Underwood's septa
In anatomy, Underwood's septa (or maxillary sinus septa, singular septum) are fin-shaped projections of bone that may exist in the maxillary sinus, first described in 1910 by Arthur S. Underwood, an anatomist at King's College in London. The presence of septa at or near the floor of the sinus are of interest to the dental clinician when proposing or performing sinus floor elevation procedures because of an increased likelihood of surgical complications, such as tearing of the Schneiderian membrane. The prevalence of Underwood's septa in relation to the floor of the maxillary sinus has been reported at nearly 32%. Location of septa in the sinus Underwood divided the maxillary sinus into three regions relating to zones of distinct tooth eruption activity: anterior (corresponding to the premolars), middle (corresponding to the first molar) and posterior (corresponding to the second molar). Thus, he asserted, these septa always arise between teeth and never opposite the middle of a tooth. Different studies reveal a different predisposition for the presence of septa based on sinus region: Anterior: Ulm, et al., Krennmair et al. Middle: Velásquez-Plata et al., Kim et al. and González-Santana et al. Posterior: Underwood Primary vs. secondary septa Recent studies have classified two