Table 1.

Protocol for subperiosteal customized implant planning and treatment

Timeline	Stage description
Stage 1 (3 months preoperative) – Preoperative inferior implant removal and curettage	Inferior implant removal with thorough bone curettage. Oral amoxicillin 875 + clavulanic acid 125 mg was performed every 8 hours for three months. A removable mucosa-supported prosthesis was applied exclusively for social needs
Stage 2 (2 months preoperative) – Preoperative CBCT-based planning and custom-made implants design	Reverse planning was carried with the resulting DICOM data. Custom-made implants were designed by Bone Easy® with inputs from the surgeon. Alveolar reduction was required to accommodate the bar, prosthetic components, and the prosthesis. A 3D-printed guide was designed for bone height reduction and endosseous fitting areas. Custom-made implants were designed with partial endosseous support to connect plates and suitable osseointegration (Figure 3). Implants were designed with a 0.7 mm thickness to adapt to the maxillary and mandibular buttresses through fixation with 2 mm×6 mm SLA treated osteosynthesis screws. Bone grafting was planned to be performed simultaneously with the placement of the mandibular implant, mostly in endosseous areas.
Stage 3 (1 month preoperative) – Custom-made subperiosteal implants design manufacturing	The implant was manufactured by selective laser melting using Truprint 1000 SLM machine, using Sintmill® to place the implants on an indexation framework for posterior mechanization. After printing the base plate, the implants were fixed by supports and submitted to heat treatment – 1hour heating to 800º C stabilized for 30 minutes and cooling for 4 hours. The frame and the implant were separated from the base and placed on a milling machine using SUM 3D software to make M2 threads and re-mechanization of the implant and abutment connection. The plates were polished on the surface that contacts soft tissue. The surface that contacts bone was left rough. The grafting zone was left unpolished. The alveolar reduction guide and the implant insertion guide were both manufactured using a 3D printer on medical-grade plastic. All devices were sterilized with Ethylene Oxide before surgery
Stage 4 Surgical procedure	Surgery was performed under general anesthesia On the maxilla, a crestal incision was performed from tuberosity to tuberosity, with one relieving incision in the midline. Buccal and palatal flaps were raised, exposing the anterior nasal spine, the pyriform apertures, the canine fossae, the zygomatic buttresses, and the posterolateral maxillae. Alveolar reduction was performed using a piezoelectric handpiece. The implant was tested and fixed with osteosynthesis screws On the mandible, a crestal incision was performed around the arch to the contralateral side. Care should be taken not to injure the neurovascular bundle. External oblique ridges, both mental foramina, mandibular symphysis, and genial tubercles, were identified and exposed to serve as anatomical landmarks. A large bur was used to design the endosseous support aided by a guide. The implant was tested, fixed with osteosynthesis screws, and bone grafting was carried in the endosseous zone (Figure 4) Abutments were placed, and flaps were closed with 4/0 vicryl® Prosthetic impressions were taken immediately after closure, and a provisional prosthesis was successfully adapted 12 h later, prior to patient discharge