Evaluation of an Innovative Hybrid Macrogeometry Dental Implant in Immediate Extraction Sockets: A Histomorphometric Pilot Study in Foxhound Dogs

A preclinical pilot study was performed to evaluate the safety, efficacy, primary stability, and wound healing of a hybrid dental implant with a unique macrogeometry design in which the coronal section is narrower and cylinder-shaped followed by a wider, tapered apical portion, each comprising approximately one half the length of the implant. Eighteen hybrid macrogeometry-designed dental implants were placed bilaterally into three foxhounds in the mandibular third and fourth premolar and first molar (P3, P4, and M1, respectively) extraction sockets of different dimensions immediately following full periosteal flap elevation and removal of teeth without socket grafting. Bone plate thickness, implant position and depth, gap distance, and insertion torque values were measured following implant installation. Surgical sites were healed uneventfully for 3 months, and then samples of soft and hard tissues surrounding the implants were retrieved to perform light microscopic and histomorphometric analyses. All 18 implants were stable and osseointegrated both clinically and radiographically. The analyses revealed that the amount of hard tissue alteration and bone fill that occurred during the healing period was significantly influenced by the thickness of the bone plate, the size of the horizontal buccal gap, and the implant diameter, position, and depth within the extraction socket. The P3 and P4 hybrid implants placed approximately 1.0 mm subcrestal from the interproximal height of bone with less gap distance (≤ 1.0 mm) exhibited minor to modest (1.5 to 2.0 mm) crestal bone remodeling relative to the implant platform. Conversely, M1 implants positioned with greater depth (≥ 2.0 mm) and gap distance (≥ 2.0 mm) that were evaluated in a buccal-lingual dimension exhibited minimal crestal change with first bone-to-implant contact within 1.0 mm (range: 0.00 to 0.89 mm) of the machined-collar surface. The thicker lingual bone plate on all M1 implants was relatively maintained and unaffected. The apical half of the implant provided high initial stability (range: 65 to 100 Ncm). The mean percentage of bone-to-implant contact was 56.34% (range: 40.15% to 72.04%). This preclinical study provided clinical and histologic evidence to support the safety and efficacy of a new hybrid macrogeometry implant design that achieved excellent primary and secondary stability in immediate extraction sockets without grafting.