A chuck mechanism for holding rotating tools in gear driven or turbine driven medical/dental devices. The chuck includes a bur tube which releasably receives a shaft of a dental tool, a tilt plate which extends through the bur tube and which has a hole through which the tool extends, and a tilt plate pusher which is moveable axially with respect to the bur tube. The tilt plate is moveable between a first, unlocked, position in which the edges of the tilt plate hole are spaced slightly from the dental tool shaft so that the shaft may be freely moved axially relative to the tilt plate, and a second, locked, position in which the tilt plate edges contact the shaft to prevent axial and rotational movement of the shaft relative to the tilt plate. The tilt plate is preferably spring biased to its locked position, and the tilt plate pusher is preferably operated by a push button to move the tilt plate to its open position. In another embodiment, the tilt plate is positively held in its locked position by a threaded piece.