Odontogenic sinusitis (Sinusitis) refers to inflammation of the maxillary sinus, secondary to dental disease, particularly that of the maxillary molars. If the dental nerve (pulp) is damaged either by severe caries or by periodontitis, it dies. If the tooth does not receive prompt root canal treatment and/or the treatment is not adequate, then the mucous membrane of the maxillary sinus can get inflamed, leading to sinusitis. Typical symptoms include Facial pain/pressure, Nasal stuffiness, Nasal discharge, Loss of smell, Cough/congestion and additional symptoms may include Fever and bad breath. The Differential Diagnosis is a chronic rhinitis. Risk factors for Odontogenic sinusitis are bad root canal fillings and Pulpal gangrene. The treatment is a adequate root canal treatment and Antibiotics. If a swollen membrane or scar tissue from a damaged membrane obscures natural drainage from the sinus, the condition will not improve even if the diseased tooth is treated. In such cases, drainage must be facilitated via the nose by means of a minor surgery.