A disposable dental contra-angle comprising a plastic housing having a sleeve, a tapered neck, a head and a disposable bur. The bur being removably coupled to a driven rotating mandrel located in the head section. The rotating mandrel having an integral axis pole member extending through and outwardly from its top and bottom portions wherein the bur is maintained in a 1:1 rotational luted connection, with virtually no slippage. The sleeve section having an elongated opening for receiving a power drive from a dental handpiece. A gear ratio mechanism located in the sleeve section rather than the head section, for either increasing or decreasing the shaft speed. A gear to gear arrangement in the head section for translating rotation from the drive shaft to the bur. In addition to having a flat surface for a luted non-slippage connection within the rotating mandrel, the bur further has a plurality of semi-circular grooves for connecting with a plurality of O-ring connections disposed within the chamber of the axis pole for prevention of axial displacement of the bur from the mandrel.

A medical handpiece, particularly a dental handpiece, for use with an internally cooled tool, wherein the tool has an axial hollow space into which the cooling fluid is conducted in an essentially radial direction through a bore of the tool shaft, and wherein the bore is arranged between two axially spaced apart sealing members which are arranged in the handpiece head and which seal the handpiece head relative to the tool shaft. The sealing surfaces of the sealing discs extend relative to the tool axis of the tool shaft essentially in a normal, conical or spherical direction.