Kinesiology of Mastication and Ventilation



Kinesiology of Mastication and Ventilation






Temporomandibular Joint


Mastication is the process of chewing, tearing, and grinding food with the teeth. This process involves an interaction among the muscles of mastication, teeth, tongue, and the pair of temporomandibular joints. The temporomandibular joint, commonly referred to as the TMJ, consists of the articulation between the condyle of the mandible and the mandibular fossa of the temporal bone. Each jaw is equipped with a pair of TMJs, each palpable during jaw movement at a point just anterior to the ear. Any movement of the jaw such as chewing, speaking, and swallowing requires movement of the TMJ. Pathology or trauma involving the TMJ can be extremely painful and debilitating because of the rich sensory innervation to this frequently used joint. Pain originating in the TMJ is often referred to other areas and perceived as headache or neck pain. This chapter highlights the relevant anatomy and kinesiology of the TMJ as a basis for understanding and treating various disorders associated with this joint.



Osteology and Related Structures


The mandible, the temporal bone, the maxillae, and the zygomatic, sphenoid, and hyoid bones are related to the structure and function of the TMJ. Although this text highlights the most important features of these bones, additional anatomic features are included in Figure 13-1 for future reference.




Mandible

The mandible, or lower jaw bone, is the largest of the facial bones (Figure 13-2). This highly mobile bone is suspended from the cranium by muscles, ligaments, and the capsule of the TMJ. Many of the important bony landmarks are described as follows.



The body is the horizontal portion of the mandible with sockets for the lower 16 adult teeth (see Figure 13-2). The ramus projects vertically from the body of the mandible. The angle of each mandible provides the attachment for the masseter and medial pterygoid muscles. The mandibular condyle is the convex portion of bone arising from the ramus. Each condyle articulates with the concave mandibular fossa of the temporal bone, forming the TMJ (see Figure 13-1). The coronoid process is the thin triangular projection of bone arising from the anterior aspect of the ramus. The mandibular notch extends between the coronoid process and the mandibular condyle (see Figure 13-2).



Temporal Bone

The mandibular fossa of the temporal bone articulates with the mandibular condyle, forming the TMJ. The anterior aspect of the mandibular fossa is marked by the articular eminence (Figure 13-3). Just posterior to the mandibular fossa is the external auditory meatus: The external opening for the ear. The zygomatic process of the temporal bone projects anteriorly, forming the posterior half of the zygomatic arch (see Figure 13-3). The zygomatic arch is formed by the union of the zygomatic process of the temporal bone and the temporal process of the zygomatic bone (cheek bone) (see Figure 13-1). The zygomatic arch serves as the proximal attachment for the masseter muscle. The temporal fossa is a slightly depressed area on the side of the skull formed by the union of five different cranial bones (see Figure 13-1).








Supporting Structures



• Articular disc: The articular disc of the TMJ rests between the mandibular condyle and the mandibular fossa of the temporal bone (Figure 13-7, A). This prominent structure consists of dense fibrous connective tissue. The disc provides joint stability, reduces joint contact pressure, and helps safely guide the condyle across the rough articular eminence of the temporal bone.



• Capsule: The TMJ is surrounded by a fibrous capsule. Laterally, the capsule thickens and is called the lateral ligament of the TMJ. The capsule and the lateral ligament provide stability to the TMJ during chewing motions (Figure 13-7, B).



Kinematics


The primary motions of the TMJ are protrusion and retrusion, lateral excursion, depression and elevation. All of these motions play an essential role in mastication (chewing).





Depression and Elevation

Depression of the mandible opens the mouth, whereas elevation closes the mouth (Figure 13-10). Both motions play a fundamental role in eating, yawning, and talking. The adult mouth can be opened an average of slightly more than 2 inches. This degree of opening is often gauged by the ability to fit three knuckles (proximal interphalangeal joints) into the mouth.



As is illustrated in Figure 13-10, A, fully depressing the mandible—opening the mouth—requires extreme anterior translation (protrusion) of each mandibular condyle relative to its mandibular fossa. Normally, the articular disc translates anteriorly along with each mandibular condyle, helping to properly guide the motion (Figure 13-10, B). The disc is “reseated” into the joint as the mandible is elevated and retrudes (retracts) during closure of the mouth. In both opening and closing the mouth, the articular disc is essential in minimizing the contact stress between the mandibular condyle and the articular eminence of the temporal bone.




Atlas




Masseter


image
(From Drake RL, Vogl W, Mitchell AWM: Gray’s anatomy for students, ed 2, St Louis, 2010, Churchill Livingstone.)




















Proximal Attachment: Zygomatic arch
Distal Attachment: External surface of the mandible, between the angle and the coronoid process of the ramus
Innervation: Cranial nerve V (branch of the mandibular nerve)
Actions:
Comments: The masseter is a thick, powerful muscle that is easily palpable just above the angle of the mandible during a biting motion. Bilateral activation of the masseters elevates the mandible, bringing the teeth together for mastication. The primary function of the masseter is to develop large forces between the molars for effective grinding and crushing of food.


image



Temporalis


image
(From Drake RL, Vogl W, Mitchell AWM: Gray’s anatomy for students, ed 2, St Louis, 2010, Churchill Livingstone.)




















Proximal Attachment: Temporal fossa
Distal Attachment: Coronoid process and anterior edge of the ramus of the mandible
Innervation: Cranial nerve V (branch of the mandibular nerve)
Actions:

Bilateral:




Unilateral:


Comments: The temporalis is a fan-shaped muscle that fills much of the concavity of the temporal fossa. The temporalis narrows into a broad tendon as it courses distally through a space between the zygomatic arch and the lateral side of the skull. This muscle contributes to both essential kinematic elements of closing the mouth: Elevation and retrusion of the mandible.


image



Medial Pterygoid


image
(From Drake RL, Vogl W, Mitchell AWM: Gray’s anatomy for students, ed 2, St Louis, 2010, Churchill Livingstone.)


Dec 5, 2016 | Posted by in MANUAL THERAPIST | Comments Off on Kinesiology of Mastication and Ventilation
Premium Wordpress Themes by UFO Themes