Related Application

This appl ication is a continuation-in-part of my co-pending appl ication Seri al No. 885,290, fi led March 10, 1978.

Background

The chucks used for releasably holding burs in high-speed dental handpieces have chucking actions that can be generally categorized as falling within two main groups. The first group includes collet chucks which are normally wrench operated and which are threadedly mounted within the rotary members (usually bur tubes) of the handpieces so that the terminal gripping fingers of the chucks ar>e forced to close or allowed to open depending on whether the wrenches are rotated in one direction or the other. The second group includes spring-gripped chucks which depend on the resilience or spring characteristics of the chucks for bur retention.

While efforts have been made to develop a fully satisfactory chuck which overcomes certain disadvantages that have come to be associated with chucks of these types, such efforts have not been entirely successful.

Wrench operated chucks, whether of the pull-to-tighten or push-to-tighten variety, tend to undergo bur "walkout" or rejection from high-speed turbine-driven dental handpieces during conditions of extremely heavy cutting, particularly in tenacious types of material such as gold alloys and some silver amalgams under which the cutting dynamics are severe. The problem is characteristically associated with high-speed handpieces -- that is, handpieces which develop rotational speeds in excess of 100,000 revolutions per minute and, more particularly, speeds of the order of 200,000 to 500,000 revolutions per minute. Handpieces capable of such high speed operation are invariably of the air turbine type, in contrast to

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electrically-powered handpieces. _* Tests have shown that axial walkout m occur even without accompanying torsional slippage of the bur. Althou the axial walkout problem is a serious one which has existed for a numb of years, the precise reasons why the problem occurs do not appear to ha been fully known, or at least have not been fully analyzed and reported i any known technical literature.

A variation of the push-to-tighten chuck is a double-ended type, that is, chuck with spring fingers at opposite ends, cooperatively associated wit a separate nut. While advantages in eliminating or reducing bur walkou can generally be anticipated with this type of chuck, there ar disadvantages which include the possibility of the nut loosening durin cutting, thereby presenting the danger of the chuck, bur, and/o tightening nut releasing during handpiece operation. Patents illustrativ of double-ended chucks are 3,619,904 and 3,488,850.

While spring grip type chucks are known to be more resistant to bu walkout, they are commonly associated with other troublesom disadvantages. Since spring action, in contrast to a positive clampin action, is responsible for bur retention, problems of durability dependability, wear and fatigue are often associated with spring gri chucks. Also, problems are often encountered in attaching or removin burs. In the use of a spring grip chuck, the bur is normally removed b utilizing a small diameter push rod which the operator must direct with force strong enough to overcome the frictional forces exerted by th spring. Conversely, in order to insert a bur, the bur must generally b placed against a soft brass or plastic slug so that it can be pushed int place without damage to the cutting surface of the bur. Majo disadvantages of spring grip chucks have resided in the fact that it i often difficult and dangerous for operators to apply sufficient force t overcome the springs for bur insertion and removal without damaging th burs, the handpieces, or both. Patents illustrative of spring grip chuck are 2,963,519, 3,088,745, 3,255,527, 3,321,209, 3,426,429, 4,021,919 an 4,012,841.

Other patents showing wrench-operated collet chucks are 3,325,899, 3,496,638, 3,813,782 and 3,888,008.

Summary This invention is concerned with a chuck assembly which provides the advantages of both spring-grip and wrench-operated chucks without the aforementioned disadvantages of prior chuck constructions. More specifically, it is an object to provide an improved chuck assembly which is relatively simple in construction, is wrench-operated for positive gripping action, is capable of withstanding the substantial torsional forces generated when such a chuck is tightened to grip a dental bur, and is remarkably free of bur walkout problems even when the high-speed handpiece is used to cut through gold alloys, amalgams, and other tenacious materials. A further object is to provide a chuck assembly which is durable, does not wear readily or break easily and is field replaceable. In addition to its other advantages, the chuck assembly is easily operated to release and secure a bur and, in contrast to at least some conventional wrench-operated chuck assemblies, does not tend to score, gouge, or otherwise damage the surface of a bur shank during normal use.

The chuck assembly consists essentially of two main elements: a rotor having a bore, and a chuck received within that bore. The term "rotor" is used herein to refer to the rotatably mounted member of a high-speed turbine-driven dental handpiece. Ordinarily, the rotor will either be the turbine itself or a bur tube secured within that turbine. While the invention might be utilized with dental handpieces other than turbine- driven high-speed handpieces, the problem of bur walkout is not encountered with low-speed handpieces and, therefore, a major benefit of the invention would not be realized.

The chuck is formed in one piece, is tubular, and defines a bore for receiving the shank of a dental bur. The chuck includes an integral bur- clamping or bur-gripping section disposed intermediate the length of the chuck (and of the rotor's bore), such section being defined by an external shoulder or bearing surface and being capable of flexing radially inwardly to clamp the mid-portion of the shank of a dental bur extending therethrough. ^- SI tr

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The external shoulder of the bur-gripping section is engagable with internal shoulder within the bore of the rotor so that as the shoulders a urged axially into forceful engagement the bur-gripping section of t chuck will flex radially inwardly to engage and grip the mid-portion of th bur shank.

Above and below the bur-gripping section — that is, spaced from opposit ends of that section — are elongated pilot passages which snugly bu slidably receive portions of the bur shank in zones spaced axially from th bur-gripping section. The rotor extends substantially the full length the chuck and includes a lower end portion which surrounds and braces th lower pilot section of the chuck to prevent flexing forces directed agains the bur during operation from being propagated beyond the lower pilot zon to the bur-gripping zone. The result is a construction which is positiv in operation and remarkably free of bur walkout or ejection in use.

In the disclosed embodiment the pilot sections and bur-clamping o bur-gripping sections of the chuck are integrally formed. The clampin section is disposed intermediate the length of the chuck and its radia deformability is achieved by providing a plurality of openings or slots i circumferentially-spaced positions about the chuck. In the best mod presently known for practicing the invention, the chuck is provided wit just two such slots arranged in diametric opposition. Not only does th two-slot construction perform at least as effectively as construction having greater numbers of slots, but the two-slot construction achieve such results while providing superior torsional rigidity. Such torsiona rigidity is particularly important because of the threaded interconnectio between the chuck and rotor and the fact that the chuck is tightened b rotating it within the rotor until the parts are in such forcefu engagement that the intermediate slotted section of the chuck is deforme or flexed radially inwardly to grip the bur. Such forceful engagemen between the chuck and rotor imposes considerable torsional strain on th longitudinally-elongated and arcuate web portions spaced by the slots o the chuck.

In addition to its superior strength and peformance characteristics, the two-slot chuck construction has the advantages of being easier and less costly to manufacture.

Other features of the structure and its operation, and other advantages and objects of the invention, will become apparent from the specification and drawings.

The Drawings Figure 1 is an enlarged sectional view of the head portion of a dental handpiece equipped with the chuck assembly of this invention.

Figure 2 is a top plan view of the handpiece of Figure 1.

Figure 3 is a further enlarged longitudinal sectional view of the chuck assembly.

Figure 4 is an exploded perspective view of the components of that assembly.

Figure 5 is a greatly enlarged fragmentary and somewhat exaggerated sectional view depicting the deformation of the intermediate portion of the chuck which results in bur retention.

Figure 6 is an enlarged fragmentary and somewhat exaggerated longitudinal sectional view of a chuck and rotor assembly constituting a preferred embodiment of the invention.

Figure 7. is a perspective view of the chuck of Figure 6.

Figure 8 is a cross sectional view taken along lines 8-8 of Figure 7.

Detailed Description Referring to Figures 1 and 2, the numeral 10 generally designates a dental handpiece having a housing 11 and a cap 12 threadedly secured to the housing at the upper end thereof. The handpiece selected for illustration

is an air-driven handpiece having a pair of ball bearing assemblies 13 a 14 supporting rotor 15 for rotation within the chamber defined by t housing. The rotor includes driving means in the form of turbine 15a a bur tube 15b. The turbine depicted in Figure 1 is an axial-flow turbi which is driven by air discharged from stator 16, the stator in tu receiving drive air supplied by drive air passage 17. The bulk of the ai discharged from the turbine is exhausted through discharge passage 18.

The rotor tube or bur tube 15b is provided with internal threads 19 at th upper portion of its axial bore 20. A sloping internal shoulder 21 i located intermediate the upper and lower ends of the bore. Shoulder 2 defines the boundary between two sections of the bore 20 of differen diameter, the lower section 20a adjacent the bur-receiving end of th handpiece having smaller diameter than upper section 20b.

As shown most clearly in Figures 3 and 4, a tubular chuck ^" 22 is dispose within the rotor tube 15b. The chuck has a bore 23 extending therethrough the lower cylindrical portion 24 of the bore defining a socket fo receiving the shank of a bur, and the upper portion 25 being of non circular cross section (preferably square) to define a socket fo receiving a suitable wrench (not shown).

Although the chuck of Figures 1-5 is formed of a single piece of material it may conveniently be considered as being composed of a plurality o sections or portions, namely a lower end portion 22a, an upper en portion 22b, and an intermediate portion 22c. The wall of th intermediate portion 22c is provided with an external shoulder adapted t engage the internal shoulder 21 of the rotor tube when the parts ar assembled as illustrated in Figure 3. The upper portion 22b is externall threaded, the threads of that portion mating with the internal threads o the rotor tube. Because of the downwardly and inwardly slopin configuration of the shoulders, the intermediate portion 22c of the chuc is pressed radially inwardly when the chuck is screwed downwardly to urg shoulders 21 and 27 into forceful engagement with each other. Since th dimensional difference between the outside diameter of a bur shank and th inside diameter of bore portion 24 is small, and since such parts ar

manufactured to close tolerance, only slight inward flexing or deformation of the wall of the intermediate bur-clamping portion or section 22c is required in order to grip the bur. To promote effective flexure without the need for applying excessive twisting force to rotate the chuck 22 within the rotor tube 15b after the sloping shoulders have made contact with each other, openings or slots 28 are formed in the wall of the inter¬ mediate bur-clamping portion 22c. The openings or slots are circu ferentially spaced and, in the embodiment depicted in Figures 1-5, are longitudinally elongated, running the full length of the intermediate bur-clamping portion 22c.

Where autoclavability is required or desired, the material of choice for the chuck as well as other parts of the handpiece is believed to be stainless steel. The slotted chuck construction shown in the drawings is intended to be fabricated out of stainless steel although it is believed apparent that other materials having the necessary properties of flexibility, strength, and durability might be used.

It should be observed that above and below the bur-clamping section 22c of the chuck are upper and lower portions 22b and 22a, respectively, which define upper and lower pilot guide passages 29 and 30. In the illustration given, such passages are portions of the cylindrical section 24 of the bore 23. As previously indicated, bore portion 24, and especially pilot passage sections 29 and 30 of that portion of the bore, are only slightly larger in diameter than the shank of the bur to be received therein. The relationship has been referred to as a snug but slidable fit; in technical terms, the spacing should be as small as manufacturing tolerances permit, hopefully of the order of magnitude of .0005 of an inch. By reason of the close but slidable fit between the shank of a bur and the upper and lower pilot passages at each end of the chuck's bur-gripping section, and the bracing effect of the surrounding rotor tube 15b, particularly the bracing effect of that rotor tube on the lower piloting portion of the chuck, concentricity between the bur and rotor may be achieved and maintained. The gripping of the shank of the chuck in an intermediate zone disposed between and spaced from the upper and lower pilot zones, and the bracing of those pilot zones, are believed to be responsible for the absence of bur walkout during operation of handpiece 10. _. .- ^' ' _ _τ ~ ^v" C-..FI

The wrench used for adjusting chuck 22 is not shown because it forms direct part of the present invention and because such wrenches are wide used and well known. Reference may be had to U.S. patents 3,235,899 a 3,888,008 for wrenches adaptable for use with the chuck assembly disclos herein. The square socket 25 has already been described for the purpose coupling the wrench to chuck 22. Notches 31 (Figure 4) are formed in t upper end of rotor tube 15b for the purpose of coupling the wrench to th tube, it being understood that in the operation of either loosening tightening the chuck, one part (the chuck or the rotor tube) must rotated while the other part (the rotor tube or the chuck) must be hel stationary.

Figure 5 depicts in enlarged and greatly exaggerated fashion t cooperative relationship between the parts during operation of the chu assembly. As the chuck 22 is screwed downwardly to force external should 27 into camming engagement with internal shoulder 21 of rotor tube 15b, t deformable intermediate portion 22c of the chuck is flexed or deform radially inwardly into tight gripping engagement with the shank 32 of dental bur. It will be.observed that the wall of the intermediate porti is flexed radially into a curved configuration and that clamping conta between the chuck and the bur occurs along a zone of substanti longitudinal extent. The length of that zone contrasts sharply with th line of contact or biting action characteristic of conventional colle chucks. The longitudinal curvature of the deformed intermediat portion 22c not only eliminates any appreciable scoring or marring of th surface of shank 22 but, at the same time, produces an extraordinaril effective gripping action which is highly resistant to bur walkout an slippage.

The one-piece chuck may be easily removed by simply unthreading it from th rotor tube 15b and extracting it through the enlarged opening 33 in the ca of the handpiece. Therefore, should cleaning of the chuck be desired, o should replacement become necessary, such operations may be readil performed by the dentist or his assistant. Since the lower section 20a o the bore of the rotor tube is smaller in diameter than the upper sectio 20b, and since the lower portion 22a of the chuck is likewise smaller tha ό REA

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the upper portion 22b, there is no possibility that during handpiece operation the chuck might somehow become loosened and released from the lower end of the rotor tube.

In the embodiment of Figures 1-5, the unitary chuck 22 is provided with four circumferentially-spaced slots 28. Chuck 22' of Figures 6-8 is substantially identical to chuck 22 except that only two diametrically- opposing slots 28* are provided. The rotor and handpiece in which the chuck 22' is mounted may be identical to the parts already described; therefore, in Figures 6-8 the same numerals are used to designate elements that do not differ from those previously described.

The effectiveness of the embodiment of Figures 6-8 appears to confirm what applicant has theorized to be the mechanics of bur walkout in high speed (200,000 to 500,000 or more rpm) dental handpieces. In a conventional wrench-operated chuck, spring fingers at the chuck's lower end are forced into tight engagement with the shank of a dental bur. Slight flexure of the exposed shank of the bur below the jaws in response to laterally directed forces against the tip of the bur tends to cause a biting and pivoting action to take place along an arc of movement opposite from the point of applied force, accompanied by a slight sliding or slipping action along that arc of movement on the same side as the applied force. With each revolution of the flexed bur, any given point on the surface of that bur engaged by a jaw of a conventional chuck alternately pivots against that jaw and then, 180° later, when the point of contact generally faces

• the point of applied force, may slip slightly downwardly from the jaw. For reasons not fully understood, walkout has not been found to be a significant problem with low or medium speed (i.e., under 200,000 rpm) handpieces. However, with high-speed handpieces, such alternate biting, pivoting, and sliding action may result in rapid walkout at some risk to dentist, patient, or both.

The characteristic of both of the embodiments disclosed herein is that piloting of the bur at the lower end of the chuck, braced by the bur tube, occurs a substantial axial distance from the area in which the bur is gripped and held. In Figure 6, the numeral 40 generally designates the

zone or area of piloting action at the lower end of chuck 22', where numeral 41 indicates the zone or area of forceful gripping contact betwe the chuck and a bur 32. The two zones 40 and 41 are spaced axially apart substantial distance. When flexing movement of the lower portion of a b takes place (such movement is shown in exaggerated form by broken lines in Figure 6), contact between the chuck 22' and bur 32 in pilot- zone 4 coupled with the reinforcement of the chuck's lower end provided by t surrounding bur tube 15b, prevent the flexing action of the bur tube fr being transmitted or propagated upwardly to the bur-clamping zone 41. primary reason why bur walkout is so effectively prevented is believed reside in the spacing of the two zones and the external bracing of th chuck's lower end by the rotor tube 15b, thereby isolating the grippin zone 41 from flexing action of the bur occasioned by lateral forc generated when the tip of the bur is forced against a work object.

Spacings and deformations are exaggerated in Figures 6 and 8 f illustrative purposes. When the intermediate bur-gripping portion of th chuck is cammed inwardly into tight-gripping contact with a bur throug forceful engagement petween external and internal shoulders 27 and 2 respectively, the side walls or web portions of the chuck on opposite side of slots 28' are urged inwardly as indicated by broken lines in Figure 8 The bur is therefore tightly gripped along diametrically-opposing surfac portions. It has been found that effective gripping action takes plac even though the areas of forceful contact are diametrically-dispose rather than being spaced at three or more points about the circumference o the bur, and it is believed that such effectiveness arises to considerable extent because of the braced piloting of the bur at the lowe end of the chuck in a zone 40 spaced axially from gripping zone 41.

Since only two slots 28' are provided, chuck 22' has outstanding torsiona rigidity and is better able than chucks having a greater number of slots t withstand the substantial twisting forces that develop when such a chuck i tightened or loosened by a wrench. Also, to the extent that formation of pair of slots requires less machining, and simpler machining procedures than the formation of a greater number of slots, the chuck of Figures 6- is advantageous in terms of ease and lower costs of

While in the foregoing, embodiments of the invention have been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.