A drill burr includes a channel, extending along a longitudinal axis of the drill burr, and fluidically connected to a water reservoir for providing a constant-flow liquid jet. The constant-flow liquid jet has a first pressure directed at the bone along the longitudinal axis of the drill burr. A pressure sensor senses a pressure change in the liquid jet from the first pressure to a second pressure. A signal processing unit is configured to translate the pressure change into information indicating a structural change in the bone along the drilling path, from a first structure to a second structure, corresponding respectively to the first pressure and the second pressure. Optionally, the signal processing unit generates an audio alarm notifying of the structural changes.