The document discusses the periodontal ligament. It describes the periodontal ligament as the connective tissue that surrounds the root and connects it to the alveolar bone. It is made up of principal fibers, cells, ground substance, blood vessels and nerves. The principal fibers are organized into groups like the alveolar crest fibers, horizontal fibers, oblique fibers, and apical fibers that provide support and resist various forces on the teeth. The periodontal ligament also contains cells like fibroblasts, cementoblasts and osteoblasts that allow for remodeling of the tissues. It carries out functions like shock absorption and sensation in addition to attachment of teeth to bone.

1. Periodontal Ligament
Dr. Arun Mohan
Dept. Of Oral Pathology
Royal Dental College

3. Periodontium:
• Tissues supporting and investing
the tooth
•It is a connective tissue organ,
covered by epithelium that attaches
the teeth to the bones of the jaws
and provides a continually adapting
apparatus for support of the teeth
during function
• Consists of cementum, periodontal
ligament, alveolar bone and part of
gingiva facing the tooth
(dentogingival junction)

4. Periodontal Ligament
• Connective tissue that surrounds the root and connects it to the bone.
• It is continuous with the C.T of gingiva and marrow spaces through
vascular channels in the bone.
• Continuous with pulp through apical foramen
Synonyms:
• Desmodont
• Pericementum
• Dentaperiosteum
• Alveolodental ligament
• Periodontal membrane

5. Evolution
Ancestrial reptiles : Tooth is ankylosed to the bone.
Higher mammals : Suspended in sockets by ligaments.
Helps in continual repositioning necessary due
to jaw growth and tooth wearing.
Specialized fibrous joint – Gomphosis (ectomesenchymal
components)

6. • In radiographs they appear as radiolucent area of 0.4-
1.5mm b/w cementum of root and lamina dura of
alveolar bone
- PDL space

7. Shape
• Hour glass shape
- thinnest around middle 3rd of root

8. Width
0.15 – 0.38 mm
• 11-16 years - 0.21mm
• 32- 50 years - 0.18mm
• 51-67years - 0.15mm
(Journal of ADA 1937)
• Width decreases with age – reduced masticatory force (hypofunction)

9. Development
cementoblasts
fibroblasts
osteoblasts Dental follicular cells

10. • Begins with root formation & prior to tooth eruption.
• At this stage, the HERS separates dental papilla from
dental follicle.
• Dental follicle consists of:
- dense fibrous and cellular tissues immediately
encapsulating the developing tooth bud
(dental follicle proper) CEMENTUM
- perifollicular mesenchyme PDL, Alv. bone

15. Components
• Fibers
• Cells
• Ground substance
• Vessels & Nerves
• Cementicles

16. FIBERS
• Collagen fibers
• Elastic fibers
• Oxytalan & Eluanin fibers

17. • HMW proteins, secreted
by fibroblasts -
aggregates into
microfibrils – fibrils –
fibers – bundles
• Types – I, III & XII
– Principal fibers
– Accessory fibers
COLLAGEN FIBERS

18. Principal fibers
5 Groups
Crest of
Alv. bone
Interradicular
septum
Crest of
Alv. bone
Fundus
of bony
socket

19. 1. Alveolar crest group
• Radiates from the crest of
alveolar bone to the cervical
part of cementum, just
beneath the junctional
epithelium
• Function –
- prevents extrusion,
tilting
- resist lateral movements

21. 2. Horizontal group
• Run at right angles to the
long axis of tooth from
cementum to bone –
immediately apical to the
Alveolar crest group
• Minor group limited to
coronal 1/4th of PDL
• Function –
- resist horizontal and
tipping forces

22. 3. Oblique group
• Most numerous – occupy
2/3rd of the ligament
• Inserted into alv bone at a
position coronal to
cementum attachment
• Function –
- resist vertical and
intrusive forces

23. 4. Apical group
• Radiates from root tip,
through PDL into fundus of
the bony socket
• Not seen on incomplete
roots
• Function –
- resist forces of luxation
- prevent tipping
- protect delicate bvs &
nerves

24. 5. Interradicular group
• Inserted into cementum from
the crest of interradicular
septum in multi-rooted teeth
• Function –
- Resist tooth tipping &
luxation
• Age related gingival
recession –
furcation involvement

25. SHARPEY’S FIBERS
• Collagen fibers of PDL which are embedded into cementum
on one side and alveolar bone on the other side
• They are smaller but more numerous in cementum
• In acellular cementum they are mineralized fully and in
cellular cementum partially

26. • Trans-alveolar fibers
– Sharpey’s fibers which pass uninterrupted through
alveolar bone and continue as principal fibers of the
adjacent PDL
- believed to be entrapped in alveolar bone during
development of interdental septum or by bone deposition
at the alveolar crest

28. PRINCIPAL FIBERS

29. Accessory fibers
• aka marginal ligament
•Encircling the neck of the
tooth like a collar
• extend from cervical part
of cementum to periosteum
of alveolar crest
• extend from cervical part
of cementum to lamina
propria of gingiva
• extend from crest of
alveolar bone to lamina
propria of gingiva

30. • Trans-septal fibers – interdental ligament
- extend from cementum of one tooth to
cementum of adjacent tooth over the interdental
alveolar crest
• Indifferent fiber plexus – asstd with principal fibers
• Intermediate plexus – meet at centre of PDL space –
identified as artifact

32. ELASTIC FIBERS
• Mature elastic fibers:
• Consist of a microfibrillar component surrounding an amorphous
core of elastin protein.
• Present in walls of afferent blood vessels – forms elastic laminae of
larger arterioles
• Oxytalan & Eluanin fibers:
• Immature elastic fibers.
• Forms peripheral attachment to elastic fibers of blood vessels.
• One end embedded in cementum/alv.bone and other end in blood
vessel walls
• Numerous in cervical region - control blood flow to cervical region

33. CELLS OF PERIODONTAL LIGAMENT
• Synthetic --
Osteoblasts
Fibroblasts &
Cementoblasts
• Resorptive –
Osteoclasts
Fibroblasts &
Cementoclasts
• Progenitor cells
• Defense cells
• Epithelial cell rests of Malassez

34. Osteoblasts

35. Cementoblasts

36. Osteoclasts
• Giant cells with 10-20 nuceli,
• Irregularly oval
• Howship’s lacunae

37. Fibroblasts • Fibroblast is the predominant
cell in the periodontal ligament.
• Plump, spindle shaped or
fusiform cells
- may show cytoplasmic
processes
• Regularly distributed throughout
the ligament, and are oriented
with their long axis parallel to
the direction of collagen fibrils.

38. • Extensive cytoplasm, abundant
organelles
• The nucleus occupies a large
volume of the cell and contains one
or more prominent nucleoli.
• Active fibroblasts with extensive
network of RER, well developed
Golgi apparatus and abundant
secretory granules containing
procollagen molecules.
• Fibroblasts also secrete Elastin,
Glycoproteins & GAGs

39. • They also have well developed cytoskeleton with a
particularly prominent actin network, provide contractlity
• The cytoskeletal elements of these cells may attach to
collagen fibers, giving it a capacity to exerting traction on
the collagen fibers and thus orient extracellular matrix.

40. • Dual function – synthesize & degrade collagen fibers
- maintain high turn over rate of fibroblasts in pdl
(highest in the body)
• Degradation of collagen includes both intracellular and
extracellular events.
• Extracellular - Secrete collagenases & Matrix Metallo
Proteinases(MMPs) and breakdown collagen fibrils. They
are phagocytosed into the cell
• Intracellular – lysosomes combine with them forming
phagolysosomes – enzymatic degeneration takes place

41. Progenitor cells

42. • Maintain tissue homeostasis
• Differentiate into fibroblasts, osteoblasts, cementoblasts
- morphogenesis, cytodifferentiation, extracellular matrix
production and mineralization.
• Found mostly around blood vessels
• Small size, responsiveness to stimulating factors and slow
cell cycle
• Small closed phase nuclei and very little cytoplasm

43. Epithelial cell rests of Malassez
• Closely packed cuboidal
cells and darkly stained
prominent nucleus with
scant cytoplasm
• Network, strands, islands
or tube like structures
near about 25μ from
surface of cementum.
• Cells separated from
surrounding CT by basal
lamina
• Abundant mitochondria, with poorly developed RERs and Golgi bodies

44. • Desmosomal attachment
between cells and
hemidesmosomes between cells
and the basal lamina
• Decreases with age
• Up to 2nd decade it is found in
apical region, later seen more
above the level of alveolar
crest, close to furcation area
• May proliferate and form cysts or tumours; or may undergo
calcific degeneration and form cementicles

45. Defense cells
• Mast cells and Macrophages; occasionally
eosinophils

46. CEMENTICLES
• 30% of human PDL.
• Seen in older patients
• Free, attached and embedded.
• Origin
1. Micro trauma
2. Degeneration of cells
• Lamellar calcifications around
nidus formed by cell Rests,
thrombus or Sharpey’s fibers

47. Vessels of PDL
• Arterial supply:
- derived from Inferior Alveolar Artery in mandible and Superior
Alveolar Artery in maxilla
- reaches PDL through
1. Branches from apical arteries before entering pulp
2. Intra alveolar arteries
3. Gingival vessels from coronal region
• Richer network in the half adjacent to bone
• Richer at the apex and cervical region of PDL
• Fenestrations of capillaries – which help in increased capacity for
diffusion and filtration – due to high turn over rate of PDL

48. • Venous drainage :
- venous channels accompany arteries
- A-V anastomosis in various regions –
bypassing the capillaries - glomera

49. Nerves of PDL
• Branches of superior and inferior alveolar nerves
• Enter from apical region & foraminas of alveolar bone.
• 2 types functionally
- Sensory fibers – Mechanoception – touch, pressure, pain
- Nociception - response to potentially
harmful stimuli
- Autonomic fibers – regulation of blood vessels
• 2 types anatomically
1.Large : Myelinated - Discernment of pressure
2.Small: Myelinated – Pain &
Non-myelinated - B.V.

50. 1. Physical function:
- Soft tissue casing for vessels and nerves
- Attachment of teeth to bone.
- Sharpey’s fibers
- Transmission Of Occlusion Forces To Bone.
- Shock absorption.
Functions of Periodontal Ligament

51. Theories of Shock Absorption

52. A) Tensional theory
•Principal fibres
•When a force is applied to the crown, principal fibres first unfold
and straighten and then transmit forces to the alveolar bone causing
an elastic deformation of the bony socket finally when alveolar
bone has reached its limit, load is transmitted to basal bone.
•Oblique fibers absorb most of the force, is placed in tension and on
release of load, an elastic recoil return the fibers to its resting
position
• Many investigators do not agree to this theory.

54. B) Visco-elastic system theory
•Fluid movement is mainly responsible for displacement of
tooth; fibres have a secondary role.
•When forces are applied, extracellular fluid from periodontal
ligament passes into marrow spaces of bone. After the
depletion of tissue fluids, the fibre bundles absorb the slack
and tighten
•Arterial back pressure cause ballooning of the vessels and
passage of blood ultrafiltrates back into the tissues, thereby
replenishing the tissue fluids.

56. C) Thixo-tropic theory
•It states that periodontal ligament behaves like a thixotrophic
gel i.e. property of becoming fluid when shaken or stirred and
then becoming semi-solid again.
•Physiologic response of periodontal ligament is explained by
changes in the viscosity of biologic system.
•According to Schroeder, presence of organized collagen
fibres makes the theory untenable.

57. 2. Homeostatic function :
- Formation and remodelling of PDL, alveolar bone and
cementum (synthetic & resorptive cells)
- Helps in maintaing the PDL width throughout lifetime
- Rate of remodelling of alveolar bone is higher than rest
of the jaw bones
- Rate of collagen turn over of PDL is highest in the body

58. 3. Sensory function:
- Nerve supply provide very efficient proprioception
(mechanoreceptors)
- Allows detection of most delicate forces of the teeth
and very slight displacement of teeth

59. 4. Nutritive function:
- Provide anabolites and remove catabolites
- Provide nutrition to PDL cells, cemtocytes and
superficial osteocytes of alv. bone
5. Eruptive function:
- cells, vascular channels and extracellular matrix
together help in eruption
- pdl fibroblasts can generate force for tooth eruption
as they are motile and contractile

60. • Initially – short, unorganized bundles,
extending from cementum and alveolar
bone
• With tooth eruption – bundles organize into
characteristic planes
- Oblique fibers
- Horizontal fibers
- Alveolar crest fibers
- Apical and interradicular fibers

61. AGE CHANGES
1. Cellular and fibrous components
•With increase in age the well organized arrangement of
bundles are lost and the structure of the ligament becomes
more and more irregular.
•The principal fibers of PDL become thicker and
cellularity is lessened.
•Elastic fibres increases
•Fibres get replaced by fat cells
61

62. 2. Calcified bodies / Cementicles
• Two types of calcified bodies are
demonstrable:
62
Larger,
irregularly
shaped
calcification
Small rounded
calcospherites

63. • They appear to form in relation to fiber bundles.
• Occasionally they increase in number and appear to
calcify a complete fiber bundle producing an ankylosis.
• Calcospherites – due to the inductive activity of
epithelial rests
OR
their degeneration
63

64. 64

65. 3. Width of periodontal ligament
•Narrower due to continuous deposition of cementum and
bone
•Masticatory forces also decreases with age
•PDL space increases/decreases due to periapical conditions
4. Vascularity
•Decreases

66. 5. Scalloping of alveolar bone and cementum
surface occurs with age
- Pdl fibers attach to the peak of these
scalloping instead of the entire surface

67. 7. Define periodontium. Explain in brief the principal fibres of
periodontal ligament (2+6=8 marks, 2017)
8. Principle fibers of periodontal ligament (5 marks, 2017)
9. Sharpey’s fibers (3 marks, 2016)
10. Functions of periodontal ligament (4 marks, 2014)
11. Explain the cells of periodontal ligament and add a note on age
changes (5+3=8 marks, 2013)
12. Define periodontium. What are the structures which constitute
periodontium. Discuss the principal fibers of periodontal ligament.
Add a note on the functions of periodontal ligament (2+2+5+5=14
marks, 2013)

68. 13. Fibres of periodontal ligament(5 marks, 2012)
14. Cells and fibres of periodontal ligament (8 marks, 2012)
15. Enumerate and describe the cells of the periodontal
ligament. Add a note on the functions of the periodontal
ligament. (10 marks, 2011)

69. Thank You