Infections from untreated upper molars and premolars can sometimes spread beyond the tooth roots into the nearby maxillary sinuses. This condition is known as odontogenic sinusitis, a sinus infection that originates from dental problems rather than typical respiratory causes.
Because the roots of upper back teeth sit very close to the sinus cavity, dental infections can easily extend into this space. Patients may experience facial pressure, persistent sinus congestion, bad taste, or discharge from the nose. Unlike common sinus infections, these cases often do not respond well to antibiotics alone.
Proper dental treatment such as a root canal or extraction is usually required to eliminate the source of infection and allow the sinus to recover.
Source: American Association of Endodontists clinical information on odontogenic infections.
