The maxillary sinus floor is formed by the alveolar process of the maxilla. Frequently, the roots of maxillary molars and premolars may protrude into the sinus cavity, with only a thin membrane separating them. Endodontic infections are characterized by mixed biofilms of anaerobic and proteolytic bacteria that can infect the root canal space and accessory anatomy of those teeth producing apical periodontitis. Due to the close relationship with the maxillary sinus, the persistence of apical periodontitis could potentially lead to odontogenic sinusitis. Understanding maxillary sinus anatomy and its relationship with the posterior maxillary dentition is crucial for diagnosing this entity.