Abstract: Objective To measure and classify the anatomical relationship between the root apex of the maxillary molars and maxillary sinus floor with Conebeam Computed Tomography, and to provide anatomical reference for clinical diagnosis and treatment as well as the assessment of operational risks. Methods CBCT images of 120 lateral maxillary molars in 60 healthy patients were selected from the database of the department of radiology of Suqian stomatological hospital. The distance between the maxillary sinus floor and root apex of the maxillary molars was measured with the 3dimensional computed tomography images using CBCT. The relationship between the maxillary sinus and the root apex of the maxillary molars was classified into 4 types by Shahbazian M method. Results The distance of buccaldistal root apex of first maxillary molar was the shortest. Among four types, the most common type was type Ⅰ(41.67%), type Ⅳ (19.85%) was most likely to cause maxillary sinusitis, and type Ⅳ (29.17%) occurred most in the buccaldistal apex of first molar. Conclusion The relationship between the maxillary sinus floor and root apex of the maxillary molars is individually different. Therefore, to improve the success rate of treatment and reduce the medical problem, the therapeutic schedules should be designed individually.

Key words: conebeam CT, maxillary sinus floor, maxillary molar, root apex