2.4. Surgical Procedures
CAVITY, CORTEX
The inserted MDIs were ball-type (Dentium, South Korea) and 2.0 or 2.5 mm wide and 10–14 mm long, depending on the available bone volume assessed on the preoperative CBCT scans. The two experienced specialists in oral surgery, both with >10 years of experience, inserted the MDIs. Participants in the 3-MDI group received 3 ball-type MDIs. Two posterior MDIs were inserted in the approximate region previously occupied by the distal surfaces of the canines. The third MDI was inserted at the midline, or as close as possible to the midline of the mandible (Surgical procedures were performed by two experienced surgeons after consulting a specialist in prosthodontics. The surgical techniques performed were the flapless or the open flap techniques, depending on the morphology and volume of the available bone. The open-flap technique was utilized when a pointed narrow ridge had to be leveled, or the mucosa of a denture-bearing area needed alterations. In cases when the flapless method was used, the first step was to punch a small amount of oral mucosa into the preparation site to ensure a stable drill position. A physiodispenser (W&H Implantmed, GmbH, Salzburg, Austria) and an external drill cooled by a saline solution were used. The bone was prepared using the pilot and final drill (Dentium drilling set); however, the final drill diameter was always smaller than the MDI diameter (1.3–1.8 mm for 2.0 mm wide MDIs; 1.8–2.3 mm for 2.5 mm wide MDIs). The depth of preparation was determined depending on the bone quality. The preparations were made one, two, or three mm shorter than the implant length (longer preparations were performed in a denser bone). The only exception was when the MDI had to end in the dense lower mandibular cortex; in that case, the whole mini-implant length had to be prepared, as the tip of the MDI could not advance into the dense D1 bone. Antibiotics were administered one hour before surgery for prophylactic reasons (2 g amoxicillin with clavulanic acid or 600 mg clindamycin). Local anesthesia was administered prior to the surgery (Ubistesine forte 4% or Mepivastesin 3%, 3M). Each MDI was inserted into the preparation site and rotated clockwise, exerting a downward pressure (self-tapping insertion technique). The implants were transferred into the preparation hole with a plastic carrier from the original package and rotated until the plastic carrier broke; then, the thumb wrench was used and finally, the torque wrench. The whole roughened threaded MDI surface had to be inserted into the bone. The transmucosal part of the smooth MDI profile emerged from the attached mucosa into the oral cavity with the platform and the ball-type head for OD retention. The final MDI insertion torque values varied between 30 and 55 Ncm in both groups (3-MDI and 4-MDI groups, respectively).All patients were given the following postsurgical instructions: no alcohol or smoking for two days, no hot beverages, ice packs for cooling, antiseptic mouth rinse (chlorhexidine gluconate 0.12%), and analgesics when necessary (nonsteroid anti-inflammatory drugs). Detailed instructions on how to maintain oral hygiene were also provided.