View source for Periodontium

{{short description|Tissues surrounding the teeth}}
{{Infobox anatomy
| Name        = Periodontium
| Latin       = periodontium
| Image       = Periodontium.svg
| Caption     = The tissues of the '''periodontium''' combine to form an active, dynamic group of tissues.  The [[alveolar bone]] ''(C)'' is surrounded for the most part by the subepithelial [[connective tissue]] of the gingiva, which in turn is covered by the various characteristic gingival epithelia.  The [[cementum]] overlaying the tooth root is attached to the adjacent cortical surface of the alveolar bone by the alveolar crest ''(I)'', horizontal ''(J)'' and oblique ''(K)'' fibers of the [[periodontal ligament]].
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The '''periodontium''' ({{ety|el|''περί'' (peri-)|around||-odont|tooth}}) is the specialized tissues that both surround and support the [[teeth]], maintaining them in the [[maxilla]]ry and [[human mandible|mandibular]] bones. [[Periodontics]] is the dental specialty that relates specifically to the care and maintenance of these tissues. It provides the support necessary to maintain teeth in function. It consists of four principal components, namely:<ref>{{cite book|chapter-url=https://books.google.com/books?id=weo4yihNCQkC&pg=PA172|title=Orban's Oral Histology and Embryology| veditors = Kumar GS  | date = 2011 | publisher=Elsevier |location=New Delhi |isbn=9788131228197 |page=172 |edition=13th |access-date=22 April 2016|chapter=8}}</ref>
* [[Gingiva]] (the gums)
* [[Periodontal fiber|Periodontal ligament]] (PDL) 
* [[Cementum]]
* [[Alveolar process|Alveolar bone proper]]

Each of these components is distinct in location, architecture, and biochemical properties, which adapt during the life of the structure. For example, as teeth respond to forces or migrate [[Medial (anatomy)|medially]], bone resorbs on the pressure side and is added on the tension side. Cementum similarly adapts to wear on the occlusal surfaces of the teeth by apical deposition. The periodontal ligament in itself is an area of high turnover that allows the tooth not only to be suspended in the alveolar bone but also to respond to the forces. Thus, although seemingly static and having functions of their own, all of these components function as a single unit.<ref>{{cite book |url= https://books.google.com/books?id=BspTzxVK6-kC |title=Carranza's Clinical Periodontology| veditors = Newman MG, Takei H, Klokkevold PR, Carranza FA |date=2012 |publisher=Saunders Elsevier |location=St. Louis, MO |isbn=9781455706389 |edition=11th |access-date=22 April 2016 }}</ref>
The [[Wnt signaling]] antagonist Sfrp3/[[Frzb]] has been recently discovered as an early developmental marker of the periodontium.<ref name="pmid29209231">{{cite journal | vauthors = Mitsiadis TA, Pagella P, Cantù C | title = Early Determination of the Periodontal Domain by the Wnt-Antagonist Frzb/Sfrp3 | journal = Frontiers in Physiology | volume = 8 | issue = | pages = 936 | date = 2017 | pmid = 29209231 | pmc = 5702314 | doi = 10.3389/fphys.2017.00936 | doi-access = free }}</ref>

==External forces and the periodontium==

The periodontium exists for the purpose of supporting teeth during their function and it depends on the stimulation it receives from the function for preservation of its structure. Therefore, a constant state of balance always exists between the periodontal structures and the external forces.<ref>{{cite journal | doi=10.1016/0889-5406(87)90232-0 | volume=92 | title=Three-dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces | journal=American Journal of Orthodontics and Dentofacial Orthopedics | pages=499–505 | vauthors = Tanne K, Sakuda M, Burstone CJ |date=December 1987 |issue=6| pmid=3479896 }}</ref>

Alveolar bone undergoes constant physiologic [[Bone remodeling|remodeling]] in response to external forces, particularly occlusal forces. Bone is removed from areas where it is no longer needed and added to areas where it is needed. The socket wall reflects the responsiveness to the external forces. [[Osteoblast]]s and newly formed osteoid line the areas of tension, whereas lines of compression are lined by [[osteoclasts]]. The forces also influence the number, density, and alignment of [[trabecula]]e inside the bone. The bony trabeculae are aligned in the path of tensile and compressive stresses to provide maximum resistance to occlusal forces with a minimum of bone substance. When forces are increased, the bony trabeculae also increase in number and thickness and bone is added to the external surfaces.

The periodontal ligament depends on stimulation provided by function to preserve its structure. Within physiologic limits the PDL can accommodate increased function by increasing its width. Forces that exceed the adaptive capacity of the periodontium produce injury called ''trauma from occlusion''. When occlusal forces are reduced the PDL atrophies, appearing thinned. This phenomenon is called ''[[Atrophy|disuse atrophy]]''.

==References==
{{Reflist}}

{{Periodontology}}
{{Mouth anatomy}}
{{Cranial fibrous joints}}
{{Authority control}}

[[Category:Periodontology]]
[[Category:Human mouth anatomy]]
[[Category:Dental anatomy]]