Page 339 - Clinical Anatomy

ECA5 7/18/06 6:51 PM Page 324

324 The head and neck

of the tooth (pulp, dentine and cement) differentiates from the underlying
mesodermal connective tissue.

Clinical features

Osteomyelitis of the jaw following dental extractions is confined to the
lower jaw and occurs only with the permanent dentition. The explanation
of this is an anatomical one.
The lower jaw is supplied only by the inferior dental artery, which runs
with the nerve in the mandibular canal; damage to this artery at extraction,
or its thrombosis in subsequent infection, therefore, produces bone necro-
sis. The upper jaw, on the other hand, receives segmental vertical branches
from the superior dental vessels and ischaemia does not follow injury to an
individual artery. The deciduous teeth of the lower jaw are placed well clear
of the mandibular canal which is, in any case, protected by the unerupted
permanent teeth; damage to the artery cannot therefore occur during their
removal.

Inferior alveolar nerve block
This is a useful procedure for the dental surgeon because it produces com-
plete anaesthesia of all the lower teeth of one side of the mandible. The
needle is passed deep to the last molar tooth on to the inner aspect of the
ramus of the mandible. Anaesthesia is produced in the lower teeth, the skin
and mucosa of the lower lip (via the mental branch of the inferior alveolar
nerve) and often, because of spread of the anaesthetic solution, there is loss of
sensation of the side of the tongue due to involvement of the lingual nerve,
which lies immediately in front of the inferior alveolar nerve (see Fig. 260).

The vertebral column

The spinal, or vertebral, column is made up of thirty-three vertebrae, of
which twenty-four are discrete vertebrae and nine are fused in the sacrum
and coccyx.
In the embryo the spine is curved into a gentle C shape but, with the
extension of the head and lower limbs that occurs when the child first holds
up its head, then sits and then stands, secondary forward curvatures
appear in the cervical and lumbar region, which produce the sinusoidal
curves of the fully developed spinal column.
The basic vertebral pattern (Fig. 228) is that of a body and of a neural arch
surrounding the vertebral canal.
The neural arch is made up of a pedicle on either side, each supporting a
lamina which meets its opposite posteriorly in the midline. The pedicle
bears a notch above and below which, with its neighbour, forms the