The Maxilla

Structure of the Maxilla

The maxilla is comprised of a body and four processes. The body is pyramidal in shape and has four surfaces: orbital, nasal, infratemporal, and anterior – each containing important anatomical landmarks.

Extending from the body are four projections, known as processes:

• Zygomatic process
• Palatine process
• Alveolar process
• Frontal process

These processes allow the maxilla to articulate with adjacent facial and cranial bones.

Maxillary Body

The body of the maxilla is pyramidal in shape and has four surfaces: orbital, nasal, infratemporal, and anterior. It also houses the maxillary sinus, the largest of the paranasal sinuses.

While the boundaries between these surfaces are often indistinct, they provide a useful framework for describing the bone’s anatomical features.

Infratemporal Surface

The infratemporal surface forms the anterior boundary of the infratemporal fossa and lies on the posterior aspect of the maxilla.

A key feature of this surface is the maxillary tuberosity, which contains several openings known as the alveolar foramina. These openings transmit the posterior superior alveolar nerve (branch of the maxillary nerve) and accompanying vessels to the upper molar teeth.

Orbital Surface

The orbital surface of the maxilla forms most of the floor of the orbit. It articulates with the lacrimal bone, the orbital plate of the ethmoid, and the orbital process of the palatine bone.

Its key features include:

• Infraorbital groove – shallow channel that transmits the infraorbital nerve and vessels.
• Infraorbital foramen – external opening of the infraorbital canal, through which the infraorbital nerve (branch of the maxillary nerve), artery, and vein emerge.
• Infraorbital margin – inferior rim of the bony orbit, which serves as the site of attachment for the orbicularis oculi muscle.

Nasal Surface

The nasal surface of the maxilla forms the lateral wall of the nasal cavity and the medial wall of the maxillary sinus.

It features a large opening called the maxillary ostium, which allows drainage from the sinus into the nasal cavity.

Other key features include:

• Nasolacrimal groove – located anterosuperior to the maxillary ostium, it contributes to the formation of the nasolacrimal canal.
• Conchal crest – a bony ridge that articulates with the inferior nasal concha.

Anterior Surface

The anterior surface of the maxilla forms the central part of the upper jaw.

It is a small, triangular area with a prominent canine eminence, a bony elevation over the root of the canine tooth. This eminence gives rise to two fossae:

• Incisive fossa – located medial to the canine eminence
• Canine fossa – located lateral to the canine eminence and serves as the origin for the levator anguli oris muscle

Maxillary Sinus

The maxillary sinus is the largest of the paranasal sinuses, typically holding a volume of 10–15 ml. It lies within the body of the maxilla and is shaped like a four-sided pyramid.

• Base – forms the medial wall of the sinus and also serves as the lateral wall of the nasal cavity.
• Apex – points laterally toward the zygomatic process of the maxilla.

The medial wall contains the maxillary ostium, the opening through which the sinus drains into the nasal cavity. This ostium opens into a groove on the lateral nasal wall known as the semilunar hiatus, located beneath the middle concha (meatus).

The roof of the sinus is formed by the floor of the orbit, while the floor is formed by the alveolar process, which is closely related to the roots of the upper molar teeth.

Maxillary Processes

The maxillary processes refer to four bony projections that extend from the body of the maxilla. They enable the maxilla to articulate with surrounding bones and contribute to the formation of key facial structures.

Zygomatic Process

The zygomatic process is a lateral projection of the maxilla that articulates with the zygomatic bone. It contributes to the formation of the zygomatic arch (cheekbone).

It is formed by the convergence of the infratemporal, anterior, and orbital surfaces. This process helps maintain the contour and structure of the midface.

Frontal Process

The frontal process of the maxilla is a bony projection that extends superiorly and medially from the body of the maxilla.

Its articulations include:

• Posteromedial – middle nasal concha
• Superior – nasal part of the frontal bone
• Posterolateral – lacrimal bone
• Anteromedial – nasal bone

Together with the lacrimal bone, it forms the lacrimal groove, which continues inferiorly as the nasolacrimal canal.

Palatine Process

The palatine process of the maxilla is a broad, flat projection that extends medially from the alveolar process. It forms the majority of the hard palate, separating the oral and nasal cavities.

Just posterior to the central incisors is the incisor foramen, which transmits the nasopalatine nerve (a branch of the maxillary nerve) and accompanying vessels.

Two additional foramina – the greater and lesser palatine foramina – are also located on the hard palate, but they lie within the palatine bone, not the maxilla.

Alveolar Process

The alveolar process is a horseshoe-shaped projection located along the inferior margin of the maxilla. It supports the upper teeth and contains channels for the passage of alveolar arteries, nerves, and periodontal ligaments.

Within the process are several important bony features. Dental alveoli are tooth sockets that house the roots of teeth. Bony ridges between adjacent alveoli are called interalveolar septa, while those within the alveoli of multi-rooted teeth (such as molars) are termed interradicular septa and provide additional support.

On the outer surface of the process, alveolar yokes appear as bony prominences caused by the underlying dental alveoli.

Facial Fractures

Fractures of the midface often involve the maxilla, due to its central position and extensive articulations with surrounding bones.

The most widely used system for classifying midfacial fractures is the Le Fort classification, which divides them into three main types based on the anatomical pattern of the fracture lines:

• Le Fort I (Horizontal) – Fracture passes above the teeth, separating the alveolar process and palatine process. It involves the lateral wall of the maxillary sinus and nasal septum.
• Le Fort II (Pyramidal) – Fracture runs from the nasal bridge through the frontal process, infraorbital margin, and maxillary sinus. It can damage the infraorbital nerve, resulting in sensory loss to the midface.
• Le Fort III (Craniofacial disjunction) – Fracture separates the midface from the cranial base via the zygomatic process, orbital floor, and nasofrontal suture. It involves the disarticulation of the maxilla from the skull base.