Periodontium: Supporting Structures

Chapter 8
Supporting Structures
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.

 The periodontium consists of tissues that
support the teeth.
 It is divided into a gingival unit and an
attachment unit or attachment apparatus.
The Periodontium
2

 The various parts of the gingival unit include:
Gingiva
Free gingiva
Attached gingiva
Alveolar mucosa
Attachment unit
Cementum
Alveolar bone
Periodontal ligament
The Periodontium
3

Gingival Unit
 The gingiva is made up of free and attached
gingiva.
4

 Gingiva is composed of very dense mucosa
called masticatory mucosa and has a thick
epithelial covering and keratinized cells.
 The underlying mucosa is composed of dense
collagen fibers.
Gingival Unit
5

Gingival Unit
6

 Masticatory mucosa is also found on the hard
palate and is designed to withstand the trauma
to which it is subjected in grinding food.
Gingival Unit
7

 The rest of the mouth is lined with a type of
mucosa called lining mucosa.
Alveolar mucosa is lining mucosa.
 The epithelium covering lining mucosa is thin,
nonkeratinized, and freely movable.
 Its mucosa is composed of loose connective
tissue and muscle fibers.
Gingival Unit
8

Free Gingiva
 Free gingiva is the gum tissue that extends from the
gingival margin to the base of the gingival sulcus.
It is usually light pink in color and averages between
0.5 to 2 mm in depth.
Gingival Unit
9

Free Gingiva (Cont.)
 The free gingival margin around a fully erupted tooth
is about 0.5 to 2 mm coronal to the cementoenamel
junction (CEJ).
 It forms a collar, which is separated from the tooth
by the gingival sulcus.
 A healthy gingival sulcus is approximately 2.5 mm in
depth.
Gingival Unit
10

 The gingival papilla is the free gingiva located in the
triangular interdental spaces.
 The shape of gingival papilla is affected by the
location of the contact area of the adjacent teeth,
the shape of the interproximal surfaces of the
adjacent teeth, and the CEJ of the adjacent teeth.
Gingival Unit
11

 The inner portion of the gingival sulcus is lined with
nonkeratinized epithelium; the outer portion is the
free gingiva, which is covered with keratinized
epithelium.
 A gingival groove often occurs on the outside of the
free gingiva and corresponds to the base of the
sulcus.
Gingival Unit
12

Attached Gingiva
 The attached gingiva begins at the base of the
gingival sulcus and is attached to the bone and the
cementum by collagenous fibers.
 It often has a stippled texture, resembling the
dimpled surface of an orange.
Gingival Unit
13

Attached Gingiva (Cont.)
 The attached gingiva is keratinized and is covered
by stratified squamous epithelium in which rete peg
formation is evident.
 The dimpling effect is caused by the rete peg
formation, which is simply the irregular binding of the
epithelium to the bone by collagen fibers.
 This causes depressions or dimples where the
epithelium is pulled tight to the bone.
Gingival Unit
14

 The color of the gingiva varies from light to dark pink
and may contain pigment, correlating to the skin
pigmentation of the person.
 The darker a person’s skin color, then the more
likely it is that the gingiva is darker and contains
melanin.
Gingival Unit
15

 The meshwork of collagenous fibers connecting the
gingiva to bone are formed by fibroblasts.
 All fibers embedded in the cementum are known as
Sharpey’s fibers; they extend from the cementum to
the papillary area of the gingiva.
 These fibers pass out from the cementum in small
bundles.
Gingival Unit
16

Gingival Unit
Attached Gingiva
(Cont.)
 Some of the fibers (A)
curve toward the
mucosa of the free
gingiva and interlace
with one another.
 Other fibers (B) pass
directly across from the
cementum to the
gingiva.
17

 Still further apically, other fibers pass from the
cementum over the alveolar crest and turn apically
between the outer periosteum of the alveolar
process and the outer epithelial covering of the
attached gingiva.
Gingival Unit
18

 On the proximal side, the connective tissue fibers
are at a higher level on the cementum because of
the curvature of the CEJ.
 This curvature allows more room for the cementum to
attach to the gingiva.
Gingival Unit
19

 Attachment is made possible by groups of
connective tissue fibers.
 The most occlusal group travels to the papillary
layer of the epithelium of the interdental papilla.
Gingival Unit
20

 The next layer of fibers passes occlusally into the
interproximal gingiva.
 The transseptal (TS) group, the next layer of fibers,
travels completely across the interproximal space
and attaches to the adjacent tooth.
These transseptal fiber bundles bind one tooth to
another.
Gingival Unit
21

Gingival Unit
Attached Gingiva
(Cont.)
 Additionally, circular
bands of connective
tissue fibers surround
the teeth, tying them
together.
22

 The function of these fibers is to keep the gingiva
closely attached to the tooth surface.
 They also prevent the apical migration of the
epithelial attachment and resist gingival recession.
 Blood supply of the gingival tissue comes from the
supraperiosteal vessels originating from the lingual,
mental, buccal, infraorbital, and palatine arteries.
Gingival Unit
23

Alveolar Mucosa
 The alveolar mucosa joins the attached gingiva at
the mucogingival junction and is continuous with the
rest of the tissues of the vestibule.
 Alveolar mucosa is composed of lining mucosa, and
its submucosa contains loose connective tissue and
fat.
 The epithelium is smooth, thin, and nonkeratinized.
Gingival Unit
24

 The attachment unit comprises the cementum,
the periodontal ligament, and the alveolar bone.
 Cementum is hard, bonelike tissue covering the
roots of the teeth.
 The periodontal ligament is the tissue that
surrounds the roots of the teeth and connects
them to alveolar bone.
 The alveolar bone is the thin covering of
compact bone that surrounds the teeth.
Attachment Unit
25

Attachment Unit
 When viewed
radiographically,
alveolar bone is
called the lamina
dura.
26

 The function of the attachment apparatus is not
only supportive but also nutritive, formative, and
sensory.
 The supportive function is to maintain the support
for the tooth in the bone and to prevent its
movement.
 The nutritive and sensory functions are fulfilled by
the blood vessels and nerves.
 The nerves act as indicators of pressure or pain
around the tooth.
Attachment Unit
27

 The formative function is to replace cementum,
periodontal ligament, and alveolar bone.
This is accomplished by specialized cells called
cementoblasts, fibroblasts, and osteoblasts.
Attachment Unit
28

 In addition to these functions, the periodontal
ligament keeps the root and bone from abrading
each other.
 The periodontal ligament also acts as a cushion
between tooth and bone on the exertion of
pressure.
Attachment Unit
29

Cementum
 Cementum can be cellular or acellular.
 Both types are formed by cementoblasts.
In the cellular type, the cementoblasts become
embedded in the cementum.
The acellular type is free of embedded cementoblasts
and is clear and without structure.
Attachment Unit
30

Cementum (Cont.)
 Acellular cementum always covers the cervical third
of the root and sometimes extends over almost all of
the root except the apical portion.
 Cellular cementum covers the apical portion of the
root and sometimes may form over acellular
cementum.
Attachment Unit
31

Cementum (Cont.)
 Cellular cementum grows by the apposition
(addition) of new layers, one on top of another.
Changes in function and pressure influence the
growth activity of cementum.
Attachment Unit
32

Cementum (Cont.)
 Both cellular and acellular cementum have collagen
fibers embedded within them.
 These fibers, known as Sharpey’s fibers, are the
embedded ends of connective tissue fibers of the
periodontal membrane.
Some are embedded in cementum, and some are in
bone.
Attachment Unit
33

Alveolar Bone
 The type of bone that lines the sockets in which the
roots of teeth are held is called alveolar bone
proper.
It is thin and compact, with many small openings
through which blood vessels, nerves, and lymphatic
vessels pass.
Attachment Unit
34

Alveolar Bone (Cont.)
 The socket in which the tooth rests is called an
alveolus.
 These alveoli are a part of the alveolar process that
surrounds and supports the teeth in the maxilla and
mandible.
Attachment Unit
35

 Bone consists of an organic matrix and inorganic
matter.
The organic matrix comprises collagen and
intercellular substance.
The inorganic matter comprises apatite crystals of
calcium, phosphate, and carbonates.
Attachment Unit
36

 The bone forming the alveoli undergoes resorption
when pressure is exerted on it and opposition when
tension is placed on it.
 The term bundle bone applies when numerous
layers of bone are added to the socket wall.
Bundle bone forms the immediate attachment of the
periodontal ligament.
Attachment Unit
37

Periodontal Ligament
 The fibers of the periodontal ligament attach to the
alveolar bone and to the cementum.
 They are arranged in the following five groups:
1. Alveolar crest group: Fibers extending from the
cervical area of the tooth to the alveolar crest.
2. Horizontal group: Fibers running horizontally from the
tooth to the alveolar bone.
Attachment Unit
38

Periodontal Ligament (Cont.)
3. Oblique group: Fibers running obliquely from the
cementum to the bone.
4. Apical group: Fibers radiating apically from the tooth
to the bone.
5. Interradicular group: Periodontal fibers between
roots of multirooted teeth.
Attachment Unit
39

 The arrangement of fibers ties the tooth to the bone
and prevents it from being pushed into the bone.
 This function is helped by the roots of the teeth and
by fluids within the periodontal ligament.
 The shapes and sizes of the roots of the teeth help
dissipate occlusal stresses in both a lateral and
apical direction.
Attachment Unit
40

 The main portion of the periodontal ligament is
composed of bundles of white collagenous
connective tissue fibers.
 These fibers extend from and are embedded in the
cementum of the tooth and alveolar bone.
They are bundled together like the many strands of a
rope.
Attachment Unit
41

 The periodontal ligament also contains fibroblasts,
small blood and lymph vessels, and nerves.
Attachment Unit
42

 The tooth itself is suspended by the periodontal
ligament and allows movement within the bony
cavity.
 Two forces allow for movement of the tooth.
1. Mesial drift allows the tooth to move forward.
2. Active eruption allows the tooth to migrate occlusally
until it occludes with an antagonist.
Attachment Unit
43

 For a tooth to move through bone, a force of
some type must be acting on it.
 This force causes pressure on the root,
periodontal ligament, and bone.
 It compresses the periodontal ligament and the
alveolar bone on one side of the root.
 If this force continues for long enough, a
biomechanical system of osteoclastic cells
(bone-destroying cells) is initiated.
Clinical Considerations
44

 On the other side of this same tooth root, the
periodontal ligament is pulled taut.
 This results in a pulling force on the alveolar
bone on that side of the socket.
 This constant tension causes an opposite
biomechanical system.
 Osteoblastic cells (bone-forming cells) start
laying down bone.
45

 Some of the forces that exert pressure on the
teeth:
1. Active eruption.
2. Mesial drift.
3. Masticatory occlusal forces.
4. Orthodontic corrective forces.
5. Traumatic occlusal forces.
46

 The first four of these forces can tip, rotate, or
move the tooth because of the bone-remodeling
system.
 The last of these forces, occlusal trauma, is
usually intermittent and consequently does not
result in tooth movement as much as tooth
mobility.
47

 The periodontal
ligament becomes
enlarged and
widened, the lamina
dura is compressed,
and the tooth
becomes loose and
mobile within the
socket.
48

Periodontium: Supporting Structures

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