DENTAL BUR

摘要

The invention relates to an improved bur for use in handpieces having a rotatable chuck with a tool bore for receiving the bur, a friction grip member for frictionally retaining the bur in the chuck and a torque lock seat of non-circular cross-section and permitting length adjustment of the bur in the drive head by concentrically supporting the bur in the drive head at any position from a fully inserted position to a maximum retracted position. The bur includes a tool body having an axis of rotation, a working end for projecting from the handpiece and a driven end for Insertion into the tool bore of the chuck. The driven end is a generally cylindrical shaft with a preselected outer circumference for fittingly engaging in the tool bore for concentric rotation of the driven end with the chuck. The shaft Including a torque lock portion for fittingly and non-rotatably engaging the torque lock seat of the chuck. The torque lock portion has at least two flat surfaces circumferentially spaced apart by intermediate cylindrical mantle portions, for providing the locking portion with a cross-section including alternating circular and straight sections and fitting into the non-circular cross-section of the torque lock seat to prevent rotation of the torque lock portion in the torque lock seat. The circular sections have the same diameter as the outer diameter of the cylindrical shaft. A total area of the flat surfaces covers at least 0.001956 square inches and the circular sections extend over at least 30% of the outer circumference of the driven end. This maintains efficient torque transfer between the chuck and the tool and ensures concentricity of the bur in the handpiece to prevent undue vibration of the bur in the handpiece.