2.2. Inclusion and Exclusion Criteria
eugnathic
An edentulous mandibular alveolar ridge width < 5.5 mm in the interforaminal region was the determining factor for inclusion in this study. Participants with wider ridges were excluded, as they could receive standard-sized implants. The available bone volume and length were measured on preoperative CBCT scans and digital panoramic radiographs. All participants were also required to have a eugnathic jaw relationship in their centric position. General exclusion criteria were not different from those accepted for any implant placement and were based on general health issues [Randomization in assigning edentulous participants into the 3- or 4-MDI groups was completed by assigning odd and even numbers to the participants. The first participant was assigned an odd number, the second an even number, and so on. Each participant assigned an odd number received 4 MDIs, while each participant assigned an even number received 3 MDIs in the mandible. However, the surgeons who inserted the implants were not blinded to the procedure; neither were the prosthodontists who manufactured and loaded the overdentures. The costs of MDIs were covered by the research grant No. 1218/2014 (Croatian Science Foundation), and the costs of mandibular ODs were covered by the health insurance of each participant. All MDIs were inserted and all new ODs were manufactured during the first two years of the study (from October 2014 to December 2016).