There is described a hand-held dental instrument for detection of carious lesions which includes a handle portion defining a longitudinal axis therethrough and at least a first working end, mounted on the handle portion, which includes a probe body extending from the handle portion and a probe tip disposed at a remote end. The compounds of this invention are defined by the Formula :wherein X, Y, Z, R1, R2 and R3 are as defined in the specification; or a pharmaceutically acceptable salt thereof. The biasing connector includes an end portion for contacting the shielding element, and a conductive tape having a first end connected to the end portion of the biasing connector and a second end adapted to be connected to a terminal providing a biasing voltage.