Influence of Peri-implant Bone Defects and Implant Diameter on Primary Stability: An In Vitro Study

Abstract Objective This in vitro study evaluated the impact of circumferential peri-implant bone defects on the mechanical stability of dental implants with different diameters under varying bone density conditions. Materials and Methods A total of sixty Helix GM ® titanium implants (3.5 mm and 4.3 mm in diameter) were inserted into standardized synthetic polyurethane blocks designed to simulate low (10 PCF), medium (20 PCF), and high (30 PCF) bone densities. For each bone density, half of the implants were placed in defect-free sites (controls), whereas the remaining implants had standardized cup-shaped peri-implant defects replicating bone loss commonly associated with peri-implantitis. Primary implant stability was quantified through insertion torque (IT) and removal torque (RT) measurements, and statistical comparisons were performed. Results Implant diameter and bone density significantly influenced implant stability ( p < 0.05). In defect-free sites, 4.3 mm implants showed higher insertion torque values than 3.5 mm implants across all densities, reaching mean values of 31.9 vs. 22.0 N·cm (10 PCF), 34.2 vs. 21.6 N·cm (20 PCF), and 46.8 vs. 31.1 N·cm (30 PCF). The presence of peri-implant defects resulted in a marked reduction in stability. Insertion torque for 4.3 mm implants decreased from 31.9 N·cm to 3.2 N·cm in low-density bone and from 46.8 N·cm to 21.6 N·cm in high-density bone. Similar reductions were observed for removal torque values. Conclusions Circumferential peri-implant bone defects significantly reduce implant mechanical stability, particularly in low-density bone conditions. Larger-diameter implants demonstrated superior stability across all bone densities, suggesting a potential biomechanical advantage in compromised bone environments.