CHAPTER 14
Oral Cavity
277
Figure 14-18C.
PDL and alveolar bone
. H&E,
3
34; inset
3
72
The
PDL
is a dense f
brous connective tissue with a direct nerve
and blood supply. It is located between the cementum and
the alveolar bone, which surrounds the tooth root. Fibroblasts are
the main cells responsible ±or the ±ormation o± the PDL. The PDL
supports the tooth root by ±orming a strong attachment between
the cementum and alveolar bone by
Sharpey f
bers
(Fig. 14-19A).
The ±unctions o± the PDL are to provide sensory in±ormation
regarding pain and pressure, to provide signals to the alveolar
bone regarding bone remodeling, and to maintain tooth position
in the dental arch. The
alveolar bone
(also called the
alveolar pro-
cess
) surrounds and supports the tooth root and is part o± the
maxilla and mandible. It is constantly remodeled and is built up
by osteoblasts and absorbed by osteoclasts. Alveolar bone has the
general characteristics o± bones. It consists o± both compact and
cancellous bones (see Chapter 5, “Cartilage and Bone”).
Enamel
Enamel
space
space
Enamel
space
DCJ
DCJ
DCJ
CEJ
CEJ
CEJ
Acellular
Acellular
cementum
cementum
Acellular
cementum
Dentin
Dentin
Dentin
DCJ
DCJ
DCJ
Cementoblasts
Cementoblasts
Cementoblasts
Predentin
Predentin
Predentin
Dental
Dental
pulp
pulp
Dental
pulp
Odontoblasts
Odontoblasts
Odontoblasts
A
Figure 14-18A.
Acellular cementum
,
cervical region o± tooth
root
.
H&E,
3
181; inset
3
158
The
periodontium
includes the
cementum
, the
PDL
, and the
alveolar bone
. These structures surround and support the
tooth in the tooth socket. Cementum is a thin layer o± hard tis-
sue ( calcif ed matrix) that does not have a direct blood supply.
It covers the dentin and seals the dentinal tubules at the root
region. Cementum is thicker at the root apex than at the cervix
region and can be divided into
acellular
and
cellular cementum
.
Acellular cementum has no cementocytes embedded within the
matrix and is o±ten ±ound at the cervical two thirds o± the root,
attached to the dentin. The junction between the dentin and
cementum is called the
dentinocemental junction (DCJ)
, and the
junction between the cementum and enamel is the
CEJ
. There are
three ±orms o± the CEJ: (1) the cementum overlaps the enamel
(60%); (2) the cementum meets the enamel end-end (30%); and
(3) there is a gap between the cementum and the enamel (10%).
Periodontium
Blood
Blood
vessels
vessels
Blood
vessels
Cellular
Cellular
cementum
cementum
Cellular
cementum
Cementocyte
Cementocyte
Cementocyte
Periodontal ligament (PDL)
Periodontal ligament (PDL)
Periodontal ligament (PDL)
Dentin
Dentin
Dentin
Predentin
Predentin
Predentin
Odotoblast
Odotoblast
Odontoblast
Dental
Dental
pulp
pulp
Dental
pulp
Cementoblast
Cementoblast
Cementoblast
Sharpey fibers
Sharpey fibers
in cementum
in cementum
Sharpey fibers
in cementum
B
Figure 14-18B.
Cellular cementum
,
apical region o± tooth
root
. H&E,
3
181; inset
3
408
Cellular cementum
is o±ten ±ound at the apical third o± the tooth
root and is similar to bone with a calcif
ed intercellular matrix.
During the process o± ±ormation o± cementum some cemento-
blasts are trapped in the matrix, and each one is surrounded by
a lacuna. These
cementoblasts
then become
cementocytes
. The
matrix o± cellular cementum is deposited more rapidly than that
o± acellular cementum.
Acellular cementum
has a slower ±orma-
tion rate and ±ormation continues throughout li±e. The slower
growing cementum allows f bers (
Sharpey f bers
,
left inset
) ±rom
the PDL to become trapped in the matrix o± the cementum to
±orm the tooth attachment. Cementum is much more resistant
to reabsorption than bones. This characteristic helps maintain
root integrity and prevents exposure o± the root dentin, which
is important as teeth are moved around during orthodontic
procedures.
Alveolar
Alveolar
bone
bone
Alveolar
bone
Dentin
Dentin
Dentin
PDL
PDL
PDL
PDL
PDL
PDL
Cementum
Cementum
Cementum
Dental pulp
Dental pulp
Dental pulp
Alveolar bone
Alveolar bone
Alveolar bone
Bone
Bone
marrow
marrow
Bone
marrow
PDL
PDL
PDL
Cementum
Cementum
Cementum
PDL
PDL
PDL
Alveolar bone
Alveolar bone
Alveolar bone
Dentin
Dentin
Dentin
C
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