The periodontal fiber or periodontal ligament, commonly abbreviated as the PDL, is a group of specialized connective tissue

Connective tissue

"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

 fibers that essentially attach a tooth

Tooth

Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 to the alveolar bone within which it sits. These fibers help the tooth withstand the naturally substantial compressive forces which occur during chewing

Mastication

Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...

 and remain embedded in the bone.

Functions of PDL are supportive, sensory, nutritive, homeostatic and eruptive.

Structure of the PDL

It consist of cells, and extracellular compartment of fibers. The cells are fibroblast, epithelial, undifferentiated mesenchymal cells, bone and cementum cells. The extracellular compartment consists of collagen fibers bundles embedded in ground substance. The PDL substance has been estimated to be 70% water and is thought to have a significant effect on the tooth's ability to withstand stress loads.
The PDL is a part of the periodontium that provide for the attachment of the teeth to the surrounding alveolar bone by way of the cementum. The PDL appears as the periodontal space of 0.4 to1.5 mm on radiographs, a radiolucent area between the radiopaque lamina dura of the alveolar bone proper and the radio opaque cementum.

Types of fibers

A)The PDL collogen fibers are categorized according to their orientation and location along the tooth. They are:

Transseptal fibers

Transseptal fibers-H extend interproximally over the alveolar bone crest and are embedded in the cementum of adjacent teeth.These fibers keep all the teeth aligned. These fibers may be considered as belonging to the gingiva because they DO NOT have osseous attachment.

Alveolar crest fibers

Alveolar crest fibers-I extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest. These fibers prevent the extrusion of the tooth and resist lateral tooth movements.

Horizontal fibers

Horizontal fibers-J attach to the cementum apical to the alveolar crest fibers and run perpendicularly from the root of the tooth to the alveolar bone.

Oblique fibers

Oblique fibers-K are the most numerous fibers in the periodontal ligament, running from cementum in an oblique direction to insert into bone coronally.

Apical fibers

radiating from cementum around the apex of the root to the bone, forming base of the socket

Interradicular fibers

Interradicular fibers are only found between the roots of multi-rooted teeth, such as molar

Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

s. They also attach from the cementum and insert to the nearby alveolar bone.
B)Elastic fibrils:
1- Oxylatan
2- Elumine
3- Elastine

Pathology

The completeness and vitality of the PDL are essential for the functioning of the tooth. Damage to the PDL may result in ankylosis

Ankylosis

Ankylosis or anchylosis is a stiffness of a joint due to abnormal adhesion and rigidity of the bones of the joint, which may be the result of injury or disease. The rigidity may be complete or partial and may be due to inflammation of the tendinous or muscular structures outside the joint or of...

 of the tooth to the jaw

Jaw

The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

bone, making the tooth loss its continuous eruption ability. Dental trauma

Dental trauma

Dental trauma refers to trauma to the face, mouth, and especially the teeth lips and periodontium. The study of dental trauma is called dental traumatology.- Types :* Tooth fractures**Enamel infraction**Enamel fracture**Enamel-dentine fracture...

, such as subluxation

Dental subluxation

Dental subluxation is an traumatic injury in which the tooth has increased mobility but hasnot been displaced from its original site in the jawbone.- Prevalence :This is a quite common condition and one of the commonest dental traumatic disorders...

, may cause tearing of the PDL and pain

Toothache

A toothache, also known as odontalgia or, less frequently, as odontalgy, is an aching pain in or around a tooth.-Causes:* Dental etiology, In most cases toothaches are caused by problems in the tooth or jaw, such as** Dental caries...

during function (eating).