## 2 Materials and Methods
### Surgical Procedures
The diameter of the last osteotomy was less than the fixture diameter to promote primary mechanical stability. Any biomaterial was applied before implant placement. Only an adsorbable hemostatic gelatin (Spongostan, Ethicon, Johnson & Johnson, New Brunswick, NJ, USA) was employed to promote clot formation and to retain membrane elevation. Flap adaptation and suturing were performed using 3-0 non-resorbable sutures (Vicryl; Ethicon, Johnson & Johnson, New Brunswick, NJ, USA). _Group C: Tilted implants_  
The first incision was made on the top of the alveolar crest, shifted on the palatal side to obtain the same level of keratinized mucosa on both sides of the flap. Then, distal and mesial vertical release incisions were performed to expose the underlying bone crest. The obtained full-thickness flap allowed us to preserve subperiosteal anatomical structures from injuries and to expose the canine draft and maxillary sinus, often available in transparency from the lateral bone wall. The tilted implant was placed first, in the vestibulo-palatal direction and adjacent to the mesial wall of the maxillary sinus; when possible, the apex of the fixtures engaged the inferior-medial wall of the inferior-distal cortical of the piriform opening. Every tilted implant was associated with an axial implant, placed according to the traditional system in the canine or lateral incisor region. Straight implant placement always occurred after tilted implant insertion according to their position and angulation. The implants placed for this group belonged to the TT line (Winsix, Biosafin, Ancona, Italy), which has a single implant body with a specific macromorphology to achieve maximum implant stability; it is also excellent for immature loading and differs in having either an internal hex (TTi) or an external hex (TTx). On a macromorphological level, they have double-threaded, double-principled coils for easy implant insertion with half the number of turns. The groove in the lower part of the loop decompresses the bone by dissipating forces and facilitates clot deposition. At the same time, it increases the implant surface by facilitating the neoformation of cells. The apex is conical and undersized by 1.3 to 1.8 with respect to the diameter of the implant; it is strongly tapered to obtain an osteotomic effect and to facilitate the inclined insertion of implants, even in the case of reduced bone availability. Because of their characteristics and eligibility for immediate loading, they were selected for this group by agreement of the surgeon and prosthetic. A lancoolate drill was employed to perforate cortical bone. A pilot drill of a 2.00 was applied to create an implant insertion site and to define the fixture's setting. A positioning pin was plugged to verify the implant location, emergence, and angulation. Drills of progressive diameter were employed up to the final fixture's diameter. The site was over-prepared vertically and sub-prepared transversely to promote primary mechanical stability. The implant neck was aimed to be positioned at bone level. The insertion torque ranging between 30 and 40 N-cm before final seating of the implant, allowing for immediate loading. A manual screwer was applied when incomplete seating of the implant occurred, and bi-cortical anchorage was established whenever possible. To compensate for the lack of parallelism between implants, angulated abutments (Extreme Abutment, EA(r) Winsix, Biosafin) at 30 degrees were screwed on tilted implants; straight abutments were screwed on axial implants. The flap was adapted around the structure. Suturing was performed using 3-0 non-resorbable sutures (Vicryl; Ethicon, Johnson & Johnson, New Brunswick, NJ, USA). Post-Surgical Protocol  
Immediately after surgery, intra-oral X-rays were performed to verify the correct implant position. Antibiotic therapy (amoxicillin and clavulanic acid 1 g or clarithromycin 1 g in case of allergy, twice daily for 7 days after surgery) and analgesic therapy (non-steroidal anti-inflammatory drugs, as needed) were prescribed for each patient.