The upper jaw (maxilla) is the central bone of the midface and thus of the facial portion of the skull (viscerocranium). The bones of the viscerocranium, except for the mandible, are referred to as midface. The viscerocranium comprises:
- 1 ethmoid bone
- 2 lacrimal bones
- 2 nasal bones
- 1 vomer
- 2 inferior nasal conchae (turbinates)
- 2 palatal bones
- 2 zygomatic bones
- 2 bones of the upper jaw = maxilla
- 1 bone of the lower jaw = mandible
In contrast to the mandible, the maxilla is firmly attached to the neurocranium. Fixation occurs via connective tissue sutures that are at the same time growth centres.
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The bones are mostly thin and membranous and form the boundaries of the cavities of the midface, in particular, the:
- maxillary sinuses
- ethmoidal cells
- sphenoidal sinus
This lightweight construction helps to reduce weight. Occlusal forces are transmitted to the skull by three pillars, in which the bony trabeculae have a characteristic trajectory. These pillars, the frontal process of the maxilla (nasal process), the zygomatic process of the maxilla (malar process), and the alveolar process, represent suitable places for the fixation of plates and screws.
The maxilla is the central bone of the midface and forms part of the orbital wall and the nasal cavity as well as the palate.
The maxilla develops into the largest cover bone in the maxillary ridge of the first branchial arch.
The maxilla consists of a central body containing the maxillary sinus, and four processes making contact with the adjacent facial bones: #pic# #pic#
The frontal process of the maxilla #pic# #pic# #pic# #pic# #pic# #pic# #pic# projects upwards and articulates with the frontal bone with its serrated upper border. Its anterior border makes contact with the nasal bone and its posterior border with the lacrimal bone.
The zygomatic process of the maxilla #pic# #pic# #pic# #pic# projects laterally and makes contact with the zygomatic bone via an irregular surface. Its lower, free border is referred to as zygomatico-alveolar crest #pic# and, from a biomechanical point of view, represents the strongest of the three facial pillars transmitting masticatory forces.
The palatine process of the maxilla #pic# #pic# forms the anterior and largest part of the hard palate. In the posterior region, through the transverse palatine suture, it connects with the horizontal lamina of the palatine bone #pic# #pic# that forms the posterior, and smaller part of the hard palate. It articulates with the contralateral palatine process via the median palatine suture. The palatine process is shorter by one molar breadth than the body of the maxilla so that the posterior segment of the alveolar arch carrying the wisdom teeth and the maxillary tuberosity forming the posterior limit of the alveolar arch diverge from the arch. The greater palatine foramen #pic# is located on the same level, at the point where the alveolar process merges into the body of the maxilla and the horizontal lamina of the palatine bone. The greater palatine canal, containing the greater palatine nerve and the descending palatine artery, terminates here #pic# #pic#. On the oral side of the bony palate, these neurovascular pathways leave grooves as they progress anteriorly sometimes referred to as palatine sulci and which, in some cases, are deepened by parallel bony processes (palatine spines).
The alveolar process of the maxilla containing the dental sockets, or alveoli #pic# #pic# #pic# #pic#, also referred to as the alveolar arch, develops only after birth with the eruption of teeth, in the same way as the mandibular alveolus, and is quickly resorbed after tooth loss. The alveolar ridges (juga alveolaria) are especially noticeable in the vestibular area. The projection of the margin between the body of the maxilla and the alveolar process is located approximately where the palatine process originates.
The body of the maxilla consists of four surfaces:
the nasal surface (facies nasalis) which is the medial surface projecting towards the nasal cavity,
the orbital surface (facies orbitalis) which is the upper surface projecting towards the orbit (orbital cavity),
the anterior surface (facies anterior) projecting towards the face, and
the infratemporal surface (facies infratemporalis) which is the posterior surface projecting towards the infratemporal fossa (zygomatic fissure).
The nasal surface of the maxilla #pic# #pic# #pic# has a large aperture referred to as the maxillary osteum connecting the maxillary sinus with the nasal cavity. In the posterior segment of the nasal surface there is an almost vertical descending groove, the greater palatine sulcus of the maxilla #pic#. It is completed by a complementary groove of the palatine bone going to the greater palatine canal #pic# and containing the greater palatine nerve and the descending palatine artery.
The orbital surface of the maxilla #pic# #pic# #pic# forms the largest part of the orbital floors. In the posterior third, a groove referred to as infraorbital sulcus originates from the inferior orbital fissure #pic# and continues into the infraorbital canal #pic#. The infraorbital nerve, artery and vein pass through the infraorbital canal.
The anterior surface of the maxilla #pic# #pic# #pic# is covered by the soft tissue of the face. Here, the infraorbital foramen is located #pic# from which exits the second trigeminal branch. The canine fossa #pic# forms the lower part of this surface posterior to the prominence formed by the apex of the canine tooth in the alveolus. It is an important landmark when the maxillary sinus is exposed during surgery. The branches of the maxillary artery that anastomose with the infraorbital artery pass here. The medial border of the anterior surface frames the pear-shaped entrance into the nasal cavity referred to as pyriform aperture and terminates inferiorly in the midline forming a small bony spine (anterior nasal spine) #pic# to which is attached the cartilaginous nasal septum. The two parts of the maxilla are connected to each other anteriorly by the intermaxillary suture.
The infratemporal surface of the maxilla #pic# #pic# #pic# forms the posterior area of the maxilla and is located behind the zygomatic process. At its mid-level, there is a tuberosity, the tuber maxillae, that develops during growth of the maxillary sinus. The maxillary tuberosity is penetrated by several (usually 2) smaller apertures (alveolar foramina) where the posterior superior alveolar nerves and arteries enter and the respective vein exits. These openings usually continue into a canal (canalis alveolaris posterior) #pic# up to the posterior molars. The posterior canal unites with the anterior alveolar canal #pic# containing the anterior superior alveolar nerves, artery and vein, the latter canal converging shortly before reaching the entrance of the infraorbital canal #pic# at the infraorbital foramen #pic# #pic# and continues in the anterior wall of the maxilla downwards and backwards to form small lateral canals continuing to the remaining roots of maxillary teeth. Usually, the canals remain open adjacent to the maxillary sinus, only covered by mucosa, so that the nerve fibres are easily affected by any maxillary sinus disease and sometimes cause pain similar to pain of dental origin. In addition to the main arteries entering at the level of the maxillary tuberosity, other bone constituents (connective tissue and medulla) are supplied by smaller, accessory arteries whose entrance apertures are referred to as nutritional foramina. These foramina are numerous in the hard palate #pic# #pic#, on the vestibular side of the alveolar process, and on the outer side of the frontal process and the adjacent anterior surface of the maxilla.
The part of the maxilla carrying the incisors is referred to as premaxilla, or premaxillary bone (os incisivum) #pic# #pic#. J. W. von Goethe discovered it in 1784 in a human being. The incisive suture connects the premaxilla with the palatine process of the maxilla. The premaxilla is a paired bone like all other bones of the viscerocranium. While the premaxilla develops from an independent primordium, it is firmly attached to the adult maxilla and forms the anterior part of the hard palate. In the skull of children and adolescents, however, it is still clearly recognisable as the suture remains open. It can sometimes also be visible in the adult skull though more rarely. The incisive canals #pic# #pic# enter from the nose on both sides of the nasal septum #pic# #pic# #pic# #pic# between the premaxilla and the palatine process. Both canals unite and end inside the oral cavity behind the central incisors at the incisive, or nasopalatine, foramen. The nasopalatine nerve and artery pass through the incisive canal to the palatal mucosa. Frequently, there are also two or more small apertures visible behind the greater palatine foramen; they are referred to as minor palatine foramina #pic# of the palatine bone forming pathways from the minor palatine canal branching from the major palatine canal to the mucosa of the soft palate.
Several muscles are attached to the maxilla both on the
Muscles of facial expression and mastication
and on the
Palatal and pharyngeal muscles - they can cause secondary dislocation of fractured skeletal parts.
The powerful palatal muscles, palatoglossus and palatopharyngeus muscles, which also fix the tongue, may cause secondary dislocation of fractures, distally and caudally, and - possibly - dislocation of the airways.
The following larger arteries run next to the maxilla and midface:
- Palatine artery
- Infra-orbital artery
- Maxillary artery
- Facial artery
- Nasopalatine artery