Adjustable tool drive arrangement

Abstract

The invention relates to an improved dental tool drive arrangement for a handpiece 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position, the tool preferably including a maximum retraction indicator for indicating to a user when the tool has been retracted to the maximum retraction position.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.

1 . A rotatable bur drive assembly for use with a medical or dental handpiece having a drive head with a first axis of rotation, the assembly comprising:
 a rotatable bur; and   a bur drive arrangement for releasably supporting the bur, the bur drive arrangement including a first end and a second end, the first end of the bur drive arrangement being insertable into the drive head for coaxial rotation in the drive head; the bur having a bur body with a second axis of rotation coaxial with the first axis of rotation, a driven portion with a driven end which is inserted through the second end of the bur drive arrangement and a working portion with a working end projecting from the second end of the bur drive arrangement and from the drive head during use; the bur drive arrangement having a first bur seat for concentrically supporting the driven end of the bur and a separate, second bur seat axially spaced apart from the first bur seat for concentrically supporting the driven portion of the bur at a location intermediate the driven end and the working portion; and a bur retaining structure axially intermediate the first and second bur seats, the bur retaining structure having a pair of opposing friction grip arms extending away from the first end and toward the second end of the bur drive arrangement, the pair of opposing friction grip arms frictionally releasably retaining the driven portion of the bur in the bur drive arrangement against axial movement in the drive head, the first bur seat being axially elongated for concentrically supporting the driven end of the bur at any position from a maximum insertion depth wherein the bur is fully inserted into the bur drive arrangement to a maximum retraction depth wherein the bur is retracted from the maximum insertion depth and the driven end of the bur is still engaged in the first bur seat, an axial length of the first bur seat being at least as long as an axial distance between the maximum insertion depth and the maximum retraction depth.   
   
   
       2 . The rotatable bur drive assembly of  claim 1 , wherein the bur includes a maximum retraction indicator for indicating to a user when the tool has been retracted to the maximum retraction position. 
   
   
       3 . The rotatable bur drive assembly of  claim 2 , wherein the bur drive arrangement includes a drive spindle for being fittingly received in a drive spindle socket of the drive head, the drive spindle having a drive torque receiving portion for receiving drive torque from the drive head, a bur supporting portion connected with the drive torque receiving portion and having the first and second bur seats, and the bur retaining structure. 
   
   
       4 - 51 . (canceled) 
   
   
       52 . The rotatable bur drive assembly of  claim 3 , wherein the bur retaining structure is positioned axially adjacent the second bur seat. 
   
   
       53 . The rotatable bur drive assembly of  claim 2 , wherein the bur includes a maximum insertion indicator for indicating to a user when the bur has been inserted to the maximum insertion depth. 
   
   
       54 . The rotatable bur drive assembly of  claim 53 , wherein the maximum insertion and retraction depth indicators are annular grooves in the driven portion of the bur for mechanical engagement by the bur retaining structure, an axial spacing of the grooves being no greater than the axial length of the first bur seat. 
   
   
       55 . The rotatable bur drive assembly of  claim 54 , wherein the bur retaining structure includes tool engaging members for mechanical engagement with one of the grooves respectively to provide a tactile indication to a user that the maximum insertion or maximum retraction positions are reached, respectively. 
   
   
       56 . The rotatable bur drive assembly of  claim 1 , wherein the bur further includes a torque lock portion of non-circular cross-section positioned at the driven end of the bur and the first bur seat has a locking socket of a cross-section complementary to the torque lock portion of the bur.