PERIODONTAL LIGAMENT

Prerna KrishanMDS 1st yearDept. of Periodontology and Implantology

A ligament is a bond, usually linking two bones together.

PDL is composed of a complex vascular & highly cellular Connective tissue that surrounds the tooth root & connects it to the inner wall of the alveolar bone . CARRANZA

DEFINITION

Various names…

- Gomphosis- Pericementum- Peridental membrane- Dental Periosteum- Periodontal membrane- Desmodont

Pdl arises from Dental Follicle…

- Tencate 1971

Undifferentiated Cells Fibroblast

Cementoblast

Dental Follicle is recognized

as the condensation of

mesenchymal tissue………

Mesenchyme deriving the

periodontium may have 2 diff

compartments :

- An “ Alveolar

Clade “

- A “ Cemental

Clade “

DEVELOPMENT OF PERIODONTAL LIGAMENT

DEVELOPMENT OF PRINCIPAL FIBER GROUPS

A.The tooth bud is formed B.The principal fibers develop C.More apically positioned D.Remodeling of collagen fiberIn a crypt of bone.The in conjunction with the bundles of collagen bundles.Collagen fibers get embbed erupting tooth. Fibers are seen. -ed into the newly formed Cementum.

• Fully developed pdl exists & functions in an extremely narrow space delimited.

• Shape - Hour Glass Shape,Double Cone Goblet• Volume :Single rooted : 30 -100 cu mmMulti rooted : 60-150 cu mm

• Width of pdl space reduces with loss of function…

• Narrowest portion of the pdl space is apical end of middle 3rd …

• Jozat (1933)

Avg pdl width : 0.23mm (20-25 yr)

Avg pdl width : 0.25mm (40-50 yr)

• Pdl grows narrower with Age…

Klein (1928)

PERIODONTAL LIGAMENT SPACE

CELLS OF PERIODONTAL LIGAMENT

FIBROBLAST• Flattened irregular disc ,

approximately 30 um in diameter.

• Role in generating force of eruption by contraction due to well developed cytoskeleton with a prominent actin network .

• In aged PDL multinucleated fibroblasts may appear , because of faulty division or fusion of mononuclear cells.

• Fibroblasts oriented parallel to the collagen fibers.

• Active : - Oval, pale staining nucleus & Greater amount of cytoplasm - Abundant RER, numerous Golgi complexes, vesicles & mitochondria…

• Resting : - Elongated cells, with little cytoplasm & flattened nucleus containing condensed chromatin…

• Actin filaments present… - Change in shape- Migration

• Myofibroblast….

• Pdl fibroblast is considerably more active, resulting in a high turnover rate…Highest turn over rate approx. 8 times that of skin and twice that of gingival collagen . SODEK 1977

• Fibroblast are aligned along the general direction of the fiber bundle

Have extensive processes which wrap around collagen bundles

Continuous Remodelling

• Any interference with fibroblastic function will result in rapid loss of supporting tissues

SYNTHESIS OF COLLAGEN

Extracellular degradation of collagen fibrilsTEN CATE AND DEPORTER IN 1975 SUGGESTED THAT COLLAGEN DEGRADATION IS ENTIRELY INTRACELLULAR IN ALL HEALTHY TISSUES WHERE THERE IS CONTROLLED TURN OVER AND REMODELLING . EXTRACELLULAR DEGRADATION OCCURS WHERE CHANGES ARE PATHOLOGICAL AND DEGRADATION IS RAPID .

INTRACELLULAR DEGRADATION

Advantages of degrading collagen intracellularly instead of extracellularly may be :Phagocytosis allows a more precise and selective control for the collagen fibers to be degraded .Whereas the release of extracellular collagenolysis afford a more rapid , extensive degradation around the cells, as observed during inflammation.

CEMENTOBLASTS • Cementoblasts forms a cementoid layer

which soon after its depostion undergoes mineralisation .

• Some of these are buried deeply in their own matrix and remain behind as cementocytes .

• Important function is accumulation of numerous glycogen granules , the number decreasing the farther the distance from cementum surface (Yamaski etal 1987 )

• Necessary for protein synthesis , contain RER, golgi comlex and mitochondria.

• Appearance depends on the degree of activity .

OSTEOBLASTS • Found within the PDL on the

surface of alveolar bone.

• Osteoblast precursors first migrate away from the bone surface into the body of the PDL before eventually taking up their functional position .

• As the bone deposits,these cells gets incorporated into the osteoid tissue as osteocytes.

• Found adjacent to the

bone surfaces.• Found in resorption lacunae.• Multinucleated with ruffled border. • Cytoplasm adjacent to the ruffled

border – highly vacuolated or foamy with numerous mitochondria.

• Osteoclasts and cementoclasts are morphologically and functionally similar but both are actually multinucleated resorptive cells .

OSTEOCLASTS

EPITHELIAL CELL

RESTS OF

MALASSEZ First described by Malassez in 1884.Most numerous in apical and cervical area.These represent the remains of epithelial root sheath of HERTWIG which are involved in mapping out the shape of roots and in differentiation of root odontoblasts .Less numerous in older individuals as compared to children . LAMININ is also associated.

Situated at a distance of 15 – 75 um from the cementum on root surface .

They are reported to contain keratinocyte growth factors and have been shown positive for tyrosine kinase A neutrophin receptor .

Epithelial rests participate in the formation of periapical cysts and lateral cysts .

HERS

Mapping the root formn Diff of root Odontoblasts

EXTRACELLULAR MATRIX CONSTITUENTS

• NON – COLLAGENOUS MATRIX PROTEINS : include alkalline phosphatase , proteoglycans and glycoproteins .

• Principal proteoglycans in periodontal ligament includes VERSICAN , DECORIN, BIGLYCAN ,FIBROMODULIN , PERLECAN ,CD 44 ,SYNDECAN 1 AND SYNDECAN 2 .

• Glycoproteins includes UNDULIN , TENASCIN FIBRONECTIN, VITRONECTIN .

PERIODONTAL LIGAMENT FIBERS

• Collagen present is type I mainly.

• Lesser amounts of type III, IV, VI and XII.

• Principal fibers are collagenous .

• Arranged in bundles .• Follow a wavy course .

TYPES OF PRINCIPAL

FIBERS

• TRANSEPTAL FIBERS • ALVEOLAR CREST

FIBERS • HORIZONTAL GROUP• OBLIQUE GROUP • APICAL GROUP • INTRRADICULAR

GROUP

• ALVEOLAR CREST FIBERS:Alveolar crest fibers extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest.The alveolar crest fibers prevent the extrusion of the tooth and resist lateral tooth movements.

• HORIZONTAL FIBERS: Horizontal fibers extend at right angles to the long axis of the tooth from the cementum to the alveolar bone.

• OBLIQUE GROUP: Oblique fibers, the largest group in the periodontal ligament, extend from the cementum in a coronal direction obliquely to the bone .They bear the brunt of vertical masticatory stresses and transform them into tension on the alveolar bone.

• TRANSEPTAL FIBERS: extend interproximally over the alveolar bone crest and are embedded in the cementum of adjacent teeth.They are a remarkably constant finding and are reconstructed even after destruction of the alveolar bone.These fibers may be considered as belonging to the gingiva because they do not have osseous attachment.

• APICAL GROUP:The apical fibers radiate in a rather irregular fashion from the cementum to the bone at the apical region of the socket. They do not occur on incompletely formed roots.

• INTERRADICULAR FIBERS: The interradicular fibers fan out from the cementum to the tooth in the furcation areas of multirooted teeth.

ELASTIC FIBERS • Although the periodontal ligament fibers does not

contain mature elastin , 2 immature forms are found .• Oxytalan and Elaunin.• Oxytalan fibers run parallel to the root surface in a

vertical direction and bend to attach to the cementum in the cervical third of the root.

• An elastic meshwork has been described in PDL as being composed of many elastin lamellae with peripheral oxytalan fibers with elaunin fibers

• Oxylatan fibers aids in fibroblast attachment and migration in PDl . (BEERSTEN et al 1974)

They are associated with neural elements .They are numerous and dense in the cervical region of the ligament .Regulate vascular flow in relation to tooth function .As they are elastic , can expand In response to tensional variations .

OXYTALAN FIBERS

ARTERIAL SUPPLY

VENOUS DRAINAGE• Many transverse connections and thickened venous network at apex are

visible.• Surrounding the root like a stocking and has polyhedral network.• Venous supply accompanies the arterial supply and venules larger in

diameter.• Specialised shunts called GLOMERA are interposed between arterial and

venous system which provide arteriovenous anastomosis .

Birn (1966) estimated the vascularity of pdl :

• Blood supply ↑ towards posterior..• All single rooted teeth… BS is greatest to the gingival 3rd .. Multi-rooted

tooth- No difference..• Mesial & Distal surfaces have more BS than Buccal & Lingual.• Larger vessels ↑ from incisors to molars.

NERVE SUPPLY1. Nerve fiber entering the PDL are

derived from two sources .2. Nerve fibers running from apical

region to the gingival margin and is joined by fibers entering laterally through the foramina of the socket wall .

3. Termination of neural elements.4. Apical region contains more neural

elements except for incisors where also in coronal half .

5. Manners in which nerve fibers terminate are clarified .

• FREE ENDINGS WITH TREE LIKE RAMIFICATIONS – most frequent . They are thought to be nociceptors and mechanoreceptor. located at regular intervals on the surface of the root.

• RUFFINI’S ENDINGS – found around root apex . They appear dendritic and are mechanoceptors .

• COILED ENDING (MEISSNERS CORPUSCLES ) – it is found in midregion of the PDL . Function not determined .

• ENCAPSULATED SPINDLE TYPE ENDINGS – they are found associated with root apex . Lowest frequency.surrounded by fibrous capsule.

LYMPHATICS • Lymphatics supplement the venous

drainage system. Except for the third molars mandibular incisors, all teeth with their adjacent periodontal tissues are drained to the submandibular lymph nodes.

• The third molars are drained to jugulodigastric lymph node and the mandibular incisors to the submental lymph nodes. From apical area of PDL, they pass through alveolar bone to inferior dental canal in mandible and infraorbital canal in maxilla and then to the submandibular lymph nodes.

CEMENTICLES • Calcified bodies called

cementicles are sometimes found in the periodontal ligament .

• Found in older individuals , and they may remain free in the connective tissue , they may fuse into large calcified masses , or they may be joined with the cementum .

• When they adherent to cementum they form EXCEMENTOSES .

• Origin is not established but it is possible that degenerated epithelial cells forms the nidus for their calcification .

FUNCTIONS OF THE PERIODONTAL LIGAMENT

• PHYSICAL• FORMATIVE AND REMODELLING • NUTRITIONAL • SENSORY

• PHYSICAL FUNCTION – Provision of a soft tissue ‘casing’ to protect the vessels and nerves from mechanical injury by mechanical forces.

• Transmission of occlusal forces to the bone.• Attachment of the teeth to the bone.• Maintenance of the gingival tissues in their

proper relationship to the teeth.• Resistance to the impact of occlusal forces

(Shock absorption).• Tensional theory , viscoelastic theory.

TENSIONAL THEORY

VISCOELASTIC THEORY

FORMATIVE AND REMODELLING

FUNCTION • Cells of the periodontal ligament participate in the formation of

cementum and bone .• Although applied forces induce vascular and inflammatory reactive

changes in the periodontal ligament cells , current evidence suggests that these cells have a mechanism to respond directly to mechanical forces by activation of various mechanosensory signaling systems ,including adenylate cyclase, stretch activated ion channels , and by changes in cytoskeletal organization.

• A rapid turnover of sulphated glycosaminoglycans in the cells and amorphous ground substance of the periodontal ligament also occurs .

• SICHER 1942 suggested that remodelling in PDL is precisely confined to an intermediate plexus in the midregion of PDL.

NUTRITIVE AND SENSORY

• Nutrients to the cementum, bone, and gingiva by way of the blood vessels .• Provides lymphatic drainage.• The relatively high blood vessel content may provide hydrodynamic

damping to applied forces as well as high perfusion rates to periodontal ligament .

• Sensory nerve fibers capable of transmitting tactile, pressure, and pain sensations by the trigeminal pathway.

• The periodontal ligament provides an efficient proprioceptive mechanism , allowing to detect the application of most delicate forces of teeth and very slight displacement of teeth.

• Also the location of foreign bodies on or between the surfaces of the teeth.

EFFECTS OF AGEING

• Decreased number of fibroblasts .• Decreased organic matrix production.• Increased amounts of elastic fiber.• Decreased vascularity.• Decrease in number of collagen fibers.• Increased cementicles .• Decreased epithelial rests of malassez.

EFFECT OF TRAUMA ON PERIODONTAL LIGAMENT

• Down’s Syndrome:- Cutress et al reported severe pdl disease in trisomy 21…- Localized ,most commonly affected sites were anterior jaw.

• Connective tissue Diseases; - Ehlers Danlos syndrome-Pdl

destruction is seen at an early age.

• Metabolic Disorders ; Acatalasia

- Hypophosphatasia… (Bone fails to mineralize)…tooth shed off with relative minor trauma…..Cemental Aplasia .

• Skin Diseases;

- Papillon Leferve Syndrome ( hyperkeratosis of Palm & skin &

premature pdl destruction – Neutrophil chemotactic defect)

DISEASES OF PERIODONTAL LIGAMENT

PeriodontitisPeriodontitis

Lateral Apical

•Aggressive Periodontitis•Lateral Periodontal Abscess

•Non Suppurative Apical Periodontitis•Suppurative Apical Periodontitis

INFECTION & PDL

PERIODONTAL LIGAMENT REGENERATION

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