Abstract: BACKGROUND: With the development of oral implantology, implant restoration has gradually become the first choice of restoration after missing teeth, and bone augmentation procedures have led to the expansion of implant indications and the improvement of the success rate of implant restoration. However, the long-term stability of bone height, width and volume after bone augmentation surgery has been one of the clinical difficulties for oral implantologists.
OBJECTIVE: To measure and analyze the bone width, height, and volume of different sites in the bone augmentation area at different time points using cone-beam CT and an automatic image alignment program.
METHODS: Seventeen patients with severe bone defects in the upper anterior region who underwent Onlay bone block grafting in the external oblique region were recruited from the Department of Stomatology, Zhejiang Tongde Hospital. There were 10 males and 7 females, with a mean age of (45.88±12.47) years. The cone-beam CT scans of the patients' Onlay bone grafts were taken at five time points: preoperatively, immediately postoperatively, 6 months postoperatively, immediately post implantation, and 6 months post implantation, and then were statistically analyzed for alveolar bone volume, width, and height in the bone augmentation area, as well as for the difference in the alveolar bone volume of the bone incremental area between patients of different sexes and age.
RESULTS AND CONCLUSION: (1) The alveolar bone volume in the bone augmentation area was higher immediately and 6 months after bone grafting than before bone grafting (P < 0.05) as well as was higher immediately after bone grafting than 6 months after bone grafting (P < 0.05). The alveolar bone height in the bone augmentation area was higher immediately and 6 months after bone grafting than before bone grafting (P < 0.05). The horizontal width of the alveolar bone at various sites in the bone augmentation area immediately and 6 months after bone grafting was higher than that before bone grafting (P < 
0.05). (2) There was no significant difference in the volume of bone graft resorption at various sites in the bone augmentation area between males and females immediately and 6 months after bone grafting (P > 0.05). Pearson correlation analysis showed a positive correlation between age and the change in bone augmentation area volume immediately and 6 months after bone grafting, but the difference was not statistically significant (P > 0.05). (3) Twenty-five dental implants with completed implant restorations functioned normally, and the survival rate of the implants was 100%. To conclude, Onlay bone graft implant restoration in the upper anterior region can significantly improve insufficient bone with favorable outcomes. However, there is some amount of bone resorption in the bone augmentation area at 6 months after Onlay bone grafting and it is necessary to open up the second surgical area. Clinicians should consider different bone augmentation procedures in accordance with the specific circumstances. 

Key words: external oblique line, Onlay bone grafts, bone augmentation, upper anterior bone defect, implant restoration, engineered tissue construction