## 2 Materials and Methods
Master cast and antagonists were mounted in a semi adjustable articulator using the actual functional occlusion of the patient. Then, a diagnostic prosthetic setup was made and tried-in the patient's mouth, in which the functional and aesthetic parameters were checked. A definitive metal reinforced, complete removable denture was delivered in both groups within four weeks after second surgery. After tissue healing was complete, low-profile OT Equator attachments (Rhein83) were screwed onto the implants using the OT Equator Square Screwdriver (Rhein83), with a torque range of 22-25 N cm, as specified by the manufacturer. The heights of the attachments ranged from 0.5 to 7.0 mm, depending on the height of the transition zone of each implant, which was easily measured using the colored Tissue Height Measurer Gauge (Rhein83) after removal of the healing screw. Next, spaces to accept the steel cage of the female housing were prepared in the mounting surface of the removable complete mandibular prosthesis, including small holes between the created space and the surface of the prosthesis to allow resin to escape. Silicone protective discs (Rhein83) were placed over the OT Equator attachments. Extra-soft retentive copings (yellow, 600 g) were initially inserted into the female steel housing, attached to the OT Equator, and finally secured to the prosthesis using self-curing acrylic resin while the patient held the prosthesis in occlusion, in a direct manner. When polymerization was complete, the prosthesis was removed and the silicone discs were removed. Excess acrylic was finished with laboratory burs, and the prosthesis was polished with laboratory grommets. One month after delivery of the prosthesis, the yellow retentive plugs were replaced with a stronger-grip type (pink, 1200 g). In both groups, the occlusion was developed to provide a lingualized occlusion with balanced contacts during function, avoiding any premature contact. However, when the opposing arch was a removable complete denture, the over-jet had to be left deliberately wide, two to five mm to avoid interference during function. Instructions were given to patients and recall visits were scheduled for occlusal adjustments and oral hygiene quality control every six months and, for retentive cap replacement, every year. Outcome measures were: implant and prosthetic success and survival rate; biological and technical complications; marginal bone loss; and patient satisfaction (Oral Health Impact Profile, OHIP-22). * Implant failure was considered if it exhibited mobility, assessed by tapping or swinging the implant head with the metal handles of two instruments, progressive marginal bone loss or infection, and any mechanical complication that rendered the implant unusable, although still mechanically stable in bone. * A prosthesis was considered a failure if it presented evidence of reprocessing except for accepted maintenance (includes patrice/matrix activation/repair/replacement, with a limit of two patrice or matrix replacements in the first year and five replacements in five years, and one relining of the base of the overdenture in five years). * Complications: Any biological (pain, swelling, suppuration, etc.) and/or mechanical (attachment loosening, fracture of the denture's base and/or fracture or detachment of the teeth) complications were evaluated. The marginal bone levels were evaluated using digital or conventional intraoral periapical radiographs taken with the parallelism technique by means of the Rinn centering device, at implant placement, at loading (baseline), and one year after loading. Radiographs were accepted or rejected for evaluation based on the clarity of the implant wires.