274
UNIT 3
Organ Systems
T. Yang / D. Cui
Mantle dentin
Mantle dentin
Mantle dentin
Circumpulpal dentin
Circumpulpal dentin
Circumpulpal dentin
Secondary dentin
Secondary dentin
Secondary dentin
Cementum
Cementum
Cementum
Enamel
Enamel
Enamel
Tertiary
Tertiary
dentin
dentin
Tertiary
dentin
Primary dentin
Primary dentin
Primary dentin
Dentinal
Dentinal
tubules
tubules
Dentinal
tubules
Dentinal
Dentinal
Matrix
Matrix
Dentinal
Matrix
Dental pulp
A
Figure 14-15A.
Dentin
,
tooth
. H&E,
3
284
Dentin
, which forms the bulk of the tooth, is covered by enamel on the
crown and cementum at the root. It is about 70% inorganic materials
(hydroxyapatite), 20% organic components (type I collagen and proteo-
glycans), and 10% water. Dentin is harder than bone and cementum but
weaker than enamel. Dentin can be classiF ed into three types: (1)
Primary
dentin
, deposited before the formation of the tooth root and tooth eruption
have been completed, includes
mantle dentin
(at the DEJ) and
circumpulpal
dentin
; (2)
secondary dentin
, produced after tooth eruption and root
formation have been completed, is deposited very slowly and is located
beneath the primary dentin; and (3)
tertiary (reparative) dentin
is produced
in response to injures (caries [
arrow
], drilling, or attrition). Tertiary dentin
is produced only by the odontoblasts that are directly stimulated when
the tooth is injured. This type of dentin has few, mostly irregular, dentin
tubules, which provide a seal to prevent bacteria and harmful molecules
from invading the dental pulp. Dentin has three basic components:
dentinal
tubules
,
dentinal matrix
, and
odontoblastic processes
(±ig. 14-15B).
T. Yang / J. Naftel
Fluid
Dentinal tubule
Intertubular dentin
Peritubular dentin
Dentin
Dentinal
tubule
Odontoblastic
process
Dental
pulp
Nerve
ending
Odontoblast
Dentin
D
e
n
tin
t
i
n
Dentin
P
re
r
e
d
e
n
tin
t
i
n
Predentin
Odontoblasts
Odontoblasts
Odontoblasts
B
Figure 14-15B.
Dentin and dentinal tubules
,
tooth
.
H&E,
3
35; inset
3
359
Dentin
is produced by
odontoblasts
, and the formation of dentin is
continuous throughout life. During the dentinogenesis process, the cell
bodies of the odontoblasts retreat, but their cytoplasmic processes remain
and are embedded in the mineralized dentinal matrix. Each odontoblastic
process resides in a narrow channel, the dentinal tubule, which is lined by
highly calciF ed peritubular dentin and traverses the entire thickness of the
dentin layers. The dentinal matrix, between the dentinal tubules, is called
intertubular dentin
and is less mineralized than the peritubular dentin.
The dentinal tubules run from the dental pulp surface to the
DEJ
. These
tubules are larger close to the pulp and more branched near the DEJ. Each
dentinal tubule contains an odontoblastic process about halfway toward
the DEJ; the rest of the space is F
lled with fl uid. Nerve F bers for pain
extend from the dental pulp to the inner part of the dentinal tubule.
CLINICAL CORRELATION
Figure 14-15C.
Dentinogenesis Imperfecta.
H&E,
3
329; inset
(
lower
) ×2
Dentinogenesis imperfecta
is an autosomal dominant genetic disorder of
tooth development caused by mutations in the
dentin
sialophosphoprotein
gene
. Affected teeth are often
blue-gray
or
yellow-brown
in color and
translucent
. Dentinogenesis imperfecta is classiF ed as
types I–III
.
Type I
is associated with
osteogenesis imperfecta
, in which bones are brittle
and easily fractured and pulp chambers are diminished. Type I collagen
defects are also associated with type I dentinogenesis imperfecta.
Type
II
is characterized by
diminished pulp chambers
and may be associated
with progressive hearing loss.
Type III
has
large pulp chambers
. Patients
suffer frequent
enamel fractures
and
enamel attrition
. ±ull crowns will
improve the appearance of the teeth and protect the teeth from damage.
Histologically,
dentinal tubules
are
irregular
and are
larger than normal
in diameter, and
uncalci±
ed matrix
may be present.
Irregular
dentinal
tubules
Diminished
pulp chamber
C
Under certain circumstances, such as in
sensitive teeth
, the exposure of
dentin to air blasts or drinking or eating cold, hot, or sweet substances
will cause movement of the fl
uid in the dentinal tubules. This move-
ment produces a mechanical disturbance that activates the nerve end-
ings of pain F
bers, inducing intense pain (
hydrodynamic theory
).
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