CROWNING
OUTLOOK
Some people in whom the disease is
localized
remain
in
normal
health
indefinitely and seem to be cured.
cromoglicate
See
sodium cromoglicate
.
crossbite
A type of
malocclusion
(an abnormal
relationship between the upper and
lower teeth) in w hich some or all of
the lower front teeth overlap the upper
front teeth. A molar crossbite, in w hich
the upper and lower back teeth overlap,
can also occur.
cross-eye
A type of
strabismus
(squint) in w hich
one of the eyes turns inwards relative
to the other, or in w hich both eyes turn
inwards towards each other.
cross-matching
A procedure to
determine
compati-
bility between the blood of a person
who requires a
blood transfusion
and
that of a
donor
.
Red blood cells from
one person are combined with
serum
(the
clear fluid that separates from
blood when it clots) from the other.
Clumping of red blood cells indicates
the presence of
antibodies
,
showing that
the blood is not compatible.
croup
A
common
disorder
in infants
and
young children, in w hich narrowing
and inflammation of the airways causes
hoarseness, stridor
(a grunting noise
during breathing), and a barking cough.
Croup may be caused by a viral or
bacterial infection affecting the
larynx
,
epiglottis, or
trachea.
Most cases are due
to a viral infection and are generally
mild. Other causes include
diphtheria,
allergy,
spasm due to insufficient
calci-
um
levels in the blood, and inhalation
of a
foreign body.
H um idifying the air
can help
to
ease breathing. In some cases,
cortico-
steroid drugs
administered through a
nebulizer,
and oxygen, may be pre-
scribed. If the infection is bacterial, it
is treated w ith
antibiotic drugs.
Crouzon’s syndrome
An autosomal dominant
genetic disorder
that causes facial deformities. Affected
people have these features: eyes that
protrude
(see
exophthalmos
)
and are
spaced widely apart; a
squint
; an abnor-
mally tall skull; a large, beaked nose;
and
an
underdeveloped
upper
jaw,
w hich makes the lower jaw look as if it
is protruding.
crowding, dental
See
overcrowding, dental
.
crown
The name for the top of the head. The
word is also used of the visible part of a
tooth. (See also
crown, dental; crowning
. )
crown, dental
An artificial replacement for the crown
of a decayed, discoloured, or broken
tooth
.
A crown made from porcelain is
usually used on front teeth, but back
teeth need the greater strength of a
crown made from gold or porcelain
fused to metal.
A crown may be fitted by filing the
tooth to form a peg and cementing
the crown over the top of it. For a badly
decayed or weakened tooth, it may be
necessary to remove the natural crown,
perform
root-canal treatment
,
then fit
the artificial crown on to a post that is
cemented in the root canal. For details
on how crowns are fitted, see the illus-
trated box below.
crown-heel length
A routine measurement of the length of
a newborn baby, taken from the
crown
of the head to the heels.
crowning
The popular name given to the phase in
the second stage of labour (see
child-
birth
)
when the baby’s head first appears
at the mother’s vaginal opening.
C
HOW CROWNS ARE FITTED
The tooth is filed down to form a peg over which the replacement is fitted. An
impression of the peg and the natural tooth is taken and a replica is made.
Using this replica as a model, the artificial crown is constructed.
Cast full
crown
Porcelain fused
to metal crown
Porcelain
jacket crown
Three-quarter
crown
1
A cracked or broken tooth,
or one that has been
heavily filled, can be replaced
by a crown.
2
The damaged area ofthe
tooth is removed and the
remaining part is shaped to
receive the crown.
3
The artificial crown, a
hollow shell, is fitted over
the shaped tooth and then
cemented in place.
POST CROWNS
If the natural tooth is badly decayed
or has been weakened, its crown is
removed and a post crown is fitted.
.
R o o t c a n a l
. T o o t h r o o t
D a m a g e d
t o o t h
1
This tooth is
so decayed
that a retaining
peg cannot be
fashioned.
2
The tooth’s
natural crown
is completely
removed.
R o o t c a n a l f i l l e d
T o o t h t r im m e d
G o ld
p o s t
in r o o t
c a n a l
C r o w n
3
A gold post is
cemented into the
root canal and the
crown is then cemented
over the post.
205
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