CHAPTER 3

HEAD AND NECK ANATOMY

Basic knowledge of the skull, facial bones, jaws,and muscles of the head and neck region arefundamental for a Dental Technician. It is important tounderstand the relationship of the bones and musclesas they work together to provide support for thedentition (teeth) and movement for mastication(chewing).

STRUCTURE OF BONE

The bones of the human skeleton provide rigidsupport for muscles and skin, and serve to protect theeasily injured organ systems of the body. Bone itself isa living, highly vascular tissue, which is made up ofboth inorganic (minerals) and organic (cells &connective tissue fiber) elements. The inorganiccomponent of bone serves as a warehouse for calciumand phosphorous, two essential minerals for the body.

Bone consists of a hard outer shell called cortical orcompact bone and an inner spongy, porous portionreferred to as cancellous bone (fig. 3-1). Within thiscancellous area are the bone marrow spaces responsiblefor manufacturing blood cells. The majority of bloodcells are made by the bone marrow found in the longbones, such as the femur or thigh bone.

A thin layer of connective tissue, calledperiosteum, surrounds each bone and providesnourishment through many vascular vessels. Theperiosteum also contains many nerve endings thatrespond to trauma with the sensation of pain. When abone breaks, it is the periosteum that hurts, not thebone itself. When new bone is required, such as when abreak occurs, it is the periosteum which provides thecells that make the new bone.

Bone can be classified as to how it develops, itslocation, and its shape. Membraneous bone formsfrom the periosteum in successive layers and is usuallyflat such as those of the skull. The long bones of thearms and legs are cartilaginous bones, which developfrom cartilage.

BONES OF THE SKULL

The skull consists of 28 bones that form theframework of the head and provide protection for the

Figure 3-1.—Structure of a typical flat bone.

brain, eyes, and ears. It can be divided into two parts:the cranium and the bones of the face. The cranium isprimarily involved in housing and protecting the brain.The bones of the face are a complex framework thathelps to form facial features, the upper jaw (maxilla)and lower jaw (mandible). With the exception of themandible and the bones of the inner ear, all skull bonesare joined together firmly along seams called sutures.An example of sutures is shown in figure 3-2. Suturesare sometimes considered immovable; however, theydo permit a small amount of movement and providemechanical protection for the brain by absorbing muchof the force if a blow to the head occurs.

The cranium is formed by eight cranial bones,which form the foundation for attachment of many ofthe muscles necessary for head movements andchewing. Figure 3-3 show the cranial bones, and Table3-1 lists them as either single or paired bones.

Frontal Bone

The frontal bone forms the front part of the skullabove the eyes, which includes the forehead and part of

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Figure 3-2.—Sutures of a skull.

Table 3-1.—Bones of the Cranium

Single Bones Paired Bones

Occipital Parietal

Frontal Temporal

Sphenoid

Ethmoid

the nasal cavity. In children, the frontal bone developsas two parts. They are usually fused together by age 5or 6. The two frontal sinuses (air spaces in the bone)are located above each eye socket.

Parietal Bones

The two parietal bones are located behind thefrontal bone. These bones form the greater part of theright and left sides and the roof of the skull. They eachhave four borders and are shaped like a curved plate.

Temporal Bones

The temporal bones form the sides and part of thebase of the skull in the area of the ear. One temporalbone is located on each side of the head. It is readilyrecognized as “fan-shaped.” Each encloses the internalear structures and have depressions called glenoidfossae that forms the articulation with the mandible.

Figure 3-3.—Cranial bones.

The zygomatic process of the temporal boneprojects out into the zygomatic bone of the face andforms the lateral part of the zygomatic arch. Both theglenoid fossae and zygomatic process can be seen infigure 3-4.

Occipital Bone

The occipital bone forms the back part of the skulland the base of the cranium. It joins with the parietaland temporal bones. In the center, underside (inferior)portion of the cranium, there is a large opening calledthe foramen magnum (fig. 3-5), through which nervefibers from the brain pass and enter into the spinal cord.

Figure 3-4.—Temporal bone.

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Ethmoid Bone

Figure 3-5.—Foramen magnum of cranial cavity viewed fromabove.

The ethmoid bone is situated in front of thesphenoid bone in the front part of the cranium (fig.3-7). Through small openings in this bone pass nervesto the roof of the mouth that are responsible for sense ofsmell.

BONES OF THE FACE

The facial skeleton consists of 14 stationary bonesand a mobile lower jawbone (mandible). These 14bones (table 3-2) form the basic shape of the face, andare responsible for providing attachments for musclesthat make the jaw move and control facial expressions.Figures 3-8 and 3-9 show the bones of the face.

Maxillae Bones

The maxillae bones are the largest bones of theface and together form the upper jaw. The maxilla(singular) consists of a body and. four processes:zygomatic, frontal, alveolar and palatine. The maxillaforms the hard palate, floor of the nose, part of theorbits (eye sockets), and the tooth sockets of the upperteeth. Above the roots of the upper teeth and below the

The occipital bone is an irregular, four-sided bone thatis somewhat curved upon itself.

Table 3-2.—Bones of the Face

Single bones Paired bonesSphenoid Bone

The sphenoid bone has a wing-like shape and isinternally wedged between several other bones in thefront part of the cranium (fig. 3-6). This bone assistswith the formation of the base of the cranium, thesides of the skull, and the floors and sides of theorbits.

VomerMandible

MaxillaryPalatineZygomatic

Lacrimal

Nasal

Inferior nasal conchae

Figure 3-6.—Sphenoid bone viewed from above. Figure 3-7.—Ethmoid bone viewed from above.

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Figure 3-8.—Anterior view of facial skeleton.

Figure 3-9.—Posterior view of facial skeleton.

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floor of the orbits are the maxillary sinuses; the largestof the sinuses.

Palatine Bones

The palatine bones are located behind the maxillae(fig. 3-10). The bones are somewhat L-shaped andform the posterior portion of the hard palate and thefloor of the nose. Anteriorly, they join with themaxillary bone.

Zygomatic Bones (Zygoma, Malar Bone)

The zygomatic bones make up the prominence ofthe cheeks and extend from the zygomatic process ofthe temporal bone to the zygomatic process of themaxilla. The zygomatic bones form the “cheek bones”and help to form the sides and floor of the orbits.

Figure 3-10.—Anterior view of palatine bones.

Lacrimal Bones

The lacrimal bones are the smallest and mostfragile of the cranial bones. These thin, scalelikestructures are located in back of the frontal process ofthe maxilla.

Nasal Bones

The nasal bones are small oblong bones somewhatrectangular in shape. They lie side by side and arefused at the midline to form the bridge of the nose(nasal septum). These bones are responsible for theshape of the nose.

Inferior Nasal Conchae

The inferior nasal conchae are curved, fragile,scroll-shaped bones that lie in the lateral walls of thenasal cavity. They provide support for mucousmembranes within the nasal cavity.

Vomer Bone

The vomer bone is a thin, flat, single bone almosttrapezoid in shape. It connects with the ethmoid boneand together they form the nasal septum.

Mandible

The mandible (lower jaw-bone) is the longest,strongest, and the only movable bone in the skull.Figure 3-11 illustrates the anatomy of the mandible.

Figure 3-11.—Anatomy of the mandible; lateral view (left), inferior view (right).

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The mandible is horseshoe-shaped, with anupward sloping portion at each end called the ramus.The rami are divided into two different processes:

Condyloid process—Also called mandibularcondyle, located posterior on the ramus and forms thehead of the mandible. It is knuckle-shaped, andarticulates in the glenoid fossa of the temporal bone toform the temporal mandibular joint.

Coronoid process—Located anterior of thecondyle, and provides attachment for the temporal’smuscle, which helps lift the mandible to close themouth.

Other important anatomical landmarks of themandible you should be able to recognize are asfollows:

Alveolar process—Supports the teeth of themandibular arch.

Mental protuberance—Also referred to as thechin and is located at the midline of the mandible.

Mental foramen—Located on the facial surfacesof the mandible on both the right and left sides, justbelow the second premolars. This opening contains themental nerve and blood vessels.

Body—The heavy, horizontal portion of themandible below the mental foramen extending from theangle to the parasyplysis region.

mandible meets with the ramus.Angle—Juncture where the body of the

Mandibular foramen—Located near the centerof each ramus on the medial side (inside), through thisopening passes blood vessels and the interior alveolusnerve, which supply the roots of the mandibular teeth.This is a common area where the dental officer willinject anesthetic to block the nerve impulses and makethe teeth on that side insensitive (numb).

BONES OF THE EAR

In each middle’ ear and located in the auditoryossicles are three small bones named the malleus,incus, and staples (fig. 3-12). Their function is totransmit and amplify vibrations to the ear drum andinner ear.

TEMPORAL MANDIBULAR JOINT

The right and left temporal mandibular joints(TMJs) are formed by the articulation of the temporalbone and the mandible. This is where TMJs connectwith the rest of the skull. Figure 3-13 illustrates theTMJ.

The mandible is joined to the cranium byligaments of the temporal mandibularjoint (fig. 3-14).

Figure 3-12.—Anatomy of the middle ear.

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Figure 3-13.—Temporal mandibular joint.

Figure 3-14.—Ligaments of a temporal mandibular joint.

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The TMJ consists of three bony parts:

Glenoid fossa—Oval depression in the temporalbone that articulates with the mandibularcondyle.

Articular eminence—Ramp-shaped segment ofthe temporal bone located anterior to the glenoidfossa.

Condyle—The knuckle-shaped portion of themandibular ramus found on the end of thecondyloid process. It is positioned underneaththe glenoid fossa and makes up the hinge joint ofthe TMJ.

MUSCLES OF THE HEAD

The muscles of the head can be classified into twogroups, muscles of facial expression and muscles ofmastication. How muscles work and function dependson the action of each muscle (movement), the type ofjoint it is associated with, and the way the muscle isattached on either side of the joint. Muscles are usuallyattached to two places: one end being joined to animmovable or fixed portion, and the other end beingjoined to a movable portion on the other side of a joint.The immovable portion is called the origin of themuscle, and the movable portion is called the insertion.When muscles of the head contract, the insertion end ispulled toward the origin.

MUSCLES OF FACIAL EXPRESSION

The muscles that are underneath the skin of theface are responsible for helping communicate ourfeelings through facial expression. The muscles of themouth help us express surprise, sadness, anger, fear,and pain. Table 3-3 lists the muscles of facialexpression and figure 3-15 illustrates these muscles.

MUSCLES OF MASTICATION

Mastication is defined as the process of chewingfood in preparation for swallowing and digestion. Fourpairs of muscles in the mandible make chewingmovements possible. These muscles can be groupedinto two different functions. The first group includesthree pairs of muscles that elevate the mandible toclose the mouth as in biting down. The last groupincludes one pair that can depress the mandible (openthe mouth), make grinding actions side to side, and canmake the mandible go forward in a protruding motion.Table 3-4 lists the muscles of mastication and figure3-16 illustrates these muscles.

ORAL STRUCTURES OF THE MOUTH

The oral cavity (mouth) contains variousstructures that aid in the digestion process of food andalso serves as an organ of speech and sensory

Figure 3-15.—Anatomy of muscles of facial expression.

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Figure 3-16.—Muscle anatomy of mastication.

Muscle

Orbicularis oris

Table 3-3.—Muscles of Facial Expression

Origin Insertion

Encircles the mouth (no Corners of the mouthattachement to bone)

Description

Located between the skin andmucous membranes of thelips. Makes lips close andpucker.

Buccinator Alveolar process ofmaxilla and mandible

Orbicularis oris at the corner Located in the walls of theof the mouth cheeks, holds food in contact

with teeth when chewing, andassists in blowing air out ofthe mouth.

Mentalis Mandible Skin of chin Raises and wrinkles the skinof the chin and decreases andprotrudes the lower lip.

Zygomaticus Major Zygomatic bone Orbicularis oris (angle of the Raises the corner of themouth) mouth when smiling.

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Table 3-4.—Muscles of Mastication

Muscle Origin

Masseter Zygomatic arch

Temporalis Temporal bone

Insertion

Mandible (externalsurface)

Coronoid process at theanterior border of theramus

Description

Closes jaw; flat, thickmuscle

Closes jaw; fan-shaped

Medial pterygoid

Lateral pterygoid

Sphenoid, palatine, andmaxillary bones

Sphenoid bone

Inner (medial) surface of Closes jaw; parallelsthe ramus masseter muscle

Anterior surface of man- Opens jaw; allowsdibular condyle grinding action side to

side, and protrudes themandible

reception. We receive food in the mouth, reducing it insize, and mixing it with saliva for the digestionprocess.

CHEEKS

LIPS

The lips are covered externally by skin andinternally by the same mucous membranes that line theoral cavity. They form the anterior border of themouth. The area of the external lips where the redmucous membrane ends and normal outside skin of theface begins is known as the vermilion border. Figure3-17 illustrates the anatomy of the lips.

The cheeks are the side walls of the mouth. Theyare made up of layers of skin, a moist inner liningcalled mucosa, fat tissue, and certain muscles. Thebuccinator muscle of the cheeks prevents food fromescaping the chewing action of the teeth.

The lips are very sensitive and act as sensoryreceptors, allowing food and liquids to be placed in the

Figure 3-17.—Anatomy of the lips.

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mouth but guarding the oral cavity against theingestion of excessively hot or cold substances. Theyalso provide a seal for the mouth to keep food andsaliva from escaping. The lips help to maintain theposition of the teeth and are very important in speech.

TONGUE

The tongue (fig. 3-18) is a vascular, thick solidmass of voluntary muscle surrounded by a mucousmembrane (epithelium tissue). Located on theunderneath side of the tongue is the lingual frenulum,which anchors the tongue in the midline to the floor ofthe mouth. The tip of the tongue is free moving and canreadily change size, shape, and position.

Surface (Dorsal Aspect)

On the surface of the tongue are rough projectionscalled papillae. They provide the tongue with frictionin handling food and also act as taste buds.

Taste Buds

The four types of taste sensations are sweet, sour,bitter, and salty-all resulting from stimulation of thetaste buds. Most are located on the tongue and the roofof the mouth. Figure 3-19 illustrates taste buds of thetongue.

Figure 3-19.—Taste buds of the tongue.

Tongue and Digestion

The tongue is an important muscle in the chewingprocess. It crushes food against the palate; it depositsfood between the chewing surfaces of the teeth for

Figure 3-18.—Dorsal aspect of tongue (left), anatomy floor of mouth (right).

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mastication; it transfers food from one area of themouth to another; it mixes food with saliva, whichassists in the digestive process; assists in swallowing;and cleans the mouth of residue.

MYLOHYOID AND GENIOHYOID

The mylohyoid muscles anatomically andfunctionally form the floor of the mouth (fig. 3-20).They elevate the tongue and depress the mandible.Their origin is the mandible and insertion is the upperborder of the hyoid bone. The geniohyoid muscles arefound next to each other, on each side of the midline,directly on top of the mylohyoid muscle. They havethe same origin and function as the mylohyoid muscle.

PALATE

The palate (fig. 3-21) forms the roof of the mouthand is divided into two sections:

Hard palate—This section is formed by thepalatine process of the maxillary bones and is located inthe anterior portion of the roof of the mouth. It hasirregular ridges or folds behind the central incisorscalled rugae.

Soft palate—This section forms a soft musculararch in the posterior part of the palate. The uvula islocated on the back portion of the soft palate. When youswallow, the uvula is drawn upward and backward bythe muscles of the soft palate. This process blocks theopening between the nasal cavity and pharynx, not

allowing food to enter the nasal cavity. The soft palatemust function properly to allow good speech quality.

Located in the posterior part of the mouth, on bothsides of the tongue, are two masses of lymphatic tissuecalled the palatine tonsils. They assist the body toprotect against infections.

TEETH

The teeth are located in the alveolar process of themaxillae and the mandible. They serve importantfunctions of tearing and masticating food, assisting inswallowing, speaking, and in appearance. The healthof the teeth affects the health of the entire body.

SALIVARY GLANDS

The functions of the three major salivary glandsare to keep the lining of our mouths moist, and to bondwith food particles creating a lubricant effect thatassists in the swallowing process of food. It acts as acleaning agent to wash away food particles thataccumulate in the mouth and on the teeth. Figure 3-22illustrates the salivary glands.

The salivary glands produce two to three pints ofsaliva daily, which greatly aids in the digestionprocess.

Enzymes are present in saliva, they act on food,and start the breakdown process. In dentistry, knowingexactly where the saliva glands and ducts (openings)are located is important in keeping the mouth dry

Figure 3-20.—Mylohyoid and geniohyoid muscles.

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Figure 3-21.—Anatomy of the palate.

Figure 3-22.—Salivary glands.

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during certain dental procedures. Table 3-5 lists thethree major salivary glands.

MASTICATION AND DEGLUTITION

The mastication process includes the biting andtearing of food into manageable pieces. This usuallyinvolves using the incisors and cuspid teeth. Thegrinding of food is usually performed by the molarsand premolars. During the mastication process, food ismoistened and mixed with saliva.

Deglutition is the swallowing of food and involvesa complex and coordinated process. It is divided intothree phases; the first phase of swallowing isvoluntarily; phases two and three are involuntary.

Phase one: the collection and swallowing ofmasticated food.

Phase two: passage of food through the pharynxinto the beginning of the esophagus.

Phase three: the passage of food into thestomach.

Table 3-5.—List of the Three Major Salivary Glands

Gland

Sublingual

Location Duct Description

On each side underneath Multiple separate ducts Smallest of salivary glands,the tongue, in the floor of secretes, thick stringy mucus.the mouth

Submandibular Posterior portion ofmandible, lingual tomandibular incisors

Parotid Inside cheek, oppositemaxillary second molar

Opens under the tongue, Walnut sized. Secretes watery fluidclose to the frenulum with some mucus. More viscous

(thick) than parotid secretion.

Parotid ducts go through Largest of salivary glands. Secretesthe buccinator muscles and clear watery fluid.enter the mouth oppositemaxillary second molars

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