The "Zero-Gap Protocol" for the Rehabilitation of Severe Jaw Atrophy via the Digital Workflow: A Preliminary Clinical...

Background: Severe jaw atrophy (Cawood and Howell Class V-VI) often renders conventional endosseous implantation unfeasible due to the lack of medullary bone and vascularization. This study presents a digital workflow for customized subperiosteal implants designed to eliminate bone segmentation errors and ensure optimal passive fit. Methods: Two clinical cases of severe atrophy-a full-arch maxillary rehabilitation and a unilateral partial rehabilitation-were treated using a prosthetic-driven CAD/CAM workflow. Key innovations included densitometric mapping using Hounsfield Units (HU) to identify high-mineralization zones (+1200 to +1800 HU) for strategic screw fixation. Intraoperatively, cobalt-chrome osteoplasty guides and PMMA check-templates were utilized to validate bone segmentation accuracy in vivo and regularize the cortical base. Results: The protocol achieved high precision with a monitored alignment deviation of 0.2 mm. At the 2-year follow-up, clinical and radiographic evaluations (CBCT) confirmed the total absence of gaps at the bone-implant interface. No signs of peri-implantitis, osteolysis, or progressive bone loss were observed, and soft tissues remained stable and healthy. Discussion: Success was driven by the rigorous management of the bone-implant interface and the use of preparatory surgical devices to bridge the gap between digital planning and surgical reality. The mechanical stability achieved through divergent fixation vectors prevented stress shielding by converting shear forces into compression, stimulating basal bone density according to Wolff's Law. Conclusions: The standardized digital workflow and the use of preparatory surgical devices in this preliminary study showed that complex rehabilitations can be performed with favorable short-term outcomes. While this approach reduces surgical time and biological stress, further prospective studies are required to confirm its clinical predictability and define next-generation subperiosteal implants as a valid alternative for the management of severely atrophic cases.