Functional states of mandibular movements and synovial pumps of the temporomandibular joint. Is it possible to provide a biomechanically correct replacement for the TMJ?

Due to its complexity, there is currently an incomplete understanding of temporomandibular joint (TMJ) function, especially in relation to the morphological interplay of the condyle and the disc as well as the disc, the Os temporale and the lateral pterygoid muscle. This also holds true for synovial flow and synovial pumps, the existence of which we postulate and for which we present a theory of their mechanism. In view of the complexity of mandibular movements and the morphology and function of the TMJ, we need to know how precisely a reconstruction of the TMJ, if necessary, must be adapted to nature. An analysis of the morphology of the functional states of the mandible, as well as the synovial pump system, should at least provide a basis for moulding reconstructions.

Biomechanics of the mandible and growth extension.

BACKGROUND AND OBJECTIVE: One way of determining the direction of growth of the mandible is to consider the temporomandibular joint and movement of the mandible as a four-joint gear system, regarding growth then as an extension of the gear system. Our aim was to examine any correlations between the type of biomechanical growth extension and change in the maxilomandibular relation after Class II therapy. SUBJECTS AND METHODS: A total of 130 lateral cephalograms-before and after orthodontic treatment-were available from 65 adolescent class II patients with open bite or deep bite. The two lateral cephalograms from each patient were superimposed on the occlusal plane. Cephalometric values and the vertical base point deviation were determined from biomechanical analyses, together with three distances and three angles. RESULTS: No correlation between the cephalometric data and distances or angles were observed. Although there were no significant differences in the distances, we did note significant differences in all three angles (p < 0.05). CONCLUSION: If gear system extension during growth is considered, this can be interpreted as meaning that the occlusal plane of those patients with an initially open bite dropped during treatment, but that it rose in patients with an initially deep bite.

Mandible, maxilla and cervical spine--a functional unit?

The motion patterns of mandibular points were recorded in vivo in closed, free movements of the mandible parallel to the sagittal-vertical plane. The points ran along loops which were valued by their area and length. All points whose loops included the same area under regarding the sense of circulation formed a straight line. Lines belonging to different areas were parallel. When the absolute areas of the oops were plotted for particular points a hollow depression with two minima resulted. The point that showed the lowest minimum in the depression corresponded to the position of the neuromuscular mandibular axis of rotation. The points running along equal loop lengths formed elliptical lines with a minimum below the condyle. The lines of constant loop area and loop length were overlaid with lateral radiographs, to match the patterns of motion with anatomical structures. The mandibular axis of rotation lay mostly cranial anterior of the condyle whereas the point with the shortest path lay mainly below this axis point, inside the bony structures. The row of teeth in the maxilla was found to be located below the line of minimal loop lengths. The cervical spine was arranged along the depression of the minimal absolute areas.

Functional conditions of the mandible: theory and physiology.

The functional conditions of the mandible are differentiated according to the number of kinematic degrees of freedom assigned to each mandibular movement. One degree of freedom: pro- and retrusive occlusal border movement. The interplay of the TMJs with the occluding teeth determines a compulsory course which corresponds to a 4-bar-chain guidance. 2 degrees of freedom: free sagittal mouth movement without tooth contact. Using graphic recordings of cyclic mandibular movements, the mobile hinge axis is identified as a mandibularly fixed line which is not directly categorized as a part of an anatomical structure. In the maxillary coordinate system, its movement describes a cylinder; sagittally, it describes a circle. The mandibular positions are clearly identifiable with 2 angles. The in vivo measurements show that neuromuscularly healthy systems supply the mandible with anticipatory guidance. 3 degrees of freedom: bolus function. The articular space in the TMJ is utilized.

Functional condition of the mandible: physical structures of free mandibular movement.

Starting with the physical definition of the concept "mobile hinge axis", which only allows 2 degrees of freedom for planar mandibular movement, it will be shown that the hinge axis of the temporomandibular joint cannot be found with a small mouth-opening rotation, as is usual but erroneous. By recording cyclic mandibular movements with a measuring system which itself possesses 6 degrees of freedom, the mobile hinge axis can be found. However, there are patients which do not use a mobile hinge axis, which is indicative of latent functional disturbances of the neuromuscular system.

Elements of a general theory of joints. 6. General kinematical structure of mandibular movements.

Movements of the mandible are recorded in vivo by a measuring system (MT 1602) that takes all 6 degrees of freedom of a rigid body into account. Class-I-patients were asked to move their mandible in the sagittal-vertical plane. The evaluation of the measurements yields an almost plane mandibular movement that only uses 2 degrees of freedom although a general plane movement normally possesses 3 degrees and although the human temporomandibular joint (TMJ) has a certain space of motion. This quantitative reduction of the degrees of freedom by one is produced by a neuro-muscularly guided dimeric link chain that cannot directly be related to anatomical landmarks. The diverse types of mandibular motion of a sound patient differ in the constant ratio of the angular velocities around the 2 axes of the dimeric link chain. Therefore, the paths of the individual mandibular points are epicycloids or hypocycloids. Patients with disorders of the TMJ and the neuromuscular feedback system do no longer show this constancy of the angular velocities' ratio. Besides that, we theoretically derive and empirically prove the fact that common axiographs do not record the "path of the hinge axis" of the TMJ, on principle. In this context we discuss some--in dentistry and anatomy widespread--fundamental misconceptions of the rigid body's kinematics.

[Arrangement of neuromuscular movement cycles of free mandibular movements following Le Fort I-operations]. / Anordnung neuro-muskulärer Bewegungszyklen freier Unterkeiferbewegungen nach Le-Fort-I-Operationen.

In orthognathic surgery the Le Fort I osteotomy changes the structure of motion of the mandible. This structure and its changes could reliably and quantitatively be described if it was evaluated by a projection of the mandibular movement upon a couple's movement in a gearing system. The comparison of Le Fort I cases with orthodontically treated class-I-cases shows significant differences.

[Structural arrangement of mandibular neuromuscular guided drive systems]. / Anordnungsstrukturen der mandibulären, neuro-muskulär gesteuerten Getriebesysteme.

The free movements of mandibular, oral apertures can be related to the couples' movements of neuromuscular throttle cranks which reveal a common specific property: a double dead position of the mandible (couple). As the neuromuscular system uses the same cyclic path of a well-defined mandibular point for the opening and the closing process of a specific mandibular movement, the mandible can follow the same or two different trajectories although the positive drive works on. The different movements of oral aperture are related to the geometrical positions of the cranks at the fixed plane. Geometrical properties and measures of the gear systems of eleven class-I-patients are reported and discussed.

[Posterior guidance of the mandible as a neuromuscular assigned dimeric joint chain]. / Die posteriore Führung der Mandibula als neuro-muskulär gegebene dimere Gelenkkette.

Measurements of the mandible's movements which take its six degrees of freedom into account show that the conventional concept of a condylar hinge axis does not hold: on principle the structure of motion of the condylar hinge axis is not different from that of the incisal edge. The spaces of movement which are related to the condylar hinge axis and the incisal edge are factually enforced by a hinge axis of the neuromuscular system. This neuromuscular hinge axis cannot directly be related to anatomical structures although in the sagittal-vertical plane it reduces the number of the degrees of freedom from three to two.

[The general even mandibular movements as couple movements in neuromuscular guided mechanism]. / Die allgemeinen ebenen Mandibulabewegungen als Koppelbewegungen in neuro-muskulär gesteuerten Getriebesystemen.

The manifold mandibular movements of oral aperture can be modelled by movements of couples in neuromuscular gear systems. These systems consist of the dimeric link chain of the neuromuscular hinge axis (rocking arm) and a neuromuscularly enforced cyclic trajectory of a well-defined point of the mandible. The neuromuscular hinge axis is the common constant of all gear systems whereas the position of the cyclic trajectory at the fixed plane (maxilla) is closely related to the specific path of the entire rigid body mandible. The presented theory is inferred by measurements of the mandible's movement that take all six degrees of freedom into account.