Avoiding the Alveolar Nerve Via a Real-Time Impedance Analysis: A Novel Method to Improve Implant Surgery Safety

Abstract

Safe lower jaw implantations require precautions to avoid damaging the alveolar nerve. The prevailing methods are preoperative. In this study, we propose a novel approach to measure the distance between a pilot-drill and the alveolar nerve by employing high-frequency impedance measurements. The objective is to provide in vivo real-time information as an early warning of the proximity of the alveolar nerve. The method is examined and tested on animal samples. The impedance measurements were performed using a high-frequency network analyzer. Overall 40 pilot drillings were distributed over five sheep mandibles, with four on each side. Drillings were performed in three steps: inside the cortical layer, inside the spongiosa, and well inside the nerve canal. The inductance measurements were performed with a connected pilot drill, followed by an immediate 3D cone-beam computed tomography (CT) to measure the distance between the tip of the drill and the nerve canal. The measurements show that impedance information is a reliable indicator for proximity of the drill to the nerve. We observe a general trend of decreasing inductance as the drill approaches the nerve and find that at very high frequencies one can detect the closeness to the nerve from characteristic ratios of impedance at nearby frequencies. We report also that using phase information increases the reliability of this method. The findings provide a solid proof of concept for the proposed method. While the results are promising at this stage, the applicability for in vivo conditions requires further studies.