Nasal septum (Obwegeser) osteotome is a basic instrument used for separating the nasal septum and maxilla during Le Fort I osteotomy. If this instrument is placed too high or tilted into the nasal cavity, sphenoid sinus and various adjacent vital structures may be damaged and serious bleeding, neurological complications, or blindness or even death may occur. The aim of this study is to determine the margin of safety for damaging the sphenoid sinus and the adjacent structures with nasal septum osteotome in the young adults: 49 male and 51 female patients between 15 and 25 ages who required a Cone Beam Computed Tomography (CBCT) examination as part of their routine examination. In the study sample consisting of CBCT images, the aimed surgical line, the line between spina nasalis anterior and vomer and the base of sphenoid sinus (undesired line), and tilt angle between surgical and undesirable lines were measured. As the primary outcome of this study, margin of safety for damaging the sphenoid sinus and adjacent vital structureswith nasal septum osteotome during Le Fort surgeries in young adults recommended as 5 mm and 12(0). For this reason the importance of planning with preoperative CBCT before Le Fort I osteotomies has been revealed.