THE SKULL AND JAWS
As an assistant to the dental officer, who provides professional treatment, the
dental specialist must have a basic knowledge of the anatomy and physiology of the
The human skull is the bony framework which gives the head its characteristic
shape. The function of the skull is to protect the soft and vital tissues of the head,
primarily the brain. The skull contains the fused flat bones of the cranium and the facial
bones, including the mandible (lower jaw), which is freely movable. The cranium is the
bony box housing the brain. The skull is composed of 22 bones, 8 in the cranium and
14 in the face. See figures 2-1, 2-2, and 2-3.
The eight bones of the cranium are frontal, occipital, sphenoid, ethmoid, two
parietal, and two temporal bones. They form the floor and the domelike vault that
encloses and protects the brain. The cranial bones are fused at joints called the coronal
suture. (A suture is a fused line of junction between two bones. It is an immovable
joint.) At birth, the bones of the cranium are not fully fused and the sutures are soft. As
the baby grows, the bones of the skull fuse firmly, making the skull a rigid box that does
not permit expansion. This means that if bleeding occurs within the adult skull or if brain
tissue swells, the increase in intracranial volume will increase pressure and damage to
the brain tissue can occur.
a. Frontal Bone. This bone forms the forehead, the anterior (front) part of the
cranial vault, and the roof of the orbits (eye sockets). Located within the frontal bone,
just behind the eyebrows, are two air spaces called the frontal sinuses.
b. Occipital Bone. This bone makes up the posterior (back) part of the floor
and the posterior wall of the cranial vault. It is the bone that supports the head on the
spinal column. The spinal cord leaves the cranium through an opening in the occipital
bone. This opening is called the foramen magnum. (A foramen is an opening in a bone
which serves as a passageway for nerves and blood vessels.) When a patient is seated
in the dental chair, the headrest should support the occipital bone.