## 2 Materials and Methods  
### Planning and Surgery  
To address the research purpose, the authors designed this study, which was conducted at the university clinic, and was approved by the Institution review board of the Department of Oral and Maxillo-Facial Sciences, \"Sapienza\" University of Rome (Ref: 038/2020). A 60-year-old male was selected to be included in this study, after attending the university clinic for implant treatment. The patient was in good health, displaying good oral hygiene (full mouth plaque score and full mouth bleeding score <25%), no need for guided bone -regeneration procedures, an absence of uncontrolled systemic diseases, a nonsmoker, and no signs of acute local inflammation at the time of implant placement. He had a failing dentition (critical loss of attachment, nonrestorable teeth, fractured teeth, root caries) in the mandible, with four mobile incisors that could not be used as a support for a surgical template, which created difficulties for correct matching, and a very narrow ridge in the frontal area. These factors predetermined the stackable bone-supported surgical template design for this patient. Radiopaque 3D markers were attached to the existing prosthesis to also serve as a radiographic template prior to CBCT acquisition. The denture was further refined with soft material (GC Soft Liner) before the acquisition of the CBCT scan, thus avoiding possible prosthesis movement and for the precise transition of the actual soft tissue of the patient in the planning software. The first CBCT was performed on the patient with Green 16 (Vatech, Fort Lee, NJ, USA) in standard conditions (94 kVp, 8.0 mA, 360\({}^{\circ}\) rotation, 9 s, FOV: 100 x 85, voxel size: 200 \(\upmu\)m) with the mouth closed, as separating the arches could cause radiological template movement. A protocol described by [PERSON] et al. [27] was implemented: after CBCT acquisition, an STL file of the denture was obtained using the laboratory scanner (Straumann 7 series lab scanner, Institut Straumann AG, Basel, Switzerland). Data obtained in digital imaging and communications in medicine (DICOM) format were then imported into a surgical planning software (coDiagnostiX, Institut Straumann AG). All of the acquisition parameters that could influence the accuracy of later steps in the generation of a virtual model, such as segmentation, as described by [PERSON] et al. [28], were assessed. Data in standard tessellation language (STL) format were imported into the software to prosthetically orient implant positions. CBCT data of the patients in DICOM (Digital imaging and communications in medicine) format and STL files of radiographic templates of edentulous patients were matched in the surgical planning software. Four conical dental implants (BLT, Institut Straumann AG) with a sandblasted/long-gri/acid-etched surface (SLActive) were planned for prosthetically-oriented positions at 35, 32, 42, 45 sites: two 4.1 mm \(\times\) 10 mm for the premolar sites and 3.3 mm \(\times\) 12 mm for the incisor sites, in accordance with the Straumann Pro Arch protocol, which consists of dental implant and SRA (screw-retained abutment) placement with immediate loading. A bone-supported surgical template with a stackable design was chosen to increase the predictability of bone reduction [29], as the patient had a very narrow ridge coronally in the frontal area, which needed to be reduced to obtain the appropriate width for implant placement. The first part of the surgical template was bone-supported and was designed to guide bone reduction. It was designed on the base of the segmentation converted to the STL file. The template was stabilized to the bone with two lateral fixation pins. The second part of the surgical template was positioned on top of the bone reduction template and served in implant placement. Several techniques to connect two different surgical templates are described in the literature, such as the use of magnets [30]. In the present study, the authors describe a more cost- and time-efficient technique.