Maxilla

The maxilla is a paired facial bone that forms the upper jaw, part of the orbit, the walls of the nasal cavity, and the hard palate. It is one of the most complex and functionally important bones in the facial skeleton. Each maxilla articulates with several other facial and cranial bones and contains the maxillary sinus, the largest of the paranasal sinuses. Together, the two maxillae support the upper teeth and contribute significantly to facial shape, speech, mastication, and respiration.

Structure

Each maxilla is an irregularly shaped bone consisting of a central body and four processes:

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

The right and left maxillae are united at the intermaxillary suture in the midline. Internally, the body of the maxilla houses the air-filled maxillary sinus.

Location

The maxilla is centrally located in the midface, between the orbit above, the nasal cavity medially, and the oral cavity below. It articulates with several surrounding bones and contributes to the orbital floor, nasal walls, and the roof of the mouth (hard palate).

Articulations

Each maxilla articulates with 9 bones:

• Frontal bone
• Nasal bone
• Lacrimal bone
• Ethmoid bone
• Inferior nasal concha
• Palatine bone
• Vomer
• Zygomatic bone
• Contralateral maxilla (via intermaxillary suture)

Processes and Features

1. Body of the Maxilla

• Maxillary sinus: A large, pyramid-shaped air space that opens into the middle nasal meatus.
• Infraorbital foramen: Opening below the orbit that transmits the infraorbital nerve and vessels.

2. Frontal Process

• Extends superiorly to articulate with the frontal bone.
• Helps form the lateral boundary of the nasal bridge.

3. Zygomatic Process

• Projects laterally to articulate with the zygomatic bone (cheekbone).

4. Palatine Process

• Forms the anterior three-fourths of the hard palate.
• Articulates with the contralateral palatine process at the median palatine suture.

5. Alveolar Process

• Houses the sockets (alveoli) for the upper teeth.
• Undergoes resorption in edentulous patients (those without teeth).

Surfaces of the Maxilla

• Anterior surface: Forms part of the facial surface; contains the infraorbital foramen.
• Orbital surface: Forms part of the orbital floor.
• Nasal surface: Forms part of the lateral wall of the nasal cavity.
• Infratemporal surface: Located posteriorly; contributes to the infratemporal fossa.

Functions

• Supports upper teeth: Through the alveolar processes.
• Forms boundaries: Of the nasal cavity, orbit, and oral cavity.
• Facilitates speech and mastication: By stabilizing the upper dental arch.
• Respiration: Forms part of the nasal passageway and houses the maxillary sinus to lighten the skull and humidify air.
• Facial aesthetics: Provides midfacial projection and contour.

Maxillary Sinus

The maxillary sinus is a large air-filled cavity within the body of the maxilla. It opens into the middle nasal meatus through the semilunar hiatus.

• Functions: Lightens the skull, warms and moistens air, and contributes to voice resonance.
• Clinical Note: The floor of the sinus is close to the roots of the upper molars; dental infections can spread to the sinus, causing maxillary sinusitis.

Development and Ossification

The maxilla develops from two centers of ossification in the maxillary prominences of the first pharyngeal arch. It undergoes intramembranous ossification, beginning during fetal development. The maxillary sinus appears prenatally but continues expanding into adolescence.

• Suture with palatine bone: Important in the formation of the hard palate; failure of fusion can result in a cleft palate.

Clinical Relevance

1. Maxillary Fractures

Maxillary fractures are common in facial trauma. The Le Fort classification describes three types of fractures:

• Le Fort I: Horizontal fracture of the maxilla above the teeth.
• Le Fort II: Pyramidal fracture involving the nasal bridge, maxilla, and orbit.
• Le Fort III: Craniofacial disjunction involving the zygomatic arches and orbit.

2. Maxillary Sinusitis

Inflammation of the maxillary sinus can result from dental infections or upper respiratory tract infections. It presents with facial pressure, pain, nasal congestion, and post-nasal drip.

3. Cleft Palate

Failure of the palatine processes of the maxilla to fuse during embryonic development leads to a cleft palate. This congenital condition may interfere with feeding and speech and requires surgical correction.

4. Dental Considerations

The roots of the upper molars are close to the floor of the maxillary sinus. Dental procedures like extractions can sometimes perforate the sinus, creating an oroantral fistula. Maxillary bone loss from tooth loss also affects denture fitting.

5. Tumors and Cysts

Benign and malignant tumors may occur in the maxillary sinus or alveolar process. Odontogenic cysts may also arise and expand into the sinus, displacing structures.

6. Orthognathic Surgery

Corrective jaw surgeries may involve repositioning the maxilla to address occlusal or aesthetic concerns, especially in cases of skeletal malocclusion.

Radiological Appearance

On radiographs and CT scans, the maxilla appears as a central facial structure forming the roof of the oral cavity and floor of the orbit. The maxillary sinus is visible as an air-filled space. Infraorbital foramen, tooth sockets, and the floor of the sinus are key radiological landmarks.

Associated Foramina

• Infraorbital foramen: Transmits the infraorbital nerve and vessels (branch of maxillary nerve – CN V2).
• Incisive foramen: Located in the anterior hard palate; transmits the nasopalatine nerve and branches of the greater palatine artery.