14.1 Introduction
Of all the structures in the head region, physical therapists are best able to treat the jaw (temporomandibular joint or TMJ) and the atlanto-occipital joint, which have already been described in Chapter 13.3.6. The special feature of the TMJ is that one joint never moves alone and the interaction with the contralateral joint must always be considered.
Symptoms arising in the head/jaw/facial region are integrated into the general term craniomandibular dysfunction (CMD). This literally describes the suboptimal functioning of the cranium (condylar path on the skull) and the mandible (the head[s] of the lower jaw) joint partners. The term temporomandibular joint disorder (TMD) is more commonly used in English. It more precisely describes the suboptimal functioning of the head of the mandible (including the articular disk located in the joint) and the temporal bone and names the bones that contribute anatomically to the TMJ.
Many craniomandibular symptoms present as different types of headache or as ear, tooth, jaw, or face pain. This frequently involves referred pain arising from structures such as muscle trigger points (where pain is projected from sections of muscle into other regions).
In addition to the systematic subjective and objective assessments, precise palpation of the muscles and, as much as possible, the articular structures is of importance. This enables the therapist to differentiate symptoms arising from referred pain (from muscular trigger points) and other causes, such as arthrotic changes in a joint or articular damage.
14.1.1 Significance and Function of the Temporomandibular Joint
The TMJ is not only needed for the function of mastication, it is also used for speaking, singing, yawning, kissing, etc. These are generally movements involving the opening and closing of the mouth.
The biomechanics of the TMJ enable movement in all three spatial axes (vertical, transverse, sagittal). Mandibular movements are never purely translational or purely rotational.
The main movements in the mandible are the following:
14.1.2 Common Applications for Treatment in this Region
As with other joints in our body, the TMJ also suffers from the following:
Capsular and noncapsular restrictions in mobility.
Pathological conditions in the disk-condyle complex (the relationship between the head of the lower jaw and the buffering articular disk as well as the opposing joint surface).
Injuries to ligaments or ligamental overuse syndromes.
Injuries to muscles or muscular overuse syndromes.
In dental literature, TMDs are commonly subdivided as follows:
Myogenic, that is, symptoms originating in the muscles.
Arthrogenic, that is, direct joint symptoms.
Myoarthropathic symptoms, that is, a combination of muscular and joint symptoms.
It is difficult to directly differentiate the above-mentioned symptoms in practice, as a TMD arising from muscular symptoms is usually directly followed by the involvement of articular structures.
14.1.3 Required Basic Anatomical and Biomechanical Knowledge
Often, there is not enough time available in physical therapy training to intensively address the head and the TMJ, in particular. A summary of the fundamental (palpable) structures is included in sections 14.6.1 and 14.6.2 to improve anatomical orientation. Therapists should initially practice on a plastic skull to obtain more confidence, before palpating the corresponding structures on patients.
14.2 Anatomy of the Bony Skull
14.2.1 Dividing the Head into Regions
To aid orientation, the skull is divided into 11 regions (▶ Fig. 14.1 ):
The following 11 bony structures found in these regions can be palpated well (▶ Fig. 14.2):
Now that rough anatomical orientation is possible, the more specific palpation of bony structures on the skull follows.
14.3 Palpation of the Bony Skull
14.3.1 Frontal Aspect of the Viscerocranium
Overview of the Structures to be Palpated
In addition to the structures mentioned above, prominent, palpable bony structures include the following (▶ Fig. 14.3):
Pressure points of the trigeminal nerve:
supraorbital foramen: exit point for the lateral branch of the supraorbital nerve (first pressure point of the trigeminal nerve) (1);
infraorbital foramen: exit point for the infraorbital nerve (second pressure point of the trigeminal nerve) (2);
mental foramen: exit point for the mental nerve (third pressure point of the trigeminal nerve) (3).
The structures that can be palpated via the lower jaw (mandible) include the following:
14.3.2 Lateral Aspect of the Skull
The dominating section of the lateral skull is formed by the side wall of the skull, the parietal bone. The temporal bone is the central bone in the lateral skull. Its surface forms a joint with the articular disk and the head of the mandible, forming the TMJ.
Overview of the Structures to be Palpated
Once again, orientation begins with the mandible (▶ Fig. 14.4):
14.4 The Jaw—Temporomandibular Joints
Compared with other joints such as the knee, many of the ligamentous and bony structures in the TMJ cannot be palpated directly and therapists must use a variety of knacks to test these structures. It is important that therapists have good spatial sense as well as comprehensive knowledge in biomechanics of one or, more precisely, both TMJs, as movement in one TMJ causes simultaneous movement in the other.
In actual fact, the jaw should be called the temporo-(disco) mandibular joint, as the temporal bone and the mandible do not articulate with one another alone.
14.4.1 Required Basic Knowledge of Topography and Morphology
The articular disk, the meniscus or joint buffer, divides the jaw into superior and inferior compartments. The superior compartment, otherwise known as the upper joint, is formed by the temporal bone and the articular disk (discotemporal), while the inferior compartment or lower joint is the articulation between the mandible and the disk. The superior compartment functions as a gliding joint, while the inferior compartment acts as a mobile hinge joint.
The basic shape of the articular disk is similar to a horizontal figure eight. It is thinnest in the middle, approximately 1 to 2 mm thick, and can be approximately 3 to 4 mm thick at the ends. It is made of taut connective tissue, with cartilaginous cells still found at the edges. The disk is fibrocartilaginous in the area lying over the head of the mandible, where it resembles a cap (▶ Fig. 14.5a, b).
The true function of the disk is to even out existing differences in articulating surfaces, namely the condylar path (temporal bone) and the head of the mandible. During movements of the jaw, rotation of the head of the mandible and the pull from the lateral pterygoid muscle causes the disk to move along the path formed by the temporal bone. The disk could therefore also be labeled a mobile joint socket.
14.4.2 Biomechanics of the Temporomandibular Joint
TMJ movements essentially consist of combined rotation and gliding. When the mouth is opened, a hingelike rotation occurs around a transverse axis running through both condyles. This is accompanied by translation in a sagittal direction, moving anteroinferiorly when the mouth is opened and posterosuperiorly when the mouth closes.
We primarily differentiate between:
movements associated with the opening and closing of the mouth; and
the required grinding movements associated with mastication.
Let us now take a more precise look at the movements that occur when the mouth is opened. The rotational-translational movement pattern at the TMJ is flowing, but will be divided here into three phases to make the complex biomechanics easier to understand.
Opening the Mouth
Muscles: Presented simply, mouth opening involves rotation initiated by the pull of the lateral pterygoid and the suprahyoid muscles and controlled by the mouth closure muscles that decelerate movement.
Joint: In phase 1 (first phase of rotation), the condyles in the inferior compartment rotate slightly. This movement is initiated by the pull of the lateral pterygoid and the suprahyoid muscles and acts to overcome the occlusion of the teeth. This causes the head of the mandible to briefly rotate anteriorly. Following the mobile joint socket principle, the articular disk ideally moves in an anterior direction along the condylar path in a similar manner to the action of a pasta machine. Its movement is decelerated by the superior stratum of the bilaminar zone and the posterior fibers of the temporalis muscle and the lateral ligament. The inferior stratum, secured onto the condyle, relaxes (▶ Fig. 14.6a).
The first phase flows over into phase 2, where more gliding occurs at the head of the mandible. The lateral pterygoid muscle pulls the disk, acting as a mobile joint socket, in an inferoanteromedial direction beneath the articular tubercle. This is also defined as protrusion. This movement is produced by the pull of the lateral pterygoid, assisted and controlled by the muscles mentioned above, and is essentially decelerated by the superior stratum of the bilaminar zone, the posterior fibers of temporalis, and the lateral ligament (▶ Fig. 14.6b). To open the mouth as wide as possible, the condyles must rotate once again at the end of the condylar path in phase 3 (second phase of rotation).
The disk was pulled underneath the articular tubercle in the second phase and is now pulled along anteriorly, as the head of the mandible rotates, and pulled up onto the articular tubercle with the assistance of the lateral pterygoid muscle and the above-mentioned muscles. Only then can the mouth open up fully by further rotating. The movement of the disk is decelerated again by the superior stratum of the bilaminar zone. The inferior stratum, secured onto the condyle, is now placed under tension (▶ Fig. 14.6c).
Closing the Mouth
The closure movement will now be addressed. The returning rotation of the head of the mandible moves the disk back to its original position (posterior direction of rotation for the head of the mandible) (▶ Fig. 14.7).
The disk moves posteriorly at the same time and its movement is decelerated by the lateral pterygoid muscle.
Grinding Movements
The movements associated with mouth opening involve simultaneous contraction of the respective muscle groups and result in a relatively symmetrical and simultaneous movement of the two joints in the same direction. In comparison, grinding movements require muscles and joints to act differently.
While the chin remains in the median plane when the mouth is opened or closed, the tip of the chin moves to the right or the left during grinding movements. We differentiate between the working side and the balancing side. Food is reduced to small pieces on the working side while the other side (balancing side) carries out the required anteroinferior translation.
Therapists can only recognize, interpret, and treat abnormalities when they understand the biomechanics discussed above.
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