Structure and Composition of Periodontal Ligament - PDL consists of principal fibres, loose connective tissue, blast and clast cells, oxytalan fibres, and Cell Rest of Malassez. - Alveolodental ligament is the main principal fiber group, consisting of five fiber subgroups: alveolar crest, horizontal, oblique, apical, and interradicular. - Transseptal fibers are principal fibers other than the alveolodental ligament. - Alveolar crest fibers run from the cervical part of the root to the alveolar bone crest. - Horizontal fibers attach to the cementum apical to the alveolar crest fibers and run perpendicularly from the root to the alveolar bone. - PDL substance is estimated to be 70% water, affecting the tooth's ability to withstand stress loads. - PDL ranges in width from 0.15 to 0.38mm, thinnest in the middle third of the root. - PDL is part of the periodontium that attaches teeth to the surrounding alveolar bone via cementum. - PDL appears as a radiolucent area between the lamina dura and cementum on radiographs. - Completeness and vitality of the PDL are essential for tooth functioning.

Development and Effects of Mechanical Forces on Periodontal Ligament - PDL cells are derived from the dental follicle after crown formation and root development. - Formation of PDL starts at the cementoenamel junction and progresses apically. - Movement of teeth involves deposition of bone on the tension side and resorption on the compression side of the PDL. - Fibroblasts in the PDL react to mechanical stress, affecting osteoblastogenesis and osteoclastogenesis. - Mechanical stimuli can lead to differentiation of osteocytes into osteoclasts, remodeling the bone structure. - Orthodontic treatment applies mechanical force to align teeth, involving physical and cellular processes.

Function of Periodontal Ligament - PDL functions include support, sensory perception, nutrition, and remodeling. - PDL provides attachment between teeth and alveolar bone, absorbing and transmitting forces during mastication. - PDL is heavily innervated, involving mechanoreception, nociception, and reflexes. - PDL maintains vitality of surrounding cells through anastomosed blood vessels. - Progenitor cells in the PDL can differentiate into osteoblasts for maintenance and repair of alveolar bone.

Clinical Significance of Periodontal Ligament - Traumatic forces of occlusion can cause widening of the PDL space, seen on radiographs. - PDL damage may result in tooth ankylosis and pathological tooth migration. - PDL cells of an avulsed tooth are at risk of drying and desiccation, affecting replantation success. - Early occlusal trauma can manifest as increased tooth mobility. - Subluxation may cause tearing of the PDL and pain during function.

Additional Topics - Effect of tobacco smoking and nicotine on periodontal health. - Ankylosis and its causes. - Effect of nutrition on periodontal tissues, including the role of vitamins D and C.

Note: The "See also" section and the references have been excluded from the groups as they do not contain additional content to be organised.