Editing Maxilla

{{Short description|Upper jaw bone}}
{{About|the maxilla in vertebrates|arthropod maxillae|Maxilla (arthropod mouthpart)}}
{{More citations needed|date=December 2007}}
{{Infobox bone
| Name          = Maxilla
| Latin         = maxilla
| Image         = Maxilla anterior.png
| Caption       = Position of the maxilla
| Image2        = Maxilla - animation 02.gif
| Caption2      = Animation of the maxilla
| Precursor     = First [[branchial arch]]<ref>{{EmbryologyUNC|hednk|023}}</ref>
| Origins       =
| Insertions    = 
| Articulations =
}}

In [[vertebrate]]s, the '''maxilla''' ({{plural form}}: '''maxillae''' {{IPAc-en|m|æ|k|ˈ|s|ɪ|l|iː}})<ref>''[[OED]]'' 2nd edition, 1989.</ref> is the upper fixed (not fixed in [[Neopterygii]]) [[bone]] of the [[jaw]] formed from the fusion of two maxillary bones. In humans, the upper jaw includes the [[hard palate]] in the front of the [[mouth]].<ref>[http://webster.com Merriam-Webster Online Dictionary]''.</ref><ref>{{cite book |title=Illustrated Anatomy of the Head and Neck |last=Fehrenbach |last2=Herring |publisher=Elsevier |year=2012 |page=55 |isbn=978-1-4377-2419-6 }}</ref> The two maxillary bones are fused at the intermaxillary suture, forming the [[anterior nasal spine]]. This is similar to the [[mandible]] (lower jaw), which is also a fusion of two mandibular bones at the [[mandibular symphysis]]. The mandible is the movable part of the jaw.

==Anatomy==

=== Structure ===
The maxilla is a paired bone - the two maxillae unite with each other at the intermaxillary suture. The maxilla consists of:<ref name=":0">{{Cite book |last=Fehrenbach |first=Margaret J. |title=Illustrated Anatomy of the Head and Neck |last2=Herring |first2=Susan W. |date=2017 |publisher=Elsevier |isbn=978-0-323-39634-9 |edition=5th |location=St. Louis |pages=61}}</ref>[[File:Sobo 1909 100 - Palatine process of maxilla.png|thumb|right|Inferior surface of maxilla]]
* The '''body of the maxilla''': pyramid-shaped; has an orbital, a nasal, an infratemporal, and a facial surface; contains the [[maxillary sinus]].
* Four [[Process (anatomy)|processes]]:
** the [[Zygomatic process of maxilla|zygomatic process]]
** the [[frontal process of maxilla|frontal process]]
** the [[alveolar process]]
** the [[palatine process]]
It has three surfaces:<ref name=":0" />
* the anterior, posterior, medial
Features of the maxilla include:<ref name=":0" />
* the [[Infraorbital groove|infraorbital sulcus]], [[Infraorbital canal|canal]], and [[Infraorbital foramen|foramen]]
* the [[maxillary sinus]]
* the [[incisive foramen]]

===Articulations===
Each maxilla articulates with nine bones: [[Frontal bone|frontal]], [[ethmoid]], [[nasal bone|nasal]], [[zygomatic bone|zygomatic]], [[lacrimal bone|lacrimal]], and [[Palatine bone|palatine]] bones, the [[vomer]], the [[inferior nasal concha]], as well as the maxilla of the other side.<ref name=":0" />

Sometimes it articulates with the orbital surface, and sometimes with the [[lateral pterygoid plate]] of the [[sphenoid bone|sphenoid]].

===Development===
[[File:Gray161.png|thumb|Anterior surface of maxilla at birth]]
[[File:Gray162.png|thumb|Inferior surface of maxilla at birth]]
The maxilla is ossified in membrane. [[Franklin P. Mall|Mall]] and Fawcett maintain that it is ossified from ''two'' centers only, one for the maxilla proper and one for the premaxilla.<ref>{{cite journal |first=Franklin P. |last=Mall |title=On ossification centers in human embryos less than one hundred days old |journal=[[American Journal of Anatomy]] |year=1906 |volume=5 |issue=4 |pages=433–458 |doi=10.1002/aja.1000050403 |url=https://zenodo.org/record/2179571 }}</ref><ref>{{cite journal |first=Edward |last=Fawcett |title=Some Notes on the Epiphyses of the Ribs |journal=[[Journal of Anatomy and Physiology]] |year=1911 |volume= 45 |issue=Pt 2 |pages=172–178 |pmc=1288875 |pmid=17232872 }}</ref>

These centers appear during the sixth week of [[prenatal development]] and unite in the beginning of the third month, but the suture between the two portions persists on the palate until nearly middle life. Mall states that the frontal process is developed from both centers.

The maxillary sinus appears as a shallow groove on the nasal surface of the bone about the fourth month of development, but does not reach its full size until after the second dentition.

The maxilla was formerly described as ossifying from six centers, viz.:
* One, the ''orbitonasal,'' forms that portion of the body of the bone which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and the lateral wall of the nasal cavity.
* A second, the ''zygomatic,'' gives origin to the portion which lies lateral to the infraorbital canal, including the zygomatic process.
* From a third, the ''palatine,'' is developed the palatine process posterior to the incisive canal together with the adjoining part of the nasal wall.
* A fourth, the ''premaxillary,'' forms the incisive bone which carries the incisor teeth and corresponds to the premaxilla of the lower vertebrates.
* A fifth, the ''nasal,'' gives rise to the frontal process and the portion above the canine tooth.
* And a sixth, the ''infravomerine,'' lies between the palatine and premaxillary centers and beneath the vomer; this center, together with the corresponding center of the opposite bone, separates the incisive canals from each other.

====Changes by age====
At birth the transverse and antero-posterior diameters of the bone are each greater than the vertical.

The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit.

The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest, owing to the development of the alveolar process and the increase in size of the sinus.

==Function==
[[File:FracLeftNasalBoneMark.png|thumb|Fracture of the left lacrimal / maxillary bone]]
The [[alveolar process]] of the maxillae holds the upper teeth, and is referred to as the maxillary arch. Each maxilla attaches laterally to the [[zygomatic bone]]s (cheek bones).

Each maxilla assists in forming the boundaries of three cavities:
* the roof of the [[mouth]]
* the floor and lateral wall of the [[nasal cavity]]
* the wall of the [[orbit (anatomy)|orbit]]

Each maxilla also enters into the formation of two fossae: the [[Infratemporal fossa|infratemporal]] and [[Pterygopalatine fossa|pterygopalatine]], and two [[fissure (anatomy)|fissures]], the [[inferior orbital]] and [[pterygomaxillary]].
-When the tender bones of the upper jaw and lower nostril are severely or repetitively damaged, at any age the surrounding cartilage can begin to deteriorate just as it does after death.{{citation needed|date=January 2016}}

==Clinical significance==
A [[maxilla fracture]] is a form of [[facial fracture]]. A maxilla fracture is often the result of [[facial trauma]] such as [[violence]], [[Falling (accident)|falls]] or [[automobile accidents]]. Maxilla fractures are classified according to the [[Le Fort fracture of skull|Le Fort classification]].

==In other animals==
Sometimes (e.g. in bony fish), the maxilla is called "upper maxilla", with the mandible being the "lower maxilla". Conversely, in birds the upper jaw is often called "upper mandible".

In most vertebrates, the foremost part of the upper jaw, to which the [[incisor]]s are attached in mammals consists of a separate pair of bones, the [[premaxilla]]e. These fuse with the maxilla proper to form the bone found in humans, and some other mammals. In [[Osteichthyes|bony fish]], [[amphibian]]s, and [[reptile]]s, both maxilla and premaxilla are relatively plate-like bones, forming only the sides of the upper jaw, and part of the face, with the premaxilla also forming the lower boundary of the [[nostril]]s. However, in mammals, the bones have curved inward, creating the palatine process and thereby also forming part of the roof of the mouth.<ref name="VB">{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 217–43|isbn= 0-03-910284-X}}</ref>

[[Bird]]s do not have a maxilla in the strict sense; the corresponding part of their [[beak]]s (mainly consisting of the premaxilla) is called "upper mandible".

[[Chondrichthyes|Cartilaginous fish]], such as sharks, also lack a true maxilla. Their upper jaw is instead formed from a [[cartilage|cartilaginous]] bar that is not [[homology (biology)|homologous]] with the bone found in other vertebrates.<ref name=VB/>

==Additional images==
<gallery>
 File:Maxilla anterior.png|Skull. Maxilla shown in green.
 Maxilla - animation 02.gif|Skull. Maxilla shown in white.
</gallery>

== See also ==
{{Commons category|Maxilla}}
{{Anatomy-terms}}
* [[Maxillofacial surgery]]
* [[Nasal septum#Structure|Maxillary crest]]

==References==
{{Gray's}}
{{Reflist}}

==Further reading==
* {{cite book |first=Harry |last=Sicher |first2=E. Lloyd |last2=Du Brul |author-link2=E. Lloyd Du Brul |title=Oral Anatomy |location=St. Louis |publisher=Mosby |year=1975 |edition=6th |isbn=0-8016-4604-9 }}
* {{cite book |editor-first=Philip |editor-last=Worthington |editor2-first=John R. |editor2-last=Evans |title=Controversies in Oral & Maxillofacial Surgery |publisher=Saunders |year=1994 |isbn=0-7216-3099-5 }}

==External links==
* {{SUNYAnatomyLabs|22|os|19|01}}

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{{Facial bones}}
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[[Category:Bones of the head and neck]]
[[Category:Dental anatomy]]
[[Category:Irregular bones]]
[[Category:Human mouth anatomy]]
[[Category:Otorhinolaryngology]]