CHAPTER 14
Oral Cavity
273
CLINICAL CORRELATION
Figure 14-14C.
Enamel Fluorosis.
Enamel fl uorosis
is the general term for enamel changes caused
by excessive
fl uoride
intake during tooth development (before age
8 years). Fluoride helps to prevent and control tooth caries, but
too much fl
uoride intake during tooth development can result in
hypomineralization
of the
enamel
surface. These changes are char-
acterized by diffuse, opaque, and white streaks that run
horizontally
across the enamel. Stains with rough, irregular enamel surfaces are
common. A fl
uoride-induced toxic effect on
ameloblasts
during
enamel formation is believed to be the mechanism of the condition.
Prevention is through controlling the fl
uoride intake, and treat-
ments include
bleaching
and
enamel
microabrasion
.
Enamel
,
Dentin
,
and Dental Pulp
D. Cui
Tail
Head
Rods (prisms)
Dental
pulp
Dental
pulp
Dentin
Dentin
Dentin
Dentin
Dentin
Dentin
DEJ
DEJ
DEJ
DEJ
DEJ
DEJ
Dentin
Dentin
Dentin
Enamel
Enamel
Enamel
Enamel
Enamel
Enamel
A
Figure 14-14A.
Enamel, tooth.
Ground specimen,
3
17; inset
3
46
Enamel
is the hardest tissue in the body and is highly mineralized. It is composed
of 96% inorganic material in the form of hydroxyapatite (crystalline calcium
phosphate), 1% organic material, and 3% water. Enamel covers the dentin of the
crown to make the tooth surface strong and suitable for chewing and to seal and
protect the dentin. Enamel cannot be renewed after enamel
formation has been
completed, because enamel is produced by ameloblasts, which disappear after
tooth eruption. However, enamel can be strengthened by fl
uoride. This ground
specimen shows the enamel, dentin, and DEJ. The basic morphological unit of
enamel is the
rod (prism)
. Each rod has a head and tail and is tightly packed with
hydroxyapatite crystals. The rods are arranged in a three- dimensional complex
and are oriented generally perpendicular to the DEJ.
DEJ
DEJ
DEJ
Dentin
Dentin
Dentin
Enamel
Enamel
lamella
lamella
Enamel
lamella
Enamel
Enamel
Enamel
Enamel
Enamel
spindle
spindle
Enamel
spindle
Enamel tuft
Enamel tuft
Enamel tuft
Incremental lines
Incremental lines
(striae of Retzius)
(striae of Retzius)
Incremental lines
(striae of Retzius)
Enamel tufts
Enamel tufts
Enamel tufts
B
Figure 14-14B.
Enamel structures
,
tooth
. Ground speci-
men,
3
68; inset (
upper
)
3
13; inset (
lower
)
3
62
The
incremental growth lines
of the
enamel
, also called
the
striae of Retzius
, can be found in either cross (bands)
or longitudinal sections (arcs) of the mature enamel. These
patterns refl
ect the changes in enamel secretory rhythm.
The
neonatal line
(see Fig. 14-7) is much more prominent
than the striae. It is a landmark that indicates the transition
from enamel produced before birth and enamel produced
after birth. This line is produced by a metabolic change that
occurs at birth. There are three defects of enamel: (1)
Enamel
tufts
are hypomineralized areas ±
lled with organic material
at the DEJ and toward the surface; (2)
enamel lamellae
are
hypomineralized, thin, sheetlike defects that can run through
the entire enamel and are commonly caused by cracks; and
(3)
enamel spindles
are thin, needlelike lines extending from
the DEJ to the enamel and are because of odontoblast pro-
cesses trapped in the enamel during early amelogenesis.
White
streaks
C
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