Loading Protocols for Dental Implants Placed in Healed Fully Edentulous Maxilla

Surgical protocol Prior to surgery antibiotic prophylaxis (2 g amoxicillin with clavulonic acid or, in case of allergy, 0.6 g clindamycin, 1 hour before the procedure) and antiedema therapy (0.004 g dexamethasone 1 hour before the procedure) was administered. Patients rinsed their mouth using 15 mL of 0.12% chlorhexidine solution for 1 minute preoperatively. The surgical procedures were performed under local anesthesia using 4% articaine, 1:100.000 epinephrine. Centers of the intended implant sites were marked according to the reference marks present in the patient's existing complete removable denture that had been used as the radiographic stent. A midcrestal incision was made, then full-thickness buccal and palatal flaps were elevated. Implant sites were prepared by strictly adhering to the manufacturer's protocol for low-density bone using drills of increasing diameter (Institut Straumann). To provide adequate primary implant stability, underpreparation was performed: 1. In low-density type D3 bone, the profile drill was skipped; and 2. In low-density type D4 bone, the final sequence and profile drills were skipped. Intermittent drilling under copious irrigation was performed with low hand pressure and a physiodispenser running between 600 and 800 rpm. A total of 144 sites were prepared, followed by placement of 144 SLActive surface (Bone Level Tapered, Institut Straumann) implants. Bone quality was assessed according to the Lekholm and Zarb classification. In sites with dehiscence or fenestration resulting in an exposed implant surface, localized bone augmentation was performed using bovine-derived xenograft (Geistlich Bio-Oss, Geistlich, Wolhusen, Switzerland) and covered with a type 1 collagen membrane (Geistlich Bio-Gide, Geistlich). Healing screws (Institut Straumann; NC healing abutment Ø4.8 mm conical 5 mm and RC healing abutment Ø5 mm conical 6 mm) were placed and primary wound closure was achieved with 5-0 single resorbable sutures (AssuCryl Lactin, Assut Sutures of Switzerland, Pully-Lausanne, Switzerland). Patients were discharged with recommendations regarding dietetic and hygienic regimens. Antibiotic protocol consisted of 2 g amoxicillin with clavulonic acid (divided into 2 doses) or, in case of allergy, 1.8 g clindamycin daily (divided into 3 doses) for the following 5 days. Antiedema therapy (0.004 g dexamethasone) was administered 24 hours postoperatively. Prosthetic protocol After dental implant placement, patients were randomly assigned to immediate loading or early loading groups.

Implants for patients from Test Group were immediately loaded using S-R abutments (Institut Straumann) with temporary restorations. Patients from Control Group did not receive any kind of prosthetic temporization and were left with healing abutments. For Test Group an open-tray impression technique was used for provisional restoration. Impressions were made using: ASilicone material (Hydrorise implant, Zhermack, Badia Polesine, Italy), splinted impression posts (RC and NC impression post, Straumann) and a plastic impression tray (Miratray, Hager Werken, Duisburg, Germany). Provisional restorations were made digitally with polymethyl methacrylate (PMMA) (Telio CAD, Ivoclar Vivadent, Schaan, Lichtenstein). Plaster models with scan bodies were digitized with a laboratory scanner (3Shape E1, 3Shape, Copenhagen, Denmark). Final virtual design of provisional restoration was performed with 3D design software (exocad Matera 2.3, Exocad, Darmstadt, Germany). Drilling of PMMA blocks was performed in a 5-axis milling machine (Zenotec Select, Wieland, Pforzheim, Germany). The following final Straumann screw retained abutments for the prosthetic bridge (Institut Straumann) were chosen according to implant angulation and surrounding soft tissue height. For the interface between the screw-retained abutments and final prosthetic work, copings for screw retained abutments (Institut Straumann) were used and bonded to the final prosthesis.

At the end of the 6-week healing period for both groups, definitive prosthetic restorations were delivered. In preparation for the definitive prosthesis, a final open-tray impression was taken with an individual tray and polyether material (Impregum Soft, 3M Espe, Seefeld, Germany). An analog ceramic layering technique was performed in the process of producing a porcelain fused to metal restoration (Shofu Vintage Halo Porcelain, Shofu Dental Corporation, Ratingen, Germany). The metal framework was made using cobalt chromium metal powder material (Starbond Easy Powder 45, Scheftner, Mainz, Germany) with additive manufacturing technologies (EOS, Krailling, Germany).

Inclusion criteria

• Patients in good general health with no current history of systemic disease or medication use that could interfere with the treatment;
• Patients with complete maxillary edentulism who had lost their teeth at least 6 to 8 weeks prior to the proposed ''allon- six'' implant rehabilitation; and
• Clinically compliant patients consenting to be enrolled into the study.

Exclusion criteria

• Active or chronic disease that affects bone metabolism or wound healing;
• Diminished mental capacities that could mitigate the ability to comply with the protocol;
• Residual roots or teeth;
• History of maxillary augmentation;
• Oral carcinoma or inflammatory changes; and
• History of head and neck radiotherapy.