Abstract:
A transmission for changing rotary motion into angularly reciprocating motion and adapted to be mounted on the output end of a dental power unit of the type having a rotary drive output and used to drive a dental tool. The transmission is comprised of a support member, a driving resinous member supported by the support member for rotary motion, and a driven resinous member supported by the support member for reciprocating angular movement by the support member. The transmission subassembly is formed by the driving resinous member, driven resinous member and support member and adapted to be mounted on the output end of the dental power unit with a rotary drive output mechanically coupled to the driving resinous member. A driving cam surface is disposed on a portion of the driving resinous member. A driven cam surface is disposed on a portion of the driven resinous member. The driving cam surface is in contact with the driven cam surface during at least a portion of the cycle of rotation of the driving cam surface. The driven cam surface is configured and dimensioned to be driven by the driving cam surface in a positive angular direction during one part of the cycle and is driven by the driving cam surface in a negative angular direction during another part of the cycle. Angularly reciprocating motion is thereby imparted to the dental tool as the driving cam surface and driven cam surface engage each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Postal et al. U.S. application Ser. No. 09/288,764, filed Apr. 8, 1999 now U.S. Pat. No. 6,247,931 B1 which is a continuation-in-part of Postal et al. U.S. application Ser. No. 08/878,995, filed Jun. 19, 1997, now U.S. Pat. No. 5,931,672. The disclosures of patents 6,247,931 B1 and 5,931,672 are hereby incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a dental tool assembly having a head that imparts oscillatory motion to a desired dental treatment device coupled to the assembly. More particularly, the present invention relates to a drive mechanism for a dental tool assembly, the drive mechanism having a rotating drive shaft that engages a first end of a driven shaft to rotate the driven shaft in an oscillatory manner. The present invention also relates to a bearing assembly for a dental tool drive mechanism, the bearing assembly supports the drive shaft for rotary motion using a bushing shape to reduce friction while also aligning the drive shaft. A dental tool is coupled to a second end of the driven shaft and is thereby rotationally oscillated. 
     2. Description of the Related Art 
     Dental tool assemblies, such as prophy angles and drills, which impart an oscillatory rotary motion to a dental treatment device coupled thereto are known in the art. In particular, such assemblies typically have a driving mechanism comprising a drive shaft with a rotation axis that is perpendicular to the rotation axis of a driven shaft to which the dental treatment device is coupled. The drive shaft of prior art driving mechanisms has an element positioned eccentric to its rotation axis and extending towards the driven shaft to engage a slot in the driven shaft. Rotation of the drive shaft thus imparts an oscillatory rotation to the driven shaft. 
     For example, U.S. Pat. No. 1,711,846 to Heilbom shows a dental filing device having a drive shaft perpendicularly oriented with respect to a file holder. A crank pin, mounted on a crank disc on an end of the drive shaft adjacent the file holder, engages within a bore in the file holder. The crank pin is positioned on the crank disc eccentric to the rotation axis of the drive shaft. Thus, rotation of the drive shaft rotates the eccentrically positioned stud, thereby causing the file holder to rotate in an oscillatory manner. 
     Similarly, the dental instrument in U.S. Pat. No. 2,135,933 to Blair has a rotary drive shaft with an eccentrically positioned stud that engages within a slot of a piston to which a massage tip is coupled. Rotation of the drive shaft causes oscillatory rotation of the massage tip. Another massage tool that imparts oscillatory motion to a head spindle to which a massage cup or brush is coupled is shown in U.S. Pat. No. 4,534,733 to Seigneur in et al. In the Seigneur in Patent, the stud that engages the head spindle is mounted eccentric to the rotation axis of the drive shaft, but is inclined to extend across the rotation axis. The portion of the stud that is aligned with the rotation axis of the drive shaft is also aligned with the rotation axis of the head spindle. The dental tool shown in U.S. Pat. No. 4,460,341 to Nakanishi also has a guide pin mounted eccentric to the rotation axis of a drive shaft and engaging within a slot of a driven shaft to which a dental treatment device is coupled. 
     In all of the above-described dental tool assemblies, a stud or pin extends into a slot to drive the element to which the dental treatment device is coupled. Because the treatment device typically must be driven at very high speeds (e.g., the recommended speed of a standard prophy angle at approximately 6,000 rotations per minute), there is a risk of the stud or pin breaking off during use. Moreover, manufacturing of the drive shaft and driven shaft is complicated by the necessity of forming a stud and a slot that are shaped for ready, secure engagement such that rotation of the drive shaft causes oscillatory rotation of the driven shaft. 
     Additionally, some of the drive shafts of the above-described patents also impart reciprocatory axial motion to the driven shaft along the longitudinal shaft of the driven shaft. When such axial motion is not desired, the driven shaft should be locked with respect to the housing in which the drive shaft and driven shaft are positioned, and thus locked with respect to the rotation axis of the drive shaft. Typically, such locking is accomplished by locking the driven element with respect to the housing such as by inter-engagement of stepped portions and/or flanges. However, such locking imparts substantial stresses against the housing and driven shaft. 
     Another drawback of the above-described devices is that they are typically formed from metal and are reusable. The sterilization process necessary in order to reuse the device is typically costly and time consuming. It therefore has been desirable to provide disposable dental tool assemblies that are used only once and therefore need not be sterilized. Such tools typically are made from plastic. 
     Because plastics are generally not as strong as metals, the driving mechanism used in the above-described devices cannot be used because of the inherent weakness of the stud. Therefore, the driving mechanisms of disposable dental tools typically have interengaging gears, such as shown in U.S. Patent No. 5,571,012 to Witherby et al. Because gears are used, the same reciprocatory rotary motion provided by the non-disposable tools cannot be achieved. However, such oscillating movement is desired for a number of reasons. The back and forth reciprocating motion provided by non-disposable dental tool assemblies permits greater speeds to be used and greater pressure to be applied than rotary type devices that do not oscillate, and also may massage the gums of the patient. Additionally, oscillatory movement generates less heat than a full rotational action. Moreover, the risks of hitting undercuts, cutting or tearing soft tissue, and splattering of agents applied by the treatment tool are reduced if not substantially eliminated. 
     Another problem faced by any drive mechanism is how to provide support and alignment for the moving parts. There are many types of bearings that may be used for this purpose. Due to the size, construction methods, and materials used in prophy angles, journal or sleeve style bearing configurations are generally used. 
     An example of such a bearing is shown in U.S. Pat. No. 5,340,310 issued to Bifulk on Aug. 23, 1994. As shown in FIGS. 3,  4  and  5  thereof, a housing having a cylindrical bore with fingers spaced from and extending axially parallel to the bore are provided for receiving a bushing having a square cross-section such that the bushing abuts turned in portions of the fingers. The fingers are flexible such that they bend outwardly allowing the bushing to be pushed past the turned in portions yet bend back to capture the bushing therein. 
     Another example of a drive mechanism is shown in U.S. Pat. No. 5,931,672 issued to R. Postal on Aug. 3, 1999. The mechanism disclosed therein uses a series of flanges and a latch that includes a position retaining surface that contacts the outer periphery of at least one of the flanges. The extreme outer edge of the flanges provide axial alignment for the drive shaft. 
     In use, this arrangement is susceptible to heat build-up on the various bearing surfaces. This problem is compounded by the difficulty in lubricating the bearing surfaces during assembly of the components. Therefore it is desirable to have a bearing surface that is less susceptible to heat build-up and is easily lubricated during assembly. It is also desirable to have a bearing arrangement that is less complex to assemble. The present invention addresses these desires for improving the bearing arrangement in prophy angle drive mechanisms. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a disposable dental tool assembly having a driving mechanism that imparts oscillatory rotary motion to a dental treatment device mounted on the assembly and to achieve this with a structure that can be economically, and reliably implemented in plastic to allow for disposability and the attendant avoidance of the spreading of infection. 
     It is a related object of the present invention to provide a driving mechanism having a drive shaft and a driven shaft each having driving surfaces shaped to engage each other and ride along each other such that rotation of the drive shaft causes oscillatory rotation of the driven shaft. 
     It is a further object of the present invention to provide a dental tool assembly having driving and driven elements that are stabilized with respect to each other against relative movement in a given direction. 
     It is another object of the present invention to provide a dental tool assembly having a drive shaft that is coupled to a driven element such that the drive shaft imparts only oscillatory motion to the driven element without also imparting axial motion to the driven element. 
     These and other objects of the present invention are accomplished in accordance with the principles of the present invention by providing a dental tool assembly having a rotating drive shaft that engages a driven shaft to impart oscillatory rotary motion to the driven shaft. The drive shaft and driven shaft are positioned transverse to each other. The drive shaft has a driving surface at its distal end that is shaped to engage a driven surface on a side of the driven shaft adjacent the drive shaft. Because of the manner in which the distal end is shaped, a stud or guide pin, such as used in the prior art, is no longer needed. Specifically, the driving surface is a cutaway, curved portion of an enlarged end of the drive shaft, and the driven surface is a cut-away side portion of the driven shaft. The cut-away portions of each shaft are shaped to interengage with substantially no play there between such that they are in continuous contact during rotation of the driving shaft. Because of the shapes of the cut-away portions, rotation of the driving shaft causes oscillatory rotation of the driven shaft. 
     The drive shaft and driven shaft are positioned within a housing. In order to prevent relative movement of the shafts with respect to the housing, a plurality of locking mechanisms are provided. First, the drive shaft is provided with a longitudinally extending pin aligned with the rotation axis of the drive shaft. The driven shaft is provided with a slot through which the pin is passed. The slot is shaped so that oscillatory rotation of the driven shaft is not inhibited by the pin, yet axial movement of the driven shaft along its rotation axis is prevented. Another locking mechanism for the drive shaft is provided in the form of at least one flange extending radially from the drive shaft and engaging a radially inwardly extending flange on the inner surface&#39; of the housing. The driven shaft is provided with a rearwardly positioned pin that fits within a bore in the housing to lock the driven shaft in the desired position for oscillation. 
     In the alternative, a bearing assembly acting as both a thrust bearing and a retainer for holding the drive shaft in place is characterized in that it includes a bushing having an inwardly facing frustoconical surface acting in concert with a journal attached to the drive shaft and having a contact surface in contact with said frustoconical surface, said bushing also having a snap-fit arrangement on a peripheral surface thereof. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     These and other features and advantages of the present invention win be readily apparent from the following detailed description of the invention, the scope of the invention being set out in the appended claims. The detailed description will be better understood in conjunction with the accompanying drawing, wherein like reference characters represent like elements throughout the various views of the drawing and: 
     FIG. 1 is an elevational, partially cut-away view of a dental tool assembly formed in accordance with the principles of the present invention; 
     FIG. 2A is a cross-sectional view of the distal end of the dental tool assembly of FIG. 1 along line  2 — 2 , with the driven shaft in the rest position; 
     FIG. 2B is a cross-sectional view of the distal end of the dental tool assembly of FIG. 1 along line  2 — 2  with the drive shaft rotated 90° from the position shown in FIG. 2A; 
     FIG. 3 is an elevational view of a drive shaft formed in accordance with the principles of the present invention; 
     FIG. 4 is a perspective view of the drive shaft of FIG. 2; 
     FIG. 5 is a perspective view of the drive shaft of FIGS. 3 and 4, rotated to another position; 
     FIG. 6 is an end view of the drive shaft of FIG. 3; 
     FIG. 7 is an elevational view of a driven shaft formed in accordance with the principles of the present invention; 
     FIG. 8 is a plan view of the driven shaft of FIG. 7; 
     FIG. 9 is a cross-sectional view along line  9 — 9  of the driven shaft of FIG. 8; 
     FIG. 10 is a perspective view of the driven shaft of FIGS. 7-9; 
     FIG. 11 is an elevational view of a driven shaft similar to that of FIG. 7 but with straight transverse walls of the driven surface; 
     FIG. 12 is a plan view of the driven shaft of FIG. 11; 
     FIG. 13 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a flexible driving member; 
     FIG. 14 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a cylindrical driving member; 
     FIG. 15 is a cross-sectional view of the dental tool assembly of FIG. 14 along lines  15 ; 
     FIG. 16 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a cylindrical driving member with shaft; 
     FIG. 17 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating multiple cam driving mechanism; 
     FIG. 18 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a lobed member; 
     FIG. 19 is a top view of the dental tool assembly of FIG. 18; 
     FIG. 20 is a perspective view of the lobed member of FIG. 18; 
     FIG. 21 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a wedge-shaped member; 
     FIG. 22 is a top view of the dental tool assembly of FIG. 21; 
     FIG. 23 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a multiple gear driving mechanism; 
     FIG. 24 is a cross-sectional view of the dental tool assembly of FIG. 23 along lines  24  showing the engagement of the driving surfaces of partial gear and follower toothed gears; 
     FIG. 25 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a rack and pinion driving mechanism; 
     FIG. 26 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a multiple cam driving mechanism; 
     FIG. 27 is a top view of the dental tool assembly in FIG. 26; 
     FIG. 28 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a multiple gear driving mechanism; 
     FIG. 29 is a side view of the multiple gear driving mechanism; 
     FIG. 30 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating an electromechanical operator; 
     FIG. 31 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a magnetic-mechanically coupled multiple clutch driving mechanism; 
     FIG. 32 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a spring like driving mechanism; 
     FIG. 33 is a perspective view of a plastic driving mechanism of the dental tool assembly incorporating a piston driving mechanism. 
     FIG. 34 is a view like FIG. 1 showing an alternative embodiment of a bearing assembly for rotational support of a drive shaft of the drive mechanism; 
     FIG. 35 is an enlarged view, partially in section, showing a bushing and its journal on a drive shaft; 
     FIG. 36 is a view similar to FIG. 35 including a housing shown in section for illustrating a snap-fit arrangement of the bushing in the housing; and 
     FIG. 37 is an axial view of the bearing assembly taken along line  37 — 37  of FIG.  34 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A dental tool assembly  10 , formed in accordance with the principles of the present invention, is shown in FIG.  1 . Dental tool assembly  10  includes a housing  12  having a proximal end  14  and a distal end  16 , with main body portion  18  extending there between. Proximal end  14  is coupled to a dental tool hand piece (not shown) known in the art. Distal end  16  has a side opening  20  at which a desired dental treatment device (not shown) is coupled. It will be understood that any dental treatment device known in the art may be used. However, the preferred embodiment of the dental tool assembly shown in the FIGS. is a prophy angle to which a prophy cup or brush is coupled to apply prophy paste. 
     Housing  12  is hollow such that first and second channels  22 ,  24  are formed therein for housing driving mechanism  28 . First, longitudinal channel  22  is formed within main body portion  18  and extends from proximal end  14  to distal end  16  along longitudinal axis  23  of main body portion  18 . Second, transverse channel  24  extends across the distal end  16  of housing  12  and opens at side opening  20  of housing  12 . Longitudinal axis  25  of transverse channel  24  is transverse and preferably substantially perpendicular to longitudinal axis  23  of housing  12 . 
     Driving mechanism  28  includes a drive shaft  30  and a driven shaft  40 . Drive shaft  30  is housed in first channel  22  and has a longitudinal rotation axis  31  which prefer-ably corresponds to longitudinal axis  23  of main body portion  18 . A proximal end  32  of drive shaft  30  preferably extends beyond proximal end  14  of housing  12  for connection to a rotary unit (not shown), such as a motor, for rotating drive shaft  30 , as known in the art. Distal end  34  of drive shaft  30  extends toward, and preferably partially into, second channel  24 . Driven shaft  40  is housed in second channel  24  and has a longitudinal rotation axis  41  which preferably corresponds to longitudinal axis  25  of transverse channel  24 . Driven shaft  40  preferably has a coupling element  42  extending therefrom through side opening  20  and out of housing  12 . A desired dental treatment device, selected from those known in the art such as a prophy cup or brush, may be coupled to coupling element  42 . 
     Drive shaft  30  and driven shaft  40  have driving surfaces that are shaped to interengage each other to result in a camming action that translates rotation of drive shaft  30  into oscillatory rotation of driven shaft  40  substantially without play between the driving surfaces, as will now be described. As shown in FIGS. 2A,  2 B, and  3 - 6 , drive shaft  30  has a drive surface  50  (which functions essentially as a cam) at distal end  34 . Preferably drive surface  50  has a substantially conical cam surface, with cone axis  51  being at a preferably 45° angle with respect to rotation axis  31 , as may be observed in FIG.  3 . The conical shape is readily appreciated with reference to FIGS. 2A,  2 B, and  3 - 6 . The tip  52  of conical drive surface  50  preferably is aligned with rotation axis  31  so that a longitudinal surface portion  54  of conical surface  50  is aligned with rotation axis  31  and a transverse surface portion  56  of conical surface  50  is substantially perpendicular, i.e., at a 90° angle, with respect to rotation axis  31  and thus with respect to longitudinal surface portion  54 : As may be seen in FIGS.  2 B and  3 - 6 , conical surface  50  is formed to one side of rotation axis  31 . Conical surface  50  may be formed by cutting away a portion of an enlarged region  30   a  of shaft  30 , thus leaving a flange-like section  58  at distal end  34 . 
     Driven shaft  40  (which essentially functions as a cam follower), shown in isolation in FIGS. 7-10, has a driven surface  60  along its side (i.e., extending along rotation axis  41  of driven shaft  40 ). The elevational view of 
     FIG. 7 is similar to the view of driven shaft  40  in FIG. 1, except that driven shaft  40  is shown with driven surface  60  facing upward, rather than downward as in FIG.  1 . Typically, driven surface  60  is formed as a cut-away portion of a side of driven shaft  40 . Driven surface  60  has alternating hills  62  and valleys  64 . Preferably, two hills  62  are provided opposite each other with a valley  64  between adjacent, juxtaposed sides of opposed hills  62 , thus spacing hills  62  apart. Viewed another way, the upwardly extending sides of the opposite valleys  64  are joined to form hills  62 . Hills  62  and valleys  64  are shaped to conform to the shape of drive surface  50  such that drive surface  50  is in continuous contact with driven surface  60  with substantially no play there between as drive shaft  30  rotates during operation of dental tool assembly  10 . Specifically, valleys  64  of driven surface  60  are conically cut-away such that conical drive surface  50  may be engaged therewith such that transverse surface portion  56  and distal surface portions adjoining transverse surface portion  56  of conical drive surface  50  are in close contact with the surfaces of a valley  64 . Because opposite sides of conical drive surface  50  are at an approximately 90° angle with respect to each other and valleys  64  are shaped to conform to conical drive surface  50  with hills  62  formed at the sides of valleys  64 , peaks  66  of hills  62  are preferably also at an approximately 90° angle with respect to each other. The contour of driven surface  60  may be better understood from a review of the elevational views of FIGS. 8 and 10. 
     The camming action of the present invention, which permits rotation of drive shaft  30  to cause oscillatory rotation of driven shaft  40  as a result of the interaction of the shapes of driving surfaces  50 ,  60 , will now be described. When drive surface  50  engages a valley  64  of driven surface  60 , driven shaft  40  is in a rest position (i.e., driven surface  60  completely faces drive surface  50  and proximal end  14  of housing  12 , rather than a side of housing  12 , as shown in FIG.  1 ). As drive shaft  30  rotates about rotation axis  31 , drive surface  50  moves along driven surface  60  until drive surface  50  engages a hill  62 . As described above, and as may be seen in FIG. 8, the peaks  66  of opposite hills  62  are positioned substantially 180° apart with the bottoms  65  of valleys  64  approximately 90° from each peak  66 . Thus, when drive surface  50  has rotated 90° from a rest position in contact with valley  64  (such as shown in cross-sectional view  2 A), drive surface  50  comes into contact with adjacent hill  62 . When transverse surface portion  56  of drive surface  50  contacts peak  66  of an adjacent hill  62 , peak  66  is also transverse to rotation axis  31  such that driven shaft  40  is rotated 90° about its rotation axis  41  from its rest position. It is noted that peaks  66  are at an approximately 90° angle with respect to each other, as may be seen in FIG. 2B, and longitudinal and transverse portions  54 ,  56  of drive surface  50  are also at an approximately 90° angle with respect to each other, as may be appreciated with reference to FIGS. 1,  2 B, and  3 . Thus, when transverse portion  56  of drive surface  50  contacts a peak  66  to rotate driven shaft  40 , longitudinal portion  54  is in contact with the opposite peak  66 . As drive surface  50  continues to be rotated upon rotation of drive shaft  30 , drive surface  50  contacts the next valley  64  (opposite the first mentioned valley), returning driven shaft  40  to the rest position. Further rotation of drive shaft  30  brings drive surface  50  into contact with the next hill  62  (opposite the first-mentioned hill), thereby rotating driven shaft  40 , in the same manner as described above but in the opposite direction, 90° about rotation axis  41 . Thus, driven shaft  40  oscillates a total of 90°, performing a quarter turn in opposite directions from a rest position. 
     As may be seen in the plan view of FIG. 8, transverse side walls  68  of driven surface  60  are curved. However, in order to provide greater clearance between side walls  68  and drive shaft  30  (particularly the outer walls of enlarged region  30   a  extending substantially parallel to rotation axis  31 ) substantially straight side walls  68   a  may, instead, be provided, as shown in FIGS. 11 and 12. Straight side walls  68   a  extend, from the widest portions of valleys  64 , along the periphery of driven surface  60  substantially perpendicular to rotation axis  41  of driven shaft  40 . 
     Because typically only oscillatory rotation, without axial reciprocation, of driven shaft  40  is desired, it is desirable to fix drive shaft  30  with respect to driven shaft  40 . In accordance with the principles of the present invention, drive shaft  30  is provided with an axially extending pin  70  that is substantially aligned with rotation axis  31 . Driven shaft  40  is provided with a corresponding slot  72 , which may extend completely through driven shaft  40 , as shown in FIGS. 2A,  2 B, and  7 - 10 . It will be understood that slot  72  need not extend completely through driven shaft  40 , as shown, as long as sufficient engagement between pin  70  and slot  72  is achieved. The axial extent of slot  72  along rotation axis  41  of driven shaft  40  is selected to provide a substantially close fit with the diameter of pin  70  to prevent axial reciprocation of driven shaft  40  along axis  41 . However, the transverse extent of slot  72  (in a direction perpendicular to axis  41 ) is selected such that 90° rotation of driven shaft  40  with respect to drive shaft  30  (45° rotation of driven shaft  40  in each direction from the rest position) is permitted without causing shifting of either shaft  30 ,  40  from respective axes  23 ,  25  of housing  12 . 
     In order to prevent movement of shafts  30 ,  40  from their proper positions within channels  22 ,  24  of housing  12 , position retaining elements are provided as follows. In order to prevent axial shifting of drive shaft  30  along axis  31 , drive shaft  30  is provided with at least one radially extending stop flange  80 . As shown in FIGS.  1  and  3 - 5 , preferably a proximal flange  82  and a distal flange  84  are provided. Flange  58  may also be considered to perform the same function as that of flanges  82  and  84  and thus may be considered a stop flange  80  as well. Housing  12  is provided with a latch  86  (inserted after assembly in order to maintain the parts of dental tool assembly  10  in place) having a position retaining surface  89  extending radially inwardly from the walls of channel  22 . Position retaining surface  89  is positioned adjacent and along a retaining surface  83  of proximal flange  82  to prevent proximal axial movement of drive shaft  30  towards proximal end  14  of housing  12 . Additional position retaining surfaces may be provided extending radially inwardly from the inner walls of channels  22  to engage proximal position retaining surfaces on flanges  58  and  84  as well. It will be understood that the position retaining surfaces formed on housing  12  need, not be in the form of a latch, but may be in any other form, such as a radially inwardly extending shoulder, that provides a sufficient surface area for engaging a proximal face of at least one of the flanges  80  on drive shaft  30 . Moreover, the position retaining surfaces on housing  12  must be securely fixed to housing  12  along axis  23  to prevent movement of drive shaft  30  along axis  23 . 
     In order to secure axial alignment of driven shaft  40  with axis  25 , a positioning pin  90  may be provided at a rear, inner end of driven shaft  40  to fit within bore  92  at a rear end of channel  24  of housing  12 , as shown in FIG.  1 . Pin  90  not only serves to maintain proper alignment of driven shaft  40  during use, but also facilitates alignment of driven shaft  40  in housing  12  during assembly. 
     Preferably, to assemble dental tool assembly  10 , driven shaft  40  is first positioned in housing  12 , with pin  90  fitting within bore  92  such that rotation axis  41  of driven shaft  40  is properly aligned with longitudinal axis  25  of channel  24 . Driven shaft  40  is rotated into its rest position such that driven surface  60  faces proximal end  14  of housing  12 . Drive shaft  30  may then be inserted into channel  22 , with pin  70  extending into slot  72  of driven shaft  40 . Latch  86  then is positioned such that position retaining surface  89  faces position retaining surface  83  to maintain drive shaft  30  in its proper position along longitudinal axis  31  of channel  22 . Dental tool assembly  10  then is ready for coupling with the desired hand piece. 
     An alternative embodiment of the present invention is illustrated in FIG.  13 . In this embodiment, the inventive plastic driving mechanism  128  is driven by a rotating member  194 , which serves as a source of rotary input power. Rotating member  194  is a simple elongated driving shaft, of the same configuration as the driving shaft in a conventional rotating prophy angle, and thus, like the other inventive embodiments of the invention may be easily substituted in existing dental apparatus in wide use at dentist&#39;s offices. Rotating member  194  is coupled to a flexible driving member  106  by any suitable coupling  107 . During use, flexible driving member  106  is rotated in the direction indicated by arrows  109 . The part of flexible driving member  106  closer to rotating member  194  rotates along a horizontal longitudinal oscillatory axis  108 . Similarly, the distal portion of flexible driving member  106  rotates along a vertical oscillatory axis  111 . 
     In accordance with this embodiment of the invention, flexible driving member  106  is maintained in a curved configuration. As can be seen in FIG. 13, flexible driving member  106  has a thickness  113  which is much smaller than its width  115 . Because of the flexible driving member  106  is maintained in a curved configuration as illustrated in FIG. 13, rotation of the proximal portion of flexible driving member  106  at a constant speed causes a snap in the angular rotation of the distal end of flexible driving member  106 . 
     This irregularity in angular speed amounts to a sort of stall during which gum tissue has an opportunity to resume an unstressed configuration. In many respects, the effect is similar to that achieved by the reciprocating motion of the prophy angle, which stresses the gum tissue in one direction, then reverses direction, relieving the stress and lessening the likelihood of tissue damage that would be more likely if one continued to apply stress and high-speed in one direction, as would be the case in the typical rotary prophy angle drive mechanism. 
     Flexible driving member  106  is maintained in the curved configuration illustrated in FIG. 13 by housing, the same as in a curved tubular housing  117 , which is illustrated in dashed lines in FIG.  13 . More particularly, it is noted that in accordance with this embodiment of the invention, a rubber prophy angle  119 , which functions as a tooth scrubbing surface and is of conventional design snaps onto a plastic support member  142 . Plastic support member  142  is mounted for rotation within a secular mouth  121 , which is configured to receive the disk shaped top of member  142 , thus securely holding member  142  and allowing only rotation in the direction illustrated by arrow  123 , in response to power input to the system by rotary member  194 . 
     The intermittent nature of the motion in the embodiment illustrated in FIG. 13 may be improved by introducing a measure of friction between member  142  and mouth  121 . 
     FIGS. 14 and 15 show an alternative embodiment of the inventive plastic driving mechanism  228 . FIG. 14 is partially in exploded perspective as will be apparent from the following description. In this embodiment, plastic driving mechanism  228  is driven by a rotary input  294 , of the type conventionally incorporated in a dental tool power source that might be used by a dentist to power a drill or other similar instrument. The output of rotary input  294  is coupled by a coupling mechanism  207  to a cylindrical driving member  209 . Cylindrical driving member  209  defines a drive surface  250  comprising a figure-eight shaped groove. As can be seen in FIG. 14, this groove extends around cylindrical driving member  209  twice, crossing over itself at point  211  to define the figure-eight shape. For the sake of clarity of illustration, cylindrical driving member  209  is shown outside of sleeve  213 . During operation, cylindrical driving member  209  is positioned within sleeve  213 . Sleeve  213  has secured within it a cam following nub  215  which is positioned within groove-shaped drive surface  250 , as illustrated in FIG. 15, during operation of the inventive plastic driving mechanism  228 . 
     As can be seen from FIGS. 14 and 15, as cylindrical driving member  209  is rotated, because it is fixed in position within a suitable housing structure, it tends to pull sleeve  213  in a reciprocating motion along the axial direction as illustrated by arrow  217 . This reciprocating motion is. coupled to support  219 . A drive member  221  is mounted for rotary movement in the directions of arrow  222  on support  219  by a shaft  223 . Finally, prophy support  242  is coupled by a shaft  225  to drive member  221 . As cylindrical driving member  209  is rotated in the direction indicated by arrow  205 , nub  215  is pulled in the directions indicated by arrow  217 , resulting in identical movement by the sleeve  213 . This reciprocating movement is coupled to shaft  225  causing prophy support  242  and prophy angle  227  to reciprocate in the directions indicated by arrow  229  and achieve the desired action of cleaning the tooth without damage to the gums. 
     Referring to FIG. 16, yet another inventive plastic driving mechanism  328  for achieving reciprocating motion in a prophy angle is shown. Generally, in this embodiment, the prophy angle is supported for rotary movement in a housing in much the same manner of the embodiments previously described. Rotary motion is converted into a periodic push which rotates the prophy angle against the prophy support. When the push is released, the prophy angle snaps back into its original position. 
     More particular, cylindrical driving member  309  is rotated in the direction indicated by arrow  311 . Rotation of cylindrical member  309  results in shaft  313  moving in a circular path. Shaft  313  is secured to cylindrical member  309 . Periodically, shaft  313  bears against a shaft  315  which is secured to the prophy angle  317 . 
     When shaft  313  bears against shaft  315  on prophy angle  317 , it moves shaft  315  and rotates prophy angle  317  in the direction indicated by arrow  319 . When this occurs, the spring  321  in a groove  323  in prophy angle  317  is compressed by a stock  325  which is rigidly secured with respect to housing  327  within which the drive member as illustrated in FIG. 16 is contained. As shaft  313  continues to move in a circular path, eventually it is rotated away from shaft  315 , releasing shaft  315  and allowing spring  321  to expand, driving prophy angle  317  in the direction of arrow  327 , thus resulting in reciprocating movement. 
     Referring to FIGS. 17 a - 17   c , yet another inventive plastic driving mechanism  428  for achieving reciprocating movement in a prophy angle is illustrated. Here the driving mechanism  428  is driven by a drive shaft  412  with rotary motion in the direction of arrow  413 . At the end of drive shaft  412  is a driving cam  414 . Drive shaft  412  is retained in position in a space  424  in housing  432  by a disc shaped position retaining element  482  having a centered hole  415  as shown in FIG. 17 a , and a second disc shaped position retaining element  484  having an off-centered hole  421  to accept drive shaft  412  as shown in FIG. 17 b . The proximal end of drive shaft  412  extends partially through a circumferential shaped driven cam  416  mounted for rotation in housing  432 . Prophy angle support  419  can be detachably mounted into housing  432  by an annular ridge  422  Ridge  422  snappingly engages an annular groove  425 . 
     A coupling element  429  connects circumferential shaped driven cam  416  to support  419  in housing  432 . A spring like member  431  springingly positions cam  416  in housing  432 . 
     Rotary motion is converted into reciprocating motion when driving shaft  412  rotates, causing the driving cam  414  to bear against circumferential shaped driven cam  416  in the direction as shown by arrow  450 . As shown in FIG. 17 c , the result is to impart the forward portion of a reciprocating motion to coupling member  429  which is coupled to driven cam  416  and prophy angle support  419 . Spring-like member  431 , attached to driven cam  416 , after a time becomes fully extended, moving in groove  452 . When the peak  433  of driven cam  416  is passed by driving cam  414 , as shown in dash-dot lines in FIG. 17 c , spring-like member  431  springs back causing driven cam  416  to return to its rest position illustrated in solid lines in FIG. 17 c . Driving shaft  412  then continues its rotational cycle in the direction of arrow  413  until the pushing and springing back of driven cam  416  is completed. 
     As driven cam  416  repeatedly returns to its rest position, prophy angle support  419  rotates in the direction indicated by arrow  434 , resulting in the desired reciprocating motion of prophy angle  429 . 
     Turning to FIGS. 18-20, still yet another mechanism for achieving reciprocating movement in a prophy angle is illustrated. In this embodiment, reciprocating motion is achieved in the inventive plastic driving mechanism  510  by applying rotary motion to a lobed member  512 . Lobed member  512  includes a pair of lobes  514  and  516 . As lobed member  512  rotates in the direction of arrow  519 , lobes  514  and  516  follow circular paths but are separated from each other by 180 degrees. In a fashion similar to that of the previous embodiments, a prophy angle support  518  on which a prophy angle  520  is mounted, is supported for reciprocating motion within a housing  522 . Prophy angle support  518  includes an elongated cam follower  524  which is alternately acted on by lobe  514  in the direction of arrow  526 , and then by lobe  516  in the direction indicated by arrow  528 . 
     More particularly, when lobe  514  bears against elongated cam follower  524 , prophy angle support  518  is moved in the direction indicated by arrow  530 . Alternatively, when lobe  516  bears against elongated cam follower  524 , prophy angle support  518  is moved in the direction indicated by arrow  532 . The result of this alternating action is the desired inventive reciprocating motion indicated by arrow  534 , as illustrated in FIG.  19 . 
     Turning to FIGS. 21-22, reciprocating motion is achieved through the use of a wedge-shaped member attached to the prophy support. More particular, the inventive plastic driving mechanism  610  comprises a rotating shaft  612  which has a pair of studs  614  and  616  attached to it. A wedge-shaped member  618  is secured to the top of prophy support  620 . Wedge-shaped member  618  includes a pair of side wedge surfaces  622  and  624 . As shaft  612  rotates in the direction of arrow  626 , alternatively stud  616  bears against surface  624 , driving it in the direction of arrow  628 , followed by stud  614  bearing against surface  624  driving it in the direction of arrow  630 . 
     In accordance with the present invention, it is also contemplated that gears may be used to achieve reciprocating motion in a dental tool driven by a rotary power source. Referring to FIGS. 23-24, an inventive plastic driving mechanism  710  is provided with an input shaft  712  which is rotated, thus rotating a partial gear  714  which comprises about 75 degrees of a circular gear and has the appearance of a pie slice. As input shaft  712  is rotated in the direction of arrow  716 , partial toothed gear  714  alternately engages smaller follower toothed gears  718  and  720  for a short period of time in the overall cycle of rotation of shaft  712 . 
     When follower toothed gear  718  is rotated, it rotates worm gear  722  to which it is attached by coupling shaft  724 . This results in worm gear  722  engaging gear  726 , causing gear  726  and prophy angle support  728  to which it is secured, to rotate in the direction of arrow  730 . 
     Similarly, when follower toothed gear  720  is rotated, it rotates worm gear  732  to which it is attached by coupling shaft  734 . This results in worm gear  732  engaging gear  726 , causing gear  726  and prophy angle support  728  to rotate in the direction of arrow  740 . 
     Referring to FIG. 25, yet another method for achieving the inventive reciprocating motion in a plastic driving mechanism  810  constructed in accordance with the present invention. In accordance with this embodiment, a drive shaft  812  is rotated in the direction indicated by arrow  814 . This results in rotating disk  816  in the same direction. A pin  818  is mounted on disk  816 . As disk  816  rotates, pin  818  follows a circular path. The result is to impart a reciprocating motion to coupling member  820  which is coupled to a rack  822  having a plurality of teeth  824  on it. Rack  822  is supported for sliding movement in the direction indicated by arrow  823  between a pair of support members  825 . In this manner, rack  822  is given a reciprocating motion. Teeth  824  mesh with teeth  826  on pinion  828 , causing reciprocating motion in pinion  828 . The result is to achieve the desired reciprocating motion as indicated by arrow  829  in prophy angle support  830 . 
     Turning next to FIGS. 26 and 27, yet another mechanism for achieving reciprocating motion is shown. Here the inventive reciprocating plastic driving mechanism  910  is driven by a drive shaft  912  with rotary motion in the direction of arrow  914 . At the end of drive shaft  912  are a pair of cams  916  and  918 . Prophy angle support  920  includes a pair of cams  922  and  924 . When cam  916  bears against cam  922  it urges prophy angle support  920  in the direction indicated by arrow  926 . Similarly, when cam  918  bears against cam  924  it urges prophy angle support  920  in the direction indicated by arrow  928 . Because cams  916  and  918  are positioned on shaft  912  at 180 degrees with respect to each other, they are bearing against cams  922  and  924  at different times, and this causes reciprocating motion in prophy angle support  920 . 
     Still yet another approach is illustrated in FIGS. 28 and 29. In this embodiment, power is provided to the inventive reciprocating plastic driving mechanism  1010  by a drive shaft  1012  which is rotated in the direction of arrow  1014 . The end of shaft  1012  has a pair of partial pie-shaped toothed gears  1016  and  1018  which have teeth that mesh with teeth on a conical gear  1020 . 
     As can be seen in FIG. 28, as shaft  1012  rotates, gear  1018  causes follower gear  1020  to rotate in the direction of arrow  1022  when the teeth of gear  1020  engage gear  1018 . At other times, when the teeth of gear  1016  engage the teeth of gear  1020 , gear  1020  is caused to rotate in the direction indicated by arrow  1024 , resulting in reciprocating motion of gear  1020  and prophy angle support  1026 . 
     Referring to FIG. 30, an electromechanical approach to the problem of providing reciprocating motion by an inventive reciprocating plastic driving mechanism  1120  is illustrated. The same may be done using an electromechanical operator  1112  to directly. provide reciprocating motion. Alternatively, a simpler electromechanical operator may be used which only provides for movement in one direction, with movement in the opposite direction being provided by a spring biased arrangement of the type illustrated and described in connection with FIG. 17, above. 
     Turning next to FIG. 31, in accordance with the present invention it is contemplated that magnetic coupling may be used to relieve the stress applied to the gums during continuous motion. Such a magnetic coupling may simply comprise a magnetic clutch. In particular, the inventive reciprocating plastic driving mechanism  1210  is provided with a driving clutch member  1212  which is magnetically coupled to a driven clutch member  1214  to achieve a magnetic-mechanical connection between the two magnet members. 
     Driving clutch member  1212  and driven clutch member  1214  may also be made of plastic, as such materials are inexpensive and widely available. As alluded to above, the invention contemplates the fabrication of all the embodiments of the invention in plastic, although substitution of other materials is possible. In any case, the inventive structures are conFig.d in a manner that provides for durability, even in relatively inexpensive and weak plastic materials. 
     When driving clutch member  1212  is rotated, a driven clutch member  1214  is caused to rotate because of the magnetic-mechanical connection, thus resulting in a transfer of power. Clutch member  1214 , in turn, is coupled to the prophy angle support  1216  in order to rotate the prophy angle  1218 . Such a magnetic clutch will release if tension applied to the gums becomes too great. Such a mechanism can be used in combination with any of the reciprocating plastic driving mechanisms described in this application to achieve an additional measure of protection. In addition, magnetic coupling may be used in place of the various forms of mechanical coupling to achieve the desired reciprocating motion in the various embodiments disclosed herein. 
     Turning next to FIG. 32, still yet another approach is illustrated. In accordance with this approach, a reciprocating plastic driving mechanism  1310  includes a plastic spring like member  1312  mounted for rotation on a support  1314  and coupled by a living hinge  1316  to a prophy angle support  1318  as illustrated. The far end  1320  of the spring like member  1312  is acted on by a stud  1322  mounted on a rotating member  1324 . When rotating member  1324  rotates, stud  1322  impacts far end  1320 , causing the other end to displace the position of living hinge  1316  causing movement of prophy angle support  1318  in the direction indicated by arrow  1326 . Because member  1312  is a spring, when the impact is over, prophy angle support  1318  moves in the opposite direction, thus resulting in reciprocating motion. 
     Turning to FIG. 33, because dental tools often have air pressure as a primary source of power, and it is this air pressure which is used to drive a dentist&#39;s drill, using a converter which converts air pressure into rotary motion, the possibility also exists to achieve reciprocating motion from air pressure directly. The same can be achieved in a reciprocating plastic driving mechanism  1410  by a number of means, including the use of a piston  1412  in a cylinder  1414 . The air pressure drives the piston  1412  in the direction indicated by arrow  1416  against the action of a spring  1418  which is compressed by the movement of the piston  1412 . Pressure maybe released by a vent  1420  causing spring  1418  to push the piston  1412  back in the direction indicated by arrow  1422 . Piston  1412  is coupled by link  1424  to a prophy angle support  1426 . The result is that link  1424  couples the reciprocating motion to prophy angle support  1426  resulting in reciprocating motion of prophy angle  1428 . 
     Referring to FIG. 34, an alternative embodiment for providing longitudinal axial positioning is provided. This embodiment also provides an alternative means of assembling dental tool assembly  1510 . A bearing assembly  1549  includes a bearing journal  1551  and a bushing  1553  that cooperate in holding drive shaft  1530  in axial alignment holding drive surface  1550  and driven surface  1560  in contact with each other. Bushing  1553  is held in position within housing  1512  by means of a snap-fit arrangement. This embodiment replaces stop flange  80  and latch  86 , as shown in FIG.  1 . 
     Referring now to FIGS. 35 to  37 , the relationship between drive shaft  1530 , journal  1551 , and bushing  1553  is shown, with bushing  1553  being shown in section. Drive shaft  1530  includes a bearing journal  1551  having an outside diameter greater than the outside diameter of drive shaft  1530 . Bearing journal  1551  may be integral with drive shaft  1530  or formed separately and attached to drive shaft  1530  by any suitable means. Journal  1551  includes a rearward contact surface  1555  part of which forms a contact area with bushing  1553 . Surface  1555  may be any shape, preferably in an appropriate shape to reduce friction and increase reliability. Bushing  1553  is generally disk-shaped and has an inwardly facing frustoconical surface  1557 . frustoconical surface  1557  has intrinsic characteristics in this configuration. Surface  1557  aids in centering drive shaft  1530  as it passes through bushing  1553  and also promotes a snug fit without being overly tight while simultaneously reducing the contact surface area with journal contact surface  1555 , all desirable characteristics. At the same time, bushing  1553  presents a very simple configuration that is readily produced, especially in plastic. 
     Referring now to FIG. 36, bearing assembly  1549  is shown in position within housing  1512  which is shown in section. For retaining bushing  1553  in position, a retaining structure on its periphery includes a ridge  1559  extending radially inwardly from an inside wall  1561  of housing  1512 . Ridge  1559  is preferably integral with housing  1512  and may be any suitable shape but is preferably radiased. In order to ensure that bushing  1553  is held firmly in position a collar  1563  extends radially outwardly from bushing  1553  and is preferably integral therewith. The inside diameter of ridge  1559  is preferably less than the outer diameter of collar  1563  thereby forming an interference fit between the two forming what is commonly referred to as a snap-fit. The snap-fit arrangement described above is only one possible arrangement and similar arrangements are also contemplated by the present invention. By way of example and not limitation, a reduced diameter area in the outer diameter of bushing  1553  could be used to form a snap-fit arrangement with ridge  1559 . In order to aid the preferred arrangement during assembly a chamfer  1565  is formed on an a leading edge of outer diameter of bushing  1553 . Housing  1512  may include a reduced diameter section  1567  at the point where bushing  1553  is to be positioned. A receiving area  1569  formed between ridge  1559  and reduced diameter section is sized to receive collar  1563 . The arrangement described above holds bushing  1553  in place which in turn holds drive shaft  1530  in place acting through journal  1551  for normal operation of dental tool assembly  1510 . 
     Housing  1512  also includes a raised portion  1571  extending outwardly from its outer surface and is preferably integral therewith. Raised portion  1571  is sized and positioned to aid a user in gripping dental tool assembly  1510 , which may include a single or multiple spiral arrangement. 
     Bearing assembly  1549  as described above has additional benefits in that it greatly simplifies assembly of dental tool assembly  1510 . During assembly, driven shaft  1540  is properly positioned within housing  1512  and then drive shaft  1530  is inserted into housing  1512  in its proper position. Bushing  1553  is then introduced to the open end of housing  1512  with drive shaft  1530  sliding through a central aperture  1573  of bushing  1553 . The fit between bushing  1553  and drive shaft  1530  is preferably toleranced so as to minimize contact between the two components yet allow for a minimal increase in diameter of drive shaft  1530  to form journal  1551  thereon. Once inserted into the end of housing  1512  bushing  1553  is then pushed down into its final position with the snap-fit occurring at the end of insertion. This then holds drive shaft  1530  and driven shaft  1540  in reasonably permanent position within housing  1512  which is the in use position for dental toll assembly  1510 . 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear that the present invention may be embodied in other specific forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. 
     For example, although housing  12  is in the form of a prophy angle, driving mechanism  28  may be used in any other desired dental tool assembly, or any other motorized device that requires oscillating rotary motion of an output end. One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and not limited to the foregoing description.