The maxillary sinus is a cavity located within the cheek bone. It is a pyramid shaped, growing space with a membrane lining the sinus called the Schneider Membrane. The ends of the roots of the upper back teeth are close to the maxillary sinus and in some cases, even inside of it.
The maxillary sinus helps in moisturizing and heating up the air when breathing, also playing an important role in vocal resonance and diminishing the weight of the head.
A baby’s maxillary sinus is almost nonexistent; as opposed to an elder person whose sinus is expected to be large. The maxillary sinus’ volume in an adult is 15mL, growing an average of 2mm per year. The natural process of sinus enlargement is called pneumatization.