TMJ Disorders and Orofacial Pain. Axel Bumann

the articular protuberance has been a subject of controversy in dentistry for many years (Lindblom 1936, Pullinger et at. 1985). A well-defined condylar position oriented to the maximal occlusion is especially relevant to extensive dental treatment (Spear 1997). In the past, to transfer the jaw relations to an articulator the condyles were always placed in their most posterosuperioi position because this relationship could be most easily reproduced (Celenza and Nasedkin 1979). Under purely static conditions the condylar position is dependent upon the shape of the fossa, the inclination of the protuberance, and the shape of the condyle. In the 1970s this led to the assignment of a geometric centric position of the condyle in the fossa (Gerber 1971). However, the dimensions of the joint space are quite variable in both the sagittal plane (anterior, posterior, and superior) and the transverse plane (medial, central, and lateral) (Pullinger et al. 1985, Hatcher et al. 1986, Christiansen et al. 1987, Bumann et al. 1997). For this reason the concept of an anatomical orientation is untenable, and the radiographic techniques (p. 148) are unsuitable for determining a therapeutic condylar position (Pullinger and Hollender 1985). Therefore the current definitions of centric relation are geared more toward the functional conditions (van Blarcom 1994, Dawson 1995, Lotzmann 1999). It has been demonstrated experimentally that the surfaces of the temporomandibular joint are subjected to loads of 5-20 N (Hylanderl979, Brehnan et al. 1981, Christensen et al. 1986). In a patient’s habitual occlusion this force is partially intercepted by the occluding premolars and molars. Tooth loss can lead to higher joint loading and regressive adaptation (van den Hemel 1983, Christensen et al. 1986, Seligman and Pullinger 1991). However, if the joint’s capacity for adaptation is sufficiently great, degenerative changes may be avoided (Helkimo 1976. Kirveskari and Alanen 1985. Roberts et al. 1987). The direction of functional loading is anterosuperior against the articular protuberance (Dauber 1987). Clear evidence for this is the presence of the load-induced secondary cartilage on the joint surfaces in this region.

       39 Sagittal relationships

      Macroscopic anatomical preparation showing the relation of the fossa, disk, and condyle to one another in the sagittal plane. Because the shapes of fossae and condyles vary so greatly, it is not possible to determine a universally applicable measurement of the condylar position. Although the physiological (i.e. centric) condylar position is defined as the most anterosuperior position with no lateral displacements (arrows), this position depends upon the basic neuromuscular tonus.

       40 Frontal relationships

      Macroscopic anatomical preparation showing the relation of the fossa, disk, and condyle to one another in the frontal plane. In this plane, too, there is no standard geometric arrangement of condyle and fossa because of the variability of the hard and soft tissues (Yung et al. 1990). In this preparation the disk (arrows) is displaced laterally. Structures of the bilaminar zone (1) can be identified in the medial portion of the joint. The close proximity of the joint to the middle (2) and inner ear (3) can also be observed.

       41 Horizontal relationships

      A right temporomandibular joint viewed from above showing the relation of the fossa, disk, and condyle to one another in the horizontal plane. The lateral portion of the joint is near the left border of the picture. Near the upper border a section through the external auditory meatus can be seen (1). The roof of the fossa has been removed. Near the center of the picture lies the transition from the pars posterior (2) to the bilaminar zone (3). The central perforation was created during sectioning, and through it can be seen the upper surface of the condyle (arrow).

       Positioning of the condyles on the protuberances is accomplished exclusively through the antagonistic activity of the neuromuscular system and from a functional standpoint requires no border position.

       42 Relationships in the frontal plane

      Schematic depiction of the joint space relationships in the frontal plane. A number of studies have reported that the dimensions found in the lateral, central, and medial parts may vary greatly (Christiansen et al. 1987, Vargas 1997). Although the lateral portion is affected more frequently by degenerative changes, the width of the joint space is usually least at its center (blue line).

       43 Contours on the temporal surface of the joint

      Schematic drawing (modified from Hasso et al. 1989) of the contours in the lateral (green), central (blue), and medial (red) regions of the joint. The entire protrusive functional path is represented as a convex bulge that can vary markedly as the result of regressive or progressive adaptation. Therefore, the loads borne by the lateral and medial portions of the joint during function are also influenced by the morphology of the articular protuberance (Öberg et al. 1971, Hylander 1979. Hinton 1981).

       44 Relationships in the medial part of the joint

      Schematic drawing (modified from Christiansen et al. 1987) of the positional relationships in the medial portion of a left temporomandibular joint. This finding also emphasizes the fundamental principles of physiological joint movements. As with all other joints, the temporomandibular joint has a passive “play” space in all directions and is thus not confined to any border position. Average values: 1 = 3.4 mm; 2 = 4.4 mm

Articular Disk

      The articular disk can be divided into three regions based upon their function: the partes anterior, intermedia, and posterior. The primary functions of the disk are to reduce sliding friction and to dampen load spikes (McDonald 1989, Scapino et al. 1996). The extracellular matrix of the Fibrocartilaginous disk consists primarily of type I and type II collagen (Mills et al. 1994b). The orientation of the collagen fibers in the disk displays a typical pattern (Knox 1967, Scapino 1983). In the pars intermedia dense bundles of collagen fibers run approximately in a sagittal direction. These intertwine with the exclusively transverse fibers of the pars anterior and pars posterior (Takisawa et al. 1982). Elastic fibers are found in all parts of the disk (Nagy and Daniel 1991) but are more numerous in the pars anterior and in the medial portion of the joint (Luder and Babst 1991). A reduction in the thickness of the disk results in an exponential increase in the load it experiences (Nickel and McLachlan 1994). The more rapidly a load is applied, the “stiffer” the disk reacts (Chin et al. 1996). The inferior stratum and the convexity of the pars posterior help stabilize the disk on the condyle.

       45 Alignment of fibers within the disk and their attachment to the condyle

      Macroscopic anatomical preparation of the disk-condyle complex of a right temporomandibular joint The collagen fibers of the pars posterior (1) and the pars anterior (2) run from the medial to the lateral pole of the condyle (Moffet 1984), making possible a wide range of movement of the disk relative to the condyle in the sagittal plane. The fibers of the pars intermedia (outlined area), on the other hand, run in a more sagittal direction. The medial pterygoid muscle (3) makes its insertion at the anteromedial region.

       46 Cranial view

      A view from above of the disk in Figure 45 after removal of the condyle, the fibers in the pars posterior (1) and pars anterior