The maxilla is the most important bone of the midface. It has a central location and provides structural support to the viscerocranium. It has functional and aesthetic significance as it has a fundamental role in facial architecture, separates the nasal and oral cavities, forms the upper jaw, and contains the maxillary sinus.

The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones. The paired bones are the maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae bones. The unpaired bones are the vomer and mandible bones. Although classified with the brain-case bones, the ethmoid bone also contributes to the nasal septum and the walls of the nasal cavity and orbit.

The maxillary bone, often referred to simply as the maxilla (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose (see Figure). The curved, inferior margin of the maxillary bone that forms the upper jaw and contains the upper teeth is the alveolar process of the maxilla (Figure). Each tooth is anchored into a deep socket called an alveolus. On the anterior maxilla, just below the orbit, is the infraorbital foramen. This is the point of exit for a sensory nerve that supplies the nose, upper lip, and anterior cheek. On the inferior skull, the palatine process from each maxillary bone can be seen joining together at the midline to form the anterior three-quarters of the hard palate (see Figurea). The hard palate is the bony plate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities.

Maxillary Bone

The maxillary bone forms the upper jaw and supports the upper teeth. Each maxilla also forms the lateral floor of each orbit and the majority of the hard palate.

The fusion of the right forms the maxilla and left maxillary bones at the midline. Each maxillary bone has the shape of a pyramid, it's base adjacent to the nasal cavity, its apex being the zygomatic process, and its body constituting the maxillary sinus. The maxilla connects with surrounding facial structures through four processes: alveolar, frontal, zygomatic and palatine. It articulates superiorly with the frontal bone, the zygomatic bone laterally, palatine bone posteriorly and with the upper teeth through the alveolar process inferiorly. Anteriorly, it forms the inferior and lateral borders of the pyriform aperture and articulates with the nasal bones medially at the anterior border of the frontal process.

Alveolar Process

The alveolar process serves as an anchor for the teeth of the upper denture. It has a horseshoe configuration, with the curved portion facing anteriorly. Located on the most inferior plane, below the hard palate, it extends posteriorly beneath the maxillary sinuses to terminate with the maxillary tuberosity. The alveolar arteries, alveolar nerves, and periodontal ligaments penetrate through channels within the alveolar process to respectively irrigate, innervate and fix the upper teeth.

Palatine Process

The left and right maxilla fuse at the midline through the palatine processes where they form the median maxillary suture. Superiorly, the union of the palatine processes forms the anterior nasal floor and the inferior border of the pyriform aperture at its most anterior aspect. Inferiorly, the anterior portion of the hard palate forms, where the incisive canal is present. This osseous channel communicates the nasal and oral cavities and serves as a conduit to the nasopalatine nerve and the sphenopalatine artery. Superiorly it initiates in the superior nasal (Stensen's) foramina that lie on both sides of the nasal septum and runs inferiorly to terminate at the incisive fossa in the oral cavity, located beneath the incisive papilla and behind the medial incisors.

Zygomatic Process

The zygomatic process is the most lateral portion of the maxilla. It forms the superolateral border of the maxillary sinus and is superior to the first maxillary molar, contiguous with the alveolar process inferiorly and with the frontal process superomedially. Along with the alveolar process, the zygomatic process plays a crucial role in providing structure to the midface. It articulates laterally with the zygomatic bone and has an essential function as it is responsible for the projection of the malar eminence and facial width. On the anterior surface, lateral to the zygomatic process and medial pyriform aperture, a depression is formed known as the canine fossa, which constitutes the anterior surface of the maxilla. Also on the anterior surface, inferior to the zygomatic process and superior to the alveolar processes, another depression forms known as the zygomaticoalveolar crest, an essential structure in classifying maxillary fractures.

Frontal Process

The frontal process lies superiorly and medially relative to each maxillary bone. Each frontal process articulates with the frontal bone superiorly and the nasal bones medially. It forms the anterior wall of the nasolacrimal groove and contributes in shaping the inferior and central portion of the forehead as well as to the nasal bridge through its union with the frontal and nasal bone.

Maxillary Sinus

Each maxillary body is hollow and contains an air-filled cavity in the center, the maxillary sinus. The maxillary sinus is the largest of the paranasal sinuses with an approximate volume of 15 ml in adults. Similar to each maxillary bone it has a pyramidal shape, with the base being the medial wall of the sinus which faces the lateral nasal wall and its apex situated laterally towards the zygomatic arch. It extends from the premolars, anteriorly, to approximately the third molar, posteriorly. As an anatomic variant, it occasionally traumatizes the zygomatic process superolaterally and the maxillary tuberosity inferolaterally. The roof of the sinus forms part of the orbital floor and contains the infraorbital canal which carries the infraorbital neurovascular bundle which exits through the infraorbital foramen, approximately 1 cm below the infraorbital rim. The floor lies superior to the alveolar process and is near the molar apices, its lowest point being in the first molar area. The sinus floor can be at the same level as the nasal floor to about 1 cm below it, varying with age. The medial wall forms part of the nasolateral wall and contains two vital structures, the maxillary sinus ostium, and the nasolacrimal duct. The maxillary sinus ostium is located in the anterosuperior portion of the medial wall and drains into the ethmoid infundibulum which opens up into the middle meatus in the nasal cavity. The nasolacrimal duct originates at the medial wall of the orbit and travels downward and courses medially through the maxillary sinus, anterior to the sinus ostium to eventually drain into the inferior meatus.