About The Maxilla

Introduction

Whilst the structure of facial bones are highly important aesthetically, they also play a role in the protection of facial nerves and have major functional implications affecting our speech, eating, and breathing capabilities. One of these bones is the maxilla. 

In this article, we will discuss the role and structure of the maxilla, as well as associated conditions and treatment options.   

Original image created by Chloe Davis using BioRender

Anatomy of the maxilla

The maxilla is part of the viscerocranium structure (a collection of bones that make up the face). Morphologically, the maxilla is made up of two irregular-shaped bones which fuse at the midline of the face during fetal development. This creates the upper jaw and aids in the formation of the orbit, mouth (palate), and nasal cavity. 

Location and structure

The anatomy of the maxilla can be broken down into five major areas; the body, and four projections:

Body

The body is the largest part of the maxilla. This pyramid-shaped part of the bone contributes to the anterior margin and floor of the bony orbit, the inferior infratemporal fossa, and the anterior wall of the nasal cavity. 

Alveolar process

The alveolar process is a porous extension of the maxilla which serves as an anchor for the upper teeth. With increasing age, this process is absorbed causing tooth loss. 

Frontal process

The frontal process is located in the middle and slightly above each maxillary bone, forming the anterior wall of the nasolacrimal groove. This helps to shape the nasal bridge and the inferior and central portions of the forehead. 

Zygomatic process

This process forms the outer part of the maxilla, forming the cheekbones (or zygomatic bones).

Palatine process

The palatine process is where the right and left sides of the maxilla fuse to form the median maxillary suture forming the roof of the mouth and the floor of the nasal cavity. Alongside the palatine bone, this process forms the hard palate.

The maxilla further interacts with other facial bones;

• Superiorly with the frontal bone
• Posteriorly with the ethmoid bone, lacrimal bones, palatine and sphenoid bone
• Medially with vomer and nasal bone
• Inferiorly to the nasal concha
• Laterally to the zygomatic bone 

The maxilla's role in the skull

The maxilla has numerous roles pertaining to communication and mastication. These actions are a product of the bone structure (such as palate size altering speech, or holding the teeth in place) or by various muscles either originating from the maxilla itself or inserting into the bone. 

These include:

• Masseter muscle, aiding in mastication by elevating the mandible and raising the lower jaw
• Buccinator muscle. This aids in actions such as smiling, whistling, and holding food in position during chewing
• Muscles which alter facial expressions, including the Levator labii superioris alaeque nasi, Levator anguli oris, and Levator labii superioris muscles
• Zygomaticus minor muscle, which raises the corners of the mouth while smiling, and can cause dimples
• Orbicularis oris, which is responsible for the facilitation of speech and facial expressions

The maxilla also serves to protect major facial nerves such as the maxillary nerve and subsequent nerve branches including the infraorbital nerve. These are involved in relaying information of pain and sensation messages from the jaw, upper teeth, and nasal cavity mucosal membranes. 

Description of the maxillary sinuses

The maxillary sinus is the largest paranasal sinus located in the body of the maxillary bone. This sinus involves two pyramid-shaped sinuses situated slightly below the nasal cavity on both sides of the nose. Anatomically, the maxillary sinus consists of air-filled cavities which contribute to:

• Protecting the face and brain in the event of trauma
• Reducing the weight of the skull
• Imparting resonance to the voicebox
• Immune protection through the mucosal lining, similar to that of the nasal passage

Functions of the maxilla

Breathing and respiration

As the maxilla forms the lateral wall and floor of the nasal cavity, it is an essential structure responsible for breathing. It is also responsible for humidification and warming of air that is breathed in, contributing to the body's defences against infection. 

In abnormal facio-cranial development, the teeth of the upper and lower jaw are misaligned (malocclusion) and nasal breathing can become obstructed. This can reduce nasal airflow and increase nasal resistance, affecting the patient's ability to breathe normally. Malocclusion is also attributed to oral breathing and may increase the incidence of upper respiratory infection in children and adolescents.¹

Chewing and eating

The maxilla holds the upper teeth and forms a portion of the jaw, including the alveolar bone. This bone in particular forms the sockets which house the upper teeth. This makes the structure vital for chewing and eating. 

Studies have identified that masticatory performance may be altered depending on the length of jaw-elevating muscles and/or the position of the mandibular head in the fossa temporalis. Therefore, jaw position and size are responsible for developing a bite (or occlusion) responsible for the range of movement used for subsequent mastication.^2,3

Cases of malocclusion can further affect regular chewing actions such as cutting and grinding. Repercussions involve displacement of the lower jaw, mandibular joint pain, and tooth deterioration.

Speech production

Speech production (or phonation) is associated with the maxilla's involvement in forming the structure of hard and soft palates within the oral cavity alongside the base of the nasal cavity. This alters air flow which influences the depth and volume of the voice. Defects to the tissue structure caused by maxillary malformation can disrupt airflow and articulation during speech production.⁴

Secondly, premature primary tooth loss of the maxillary incisors has also been identified to affect speech articulation in children when compared to those who did not experience tooth loss, due to the altered airflow during the action of speaking.⁵

Aesthetic appearance

Whilst the maxilla is functionally vital, it also makes up a major portion of the face. Aesthetically, the anterior maxilla can affect the appearance of the upper front teeth and the overall shape of the facial skeleton, such as cheek contouring. 

Maxilla disorders and conditions

Infection

Inflammation of maxillary sinuses as seen in infections, such as maxillary sinusitis, is a common after-effect of cold or flu, or as an extension of dental infection. Inflammation to this area causes symptoms such as fever, pain or pressure near the cheekbone region, toothache, and a runny nose.

Bacterial infection or immunosuppression has also been noted for potentially increasing the progress of periodontal disease. In this condition, the alveolar process is subject to bone resorption, leading to tooth loss. 

Trauma 

Trauma to the maxilla through injury can cause fractures to the bone. This refers to when the bone becomes cracked or broken. Maxilla fractures, or midface fractures, are commonly categorized into the Le Fort classification:

Le Fort Type 1 (floating palate)

• Known as a Guerin fracture 
• The fracture is horizontal, separating the teeth and the upper face
• The fracture passes through the alveolar ridge, the inferior wall of the maxillary sinus, and the lateral nose

Le Fort Type 2 (floating maxilla)

• Fracture to the pyramidal structure of the maxilla
• Fractures can pass through the lateral wall of maxillary sinuses, nasal bones, alveolar ridge, and inferior orbital rim

Le Fort Type 3 (floating face)

• Injury is transverse or horizontal
• Injury begins in the nasofrontal area, extending to orbital walls, pterygoid plates, and zygomatic arch (cheekbones)
• Can cause complete dislocation of the midface from the base of the skull (craniofacial dislocation)

Congenital birth defects

Around 70% of all genetic disorders show symptoms that affect the maxillofacial region. Anatomically, congenital birth defects typically affect the development and growth of the maxillary bone which can affect major functions such as breathing and eating. 

A common example of maxillary defects includes cleft palate syndrome. This malformation is a common facial defect that arises during fetal development in around 0.2% of the population. This anomaly occurs when the soft or hard palate does not fuse correctly. This can cause a split in the roof of the mouth and upper lip, or, less commonly,  cause a cleft in the muscles of the soft palate. These gaps can cause difficulty feeding, difficulty swallowing, and a nasal speaking voice.⁶

Other disorders affecting the maxillofacial region can include: 

• Trecher Collins’s syndrome 
• Pierre Robin sequence 
• Achondroplasia 

Maxillary dental issues

As the maxilla houses the upper set of teeth, conditions involving bone resorption or structural abnormalities can cause dental issues. 

Periodontal disease or gingivitis normally affects those with poor dental hygiene. Resultant inflammation caused by infection can cause the alveolar process to break down over time leading to tooth loss.   

Maxilla recession, when the maxilla is underdeveloped or set back, can also cause oral/dental malocclusion complications arising from teeth grinding and wearing down tooth enamel. 

Maxilla surgery 

Maxillofacial surgery focuses on facial reconstruction after extensive trauma has occurred to the maxilla causing a major fracture/lesion, or may be offered to those in need of cosmetic surgery to correct jaw abnormalities. 

In some fracture cases surgery may not be required, as the bone may be able to heal without intervention. If trauma is extensive, or cancer is present, maxillary surgery can involve the removal of part, or all, of the upper jaw bone. 

Maxilla and orthodontics

Orthodontic treatments aim to correct jaw and occlusion abnormalities, reshape the dental arch, and improve aesthetic jaw/cheek contouring.

Depending on the targeted area for treatment, this may involve the use of;

• Orthodontic headgear – this describes either a device worn externally on the head or a reverse pull facemask
• Tooth extraction
• Anchorage implant control using archwires

Maxillary osteotomy may also be used to aid tooth alignment if orthodontic treatment is unsuccessful. This surgery can aid breathing and improve aesthetic appearance by expanding the palate and by opening the nasal cavity. 

Maxilla and maxillofacial prosthetics

Maxillofacial prosthetics aims to rehabilitate patients who may experience maxillo-facial injuries. Generally, reconstructive prostheses are utilized to replace missing or extensively damaged bone or tissue structures caused by trauma, congenital defects, or cancer treatment.  Implant placement can improve oral functions by:

• Restoring usable dentition
• Separating the mouth and nasal tissue
• Restoring the roof of the mouth
• Providing support for overlying soft tissue
• Improving aesthetic appearance

Maxilla and Maxillofacial Imaging

X-rays

X-ray imaging provides a 2D image of the maxillo-facial region through the use of ionizing radiation. This can be utilized to identify fractures or malformation of the maxilla. 

CT scans

During events of significant trauma, computed tomography scanning (or a CT scan) may be utilized to provide a series of 2D cross-sectional images of the facial region. 

MRI scans

Magnetic reconnaissance imaging (or MRI) is also useful in identifying cranial nerve deficits, vascular dissection and mass discovery within the soft tissue. However, this technique is not recommended for those with a pacemaker or other metallic foreign bones, particularly within the facial region. 

Summary

The maxilla is an important part of the skull. It performs a number of important activities, including speech production, feeding, and breathing. Maxillary functions can be affected by congenital diseases and facial trauma. There are a variety of treatment methods available to help with maxillary function.