US20090325123A1 - Bur for Adjustable Tool Drive Arrangement - Google Patents

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position, the tool preferably including a maximum retraction indicator for indicating to a user when the tool has been retracted to the maximum retraction position.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.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application is a continuation application of U.S. application Ser. No. 11/921,860, filed Dec. 10, 2007, which represents a National Stage application of PCT/CA2006/000954 filed on Jun. 9, 2006 entitled “Adjustable Dental Tool Drive Arrangement” and is a continuation-in-part of U.S. patent application Ser. No. 11/262,959, entitled “Adjustable Tool Drive Arrangement”, filed Nov. 1, 2005 and claims the benefit of U.S. Provisional Patent Application Ser. No. 60/689,052, entitled “Dental Burr And Drive Spindle”, filed Jun. 10, 2005, which applications are included herein by reference in their entirety.
FIELD OF THE INVENTION
• The present invention relates generally to handpieces for rotating tools. More particularly, the present invention relates to an improved drive arrangement for a rotatable tool and the tool.
BACKGROUND OF THE INVENTION
• Numerous handpieces for rotating tools exist. Turbine driven handpieces are widely used in dental offices and medical labs around the world. Most handpieces include a handle and drive head for supporting the rotating tool. A connector, often a swivel connector, connects the handpiece to various air, water, light and power supply conduits, generally combined in a so-called umbilical cord. The drive head houses a tool drive arrangement, generally composed of a tool retaining mount or chuck, and a motor or turbine, rotatably mounted in the head for driving the chuck. The chuck releasably holds the tool, such as a dental bur, for rotation about an axis of rotation.
• In known handpieces, the tool is releasably held by the chuck against axial movement in the drive arrangement. Screw lock or pushbutton lock arrangements are provided for the manual locking and releasing of the tool in and from the chuck. The known drive arrangements are not designed to allow for length adjustment of the tool, which means the tool, once fully inserted in the drive arrangement will always protrude the same length from the drive head. However, as a dental procedure progresses, a dentist may need to use dental tools of different length. This creates the need for repeated tool changes, which is time consuming and cost intensive, since a collection of different length tools must be purchased.
• In an attempt to find a time and cost efficient solution, dentists often try to adjust the protruding length of the bur by somewhat retracting the bur from the drive head until the desired length is reached. However, this adjustment is made without knowledge whether the bur will remain properly engaged within the drive mechanism and safely secured within the drive head. This is a dangerous practice, since prior art handpieces are not designed to hold the bur in any position other than fully inserted into the drivehead. The tool when retracted may remain within the drive head in the prior art handpieces due to the retaining force of the friction arms normally included in the chuck. However, concentrical support of the tool within the drive head and reliable torque transmission from the drive to the tool are not ensured.
• Conventional handpiece designs provide for concentrical support of the tool in the fully inserted condition. Support is provided at a rear, inserted end of the tool and at an intermediate location of the tool corresponding to the area of the bottom bearing in the drivehead. However, upon even a minor retraction of the tool from the fully inserted position, the tool is disengaged from the concentrical support at the rear end of the tool. The tool must then be maintained in axial alignment with the rotating drive by way of the friction arms of the chuck. However, those friction arms are somewhat flexible by design and generally do not provide sufficient force to maintain the rear end of the tool concentrically aligned in the drive when lateral forces are applied to the working end of the tool during use. Therefore, operation of a conventional handpiece at a tool Insertion depth other than fully inserted can result in loss of concentricity, vibration of the bur during rotation, excessive wear, damage to the drive assembly, permanent deformation of the tool securing mechanism and drive spindle components, inefficient torque transfer, increased bur slippage (both rotational and axial), and most dangerously, accidental disengagement of the bur from the handpiece during use.
• Therefore, a need exists for a dental tool and handpiece design allowing for tool depth adjustment without a loss of concentricity.
• Prior art chucks of dental handpieces are almost exclusively designed to hold the dental bur by way of friction fit only. Examples of such constructions are found in U.S. Pat. No. 3,869,796, U.S. Pat. No. 4,595,363, U.S. Pat. No. 5,275,558, and U.S. Pat. No. 5,549,474. Only low torque transmission is possible between the chuck and the bur in such constructions, higher torque leading to slippage of the bur. At the high rotational speeds achieved by modern dental handpieces, bur slippage, in both the axial and rotational directions, can become a problem. Rapid deceleration of the bur can also lead to rotational slippage, for example, when the drive continues to rotate while the bur is locked or snagged. Friction between the drive assembly and the dental bur during rotation leads to significant wear of both elements over time. This friction can also produce significant heat, as can friction generated in push-button lock handpieces when the user maintains pressure on the push-button during operation. Friction heat can cause permanent damage to the drive spindle components, especially the flexible friction arms of the chuck, which are normally made of heat tempered material. The damage can lead to rotational slippage and even axial slippage of the tool, possibly resulting in an accidental release of the tool from the handpiece. Accidental release of a dental bur during high speed rotation can pose a threat to both the patient and the dentist. Continued wear of the bur and drive assembly during operation necessitates routine maintenance and repair of expensive handpiece components.
• Thus, a drive spindle design is desired which not only allows for adjustment of the exposed tool lengths but preferably also prevents rotational slippage of the tool at all possible tool retraction positions to avoid frictional wear and resulting heat damage to the drive spindle.
SUMMARY OF THE INVENTION
• It is an object of the present invention to obviate or mitigate at least one disadvantage of prior art handpiece designs.
• In a first aspect, the invention provides a tool for use in a 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.
• In a preferred embodiment, the tool includes 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.
• In a further preferred embodiment, the tool includes a tool body having an axis of rotation, the tool body being divided into a driven portion with a driven end for insertion into the tool supporting element of the drive arrangement, and a working portion for projection from the drive head during use. The driven portion of the tool further includes a torque lock portion in the form of a non-circular shaft portion for engagement of the tool supporting element, the tool supporting element having a complementary shape to the torque lock portion. The tool further includes a maximum retraction indicator on the torque lock portion for indicating to a user when the tool is retracted from the fully inserted position to the maximum retraction position.
• In another preferred embodiment, the torque lock portion of the tool includes a non-round shaft portion and the maximum retraction indicator is located on the non-round shaft portion of the tool.
• In yet another preferred embodiment, the maximum retraction indicator is a mechanical indicator for mechanical interaction with a tool retaining member in the drive arrangement for releasably retaining the driven portion in the tool passage. More preferably, the tool includes an engagement surface for engagement by the tool retaining member and the maximum retraction indicator is a structure in the engagement surface for mechanical interaction with the retaining member.
• In one aspect, the maximum retraction indicator is a visible indicia located on the driven portion, intermediate the driven end and the working portion, to be hidden from view when the tool is inserted at a depth between the maximum and minimum insertion depths and visible to a user when the tool is retracted from the drive head to the maximum retraction position or further. Preferably, the maximum retraction indicator is selected from the group of at least one dot, line, colored line, etched line, a line having a surface roughness different from the remainder of the driven portion, a change in diameter of the tool and a groove. The line or groove can be continuous or broken, such as a line of dots. The line or groove can extend in circumferential or longitudinal direction of the tool or at any angular orientation therebetween. The maximum retraction depth can be indicated by an end or an edge of the line or groove. The maximum retraction depth can also be indicated by a change in the overall appearance of the line or groove, such as a change in color, a change in size, a change in any other characteristic, or any combination thereof.
• In another aspect, the maximum retraction indicator is a mechanical indicia located on the driven portion for engagement by a portion of the tool supporting element when the maximum retraction depth is reached. Preferably, this mechanical engagement provides a tactile indication, possibly even an auditory indication (click), to the user that the maximum retraction depth is reached. In a preferred embodiment, the mechanical indicia is a stop on the driven portion of the tool for mechanical interaction with the tool retaining member of the tool supporting element when the tool is retracted to the maximum retraction depth. Preferably, the tool supporting element includes a tool retaining member for frictionally retaining the tool and the tool further includes a contact surface on the driven portion for engagement by the tool retaining member at insertion depths from the maximum insertion depth to at least the minimum insertion depth. The stop is preferably a stop shoulder or groove on the contact surface of the tool for axial engagement by the tool engaging-member when the tool is retracted from the maximum insertion depth to the maximum retraction depth.
• In one variant, the contact surface is a detent on the driven portion and the stop is an axial end shoulder of the detent. In a particularly preferred embodiment, frictional engagement of an elongated detent by the tool retaining member allows the tool to be positioned in the handpiece at any insertion depth between the minimum insertion depth (or maximum extraction depth) and the maximum insertion depth. In another variant, the tool comprises two or more detents on the driven portion, each having a stop shoulder for axial engagement with the tool engaging member for defining one or more intermediate insertion depths between the minimum tool insertion depth and the maximum retraction depth. In a particularly preferred embodiment, the detent is a groove extending circumferentially about the driven portion of the tool.
• In a particularly preferred embodiment, the contact surface and the mechanical indicia are both located on the torque lock portion of the tool.
• Those skilled in the art will appreciate that the tool insertion depth indicator and tool retaining member can be achieved by other means than those described in the preferred embodiments of the invention without deviating from the essence of the invention. It will also be apparent that more than one tool retaining member can be provided in the tool supporting element while preserving the core function.
• It is a significant advantage, of an adjustable length tool drive arrangement and tool in accordance with the invention allowing axial adjustment of tool insertion depth in a dental handpiece, that the number of times a dentist must exchange tools for selection of different tool lengths during the course of a dental procedure is reduced. This reduces the time required to perform the procedure and can reduce operating cost, since fewer tools of specific length need to be purchased and maintained. It is another significant advantage that, by providing the preferred maximum retraction indicator, excessive wear and damage due to insufficient insertion of the tool in the handpiece and the concomitant loss of concentricity are avoided.
• In an alternate embodiment, the maximum tool retraction indicator is a combination of a mechanical and a visual indicator.
• Tools in accordance with the invention are intended for use with a handpiece chuck which is a generally cylindrical member having a tool receiving axial bore. A portion of the wall surrounding the bore is resiliently deformable and forms the resilient tool engaging member to allow insertion of the driven portion of the tool into the bore. When the tool is inserted, the chuck wall portion forming the tool engaging member radially inwardly engages the driven portion to frictionally retain the tool in the bore. Axial engagement of the tool engaging member with a first stop shoulder on the contact surface of the tool provides a maximum tool retraction indication. The resilient wall portion of the chuck may form of a pair of diametrically opposed axially extending retaining arms, or friction grip arms, at least one of which has a radially inwardly projecting protrusion extending therefrom for frictionally engaging the contact surface of the tool and for axially engaging a mechanical retraction depth indicator on the tool, such as the maximum retraction depth indicator. The chuck may further include a ram for selectively forcing apart the retaining arms to allow insertion and/or removal of the tool. Various tool drive arrangements are contemplated in accordance with the present invention, which can allow for torque transfer from the drive directly to the rotatable tool.
• Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
• i.FIG. 1 is a cross-sectional view of a known dental handpiece suitable for use with a tool drive arrangement in accordance with the present invention;
• ii.FIG. 2 illustrates a perspective view of a rotatable tool and drive spindle components of a tool drive arrangement in accordance with a preferred embodiment of the present invention;
• iii.FIGS. 3A to 3F show perspective views of dental tools including different types of maximum retraction indicators in accordance with various preferred embodiments of the tool aspect of the invention;
• iv.FIG. 3G shows an alternative preferred embodiment of the dental tool with two mechanical depth indicators, including the maximum retraction indicator, located on the locking portion of the tool, as well as a visual indicator of maximum retraction;
• v.FIG. 4A is an axial end view of the dental bur shown inFIG. 3D illustrating a torque lock;
• vi.FIG. 4B is an axial end view from the driven end of the dental bur ofFIG. 3F or3G illustrating an alternative torque lock to that exemplified inFIG. 4A;
• vii.FIG. 4C shows a cross-sectional end view through the locking portion of the dental bur ofFIG. 3G taken through line A-A;
• viii.FIG. 5 illustrates a perspective view of a preferred embodiment of a dental bur type tool of the invention having a mechanical maximum retraction indicator in the form of a single, axially elongated detent for continuous depth adjustment;
• ix.FIGS. 6A and 6B illustrate perspective front and rear end views of a preferred embodiment of a chuck of the tool supporting element aspect of the present invention;
• x.FIGS. 6C and 6D illustrate alternative preferred embodiments of the chuck of the tool supporting element aspect of the present invention, illustrating a double-tab variant (6C) and a single-tab (or asymmetrical tab) variant (6D);
• xi.FIG. 7 illustrates an end view from the tool receiving end of the drive spindle ofFIG. 2, but shown in assembled condition;
• xii.FIG. 8 illustrates an end view from the driven end of the drive spindle ofFIG. 7;
• xiii.FIGS. 9A and 9B illustrate axial cross-sections of the tool drive arrangement ofFIG. 2;
• xiv.FIG. 10 illustrates an axial cross-section through the tool and tool drive arrangement combination ofFIG. 2, in an assembled condition and with the dental tool ofFIG. 3D inserted into the spindle to the maximum insertion depth;
• xv.FIG. 11 illustrates the assembled drive arrangement and tool combination shown inFIG. 10, but with the tool retracted to the maximum retraction length;
• xvi.FIG. 12 illustrates an alternative preferred embodiment of the tool drive arrangement of the invention having a drive spindle and the asymmetrical chuck ofFIG. 6D, in combination with the tool ofFIG. 3G;
• xvii.FIGS. 13A and 13B illustrate axial cross-sections through the drive arrangement ofFIG. 12 in an assembled condition withFIG. 13B rotated 90° about the axis in relation toFIG. 13A;
• xviii.FIG. 14 illustrates an axial cross-section through the drive arrangement as shown inFIG. 13A, with a dental tool as shown inFIG. 3G inserted into the spindle; and
• xix.FIG. 15 shows a cross-section through the locking socket of the sleeve ofFIG. 13B, taken along line C-C, and illustrates a locking portion of the tool ofFIG. 3G positioned therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Generally, the present invention provides a tool drive arrangement for a handpiece with a drive head, the tool drive arrangement permitting length adjustment of a 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.
• In one embodiment, the invention provides a tool drive assembly including the tool drive arrangement, a rotatable tool and a rotatable tool supporting element for concentrically supporting the tool from the fully inserted position to the maximum retracted position. The tool preferably includes 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.
• More particularly, the rotatable tool drive assembly in accordance with the invention includes a rotatable tool and a tool supporting element for releasably supporting the tool. The tool supporting element is insertable into a drive head for coaxial rotation in the drive head. The tool has a tool body having an axis of rotation and is divided into a driven portion, with a driven end for insertion into the tool supporting element, and a working portion for projecting from the drive head during use. The tool supporting element has a tool passage for coaxially receiving the driven portion of the tool and supporting it at different insertion depths, the tool passage including a first tool seat for concentrically supporting the driven end of the tool and a second tool seat for concentrically supporting the driven portion at a location intermediate the driven end and the working portion. In a preferred embodiment, the first tool seat is axially elongated for concentrically supporting the driven end at any position from a maximum insertion position, wherein the tool is fully inserted into the tool passage, to a maximum retraction position, wherein the tool is retracted from the maximum insertion position.
• The invention will now be described in more detail with reference to specific preferred embodiments of the invention directed to an improved tool drive arrangement and tool, wherein the tool is a dental tool such as a bur, and the tool supporting element is a drive spindle, such as a drive spindle for use in a high speed turbine-driven dental handpiece. Although specific reference is made in the following to a dental bur and a drive spindle for a high speed dental handpiece, it will become apparent to those skilled in the art that all structural and functional features of the invention are equally applicable to rotatable dental and medical tools in general and to medical and dental handpieces and other handpieces for supporting high speed rotating tools.
• A high speeddental handpiece100, as shown inFIG. 1 generally includes ahandle102, a tool supportingdrive head101, and a swivel connector (not illustrated) for connecting the handpiece to various air, water, light and power supply conduits, generally combined in a so called umbilical cord (not shown). Thedrive head101 includes atorque producing drive105, typically a motor or turbine rotatably mounted in the drive head, and having aspindle socket109 for housing atool supporting element103, here adrive spindle10. Thetool supporting element103 typically includes a tool receiving and retaining portion, here achuck20, constructed to releasably retain atool106, such as a dental bur, for rotation about an axis ofrotation108. Thetool supporting element103 may be retained in thedrive head101 by any means known in the art, for example, by press-fitting thetool supporting element103 in thespindle socket109 of the drive head.
• Referring now toFIGS. 1 to 3G, adental tool106, such as thedental bur50, typically has an elongatedbody52 divided into a generally cylindrical drivenportion54 for insertion into thedrive head101 of adental handpiece100 for receiving drive torque from thedrive105 of the handpiece, and a workingportion56 for projecting from thedrive head101 of the handpiece in an operating condition. The working portion has a workingend58 for engagement with a working surface, such as a tooth surface (not illustrated), during a dental procedure. The user, typically a dentist, must purchase a collection of burs varying in shaft length as well as in the structure of the workingend58 of the workingportion56. Thedental bur50 is generally inserted into thespindle10 in thedrive head101 and is removably supported therein by thechuck20 for rotation with thespindle10 about the axis ofrotation108.
• As illustrated inFIG. 2, a preferred embodiment of the tool drive arrangement of the present invention provides animproved drive spindle10, to be described in more detail below, for use with an improveddental bur50 in accordance with the tool aspect of the invention.
• Different preferred embodiments of the tool aspect of the present invention are now described by reference to the various preferred dental bur embodiments shown inFIGS. 3A to 3G. Thedental bur50 illustrated inFIGS. 3A to 3G includes abody52 having an axis ofrotation52a, a workingportion56 for projecting from the drive head101 (seeFIG. 1) of adental handpiece100 during use, and a drivenportion54 for insertion into the drive head for directly or indirectly receiving drive torque. All illustrated burs include amaximum retraction indicator107, which can be either avisible indicator57 as shown in the burs ofFIGS. 3A to 3C, amechanical indicator59 as shown in the bur ofFIG. 3D or3F, or a combination of visible and mechanical indicator as shown inFIGS. 3E and 3G.
• Avisible indicator57, as shown in the burs ofFIGS. 3A to 3C,3E and3G is preferably provided on or in the surface of the drivenportion54 of thebur50 such that the indicator is not visible at the maximum tool insertion depth. When the drivenportion54 is retracted from the maximum insertion depth toward the maximum retraction depth, for depth adjustment, thevisual indicator57 becomes apparent to the user, preferably only when the maximum tool retraction position (or minimum tool insertion depth) is reached. A few examples of visual indicia include, but are not limited to, 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. Thevisual indicator57 can extend completely or partially circumferentially about the drivenportion54 as shown inFIGS. 3B and 3G, respectively, axially along the drivenportion54 as shown inFIG. 3A, or at an angular orientation to the axis of rotation108 (not shown). If thevisible indicator57 extends axially as shown inFIG. 3A, the maximum retraction position can be indicated by the start or end of the indicator, by an edge of the indicator, or by a change in the overall appearance of the indicator, such as a change in color, a change in size, a change in any other characteristic, or any combination thereof. This is shown inFIG. 3A which illustrates abur50 with avisual indicator57 havingsections57ato57cof different characteristics (preferably colour), whereby the maximum extraction depth is indicated by the transition fromsection57btosection57cbecoming visible to the user.
• As exemplified in the embodiment ofFIG. 3D, thebur50 has acontact surface60 on the drivenportion54 for frictional engagement by atool engaging member15 of thespindle10, to be discussed in more detail below in relation toFIG. 2. Thetool engaging member15 engages thecontact surface60 at insertion depths of the tool from an engagement depth, at which contact between thetool engaging member15 and the drivenportion54 is initiated, to a maximum insertion depth, at which thebur50 is fully inserted into thehandpiece100. In this embodiment, the mechanical typemaximum retraction indicator59 includes afirst stop shoulder68 on thecontact surface60 for axial engagement with thetool engaging member15 when thebur50, is retracted from the maximum insertion depth (D_max) to a maximum retraction depth (D_min) between the engagement depth and the maximum insertion depth (seeFIGS. 10 and 11).
• The bur ofFIG. 3E includes both thevisible indicator57 shown inFIG. 3B and themechanical indicator59 shown inFIG. 3D. The bur shown inFIG. 3G includes avisible indicator57 in the form of a laser mark as well as themechanical indicator59 as shown inFIGS. 3D to 3F.
• In a preferred embodiment as shown inFIG. 2, the mechanical typemaximum retraction indicator59 is adetent51 located on the drivenportion54, the detent having a firstaxial stop shoulder68 for axial engagement by thetool engaging member15 of thedrive spindle10 for indicating the minimum insertion depth (D_min) (or maximum retraction depth) of thebur50 in thedrive spindle10. D_minis essentially the depth at which the workingportion56 is maximally extended from the handpiece while the drivenportion54 is still concentrically supported in thedrive spindle10 and properly engaged with the drive mechanism in the handpiece for reliable torque transfer. D_mincan be easily determined for various handpiece and spindle designs without undue experimentation. A conservative D_mincan be also be selected which is greater than the depth at which the workingportion56 is maximally extended from the handpiece. The difference between D_minand D_maxprovides a length of axial play along which thebur50 can be safely adjusted in thedrive spindle10.
• As illustrated in the preferred embodiment shown inFIG. 2, a secondretraction depth indicator107acan be provided on the drivenportion54 for defining a corresponding second or intermediate insertion depth of the drivenportion54 in thedrive spindle10 between D_minand D_max, and including D_max. The preferred embodiment illustrated inFIG. 3D shows two annularcircumferential detents51 on the drivenportion54, those being the maximumretraction depth indicator59 and an intermediateinsertion depth indicator59a, having first and second stop shoulders68 and68arespectively for axial engagement with thetool engaging member15 upon retraction (seeFIG. 2) of the drivenportion54 from the maximum insertion depth toward the intermediate insertion depth, D_min, or the engagement depth. Axial engagement of the firstaxial stop shoulder68 by thetool engaging member15 indicates that D_minis reached. In the variant shown inFIG. 3D, axial engagement of thesecond stop shoulder68aby thetool engaging member15 occurs when the tool is inserted to essentially D_max(seeFIG. 10). Thesecond stop shoulder68athus serves to retain the drivenportion54 at D_maxduring operation of the handpiece, while thefirst stop shoulder68 serves to retain the drivenportion54 at D_minduring operation with a maximally extended bur50 (seeFIG. 11).
• The bur exemplified inFIG. 3G also includes an intermediate mechanicalretraction depth indicator59aon the drivenportion54. Intermediate retraction depth indicators (mechanical and/or visual) can be provided on the bur to indicate to a user when the maximum insertion depth (D_max) or any desired intermediate insertion depth has been reached. With the mechanical indicator, the user preferably perceives a tactile indication (i.e. a snap) and/or auditory indication (i.e. a click) upon engagement of a mechanical indicator by thetool engaging member15.
• Alternative embodiments of the mechanical retraction depth indicator of the present invention include, but are in no way limited to: (a) a single axially elongateddetent51 on the drivenportion54 as illustrated inFIG. 5, for continuous depth adjustment wherein frictional engagement of thecontact surface60 of thedetent51 by thetool engaging member15 allows the tool to be securely positioned in the handpiece at any insertion depth between D_minand D_maxduring operation of the handpiece, D_minbeing indicated by axial engagement of thefirst stop shoulder68 by thetool engaging member15; (b) a plurality ofinsertion depth indicators59 as shown inFIGS. 3D and 3G, each having astop shoulder68 located on the drivenportion54 for defining a plurality of corresponding intermediate insertion depths between D_minand D_max, D_minbeing indicated by the firstaxial stop shoulder68 of the maximumretraction depth indicator59; (c) a contoured annular maximum retraction depth indicator that gradually tapers radially outward axially from the first stop shoulder in the direction of the working portion56 (not illustrated), wherein frictional engagement of the contact surface of the tapered annular detent by thetool engaging member15 allows the drivenportion54 to be positioned in the handpiece at any insertion depth between D_minand D_max, D_minbeing indicated by the firstaxial stop shoulder68.
• Although for ease of manufacture themechanical indicator59 described above is preferably in the form of a recesseddetent51 on thecontact surface60 of the drivenportion54, it will be readily understood that the indicator, and especially thestop shoulder68, could be in the form of an elevation protruding from the surface of the drivenportion54. As will become apparent to persons of skill in the art, other indicator variants can serve as the mechanical indicator to indicate when a desired insertion depth has been reached and as such are considered to be within the scope of the present invention.
• In accordance with a preferred embodiment, a detent is any type of recess located on thebody52 of thebur50, but is preferably an annular, circumferentially extending groove on the drivenportion54. An axially elongated detent or a plurality of axially spaced apart annular detents on the drivenportion54 allow for safe and controlled axial adjustment of thebur50 in thedrive spindle10 at a range of depths between D_minand a predetermined D_min, thereby providing for “depth indexing”. The provision of safe tool depth adjustment and controlled depth indexing in a dental handpiece satisfies a long felt need in the art.
• Operation of the handpiece at tool insertion depths between D_minand the engagement depth is also possible due to frictional engagement of the drivenportion56 by thetool engaging member15 but is not preferred due to the disadvantages associated with bur overextension.
• The terms “maximum retraction indicator, “maximum retraction depth indicator”, minimum insertion depth indicator”, “minimum tool insertion depth indicator”, and similar terms, are used interchangeably herein. Similarly, the terms “maximum retraction position”, “maximum retraction length”, “maximum retraction depth”, “minimum insertion depth”, and similar terms, are used interchangeably herein. In this context, the terms “retracted” or “retraction” indicate that the tool is retracted from the maximum insertion depth, at which depth the tool is fully inserted into the drive spindle, toward the working end of the drive spindle. In contrast, the terms “inserted” or “insertion” refer to insertion of the tool into the working end of the drive spindle toward the driven end of the spindle.
• In a preferred embodiment of the present invention, illustrated inFIGS. 2 and 7 to11, the tool supporting element, in this embodiment thespindle10, is insertable into thespindle socket109 of thedrive head101 for coaxial rotation in the drive head. Thetool106, here thebur50, has atool body52 with axis ofrotation108, a drivenportion54 with drivenend55 for insertion into thespindle10, and a workingportion56 for projecting from the drive head during use. As shown inFIGS. 10 and 11, thespindle10 has atool passage12 for coaxially receiving the drivenportion54 of the tool at different insertion depths, thetool passage12 including afirst tool seat14 for concentrically supporting the drivenend55 of thebur50 and asecond tool seat16 for concentrically supporting the drivenportion54 of thebur50 at a location intermediate the drivenend55 and the workingportion56. Thefirst tool seat14 is axially elongated for concentrically supporting the drivenend55 at any position from a maximum insertion position (D_max), wherein thebur50 is fully inserted into the tool passage12 (FIG. 10), to a maximum retraction position (D_min), wherein thebur50 is retracted from the maximum insertion position (FIG. 11). In a preferred embodiment of thefirst tool seat14, the axial length (depth) of the first tool seat is at least equal to 10% of the axial length of the drivenportion54 of thebur50 used in combination with thespindle10. To obtain a sufficiently large retraction length, the axial length (depth) of thefirst tool seat14 is more preferably at least 15% of the axial length of the drivenportion54, most preferably at least 20%. Practical retraction ranges are achievable when the axial length (depth) of thefirst tool seat14 is 15 to 60% of the axial length of the drivenportion54, more preferably 20 to 75%, although other length ratios are also within the confines of the present invention. The axial length of thefirst tool seat14 can also be selected independent of the length of the drivenportion54 of thebur50 used in combination therewith, preferred seat lengths being at least 1.5 mm, more preferably at least about 2 mm, more preferably about 2-7 mm and most preferably about 5 mm.
• Thespindle10 of the preferred embodiment of the tool supporting element shown inFIG. 2 (as shown inFIGS. 9A,9B,10,11) includes a torque receiving element in the form of a generallycylindrical casing sleeve30 which fits into thespindle socket109 of thedrive head101 for receiving rotational torque from thedrive105. Thecasing sleeve30 houses a tool supporting element, in the form of achuck20, for releasably supporting thebur50, and aram40 for selectively releasing thebur50 from thechuck20. Thechuck20 includes thetool passage12 in the form of a tool receivingaxial bore22 for receiving the drivenportion54 of thebur50 coaxial with the axis ofrotation108. The axial bore preferably extends from a drivenchuck end21 of thechuck20 to thetool receiving end23. Thechuck20 further includes a tool retaining member in the form of a resilienttool retaining arm24. Thetool passage12 includes thefirst tool seat14 for supporting the drivenend55 of thebur50 and thesecond tool seat16 for supporting the drivenportion54 at a location intermediate the drivenend55 and the workingportion56. In thespindle10 embodiment exemplified inFIGS. 9A and 9B, thefirst tool seat14 is located in thechuck20 and thesecond tool seat16 is located in theram40. In this embodiment, thefirst tool seat14 has a sufficient extent in axial direction (sufficient depth) to concentrically support the drivenend55 of the tool even when the tool is retracted from the maximum insertion depth D_max, at which depth the drivenportion54 is fully inserted into thetool passage12, to a retracted position at which position thetool retaining member15 still engages the drivenportion54.
• Thetool retaining arm24 is formed by a resilient portion of thechuck wall13 surrounding theaxial bore22. The retainingarm24 is preferably radially resiliently deflectable for insertion of the drivenportion56 into thebore22. The retainingarm24 preferably has atool engaging tab25 for contact with thecontact surface60 of thebur50. The retaining arm is made of a sufficiently strong material (preferably stainless steel) to bias thetool engaging tab25 against thecontact surface60 with sufficient force, once the drivenportion54 is inserted into theaxial bore22, to frictionally engage thebur50 for torque transfer and to prevent axial movement of thebur50 in thedrive spindle10 during operation of thehandpiece100. The selection of appropriate materials for thechuck20 and the retainingarm24 is not part of the present invention and is well within the abilities of the art skilled person. It will also be readily apparent to the art skilled person that thechuck20 may be provided with multiple retainingarms24, such as the pair of diametrically opposite retainingarms24 shown in the embodiments ofFIGS. 6A to 6D. In one embodiment, the retainingarm24 extends towards thetool receiving end23 of thechuck20 in the spindle (seeFIGS. 10 and 11) and thetool engaging member15 is located near thetool receiving end23 for frictional engagement with the drivenportion56. This orientation allows for a larger retraction range than with a retainingarm24 extending toward the drivenchuck end21 of thechuck20 in the spindle (FIGS. 12 and 14) since thebur50 must still be held by the retainingarm24 at maximum retraction.
• In the embodiment of the tool drive arrangement of the invention shown inFIGS. 10 and 11, thechuck20 is constructed for interaction with the mechanicalmaximum retraction indicator59 on thebur50 to indicate D_min. To that end, thetool engaging tab25 protrudes radially inwardly from the retainingarm24 and is sized and shaped to not only fit into the mechanicalmaximum extraction indicator59, in this embodiment anindicator groove70, but to also to generate a tactile sensation for the user to indicate that D_minhas been reached. In this manner, the user will preferably insert thebur50 into thechuck20 until D_maxis reached, which is apparent from the fact that no further insertion of the bur is possible, and then retract thebur50 to the desired position. Over-retraction of thebur50 from thechuck20 is avoided by the tactile sensation of thetool engaging tab25 snapping into theindicator groove70 which is felt, and in some cases heard, by the user when D_minis reached.
• Engagement of thetool engaging tab25 of the retainingarm24 with theindicator groove70 also provides an additional safety feature not available in conventional handpiece designs. ISO recognizes excessive heat as one of the major contributing factors to chuck fatigue and failure in conventional handpieces. To avoid the generation of excessive heat by the user maintaining pressure on the bur release push button of a turbine handpiece, one of the ISO standards stipulates the minimum set back force of the push button resetting spring. The intention of that standard is to avoid friction between the push button mechanism and the spindle of the handpiece during rotation of the turbine. Excessive heat not only reduces lubrication, but more importantly can lead to relaxation of the spring force of the bur retaining arms of the chuck. Those arms are generally made of tempered steel and excessive heat leads to creep of the tempered material, thereby relaxing their resetting force. Once relaxation has occurred, the bur may no longer be reliably retained in the chuck. This problem is overcome with the embodiment of the tool drive arrangement of the invention shown inFIGS. 10 and 11, for example, wherein thetool engaging tab25 on the retainingarm24 engages theindicator groove70. This mechanical engagement can be achieved even after heat relaxation of the retainingarm24, so that thebur50 is more reliably retained in thechuck20.
• In one variant, as illustrated inFIGS. 10 and 11, thebur50 includes theindicator groove70 as well as amaximum insertion groove72 into which thetool engaging tab25 snaps when thebur50 is fully inserted into thechuck20. This provides a tactile sensation to the user at both maximum insertion (D_max) and maximum retraction (D_min) of thebur50. In another variant (not illustrated), thebur50, in addition to theindicator groove70 and themaximum insertion groove72, includes one or more intermediate insertion grooves located therebetween (not shown) which each cooperate with thetool engaging tab25 to provide a tactile sensation to the user. These additional grooves can be spaced along the drivenportion54 at selected intervals to provide a ‘depth indexing’ or ‘retraction length indexing’ function. In yet a further variant (not illustrated), the multiple annular indexing grooves can be replaced with a helical indexing groove extending along the drivenportion56 of thebur50, allowing for depth indexing of the bur by rotating thebur50 relative to thechuck20 while thetool engaging tab25 is engaged in the helical groove. Multiple helical grooves can also be provided.
• In the preferred embodiment exemplified inFIGS. 9A and 9B, thechuck20 includes a pair of diametrically opposed retainingarms24 formed by two semi-circular wall portions of thechuck20 which are separated byaxial slits26. The tool engaging tab25 (seeFIGS. 6A and 6B) is formed by one or more protrusions extending radially inward from an inner surface of the retainingarms24 about thecentral axis29 for frictionally engaging thecontact surface60 of the drivenportion54 to prevent axial movement of thebur50 during operation of thehandpiece100, and for axial engagement with the firstaxial end shoulder68 of the maximum retraction indicator59 (seeFIG. 2) for indicating when D_minis reached.
• In another variant (FIG. 6C), thetool engaging tab25 is formed by a pair of diametrically opposed annular ridges protruding from the inner surfaces of two opposedsemi-circular retaining arms24. The retaining arms and tool engaging tabs can be constructed and achieved by any means known to those skilled in the art. For instance, the retainingarms24 may be straight with generally parallel axially extending sides, as shown inFIGS. 6A and 6B, or they may be tapered as shown inFIGS. 6C and 6D. It will further be appreciated by those of skill in the art that there may be more than two retaining arms, preferably arranged in a symmetrical fashion for vibration-free rotation at high speeds.
• Thetool engaging tabs25 may be of any suitable shape and design, for example, they may be square or rectangular in profile (FIGS. 10,11), angled at one axial end in profile (FIGS. 6A to 6C), angled at both axial ends in profile (FIG. 6D), or they may have a different shape altogether, such as rounded, so long as the retaining function is reliably achieved. To aid in guiding thebur50 into thechuck20, the surface of thetabs25 at the tool receiving end of the retainingarms24 can be angled toward thecentral axis12 of the tool receiving bore22, similar to the tab shown inFIG. 6D. In the tool drive arrangement illustrated inFIG. 12, which encompasses the chuck ofFIG. 6D, theangled tab25 actually aids in aligning thelugs44 of theram40 within theaxial slits26 of thechuck20 in the assembled condition of thespindle10.
• The depth to which atool engaging tab25 extends into amechanical retraction indicator59 or59a, preferably adetent51 orgroove70 on thebur50, can be varied, for example, depending on design and materials. The tab height may be less than, equal to, or more than the depth of the groove. When thetab25 height is equal to or less than the depth of thedetent51, orgroove70, this prevents excessive deformation of the retaining arms when the bur is inserted therebetween with the tab or tabs engaged in amechanical indicator59 or59a. Such an arrangement also ensures maximal frictional engagement of the bur by the retaining arms for reduced rotational and axial slippage.
• In the embodiment of the tool drive arrangement shown inFIG. 2, as seen inFIGS. 9A and 9B, thedrive spindle10 further includes aram40 for radially forcing apart the retainingarms24 during insertion and retraction or removal of thebur50. In this embodiment, theram40 is mounted in thecasing sleeve30 at thetool insertion end13 of thedrive spindle10 and is axially aligned with and adjacent to thechuck20. Theram40 has acentral tool opening42 for passage of thebur50 and a pair of diametrically opposed lugs44 extending axially from theram40 toward thechuck20 in the assembled condition of thespindle10. Thelugs44 are shaped to engage theaxial slits26 of thechuck20 in the assembled condition. Thelugs44 are preferably longitudinally tapered to force apart the retainingarms24 when theram40 and chuck20 are forced toward one another. Theram40 is preferably fastened to thecasing sleeve30 and thechuck20 is preferably movable in thecasing sleeve30 to allow for movement of thechuck20 relative to theram40 for use of thespindle10 in pushbutton release handpieces. Activating the pushbutton of such a handpiece (not illustrated) will move thechuck20 in thecasing sleeve30 toward theram40 whereby the retainingarms24 are radially forced apart by thelugs44, as will be readily apparent to the person skilled in the art. Theram40 is permanently or releasably fastened to thecasing sleeve30, for example, by a threaded connection or a press-fit. Other possible fastening methods include welding or gluing and the like. However, the fastening method used must ensure that theram40 will not move relative to thecasing sleeve30 when the ram and chuck are forced against one another for the opening of the retainingarms24.
• In one variant of thespindle10, thecasing sleeve30 represents the torque receiving element of the spindle. Thesleeve30 fits sufficiently closely into thespindle socket109 of the drive head101 (seeFIG. 1) to ensure reliable torque transfer from thedrive105 to thespindle10. Rotational torque is then transferred from thespindle10 to thebur50 through engagement of thelugs44 of theram40 in theaxial slits26 of thechuck20 and frictional engagement of the retainingarms24 with thecontact surface60 on thebur50. In a preferred variant of thespindle10, as shown inFIGS. 6A and 6B, torque is transferred directly from thedrive105 to thechuck20 by way of atorque key28 on the drivenchuck end21 of thechuck20, which is shaped for fitting engagement with a torque socket (not illustrated) at a bottom of thespindle socket109. Thetorque key28 is formed by providing the drivenchuck end21 with any non-circular outer cross-section. Thetorque key28 and the torque socket preferably have complementary shapes, but non-complementary shapes providing an interference fit can also be used as long as rotation of thetorque key28 relative to the torque socket is reliably prevented. In a preferred embodiment, thenon-circular torque key28 is shaped from a generally cylindrical end portion of thechuck20 which is provided with two diametrically opposed flattened surface portions (seeFIGS. 6B and 8).
• In a preferred embodiment of the drive arrangement, the drive arrangement further includes a structure for locking thebur50 against rotation in thetool passage12 of thedrive spindle10. This unique torque transfer arrangement is preferably combined with thetorque key28 and torque socket arrangement described directly above to provide for direct torque transfer from thedrive105 to thebur50 without the possibility of any slippage and the associated heat generation and possible thermal damage to components of the drive arrangement, especially the temperedtool retaining arms24. The torque transfer arrangement includes a lockingportion53 on thebur50, which has an outer non-circular cross section (seeFIGS. 3D,4A to8,10,11) and a lockingsocket27 in thechuck20, which has a complementary or interlocking cross-section. The lockingportion53 is shaped to slidably fit into the lockingsocket27 to allow length adjustment of thebur50 by retracting thebur50 from the fully inserted position in accordance with the principle aspect of the invention.
• Preferably, the lockingsocket27 is co-extensive with thefirst tool seat14, which means thefirst tool seat14 is shaped as a locking socket of a cross-sectional shape permitting fitting and slidable insertion of the lockingportion53 of thebur50 while positively preventing rotation of the lockingportion53 in the lockingsocket27.FIG. 4A shows an axial end view of a preferred embodiment of adental bur50 in accordance with the present invention having a lockingportion53 of triangular cross-section.FIG. 8 illustrates an end view of thedrive spindle10 of the preferred embodiment ofFIG. 2, illustrating the cross-sectional shape of the lockingsocket27 which is not directly complementary to the cross-section of the lockingportion53 shown inFIG. 4, but nevertheless provides an interference fit of the lockingportion53 in the lockingsocket27 to guarantee a reliable interlocking between the lockingportion53 and the lockingsocket27. In this embodiment, the lockingsocket27 is a multi-faceted socket formed in a portion of thetool passage12 of thechuck20 near the drivenend21 of the chuck. Themulti-faceted locking socket27 provides multiple possible insertion orientations for thetriangular lock portion53 to improve the chance of aligning the lockingportion53 with the lockingsocket27 without the aid of visual pre-alignment.
• In a particularly preferred embodiment, the lockingsocket27 extends substantially the whole length of thetool passage12 for maintaining concentricity during rotation. It is preferable that the lockingportion53 and the lockingsocket27 be rotation symmetrical, which means symmetrical about the axis of rotation to prevent excessive vibration of thebur50 orchuck20, and thus the handpiece, during high speed rotation. In the alternative, the lockingportion53 and/or the lockingsocket27 can also be momentum symmetrical, which means weight balanced about the axis of rotation, again to prevent excessive vibration in the handpiece.
• To improve the ease of proper alignment of the lockingportion53 with the lockingsocket27, a particularly preferred embodiment of thechuck20 includes abur aligning member53a(FIG. 7) near the bur insertion end of thedrive spindle10. Thebur aligning member53apreferably corresponds in shape and orientation with thenon-circular locking socket27, which is generally located deep in the drive head of the handpiece. Thisbur aligning member53aallows for pre-alignment of the lockingportion53 with the lockingsocket27 upon insertion of the drivenportion54 into thedrive spindle10. Thebur aligning member53aforms part of thetool engaging tab25 in the embodiment shown inFIG. 6.
• In an alternate preferred embodiment of the tool drive arrangement of the invention, shown inFIG. 12, all parts perform the same function, although thechuck20 and ram40 are positioned in thespindle10 in an axially opposite orientation to that in the embodiment ofFIG. 2. Thebur50 is inserted first into thechuck20 and subsequently enters the axially aligned andadjacent ram40. In this orientation, thefirst tool seat14 is formed in theram40 and a portion of thesleeve30 for supporting the drivenend55 of the tool during length adjustment, and thesecond tool seat16 is located in thechuck20 for supporting the drivenportion54 of the tool at a position between thedriven end55 and the workingportion56.
• In the variant illustrated inFIG. 12, drive torque is transferred to thesleeve30 through frictional engagement with thespindle socket109, for example by press-fitting thespindle10 into thespindle socket109. Theram40 is securely fitted into the spindle and engages thechuck20 in an orientation wherein lugs44 extending from theram40 toward thechuck20 engageaxial slits26 formed in thechuck20, similar to the embodiment shown inFIG. 2. However, torque is transferred differently from the embodiment ofFIG. 2. For torque transfer in the embodiment ofFIG. 12, as shown inFIGS. 13B and 15, aconstricted portion30aof thecasing sleeve30 provides a lockingsocket27 to prevent rotation of the lockingportion53bur50 relative to thesleeve30. The lockingsocket27 can be designed in any suitable manner. For instance, as shown inFIG. 15, theconstricted portion30acan have a non-circular cross-section complementary to the non-circular cross-section of the lockingportion53 of thebur50 or, alternatively, it can provide an interference fit to form a lockingsocket27, as described elsewhere above. Theconstricted portion30aalso prevents rotation of theram40, specifically thelugs44, relative to thesleeve30. This not only maintains the ram in the same rotational position in thesleeve30 at all times, but also thechuck20 due to the interaction between thelugs44 of theram40 and theaxial slits26 in thechuck20.
• In the tool drive arrangement ofFIG. 12, as shown inFIG. 13B, atool engaging tab25 projects from one retainingarm24, while thesecond retaining arm24ahas a relatively flattenedtab25a, which essentially acts as a pressure pad against thecontact surface60 of themechanical indicator59 of thebur50 during operation. The pressure pad may be in the form of a flattenedtab25a, as shown, or it may simply be a retaining arm without any tab. Asingle tab25 pluspressure pad25aarrangement, which means an asymmetrical tab arrangement, is preferred forburs50 which have themechanical retraction indicator59 located on the lockingportion53 of the bur50 (seeFIG. 3G). In this embodiment, the depth of thedetent51 is asymmetrical about the circumference of the lockingportion53 of thebur50 due to the non-circular cross-section of the locking portion53 (seeFIGS. 4B and 4C). During operation, thebur50 is oriented in thespindle10 such that thetab25 engages the deeper portion of thedetent51 and thepressure pad25aengages the shallow portion of thedetent51 where the surface of thebur50 has been flattened to form the triangular locking portion53 (FIG. 4C). This orientation is achieved by the specific shape of the lockingsocket27 in thesleeve30 as shown inFIG. 15. The provision ofasymmetrical tabs25 and25a, as in this embodiment, is especially advantageous for tools with three-sided non-circular locking portions. The use of asymmetrical tabs and a shaped lockingsocket27 which forces thebur50 into the same rotational position relative to thechuck20 significantly reduces wear. Use of a symmetrical chuck having identical tabs would result in one tab always being in contact with a flattened locking surface on the tool while the other would engage the circular external surface of the tool shaft in the lockingportion56, resulting in wear on that external surface.
• A person skilled in the art will appreciate that an asymmetric or single-tab chuck must be counterbalanced to prevent excessive vibration during rotation, in particular at the high rotation speeds encountered with an air turbine handpiece. This can be achieved by balancing the weight of the retainingarms24 and24a, or preferably, by balancing the overall spindle system about the central axis for smooth rotation. For example, material can be removed, added, or repositioned in one or more of thesleeve30, thechuck20 or theram40, to accommodate for any difference in weight between the two retainingarms24 and24a, or to balance any other asymmetrical components of thespindle10. In the embodiment shown inFIGS. 13B and 15, the sleeve has been designed to counterbalance the system due to the asymmetrical design of the chuck. The design of the lockingsocket27 is also counterbalanced to prevent vibration during rotation.
• In an alternative embodiment toFIG. 12 (not shown), the ram is in torque-receiving communication with the drive mechanism in the handpiece by way of atorque key28, similar to thetorque key28 on thechuck20 of the embodiment shown inFIG. 2. The lockingsocket27 in this alternate preferred embodiment (not shown) is preferably located within the tool-receiving bore of theram40 but may also be located in thesleeve30, similar to theconstricted portion30aof thesleeve30 shown inFIG. 13B. The lockingsocket27 is preferably elongated and radially supports thebur50 to maintain concentricity during rotation at various insertion depths between D_minand D_max. The socket is preferably complementary in shape to the non-circularcross-sectional locking portion53 of thebur50, or provides an interference fit similar to that exemplified inFIGS. 6A and 6B.
• As shown inFIG. 15, theconstricted portion30 of thesleeve30 forming the locking socket for torque transfer to thebur50 has an asymmetrical shape to always align the bur in the socket in the same orientation relative to the sleeve. In particular, the cross-sectional shape of theconstricted portion30aincludes a flat portion for engagement with a flattened section on the lockingportion53 of thebur50, which flat portion is diametrically opposite a circular portion of sufficient diameter to fittingly engage a externally circular section of the lockingportion53. The spacing of the diametrically opposite flat and circular portions of the locking socket in the sleeve30 (constrictedportion30a) is selected to be substantially equal to the dimensions of the lockingportion53 of thebur50 so that the locking portion is fittingly insertable into the locking socket and locked against rotation therein for reliable torque transfer from thesleeve30 to thebur50.
• Other non-circular cross-sectional locking portions and complementary locking sockets are also contemplated, for example, square-, rectangle-, octagonal-, diamond-, star-, and flattened circle-shape among others. A non-circular locking portion can also have a generally circular shape with one or more indents, notches or axial grooves projecting radially inward into the lockingportion53. A variant in which the lockingportion53 of thebur50 directly engages a lockingsocket27 formed in a portion of the drive mechanism, for example a turbine, for direct torque transfer is also contemplated.
• It is contemplated that a dental tool in accordance with the present invention can have any type of working tip for contacting a tooth surface known in the art. Furthermore, a portion or all of the tool may be provided with a wear resistant coating. One or more of the components of the rotatable tool drive arrangement of the present invention may be provided with a low friction coating, for example thelugs44 of theram40. It is contemplated that a tool according to the present invention may further comprise an axial channel to allow passage of air or liquid from the handpiece to a surface of a tooth. It is also contemplated that the tool of the invention may be a tool other than a dental bur.
• The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Claims (20)

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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 5, wherein the mechanical indicia is an annular groove and the stop is a lateral wall of the groove.

10. The tool ofclaim 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 ofclaim 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 ofclaim 12, wherein the plane is further oriented perpendicular to a radius of the shaft.

14. The tool ofclaim 13, wherein the cylindrical and planar mantle portions are circumferentially evenly distributed.

15. The tool ofclaim 14, wherein the cylindrical and planar mantle portions extend over equal portions of the circumference of the locking portion.

16. The tool ofclaim 14, wherein the torque lock portion forms a major part of the driven portion.

17. The tool ofclaim 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 inclaim 17, wherein the locking portion further includes a mechanical stop for mechanical engagement with the grip member.

20. The tool as defined inclaim 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.

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