272
UNIT 3
Organ Systems
CLINICAL CORRELATIONS
Figure 14-13A.
Gemination
,
Incisor
.
Gemination
is a variation in tooth structure that occurs when
two teeth develop from the same tooth bud, resulting in a
larger
than normal tooth crown
, but with a
normal number of teeth
.
The gemination results from a disturbance that occurs at the
cap stage
. During the cap stage, the tooth germ is undergo-
ing early morphogenesis and beginning to form the shape of
the tooth. Gemination represents the unsuccessful division of a
single tooth germ into two tooth germs. There is a deep cleft on
the surface of the tooth, giving the appearance of two crowns.
The radiograph at left shows two crowns (
arrows
) sharing one
root. Occasionally, x-ray images may show two independent
pulp chambers and root canals. The cause of gemination is
unknown.
B
Figure 14-13B.
Amelogenesis Imperfecta.
Amelogenesis imperfecta
is a group of hereditary disorders
that affect the
dental enamel formation
at the
apposition
and
maturation stages
. The teeth are covered with a thin, defec-
tive enamel or lack enamel covering. Mutations in different
genes may affect enamel proteins, such as
amelogenin
, which
is involved in enamel mineralization. The most common forms
of amelogenesis imperfecta include
hypoplastic
and
hypocal-
ci±
ed
types. In the hypoplastic form, the teeth do not have a
sufF
cient amount of enamel, whereas in the hypocalciF
ed form,
the quantity of enamel is normal, but it is soft and easily worn.
Affected teeth are most often
yellow-brown
and
blue-gray
in
color, and are vulnerable to
dental caries, damage, and loss.
Full crowns
will improve the appearance of the teeth and pro-
tect the teeth from damage.
Enamel
pearl
C
Figure 14-13C.
Enamel Pearl.
Enamel pearl
is an
ectopic formation
of
enamel
that is usually
found close to the
CEJ
between tooth roots. Localized failure of
Hertwig epithelial root sheath
to separate from the dentin may
be the cause of this anomaly. The enamel pearl results from a
disturbance during the
apposition
or
maturation stages
during
the tooth development. An enamel pearl may lead to
periodon-
tal disease
because of the extension of a
periodontal pocket.
Histologically, enamel pearls have
reduced enamel epithelium
and are surrounded by normal
cementum
. X-rays can reveal
enamel pearls. Enamel pearls cannot be removed by scaling,
but they can be ground away to restore the normal shape of the
tooth. An enamel pearl on a molar is shown here.
Cleft
A
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