniscal displacement without reduction associated with DJD and perforation; and d) 100% of the TMJs with perforation.

Electromyographic evaluation of the Myo-Monitor

D entists are frequently confronted with the problem of restoring good health to their patients’ masticatory systems by means of prosthetic devices. During the fabrication of a prosthesis, the dentist must select a mandibular position which is esthetically acceptable and an occlusal vertical dimension which does not encroach upon the closest speaking space or the interocclusal distance. This position should also be compatible with a healthy, functioning neuromuscular system. When edentulous or partially edentulous patients present the problem of mandibular positioning, “centric relation” has been used extensively as a starting point in prosthodontic therapy for the establishment of the occlusion. Attempts to establish centric relation are influenced by the patient’s ability to relax, the dentist’s ability to guide the mandible to its retruded position, and the dentist’s ability to determine when his efforts have been successful. An error in any of these three criteria can result in a mandibular orientation which may not be within the limits of that patient’s tolerance. Finally, the relationship must be compatible with the neuromuscular system of the patient. An alternate method of determining a physiologic maxillomandibular orientation, which could reduce both dentistand patient-induced errors, is desirable. The MyoMonitor+ has been suggested as a means for determining such an orientation. The Myo-Monitor is an electric stimulator which delivers a variably adjusted voltage through two mesh-plate electrodes. These adhesive-backed electrodes are positioned slightly anterior to the right and left external auditory meatuses. A third electrode is placed on the posterior midline of the neck and serves as a grounding device. It is stated in the instruction manual which accompanies the instrument that, when the unit is set to Pulse, “This circuit is programmed to deliver a stimulus of approximately 2-millisecond duration, at 1 f/2-second intervals, through each electrode. The interval provides sufficient resting time for the mandible to return completely to the rest position, between muscle contractions. With rest, the muscle can respond indefinitely, and yet not fatigue itself.

Vibration of the temporomandibular joints with normal radiographic imagings: comparison between asymptomatic volunteers and symptomatic patients.

In order to estimate the effect of a background noise during temporomandibular joint (TMJ) vibration analysis, 40 recordings from sensors not attached to subjects and sensors attached to subjects without any jaw movement were evaluated. Both of them showed very small energy density, close to 0, throughout 0 to 600 Hz and flat frequency distributions. To evaluate the vibration energy of asymptomatic TMJs with normal joint anatomy and symptomatic TMJs with normal arthrographic imagings, 20 TMJs from 10 clinically normal and asymptomatic volunteers with bilateral normal TMJ computerized tomography (CT) scanning (N-control) were analyzed at four mandibular positions. Results from intercuspal position and maximal opening were identical to the background noise. Results from closing and opening phase showed higher energy, especially below 150 Hz, than the background noise. Surface vibrations of 83 TMJs from patients with arthrographically normal imagings but having symptoms (NID) showed significantly higher energy than the N-control group above 300 Hz. When the total vibration energy (I(T)) is used to set the threshold for the separation of internal derangement, at I(T) = 2.06, the diagnostic specificity for the NID group is 75%, while the diagnostic sensitivity is 82.4% for internal derangement. At the same time, 98.3% of the N-control group was involved below the threshold.