This document discusses the structure and function of fibroblasts in the periodontal ligament. It describes the key organelles in fibroblasts, including the rough endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, and components of the cytoskeleton. It discusses how fibroblasts are involved in synthesis and degradation of the extracellular matrix through these organelles. The document also examines cell junctions between fibroblasts and characteristics of other cell types in the periodontal ligament, such as cementoblasts and osteoblasts.

1. Dr Heenal Adhyaru
Department of Periodontology
1

2.  PERIODONTIUM: The
tissues that invest and
support the teeth
including the gingiva,
alveolar mucosa,
cementum, periodontal
ligament, and alveolar
and supporting bone.
(GTP 2001)
 PERIODONTIUM:
1. Gingiva
2. Periodontal ligament
3. Cementum
4. Alveolar bone
2Glossary of periodontal terms, 2001 4th edition

3.  The periodontal ligament is composed of a
complex vascular and highly cellular connective
tissue that surrounds the tooth root and
connects it to the inner wall of the alveolar
bone.
3Carranza's Clinical Periodontology 10th edition

4.  Periodontal ligament:
The connective tissue
that surrounds and
attaches roots of
teeth to the alveolar
bone. (GTP 2001)
4Glossary of periodontal terms, 2001 4th edition

5.  Terms:
 Desmodont, gomphosis, pericementum,
dental periosteum, alveolodental ligament,
periodontal membrane.
 Because it is a complex soft connective
tissue providing continuity between two
mineralized connective tissues, the term
periodontal ligament appears to be the
more appropriate.
5Orban’s Oral Histology and Embryology, 12th edition

6. PDL
Cellular
element
Extra cellular
substance
Fibers
Ground
substance
6Orban’s Oral Histology and Embryology, 12th edition

7.  The principal cells of the healthy,
functioning periodontal ligament are
concerned with the synthesis and
resorption of alveolar bone, the fibrous
connective tissue of the ligament and
cementum.
 Compared with most connective tissues, the
periodontal ligament is highly cellular.
7Orban’s Oral Histology and Embryology, 12th edition

8. B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 8

9.  The cells of the
PDL may be
divided as:
1. Synthetic cells
 Fibroblasts
 Osteoblasts
 cementoblasts
2. Resorptive cells
 Osteoclasts
 Fibroblasts
 cementoclasts
3. Progenitor cells
4. Epithelial rests
of Malassez
5. Defense cells
 Mast cells
 Macrophages
 Eosinophils
9Orban’s Oral Histology and Embryology, 12th edition

10.  The fibroblasts lie between the collagen
fibers and although various shapes have
been described it is likely that their
appearance is governed by the surrounding
matrix (Ross 1968).
 If the PDL is sectioned both transversely
and longitudinally, it can be deduced that
the cells take the form of a flattened
irregular disc, approx. 30 ɥm in diameter.
(Berkovitz, 1988).
 However, a defined 3D reconstruction of
PDL fibroblasts has yet to be accomplished.
10
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition.

11.  Nucleus:
 Flatterned disc
shape
 Diameter approx
10ɥm (Shore and
Berkovitz, 1979)
 Occupy upto
30% of cell
volume.
(Beertsen and
Everts, 1977;
Yamasaki et al,
1987a)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 11

12.  When stained with colloidal silver (Crocker
and Nar, 1987) it demonstrates either one
or two regions of acidic proteins which are
associated with the nucleolar organizer
regions (Shore et al., 1991)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 12

13.  In the aged PDL, multinucleated fibroblasts
may appear, arising either from fusion of
mononuclear cells or perhaps by faulty
division. (Sasaki and Grant, 1993)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 13

14.  As fibroblasts produce the ECM of the
PDL, which demonstrates a very high rate
of turnover (Sodek, 1977), the cells contain
significant amounts of the organelles
involved in protein synthesis and
degradation.
 Cho and Garant (1981a) have demonstrated,
using tritiated proline in a pulse-chase
experiment, that the synthetic pathway is
from rough endoplasmic reticulum (RER) to
Golgi complex and via secretory vesicles to
the cell membrane.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 14

15.  Rough Endoplasmic Reticulum:
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 15

16.  Golgi complex:
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 16

17.  Mitochondria:
 Distributed throughout the cell, except for
the finest cell processes.
 Their profiles vary from elongated to
round, reflect either an inherent variability
of shape or simply the plane of section.
 They occupy approx. 3 – 3.5% of the cell
volume in humans (Yamasaki et al., 1987a)
 This value not seem to altered by different
occlusal loading levels or eruption in rates
(Shore et al., 1982, 1985)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 17

18.  Lysosomes:
 They are in the form of large membrane-
bound vesicles containing a homogeneous
matrix that is more electron-dense than
the surrounding cytoplasm.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 18

19.  PDL fibroblasts contain small fragments of
collagen fibrils within membrane bound
vesicles (Ten Cate, 1972; Listgarten, 1973;
Beertsen et al., 1974; Eley and Harrison,
1975; Frank et al., 1976; Shore and
Berkovitz, 1979)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 19

20.  Intracellular collagen profiles:
 This constitute the temporal sequence of
the intracellular degradation of collagen
(Ten Cate et al., 1976)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition. 20

21.  Cytoskeleton:
 Cell possess a cytoskeleton that provides a
structural framework, facilitates
intracellular transport, supports cell
junctions and transmits signals about cell
contact and adhesion, and permit motility.
 The three structural elements of the
cytoskeleton are
 Microfilaments
 Intermediate filaments
 Microtubules
Ten Cate’s Oral Histology 8th edition 21

22.  Microfilaments:
 Microfilaments are of 5-7 nm in diameter
and are composed predominantly of
polymerized actin (F actin), although other
proteins are present as well (Brinkley,
1982)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 22

23.  The microfilaments
are present in the
cytoplasm of the cell
either as a network
that fills the cell
processes (Beertsen et
al., 1974) or as bundles
beneath the cell
membrane that
resembles stress
fibers seen in
fibroblasts in vitro
(Beersten et at., 1974;
Shore and Berkovitz,
1979)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 23

24.  It is possible that the cells undergo
continual short term localized movements in
order to maintain the matrix around them.
 As the PDL has an extremely high rate of
turnover and therefore a constant need for
fibril orientation, this local motility may be
of considerable significance in maintaining
PDL integrity.
 That the presence of stress fibers may be
linked to fibril orientation.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 24

25.  Microtubules:
 Microtubules are tubular or cylindrical
structures with an average diameter of 25
nm and are composed of the protein tubulin.
 They are randomly arranged in cytoplasm
(Shore and Berkovitz, 1979)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 25

26.  Microtubules are linked to fibroblast
motility and in facilitating protein export
(Ehrlich and Bornstein, 1972).
 The distruption of microtubules leads to
internal accumulation of procollagen (Cho
and Garant, 1981b)
 They are often seen to radiate from
centrioles, structures which themselves
consist of a hollow tube of microtubules.
 A structure frequently associated with the
centriole of PDL fibroblasts is a solitary
cilium.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 26

27.  Solitary cilia lie within invaginations of the
cell membrane with their distal ends
protruding into the surrounding matrix.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 27

28.  Cilium lacks the central doublet of
microtubules and dynein side arms
associated with the outer doublets.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 28

29.  Degree of polarization of PDL fibroblasts
and their organelles in relation to collagen
secretion and /or motility can be
considered on two levels:
 Whether individual cells are polarized in terms
of shape and organelle content and
 Whether the population of cells within the
tissue as a whole is polarized in a particular
orientation.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 29

30.  Beertsen et al. (1979) and Garant and Cho
(1979, 1989) have suggested that both the
Golgi complex and the centriolar region of
PDL fibroblasts may be situated between
the leading edge of the cell and the
posteriorly located nucleus.
 Significant number of cells appeared to be
polarized in opposing direction i.e. some
cells may be moving apically while
neighboring cells are moving incisally.
 Microtubules have also been considered as
indicators of polarity.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 30

31.  Intermediate filaments (IF):
 They are approximately 10 nm in diameter
and have a diverse protein composition.
 They are important in the maintenance of
cell shape and contact between adjacent
cells and extra cellular matrix.
 In cells of mesenchymal origin they are
polymers of the protein Vimentin while in
epithelial cell, they consists of
cytokeratins.
 The filaments form bundles, called
tonofilaments which anchor onto
desmosomes.
Ten Cate’s Oral Histology 8th edition 31

32.  In humans, PDL may possess significant
accumulations of IFs particularly within cell
processes (Yamasaki et al., 1987b;
Berkovitz, 1988)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 32

33.  Webb et al (1994) suggests that
periodontal fibroblasts and cementoblasts
co express vimentin and cytokeratin
immediately before and during the active
phase of eruption.
 Once eruption has ceased, the expression
of cytokeratin ceases also.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 33

34.  Intracellular contact:
1. Tight junctions (Zonula occludents)
2. Adhesive junctions
1. Cell to cell
1. Zonula adherens
2. Macula adherens (desmosomes)
2. Cell to matrix
1. Focal adhesions
2. hemidesmosomes
3. Communicating (gap) junctions
Ten Cate’s Oral Histology 8th edition 34

35.  On molecular level,
intercellular junctions
typically consists of three
components:
1. A transmembrane
adhesive protein
2. A cytoplasmic adapter
protein
3. A cytoskeletal filament
 These three components
differ depending on the
type of junctions
Ten Cate’s Oral Histology 8th edition 35

36.  Contacts not normally being found in
significant numbers between fibroblasts of
adult connective tissues (Gabbiani, 1979;
Moxham et al., 1984)
 In the PDL, two major types of contact are
seen:
 Gap junction
 Simplified desmosomes
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 36

37. Gap junction Simplified desmosomes
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 37

38.  Cell surface receptors:
 Specific cell surface receptors shown to be
present on PDL fibroblasts are those for
 EGF-Epidermal growth factor (Thesleff et al.,
1987; Topham et al., 1987; Cho et al., 1991)
 IL-1ß: Interleukin-1ß (Saito et al., 1991)
 In addition, in vitro studies suggest the
presence of receptors for I-LGF (insuline
like growth factor), PDGF (platelet derived
growth factor), growth hormone (Blom et
al., 1992; Matsuda et al., 1992) and
parathyroid hormone (Ngan et al., 1988)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 38

39.  Cementoblasts are the cells responsible for
secreting the organic matrix of cementum.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 39

40.  When active they may appear as a distinct
layer of cells on the root surface,
somewhat similar to the osteoblastic layer
but usually not as regular in arrangement.
 Some of the cementoblast cell processes do
not approach cementum and their
cytoplasmic contents are not polorized, the
cells may contribute matrix to the PDL.
 Synthetic pathway similar to fibroblasts
and they appear to have less RER but more
mitochondria than PDL fibroblasts
(Yamasaki et al., 1987b)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 40

41.  One prominent feature is the accumulation
of numerous glycogen granules, the number
decreasing the further the distance from
the cementum surface (Yamasaki et al.,
1986)
 They also appear to contain significant
quantities of both intermediate and actin
filaments.
 Intercellular contacts: gap and simplified
desmosome (Yamasaki et al., 1987b)
 Receptors for growth hormone (Zhang et
al., 1993) and EGF (Cho et al., 1991)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 41

42.  Osteoblasts within the PDL are found on
the surface of the alveolar bone.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 42

43.  The cells do not appear to possess
receptors for EGF (Martineau- Doize et al.,
1987)
 Intercellular contacts: gap junction and
simplified desmosome.
 They also form contacts via gap junctions
with osteocytes lying within lacunae in the
adjacent bone, thus forming a coordinated
system throughout the bone tissue (Holtrop
and Weinger, 1972)
 As bone deposition proceeds, osteoblasts
become incorporated in the matrix as
osteocytes (in which the organelle content
is reduced).
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 43

44.  Cells that may be osteoblast precursors are
often seen beneath the osteoblast layer in
the vicinity of adjacent blood capillaries.
 As they proceed through the stages of
differentiation from precursor via
committed osteoprogenitor to
preosteoblast, they first migrate away
from the bone surface into the body of
the PDL before eventually taking up their
functional position (Roberts et al., 1987)
 Once in the functional state, the cells may
remain active for a period of up to 20 days.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 44

45.  When osteogensis is not occurring, a
distinct layer of osteoblasts is absent.
 Osteoblasts (and osteoclasts) are present
over only approximately 10-15 % of bone
surfaces (Jowsey et al., 1965); the
remaining 85-90% of the bone surface is
covered by flattened cells with scanty
cytoplasm, the so called bone-lining cells.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 45

46.  Although it has been claimed that bone
resorption may be mediated via osteocytes
(Belanger, 1971), resorption of bone
surface is accomplished via a distinct cell
type, the osteoclast.
 They are found on the surface of the
alveolar bone:
 Found within resorption lacunae
 They are large and multinucleated
 They have a ‘ruffled border’ adjacent to the
resorbing surface, enclosed by a smooth ‘clear’
zone
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 46

47. B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 47

48.  They do not cover the whole of the
resorbing surface at any one time (Owen
and Shetlar, 1968); rather they ‘service’ a
much larger area by demonstrating
considerable motility (Hancox, 1972; Jones
and Boyde, 1977)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 48

49.  The multinucleated cells associated with
the resorption of cementum and dentine
have sometimes been referred to as
cementoclasts and odontoclasts.
 However the evidence suggests that all
multinucleated resorptive cells involved in
the removal of mineralized tissues are
morphologically and functionally similar
(Yaeger and Kraucunas, 1969; Freilich, 1971;
Addision, 1979)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 49

50.  Epithelial cells represent the remains of
the developmental epithelial root sheath of
Hertwig, which is involved in mapping out
the shape of the roots and in the
differentiation of root odontoblasts
(Thomas and Kollar, 1988)
 The epithelial cell rests (ECR) can be
distinguished from the fibroblasts:
 Close packing of their cuboidal cells
 Stain more deeply
 Completely surrounded by connective tissue
cells (Brunette et al., 1979)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 50

51.  Immediately after disruption of the root
sheath, the ECR are found in groups of one
or two cells, with only a partial basal lamina.
 Subsequently, the epithelial rests become
more cellular and are contained within an
almost complete basal lamina with narrowed
intercellular spaces.
 As laminin is chemotactic to epithelial cells,
the basal lamina may therefore play a role
in the formation, differentiation and
maintenance of the ECR (Hamamoto et al.,
1991).
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 51

52.  ECR a high nuclear-cytoplasmic ratio.
 They exhibit basal cell-like,
undifferentiated and hyperproliferative
characteristics, as indicated by expression
of cytokeratins 5, 6, 14, 16 and 19 (Salonen
et al., 1991)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 52

53. B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 53

54.  ECR are located closer to the cementum.
 Average distance 27ɥm in apical region and
41ɥm in cervical region. (Valderhaug and
Zander, 1967)
 Distribution changes with age: more
numerous in children and less numerous in
older individuals (Reitan, 1961; Simpson,
1965; Wesselink and Beertsen, 1993)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 54

55.  Up to the second decade of life, ECR are
found most commonly in the apical region of
the PDL, whereas later in life the majority
of cell rests are located cervically in the
gingiva of the alveolar crest (Reeve and
Wentz, 1962)
 In this cervical region, some of the ECR are
presumably derived from the gingival
epithelium and the junctional epithelium
(Wentz et al., 1950)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 55

56.  As non functional cells usually disappear,
the persistence of ECR suggests that they
are not totally inactive and may sub-serve
some function (Spouge, 1980).
 They take up tritated thymidine, indicating
some degree of turnover (Trowbridge and
Shibata, 1967; McCilloch and Melcher,
1983c)
 Show intense binding of EGF indicating ECR
are activated by a local rise in tissue level
of this GF. (Thesleff, 1987)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 56

57.  Functions:
 ECR secrete enamel like proteins onto the
root surface (Slavkin et al., 1988; Luo et al.,
1991)
 Mediating repair cementogensis (Brice et
al., 1991)
 Factor liminting the resorption and
maintenance of the periodontal space. (Loe
and Waerhaug, 1961; Lindskog et al, 1983)
 Cells have been implicated in the aetiology
of periodontal cysts
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 57

58. B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 58

59.  The question arises as to whether
periodontal fibroblasts, cementoblasts and
osteoblasts all arises from a common
precursor or whether each cell type has its
own specific precursor cell.
 Nuclear size can help distinguish some cell
type (Roberts et al., 1981), while receptors
to EGF are present during root
development on preosteoblasts and
periodontal fibroblasts, but not on
precementoblasts, cementoblasts and
osteoblasts. (Cho et al., 1991)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 59

60.  Dividing progenitor cells within the PDL are
located predominantly paravascularly (Gould
et al., 1982; McCulloch and Melcher, 1983b,
c; Roberts et al., 1987) and give rise to
cells that can migrate towards the bone and
cement surfaces, where they differentiate
into osteoblasts and cementoblasts
(McCulloch and Melcher, 1983b)
 This population may represent stem cells
that are not terminally differentiated but
that continue to divide at a slow rate.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 60

61.  McCulloch and Melcher (1983c)
investigated the relationship between cell
density and cell generation within the PDL.
 Labelling indices are highest in zones
adjacent to blood vessels.
 Also in the middle of the ligament where
cell density was lower, compared with zones
adjacent to bone and cementum, where cell
density was higher.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 61

62.  Yee (1979), Gould et al. (1980) and Gould
(1983) have studied the morphology of
progenitor cells in the PDL.
 They have relatively undifferentiated
appearance (e.g. small size, scarcity of
intracellular organelles, and a high nuclear-
cytoplasmic ratio), some cells have been
shown to be relatively well differentiated,
containing much RER and even intracollagen
profiles.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 62

63.  The cell cycle time for roughly one half of
the cells in the normal PDL has been
calculated to be less then 48hrs. (Roberts,
1975a; Roberts et al., 1981)
 For PDL fibroblasts, Gould et al. (1983)
have calculated a turnover time of 45 days,
there being a slight increase with age.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 63

64.  Using orthodontically induced osteogenesis as
the model system, Roberts and Chase (1981)
found that the initial layer of osteoblasts was
unlabelled.
 This implies that among the cells of normal PDL
are preosteoblasts that are sufficiently
differentiated to become osteoblasts without
synthesizing DNA.
 All cells across the ligament synthesize
collagen using tritiated proline (Beertsen and
Everts, 1977; Rippin, 1978) indicating that such
preosteoblasts contribute to the formation of
PDL collagen before finally differentiating into
osteoblasts (Roberts et al., 1982)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 64

65.  Roberts et al. (1981, 1982 and 1987) and
Roberts and Ferguson (1989) used nuclear
size (Nuclear diameter) to classify cells in
the PDL after orthodontically induced
osteogensis.
A. 40-79 ɥm3 : small precursor cells
B. 80-119 ɥm3 : typical PDL fibroblasts
C. 120-169 ɥm3 : G1 preosteoblasts
D. >170 ɥm3 : G2 preosteoblasts
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 65

66.  McCulloch et al. (1987) have provided some
evidence that raises the possibility that
cells may migrate out from the endosteal
spaces in the alveolar bone and into the
ligament, thereby augmenting the
populations of fibroblasts, osteoblasts and
cementoblasts.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 66

67.  Osteoclasts are derived from haemopoietic
stem cells.
 This cells enter the ligament as
mononuclear cells from the haemopoietic
system as required and then fuse to form
the typical large, multinucleated giant cell.
1. Fusion of monocytes or macrophages or
both.
2. Share a common progenitor with cells of
the monocyte-macrophage line
3. From pluripotent haemopoietic stem cell
entirely separate from that of the
monocyte-macrophage line.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 67

68.  The PDL contains defence cells:
 Macrophages,
 Mast cells and
 Eosinophils.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 68

69.  Macrophages:
 MuCulloch et al. (1989) described the
detailed distribution of the macrophage in
the healthy PDL using electron microscopy.
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 69

70.  Macrophages comprise of 4% of the cells
of the PDL
 They are located close to blood vessels.
 As the labelling index of perivascular cells
is high compared with other regions of the
ligament, it is possible that lymphokines
released from macrophages may be involved
in cell kinetics.
 Dual role:
 Phagocytosing dead cells
 Secreting growth factors
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd edition 70

71.  Mast cells:
 Granules released by mast cells may be
phagocytosed by fibroblasts, suggesting
that other interactions may occur between
mast cells and fibroblasts (Atkins et al.,
1985)
B K B Berkovit’s The periodontoal ligament in health
and disease, 2nd editio 71

72.  Carranza's Clinical Periodontology, 10th
edition.
 Glossary of periodontal terms, 2001 4th
edition
 Orban’s Oral Histology and Embryology,
12th edition.
 Ten Cate’s Oral Histology 8th edition.
 B K B Berkovit’s The periodontoal
ligament in health and disease, 2nd
edition.
72