| 摘要 |
The invention relates to an improved dental tool drive arrangement for a hand-piece with a drive head, the tool drive arrangement permitting length adjustment of the tool in the drive head by concentrically supporting the tool in the drive head at any position from a fully inserted position to a maximum retracted position. The tool drive arrangement preferably includes a tool and a rotatable tool supporting element for concentrically supporting the tool from the fully inserted to the maximum retracted position, the tool preferably including a maximum retraction indicator for indicating to a user when the tool has been retracted to the maximum retraction position. This provides a significant advantage over the prior art by allowing a user to adjust the exposed length of a rotatable tool, preferably a dental bur, without exceeding safe operating limits. The invention also relates to an improved drive spindle which allows depth adjustment of a tool in a dental handpiece while maintaining efficient torque transfer and concentricity during high speed rotation.
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