The periodontal ligament
Soft richly vascular cellular connective tissue surrounds the Root & joins the Cementum to Alveolar bone its separated from the above Gingiva by alveolar crest fibersthe most important part of periodontal ligament is the
Principle fibres ; Alveolar crest fibers Horizontal fibers Oblique fibers Apical fibers Interradicular fibers in multirooted teethPrincipal Fibers have a
Wavy course Sharpeys fibres that parts of Principal Fibers that inserted into CementumIts function ;
Distribute & resorb force into bone Its essential for mobility that determine by width, length & quality of periodontal ligamentIts Developed from Connective tissue (dental sac) that surrounds Tooth bud
Intermediate plexus (indifferent fiber plexus)Individual fibers have 2 separate parts one of them is spliced with other , after eruption, the fibers arranged well but not embedded in Cementum & bone
How does principle fiber develop ?
During tooth formation, 1st of all short small bundles embedded in Cementum & Bone are seen ,then there length & thickness continuo to increase until they had united together& when the teeth reached in contact with the opposites, they had become organized in bundles
Collagen fiber
Its Protein, composed from Amino acids (glycine, proline, hydroxyline & hydroxyproline) Amount of Collagen determines by its hydroxyproline content Synthesized by fibroblast ,chondroblast ,osteoblast & odontoblastPeriodontal ligament do not contain mature elastin Its contain immature form (oxytalan & eluanin) Oxytalan runs parallel with Root surfaces & bent to attach to Cementum in cervical 3rd of Root They thought that its regulate vascular flow
In addition to Principal fibers, periodontal ligament also has
Fibroblast, osteoblast, cementoblast, osteoclast, odontoclast macrophage, nerve cell epithelial cells (epithelial rest of mallassez) , mesenchymal cellsGround substance consist of proteoglycans as hyaluronic acid glycoprotein like fibronectin water (70%)
Fibroblast
phagocytes old collagen & degrades them by hydrolysis
Collagen turnover is regulated by intracellular degradation of Collagen not by the action of collagenase
Functions of periodontal ligament
Shock absorptionIt supports tooth & transmitting force to the bone as extra cellular fluid passes to marrow through cribriform plate lead to blood vessels stenosis ,arterial back pressure causes ballooning of vessels & passage of blood ultrafiltrates into tissue, thereby return tissue fluid to normal
Transmission of occlusal forces to the bone
Principal fibers like suspension bridge or hammock when axial force applied to a tooth, tendency toward displacement of Root into alveolus will happen, so oblique fibers will assume full lengthDuring application of Horizontal force; 2 phases of tooth movement,1st within confine of periodontal ligament,
2nd produces displacement of Facial & oral plates, tooth rotates around axis that change with increase force
With increase force ; Tension zone (stretched principal fibers) & pressure zone ;compressed principal fibers & then distortion of bone Will occur
Other functions
Formative By builder cells Nutritional; by blood vessels that supply nutrition to the area sensory Properioceptive nerve fibers located within Periodontal ligament can detect & localize external force acting on individual tooth
Normal width of periodontal ligament is around 0.1-0.4 mm
With increase function within physiological limits there will be increased width, thickness of fiber bundles & increased diameter & no.of sharpeys fibersHeavy occlusal force induces injury in Periodontal ligament which is called Trauma from Occlusion (T.O.)
When function reduced ; Lead to disused atrophy in which there are reduction in width & Reduction in no. & density of Collagen fiber bundles that become disoriented
Cementum will be thickened & Increase distance from CEJ to Alveolar crest
Root cementumSpecialized calcified tissue covering the root
it differs from bone as its had no blood supply, no innervation & didn't undergo remodeling
Functions
It attaches periodontal ligament fiber to Root It contributes to process of repairIts of 2 types; primary & secondary
Root cementum
Primary ( Acellular) form with tooth formation ,coronally Secondary (cellular) formed after tooth eruption in response to functional demand, laid down on top of primary Cementum apicallyCementocytes
Some cementoblast or other Periodontal cells become incorporated into cementoid that seen in 2ndary CementumSuch cells are lying within lacunae & connected with each others & with the adjacent periodontal ligament through network of cytoplasmic processes running through canaliculi
Cementogenesis
Collagen fibers lay down by Cementoblast in Interfibrillar ground sub.to form precementum or cementoid Mineralization started from Cementodental Junction by lay down Hydroxy Apetite Crystals on surface of febrile then ground substanceCementum thickness in cervical area about hair diameter
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Cementum deposition
continues throughout life in apical region to compensate for tooth attritionCementum resorption
Could be happened due to local or systemic causes