Maxilla

Inferior surface of maxilla

In humans, the maxilla consists of:

• The body of the maxilla
• Four processes
  • the zygomatic process
  • the frontal process of maxilla
  • the alveolar process
  • the palatine process
• three surfaces – anterior, posterior, medial
• the Infraorbital foramen
• the maxillary sinus
• the incisive foramen

Development

Anterior surface of maxilla at birth

Inferior surface of maxilla at birth

The maxilla is ossified in membrane. Mall and Fawcett maintain that it is ossified from two centers only, one for the maxilla proper and one for the premaxilla.[5][6]

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.

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 bones (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

Each maxilla also enters into the formation of two fossae: the infratemporal and pterygopalatine, and two 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.

A maxilla fracture is a form of facial fracture. A maxilla fracture is often the result of facial trauma such as violence, falls or automobile accidents. Maxilla fractures are classified according to the Le Fort classification.

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 incisors are attached in mammals consists of a separate pair of bones, the premaxillae. These fuse with the maxilla proper to form the bone found in humans, and some other mammals. In bony fish, amphibians, and reptiles, 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 nostrils. However, in mammals, the bones have curved inward, creating the palatine process and thereby also forming part of the roof of the mouth.[7]

Birds do not have a maxilla in the strict sense; the corresponding part of their beaks (mainly consisting of the premaxilla) is called "upper mandible".

Cartilaginous fish, such as sharks, also lack a true maxilla. Their upper jaw is instead formed from a cartilaginous bar that is not homologous with the bone found in other vertebrates.[7]

• 
  Skull. Maxilla shown in green.
• 
  Skull. Maxilla shown in white.

Wikimedia Commons has media related to Maxilla.

• Maxillofacial surgery
• Maxillary crest

This article incorporates text in the public domain from page 157 of the 20th edition of Gray's Anatomy (1918)

• Sicher, Harry; Du Brul, E. Lloyd (1975). Oral Anatomy (6th ed.). St. Louis: Mosby. ISBN 0-8016-4604-9.
• Worthington, Philip; Evans, John R., eds. (1994). Controversies in Oral & Maxillofacial Surgery. Saunders. ISBN 0-7216-3099-5.

• Anatomy photo:22:os-1901 at the SUNY Downstate Medical Center