Antibiotic prophylaxis with amoxicillin 2 g was administered to all patients 1 hour before surgery in all patients. All implants were placed in healed sites and the bone socket was prepared using a standard atraumatic technique with a sequence of drills of increasing diameter at the decided length. The implant site was always underprepared, taking in consideration the bone density. All implants (BTI Biotechnology Institute, Alava, Spain) had a microtextured surface and a conical shape. Shorter implants (6.5 mm) had a straight, noncutting, apex shape. They were all placed with at least 25 Ncm torque to obtain adequate primary stability. All short implants were wet with liquid pure platelet-rich plasma (P-PRP) and prepared using the protocol described elsewhere.

After implant placement, the flap was repositioned and sutured with 5-0 (Ethicon Inc, Johnson & Johnson, Piscataway, NJ) nonabsorbable sutures. Activated liquid P-PRP was sprayed onto or was injected at the suture site with the aim of enhancing primary soft tissue closure and further healing. Postsurgical instructions were provided to patients to control bleeding and avoid detaching sutures during the first healing period. Sutures were removed after 10 days.

A provisional restoration, made by composite resin (GC Gradia, GC Corporation, Tokyo, Japan), was delivered after a 5-month healing period for maxillary implants and after 3 months for mandibular implants. Immediately after placement the provisional restoration was not occluding. In the following 3 months, progressive loading was accomplished through monthly apposition of composite resin on the occlusal surface, achieving contact with the opposite occlusal surfaces after 2 months. After 3 months the provisional prostheses were substituted with the final prostheses made of metal-reinforced composite or metal-ceramic crowns. Composite crowns were applied when an opposite composite prosthesis (composite restorations or removable prosthesis) was present to avoid excessive abrasion over time. In all other cases metal-ceramic crowns were placed. Implant abutments all had internal connections. Platform switching was not applicable for 6.5-mm implants, but it was about 0.35 mm for longer implants, respecting the limitations of the abutment manufacturer (BTI Biotechnology Institute).