The first antagonistic muscle pair in the angle of the mouth comprises the orbicular muscle of the mouth and the buccinator muscle as well as their accessory muscles. They form the muscular basis of the lips and cheeks. The fibers of these two muscles cross at the modiolus.
The muscles of facial expression (also known as "mimic muscles") do not run from one bone over a joint to another bone but often only attach to the skin, without an intermediate tendon. The facial expression muscles move the facial skin and give the face its expressiveness. The numerous furrows, dimples, and creases that are produced by these muscles are an expression of a person's mood. The facial expression muscles are mainly arranged around the orifices of the mouth, nose, and eyes, as well as the ears, because the position and shape of these openings in the face determine the particular expressive quality of the face.
Several functional groups of muscles attach to the hyoid; these are involved in both jaw movement and the swallowing process. According to the theoretical classification, they can be characterized as mouth-opening muscles. A distinction is made between the suprahyoid muscles (above the hyoid) and the infrahyoid muscles (below the hyoid).
The temporal muscle (musculus temporalis) is the strongest mouth-closing muscle. Its origin is in the whole temporal fossa, which is almost completely filled. It is made up of a fan-shaped muscle bundle, whose fibers combine to form a very sturdy tendon that runs within the zygoma to the muscular process of the ramus of the mandible. The muscle insertion is actually the whole anterior edge of the ramus of the mandible. The individual bundles of fibers of the fan of muscle partly run in opposite directions.
The TMJs and teeth are the rigid guide elements of mandibular movement; muscle guidance forms the third element. Muscles of mastication, as an active part of the locomotor system, move the mandible against the cranium and produce masticatory pressure. The TMJ is relatively elastic and unstable because of the intrinsic mobility and compressibility of tissue and the bisection of the joint by the disc. Tooth guidance functions within small deflections of movement (ie, only movements with tooth contact are maintained). All movements outside of tooth contact are mainly guided by the interaction of the different masticatory muscles. Each person develops a differentiated habit of masticatory movements for different food consistencies.
Muscle contractions are triggered by nerve impulses. In the case of voluntary movements, the nerve impulses are transmitted by motor nerve pathways from the cerebral cortex via the spinal cord to the motor end plates on the individual muscle fibers. The number of muscle fibers in a muscle may be as high as two million. Each muscle fiber can be stimulated independently and contract separately from the other fibers. All the muscle fibers can be stimulated at once by the nervous system, or only some of them can be stimulated and a movement can be performed with graduated expenditure of energy. Destruction of nerve conduction results in paralysis of the muscle and inactivity atrophy; ie, the muscle shrinks or atrophies. Muscle mass will increase if put under heavy strain.
A muscle is an organ of movement made up of many muscle cells that uses its contractive ability to move the bones or, as a hollow muscle or sphincter muscle does, make cavities smaller and close openings. The individual muscle cells are joined together by connective tissue membranes or sheaths, which in turn merge to form tendons and are thus able to transfer forces (Fig 7-33).
When depicting the occlusal contact points in detail, it is essential to view these contacts in articulation or establish the paths they follow during mandibular movement. The articular movements of the centric stops run on precisely fixed occlusal guidance paths of their antagonists (Fig 7-30).
In dynamic occlusion, different physiologic sliding movement situations arise within the dentition, and these are described by different concepts of occlusion.
Occlusion (Latin, occludere = to close; closure of the teeth) generally denotes each contact between the teeth of the maxilla and the teeth of the mandible in a dentition.The status of tooth contacts in occlusion is covered by various terms intended to describe the diversity of possible mandibular positions in which tooth contact takes place. There are also terms used to describe the tooth contacts that deviate from normal. The following paragraphs outline the distinctions among terms.