## 2 Materials and Methods
### Surgical Protocol  
In this laboratorial study, four artificial bone models (Bonemodels(r), Castellon, Spain) were used, simulating four distinct bone densities according to the classification proposed by [PERSON] and [PERSON] [20] (Figure 1). Although this classification was originally developed for human bone, previous studies have used polyurethane blocks with similar mechanical properties to represent D1-D4 bone types, allowing reproducible comparisons in in vitro settings [20; 21]. Each bone model was sectioned into two halves to comply with the field of view (FOV) constraints of the CBCT scanner (NewTom Go, NewTom I Cefla S.C., Imola, Italy), resulting in eight mini bone blocks, each comprising two density zones (D1/D2 and D3/D4) (Figure 2). Each mini block was identified with an alphanumeric code (e.g., A1 and A2 corresponding to the two halves of the first block). All mini blocks were scanned using CBCT and intraoral scanning (KaVo LS 3, Nobel Biocare USA, LLC, Yorba Linda, CA, USA) to enable digital implant planning and the subsequent design of the surgical guides. The coDiagnostiX(r) software (Dental Wings GmbH, Chemnitz, Germany) was used for virtual planning of implant positioning and for the design of the surgical guides (Figure 3). Each guide was labeled with the identifier of the corresponding mini block. The guides were fabricated using a 3D printer (Phrozen Sonic Mini 8K, Phrozen Technology, Hsinchu City, Taiwan) with ABS-like resin (Creamy White, Phrozen Tech Co., Ltd., Xiangshan Dist., Hsinchu City, Taiwan). After printing, all guides underwent post-processing, including washing and polymerization. Titanium sleeves (Straumann(r), Institut Straumann AG, Basel, Switzerland) with a 5/5 mm diameter were manually inserted into the guides. Implant placement was performed using guided surgery kits specific to each implant type, supplied by Straumann(r), in combination with the iChiopro surgical motor (Bien-Air, Bienne, Switzerland). Figure 1: Artificial bone models with four distinct bone densities (D1–D4), shown from the inferior perspective. Figure 2: Mini bone block (each block containing two different bone densities). A total of 120 implants were inserted into the mini bone blocks following two distinct surgical protocols:  
Partially guided surgery using the milling cutter drill (\(n=60\));  
Partially guided surgery without the milling cutter drill (\(n=60\)). The implant placement was performed by the same experienced dentist, who had formal training in implantology and digital dentistry and was fully familiar with the guided surgery protocols and kits employed. Using a single operator ensured consistency across procedures, although it limited the generalizability of results due to the absence of inter-operator variability. The drilling and placement protocols were conducted in accordance with the manufacturer's guidelines, tailored to the specific implant design and simulated bone density. Following implant placement, a final digital impression was obtained using appropriate scan bodies from Straumann(r). For BL and BLT implants, CARES(r) RC Mono Scan bodies (\(\mathcal{O}\)4.1 mm, height 10 mm, PEEK/TAN) were used, and for BLX implants, CARES(r) RB/WB Mono Scan bodies (\(\mathcal{O}\)3.8 mm, height 10 mm, PEEK/TAN) were employed. Scanning was performed using the Trios v.4 intraoral scanner (3 Shape(r), Copenhagen, Denmark), for the purpose of evaluating deviations between planned and final implant positions. Deviations between the preoperative virtual planning and the postoperative implant position were assessed using the \"Treatment Evaluation\" tool in the coDiagnostiX(r) software (Institut Straumann AG, Switzerland). To ensure precise overlay of the pre and postoperative scans, three small dots of dental composite resin were applied to each bone block as fiducial markers. These markers facilitated the identification of anatomical landmarks during the digital alignment process, ensuring optimal overlay precision (Figure 4).