Oral Anatomy: Enamel, dentin, and pulp

Chapter 20
Enamel, Dentin, and Pulp
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Copyright © 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Previous editions copyrighted 1977, 1982, 1986, 1990, 1994, 1998.

 Enamel develops from the enamel organ, which
is derived from ectoderm.
 Dentin and pulp develop from the dental papilla,
which is derived from mesoderm.
 The mesoderm of the dental papilla determines the
shape of the developing crown of the tooth.
Introduction
2

Dental Papilla
 As the enamel organ
goes into the cap
stage, mesenchymal
cells adjacent to the
cap become more
rounded and
condensed and are
then called dental
papilla cells.
 Condensation
continues into the bell
stage.
3

Dental Papilla
 During the bell stage
the inner enamel
epithelial cells (IEE)
become taller and are
known as
preameloblasts.
 Peripheral cells of the
dental papilla
adjacent to the
preameloblasts
become low columnar
or cuboidal cells
called odontoblasts.
4

 Odontoblasts move away from preameloblasts
toward the center of the dental papilla and
secrete a matrix of mucopolysaccharide ground
substance and collagen fibers.
 This causes the preameloblast to change its
polarity (the nucleus moves from the center of
the cell to the end nearest the stratum
intermedium).
 When the change in polarity occurs the cell is
called an ameloblast and begins to secrete an
enamel matrix.
Dental Papilla
5

Dental Papilla
 The enamel matrix consists of
mucopolysaccharide and organic fiber and forms
next to the dentin matrix forming the future
dentinoenamel junction (DEJ).
6

 The ameloblast then moves toward the outer
enamel epithelium (OEE).
 At this point dentin and enamel begin to lay
down hydroxyapatite crystals and calcify.
Dental Papilla
7

 Enamel is the hardest structure of the body.
 It is about 96% inorganic and 4% water and a
fibrous organic material.
 The inorganic structure is composed of many millions
of crystals of hydroxyapatite.
Enamel Composition
8

Enamel Composition
 Two parts of enamel:
1. Rod sheath: outlines rod
and contains most of the
fibrous organic
substance.
2. Rod: made up of
hydroxyapatite crystals,
primary unit of enamel’s
structure.
9

Enamel Composition
 The rod is a column of enamel that runs from the
DEJ to the surface of the tooth.
 It is somewhat perpendicular to the DEJ and to
the surface of the crown.
10

 Ameloblasts act together to form one enamel rod
by laying down fibers and a matrix composed of
a glue-like material called ground substance.
 Millions of hydroxyapatite crystals are deposited
into the matrix.
 Enamel rods fit together tightly because of a
cementing substance called interrod substance.
Enamel Composition
11

 When the ameloblasts deposit the
hydroxyapatite crystals into the matrix, the
secreting ends of the ameloblasts bulge outward
in the direction of the DEJ.
 This asymmetrical bulge is called the Tomes process
of an ameloblast.
Enamel Composition
12

Enamel Composition
 A “typical” enamel rod with keyhole shape. (A)
 Cross section of rod shows upper-end crystals
cut vertically and lower-end crystals cut at an
angle, giving each a distinct appearance. (B)
13

Development of Enamel
14
 Deposition of the
matrix is the
mineralization stage
of enamel rod
calcification. (A)
 Maturation stage is
the second stage of
calcification. (B)
 Crystals grow in size
until tightly packed
together.

 The brownish lines that develop in the enamel
are called the striae of Retzius.
 They can be seen in a longitudinal section of a
tooth and can also be seen on the surfaces of a
number of teeth.
 Surface manifestations of the striae of Retzius
are known as imbrication lines.
15

16

 As the ameloblast moves away from the DEJ
toward the OEE, it begins to compress the two
layers in the middle, the stratum intermedium
and the stellate reticulum.
 These two middle layers eventually lose their
identity, and the ameloblasts contact the OEE.
 This is the signal for the ameloblasts to cease
formation of enamel.
Fate of Enamel Organ
17

 The ameloblast lays down a layer over the
enamel, called the primary enamel cuticle or
Nasmyth’s membrane.
 This membrane covers the crown and remains there
for many months after eruption.
 The ameloblast then flattens out and blends with
the outer enamel epithelial cells.
 This is called the reduced enamel epithelium.
18

 This reduced enamel epithelium produces an
adhesive-like secretion called the secondary
enamel cuticle or epithelial attachment.
 This epithelium adheres to the tooth and is
known as the attachment epithelium.
 It is found at the base of the gingival sulcus.
19

 There are a number of enamel abnormalities.
 Some are seen with clinical examination, others are
by radiographic examination, and still others by
histologic examination of the sectioned tooth.
Abnormalities of Enamel
20

Hypocalcified Enamel
 Hypocalcified enamel appears white to whitish
yellow in color.
 Results from an insufficient growth of the enamel
crystals or an insufficient number of crystals
deposited in the matrix.
 Because the enamel is less dense than normal, it
may decay more rapidly.
21

Hypoplastic Enamel (Cont.)
 The density of hypoplastic enamel is generally
normal, but the enamel is thin.
 The enamel will have a yellow to gray hue and may
be seen radiographically as a thinner than normal
layer of enamel.
22

Enamel Lamellae
 Hairline cracks in the enamel caused by
developmental problems or trauma are called
enamel lamellae.
 Enamel lamellae may extend from the enamel into
the dentin.
23

Enamel Lamellae (Cont.)
 Trauma is the most common cause.
 Less common is a developmental defect
 This occurs as a result of ameloblasts ceasing
enamel production and leaving a space between
enamel rods.
• Usually seen histologically and not clinically.
24

Enamel Tuft
 An enamel tuft is a small area of hypocalcified
enamel seen at the DEJ and extending about a
third of the way through the enamel.
 Only seen histologically and has no clinical
significance.
25

26
Enamel Spindle
 Seen only histologically, an enamel spindle is a
cellular extension of the odontoblast that becomes
trapped between ameloblasts and ends up in the
enamel.

 Dentin is about 70% inorganic and 30%
organic.
 Inorganic: hydroxyapatite crystal.
 Organic: collagen, mucopolysaccharide ground
substance, and water.
Dentin Composition
27

Dentin Composition
 Dentin comprises
three distinct areas.
28

1. Dentinal tubule: long tube, running from the
DEJ or DCJ to the pulp.
a. Each dentinal tubule contains an odontoblastic
process.
2. Peritubular dentin: area of higher crystalline
content immediately surrounding the dentinal
tubules.
3. Intertubular dentin: bulk of the dentinal
material.
Dentin Composition
29

Formation of Regular Dentin
(Primary Dentin)
30
 The odontoblast
secretes a dentin
matrix at the future
DEJ or DCJ and
begins to move
toward the pulp.
 It leaves part of the
cell behind and
stretches all the way
from the DEJ or DCJ
inward to the
periphery of the pulp.

 The secreted matrix spreads peripherally, meets
with other dentin matrices, and calcifies, forming
intertubular dentin.
 The intertubular dentin shrinks in diameter; the
space left behind fills in with dentin known as
peritubular dentin.
 When the tooth erupts into the oral cavity, the
dentin is known as primary or regular dentin.
 Dentin continues to form as either secondary or
reparative dentin.
Formation of Regular Dentin
(Primary Dentin)
31

Secondary Dentin
 The layer formed inside regular dentin and closest to
the pulp is secondary dentin.
 Starts forming when the tooth erupts and contacts
the opposing tooth.
 Formed by the same odontoblasts that form regular
dentin.
 As secondary dentin forms, the size of the pulp
chamber decreases.
Formation of Secondary and
Reparative Dentin
32

Reparative Dentin
33
Secondary Dentin (Cont.)
 Most noticeable when comparing radiographs of
newly erupted permanent maxillary central incisors
with radiographs of the same teeth that have been
erupted for a number of years.

Secondary Dentin (Cont.)
 Newly erupted teeth have large pulp chambers and
prominent pulp horns.
 As secondary dentin formation proceeds, a
decrease in the size of the pulp canals, chambers,
and pulp horns occurs.
Reparative Dentin
34

Reparative Dentin
 Reparative dentin is formed in response to local
trauma and located immediately beneath the area of
trauma.
 Trauma may be one of several varieties: occlusal,
mechanical, or chemical trauma.
Reparative Dentin
35

Reparative Dentin (Cont.)
 Occlusal trauma exists when one tooth or part of a
tooth is subjected to more occlusal stress than
normal.
 Usually relates to the cusp area of the tooth.
 The odontoblast layer beneath the cusp responds to
the trauma by quickly producing dentin.
 This dentin has very few, if any, dentinal tubules,
and is very dense and unorganized.
Reparative Dentin
36

 Mechanical trauma is usually the result of cavity
preparations in the tooth.
 Cavity preparations generally extend through the
enamel and into the dentin.
 This preparation leads to death of odontoblasts in
that area.
 These odontoblasts are replaced with reserve
mesenchymal cells from adjacent pulpal tissue,
which change into odontoblasts and produce
reparative dentin.
Reparative Dentin
37

 Chemical trauma can result from acids produced by
the bacteria that cause dental caries.
 Chemical trauma can also occur from substances
used to fill teeth in the cavity preparation.
 Lining the cavity preparation protects the pulp and
also helps soothe the pulpal tissue.
Reparative Dentin
38

Reparative Dentin
Reparative Dentin
(Cont.)
 Mechanical and
chemical traumas are in
areas where there has
been decay or cavity
preparations, such as
occlusal grooves or
cervical or interproximal
areas.
39

 There are several abnormalities found in dentin.
 Most of the more common abnormalities cannot
be seen without sectioning the tooth and
studying it with a microscope.
Abnormalities in Dentin
40

Interglobular Dentin
 During the process of calcification, some areas of
poorly calcified dentin become entrapped.
 These are known as interglobular dentin.
 They are found next to the DEJ in the crown and the
dentinocemental junction in the root.
 The root interglobular dentin is called the granular
layer of Tomes.
41

Dead Tracts
 Dentinal tubules that are empty because of the
death of the odontoblasts that originally occupied
them are known as dead tracts.
 Because the tubules are empty they provide a
pathway to the pulp for bacteria involved in decay.
42

Sclerotic Dentin
 When the dentinal tubules fill in with a dentin
material it is called sclerotic dentin.
 The cause is related to occlusal trauma or decay.
 The odontoblastic processes retract and begin
secreting a matrix substance, filling in the empty
tubule.
43

Pulp
44
 Pulp develops from mesodermal tissue of the
dental papilla.
 Eventually consists of blood vessels, lymphatic
vessels, nerves, fibroblasts, and collagen fibers,
as well as other cells of connective tissue.

 Nerves of the pulp are primarily sensory and
transmit only one type of sensation: pain.
 There are some autonomic sympathetic nerves
that innervate smooth muscle cells in the walls
of blood vessels and cause them to constrict.
 This reaction is important in vascular changes in
the pulp caused by irritation to the tooth.
Pulp
45

Pulp
 Young pulpal tissue is
cellular, with a lesser
concentration of fibers
than older pulp.
 Cells present include
fibroblasts,
macrophages, and
mesenchymal cells.
 As pulp ages,
mesenchymal cells
form odontoblasts.
46

 Pulp stones are the primary abnormality in pulp.
 They are small, circular, calcified areas.
 True pulp stones originate from odontoblasts.
 Very rare.
 False stones are the most common.
 Originate from dead cells with concentric layers of
calcium phosphate around them.
 Diffuse calcified stones are very tiny calcified
structures found in groups.
Abnormalities in Pulp
47

 Free pulp stones are
in middle of pulp.
 Attached pulp stones
attached to dentin at
periphery of pulp.
 Embedded stones
were attached to
dentin and became
surrounded by
secondary dentin.
48

 Pulp stones usually do not affect the health of
the pulp.
 They may be seen as small globular
radiopacities on radiographs.
49

Oral Anatomy: Enamel, dentin, and pulp

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Oral Anatomy: Enamel, dentin, and pulp

Similar to Oral Anatomy: Enamel, dentin, and pulp (20)

More from HeatherSeghi

More from HeatherSeghi (20)

Recently uploaded

Recently uploaded (20)

Oral Anatomy: Enamel, dentin, and pulp