[Semi-automatic generation of finite element meshes fo dental preparations].

An air operated tool characterized in that the tool chuck thereof has a pilot portion which is coaxial with the air motor rotor onto the shaft of which said chuck is screwed, and which engages a ball bearing in the tool housing so that the chuck and rotor will run true about their common axes despite eccentricity of the chuck threads. Moreover, the pilot portion of the chuck extends axially within the ball bearing thus to increase the effective diameter of the rotor shaft and to shorten the axial overhang of the chuck relative to the ball bearing so as to provide a compact tool in which the accuracy of rotation and strength are enhanced.