Maxilla
The maxilla is a paired bone containing an air-filled cavity - maxillary sinus. The maxillae are parts of the viscerocranium of the skull. This bone has a central body and four processes.
The two maxillary bones (maxillae) are fused in the midline by the intermaxillary suture to form the upper jaw. The fusion of both maxillae creates a projection called the anterior nasal spine, which is the anterior point of the upper jaw that serves as a cephalometric landmark.
Each maxilla has five parts, including the body of the maxilla and four processes:
Body of the maxilla
The body is the central portion of the maxilla housing the maxillary sinus and supporting all processes.
The maxillary body has four surfaces: anterior, orbital, nasal, and infratemporal surfaces.
The anterior surface features the following landmarks:
Nasal notch - close to the anterior nasal spine, on the medial margin;
Infraorbital margin - it forms the inferior margin of the orbit;
Infraorbital foramen - below the middle part of the infraorbital margin;
Canine fossa - inferior to the infraorbital foramen.
The orbital surface is the superior surface. It forms most of the orbital floor and features the infraorbital groove leading into the infraorbital canal.
The nasal surface forms a part of the lateral wall of the nasal cavity and features a large opening - the maxillary hiatus, which leads to the maxillary sinus.
The infratemporal surface is the posterior surface of the maxilla, and it presents the maxillary tuberosity with small openings called alveolar foramina that lead into the alveolar canals.
Frontal process
The frontal process is an extension of the maxilla projecting upward, medially, and slightly backward for articulation with the frontal bone. The frontal process of the maxilla features the lacrimal groove, which is a vertical groove located on the posterior aspect of the process.
Zygomatic process
The zygomatic process is the short lateral extension of the maxilla for articulation with the zygomatic bone.
Palatine process
The palatine process is the medial extension of the maxilla, shaped like a horizontal plate. It forms the largest part of the hard palate. The opening of the incisive canal named the incisive foramen can be found on the anterior part of the palatine process.
Alveolar process
The alveolar process is an inferior crested extension of the upper jaw which houses the teeth (the lower jaw or mandible also has alveolar processes).
The curved free margin of the alveolar process is called the alveolar arch.
The alveolar arch of the maxilla (as the alveolar arch of the mandible) features the following landmarks:
Dental alveoli - sockets in the alveolar process where the roots of the teeth lie;
Interalveolar septa - bony ridges between adjacent dental alveoli;
Interradicular septa - bony ridges forming compartments in dental alveoli for the roots of the teeth;
Alveolar yokes (juga alveolaria) - eminences on the outer surface of the jaw produced by the projections of the dental alveoli.
Sutures
Besides intermaxillary sutures, maxillae have two or three more sutures. All of them are located on the palatine process, and two of them define the hard palate.
The first one is a sagittally oriented median palatine suture connecting both maxillae and also both horizontal plates of the palatine bone as it extends from maxillae to palatine bones.
The second one is a horizontally oriented transverse palatine suture separating the palatine process of the maxillae from the horizontal plates of the palatine bone.
The third suture is not always present, but if it is, it is situated on the anterior portion of the palatine process, separating the anterior part of the maxillae which contains dental alveoli. It is called the incisive suture.