The working models (maxilla and mandible) have to be adjusted in the articulators so that the movement paths of the device are congruent with the occlusal guidance paths of the rows of teeth being depicted.
Analysis of the guidance parameters for mandibular movement shows how the movement capabilities of the temporomandibular joint (TMJ), the neuromuscular system, and the shape and arrangement of the teeth relate to each other. All the parts of the system are in harmony. The shape and arrangement of the occlusal surfaces must be related to the TMJ for a properly functioning denture.
The nerve supply to the oral cavity, masticatory muscles, and parts of the face is provided by the three-part nerve, the trigeminalnerve. This paired nerve emerges from the medulla oblongata and is the fifth cranial nerve. It carries sensory fibers (sensory root, radix sensoria, portio major) to the facial skin, the mucous membranes of the mouth, the nasal cavity, and the paranasal sinuses, as well as sensory fibers to the conjunctiva of the eye and to the lacrimal glands. In addition, sensory nerves of taste from the anterior area of the tongue to the brain are carried in the trigeminal nerve. The trigeminal nerve also carries motor fibers (motor root, radix motoria, portio minor) to the muscles of mastication and thereby regulates the movement of the mandible.
The nervous control of the human body, independently regulating vital functions such as respiration, metabolism, and digestion, is largely not subject to our will.There is a close functional connection between the autonomic and somatic nervous systems. The center of the autonomic nervous system mainly lies in the diencephalon and the medulla oblongata. In the autonomic nervous system, two antagonistic regulatory divisions can be distinguished: the sympathetic nervous system and the parasympathetic nervous system.
Cranial nerves
Cranial nerves are found paired as ganglia in the medulla oblongata at the base of the brain (Fig 7-55). Pairs of cranial nerves already leave the brain while inside the cranial cavity. The cranial nerves are numbered in Roman numerals in the order they exit from the brain from front to back.
The cranial nerves can be divided into three groups, classified according to their function:
- Sensory nerves (I, II, VIII, IX)
- Nerves responsible for eye movement (III, IV, VI)
- Pharyngeal arch nerves (V, VII, IX, X, XI)
I. Olfactory nerve (nerve of smell, nervus olfac-torius; also known as fila olfactoria): Consists of processes of the olfactory epithelium of the nasal mucosa and extends to the olfactory bulb as a protuberance of the forebrain (proencephalon); it is not regarded as a true cranial nerve.
II. Optic nerve (N opticus; also known as fasciculus opticus): A protuberance of the diencephalon as a fiber tract at the rear of the eyeball; it is encased in meninges and is hence part of the brain. With its terminal branches, it supplies the retina of the eye.
III. Oculomotor nerve (N oculomotorius): A cranial nerve emerging from the midbrain whose fibers mainly supply the eye muscles; the parasympathetic fibers control narrowing of the pupils.
IV. Trochlear nerve (N trochlearis): A nerve emerging dorsally from the midbrain that supplies the outer muscles of the eye.
V. Trigeminal nerve (N trigeminus; see detailed description later in this chapter).
VI. Abducens nerve (N abducens): A motor nerve that supplies the outer muscles of the eye.
VII. Facial nerve (N facialis): Responsible for supplying the muscles of facial expression, parts of the sense of taste, the salivary glands of the mandible, and the lacrimal glands.
VIII. Vestibulocochlear nerve (N vestibuloco-chlearis): A sensory nerve arising in the pons of the myelencephalon responsible for supplying the organ of balance and the cochlea in the ear.
IX. Glossopharyngeal nerve (N glossopharyn-geus): The main nerve of taste for the tongue; responsible for movement of the esophagus and for the parotid gland.
X. Vagus nerve (N vagus): Supplies the muscles of the larynx and is responsible for the digestive tract as far as the curvature of the large intestine.
XI. Accessory nerve (N accessorius): A motor cranial nerve that supplies the sternocleidomastoid muscle in the neck and functions as a supplementary nerve to cranial nerve X.
XII. Hypoglossal nerve (N hypoglossus): runs as a motor nerve from the medulla oblongata to the tongue and ensures tongue movement.
The brain (cerebrum) is the more highly developed center of the nervous system (Figs 7-52 and 7-53). It lies in the cranial vault and is made up of five segments, divided according to their form and development:
Two nervous systems are involved in nervous control: the somatic nervous system and the autonomic nervous system. Both systems have the spinal cord (medulla spinalis) and the brain (cerebrum) at their center. The peripheral pathways, which are the neurites (nerve fibers) of the nerve cells, run from the centers outward. If these neurites conduct an impulse from the periphery to the center, they are esthesodic fibers (ie, they convey sensory impulses). If an impulse is transmitted from the center to the effector organ, they are fibers that stimulate movement.
Neurites and dendrites have a similar cellular structure (Fig 7-51), which can be broken down as follows:
The ability to react to external stimuli is a basic characteristic of living tissue. In single-celled organisms, all the stages of receiving, transmitting, processing, and responding to stimuli take place in a single cell. In more highly developed, mul-ticellular animals, the stimulus is transmitted by special conductive tissues—the nerves. Receiving, conducting, and processing stimuli enables living beings to orient themselves in their surroundings and to act and react independently.
The second antagonistic pair of facial expression muscles comprises the levator muscle and the depressor muscle of the angle of the mouth with their accessory muscles.