The influence of bone block graft position on bone dimensional changes in staged onlay horizontal ridge augmentation: A 6-month retrospective cohort study.

OBJECTIVES: To analyze changes in bone dimensions and their modulating factor in bone dimensions 6 months after horizontal ridge augmentation using autogenous bone grafts. MATERIALS AND METHODS: Thirty-eight patients with horizontally atrophic alveolar ridges of a single edentulous tooth at the maxillary anterior site were divided into two groups based on the fixation position of the bone block during ridge augmentation surgery (H(0), vertical distance from the upper edge of the bone block to the alveolar crest). Patients were classified into a crestal level (CL) group if H(0) </= 1 mm and a sub-crestal level (SCL) group if H(0) > 1 mm. The width and height of the alveolar ridge were recorded using CBCT both before and 6 months after the augmentation procedure. RESULTS: The CL group comprised 20 patients with 23 implants, whereas the SCL group comprised 18 patients with 22 implants. All the augmentation sites exhibited vertical bone resorption. Vertical bone resorption in the SCL group (1.94 +/- 2.11 mm) was significantly higher than that of the CL group (0.61 +/- 0.64 mm). The SCL group showed significantly lower horizontal bone gain than the CL group (SCL: 1.02 +/- 2.30 mm; CL: 3.19 +/- 3.17 mm) at the cervical level. Peri-implant marginal bone loss increased significantly in the SCL group (1.00 +/- 2.71 mm) compared to the CL group (0.64 +/- 0.40 mm). CONCLUSION: The bone height decreased after horizontal ridge augmentation using autogenous onlay grafting. The fixation position of the bone block was a modulating factor. The SCL group showed more vertical bone loss, less horizontal bone gain 6 months after surgery, and more marginal bone loss after restoration.