Kirsten M. Thieme

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.

Variations in cyclic mandibular movements during treatment of Class II malocclusions with removable functional appliances

The aim of the study was to establish whether juveniles with a Class II malocclusion change the neuromuscular control of mandibular movements during the course of orthodontic treatment with removable functional appliances (RFAs). Neuromuscular control can be indirectly evaluated by recording cyclic planar mandibular movements which were freely carried out by the patients (28 girls, 14 boys, aged 11.1 ± 1.1 years at the start of treatment) and measured with an ultrasonic device before, during, and after Class II functional appliance therapy, with either an activator or a bite jumping plate. The cyclic movements represented simultaneous rotations of the mandible around a maxillary and mandibular fixed axis (MFHA) and could be characterized by μ(α)-diagrams (μ = swing angle of MFHA, α = mouth opening angle) and path length (L) of the MFHA. The μ(α)-diagrams clearly divided into four parts: movement representing protrusion, mouth opening, and two parts of backward closing as known from Posselt diagrams. Parameters from the Posselt and μ(α)-diagrams were checked by one-factor analysis of variance on a 5 per cent significance level for group dependency. For one-third of the patients investigated, no significant changes were seen in any parameter pre- or post-therapy. However, patients showing an initially large mouth opening capacity or a very short condylar path changed their neuromuscular control to that of Class I subjects. Analysis of μ(α)-diagrams provides the possibility of assessing changes in the neuromuscular control of the mandible during Class II treatment.

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.