Abstract: Objective　 To analyze the height of the alveolar bone, and the relationship between the root of maxillary posterior teeth and the maxillary sinus floor, to provide a reliable reference for clinical diagnosis and treatment. Methods　Five hundred adult patients referred to cone-beam computed tomography (CBCT) scans for medical reasons were selected for study. The height of alveolar bone and the shortest distance between maxillary sinus floor and root tip were measured. The relationship between the maxillary sinus wall and the roots of the posterior teeth was classified, including vertical and horizontal relationships. These data were grouped according to the teeth and age, and the differences in the teeth and age were analyzed. Results　 The height of the alveolar bone of the maxillary premolars was11.31±7.39 and 9.52±7.98mm, which was significantly higher than that of maxillary molars, and the height of the alveolar bone decreased with age. The average distance between the mesiobuccal root of the second maxillary molar and the maxillary sinus floor (1.73±3.63 mm) was the shortest among the maxillary roots. The average distance between the root of the first maxillary premolar and the maxillary sinus floor (9.53±5.79 mm) was the longest among the maxillary roots. The distance decreased with age. In the vertical relationship between the maxillary molar root and maxillary sinus floor, the percent of three roots not in contact with the floor was significantly higher than other categories. In horizontal relationship, the floor of maxillary sinus was most frequently observed at the level between the bifurcation and apices of roots. The relationship between root and maxillary sinus was more closely related with the increase of age. Conclusions　The relationship between the maxillary sinus floor and root is individually different according to the teeth and age. Using the CBCT can accurately analyze the anatomical structure of the maxillary posterior region, design the individually therapeutic schedules, and reduce the occurrence of the iatrogenic problem.

Key words: Cone-beam computed tomography, maxillary sinus floor, alveolar bone, the root of maxillary posterior teeth