Periodontal Ligament

PDL Periodontium PDL – Definition Synonyms Macroscopic features Development Functions Microscopic features Cementicles Blood & nerve supply Clinical consideration

Periodontium The tissues which invest & support the tooth are

collectively called periodontium

Components: 2 Mineralized Tissues

- Alveolar Bone

- Cementum 2 Fibrous Tissues

- Periodontal Ligament

- Lamina Propria of Gingiva

Periodontal Ligament

It is a fibrous connective tissue that is noticeably cellular & vascular, which surrounds the tooth root & anchors it to the bony socket.

Synonyms

Desmodont Gomphosis Pericementum Dental periostum Alveolar ligament Periodontal membrane

Macroscopic features It is a soft fibrous connective tissue Interposed between roots of teeth & inner wall of alveolar

socket (Periodontal space) It is neither a true ligament or membrane

Width - variable - Ave: 0.15 – 0.38 - Decreases with age - Reduced function – Reduced width of ligament

Shape “Hour glass” shape Narrowest in middle 3rd of root & widens

both apically & near the crest

Development Develops from Dental Follicle.

Follicle Cells: Cementoblast – Cementum Osteoblasts – Bone Fibroblast – Fibres & Ground substance of

PDL

Functions

Supportive / physical Sensory Nutritive Homeostatic / formative /

developemental

Supportive

Attaches the tooth to the bone Transmits masticatory forces to the bone Acts as a shock absorber against external forces Maintains the proper relationship between

gingiva & the tooth Protects the vessels & nerves from injury by

mechanical forces by cushioning

Tooth support & Shock absorption

3 theories

Tensional theory Viscoelastic system theory Thixotropic theory

Tensional theory

Ascribes to the principal fibres of the PDL the major responsibility in supporting the tooth & transmitting forces to the bone

Viscoelastic system theory

According to this theory displacement of tooth is largely controlled by fluid movements, fibres have only secondary role

Thixotropic theory

PDL has rheologic behaviour of a thixotropic gel

sensory

The PDL through its nerve supply provides efficient proprioceptive mechanism

Nutritive

The PDL transmits blood vessels which provide anabolites & remove catabolites from cells of ligament, cementum, alveolar bone

Homeostatic

Synthesis Resorption

PDL stabilizes & reorganizes alveolar bone & helps in cementum formation through its cells

Microscopic features

Synthetic cells - Osteoblasts - Cementoblasts - Fibroblasts

Resorptive cells - Osteoclasts - Cementoclasts - Fibroblasts Progenitor cells

Epithelial cell rests of malassez

Connective tissue cells - Mast cells - Macrophages

Cells Extracellular substance

Fibers - Collagen (type I & III) - Oxytalan - Elaunin

Ground substances - Proteoglycans - Glycoproteins

Structures present in Connective tissue cells

- Blood vessels - Lymphatics - Nerves - Cementicles

PDL

Osteoblasts

Bone-forming cells derived from either multipotent mesenchymal cell or perivascular cells called preosteoblasts.

Cover the periodontal surface of alveolar bone & constitute a modified endosteum

Functions of Osteoblasts: Formation of organic matrix of bone (osteoid) Mineralization of matrix

Cementoblasts

Cementun forming cells derived from undifferentiated ectomesenchymal cells of the dental follicle and they resemble osteoblasts

Distrubuted along cementum surface of PDL

Function: Formation of cementoid

Fibroblasts

Most numerous connective tissue cells Plump spindle-shaped or fusiform Large cells with extensive cytoplasm containing

abundant cellular organells They are oriented parallel to collagen fiber bundles

Function: synthesis & degradation of collagen

Osteoclasts

Multinucleated large cells, Approximately 20-100 in diameter Found in Howship’s lacunae Has brush or ruffled border

Function: Resorption of bone

Cementoclasts

Resembles osteoclasts

Function: Resorbs cementum

Progenetior cells Undifferentiated Mesenchymal Cells that have a capacity to

undergo mitotic division They have small close-faced nucleus & little cytoplasm

Daughter cell

Differentiates into functional type

Daughter cell

Remains undifferentiated

Progenitor cell

Divides further

Undifferentiated Mesenchymal Cells

Epithelial cell rests of Malassez

Remnants of HERS

Found close to cementum

Persists as a network, strands, islands or tubule like structures near or parallel to root surface

Cells exhibits tonofilaments & are attached to one another by desmosomes

They are isolated from the connective tissue cells by a basal lamina

Decreases with age

Physiologic role unknown

Undergo rapid proliferation & give rise to certain pathologic conditions like cysts & tumors of jaw

Epithelial cell rests of malassez

Mast cells

Small round / ovoid cell with Small, pale & centrally placed nucleus

Cytoplasm contain numerous metachromatic granules

Granules possess histamine, heparin, serotonin and other inflammatory mediators

Granules stain with metachromatic dyes like Azure A & Toludine blue

Macrophages

Scavenger cell Round or ovoid cell with horse shoe /

kidney shaped nucleus Cytoplasm contain numerous lysosomes Derived from blood monocytes Usually located near blood vessels

Collagen fibers Collagen is a high molecular weight protein to which

small number of sugars are attached

Collagen are rod like macromolecules & are arranged to form fibrils

Fibrils are packed to form bundles

PDL has Predominantly collagen type I & III

Principal fibers

Collagen fibers are found to be gathered into bundles & organized into functional groups having clear orientation relative to the periodontal space. These are termed as principal fibers

They run a wavy course from cementum to bone & straighten out under load

Principal fibers Alveolar crest group Horizontal group Oblique group Apical group Inter-radicular group

Accessory fibers Gingival fibers Trans-septal fibers

A. Principal fibersB. Trans-septalC. Gingival groupD. Alveolar bone

Alveolar crest group Fibers radiate from crest of alveolar process

& attaches to the cervical part of cementum

Function: Prevent extrusion of tooth Resist lateral tooth movement

Alveolar crest fibers

Horizontal group Fibers run at right angles to the long axis

from cementum to bone

Function: Resist tooth displacement against lateral

pressure

Horizontal fibers

Oblique group Most numerous of all fibers Fibers run obliquely attached to cementum apically

from their attachment to bone

Function: Suspend the tooth in socket They bear vertical occlusal forces Transform the masticatory stress on to the alveolar

bone

Oblique fibers

Apical group Fibers radiate from apical region of root to

surrounding bone Absent on incompletely formed roots

Function: Prevent oral tipping of tooth

Apical fibers

Inter-Radicular group Seen in multi-rooted teeth

Fibers radiate from crest of inter-radicular septum to the furcation area

Inter-radicular fibers

Trans-septal fibers

Extend inter-proximally over alveolar crest & are embedded in the cementum of adjacent teeth

Trans-septal fibers

Sharpey’s fibers

Principal fibers of PDL embedded in bone or cementum

Sharpey’s fibers

Intermediate plexus

Light microscopic examination of longitudinal section of PDL gives an appearance, that as though fibers arising from cementum & bone are joined in mid region of the periodontal space giving rise to a zone of distinct appearance. This is called as intermediate plexus

It was belived that intermediate plexus provides a site where rapid remodelling of fibers occurs allowing adjustments in PDL to accommodate small tooth movement

EM, radio-autography studies & surgical experiments, intermediate plexus is considered as an artifact arising out of the plane of sectioning

Oxytalan & Elaunin fibers Immature elastic fibers found in the PDL

Run in axial direction, one end being embedded in cementum or bone & other in the wall of a blood vessel

Function: Supports the blood vessels of the PDL

Oxytalan fibers

Ground substances Space between cells, fibers, blood vessel &

nerves in Periodontal ligament space is occupied by ground substance

Compound of proteins & polysaccharides

Proteoglycans & glycoproteins

Interstitial tissues

Loose connective tissue surrounding blood vessels, nerves & lymphatics of PDL

Cementicles Small foci of calcified tissue which lie free in the

PDL They represent areas of dystrophic calcification Commonly seen in older individuals

Size: 0.2 – 0.3mm in diameter

Too small to be seen in x-ray No clinical significance

Types: Free Attached Embedded

Origin: Calcification of Degenerated epithelial cells Calcification of sharpey’s fibers Calcification of thrombosed blood vessels Cemental tears

Free cementicle

Embedded cementicle

Blood & nerve supplySource of arterial supply Apical vessels Inta-alveolar vessels Gingival vessels

Venous drainage Venous vessels run axially to drain to apex Arterio-venous anastomoses

Lymphatics Follow the path of blood vessel & provides lymph

drainage of PDL Lymph flow PDL adjacent alveolar bone

Nerve supply Large diameter Myelinated Nerve fibers Myelinated Small diameter Unmyelinated

Nerve endings

Free endings Ruffini endings Coiled endings Spindle type endings

Free endings Ramify in a tree like fashion Originate mainly from unmyelinated fibers Located at regular intervals along length of root Both nociceptor & mechanoreceptor

Ruffini endings Appear denritic Simple & compound Found around root apex Mechanoreceptor

Coiled endings Found in mid region of PDL

Spindle like endings Located at root apex

Clinical consideration

Restorative dentistry Prosthetic dentistry Orthodontic tooth movement Periapical inflammation Gingival inflation