## 2 Materials and Methods
### Surgical Protocol  
All treatments were performed by the same expert operator. Dental and medical history was obtained and clinical examinations and panoramic radiographs were performed on all patients.  
Depending on the anatomical conditions, preliminary screening was performed on panoramic radiographs, with patients wearing thermoplastic radiographic guides with small gutta-percha balls as landmarks. When needed, for three-dimensional evaluation of bone volumes, cone beam computed tomography (CBCT) scans were taken still using the thermoplastic radiographic guide [20; 21]. Such guides were also used during surgery to facilitate the ideal implant positioning.  
Healthy periodontal conditions' stability and periodontal risk factors' control were achieved in all partially edentulous subjects. All patients received professional oral hygiene prior to the implant surgery and prophylactic antibiotic therapy with 2 g of amoxicillin plus clavulanic acid orally one hour prior to the intervention [22]. Patients allergic to penicillin were given 500 mg of clarithromycin 1 h prior to the surgery. Patients rinsed with a chlorhexidine mouthwash 0.2% for 1 min just prior to the intervention [23]. Local anesthesia was administered using mepivacaine with adrenaline 1:100,000 or 1:50,000.  
Crestal incisions were made and, in the presence of large bone volumes at implant sites, minimal flaps were elevated up to the coronal portion of the alveolar process. In the presence of reduced bone volumes, larger flaps were elevated, exposing the mental forarina in mandibles or the prominence of the maxillary sinuses.  
When present, residual teeth/roots were carefully extracted to minimize damage to the buccal plate, and sites were thoroughly cleaned from all granulation tissue. SPI-Contact (Thommen Medical; Grenchen, Switzerland) conical-cylindrical implants with a smooth 1.5 mm long collar, 11 mm in length, and 4.5 mm in diameter were inserted. Implants were placed following the protocol suggested by the manufacturer, except for the use of a 4.0 mm profile drill in order to underprepare the sites thus achieving a higher insertion torque. However, in a small number of patients (10%) Anyone (MegaGen Implant, Gyeongbuk, South Korea) implant 4 \(\times\) 11.5 mm were placed. In case of anatomic limitation, distal implants were distally tilted in the premolar areas (Figure 1) [24].  
Implants were placed with the 1.5 mm polished neck in a supracrestal position, also in the case of post-extractive implants. They were inserted with a torque of 70 Newton/cm and, once the motor stopped, implant stability was confirmed manually using the SPI-MONO torque ratchet ([PERSON], Grenchen, Switzerland). If one of the four implants could not be placed with a minimum torque of 35 Ncm, a fifth implant was added near to the implant which did not achieve the required torque [25]. If two or more implants could not achieve a torque above 35 Ncm, implants were submerged and loaded conventionally after 3 months [26].  
To decrease possible interference with the peri-implant bone, a manual bone profiler was used and healing abutments were placed. To maximize the primary wound closure, a platelet rich fibrine membrane (PRF) was placed to cover the site. PRF has also been shown to be successful in promoting hard and soft tissue healing even in oro-maxilofacialsurgery [27]. Subsequently, healing abutments were positioned and single resorbable sutures (Vicryl 4-0 SH1 plus 22 mm 1/2c; Ethicon, New Brunswick, NJ, USA) were placed.  
After surgery, analgesics (ibuprofen 600 mg) were suggested to be taken twice a day during meals on patient demand. A soft diet was recommended for 45 days. Oral hygiene procedures were professionally implemented during the days following surgery. Patients were instructed to avoid brushing at the surgical site and rinsing until suture removal, about 10 days after surgery. They were trained to clean the prostheses with a gauze moistened with 0.2% chlorhexidine, then to use a soft and then medium toothbrush and finally the waterjet.