An apparatus and method for mineralising demineralised and hypo-mineralised biological material such as tooth or bone. The apparatus has a probe electrode for receiving a mineralisation agent and a counter electrode. It is also provided with a controller to control the electrical signal provided to the probe such that the extent of mineralisation of the biological material is controlled by modulating or changing the electrical signal provided by the probe based upon the measured output of the circuit formed from the probe, counter electrode and biological material. The electrical output provides a measure of the extent of mineralisation of the biological material which is compared with data from a reference technique which gives 3D structural information on an area of interest in the biological material.