The optimal timing of functional endoscopic sinus surgery for odontogenic infections precipitated by retention cysts of the maxillary sinus was investigated.

Five adults who underwent functional endoscopic sinus surgery were examined.

The root apexes of all teeth that had odontogenic infection protruded into the maxillary sinus. All teeth with odontogenic infections precipitated by the retention cysts had percussion pain, indicating they had periodontitis and pulpitis around the root apex. They were vital teeth, indicating they did not have pulp necrosis. The small area of cyst wall attached to the floor of the maxillary sinus and root apex were left intact. The teeth that had odontogenic infections precipitated by retention cysts continued to be vital with no symptoms.

Functional endoscopic sinus surgery should be performed before periodontitis and pulpitis of the root apex progress to ascending pulpitis and pulp necrosis. In other words, functional endoscopic sinus surgery should be performed while the affected tooth is still vital.