Challenging the Misch SA4 staging protocol: one-stage lateral sinus augmentation with simultaneous implants in sub-3-mm residual bone height – a split-mouth case report

Objectives: This split-mouth case report evaluates the feasibility of simultaneous implant placement with lateral-window sinus augmentation in the severely atrophic posterior maxilla (Misch SA-4; residual bone height <3 mm), comparing two three-dimensional grafting strategies: an autogenous bone ring versus an allogeneic demineralized dentin block. Case presentation: A 52-year-old man presented with bilateral posterior maxillary atrophy (residual bone height: 2.8 mm on the right, 2.4 mm on the left). Simultaneous lateral sinus augmentation and implant placement were performed in a single surgical session. The left side received an autogenous corticocancellous bone ring harvested from the mandibular symphysis, while the contralateral side was reconstructed using a processed allogeneic demineralized dentin block. Tapered implants were placed into both graft types, achieving primary stability of 35 N·cm (autogenous) and 32 N·cm (allogeneic). Results: At the 6-month follow-up, both implants demonstrated osseointegration without peri-implant radiolucencies or sinus complications. Implant stability quotient values were 74 (autogenous) and 70 (allogeneic), both exceeding thresholds associated with predictable osseointegration. The patient remained asymptomatic throughout healing, and prosthetic rehabilitation was initiated. Conclusion: This case demonstrates that simultaneous implant placement with lateral window sinus augmentation can be successfully performed with residual bone heights below 3 mm when structural block grafts provide three-dimensional support. Both autogenous bone rings and allogeneic dentin blocks achieved comparable clinical outcomes, though the allogeneic option eliminates donor-site morbidity. While these findings support extending one-stage protocols to the extreme Misch SA4 spectrum, longer follow-up and larger comparative studies are needed to establish definitive recommendations.