DISCLOSING AGENTS
DISLOCATION, JOINT
disclosing agents
Dyes that make the
plaque
deposits on teeth more visible
so that they can be seen and removed.
discoid lupus erythematosus
A form
of the chronic autoimmune disorder
lupus erythematosus.
discoloured teeth
Teeth that are ab-
normally coloured or stained. Extrinsic
stains, on the tooth's surface, are com-
mon, but are usually easily removed by
polishing. They can be prevented by
regular tooth cleaning. Smoking tobac-
co produces a brownish-black deposit.
Pigment-producing bacteria can leave a
visible line along the teeth, especially
in children. Some dyes in foodstuffs can
cause yellowing; dark brown spots may
be due to areas of thinned enamel
stained by foods. Some bacteria pro-
duce an orange-red stain. Stains may
also follow the use of drugs containing
metallic salts.
Intrinsic stains, within the tooth's sub-
stance, are permanent. Causes include
death of the pulp or the removal of the
pulp during
root-canal treatment
and
the use of the antibiotic
tetracycline
in
children. Mottling of the tooth enamel
occurs if excessive amounts of fluoride
are taken during development of the
enamel (see
fluorosis). Hepatitis
during
infancy may cause discoloration of the
primary teeth. The teeth of children
with
congenital
malformation of the
bile
ducts
may be similarly affected.
Many stains can be covered or dimin-
ished with cosmetic dental procedures.
disc prolapse
A common disorder of
the
spine
, in which an intervertebral
disc
ruptures and part of its pulpy core pro-
trudes. It causes painful and at times
disabling pressure on a nerve root or,
less commonly, on the spinal cord. The
lower back is most commonly affected.
A prolapsed disc may sometimes be
caused by a sudden strenuous action,
but it usually develops gradually as a
result of degeneration of the discs with
age. If the sciatic nerve root is com-
pressed, it causes
sciatica
, which may be
accompanied by numbness and tin-
gling, and, eventually, weakness in the
muscles of the leg. A prolapsed disc in
the neck causes neck pain and weak-
ness in the arm and hand.
Symptoms improve with time and anal-
gesic drugs. However, in severe cases,
surgical techniques, such as
decom-
pression
of the spinal canal or removal
of the protruding material and repair of
the disc, may be necessary.
DISC PROLAPSE
disc, slipped
See
disc prolapse.
disease
Illness or abnormal functioning
of a body part or parts due to a specific
cause, such as an infection, and identi-
fiable by certain
symptoms
and
signs.
disinfectants
Substances that kill micro-
organisms and thus prevent infection.
The term is usually applied to strong
chemicals that are used to decontami-
nate inanimate objects, such as items
of medical equipment.
dislocation, joint
Complete displace-
ment of the
2
bones in a joint so that
they are no longer in contact, usually as
a result of injury. (Displacement that
leaves the bones in partial contact is
called
subluxation
.) It is usually accom-
panied by tearing of the joint ligaments
and damage to the membrane that en-
cases the joint. Injury severe enough to
cause dislocation often also causes bone
to fracture. Dislocation restricts or pre-
vents the movement of the joint; it is
usually very painful. The joint looks
misshapen and swells. In some cases,
dislocation is followed by complica-
tions, for example, paralysis.
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