Abstract: Objective To measure the changes in bone height and bone volume in the transcrestal sinus floor elevation using absorbable collagen sponge by cone beam computed tomography (CBCT) and three-dimensional measurement by mimics, and to analyze the factors affecting bone formation in the sinus. Methods A total of 14 patients (24 implant sites) were selected from December 2019 to December 2021 in the Department of Stomatology, The First Affiliated Hospital of Dalian Medical University. All patients underwent transcrestal sinus floor elevation using only the absorbable collagen sponge by grinding method, and the lifting space of the sinus floor was maintained by collagen sponge and implant. The perforation of the sinus floor mucosa was recorded during the operation. The height of new bone was measured by CBCT before and 6 months after the operation. Immediately and 6 months after surgery, the protruding length (PL) and lifting length (LH) of the maxillary sinus floor were examined by CBCT. New bone height (NBH) was measured 6 months after the operation. The CBCT image data were imported into Mimics Research software. Mimics software was used for modeling and registration, and Boolean arithmetic was used to calculate the new bone volume in the maxillary sinus. The factors affecting osteogenesis were analyzed by one-way ANOVA and stepwise multiple linear regression, and the regression simulation prediction equation was established. Results A total of 24 implants were implanted and the short-term retention rate was 100%. The mucoperiosteum of the maxillary sinus floor was perforated at three sites during the preparation of the implant socket, and the perforation rate was 12.5%. There was no perforation in the process of collagen sponge filling and implant implantation. And all implants achieved good osseointegration on imaging 6 months after surgery and successfully loaded. The average new bone height in the sinus was（3.09±0.99）mm and the volume of new bone in the sinus is （320.24±85.79）mm³ 6 months after the operation. According to Pearson correlation analysis, there was a linear correlation between LH, PL, and NBH and new bone volume (P<0.05), one-way ANOVA showed statistically significant difference between sinus floor morphology groups (P<0.01), and new bone volume in the round group was higher than that in the oval and pointy round groups (P<0.05). Sinus floor morphology, gender, and PL were included in the multiple linear regression model, with a determination coefficient of 0.753. Conclusion Collagen Sponge, as the filling material for transcrestal sinus floor elevation without grafting technique, has good operation performance and can maintain the osteogenic space in the sinus cavity together with the implant to form new bone of a certain volume. In addition, the new bone formation may be related to LH, gender, PL, and sinus floor morphology.

Key words: Transcrestal sinus floor elevation, Collagen sponge, Bone increment, Bone volume