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PERIDENTAL MEMBRANE. 135
The cementum is penetrated through all its layers by fibers of the
])ericlental membrane which have been imbedded in the matrix of the
tissue and calcified along with it. The first layer,—that is, the one next
to the dentin,— is usually structureless aud shows no fibers in it, at
least in its inner half. In ground sections the imbedded fibers often
appear in a number of layers, while they are not apparent in the rest
of the thickness. This is because just before and just after the forma-
tion of the layers in which they appear the fibers were cut off and
reattached, chauging their direction, so that in the other layers the
fibers are cut transversely or obliquely. This is illustrated in Fig. 117.
These imbedded fibers are very numerous in some places. If properly
stained, the tissue seems almost a solid mass of fibers. In ground sec-
tions these have sometimes been mistaken for minute canals from the
fact that they are not always as fully calcified as the cementum matrix,
and shrinkage causes the appearance of little open canals.
Hypertrophies of the cementum (formerly often called exostoses, or
excementoses) are very common. The increased thickness may be of
one lamella or of several lamellre in the region of the hypertrophy, or
all of the layers from first to last may take part in it. Small local
thickenings of a single lamella are seen in connection with the peri-
dental membrane wherever a specially strong bundle of fibers is to be
attached to the root to support the tooth against some special strain.
Peridental Membrane,
The peridental membrane may be defiued as the tissue which fills
the space between the root of the tooth and the bony wall of its
alveolus, surrounds the root occlusally from the border of the alveolus,
and supports the gingivus. It has been referred to under many names,
as pericementum, dental periosteum, alveolo-dental periosteum, etc.
While this tissue performs the functions of a periosteum for the bone
of the alveolus, it differs in structure from the periosteum in any
position, so that any name including the word periosteum or implying
a double membrane should be avoided.
The peridental membrane belongs to the class of fibrous membranes,
and is made up of the following structural elements
1. Fibers. 2. Fibroblasts. 3. Cementoblasts. 4. Osteoblasts. 5.
Osteoclasts. 6. Epithelial structures which have been called the glands
of the peridental membrane. 7. Bloodvessels. 8. Xerves.
The peridental menil)rane performs three functions : a physical
function, maintaining the tooth in relation to the adjacent hard and
soft tissues ; a vital function, the formation of bone on the alveolar
wall and of cementum on the surface of the root ; and a sensory
PERIDENTAL MEMBRANE. 135
The cementum is penetrated through all its layers by fibers of the
])ericlental membrane which have been imbedded in the matrix of the
tissue and calcified along with it. The first layer,—that is, the one next
to the dentin,— is usually structureless aud shows no fibers in it, at
least in its inner half. In ground sections the imbedded fibers often
appear in a number of layers, while they are not apparent in the rest
of the thickness. This is because just before and just after the forma-
tion of the layers in which they appear the fibers were cut off and
reattached, chauging their direction, so that in the other layers the
fibers are cut transversely or obliquely. This is illustrated in Fig. 117.
These imbedded fibers are very numerous in some places. If properly
stained, the tissue seems almost a solid mass of fibers. In ground sec-
tions these have sometimes been mistaken for minute canals from the
fact that they are not always as fully calcified as the cementum matrix,
and shrinkage causes the appearance of little open canals.
Hypertrophies of the cementum (formerly often called exostoses, or
excementoses) are very common. The increased thickness may be of
one lamella or of several lamellre in the region of the hypertrophy, or
all of the layers from first to last may take part in it. Small local
thickenings of a single lamella are seen in connection with the peri-
dental membrane wherever a specially strong bundle of fibers is to be
attached to the root to support the tooth against some special strain.
Peridental Membrane,
The peridental membrane may be defiued as the tissue which fills
the space between the root of the tooth and the bony wall of its
alveolus, surrounds the root occlusally from the border of the alveolus,
and supports the gingivus. It has been referred to under many names,
as pericementum, dental periosteum, alveolo-dental periosteum, etc.
While this tissue performs the functions of a periosteum for the bone
of the alveolus, it differs in structure from the periosteum in any
position, so that any name including the word periosteum or implying
a double membrane should be avoided.
The peridental membrane belongs to the class of fibrous membranes,
and is made up of the following structural elements
1. Fibers. 2. Fibroblasts. 3. Cementoblasts. 4. Osteoblasts. 5.
Osteoclasts. 6. Epithelial structures which have been called the glands
of the peridental membrane. 7. Bloodvessels. 8. Xerves.
The peridental menil)rane performs three functions : a physical
function, maintaining the tooth in relation to the adjacent hard and
soft tissues ; a vital function, the formation of bone on the alveolar
wall and of cementum on the surface of the root ; and a sensory
