A dental drill system with electrical-impedance sensing indicates when a bit of the drill system approaches cortical- cancellous bone, or bone-soft tissue interfaces. The drill system has a dental drill handset having a cannula bearing electrically coupled to a drilling bit, the drilling bit having an electrically insulated portion and an exposed portion. The cannula bearing is coupled to an electrical impedance spectroscopy sensing device configured to measure impedance between the cannula bearing of the dental drill handset and a ground plate, and a processing system uses EIS measurements to distinguish when the bit of the drill system approaches cortical- or cancellous bone, or bone-soft tissue interfaces.
