Abstract:
Provided are abrasive assemblies and related methods that combine a head portion including an integral abrasive member and a drive portion including a resilient cylindrical mandrel. The abrasive member has a receptacle that is complemental to a working end of the mandrel when both members are relaxed. As the abrasive member engages to, or disengages from, the mandrel, the receptacle resiliently expands and the working end of the mandrel resiliently compresses, each in cooperation with the other. Optionally, the abrasive member is maintained in compression in both directions parallel and perpendicular to the longitudinal axis of the mandrel. Advantageously, these assemblies provide for superior retention and slip resistance, ease-of-use, and high manufacturing tolerances.

Description:
FIELD OF THE INVENTION  
       [0001]    Provided are assemblies and related methods for abrading applications. More particularly, these assemblies and methods are directed to shaping, grinding and polishing applications for dental materials. 
       BACKGROUND  
       [0002]    Dental abrasives are commonly used in the dental industry for shaping, grinding and polishing a variety of dental materials, such as natural teeth, dentures and restorative resins. These dental procedures are useful in optimizing bite function and providing a natural and aesthetic appearance for the patient. 
         [0003]    Dental abrasive assemblies can assume many different configurations, depending on the desired application. For example, some assemblies use abrasive particles coated on a rotating disc. The disc typically has a circular or non-circular hole located at the center of rotation. The hole in the disc engages to a suitable rotary power tool configured to spin the disc at high speeds during use. 
         [0004]    Other assemblies use an integral polymeric composite embedded with abrasive particles. The composite can be molded into a suitable shape to facilitate polishing of the dental substrate. Again these molded composites are generally coupled to a rotary power tool to bring the abrasive particles to bear on the substrate to be polished. These moldable composites have the advantage of providing great freedom to optimize the shape of the abrasive member to suit the particular application at hand. 
         [0005]    Both coated abrasive discs and composites naturally wear out rapidly during an abrading operation. To facilitate the replacement of these discs and composites, abrasive assemblies often include a disposable “head” component along with a non-disposable “drive” component. The head component includes the dental abrasive and is configured to allow a dental practitioner to conveniently engage and disengage it from the drive component. 
       SUMMARY  
       [0006]    While the use of a removable head component does provide a convenient way to replace the coated abrasive articles during or between abrading operations, several technical issues remain. For example, both the engagement and disengagement forces should be relatively low to allow easy user replacement of the head component. Yet, at the same time, these forces should be sufficiently high to prevent the abrasive member from wobbling or unintentionally dislodging from the power tool. Further, the mechanical coupling between the head and the drive components should also be sufficient to efficiently drive the head portion at high rotational speeds without slippage. 
         [0007]    Provided are abrasive assemblies that combine a head portion including an integral abrasive member and a drive portion including a cylindrical mandrel. The abrasive member has a receptacle adapted to receive a working end of the mandrel. As the abrasive member engages to, or disengages from, the mandrel, the receptacle resiliently expands and the working end of the mandrel resiliently compresses, each in cooperation with the other. In some embodiments, the receptacle and working end of the mandrel are shaped to provide contact over an extended area between the two components. Optionally, the abrasive member is compressed in both directions parallel and directions perpendicular to the longitudinal axis of the mandrel. 
         [0008]    In one aspect, a rotary dental abrasive assembly is provided. The rotary dental abrasive assembly comprises: a unitary abrasive member having a generally circular receptacle with a minimum inner diameter when the abrasive member is relaxed, the member comprising a resilient polymer composite comprising abrasive particles; and a generally cylindrical mandrel having an outer surface, a longitudinal axis and a bulbous working end received in the receptacle, the working end being divided into a plurality of sections by elongated slots extending from the outer surface of the mandrel toward the longitudinal axis, wherein the working end has an maximum outer diameter when relaxed and the plurality of sections and the abrasive member cooperatively deflect as the abrasive member is engaged to, and disengaged from, the mandrel. 
         [0009]    In another aspect, a rotary dental abrasive assembly comprising: a unitary abrasive member having a generally circular receptacle with a concave inner surface, the member comprising a resilient polymer composite with abrasive particles distributed therein; and a generally cylindrical mandrel having an outer surface, a longitudinal axis and a bulbous working end received in the receptacle, the working end being divided into a plurality of sections by elongated slots radially extending from the outer surface of the mandrel toward the longitudinal axis, wherein the inner surface is complemental with the working end of the mandrel and the plurality of sections and the abrasive member cooperatively deflect as the abrasive member is engaged to, and disengaged from, the mandrel. 
         [0010]    In still another aspect, a method of assembling a rotary dental polishing assembly is provided comprising: providing a mandrel having an outer surface, a longitudinal axis and a bulbous working end divided into a plurality of sections, the sections separated from each other by elongated slots extending from the outer surface toward the longitudinal axis; urging the working end toward a receptacle located on an abrasive member thereby inducing the plurality of sections to deflect resiliently toward each other as portions of the abrasive member around the receptacle resiliently expand; and retaining the working end against the receptacle such that the abrasive member contacts the mandrel along both concave and convex surfaces of the working end. 
         [0011]    Advantageously, these abrasive assemblies and methods allow for increased manufacturing tolerances in both the abrasive member and mandrel. This benefit is achieved because the resilience of one member compensates for the manufacturing variability in the other member, and vice versa. Moreover, the resiliency of the mandrel provides freedom to use abrasive members with higher abrasive loadings, while still maintaining the same degree of retention and frictional engagement. The resilience of the mandrel also allows the walls of the abrasive member to be made thicker while maintaining the same retention and frictional engagement. Finally, the assembly as a whole can tolerate a much greater degree of mandrel wear while retaining adequate coupling between the abrasive member and mandrel. This increases reliability of the coupling and extends the operational lifetime of the mandrel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a dental abrasive assembly according to one embodiment; 
           [0013]      FIG. 2  is a plan view of the assembly in  FIG. 1 ; 
           [0014]      FIG. 3  is a side cross-sectional view of the assembly in  FIGS. 1-2  according to section “ 3 - 3 ” identified in  FIG. 2 ; 
           [0015]      FIG. 4  is a magnified side cross-sectional view of the assembly in  FIGS. 1-3  presenting the circled region of  FIG. 3  in greater detail; 
           [0016]      FIG. 5   a  is a head-on view of a first component of the assembly in  FIGS. 1-4 ; 
           [0017]      FIG. 5   b  is a fragmentary elevational view of the component in  FIG. 5   a;    
           [0018]      FIG. 6  is a cross-sectional view of a second component of the assembly in  FIGS. 1-4 ; 
           [0019]      FIG. 7  is a plan view of a dental abrasive assembly according to another embodiment; 
           [0020]      FIG. 8  is a side cross-sectional view of the assembly in  FIG. 5  according to section “ 8 - 8 ” identified in  FIG. 5 ; 
           [0021]      FIG. 9  is a magnified side cross-sectional view of the assembly in  FIGS. 5-6  presenting the circled region of  FIG. 6  in greater detail; 
           [0022]      FIGS. 10   a  and  10   b  are perspective and cross-sectional views, respectively, of an abrasive member according to still another embodiment; and 
           [0023]      FIGS. 11   a  and  11   b  are perspective and cross-sectional views, respectively, of an abrasive member according to yet another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    An abrasive assembly according to one embodiment is shown in  FIGS. 1-4  and broadly designated by the numeral  100 . The assembly  100  includes an abrasive member  102  and a mandrel  104  (visible in  FIGS. 1 ,  3  and  4 ) that is coupled to the abrasive member  102 . 
         [0025]    As shown in the  FIGS. 1-2 , the abrasive member  102  is a molded brush having a unitary construction, with a central annular hub  106  and a plurality of fingers  108  extending outwardly from the hub  106  in generally radial directions. In the embodiment shown here, the abrasive member  102  has thirty fingers  108 . However, the number of fingers used could easily be made greater or smaller depending on the desired application. The hub  106  is symmetrically disposed about a longitudinal axis  122  that is perpendicular to the plane of the page in  FIG. 2 . Also symmetric about the longitudinal axis  122  and located on the opposite side of the hub  106  (visible in  FIGS. 3 and 4 ) is a generally circular receptacle  110 . 
         [0026]    The abrasive member  102  is made from a composite abrasive, preferably a resilient polymeric composite abrasive. In some embodiments, the composite abrasive includes a thermoplastic material and abrasive particles distributed in the thermoplastic material. 
         [0027]    In some embodiments, the abrasive member  102  comprises one or more thermoplastic elastomers. Thermoplastic elastomers include segmented polyester thermoplastic elastomers, segmented polyurethane thermoplastic elastomers, segmented polyamide thermoplastic elastomers, blends of thermoplastic elastomers and thermoplastic polymers, and ionomeric thermoplastic elastomers. Such segmented thermoplastic elastomers are further described in U.S. Pat. No. 5,903,951. Preferred thermoplastic elastomer polymers are segmented polyester thermoplastic elastomers, including those commercially available as HYTREL, available from E.I. duPont de Nemours, Wilmington, Del. 
         [0028]    The abrasive member  102  need not be made from a thermoplastic elastomer. Instead, the abrasive member  102  may be comprised of a polymeric composite prepared from a conventional rubber or elastomeric material. These elastomeric materials include, for example, silicones, polyurethanes, and fluoropolymer elastomers. 
         [0029]    In some embodiments, the abrasive particles are uniformly distributed in the abrasive member  102 . The abrasive particles may be organic, inorganic, or a composite of either organic, inorganic, or both. The abrasive particle composition, concentration, and size can be tailored according to the nature of the intended workpiece surface and the desired effect of the molded brush on the workpiece surface. 
         [0030]    Suitable inorganic particles can include those of silicon carbide, talc, garnet, glass bubbles, glass beads, cubic boron nitride, diamond, and aluminum oxide, including ceramic aluminum oxide such as that available as CUBITRON from 3M Company, St. Paul, Minn. Suitable organic abrasive particles include particles of comminuted thermoplastic or thermoset polymeric materials. 
         [0031]    In some embodiments, the molded brush includes composite abrasive particles. Composite abrasive particles include agglomerates comprising inorganic particles adhered in an organic polymeric binder. Precisely shaped abrasive particles may also be employed. Sizes of abrasive particles may vary from mean particle diameters of less than  1  micrometer to particle mean diameters of up to about half the thickness of the molded brush bristle tip. The concentration of abrasive particles in the molded brushes may vary from zero to more than 50%. 
         [0032]    As another option, the molded brushes may contain additives such as lubricants, colorants, coupling agents, compatibilizers, mold release agents, nucleating agents, and the like, as is known in the art. 
         [0033]    Abrasive particles and additives may be incorporated into the moldable organic polymer at the time of molding, or alternatively, abrasive particles and/or additives may be compounded with the moldable organic polymer prior to molding. Subsequently, a masterbatch can be molded, or mixed with additional moldable organic polymer, or other masterbatches, and then molded. 
         [0034]    The preferred dimensions and materials described herein are selected so as to allow molding the brush while maintaining the thermoplastic material at a sufficiently high temperature to fill the mold. With the benefit of the teachings found herein, one of skill in the art could select thicknesses, materials, and temperatures to mold brushes not necessarily falling within the particularly preferred dimensions set forth herein. Moreover, the location of the mold gates and thickness of the hub could be optimized by one of ordinary skill in the art. Further details on configurations of integrally molded brushes and methods of making the same are found in U.S. Pat. No. 5,903,951 (Ionta et al.). 
         [0035]    As shown in  FIGS. 3 and 4 , the assembly  100  further includes a mandrel  104  that is complementary to the abrasive member  102  and has a generally cylindrical shape. The mandrel  104  is generally symmetrical about its longitudinal axis  122 , but need not have a uniform diameter or cross-sectional shape along its longitudinal axis  122 . For example, as shown by the cross-sectional view of  FIG. 3 , the mandrel  104  includes sections having different diameters. Preferably, the mandrel  104  is made from a metal such as a 300- or 400-series stainless steel that permits autoclaving without issues of corrosion. Alternatively, the mandrel could be made from metals such as bronze or titanium, or even non-metallic materials, such as filled polymeric composites. 
         [0036]    The mandrel  104  has a barrel section  112  and a bulbous working end  114  extending outwardly from the barrel section  112 . The working end  114  has a maximum diameter that is somewhat smaller than that of the barrel section  112 . Additionally, the working end  114  has a local diameter that varies with respect to its longitudinal axis  122 , and further includes a neck  116  immediately adjacent the barrel section  114 . By virtue of having a neck  116  with reduced diameter next to the barrel section  112 , the working end  114  has an undercut that assists in retaining the abrasive member  102  on the mandrel  104  upon engagement. Optionally and as shown, there is a small gap between the bottom surface of the receptacle  110  and the outermost tip of the working end  114 . 
         [0037]      FIGS. 5   a,    5   b  and  6  show additional features of the mandrel  104  and the abrasive member  102  in their relaxed configurations. 
         [0038]      FIG. 5   a  is a head-on view of the working end  114  of the mandrel  104 . As shown, the working end  114  is split into four discrete sections  124  by a pair of elongated slots  120  extending along radial directions from an outer surface  118  of the mandrel  104  toward the longitudinal axis  122  of the mandrel  104 . The pair of elongated slots  120  intersect each other at the longitudinal axis  122 , thereby dividing the working end  114  into sections  124  that are similar in size and shape. As further shown from the side view in  FIG. 5   b,  the pair of elongated slots  120  not only traverse the working end  114  but also traverse a substantial length of the barrel  112 . 
         [0039]    While the particular number and orientation of the slots  120  shown were found to be especially suitable, these should not be deemed to be limiting. For example, if a reduced degree of deflection is desired, just a single slot may be used to divide the working end  114  into two sections. On the other hand, if a greater degree of deflection is desired, additional slots may be used to divide the working end  114  into more than four sections. In these alternative embodiments, the cross-sectional area of the sections decreases with the increasing number of divisions, thereby providing increased flexibility. If desired, the degree of deflection for a given compressive force can also be tailored by controlling the length of the slots  120  along the longitudinal axis of the barrel  112 . 
         [0040]    The mandrel  102  also includes a shoulder  144 , located where the relatively large barrel  112  joins the relatively small working end  114 . The shoulder  144  extends around the circumference of the mandrel  104  and provides a hard stop when seating the abrasive member  102  on the working end  114  of the mandrel  104 , as shown in  FIGS. 3 and 4 . In some embodiments, the shoulder  144  has an overall diameter ranging from 60 to 90 percent of the maximum outer diameter  126  of the working end  114 . 
         [0041]    As shown in  FIG. 3 , the mandrel  104  also includes a drive end  115  located remote from the working end  114 . As shown, the drive end  115  has features such as notches or undercuts that are asymmetric about the longitudinal axis  122  to facilitate mechanical coupling between the mandrel  104  and a power tool. A suitable power tool is capable of rotating the abrasive member  102  at high speeds during an abrading operation. 
         [0042]    The complemental abrasive member  102  is shown in its relaxed configuration in  FIG. 6 , which reveals further aspects of the receptacle  110  and the hub  106 . In particular, the receptacle  110  has an inner surface including concave side surfaces  132  and a generally flat bottom surface  134 . The receptacle  110  has an overall shape generally complemental to that of the working end  114  when the mandrel  104  is relaxed. As shown, for example, the concave side surfaces  132  of the receptacle  110  substantially match the corresponding convex surfaces on the side surfaces of the working end  114 . Additionally, the flat bottom surface  134  complements the tip of the working end  114 , which is also flat. 
         [0043]    Optionally and as shown, at least a portion of the side surfaces  132  or the bottom surface  134  complemental with the working end  114  faces in a direction with a component toward the direction of disengagement of the working end  114  from the receptacle  110 . In other words, at least a portion of the inner surface complemental with the working end  114  has a normal vector with an axial component parallel to the longitudinal axis  122 , where the axial component defines the direction of disengagement of the working end  114  from the receptacle  110 . 
         [0044]    As further defined in  FIG. 6 , the receptacle  110  has a passageway  138  with a minimum inner diameter  128  that provides a pre-determined level of resistance when the working end  114  of the mandrel is both engaged to, and disengaged from, the receptacle  110 . The receptacle  110  also has a certain maximum inner diameter  130  located between the passageway  138  and the bottom surface  134 . 
         [0045]    The hub  106  surrounds, and is concentric with, the receptacle  110 . As shown in  FIG. 6 , the hub  106  has a first hub diameter  140  when the abrasive member  102  is relaxed. Optionally, however, the hub  106  could assume other shapes, including shapes with variable diameter. In such cases, the first hub diameter  140  represents the largest diametric dimension of the hub  106  along the longitudinal axis  122 . 
         [0046]    Using gentle finger pressure, a dental practitioner snaps the abrasive member  102  onto the mandrel  104  to provide the configuration illustrated in  FIG. 3 . As shown in this figure, the working end  114  of the mandrel  104  is received in the receptacle  110  when the abrasive member  102  and the mandrel  104  are mutually engaged. As previously noted in  FIGS. 5   a  and  5   b,  the working end  114  displays a maximum outer diameter  126  when relaxed. By virtue of the working end  114  being divided into four discrete sections  124  separated by the grooves  120 , the working end  114  is resiliently compressed to a certain diameter somewhat smaller than the outer diameter  126  when the mandrel  104  is engaged to the abrasive member  102 . 
         [0047]    In more detail, as the dental practitioner urges the working end  114  toward the receptacle  110 , the four sections  124  of the mandrel  104  and the hub  106  of the abrasive member  102  cooperatively deflect to allow the bulbous working end  114  to slide past the passageway  138 . In other words, the sections  124  resiliently deflect inwardly toward each other as the receptacle  110  resiliently expands in diameter. The sections  124  have a tendency to spring back, or expand back, to their relaxed configurations. Advantageously, this exerts outward pressure on the inner surfaces of the receptacle  110  to assist in securing the abrasive member  102  on the mandrel  104 . 
         [0048]    As the working end  114  is fully seated in the receptacle  110 , the sections  124  relax toward their original configuration and the receptacle  110  shrinks back toward its original diameter to create an interference fit. Advantageously, the abrasive member  102  contacts the mandrel  104  along both concave and convex surfaces of the working end  114  to assist in retaining the abrasive member  102  on the mandrel  104 . As a further advantage, residual compressive forces acting between the abrasive member  102  and the mandrel  104  help prevent slippage, or relative rotation between the abrasive member  102  on the mandrel  104  during an abrading operation. The use of a unitary abrasive member  102  is also advantageous because abrasive particles directly contact the working end  114  of the mandrel  104 , thereby enhancing the frictional coupling between the two components. 
         [0049]    Advantageously, the minimum inner diameter  128  of the receptacle  110  and the maximum outer diameter  126  of the working end  114  are sized to provide both an interference fit and mechanical retention between the abrasive member  102  and mandrel  104 . Preferably, the degree of interference between the abrasive member  102  and mandrel  104  exceeds 100 micrometers along the diameter of at least a portion the assembly  100 . More preferably, the degree of interference exceeds 250 micrometers along the diameter of at least a portion of the assembly  100 . 
         [0050]    When the working end  114  is received in the receptacle  110 , the hub  106  expands to assume a second hub diameter  142  that is greater than the first hub diameter  140 . The second hub diameter  142  is measured at the same position along the hub as the first hub diameter  140 . Preferably, the difference between the second hub diameter  142  and the first hub diameter  140  ranges from 1 to 50 percent of the difference between the maximum outer diameter  126  of the working end  114  and the minimum inner diameter  128  of the passageway  138  of the receptacle  110 . More preferably, the difference between the second hub diameter  142  and the first hub diameter  140  ranges from 10 to 40 percent of the difference between the maximum outer diameter  126  and the minimum inner diameter  128 . Most preferably, the difference between the second hub diameter  142  and the first hub diameter  140  ranges from 15 to 30 percent of the difference between the maximum outer diameter  126  and the minimum inner diameter  128 . 
         [0051]    The compressibility of the mandrel  104  also reduces the required degree of expansion of the abrasive member  102 . Preferably, the abrasive member has a diameter (e.g. hub diameter or other radial dimension) that increases when the abrasive member  102  engages the mandrel  104  and the inward deflection of the sections  124  reduces the increase of the diameter by an amount ranging from 10 to 90 percent of the increase that would have been observed had the sections  124  been rigid (see Examples). More preferably, the inward deflection of the sections  124  reduces the increase of the diameter by an amount ranging from 30 to 70 percent of the increase that would have been observed had the sections  124  been rigid. Most preferably, the inward deflection of the sections  124  reduces the increase of the diameter by an amount ranging from 40 to 60 percent of the increase that would have been observed had the sections  124  been rigid. 
         [0052]    In some embodiments, at least some portion of the abrasive member  102  is urged into one or more of the grooves  120  when the abrasive member  102  and the mandrel  104  are engaged to each other. This has a particular advantage of providing additional mechanical retention at the interface between the mandrel  104  and abrasive member  102  that restricts rotational slippage between these two components during an abrading operation. 
         [0053]    The distribution, or sharing, of significant structural deflection between the abrasive member  102  and the mandrel  104  is advantageous in providing increased manufacturing tolerances for both of these components. As a further advantage, the composite material used to make the abrasive member  102  can be made substantially stiffer because the mandrel  104  is compressible. This in turn permits higher abrasive particle loadings and/or higher glass transition temperature (T g ) thermoplastic to be used than previously possible, thus facilitating the optimization of the abrasive member  102 . If the stiffness of the abrasive member  102  is fixed, this configuration is still beneficial because it provides greater latitude to adjust the dimensions of the abrasive member  102  according to the application at hand. 
         [0054]    As a further unique advantage, the assembly  100  not only induces compression of the abrasive member  102  along radial directions, but also along axial directions. For example, portions of the abrasive member  102  adjacent the neck  116  are compressed along directions parallel to the longitudinal axis  122  by opposing forces acting on the abrasive member  102  by the working end  114  and the shoulder  144 . By compressing the abrasive member  102  along directions parallel and directions perpendicular to the longitudinal axis  122 , the assembly  100  creates an interference fit over an extended area along the interface the abrasive member  102  and the mandrel  104 , further enhancing the frictional coupling between the two components. 
         [0055]    The combination of an expandable abrasive member  102  with a compressible mandrel  104  also presents practical advantages to the dental practitioner. Using two compliant, complemental members creates an interference fit that is evenly distributed over an extended interfacial area. This reduces slippage between the abrasive member  102  and the mandrel  104 , and provides a high degree of control in the abrading operation. Spreading the interference fit over a comparatively large area also helps avoid “wobbling” of the abrasive member  102  at high rotational speeds. The use of two compliant members allows for higher filler loading in the abrasive member  102  while preserving low engagement and disengagement forces. Finally, the complemental configuration minimizes the effects of wear in the mandrel  104 , extending its operational lifetime. 
         [0056]      FIGS. 7-9  show an abrasive assembly  200  according to an alternative embodiment. As shown in these figures, the assembly  200  includes an abrasive member  202  having a receptacle  210  and a mandrel  204  having a working end  214 . Like the assembly  100 , the working end  214  is received in the receptacle  210 . Unlike the assembly  100 , however, the receptacle  210  is an aperture in communication with opposing sides of the abrasive member  202 . When fully engaged, the outer tip of the working end  214  is recessed within the receptacle  210  such that inadvertent contact cannot occur between the metallic working end  214  of the mandrel  204  and the patient&#39;s tooth or gingival tissue during an abrading operation. 
         [0057]    Other aspects of the assembly  200  are similar to those of assembly  100  and shall not be repeated here. 
         [0058]      FIGS. 10   a,    10   b,    11   a,  and  11   b  show abrasive members  302  and  402  according to two additional embodiments. The abrasive member  302  has a pointed tip to allow a practitioner to access recessed areas of a patient&#39;s dental structure. In this embodiment, the abrasive member  402  has a ridged “cup” shape to allow a practitioner to access, for example, interproximal areas. Both of abrasive members  302 , 402  have receptacles adapted for use with the mandrel  104 . Other aspects of the abrasive members  302 , 402  have been substantially described in the context of previous embodiments and will not be repeated here. 
       EXAMPLES 
     Abrasive Disc Preparation 
       [0059]    Abrasive discs with a configuration similar to that shown in  FIGS. 1-4 , and  6  were designed to particular dimensions, and steel injection molds were fabricated according to those dimensions, which are shown in Table 1. Three different hub minimum inner diameters were made for testing purposes. For reference, the hub minimum inner diameter corresponds to  128  in  FIG. 6 , and the disc outer diameter is measured from bristle tip to bristle tip through the center of the hub, e.g.  3 - 3  in  FIG. 2 . The comparative abrasive disc having a metal eyelet hub had the minimum inner diameter measured across the center of the eyelet opening. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Hub minimum inner 
                   
               
               
                   
                 diameter 
                 Disc outer diameter 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Example 1 
                 0.072 in. (1.83 mm) 
                 0.564 in. (14.3 mm) 
               
               
                   
                 Example 2 
                 0.075 in. (1.91 mm) 
                 0.564 in. (14.3 mm) 
               
               
                   
                 Example 3 
                 0.078 in. (1.98 mm) 
                 0.564 in. (14.3 mm) 
               
               
                   
                 Comparative 
                 0.086 in. (2.18 mm) 
               
               
                   
                   
               
             
          
         
       
     
         [0060]    Plastic pellets having the composition shown in Table 2 were compounded according to conventional methods. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Component 
                 Manufacturer 
                 Wt % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Hytrel 6356 
                 Dupont, Wilmington, DE 
                 20.755 
               
               
                 thermoplastic elastomer 
               
               
                 Hytrel 5526 
                 Dupont 
                 20.755 
               
               
                 thermoplastic elastomer 
               
               
                 Silicone Masterbatch 
                 Dow Corning, Midland, MI 
                 14.000 
               
               
                 MB 50-010 
               
               
                 P400 Treibacher Alodur FRPL 
                 Treibacher, Austria 
                 38.000 
               
               
                 Aluminum oxide 
               
               
                 Pigment blend 
                 Clariant, Minneapolis, MN 
                 6.49 
               
               
                 TOTALS 
                   
                 100.000 
               
               
                   
               
             
          
         
       
     
         [0061]    The plastic pellets were loaded into an extruder at 450 deg. F. (232 deg. C.) and injected into the injection mold, the mold was cooled and the finished part was removed, thus producing a finished abrasive disc. 
         [0062]    The mandrel used for all examples was of monolithic construction and made from stainless steel. The mandrel was commercially available as an RA Mandrel, available with SOF-LEX brand Finishing and Polishing System, 3M ESPE, St. Paul, Minn. Abrasive discs of the comparative example having a metal hub were also available with the SOF-LEX brand System. 
       Measurement of Removal Force 
       [0063]    The abrasive disc was inserted into the fixed jaw of an Instron (Norwood, Mass.) and a mandrel was inserted into the hub of the disc. The mandrel was then connected to the movable jaw which pulled the mandrel out of the hub. This removal force was measured in kilograms (kg). The sample size was five for each hub size. The results shown in Table 3 show the three sizes have slightly less removal force than the comparative example, but all three sizes had acceptable function in actual use. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Hub minimum inner 
                   
               
               
                   
                 diameter 
                 Removal force 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Example 1 
                 0.072 in. (1.83 mm) 
                 0.778 kg 
               
               
                   
                 Example 2 
                 0.075 in. (1.91 mm) 
                 0.726 kg 
               
               
                   
                 Example 3 
                 0.078 in. (1.98 mm) 
                 0.556 kg 
               
               
                   
                 Comparative 
                 0.086 in. (2.18 mm) 
                 0.848 kg 
               
               
                   
                   
               
             
          
         
       
     
       Measurement of Rotational Force of Disc on Mandrel 
       [0064]    The abrasive disc was fixed in position and a mandrel was inserted into the hub. The mandrel was then connected to a torque tester which measures the rotational force required to cause the mandrel to slip in the hub. The sample size was 5 for each hub size. The data is shown in Table 4 and show that the rotational forces are less than the comparative example but adequate to function well under load when polishing a tooth. 
         [0000]                                                  TABLE 4                       Hub minimum inner               diameter   Rotational force                                        Example 1   0.072 in. (1.83 mm)   0.134 inch-pounds                   (0.015 Newton-                   meters)           Example 2   0.075 in. (1.91 mm)   0.097 inch-pounds                   (0.010 Newton-                   meters)           Example 3   0.078 in. (1.98 mm)   0.066 inch-pounds                   (0.0007 Newton-                   meters)           Comparative   0.086 in. (2.18 mm)   0.23 inch-pounds                   (0.025 Newton-                   meters)                        
Measurements with Abrasive Disc and Hub Disengaged (Relaxed)
 
         [0065]    Measurements were made with pin gauges for the abrasive disc minimum inner diameters, and an optical comparator for the mandrel outer diameters. The maximum inner diameter of the hub was less accessible to measuring devices, so was based on the designed dimension. The results are shown in Table 5. For reference, hub minimum inner diameter and mandrel minimum outer diameter correspond to  128  in  FIG. 6 , and hub maximum inner diameter and mandrel maximum outer diameter correspond to  130  in  FIG. 6 . 
         [0000]                                                                      TABLE 5                                       Degree of                           interference                   Mandrel   Mandrel   (mandrel                   minimum   maximum   min. o.d.           Hub minimum   Hub maximum   outer   outer   minus hub           inner diameter   inner diameter   diameter   diameter   min. i.d.)                                    Example 1   0.072 in. (1.83 mm)   0.088   0.089 in.   0.092 in.   0.017 in                (2.24 mm)    (2.26 mm)    (2.34 mm)    (0.43 mm)       Example 2   0.075 in. (1.91 mm)   0.088   0.089 in.   0.092 in.   0.014 in.                (2.24 mm)    (2.26 mm)    (2.34 mm)    (0.36 mm)       Example 3   0.078 in. (1.98 mm)   0.088   0.089 in.   0.092 in.   0.011 in.                (2.24 mm)    (2.26 mm)    (2.34 mm)    (0.28 mm)       Comparative   0.086 in. (2.18 mm)   N/A   0.089 in.   0.092 in.   0.003 in.                    (2.26 mm)    (2.34 mm)    (0.08 mm)                    
Measurements with Abrasive Disc and Hub Engaged
 
         [0066]    To measure the extent of mandrel compression during engagement with the abrasive disc, measurements of the outer diameter of the disc&#39;s hub were made using an optical comparator. The measurements were taken on the outside of the hub at a point corresponding to the minimum inner diameter of the inside of the hub, refer to  140  in  FIG. 6 . A first measurement (relaxed) was made without a mandrel inserted into the hub. A second measurement (slotted mandrel) was made with a slotted mandrel inserted into the hub of Example 2. A third measurement (solid mandrel) was made with a modified mandrel inserted into the hub of Example 2. To simulate a solid mandrel without slots, the slots of a slotted mandrel were filled with epoxy cement to prevent flexing of the segments. The results are shown in Table 6. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Hub outer 
                   
                   
               
               
                   
                 diameter, 
                 Hub outer diameter, 
                 Hub outer diameter, 
               
               
                   
                 relaxed 
                 slotted mandrel 
                 solid mandrel 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 2 
                 0.184 in. 
                 0.188 in. (4.78 mm) 
                 0.192 in. (4.88 mm) 
               
               
                   
                 (4.67 mm) 
               
               
                   
               
             
          
         
       
     
       Performance During Actual Use 
       [0067]    The abrasive discs and mandrels were assembled into a low speed air-driven handpiece (Model No. PD-58, Patterson Dental, St. Paul, Minn.), operated at 0-17,000 rpm. This handpiece was outfitted to a conventional airmotor (Model No. PD-20 BC/RM, Patterson Dental, St. Paul, Minn.) and dental unit (Model #5200, Forest Dental Products, Hillsboro, Oreg.) and used to shape and polish a simulated restoration of Filtek Supreme composite (3M ESPE) with satisfactory results. 
         [0068]    All of the patents and patent applications mentioned above are hereby expressly incorporated by reference. The embodiments described above are illustrative of the present invention and other constructions are also possible. Accordingly, the present invention should not be deemed limited to the embodiments described in detail above and shown in the accompanying drawings, but instead only by a fair scope of the claims that follow along with their equivalents.