Feasibility of Using a Flex Constant to Monitor Implant Stability Changes in a Porcine Model

This experimental study investigated the feasibility of using a flex constant (displacement-to-force ratio) to monitor changes in dental implant stability in a porcine model. The stability change was incurred by thawing a porcine model from a frozen state. The changes were simultaneously monitored using resonance frequency analysis (RFA) for comparison. A Straumann BL ∅4.1×10 mm SLA implant was placed in the retromolar area of a fresh porcine mandible following the manufacturer's surgical protocol, with the motor set at a torque of 35 N·cm. The porcine mandible was frozen to create a high-stability condition and thawed at room temperature to yield a low-stability condition. Before thawing, a regular connection (RC) locator abutment, 6 mm in length, was connected to the implant platform and secured with a torque of 10 N·cm. A custom-made motor-sensor unit, comprising a haptic unbalanced motor and a digital accelerometer, was press-fit onto the locator abutment. The motor applied a harmonic force (F) to the abutment-implant system, and the accelerometer measured the corresponding displacement (∆x). The flex constant was obtained as ∆x/F. Implant stability quotient (ISQ) was also measured using Penguin RFA for comparison. To demonstrate the feasibility, only one mandible with one implant was tested. Three rounds of tests were performed to ensure repeatability. For all three rounds of tests, ISQ dropped from high values (>80) in the frozen state to a low value (65-75) in the thawed state, occurring about 30-40 min after thawing. The drop in ISQ indicated reduction in implant stability when the frozen mandible thawed. The flex constant increased from 0.4 to 0.5 μm/N in the frozen state to 0.9-1.8 μm/N in the thawed state, with the transition occurring 30-50 min after thawing began. The increase in the flex constant implied larger displacement under the same force, indicating reduced stability. A transition peak was also observed in the flex constant measurement between the frozen and thawed states, likely due to thermal expansion and moisture condensation at the interface between the motor-sensor unit and the locator abutment. Test results from the porcine model indicate that a flex constant can reflect the changes in dental implant stability as an RFA device.