Abstract: PURPOSE: The aim of the study was to evaluate the clinical effectiveness of conservative surgery for odontogenic cysts (OCs) intruding into posterior part of maxillary sinus through clinical and radiological examination, as well as to discuss its superiority and validity. METHODS: This retrospective study included patients with OC intruding into posterior part of maxillary sinus from December 2011 to December 2014. Clinical and radiological examinations were performed for each patient, and both evaluations had three grades of excellent, good and poor. Cases evaluated as excellent and good were considered success. Fisher's exact probability was performed to compare the effective rate of the 2 examinations with SPSS 17.0 software package. RESULTS: There were 21 cases who underwent conservative surgeries, 19 out of them came back for follow-up. The follow-up interval was from 3 months to 31 months (mean, 14.4 months). Suppurative inflammation was observed in 1 patient, and the success rate was 94.74% (18/19). Two cases presented mild facial paresthesia but recovered 3 months later. Facial asymmetry and permanent nerve damage were absent. Relapse occurred in 1 case of keratocystic odontogenic tumor, and conservative surgery was re-performed. CT images showed sinus cavity increased after surgery, and new bone formation could be seen on the sinus floor. The maxillary sinusitis disappeared or recovered significantly. CONCLUSIONS: Sinus mucosa and bony wall preservation can protect normal physiological function and contour of the maxillary sinus, leading to fewer postoperative complications and higher success rate.

Key words: Odontogenic maxillary sinus disease, Conservative surgery, Efficacy evaluation