Purpose: To evaluate the ideal implant insertion time in human bone biopsies after sinus elevation with a composite graft consisting of an equal amount of biomaterial and autologous bone, by comparing the bone regeneration obtained 4 to 5 months after surgery with that obtained after 6 to 8 months, and using the adjacent native bone as reference. Materials and Methods: Twenty-six biopsy specimens of 11 patients were analyzed. Two groups were created depending on the time of implant insertion: group t1 at 4 to 5 months (n = 13) and group t2 at 6 to 8 months (n = 13). The same volume of grafted bone and native bone were analyzed for each biopsy with microcomputed tomography (microCT) and gene expression analysis. Results: Statistically significant differences were found in bone mineral density (BMD), bone volume fraction, and trabecular separation (TbSp) between native and grafted bone in both groups, with higher grafted bone values, except for the variable TbSp, which was lower in the grafted bone. This decrease in TbSp in the grafted bone in both groups can be explained by the significant increase in trabecular thickness in group t2 and the trabecular number in group t1, compared with native bone. No significant differences were found between the two groups in the morphometric parameters and BMD of the grafted bone. Also, no significant changes in the messenger RNA (mRNA) levels of bone formation, bone resorption, and inflammatory markers were found between both groups, with the exception that alkaline phosphatase mRNA levels were significantly lower in group t1 relative to native bone. Conclusion: This composite graft showed no differences in threedimensional microstructure, BMD, or at the molecular level between 4 to 5 months and 6 to 8 months of healing time. Thus, this time can be shortened to 4 months with the security of a grafted area of mature bone. Keywords: clinical study, composite graft, dental implant, gene expression, microcomputed tomography (microCT), sinus lift (SL)