A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part I: Development of the measuring system

Analysis of sagittal condylar path inclination in consideration of Fischer's angle

This study investigated the sagittal condylar path during protrusive and lateral excursions by analysing the actually measured jaw movement data and re-evaluated the setting of the sagittal condylar path inclination in consideration of Fischer's angle. Protrusive and lateral excursions of 10 healthy subjects were measured using a three-dimensional mandibular movement analysing system. Condylar path inclinations at the hinge-axis point and the corresponding external point laterally extending from the condyle were evaluated in the sagittal plane. Fischer's angle was defined as the difference between the sagittal condylar inclinations during protrusive and lateral excursions on the non-working side, by keeping the corresponding horizontal distance from the intercuspal position (ICP) equivalent at the incisal point. Analysis was performed at three different magnitudes of excursions, where the incisal point was located at 1, 3 and 5 mm away from the ICP. There was no significant difference in the sagittal condylar path inclination or the Fischer's angle between two condylar reference points. However, they were significantly different across the three different magnitudes of excursions for both condylar reference points, i.e. sagittal condylar path inclination (P = 0.003 for protrusive excursion, and P < 0.001 for lateral excursion respectively; two-way repeated-measures anova), and Fischer's angle (P = 0.013, two-way repeated-measures anova) became smaller as the incisal point became distant from the ICP. Moreover, 3- and 5-mm eccentric positions were included in the 95% CI where Fischer's angle equals zero and were considered to be clinically acceptable to adjust the sagittal condylar inclination on the semiadjustable articulators.

The kinematic center: a reference for condylar movements

The kinematic center of the temporomandibular condyle is that condylar point which follows as much as possible the same movement path during different types of mandibular movements. In this study, the location of the kinematic center with respect to the palpated lateral pole of the condyle was investigated. Also, the lengths of the condylar movement path reconstructed by means of the kinematic center and the palpated condyle were compared. Mandibular movements were recorded with 6 degrees of freedom in 20 healthy subjects. A software procedure calculated the location of the kinematic center as that mandibular point for which the protrusive and opening movement path showed a minimal difference. For each subject, its average location was calculated on the basis of 16 pairs of protrusive and opening movements. The kinematic center was located posteriorly and superiorly with respect to the palpated condylar point (p < 0.0001). The standard deviation in the anterior-posterior coordinate of the average kinematic center was smaller than that in the superior-inferior coordinate (p < 0.0001). During opening, the path length of the kinematic center is longer than that of the palpated lateral pole of the condyle (p < 0.0001). In contrast to left-right differences found in the path lengths of the lateral pole of the condyle, no left-right differences were found for the kinematic center.

OKAS-3D: optoelectronic jaw movement recording system with six degrees of freedom

OKAS-3D is a further development of the single floating circle target tracker. This tracker consists of a cathode ray tube display, a lens in front of the display and a circular light-sensitive photocell placed in the image field of the lens. A small circular trace generated on the screen is focused around the photocell. The sinusoidal electrical output of the photocell contains all the relevant information regarding the position of the photocell relative to the image of the circular light trace. This gives the tracker the properties of a servo-controller with position feedback. In OKAS-3D three pairs of photocells are located on two lightweight frames attached to the upper and lower frontal teeth by individually adapted clutches. By using the formulas of rigid body mathematics, the motion of any point of the mandible can be reconstructed. The system permits a high sampling frequency of at least 300 Hz per photocell co-ordinate. The noise, linearity and accuracy are better than 0.08 mm, 0.07 mm and 0.13 mm for points in the lower incisal region, and better than 0.25 mm, 0.17 mm and 0.27 mm for points in the condylar region. Thus jaw movements can be recorded with a high spatial and temporal resolution.

Investigation of the effects of a variable lateral guidance incline on the pantronic registration of mandibular border movement: Part II

This study was designed to test the hypothesis that changes in lateral guidance inclination could affect the condylar registrations in the recordings of an electronic pantography. In seven healthy subjects, pantronic registrations of immediate side shift, progressive side shift, and orbiting and protrusive condylar paths were recorded with lateral anterior guidance inclinations of 0, 20, 30, 45, and 60 degrees from the same pin height. Analysis of variance with repeated measures showed a significant decrease in the immediate side shift (p 0.016) and the progressive side shift (p 0.051) as the lateral guidance angle increased and no significant effect on the orbiting registrations. These observations, together with those from other studies, suggest that the concept of fabricating the working-side tooth guidance exactly according to instrument condylar settings (which themselves may be subject to a variable recording lateral anterior guidance) appears untenable and demands further study.

The recording and analysis of EMG and jaw tracking. I. The recording procedure

A computer-based system is described which records and analyses electromyographic (EMG) signals and tracking data for mandibular movements during function. EMG signals were obtained bilaterally from six muscles and a Sirognathograph monitored the position of the lower incisor teeth in three dimensions. Directed jaw movement tasks by subjects were monitored. These data were continuously sampled at a rate of 1 KHz per channel over an operator controlled period. Analysis of the data was performed off-line following the experiment. Individual chewing cycles associated with masticatory function were identified and the timing and dimensions of each chewing envelope established. Corresponding EMG values were also determined and displays of EMG and jaw movement were plotted on a common time base. An average chewing cycle and correlated EMG activity could also be displayed on a high resolution monitor and plotted for a hard copy to enable a comparison to be made between subjects with and without jaw dysfunction.

Twin-tables technique for occlusal rehabilitation: Part I--Mechanism of anterior guidance

Anterior guidance and the condylar path have been considered independent factors. In a recent study, it was revealed that the anterior guidance influenced the working condylar path and even changed when the lateral incisal path deviated from the optimal orbit. This supports the hypothesis that anterior guidance and condylar path are dependent factors. When setting anterior guidance, it is recommended to set the working condyle so that it moves straight outward along the transverse horizontal axis. The angle of hinge rotation created by the angular difference between anterior guidance and condylar path assists the posterior disclusion, but is not solely responsible. The anatomy of the cusps is created by establishing the appropriate form of the posterior cusps aligned to the condylar path so that it also contributes to posterior disclusion. Posterior disclusion is crucial in controlling harmful lateral forces. The molars must disclude slightly more than the deviation in the condylar path to avoid occlusal interferences.

Incisal relationships during speech

The dimensions of movement of the mandible during the reading of a standard passage of text have been measured and enable a speech envelope to be described. The relationship between closest speaking space and the vertical overlap of the incisor teeth shows that there is a trend in this direction, but it is not as definitive a correlation as has been previously assumed. The relationship between the anterior speaking space and the horizontal overlap of the incisor teeth shows a similar trend but with a much reduced correlation. There was often a small space of approximately 0.2 mm between the mandibular incisor teeth and the palatal aspects of the maxillary incisor teeth that, although a common finding in this study, was by no means a constant feature for all subjects.

A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part II: A study of the Bennett movement

Fifty adults with orthognathic maxillomandibular relationships were selected as the test group. The movement of the working condyle was examined during lateral movement of the mandible with an electronic system capable of measuring six degrees of freedom of the mandible with an accuracy of +/- 0.06 mm. The results were: Orbits of the points on the terminal hinge axis d mm from the midpoint during lateral movement of the mandible varied appreciably as the value of d changed. The orbits more affected were the working side on the horizontal and frontal planes. The point on the working side moved forward, laterally, and downward as the value of d was small; and it moved backward, laterally, and upward as the value of d increased. Depending on the value of d, orbits moved in opposite directions. As the value of d varied from small to large, the point on the working side moved only laterally along the terminal hinge axis when d was 55 mm. From this observation, the Bennett movement is explained as the lateral shift of the working condyle along the terminal hinge axis. Reports concerning the directions and mode of motion of the Bennett movement differ because of the lack of specification of location of the positions (targets) assigned for measurement.