The maxillary sinus is a hollow space under the cheek bones, which serves to lighten the skull, while providing a bony framework for attachment of the facial soft tissues. Often, the upper back tooth roots lie in or near the sinus floor (Figure 1). Because of this, the nerves which provide the upper back teeth with sensation may detect pressure changes that occur in the sinus. Changes in altitude and fluid in the sinuses from allergies and infections can apply pressure to the nerves, causing pain. This is important from a dental perspective, because sinus infections can be misdiagnosed as a tooth abscess (and vice versa).
Although most sinus issues are due to viruses and allergens (dust, pollen, etc.), these conditions produce inflammation (sinusitis), which causes fluid to accumulate in the sinus. The chronic presence of fluid in the sinus produces an environment conducive to bacterial colony formation. Thus, there is at least a theoretical pathway for bacteria to get into the upper teeth by way of the sinus.