Comparison of the long-term survival rates of dental implants in onlay versus interpositional bone grafts for augmentation of the atrophic mandibular ridge.

This retrospective cohort study was performed to compare the long-term survival rates of implants placed following onlay versus interpositional bone grafting in the atrophic mandible. Forty-eight patients with an adequate bone width who required ridge heightening were included. Twenty-six patients received an interpositional bone graft by sandwich technique (sandwich group) and 22 received an onlay graft (onlay group). The results showed a significant difference in implant failure: 17 of 52 implants (32.7%) placed in the onlay group failed, compared with 1 of 63 implants (1.6%) placed in the sandwich group (P < 0.001). Cox regression demonstrated a significantly lower hazard of implant failure in the sandwich group when compared to the onlay group (hazard ratio = 0.022, P = 0.002). Mean marginal bone loss (MBL) from implant placement to final follow-up was significantly lower in the interpositional sandwich group (2.98 ± 1.34 mm; mean follow-up 92.50 ± 20.45 months) than in the onlay group (4.50 ± 0.58 mm; mean follow-up 81.81 ± 18.54 months) (P = 0.004). In the multivariate analysis (general linear model), augmentation type (P < 0.001), follow-up duration (P < 0.001), initial bone gain (P = 0.030), and gingival biotype (P = 0.010) were significantly associated with MBL, while keratinized tissue width was not (P = 0.080). Within the limitations of this study, dental implants placed after interpositional sandwich grafting showed higher long-term survival and less MBL than implants placed after onlay grafting in the atrophic mandible.