The effect of experimental stress and experimental occlusal interference on masseteric EMG activity.

This experiment attempted to study the separate and combined effects of occlusal interference and transient stress on masseteric activity among eight nonclinical human subjects. Before each of two sessions, subjects were fitted with an occlusal interference or an occlusally inert (control) molar clasp. During each session they viewed horrific and idyllic videotapes while masseter EMG was recorded bilaterally. Electrodermal measures validated that the horrific videotapes were stressful. Studies showed that the occlusal variable worked less well. The EMG was elevated contralateral to both clasps and during videotape viewing. The EMG effects from videotape viewing were relatively pronounced without the occlusal interference. Research implications are discussed.

The instantaneous hinge axis - its reproducibility and use as an indicator for dysfunction.

This study investigated irregularities in hinge movement in 113 subjects. These irregularities were analyzed by computer with an instantaneous three-dimensional "screw axis method." The variation in hinge movement was measured by the dispersion of the hinge axis instant centers. Dispersion of instant centers was greater for muscle pain patients than for the normal, indicating that instant center data could make a contribution to diagnosis and treatment planning.

Occlusal forces during chewing and swallowing as measured by sound transmission.

Forces during the phase of occlusal contact during chewing and swallowing are surprisingly high (36.2% and 41%), about 40% of the subject's maximum biting force. Previous studies using transducers in fixed partial dentures measured only a portion of the total force and have given the impression that chewing forces are much less than the data reported in this study. The importance of occlusal stability in the intercuspal position is of utmost clinical significance. Steep anterior guidance does not appear to expose the teeth to extreme lateral forces. The gliding contacts of the teeth while entering and leaving the intercuspal position have been shown to be of short duration and low magnitude when compared with the forces generated in the intercuspal position. During chewing, the peak occlusal force occurred well after the peak EMG activity. EMG activity by itself does not directly correlate with the force generated during chewing. The sound transmission method for measuring interjaw force during chewing, which was developed as part of this project, proved to be practical for research purposes. No intraoral devices are required, and the time relationship to force is accurate to within 15 ms.

Chewing patterns in normal children.

Chewing patterns are precisely plotted in deciduous, mixed and permanent dentitions. These show a progression from a large component in the opening movement with a more medial closing path in the deciduous dentition, to a more vertical overall pattern with the closing path lateral to the opening path in the early permanent dentition.

Mandibular movement recordings and articulator adjustments simplified.

Research data from several hundred patient recordings using the Lee method have been utilized to design a simplified jaw movement analyzer and articulator. The study also shows that most patient's movement characteristics can be satisfied with standard preformed articulator controls.

An evaluation of mandibular border movements: their character and significance.

1. A comparison of protrusive and lateral condylar border movement pathways of 163 subjects revealed considerable similarity when the frequency of 80% of the pathways was compared with the average pathway. 2. A description of the pathways of posterior cusps during lateral contact gliding movement must consider three simultaneously acting guidance factors: (1) the nonworking condyle pathway, (2) the amount of Bennett movement or the working-side condyle displacement, and (3) the anterior guidance or working-side tooth contacts. 3. A Bennett movement of 2.5 to 3.5 mm caused a dramatic flattening of lateral movement pathways of the molar cusp as seen in the frontal plane. The steepness of neither the anterior guidance nor the nonworking condylar pathway had much influence on the molar cusp pathway in the presence of this excessive Bennett movement. 4. Viewed in the horizontal plane, excessive Bennett movement contributed to the greatest potential for collisions of molar cusps during lateral movements. This phenomenon was more pronounced on the nonworking side. 5. When the Bennett movement was 0.75 mm or less the tracing in the frontal plane showed that the 40-degree anterior guidance became the dominant influence over molar cusp lateral movement pathways.

A method of transferring mandibular-movement data to computer storage.

A method was briefly described which photographed engraved blocks of mandibular-movement recordings and transferred the information into computer memory. A photographic platform was designed to allow uniform photographing of the engraved blocks. The photographed information was then projected onto graph paper where it was traced. The traced information, with the centric point labeled, was transferred into computer memory via a Computek 531 tablet. An RMS (root-mean-squared) deviation test was conducted to estimate the reliability of this technique. The maximum deviation (0.363 mm.) was found for z coordinate of the left-side recording. Labeling the centric point in computer memory is very important. This allows careful and detailed study of movements in the area where clinical evaluation is of utmost importance to the dentist. As more data are collected and evaluated, questions related to occlusion, such as tooth stability, effect on periodontal health, relationship to orthodontic success, and the like, may be clarified.