Bur for 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position, the tool preferably including a maximum retraction indicator for indicating to a user when the tool has been retracted to the maximum retraction position.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 dental tool for use in a dental handpiece having spaced apart front and rear tool seats for rotatably supporting the tool and an intermediate friction grip for releasably retaining the tool in the handpiece, the rear tool seat being axially elongated to support the tool at different insertion depths from a maximum insertion depth at which the tool is fully inserted into the handpiece to a maximum retraction depth at which the tool is maximally retracted from the rear seat without disengaging from the rear seat, the tool comprising
 a tool body having an axis of rotation, the tool body having a driven portion for insertion into the handpiece and a working portion for projecting from the handpiece during use, the driven portion having a driven end for fitting insertion into the rear seat at the different insertion depths; and   and a maximum retraction indicator on the driven portion for indicating when the tool is retracted from the rear seat to the maximum retraction depth to prevent further retraction and disengagement of the driven end from the rear seat.   
   
   
       2 . The tool of  claim 1 , wherein the maximum retraction indicator is a visible indicia located on the tool intermediate the driven end and the working portion to be hidden from view when the tool is inserted at a depth between the maximum insertion depth and the maximum retraction depth and visible to a user when the tool is retracted from the handpiece to the maximum retraction depth or beyond. 
   
   
       3 . The tool of  claim 2 , wherein the maximum retraction indicator is selected from the group consisting of a dot, a line, a colored line, an etched line, a laser mark, a line having a surface roughness different from the remainder of the driven portion, a detent and a groove. 
   
   
       4 . The tool of  claim 1  for use in a handpiece further including a friction grip chuck, wherein the maximum retraction indicator is a mechanical indicia located on the driven portion for engagement by the chuck when the maximum retraction depth is reached. 
   
   
       5 . The tool of  claim 4 , wherein the mechanical indicia is a stop on the driven portion for mechanical interaction with the chuck when the tool is retracted to the maximum retraction depth. 
   
   
       6 . The tool of  claim 5 , further comprising
 a contact surface on the driven portion for engagement by the chuck at insertion depths from the maximum retraction depth to the maximum insertion depth;   the stop being a stop shoulder on the contact surface for engagement by the chuck when the tool is retracted from the maximum insertion depth to the maximum retraction depth.   
   
   
       7 . The tool of  claim 1 , wherein the driven end includes a torque lock portion of non-circular cross section for connecting with a rotational torque generating element of the handpiece. 
   
   
       8 . The tool of  claim 4 , wherein the driven portion has a torque lock portion of non-circular cross section for connecting with a rotational torque generating element of the handpiece, the mechanical indicia being located in the torque lock portion of the tool. 
   
   
       9 . The tool of  claim 5 , wherein the mechanical indicia is an annular groove and the stop is a lateral wall of the groove. 
   
   
       10 . The tool of  claim 4 , wherein the driven portion includes at least one non-cylindrical portion for engagement in a torque socket of complementary shape in the handpiece, the torque lock portion extending from the driven end and the mechanical indicia being positioned in the torque lock portion. 
   
   
       11 . A rotatable dental tool for use in a dental handpiece having a rotatable tool supporting element for rotatably supporting and axially retaining the tool, the tool supporting element having an axial tool bore, the tool comprising
 a tool body having an axis of rotation, a driven end for insertion into the handpiece and a working end for projecting from the handpiece during use,   a shaft at the driven end for engagement with the tool supporting element, the shaft including a cylindrical portion with a preselected outside diameter for fitting insertion into the tool bore and a locking portion for engagement in the torque lock portion;   the locking portion of the shaft including at least two cylindrical mantle portions located symmetrical to the axis of rotation and having the same outside diameter as the cylindrical portion, and intermediate planar mantle portions connecting the cylindrical mantle portions, the locking portion thereby having a non-circular cross-section and an outside diameter for fitting and concentric engagement in the tool bore.   
   
   
       12 . The tool of  claim 11 , wherein the locking portion of the shaft includes at least 3 cylindrical mantle portions and a plane of the intermediate planar mantle portions is oriented parallel to the axis of rotation. 
   
   
       13 . The tool of  claim 12 , wherein the plane is further oriented perpendicular to a radius of the shaft. 
   
   
       14 . The tool of  claim 13 , wherein the cylindrical and planar mantle portions are circumferentially evenly distributed. 
   
   
       15 . The tool of  claim 14 , wherein the cylindrical and planar mantle portions extend over equal portions of the circumference of the locking portion. 
   
   
       16 . The tool of  claim 14 , wherein the torque lock portion forms a major part of the driven portion. 
   
   
       17 . The tool of  claim 1 , wherein the tool is a dental bur. 
   
   
       18 . A bur for use in a dental handpiece having a rotatable chuck with a tool bore for receiving the tool and a grip member for frictionally retaining the tool in the spindle, the tool comprising
 a tool body having an axis of rotation, a working end for projecting from the handpiece and a driven end for insertion into the chuck,   the driven end having a cylindrical shaft with a preselected outer diameter for fittingly engaging in the tool bore for concentric rotation of the driven end with the chuck, the shaft including a locking portion having at least two detents circumferentially spaced apart by intermediate cylindrical mantle portions, for providing the locking portion with a cross-section including alternating circular and non-circular sections, the circular sections having the same diameter as the outer diameter of the cylindrical shaft.   
   
   
       19 . The tool as defined in  claim 17 , wherein the locking portion further includes a mechanical stop for mechanical engagement with the grip member. 
   
   
       20 . The tool as defined in  claim 18 , wherein the locking portion is axially elongated to allow positioning of the tool in the tool bore at any location from a maximum insertion position wherein the driven end is fully inserted into the chuck and a maximum retraction position wherein the driven end is partially inserted in the chuck but still concentrically supported in the tool bore, the mechanical stop being positioned on the locking portion for engagement with the grip member when the tool is in the maximum retraction position.