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Maxilla

Synonym: upper jaw bone
German: Maxilla

1 Definition

The maxilla is after the lower jaw bone the largest of the facial bones. The right and left maxilla together form the upper jaw.

The bone forms the boundary walls of three major body cavities: the roof of the oral cavity, the bottom and the side wall of the nasal cavity and the bottom of the orbit.

2 Anatomy

The maxilla can be anatomically divided into a body (corpus maxillae) and its bony processes, the malar process processus zygomaticus, the processes frontalis, the processus alveolaris and the palatine process of the maxilla processus palatinus.

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2.1 Corpus maxillae

2.1.1 Facies anterior

The facies anterior of the maxilla faces forward and laterally. In the lower section it exhibits a series of bony elevations that mark the location of dental roots of the upper jaw. Above the incisor roots is a depression, the fossa incisiva (incisor pit). It is the origin of the musculus depressor septi nasi and the alar of the musculus nasalis. The origin surface of the musculus orbicularis oris starts caudal to the fossa incisiva - bordering on the alveolar ridge.

Further laterally from the fossa incisiva there is another, larger, deeper bone recess, the fossa canina. It is separated from it by a vertically extending bony ridge, the eminentia canina, which corresponds to the long root of the canine tooth. It is the origin point of the musculus levator anguli oris.

Above the canine fossa is the foramen infraorbitale, through which the nervus infraorbitalis and the vessels of the same name run. Above the foramen one can see the lower orbit which serves as the origin of the [[musculus levator labii superioris alaeque nasi|] musculus levator labii superioris]. The anterior surface of the maxilla ends mediall at the apertura piriformis. The bony edge of the aperture extends caudally into a peaked bony process, which together with the continuation of the opposite side forms the spina nasalis anterior.

2.1.2 Facies infratemporalis

The facies infratemporalis forms part of the fossa infratemporalis. It is convex and directed toward the lateral and occipital. It is separated from the facies anterior by the processus zygomaticus and by a bony crest that runs from the first molars upward. Approximately in its centre there are the openings for the alveolar canals, through which the branches of the arteria alveolaris superior posterior and nervus alveolaris superior posterior run.

In the caudal section of the facies infratemporalis there lies a rounded bony mound that is known as tuberositas maxillaris. On its lateral side it is roughened because the maxilla articulates here with the pyramidal process of the os palatinum. Moreover, it serves as the point of origin of some of the fibres of the musculus pterygoideus medialis. Immediately above the tuberositas maxillaris there is a smooth surface on the bone, which forms the front margin of the fossa pterygopalatina and possesses a recess for the nervus maxillaris.

2.1.3 Facies orbitalis

The triangular and smooth facies orbitalis forms the largest part of the orbital floor. Medially it is surrounded by an irregularly extending edge, which shows a recess at its front, the incisura lacrimalis. Behind the incisura lacrimalis the maxilla articulates with the os lacrimale, the lamina papyracea of the os ethmoidale, and the processus orbitalis of the palatine bone.

Occipitally the facies orbitalis is bounded by a rounded bone edge forming the front edge of the fissura orbitalis inferior. Frontally it encounters the lower orbital rim which merges medially into the processus frontalis and laterally into the processus zygomaticus.

One striking structure of facies orbital is the sulcus infraorbitalis, in which the arteria infraorbitalis, the vena infraorbitalis and nervus infraorbitalis run. The sulcus ends rostrally in canalis infraorbitalis which reappears as the foramen infraorbitale at the lower orbital rim of the bone surface.

2.1.4 Facies nasalis

The facies nasalis" runs with an irregularly formed bone margin into the maxillary sinus sinus maxillaris. The concave surface of the bone below this opening forms part of the meatus nasi inferior of the nasal cavity. Behind this there is a rough area that articulates with the perpendicular plate lamina perpendicularis of the os palatinum. The caudal portion of this area is crossed by a small furrow, which runs obliquely forward and downward. It is covered by the os palatinum up to the canalis pterygopalatinus.

Tthe facies nasalis exhibits frontally another flat section of bone, which forms part of the middle meatus (meatus nasi medius). It is separated by the crista conchalis, a small sloping bone crest, from the rear part of the facies nasalis. Here the upper jaw articulates with the inferior turbinate (concha nasalis inferior). At the higher end of the cresta conchalis one sees a deep bone trough, the sulcus lacrimalis maxillae, which is closed off by the os lacrimale and the inferior turbinate from the canalis nasolacrimalis in the articulated skull. It conducts the respectively named ductus nasolacrimalis (nasolacrimal duct).

2.2 Processus zygomaticus

The maxillary process processus zygomaticus is a strong, triangular bone extension which lies in the angle between the anterior, orbital and infratemporal surfaces of the maxilla. It projects laterally in a rough jagged surface that articulates with the zygomatic bone. Dorsally it is concave and forms a part of the intemporal fossa fossa infratemporalis.

2.3 Processus frontalis

The frontal process processus frontalis is a bone plate that points at the cranial end of the maxilla upward, media and occipital, next to the nose. The lateral side of the frontal process is smooth and transitions continuously into the facies anterior of the maxilla. It serves as the origin of the musculus levator labii superioris, the musculus orbicularis oculi and the ligamentum palpebrale mediale

The medial surface forms a part of the lateral nasal wall. Its upper part articulates with the os ethmoidale and seals the front ethmoid bone cells. Beneath it one can see a sloping bony crest, the crista ethmoidalis whose posterior end articulates with the concha nasalis media.

The top edge of the frontal process articulates with the os frontale, the anterior edge with the os nasale. The trailing edge is thick and is notched by a furrow which merges into the sulcus lacrimalis maxillae of the facies nasalis.

2.4 Processus alveolaris

The alveolar process ( processus alveolaris maxillae) is a thick,spongy bone crest which runs in a horseshoe shape around the hard palate. It is thicker occipitally than rostrally and exhibits numerous depressions, the tooth sockets, in which the teeth are fixed. The size and shape of the tooth socket alveolus varies with the type of the tooth being enclosed. The tooth socket for the canine tooth is the deepest. The tooth sockets of multirooted teeth show small bony septa.

At the facial surface(s) of the alveolar process the roots of the incisors and canines can be seen as vertical elevations. This arch shaped structures are called juga alveolaria. Behind the first molar the musculus buccinator has its origin on the facial surface of the alveolar process.

2.5 Processus palatinus

The palatinus process processus palatinus of the upper jaw bone is a very pronounced bone appendage which together with its counterpart forms a large part of the nasal floor and the hard palate. It is rostrally thicker than occipitally.

The inferior surface of the palatine process is rough and concave. It is perforated by many foramina, which protect the nutritive supply of blood vessels and nerves of the palatal mucosa. Directly behind the incisors a striking structure can be recognised, the incisive foramen foramen incisivum. In its opening two small channels are visible, the canalis incisivus dexter and sinister. Through these run the arteria palatina descendens and the nervus nasopalatinus. In the middle of the palate, where the two palatal processes coalesce, we can see the sutura palatina mediana. The margin to the os palatinum is formed by the sutura palatina transversa.

The superior surface of the palatine process is smooth and concave. It forms a significant portion of the bony nasal floor. Rostrally the upper opening of the canalis incisivus is able to be recognised. The medial border rises to a bone ridge which fuses with the crest of the opposite side to the Crista nasalis which receives the vomer. Rostrally the crista forms a pointed projection, the spina nasalis anterior. The lateral edge transitions into the body of the maxilla bone.

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