Because of the close contact between maxillary sinus and maxillary posterior teeth, procedural errors such as perforation of the sinus may occur during surgical intervention resulting in oroantral communication, which if not corrected, would develop into a fistula. The aim of this study was to evaluate the relationship between maxillary posterior teeth and maxillary sinus floor in a population of the western area of Saudi Arabia, and if age, gender, and size may affect such distance. This retrospective study evaluated 539 cone-beam computed tomography (CBCT) radiographs of patients over 20 years of age. Patients were divided into four groups according to age: group I (20-30 years), group II (31-40 years), group III (41-50 years), and group IV (more than 50 years). From coronal and sagittal images of CBCT, the vertical distance between the posterior maxillary root and the maxillary sinus was measured and classified according to its proximity to the maxillary sinus. Gender and size did not significantly affect the distance between maxillary posterior root and maxillary sinus. However, there was a significant increase in this distance with increased age. Mesiobuccal root of the second molar was the nearest root to the maxillary sinus (0.8 ± 1.62, p < 0.001), while the buccal root of the first premolar was the farthest root (5.39 ± 3.26, p < 0.001). Regarding the population of this study, the buccal roots of the second molars are the closest to the sinus floor. Complications associated with maxillary molar extraction and implantation are greater at a younger age. Because the distance between posterior maxillary teeth and maxillary sinus was mostly type 1 (0-2 mm), clinicians are advised to perform CBCT to get a better understanding of the relationship between maxillary posterior roots and maxillary sinus before surgical intervention.