## 2 Materials and Methods  
This study was designed as a comparative, case-control, in vitro study and was performed at the Department of Medicine, Surgery, and Pharmacy of the University of Sassari, Italy. Mechanical tests were performed at the Department of Engineering of the University of Ferrara (compressive test), and at the Faculty of Materials Science and Engineering, Warsaw University of Technology (dynamic test). Data were analyzed at the Department of Medicine, Surgery, and Pharmacy of the University of Sassari. A prosthetically driven, virtual implant planning of a training model simulating a complete edentulous mandible (Dentalstore & Edizioni Lucisano SRL, Milan, Italy), to be rehabilitated with six implants, was considered for this in vitro study. The model was digitalized using an intra-oral scanner (Mediti i700, Mediti Corp., Seoul, Republic of Korea). After that, cone-beam computed tomography of the same model was performed (Cranex v.3 Dx, Soredex, Globatech Srl, Rome, Italy). Two medical-certified software programs were used to design the virtual wax-up (DentalCAD 3.1 Rijeka, Exocad GmbH, Darmstadt, Germany) and then to virtually plan the implant's position (RealGUIDE 5.1, 3 DIEMME, Cantu, Italy). The DICOM (Digital Imaging and Communications in Medicine) and STL (Standard Triangle Language) files were matched using common reference points. Then, six OSstem TSIII implants (Oostem Implants, Seoul, Republic of Korea) of 4 mm in diameter and 10 mm in length were planned in the lateral incisor, first premolar, and first molar positions. Implants were virtually planned fairly perpendicular to the occlusal plane, with a discrepancy of 6\({}^{\circ}\) (lateral incisors), 4.5\({}^{\circ}\) (premolars), and 0\({}^{\circ}\) (molars). In addition, three anchor pins were planned in the buccal position. After virtual implant planning was completed and approved, the virtual implant positions were exported to dental CAD software (DentalCAD 3.1 Rijeka, Croatia, Exocad GmbH). (Figure 1) According to the protocol of the present research, a one-piece restoration, composed of 12 dental units, was designed with two different configurations, named groups 1 and 2. In group 1 (test group), a solid (monolithic) restoration was designed, while in group 2 (control group), a cutback was performed to allow the placement of a metal reinforcement (Figure 2). After the CAD process was completed, the two prototype models were printed (CAM, computer-aided manufacturing) in a qualified milling center (New Ancorvis SRL, Bologna, Italy) using a certified resin material (Polycarbonate-like, VisJet M2R-TN [3D System Inc., Rock Hill, SC, USA], [https://3 dprinting.com/products/resin/visjet-m2r-tn/](https://3 dprinting.com/products/resin/visjet-m2r-tn/) (accessed on 15 July 2024). Six digital lab analogs (Oststem Europe s.r.o., Prague, Czech Republic) were screwed into each prototyped model. Finally, six OT Equator attachments (Rhein'83, Bologna, Italy) were screwed onto the digital analog at 25 N/cm, according to the company's guidelines. All the temporary restorations and the metal reinforcements were milled in a private center (Just Dental Polymers, Vigonza, PD, Italy). In the test group (composite ONLY), a patented composite material, made of poly(methyl methacrylate), leucite, and alumina, was used (ONLY, Just Dental Polymers, Vigonza, Italy). The mean average molecular weight of PMMA is \(\sim\)350,000 according to gel permeation chromatography (GPC) analysis. The inorganic percentage is about 10-12%. The ratio of alumni and leucite depends on the color. The composition of leucite is as follows: SiO2, 70-75%; Na2O, 12-15%; K2O, 0-1.5%; CaO, 7-12%; MgO, 0-5%; Al2O3, 0.1-2.5%; Fe2O3, 0-0.5%. In the control group, conventional titanium-reinforced PMMA was used (PMMA group). All the materials were assembled by an expert dentist and dental technician (MT) as follows. Temporary cylinders were shortened and screwed onto the OT Equator attachments at 15 N/cm. Then, the screw-hole was closed with Teflon.